SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report by SimplyInfo.org

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Fukushima Daiichi Decay Heat & Corium Status Report Author - Dean Wilkie - Nuclear Engineer Editor - Nancy Foust

Introduction Our research team determined the need for a more detailed follow-up report on the melted fuel (corium or fuel debris) at the Fukushima Daiichi nuclear site involving reactors 1-3. We have written numerous articles in the past concerning the melted fuel at the reactors. This ongoing work compelled us to take a current look at the heat generation (decay heat), potential movement and location of the corium. This report summarizes some of the results of previous reports concerning heat generation and corium behaviors, along with new analysis. A review of the Three Mile Island and Chernobyl nuclear accidents concerning the melted fuel is also discussed. These two disasters provide much of the existing understanding of decay heat and corium, post meltdown. This report also provides our best estimate of the melted fuel (corium) locations within the nuclear facilities.

A bibliography and terminology definitions are available at the end of the report.

Decay Heat In Spent Fuel And Corium What Is Decay Heat?

Decay heat is a term used extensively in the nuclear industry to measure the amount of thermal heat which is being generated by a fuel assembly. This terminology is used for both pressurized water reactors (PWR) and boiling water reactors (BWR). Heat generated from the fission process in a reactor core is the primary source to heat the water, generate steam and produce electricity. Following a reactor shutdown, the decay heat is developed by the decay of fission products that are made during the fission process.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Decay heat levels in corium (melted fuel or fuel debris) are exhibited in the same manner as in a reactor with the exception that the heat generation is due solely to the decay of fission products and the heat generated by spontaneous fissions within the corium.

Decay Heat In Fission Reactors

There are some rules of thumb used by nuclear engineers to determine what the decay heat level is within an operating core just after the reactor is shutdown. This decay heat level, which is different from one facility to another must be removed from the core in order to prevent the fuel from overheating and potentially melting.

Decay heat is estimated based on the thermal, not electric power of a reactor. Reactor power is typically measured in megawatts (MW). The expression for thermal power is MWt and for electric power is MWe. MWe level is obtained by multiplying the MWt value of a reactor by the “efficiency factor” for the specific reactor and in Fukushima’s case, that efficiency factor was approximately 33%. Thus a reactor which operated at 784 MWe would have a total MWt power rating of 784/.33 or 2375 MWt. At the moment of reactor shutdown the decay heat level in the reactor is approximately 6% of the MWt rated power. The example in our case would be 6% of 2375 MWt. or 156 MW of power.

Decay heat is dependent on the power level the reactor operated at and the nuclear fuel burnup limit placed on the reactor facility. Every nuclear facility has a limit for how long a fuel assembly can be used and it is measured by setting a limit on a total of megawatt days. This accumulated amount is measured by the number of megawatts the reactor continuously operates at whether at full power or in startup or shutdown. The units are Megawatt Days (MWD). The Fukushima reactors are typically in the 20-40 Gigawatt Day limit.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Decay heat power comes mainly from these sources:

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Unstable fission products that decay via α, β-, β+ and γ ray emission to stable isotopes

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Unstable actinides that are formed by successive neutron capture reactions in the uranium and plutonium isotopes present in the fuel

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Fissions induced by delayed neutrons

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Reactions induced by spontaneous fission neutrons

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Structural and fuel cladding materials in the reactor that may have become radioactive

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Heat production due to delayed neutron induced fission is usually neglected in heat transfer calculations

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Heat production due to spontaneous fission is usually neglected in heat transfer calculations

Heat production due to spontaneous fissions is applicable at the Fukushima reactors since this type of fission is ongoing at some intervals within the corium. Our assessment will try to account for the estimates of heat generated from these types of fissions. Spontaneous fissions in such large uncontrolled quantities of corium will be significant and likely can go on for an indeterminate period of time.

In a nuclear reactor, the fission of heavy atoms such as isotopes of uranium and plutonium results in the formation of highly radioactive fission products. These fission products radioactively decay at a rate determined by the amount and the type of radioactive nuclides present. Nuclear fission products/isotopes decay (disintegrate) to a stable state by emitting gamma and beta radiation which is accompanied by thermal heat. The emitting of beta and gamma disintegrations is typically measured in disintegrations per second.

After the reactor is shutdown, heat continues to be generated by the decay of fission products even though the “fission” power generated heat would be stopped. Fission products can be short lived, ie: only require shorter periods of time (seconds, minutes, hours) to reach a stable state, or long lived which requires longer periods of time (days, weeks, years) to reach a stable state. The amount of decay heat produced in the reactor will exponentially decrease as more

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and more of the radioactive material decay to some stable form. Decay heat may decrease to about 2% of the pre-shutdown power level within the first hour after shutdown and to 1% within the first day. Decay heat will continue to decrease, but it will decrease at a much slower rate.

Past Research Unit 4 Fukushima Daiichi Spent Fuel Melt Potential & Decay Heat This previous report addressed concerns that the spent fuel remaining in unit 4’s spent fuel pool back in 2012 could melt if the pool lost water. At the time the spent fuel pool had sustained structural damage and TEPCO was still working on a plan to remove this fuel. By late 2014 TEPCO and their contractors had removed all of the spent fuel from unit 4’s pool.

The research for this report found that the temperatures, even with a loss of cooling water, would not be enough to melt the fuel. The potential radiation levels involved in unshielded spent fuel would still be a serious problem. It is worth noting this as the report did not absolve all risks from this pool. A fairly narrow scope was chosen for this project.

The specifications for this scenario were determined to be as follows: ●

As of 2012 decay heat levels for the spent fuel would be <.2%

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Decay heat levels for the same as of 2016 would be around <.1%

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Fuel temperatures at 26 months would be 800°C

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Fuel temperatures at 35 months would be 600°C

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The fuel cladding would remain below the combustion temperature of 1100°C -1200°C

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Temperatures would also be below the oxidation temperature for cladding of 900°C

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Temperatures would be below the 1425°C - 1540°C melting point for steel alloys used in nuclear fuel

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Three Mile Island

The Three Mile Island Unit 2 reactor is a now defunct Pressurized Water Reactor (PWR). These reactors operate at elevated pressures within the core to prevent boiling. PWR reactors utilize a large tank called a pressurizer which is used for pressure control and to dampen system pressure changes by having a small gas portion at the top of the tank.

The Three Mile Island accident involved a small water leak from the reactor system that was not properly diagnosed until after the reactorâ&#x20AC;&#x2122;s nuclear fuel core became severely damaged. Damage officially took place at 4 A.M. on Wednesday, March 28, 1979. Within seconds of the reactor shutdown, the power-operated relief valve on the reactor cooling system opened, as it was supposed to. 10 seconds later it should have closed, but it remained open, leaking reactor coolant water to the reactor coolant water drain tank. High pressure water pumps turned on automatically and pushed replacement water into the reactor system due to the loss of water. Coolant water rushed into the pressurizer as water and steam were released through the relief valve. This caused a rise in the water level inside the pressurizer.

