Nuclear safety, radiation, waste and reprocessing (Bryan Leyland)

Nuclear safety, radiation, waste and reprocessing

Bryan Leyland MSc, FIEE(rtd), FIMechE, FIPENZ

Visit to nuclear facilities In July 2011 I was one of 3 Kiwis invited to go on a study tour of nuclear facilities for waste reprocessing, concentration and shipping The tour was organised to ensure that some people in New Zealand would have a good understanding of the processes involved in dealing with nuclear waste Neither during the visit or since, has any pressure being exerted upon me to “gild the lily�

Melox facility - France

Details at: http://insaf-net.org/mox_wg/AREVA.pdf

Re-processing at Melox This plant is in the south of France.

Used uranium is recycled to produce Mixed Oxide Fuel (MOX) a mixture of enriched uranium and plutonium recovered from the waste (The plutonium is NOT “weapons grade�)

We had to change into clothes that they provided and we went through radiation detectors several times.

During the tour through the plant we absorbed 23 micro Sieverts of radiation. The flight to the UK would have exposed us to about 100 times more

Reprocessing Recovers materials with high energy potential and saves natural uranium 10% of France’s electricity generation is from Mixed Oxide Fuel – MOX fuel

It reduces uranium consumption by 25% Minimises high level waste

5 times reduction in volume 10 times reduction in radiation

Burns up plutonium

Write

Fuel pellets and rod

Sellafield Nuclear Site – Great Britain

Details at: http://www.visitcumbria.com/wc/sellafield-nuclear-reprocessing-facility.htm

UK Store for high level waste

Shipping The fuel from the Melox (MOX) plant in the South of France and the wastes from Sellafield are shipped to Japan via the Tasman Sea They are assembled in 130 ton flasks and loaded into a specialized ship capable of carrying 20 flasks

If high-level wastes are being transported, they send two identical ships with only one carrying the waste The ships also carry armed policemen

Fuel flask

Nuclear Power The safest and most environmentally friendly form of major power generation safer than hydro, gas and coal fired generation cooling water is the only significant environmental impact

The risks of power generation Coal-fired power stations kill thousands of people from emissions, accidents and mining disasters.

Dam failures have killed many people.

Gas-fired power stations have exploded and killed many people. Others die during gas production Nuclear power stations have killed about 45 people at Chernobyl. None have - or will- die at Fukushima. Noone died at Three Mile Island

Death rates Death rates based on based on power power produced produced 161 deaths per TWh (000GWh) 36/TWh

Nuclear 0.04/TWh

Safety aspects of nuclear power Reactors cannot explode like a nuclear bomb

Nuclear provides 17% of the world’s electricity It has killed less than 100 people

most at Chernobyl the equivalent of a Model T Ford

Nuclear waste gets less dangerous over time Moderate levels of radiation are not dangerous

Banqiao Dam

Banqiao dam in China failed in 1975 killing >175,000 people

Yenisei river •

Krasnoyarsk

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6000 MW

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Lake Baikal •

Sayano-

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Shusenskaya

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6400 MW

Concrete arch-gravity dam 242 m high crest length 1074 m

The 6400 MW station The accident happened at 8:13:25 local time 75 lives were lost Single gantry crane lifts all 11 spillway gates

Inside the powerhouse

Generator rotor

Turbine runner

How dangerous is radiation?

We are continually exposed to radiation Sunlight is dangerous in large quantities, good in moderate quantities and we have vitamin D problems with too little Careful studies of people living in areas with high natural radiation (>200 milliSieverts) and the survivors of Hiroshima and Chernobyl show that below about 200 milliSieverts radiation is not dangerous The limit for nuclear power stations is 1 milliSievert!

For most people, our highest radiation is experienced during international flights and from x-rays

Is radiation dangerouss?

There is evidence that exposure to moderately high levels of radiation gives some immunity against cancer in later life the theory is that a high dose of radiation stirs up your natural resistance and this serves you well in later life

www.radiationandreason.com

Radiation safety levels Regulations promulgated 50 years ago assume that all radiation is dangerous Ignored the fact that while too much sunlight is dangerous, too little can also cause problems Recent research has shown that below a certain level radiation is quite safe and may be beneficial

How dangerous are low levels of radiation?

Death rates Regulated levels are ~1 mSv 1000 mSv is safe!

Safe

Dangerous Fatal

Long term cancer risk Taiwan Radiation from contaminated reinforcing steel Predicted total cancer deaths from radiation Total cancer deaths from natural causes Actual total cancer deaths 2.7% of general public rate

56 186 5

Iran Natural radiation at Ramsar at 260 mSv is 25 times higher than the US EPA maximum. “Residents have healthier and longer lives�

Are small doses of radiation good for you?

Natural radiation hotspots •

Average natural dose to all Iranians

milli Gray

~100

Dose in Ramsar, Iran

~10,000

Dose in Kerala, India

~2000

Dose in Guapari, Brazil

100~90,000

Taiwan

Chernobyl

Health effects

Chernobyl If Chernobyl is an argument against modern reactors the logical conclusion is that no-one should drive a modern motorcar or travel in a cruise liner the Model T Ford did not have seatbelts or 4 wheel brakes The Titanic did not have radar

Fukushima

Long term waste disposal If a nuclear station is shut down and sealed off and noone enters, no-one will ever get hurt A hydro station with a large dam requires active monitoring and maintenance for ever

High level waste is dangerous but it is easy to shield against the radiation A natural nuclear reaction took place in Gabon 2 billion years ago. It lasted for thousands of years and produced the same wastes as a modern reactor.

Research shows that the waste material did not migrate and eventually decayed.

Radiation levels Tumour therapy > 40,000mSv per month Healthy tissue gets > 20,000 mSv per month, ok Suggested safe level 100 mSv per month, 50 times the evacuation level of 2 mSv per month nuclear stations regulated to 0.1 mSv per month, 1 mSv/yr

We should accept nuclear radiation for the benefit of society at levels known to be safe

Nuclear Power In a nuclear power station, uranium undergoes nuclear fission and generates heat The heat is used to boil water and this, in turn, drives a conventional steam turbine The amount of heat is controlled by rods that control the fission

When the fuel is depleted, it is taken away and stored until it cools down and then either stored permanently or reprocessed

Modern Nuclear Stations A new generation of modern, safe and simple nuclear power stations is now available Some of them are “inherently safe” and cannot suffer a “meltdown” Those that need emergency cooling no longer rely on diesel generators

Thorium reactors are on the horizon. More efficient and cannot melt down. Called the “chemist’s” reactor because of unique challenges they face, they will require extensive development and testing like uranium fueled reactors have had for decades.

Westinghouse AP 1000 Under construction in China and US

Passive cooling system

SuperSafe and Simple GE/Toshiba development 10- 50 MW No onsite refueling for 30 years Passive safety

622 MW PRISM fast reactor GE/Hitachi •

Burns used uranium and wastes from conventional reactors

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Rapid construction 36 months

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Passive cooling

Steam out

Reactor unit 1

Reactor unit 2

LFTR Thorium Reactor •

Very safe - fuel is drained if it gets too hot

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Runs on Thorium

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Very high burnup

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Little high level waste

A Sustainable option •

Small, sealed intrinsically safe nuclear reactors

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GT-MHR 325 MW

Hyperion 25 MW

B&W 4x125

These reactors can realize the dream of distributed generation - eliminating the need for new transmission lines.

Questions