Control room operators reduced the flow of water to the pressurizer due to readings that indicated a high water level. Under the assumption that the coolant system was overfilled with water, they feared the system could rupture. During these events the pressurizer water level was considered to be the sole reliable indication of the water level of the coolant system.

The open relief valve and the lack of replacement water allowed steam to form in the coolant system. Steam within the coolant system pipes caused violent vibrations in the reactor coolant pumps. Control room operators shut down the coolant pumps in an attempt to prevent damage.

The operators still continued to believe the system was nearly full of water because the pressurizer water level remained high. As the reactor coolant water boiled away, the reactorâ&#x20AC;&#x2122;s fuel core was uncovered and became even hotter. The fuel rods were damaged and released radioactive material into the reactor coolant water.

Operators began high pressure injection of water into the cooling system late in the afternoon to increase pressure and to collapse steam bubbles. There were also attempts to lower the

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pressure within the coolant system as part of this process. Forced cooling of the reactor was restored around 7:50 PM when they were able to restart one reactor coolant pump. 15 hours transpired without forced flow cooling within the reactor vessel. Water levels had lowered, partially uncovering the core. This lead to overheating and a partial meltdown.

The melting temperature of the zircaloy fuel cladding was exceeded, resulting in relocation of the molten zircaloy and some liquefied fuel to the lower reactor core regions, solidifying near the coolant interface. Based on the final state of the reactor core, it is believed that as fuel rods failed and became molten, core material migrated to the lower reactor internal area.

The majority of the molten material flowed down through the region of the southeastern assemblies and into the gap between the core and the wall of the reactor vessel. A portion of the molten core material flowed to the outer region of the reactor vessel and migrated down into the lower internals and lower reactor head region. Limited damage to the core support assembly occurred as the core material flowed to the lower head region.

It is estimated that about 17 - 20 tons of fuel debris and melted reactor internals relocated to the lower core and lower head region of the reactor vessel. Several in core instrument guide tubes were melted but reactor vessel itself did not fail during the accident.

The relocation took place over roughly 2 minutes. The entire process took 224 minutes from the initial reactor shutdown (scram). The corium in the bottom head (lower) region of the reactor vessel eventually solidified into a mass that ranges from 1.5 to 17 inches (5 to 45 cm) in thickness.

Samples obtained from the reactor found two masses of corium. One within the fuel assemblies and one in the lower head of the reactor vessel. These samples were dull grey, with some yellow areas. The corium mass was found to be homogenous, primarily composed of molten fuel and cladding.

The corium make up was stainless steel, inconel, roughly 70% uranium, 13.75% zirconium (from fuel cladding) and 13% oxygen. With these percentages based on weight. There were

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also trace amounts of silver and indium that originated in the control rods. Chromium (III) oxide, an inorganic compound of chromium was found in one of the TMI corium samples.

The corium sample porosity was between 5.7% and 32% with an average of 18Âą11%. The density of uranium (10.4 g/cm3) and zirconium (5.6 g/cm3) are outside the ranges found in the corium samples. Density of the samples was between 7.45 and 9.4 g/cm3. This is expected due to finding a variety of materials within the corium and the porosity of the solidified corium.

The corium decay heat was 0.13 W/g (watts per gram) at 224 minutes after scram. It had dropped to 0.096 W/g by 600 minutes after scram.

The peak temperatures of the fuel melt are estimated to be between 2600 and 2850Â°C. The mixing of uranium and zirconium within the corium is one indicator of these high temperatures. Porosity that is striated and interconnected indicates that the corium may have been in a liquid phase for an extended period of time. This allowed steam or vaporized materials to flow through the melted corium.

The TMI-2 fuel melt was never totally uncovered by water and always had some water, although at times limited, within the reactor vessel during and after the accident. The following image of the TMI-2 reactor vessel cut away shows the melted fuel within the reactor vessel.

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Major points of the TMI-2 accident: ●

Molten fuel and core materials migrated to the lower region of the reactor vessel

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Molten fuel and core materials followed a path of least resistance due to the extreme temperatures in the corium. Open areas provided a free flow path and materials of lower melt points allowed a continued flow of the corium materials

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About 19,000 kg of fuel (17-20 tons) and associated reactor core materials relocated in about 2 minutes. This began about 3 hours after the initial reactor scram.

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The corium mass was found to be homogenous, primarily composed of molten fuel and cladding

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The corium make up was included uranium with zirconium, stainless steel and inconel and smaller amounts of other materials.

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The peak temperatures in the corium were between 2600 and 2850°C

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The Chernobyl Disaster 30 years ago in Ukraine, at the Chernobyl Nuclear Power Station one of the world’s worst nuclear accidents took place. An attempt to run a test that ramped down the reactor and used residual power from a still turning steam turbine to supply power to a main pump went horribly wrong. A scram was initiated towards the end of the test. This caused an increase in the reaction rate in the lower portion of the reactor core rather than lowering the reaction rate due to water displacement and existing steam voids. This set off a massive power spike that resulted in the core overheating and that in turn caused the initial explosion. Based on mathematical estimates this caused the massive steam explosion that ripped apart the reactor. Seconds later a second explosion ripped apart the reactor building and ejected the core, reactor materials and portions of the building. This final explosion is assumed to have been the reactor core undergoing a runaway criticality. The graphite moderator materials from the reactor caught fire adding to the dispersal of radiation to the environment.

Many studies have been performed on the corium. Some photographs have been made available which show the corium flowing from piping, forming what has become known as the “Elephant’s Foot”. Remaining questions, even at the Chernobyl site, have been, “What is the current status of the corium at Chernobyl? Are portions of the corium still thermally hot? Is the corium still slumping or eroding the concrete below the masses?

At Chernobyl, the liquefied corium migrated to the basement of the plant, taking some extended horizontal pathways. As the corium flowed outward and downward it formed stalactites and stalagmites as it gradually cooled and solidified. The most well known is the "Elephant's Foot", located under the bottom of the reactor in a steam distribution corridor.

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The images below show the corium flow and building locations.

The corium at Chernobyl was formed in three phases. The first phase of corium melting took several seconds when temperatures exceeded 2600Â°C. About 30% of the reactor core melted into a liquefied zirconium and uranium oxide. Hot particles found after the disaster showed compounds of Zr-U-O and UOx-Zr. They were found both individually and together in various examined hot particles.

The second phase took place over six days. This liquid phase was a molten corium concrete interaction (MCCI). Structural materials such as sand, concrete and serpentinite were melted and absorbed into the corium while giving off various volatile gasses. This phase created silica materials found in the later solidified corium.

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In the third phase, lamination of the corium occurred. This behavior is where various components of the corium stratify into layers based on the weight and other properties of the various materials. 8 days after the initial meltdown the corium burned through the lower biological shield. It then spread across the reactor room floor. The molten corium accumulated in room 305/2, until it reached the edges of the steam relief valves. It then migrated downward to the steam distribution corridor. It also burned through into room 304/3. These locations can be seen in the graphic above. Radioactivity was released in these phases including when it reached standing water in lower areas of the reactor building.

The corium at Chernobyl had a maximum temperature around 2255°C. It remained above 1660 °C for at least the first 4 days. The corium composition can contain uranium from the fuel, zircaloy fuel cladding, various metals, with some containing concrete melted into the corium and serpentinite. Serpentinite was used as thermal insulation around the reactor vessel.

Three kinds of corium were found in the basement levels of the reactor building; black, brown (including brown sub-types) and metal. They are considered to be silicate glasses with inclusions of these other materials within them. The porous types of corium indicate rapid cooling as the corium interacted with water.

The inclusions within the corium can contain any of these materials: ●

Uranium (oxides) from the uranium based fuel pellets

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Zirconium, zirconium oxides or zirconium dioxide

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Various ratios and compositions of zirconium and uranium

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Chernobylite, a unique mixture of zirconium silicate with up to 10% uranium included

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Silicate glass that contains uranium that may also include magnesium oxide, sodium oxide and zirconium oxide

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Solidified layers of metal or spherical inclusions with a composition of Fe-Ni-Cr

The various types of corium from Chernobyl, in more detail, can be broken down into the following categories.

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Black ceramics: This is a glassy dark black material with a pitted surface, cavities and some porosity. Black ceramic corium is usually located near where corium originated. It can contain about 4 to 8 wt.% of uranium, depending on the exact subtype of black ceramic corium.

Brown ceramics: These are a glass-like brown material. It can be glossy or dull and usually located on a layer of a solidified molten metal. Small metal spheres may be dispersed within this material. It contains 8â&#x20AC;&#x201C;10 wt.% of uranium. Multicolored ceramics can contain 6â&#x20AC;&#x201C;7% of uranium within this type of corium.

Granulated corium: This slag type material is irregular and a gray-magenta to dark-brown color. It contains glassy granules and a crust. These were formed by extended contact of brown ceramics with water. They were found at Chernobyl in large quantities in the pressure suppression pool.

Pumice corium: This highly porous material resembled pumice found near volcanoes. The gray-brown porous corium forms from molten brown corium that is foamed by steam when immersed in water. This type of corium was found in the pressure suppression pool near the openings where it flowed downward. These materials once cooled are light enough to be carried away with water flows.

Metal corium: These consist of mostly molten or solidified metals. These also contain an amount of uranium from the fuel or other radionuclides from the meltdown, making them highly radioactive.

The corium at Chernobyl distributed in three directions. Stream 1 was brown corium and molten steel. The steel formed a layer on the floor of the steam distribution corridor with the brown corium stratified on top. Some of the brown corium continued to flow and ended up in the pressure suppression pool where it turned into pumice or granulated type corium.

Stream 2 was mostly black corium. It migrated to the opposite side of the steam distribution corridor from stream 1.

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Stream 3 was mostly black corium. It flowed into the other areas of the building where corium has been found.

The "Elephant's Foot" contains about two metric tons of black corium and is assumed to have burned 2 meters into the concrete floor. The formation developed a tree bark like texture as it solidified. It is highly radioactive and extremely solid. Investigators used an AK-47 to split off samples. Exploration of the Elephantâ&#x20AC;&#x2122;s Foot has been done without any remote control equipment due to the high radiation levels.

The corium and debris at Chernobyl still contains enough radioactive material to cause widespread contamination should some event cause it to be thrown to the environment. The existing concrete sarcophagus is degrading with age. Fears that the original sarcophagus could collapse and release large amounts of radioactive dust to the environment prompted an international effort for a new sarcophagus. Workers have constructed a new structural arch covering that was rolled into place in December 2016.

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Major points of the Chernobyl accident: ●

Chernobyl is expected to be a threat for at least another 3000 years

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Some damaged portions of the reactor building fell into the super heated reactor core area including concrete, steel, even office chairs. The radioactive mass located in the building basement area weighs approximately 2,000 tons+

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The core increased by 3000 degrees Celsius in a matter of seconds

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Of the 200 ton reactor core, 10 tons is estimated to have been ejected in the explosions and spread to Europe and Scandinavia. Traces of Chernobyl were found as far away as the US and Japan

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95% of the fuel remains within the reactor building. It has a radioactivity of about 670 PBq (petabecquerels)

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Five types of corium have been found at Chernobyl. Black, brown, granulated, pumice and metal types of corium have been found, primarily in the building basements

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The corium materials are mostly glass formations of silicate with inclusions of other materials

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The pumice type corium is brown corium that dropped into water and cooled rapidly

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Uranium is leaching from the reactor building at a low rate of 10 kg (22 lb) per year, indicating the corium is not dissolving in water

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New uranium minerals such as Na4 and uranyl carbonate have been found on some of the corium

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Over the next 100 years the self irradiation of the corium is not sufficient to change the composition of the glass. (2×1016 α decays per gram and 2 to 5×105 Gy of β or γ)

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Ten years after the accident the elephant’s foot gives off one tenth the radiation it originally did. The current rate is about 10,000 REM per hour.

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Fukushima Daiichi Decay Heat Graphs The following graph shows the Fukushima Daiichi units 1-3 decay heat curve over a period from 3-11-2011 to 3-17-2011. Note how steep the decay curve is at the beginning which is due to the short lived fission products decaying to stable states.

Graph source: MIT Nuclear Science

The following two graphs, developed by SimplyInfo.org, show the decay heat curve over a 1 year period after the initial disaster. The first graph is of Unit 1 and the second graph is of Units 2 & 3.

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Fukushima Corium Heat A number of variables affect the status of the corium, and therefore the heat retained within the corium and facilities at Fukushima Daiichi.

The corium mix forms a crust which acts as an insulator, keeping the internal temperature elevated. It is also subject to the climate conditions within the facility including freezing and thawing cycles.

TEPCO (Tokyo Electric Power Company) has felt the need to continue to inject water through the reactor vessel core spray and feedwater lines since the initial disaster phase. This has been

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used to claim the reactors are in a cold shutdown condition. Without a heat removal system as would be available in normal reactor operations, the injected water simply boiled off for months. NHK (NHK World) reported that some of this early water injection may have flash turned to steam and leaked out to the environment through containment failure locations. This increased the radioactivity released to the environment. By June of 2011 the Japanese government reported to the IAEA (International Atomic Energy Agency) that roughly 40% of the injected water boiled off while the other 60% leaked out of the reactors.

TEPCO’s declaration of cold shutdown mode is a standard terminology used for an undamaged functioning reactor to show a stable state. Cold shutdown conditions in a normal reactor are met when, in addition to being shut down, its coolant system is at atmospheric pressure and at a temperature below 100 °C (210 °F). This temperature is low enough that the water cooling the fuel in a light water reactor does not boil even when the reactor coolant system is depressurized. TEPCO fails to admit that there is no “system” left which can contain water, maintain pressure or temperature.

This injected water is assumed to eventually come in contact with the corium. As it does it can flash to steam or drain off the corium crust. Water interaction with the corium can result in steam and hydrogen production. If submerged in water, the corium would displace internal heat from within the corium, which could heat the water to a boil.

Fukushima Daiichi Corium Research We believe that the corium consists of a combination of fuel, structural components and control rods as well as fractional portions of fission particles. The composite corium displays these same tendencies of decay heat generation. The specific decay heat of the corium, how thermally hot it initially is and how that heat dissipates over time, is dependent upon the specific percent of fuel content. TEPCO has not admitted to obtaining any corium samples to date. This is listed as future work under the decommissioning plans.

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As a result we have the following assumptions for the corium:

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Following the reactor scrams at the operating Fukushima reactors, there was a period of roughly 50 minutes where the operators were trying to recover the plant from the earthquake damage and loss of AC power feeding into the facility

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The decay heat level within units 1-3 were initially at approximately 6% of the total rated reactor thermal power output right after the scram and continued to decay exponentially

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At 1 hour after shutdown, the decay heat level would be 2.5%

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At 2 hours after the shutdown, the decay heat level would be approximately 1.5%

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After a day, the decay heat falls to 0.4%

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After a week, it will be only 0.2%

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After 5 years, it would be approximately < 0.02 to 0.10%

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Generation of decay heat within a homogeneous mixture as seen in the corium has not been extensively studied for long term decay heat levels

Neutron Radiation Based Corium Location One technology that seems an obvious tool for use at Fukushima Daiichi is the neutron detector. We have yet to see any reports of its use at the disaster site. The only efforts to attempt to identify neutron counts have been by looking for certain isotopes in the air filters used to remove contaminants from the air exiting the containment structures. This is a very inexact method of neutron detection and also tells little about the location of the corium.

A neutron detector can detect neutrons released by a fissioning reactor or spontaneous fissions from corium, even if it is located underground. This technology would give TEPCO reliable information about the location of the corium with minimal effort.

Sandia National Labs has developed a highly efficient portable neutron camera that can penetrate heavily shielded radiation sources and discern between a neutron source and background radiation. This can pinpoint a radioactive source location and detects the fast

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neutrons created by spontaneous fission. This technology could be of considerable use at Fukushima Daiichi.

The image below shows neutron detectors in use at Chernobyl to monitor neutrons in the reactor debris.

SimplyInfo.org Corium Experiments Two Simplyinfo.org members (Edano & Dean) conducted hands on experiments to simulate what might happen if nuclear fuel melted within a reactor vessel and then penetrated the bottom head. The experiments were performed using two different materials to represent the fuel within

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the reactor vessel.

The first set of experiments involved melted glass with a model of the reactor pedestal. That experiment was similar to what is understood about a rapid core melt and used a larger volume of material. The full report of this experiment can be found on our website and at the link in the resources.

The second set of experiments consisted of running tests using lead as the melt material. Lead had been used to stand in for melted reactor fuel in some of the very early experiments at Brookhaven National Lab in the US. Our lead experiments used a clay pot as the pedestal with a clay saucer to represent the containment structure floor. These experiments used the minimum estimated core melt volume and converted it into a scaled down amount of lead. The full report of this experiment can be found on our website and at the link in the resources.

In each case it was demonstrated that the melted fuel corium would leave the pedestal area directly below the reactor vessel and exit the doorway to the drywell. It would then flow to near or at the edge of the primary containment steel vessel wall across the drywell floor.

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Experiment 001

Image below of the result of experiment one

The image below shows a cross section of where the primary containment steel vessel interfaces with the transition area that goes to the Suppression Chamber (Torus) area below. In the experiment using glass there was a sufficient melt quantity that would have been able to interact with this area and likely would have melted through the steel vessel, interacted with the sand cushion area and migrated down into the torus area likely settling on the floor.

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The experiment using glass as representing the nuclear fuel and clay pots sized to be similar to that of the reactor vessel and pedestal area just below the vessel were clearly able to demonstrate the following:

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The full quantity of glass melted and left the bottom of the clay pot representing the reactor vessel

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The glass melt began filling the region below to a height where it left the doorway representing the pedestal area

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The glass melt then spread out in a direct path which fanned out and eventually reached a distance representing well beyond the containment vessel outer steel wall area.

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This experiment gives ample assurance that the corium in the Fukushima Daiichi reactors which left the reactor vessel could exit the pedestal area and interact with the edge of the containment vessel. Penetration through the steel and concrete into the torus room area is feasible.

Experiment 002

This series of lead based experiments included one using a smaller volume of lead to represent a partial core melt and the second a full core melt volume. The first experiment used the clay saucer as the floor material, the second used steel as the floor material.

The first experiment of the series with the smaller volume showed that the corium would flow into the pedestal but the small volume would not have been able to leave the pedestal. Lead material did attempt to leave the pedestal but lacked the volume to exit completely.

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The second of the series used enough lead to represent the full core melt volume. This experiment did show the corium would have flowed out the pedestal doorway. The use of a steel floor material also prevented the clay from acting as a heat sink on the lead. This was significant as the lead rapidly cools but a corium mass would not cool as quickly. The steel floor allowed for the lead to flow in a manner more in line with expected corium behavior.

In the second of the series, the lead both left the pedestal and had enough volume to attack the pedestal walls. This has been established by NDF (Nuclear Damage Compensation & Decommissioning Facilitation) as a concern as they try to confirm the total damage to the reactors.

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*Note: the lead in the photo below that flowed outside of the rear pedestal boundary was partially due to the pedestal model being lifted before the lead had completely cooled.

The two lead experiments differed in that the first saw concentric rings with a hole in the center of the underside. The second experiment showed a flat center with gas pockets on the outer edges and no concentric rings.

The experiments in lead and glass both showed that a full meltdown would easily exit the pedestal. To date the current admissions by various agencies involved in the decommissioning seem to indicate that full meltdowns that exited the reactor vessels took place in all three reactors.

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Muon Detection Of Corium The most definitive experiments that TEPCO has conducted involved the use of muon technology. This strategically placed muon detectors in or near the Unit 1 and 2 reactor buildings in such a manner to obtain an image of the reactor vessel. The results of the muon scans revealed that all of the reactor fuel appears to have exited the Unit 1 reactor vessel and a major portion or all of the fuel has exited the Unit 2 reactor vessel.

The first scan of unit 2, conducted by Nagoya University found most (roughly 70%) of the fuel is assumed to have been ejected from the reactor vessel. The second scan of unit 2 was presented by TEPCO to still have some fuel remaining in the reactor vessel. An additional analysis by our research team showed that TEPCOâ&#x20AC;&#x2122;s interpretation may be incorrect and there may be no fuel in the reactor vessel of unit 2.

This muon scan information has been acknowledged by TEPCO and is one of the baseis for our position that the corium in Units 1-3 have exited the reactor vessels. The images below are a representation of the muon scans and show that no fuel is in the Unit 1 reactor. If fuel were present there would be a very dark image in that part of the reactor vessel.

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Unit 2, second muon scan after refinement by Fast Fourier Transform analysis

Radiation & Temperature Based Corium Estimates There have been various investigations performed and a host of reports written on where the melted fuel (corium) may be located within Units 1-3. The estimated percentage of fuel melt which remained within the reactor vessels and that which leaked out has varied as well. TEPCO has been reluctant to exhaust efforts to definitively locate where the corium is located. Efforts to map it, get nuclear instrument mapping for gamma, beta, and alpha particles as well as neutrons has not been fully conducted. In addition, gamma camera scanning along with 3d scanning has taken place but only in already accessible areas of the reactor buildings. This has not been done in the more problematic areas of the buildings and has not been done in

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containment. What data has been collected by 3d scan has been mostly kept within TEPCO and JAEA’s (Japan Atomic Energy Agency) confines and is not available to the wider scientific community or the public.

To date most of the data we have been able to gather are entries into various parts of the buildings utilizing gamma radiation detectors. TEPCO has refused to utilize the more important neutron detector instrumentation which would be much more precise. The interaction of the corium and the neutron detectors specifically measures neutrons emitted from the corium masses. TEPCO has acknowledged that subcritical neutron multiplication is an issue in the corium and will be for an extended length of time (in years).

Corium Estimation By Temperature TEPCO has created very rough estimates of where the corium may reside based on using what they called a “heat balance” method. Temperature readings taken at various locations are used to estimate where they think the bulk of the corium might be. This is a very inexact method of detection.

This estimation process takes water injected through the feedwater system and the core spray system and obtains a temperature near where these pipes reach the RPV (reactor pressure vessel). Additional readings are taken within the RPV where temperature instrumentation is still working. Temperature readings are also taken for the PCV (containment) and at various locations within the SC (suppression chamber aka: the torus). Then they look to see where the temperatures within are higher and where available the temperature of collected water.

TEPCO estimates 45% of the heat source for unit 1 may reside in the PCV (primary containment vessel). They give no further clarification for the RPV or other locations in the reactor building. For unit 2 they estimate 3 - 6% of the decay heat may be coming from the RPV, therefore they estimate possibly the same percentage of the fuel resides in the RPV. The estimate for unit 3 is 2 - 7% of the heat source, therefore that much corium is in the RPV.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Corium Estimation By Radiation TEPCO has not formally produced estimates by this method. It is of course an obvious way to roughly estimate where fuel debris or corium may be located. We have utilized the publicly available radiation data for units 1 - 3 to estimate potential locations of corium. This is covered later in the report under the individual reactor estimates from our research.

Computer Modeling Estimates Estimates have been made using a number of computer modeling codes to try to recreate the meltdowns at Fukushima Daiichi. MAAP, MELCOR, SAMPSON and BSAF codes have been used with varying quality and results. Computer modeling can be heavily influenced by the data and assumptions put into the program to run the analysis. Some early modeling attempts assumed the initial water injections to the reactors worked as planned. It was later discovered that this wasnâ&#x20AC;&#x2122;t the case. This incorrect assumption would then influence the resulting computer analysis. While these tools are useful for seeing how something might transpire they are not definitive in their ability. We cover the computer model results by reactor unit later in this report.

Reactor Structures & Corium Paths Another critical issue is the structural layout of the area below the reactor vessels called the pedestal. The opening location of the pedestal and the proximity of the large downcomer vent pipes which connect the primary containment drywell to the suppression chamber (aka: torus) are of critical importance. It is likely that the corium would flow out of the pedestal area into the drywell and would flow directly towards the nearest downcomer vent pipe and begin to interact with the containment drywell steel wall. There is a thin layer of concrete above the sand trap area and over the lip of the drywell below the downcomer vent line.

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Location of corium from these scenarios could be as follows.

A large mass of corium located directly below the reactor vessel deposited on the concrete floor, the water sump area and the equipment located in that area. The corium would immediately interact with any water located in that area as well as immediately begin ablating the concrete and melting downward forming a melt head or pocket. How fast the reactor vessel fails does have an impact on the ability of the corium to migrate. A slow leak of molten fuel from the reactor vessel would tend to burn directly down into the pedestal floor. A more rapid leak of the molten fuel or a sudden total failure of the bottom of the reactor vessel would create conditions favorable to rapid lateral migration of the corium.

Our assumption is that there was a relatively small amount of water located in the pedestal or containment drywell floor areas. Our findings based on activation of the containment spray systems and the water capacity of the drywell floor indicate there was likely no significant amount of water in the drywell floor area before the RPV failure. So the Simplyinfo.org corium spread experiments would show the potential for fuel migration to be accurate. Without significant water on the floor nothing would stop the corium.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

The mass of corium would flow out of the pedestal door into the drywell area and continue to travel out away from the pedestal doorway. It would interact with the concrete as it flowed towards the outer wall of the drywell. The mass of corium would then make contact with the areas represented in the image below.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

The thin concrete ligament of the containment steel lining where the floor meets the wall would quickly spall and chip away from the steel lining due to its width and lack of adherance. The corium would then continue to interact with the steel wall of the liner.

If enough quantity of corium is present, the exposed carbon steel lining of the primary containment drywell would reach a melting temperature and could breach, allowing the corium to enter the sand pocket area. The corium temperatures would likely liquefy the sand and potentially plug or drain out of the sand pocket drain pipe which goes into the torus room.

If the corium spread is deep enough (approximately 7 inches) there would be a direct path which would allow the corium to begin entering the large downcomer vent pipe which connects directly to the suppression chamber (aka: torus). Corium which enters this area would collect

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

along the downcomer pipe and could also deposit into the suppression chamber tube which is located within the torus room.

The diagram below shows the potential route for corium to migrate into the suppression chamber (aka: torus) tube and torus room.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Molten Corium Concrete Interaction Molten Corium Concrete Interaction (MCCI) also plays a role in the total amount of corium materials after an accident and the paths corium may take. Concrete is assumed to decompose or melt at 1600 K (2420°F). TEPCO estimated the temperature inside the core reached 2,800 °C (5027°F) within six hours. Temperatures within the corium would obviously be higher.

The MCCI is also dependent on the composition of the concrete used for the basemat and containment concrete structures. Faster erosion takes place with siliceous concrete than with limestone concrete. Downward (axial) corrosion is faster than radial corrosion by a factor of 2. The initial heat of the corium influences the MCCI. The heat transfer between the corium and the concrete drives the erosion. Gasses from the MCCI will generate significant aerosol mass and will oxidize metal components releasing chemical energy. Both of these can add to the radioactive fission product source term for the meltdown. Attempts to cool the corium or other contact with water may cause the water to evaporate and the corium to reheat due to fission product decay.

NDF, the joint decommissioning authority, has published an estimate of MCCI for unit 1. At unit 1 it is assumed that corium spread over 40% of the drywell floor and interacted with the concrete floor. This is based on the SAMPSON computer models. Similar estimates have not been produced for units 2 or 3.

Corium Locations

There has been considerable interest in where the corium masses are located at Units 1-3 at Fukushima Daiichi. TEPCO has reluctantly admitted, after years of denial, that the fuel situation is worse than originally stated. They now admit that fuel melted within the reactor vessel, relocated to the bottom of the vessel and has leaked out to the concrete pad below in the reactor pedestal area for units 1 to 3. More recent NDF reports give slightly more realistic admissions of the extent of the meltdowns.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

TEPCO has issued many radiation surveys and they have put robots inside the areas of the building where they guardedly determined they wanted to explore. As a result, to this day TEPCO has refused to use all available modern technology and instrumentation to more accurately locate the corium masses. The extent of TEPCOâ&#x20AC;&#x2122;s investigation efforts have been some scope investigations into containment, a limited robot inspection of unit 1 and the muon scans of unit 1 and 2. The muon scans appeared to show that all or most of the fuel left the unit 1 and 2 reactor vessels. Beyond that there have been no efforts to use other internationally suggested techniques to identify and zero in on more precise locations for the corium. We want to show a sampling of what has been hypothesized to date on potential locations, all of which are based on analysis/speculation.

Some estimates of the total fuel available for each reactor and the estimated total melted have been provided by joint work between JAEA, IRID and NDF. These estimates are established based on various computer modeling codes. The first image shows early MAAP and MELCOR code based estimates.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

A newer set of evaluations published in an NDF report show additional estimates of where the melted fuel may be located. These are also based on computer models

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Corium Location Estimation Unit 1 TEPCO Analysis (Multiple Methods)

A 2011 report from TEPCO considered as much as 65 cm of the containment vessel's concrete floor, reaching as close as 37 cm to the vessel's outer steel shell had been eroded by corium.

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Our Analysis

Unit 1 has been a challenge for anyone to find obvious evidence of a single location for the corium. We looked at all potential sources of information including the compiled investigations of unit 1.

Radiation Mapping

Radiation mapping for unit 1 showed a few locations with moderate readings for potential corium and one extremely high reading. Water acts as shielding for radiation so areas covered in water could act to lower ambient readings in the air nearby. The one area of extremely high

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

radiation in the torus room also showed visual evidence of materials that match the defined types of corium and their respective behaviors. Readings in this area were as high as 1 million Sieverts per hour. TEPCO told the press that they thought the meter was damaged and gave inaccurate readings but this set of readings continues to be used in decommissioning documentation years later. This area is underwater and shows what appears to be pumice type corium in the same location as the high radiation. This section of the torus room would have been partially full of standing water at the time of the meltdowns due to the tsunami.

Elevated readings were also found against the torus tube itself. The highest readings were found at the height where the end of the downcomers terminate. This closed end of the downcomer could be a potential location for corium debris to collect. Unit 1â&#x20AC;&#x2122;s torus tube has also had ongoing problems with excess hydrogen production that they have had to extract to prevent build ups to explosive levels.

The image below shows radiation levels compiled from various investigations at the plant. The bold red colors show where we estimate corium may have flowed or concentrated.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Visual Evidence

Photos and video from within unit 1 showed extensive black charred damage inside containment. Imagery from the torus room showed evidence of scorching and high heat at various locations. Near the area where the estimated corium is located has more scorch marks and other evidence of high heat vs. other areas of the torus room. TEPCO has yet to publicly confirm this area as a potential location of corium but a significant body of evidence points that way.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Conclusion Unit 1 has not shown a clear “smoking gun” single location for the bulk of the corium. TEPCO’s various analysis assume all of the fuel is out of the RPV but doesn’t clearly find a location for the corium. Readings inside containment didn’t point to a single large high radiation source. The highest known readings are in the torus room. The torus room has also been admitted to be a source of high radiation water and that water leaking out to the groundwater could be a danger to the environment. TEPCO’s heat balance method found it unlikely much if any corium remained in the RPV but failed to clearly identify a location. It may be possible that corium from unit 1 is distributed around significantly enough that it does not have a sole main location.

Corium Location Estimation Unit 2 TEPCO Analysis (Multiple Methods)

A 2011 report from TEPCO considered as much as 12 cm of the containment vessel's concrete floor had been eroded by the corium.

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Our Analysis

Unit 2 has been the less severe in appearance unit of the three meltdowns. Most of the building and systems are still intact. This has helped more clearly determine where the corium may be or to rule out large areas of the reactor systems and the building.

Radiation Mapping

The highest levels of radiation have all been found inside containment. The only areas with elevated readings outside containment are where containment is entered in some manner. The reactor well area on the refueling floor is one such location. Another location was found within

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the last year. This being the control rod drive hatch that enters into containment. As shielding was removed they discovered the area where the hatch gasket melted was over 2 Sieverts.

The highest readings for Unit 2 based on publicly available data is in the location of the reactor pedestal. Sandia National Lab produced a computer modeling report that showed their conclusion for unit 2 was a slow failure of the bottom of the RPV. This would lead to corium slowly falling to the pedestal floor area. In this scenario, the slow addition of molten fuel would cause the corium to burn down into the pedestal rather than abruptly flowing out the pedestal doorway.

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

Visual Evidence Unit 2â&#x20AC;&#x2122;s containment shows heavily blistered paint but a distinct lack of charring or splattered materials. This appears as if the paint has been steamed off rather than burnt. One set of scope inspection photos from TEPCO showed what looked like black formerly molten debris around the CRD rail opening into the pedestal.

A later decommissioning report admitted they also saw that part of the bottom head was failed. This matches with Sandiaâ&#x20AC;&#x2122;s estimation of reactor vessel failure. Images from the torus room found an almost pristine visual situation. The torus tube and torus room do not appear have been directly involved in the meltdown process.

TEPCO also discovered that the water level in the bottom of the containment drywell was so low that water could not flow into the torus tube via the downcomer vent pipe. They also found no evidence of a break between the drywell floor into the torus room itself. TEPCO puts in water and it does not build up within the containment drywell. It also does not flow into the torus tube or torus room. The water exit path must be from the drywell floor out and away through another means. Yet there isnâ&#x20AC;&#x2122;t any known drain system in the drywell floor.

Conclusion

Our current assumption with unit 2 is that the corium fell to the pedestal and has eroded down into the basemat concrete of the building. How far is not fully understood. Existing burn through rate estimates used in our Unit 2 Report show it is possible for the corium to have potentially burned all the way through the basemat concrete under the right conditions. Even if that more extreme scenario has not taken place, the corium concentration within the pedestal and down into the basemat may have created damage to the basemat concrete. This could have caused paths for the cooling water to leak out of the building. Our current conclusion based on all available information is that the corium has collected in the concrete below the pedestal with a further possibility of a burn through.

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Corium Location Estimation Unit 3 TEPCO Analysis (Multiple Methods)

A 2011 report from TEPCO considered as much as 20 cm of the containment concrete floor was eroded by corium. Further analysis by TEPCO has been limited. Their best estimate currently assumes the bulk of the corium to be in the containment structure.

Our Analysis

Unit 3 has been an extremely difficult situation to reach conclusions. High radiation levels within the reactor building and the areas surrounding it have made investigative work problematic.

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Muon scans have not taken place yet due to these high radiation levels. Radiation mapping and visual evidence so far have been the key tools for estimates for this unit.

Radiation Mapping

Unit 3 has not shown any specific locations of extremely high radiation. Levels around 1-4 Sieverts/hour have been found near the reactor well and near containment hatch doors. Radiation levels inside containment were even lower. Complicating this is the large amount of standing water inside the containment structure. This may be shielding radiation levels deep below the water. Radiation levels in the torus room were lower than those near the containment hatches and refueling floor leading to the assumption that the torus tube and torus room are not heavily involved in the meltdown progression.

Visual Evidence Visual evidence is complicated by the massive damage to unit 3â&#x20AC;&#x2122;s reactor building due to the hydrogen and steam explosions that took place. The torus room and remaining areas of the reactor building did not show signs of charring or similar evidence that would indicate concentrations of corium in any one area. The torus tube and interfaces between the containment structure and the torus room are assumed to be intact due to the containment structureâ&#x20AC;&#x2122;s ability to hold water. Inside containment showed light colored thick materials splattered on the intact structures. There appeared to be a lack of charring as was seen inside unit 1. Additional scope inspections underwater inside containment would give useful information regarding any potential corium in the pedestal or drywell areas.

Conclusion Unit 3â&#x20AC;&#x2122;s lack of investigation has caused clear determinations to be a challenge. Unit 3 managed to hold on slightly longer than the other two reactors before the last of the systems failed. This unit also had the largest visual failure when the hydrogen and steam explosions ejected a

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massive column of black smoke or steam high into the sky. Fused black and spherical glass particles have been found in the evacuation zone and far further away that have been linked back to the meltdowns at Fukushima Daiichi. If they were due to unit 3’s explosion currently can not be conclusively determined, but this has caused considerable speculation. The debris from unit 3’s explosion was also extremely radioactive. TEPCO brought in workers with heavy equipment to remove it immediately after the meltdowns to enable other workers to approach the building. Later work to clear away the remaining debris near unit 3 was done with remote controlled equipment.

Unit 3 could have ejected a portion of the reactor fuel as small fused particles. The other option would be that most of the fuel remained between the RPV and the reactor pedestal. Further investigations should help determine which scenario may have taken place.

Overall Conclusions From our research into decay heat and from the information above, we have come to the following conclusions in respect to accurately predicting the decay heat levels within the corium:

●

TEPCO has not given sufficient details on precise temperatures currently being generated within the corium, the reactor vessels or any remaining fuel assemblies because they have collected vague or limited data

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It is currently impossible to determine the precise quantity and location of the melted fuel that escaped the reactors. Absent these crucial parameters it is not possible to accurately calculate the exact heat generation rate nor the temperature profile of the melted corium

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TEPCO’s efforts to determine temperatures or fission gases lack the needed accuracy to make larger conclusions

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Significant heat would still be produced from ongoing isotope decay processes for the many longer lived isotopes

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It is theoretically possible that the bulkiest corium may still be slowly burning into the concrete or steel vessel material

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â&#x2014;?

Spontaneous fissions are still ongoing due to a high neutron population and interaction of those neutrons with isotopes within the corium and reactor vessels

Conclusions on the corium locations have been at varying degrees of certainty. As more data is collected, this process becomes more refined. Currently unit 1 appears to have no clear location for corium to be concentrated in large amounts. The assumed corium mass in the torus room of unit 1 may not constitute a large percentage of the total core. The unit 1 corium may either have become widely distributed or a collected location of corium has yet to be found.

Unit 2 appears to have had the corium concentrate within the pedestal or below it. Unit 3 remains difficult to pin down but so far appears it may be within the RPV and containment drywell with a further possibility that some of the fuel materials were ejected in the explosion. The latter needs more data to make a more confident theory of that possibility.

Further efforts to clearly determine where the corium may have concentrated in each unit would provide additional data towards estimating the corium decay heat levels more precisely. Factors such as being covered with water, the volume of any corium mass and the composition of materials within these masses would help refine decay heat estimates.

References 1. Ragheb, M. "DECAY HEAT GENERATION IN FISSION REACTORS." N.p., 22 Mar. 2011. Web. 10 Oct. 2016. http://www.ewp.rpi.edu/hartford/~ernesto/F2011/EP/MaterialsforStudents /Petty/Ragheb-Ch82011.PDF

2. "Decay Heat." Wikipedia. Wikimedia Foundation, n.d. Web. 04 Oct. 2016. https://en.wikipedia.org/wiki/Decay_heat

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3. Nusbaumer, Oliver. "Decay Heat in Nuclear Reactors." N.p., n.d. Web. 04 Oct. 2016. http://decay-heat.tripod.com/

4. Spencer, B. W., K. Wang, C. A. Blomquist, L. M. McUmber, and J. P. Schneider. "Fragmentation and Quench Behavior of Corium Melt Streams in Water." US Department Of Energy - OSTI (1994): n. pag. US Department Of Energy. Web. 04 Oct. 2016. http://www.osti.gov/scitech/servlets/purl/10136350

5. "The TMI-2 Accident - In Brief - ANS." ANS. N.p., n.d. Web. 28 Oct. 2016. http://www.nuclearconnect.org/the-tmi-2-accident-in-brief

6. "Three Mile Island Accident." Wikipedia. Wikimedia Foundation, n.d. Web. 04 Oct. 2016. https://en.wikipedia.org/wiki/Three_Mile_Island_accident

7. "Three Mile Island Nuclear Station, Unit 2 (TMI-2). Use of ..." United States Nuclear Regulatory Commission. N.p., 01 Feb. 2005. Web. 14 Oct. 2016. http://pbadupws.nrc.gov/docs/ML0503/ML050380143.pdf

8. "What Caused the Disaster | The Chernobyl Gallery." The Chernobyl Gallery Cause. N.p., 2016. Web. 06 Oct. 2016. http://chernobylgallery.com/chernobyl-disaster/cause/

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9. "After 30 Years, Chernobyl Repair Racing against Time." CBSNews. CBS Interactive, 24 Apr. 2016. Web. 08 Oct. 2016. http://www.cbsnews.com/news/after-30-years-chernobyl-repair-racing-against-time/

10. By. "30 Years Past, Chernobyl Plant to Remain a Threat for 3,000 Years." The Seattle Times. N.p., 25 Apr. 2016. Web. 08 Oct. 2016. http://www.seattletimes.com/nation-world/30-years-past-chernobyl-plant-to- remain-a-threat-for3000-years

11. "Chernobyl Disaster; Lava Like Fuel Containing Materials." Wikipedia. Wikimedia Foundation, n.d. Web. 02 Oct. 2016. https://en.wikipedia.org/wiki/Chernobyl_disaster#Lava-like_fuel-containing_ materials_.28FCMs.29

12. NautilusMag. "Chernobyl’s Hot Mess, “the Elephant’s Foot,” Is Still Lethal - Nautilus." Nautilus. N.p., 04 Dec. 2013. Web. 10 Oct. 2016. http://nautil.us/blog/chernobyls-hot-mess-the-elephants-foot-is-still-lethal

13. "How Did This Worker Approach This Fuel Mass at Chernobyl?" Physics Forums. N.p., n.d. Web. 10 Oct. 2016. https://www.physicsforums.com/threads/how-did-this-worker-approach-this-fuel-mass-atchernobyl.672660/

14. "Neutron Scatter Camera for Radiation Detection." Sandia National Laboratories : Licensing/Technology Transfer. N.p., 18 Oct. 2013. Web. 11 Oct. 2016. https://ip.sandia.gov/technology.do/techID=57

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15. D. Wilkie. "SimplyInfo.org's Fukushima Corium Research Experiment Results." SimplyInfo. Ed. N. Foust. SimplyInfo.org, 12 Dec. 2013. Web. 30 Oct. 2016. http://www.fukuleaks.org/web/?p=11930

16. Edano, S. "Corium Experiments; Pedestal Behaviors Using Lead." SimplyInfo. Ed. N. Foust. SimplyInfo.org, 16 Apr. 2014. Web. Web. 30 Oct. 2016. http://www.fukuleaks.org/web/?p=12682

17. "Researchers Confirm 100% Of Fukushima Unit 2 Core May Have Melted." SimplyInfo. Ed. N. Foust. SimplyInfo.org, 26 Sept. 2015. Web. 30 Oct. 2016. http://www.fukuleaks.org/web/?p=15057

18. "Something Incredible Found In Fukushima Muon Scan." SimplyInfo. Ed. N. Foust. N.p., 01 Aug. 2016. Web. 30 Oct. 2016. http://www.fukuleaks.org/web/?p=15666

19. "Muon Scan Finds No Fuel In Fukushima Unit 1 Reactor Vessel." SimplyInfo. Ed. N. Foust. SimplyInfo.org, 19 Mar. 2015. Web. 30 Oct. 2016. http://www.fukuleaks.org/web/?p=14602

SimplyInfo.org Fukushima Daiichi Decay Heat & Corium Status Report

20. Conversation and notes in early 2016 among the SimplyInfo.org research team https://docs.google.com/document/d/1IIkV40GIEXPj3kGvleo DfuAeWs8Tib2cg7DJ8j50Km4/edit?pref=2&pli=1

21. Joieau. "Let's Play: Where's the Corium?" Daily Kos. Daily Kos, 02 Dec. 2011. Web. 11 Oct. 201 http://www.dailykos.com/story/2011/12/02/1041766/ -Lets-Play:-Wheres-the-Corium

22. Gauntt, R., D. Kalinich, and J. Cardoni. "Fukushima Daiichi Accident Study (Status as of April 2012)." SANDIA REPORT SAND2012-6173. Sandia National Lab, July 2012. Web. 30 Oct. 2016. http://energy.sandia.gov/wp-content//gallery/uploads/Fukushima_SAND2012-6173.pdf

23. "SimplyInfo.org: NDF Report Selected Translations 2016." SimplyInfo.org, 2016. Web. https://docs.google.com/document/d/1KBjJ7L6jdFvDKPBV11e7Fm2EEnifoaK8 DzKiVTkediU/edit

24. "Unit 1, Where The Melted Fuel Is." SimplyInfo. Ed. N. Foust. SimplyInfo.org, 27 June 2012. Web. 30 Oct. 2016. http://www.fukuleaks.org/web/?p=6340

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25. "More On Unit 1â&#x20AC;˛s Torus Situation." SimplyInfo. Ed. N. Foust. SimplyInfo.org, 16 Oct. 2012. Web. 16 Oct. 2016. http://www.fukuleaks.org/web/?p=7978

26. Wilkie, D., S. Edano, MD, and P. Melzer, PhD. "SimplyInfo.org Fukushima Daiichi Unit 2 Extended Report 2015." SimplyInfo. Ed. N. Foust. SimplyInfo.org, 23 Feb. 2015. Web. 30 Oct. 2016. http://www.fukuleaks.org/web/?p=14318

27. "Multiple Research Articles; Fukushima "Black Stuff"" SimplyInfo. Ed. N. Foust. SimplyInfo.org, n.d. Web. 30 Oct. 2016. http://www.fukuleaks.org/web/?s=black+stuff

Definitions

Corium: Corium is a molten mixture of a nuclear reactor core and usually other materials such as control rods, fuel cladding, structural materials from the reactor and in some cases molten concrete. The material is formed due to the high heat in a nuclear meltdown. Fission products: These products of nuclear fission, in the case of uranium in a nuclear reactor, the nucleus splits into two smaller nuclei, releasing neutrons, gamma rays and heat energy. The fission products may also undergo beta decay. Actinides: One of 15 metallic chemical elements with atomic numbers from 89 to 103. These are all radioactive. Zircaloy: Zirconium alloys are zirconium mixed with other metals. The majority of these alloys are zirconium with a small percentage, usually around 5 percent, of another metal. Other metals

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used include tin, iron, chromium, nickel or niobium. This material is commonly used as cladding on nuclear fuel rods. Chromium (III) oxide: An inorganic oxide of chromium with a green appearance that is also used as a pigment. Indium: A soft metal with a low melting point, sometime used in solder. The metal is toxic if ingested or inhaled.

Zr-U-O: A compound of zirconium, uranium and oxygen.

UOx-Zr: Uranium oxides mixed with zirconium. This was found at Chernobyl in many of the fuel particles collected for analysis. These substances were created during the meltdown process as uranium from the fuel mixed with zirconium from the fuel cladding. More on this topic can be found here: http://www.radioprotection.org/articles/radiopro/pdf/2002/05/rad20021pC1-1055.pdf Hot particles: Microscopic pieces of radioactive material. These are small enough to be inhaled.

Fe-Ni-Cr: An iron, nickel and chromium compound including inconel, a trade name for a superalloy frequently used for nuclear reactor components. Na4: 4-[5-(2-Carboxy-1-Formyl-Ethylcarbamoyl)-Pyridin-3-Yl]-Benzoic Acid

Uranyl carbonate: A carbonate (a salt of carbonic acid) of uranium. This same compound is found in contaminated water that leaks from uranium tailings after the mining process Muon: An unstable subatomic particle. Their considerable mass allows them to penetrate deeper into matter. Muons from cosmic rays are used to detect nuclear material as they have a harder time penetrating dense nuclear materials compared to less dense materials such as concrete or steel.

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Basemat: The thick concrete foundation of a reactor building below the containment vessel. Inconel: A group of austenitic nickel â&#x20AC;&#x201C; chromium based superalloys. Inconel is also the initial trade name for these materials as they were developed in the 1940â&#x20AC;&#x2122;s.

To find out more visit our website at www.SimplyInfo.org Inquiries can be sent to: info@SimplyInfo.org

Cover Image Credit: TEPCO