THE ENERGY ADVOCATE: excerpts September, 2016 (Howard Cork Hayden)

The Energy Advocate is a monthly science publication about many topics related to energy. It is published in Pueblo West, Colorado in paper format by Howard Cork Hayden, Ph.D., Professor Emeritus of Physics, University of Connecticut. Website: http://www.EnergyAdvocate.com. This should be interesting reading for students, teachers, parents, and leaders in business and government.

To subscribe, contact Cork Hayden at e-mail: corkhayden@comcast.net.

This article contains excerpts from the September, 2016 issue.

Nuclear Notes: As far as journalists are concerned, food comes from the grocery store and electricity comes from the socket. So it is that the media promote the vision that nuclear power is passé , fossil fuels are destroying the planet, and that we’ll be running on wind and solar very soon.

Likely, you have never learned from the news media that there are four nuclear power plants under construction in the US. According to the Nuclear Energy Institute [1], two 1250MW units (Summer-2 and Summer-3) are being built in Jenkinsville, South Carolina, to add to the 1006-MW boilingwater reactor (Summer-1) that has been producing power since 1982. Two 1250-MW units are also under construction at the Vogtle Power Station in Waynesboro, Georgia, which already has two 1229-MW units that were commissioned in 1987 and 1989. The plants under construction were approved long ago, before the anti-nuclear hysteria surrounding the expensivebutharmless accident that occurred at Three Mile Island put a halt to new construction.

That’s a total of 5,000 MW of around-the-clock steady power under construction.

Worldwide, there are 63 nuclear power plants under construction for a total of 61,845 MW [1]. China is building 22 plants, mostly of the 1000-MW variety. As to current standing, the World Nuclear Association informs us [2] Today there are some 440 nuclear power reactors operating in 31 countries plus Taiwan, with a combined capacity of over 385 GWe. In 2014 these provided 2411 billion kWh, over 11% of the world's electricity .… In the USA, the Nuclear Regulatory Commission has approved more than 140 uprates totalling over 6500 MWe since 1977, a few of them “extended uprates” of up to 20%.

Uprates are regulated by the Nuclear Regulatory Commission. Some are very minor— perhaps 2%— and are within original design specifications. Extended uprates involve such things as stronger pipes and often installation of bigger turbines and generators.

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A little nuclear physics is in order here. The slower a neutron travels near a uranium235 nucleus, the more likely it is to be absorbed to create U-236, the beast that fissions— breaks apart into two separate atoms—releasing a huge amount of energy in the process.

The fission process also releases 2 or 3 neutrons, but they are very energetic. As the neutrons collide with other atoms in the vicinity, they give up energy and slow down, in a process called moderation . If the neutrons run into heavy atoms, they bounce off with very little loss of energy. If they run into hydrogen nuclei—protons, which have the same mass as the neutrons—on average, they give up half their energy. A mere 10 halvings of energy reduces their energy to about 0.1% of the starting value, and the next ten do the same. Within a few centimeters within water (H2O), the neutrons are thermalized. The reactors that use water as a moderator are called light-water reactors.

Most reactors being built in the world are Pressurized Light-Water Reactors (PWR). In these units, the water in the reactor serves as the moderator (cooling the generated neutrons down to “slow” conditions) and as the means of heat transport. The water is not allowed to boil, but is instead fed to a steam-generator that produces steam for the turbine.

Four reactors (Rajasthan 7 and 8, and Kakrapar 3 and 4 in India) are Pressurized Heavy-Water Reactors that will each produce 630 MW. Heavy-water moderates the neutrons with water in which the hydrogen atoms have been replaced with an isotope of hydrogen (called deuterium, D) that has a neutron in the nucleus. Appropriately, heavy water has the chemical formula D2O. When a neutron collides with a nucleus of D it bounces of something twice as heavy as itself, so it does not lose as much energy in the collision. It takes over 10 cm for the neutrons to become thermalized. Canadian deuterium (CANDU) reactors are designed around that fact, and can use natural uranium (0.7% U-235), where the U-235 atoms are farther apart than they are in enriched uranium (6% U-235).

[1] “Nuclear Units Under Construction Worldwide,” http://www.nei.org/KnowledgeCenter/Nuclear-Statistics/WorldStatistics/Nuclear-Units-Under-ConstructionWorldwide [2] “Plans For New Reactors Worldwide,” April 2016, http://www.worldnuclear.org/information-library/current-andfuture-generation/plans-for-new-reactorsworldwide.aspx

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STEM Notes: Anybody who watches the Olympics notices that gymnasts are small people. The phenomenal Simone Biles, only 4-feet-eightinches (1.42 m) tall, won four gold medals and one bronze medal in the 2016 Olympics, for example. There is some good physics behind that reality.

For simplicity, imagine that we have two sticks, the larger of which is exactly twice a long, twice as wide, and twice as thick as the smaller, and made of exactly the same material. We want to set them into rotation about the end point, from rest to (say) 20 revolutions per minute. It actually requires 32 (yes, 32) times as much torque (twisting force) to accomplish the task: a factor or 8 because the rod weighs 8 times as much, and a factor of 4 because the effort depends on the square of the length. More generally, if the larger body is α times is big in each dimension, the required effort is α 5 (five factors of α ) times as large.

The same would be true of any two three-dimensional bodies (wheels, arms, legs, heads, …) that are directly proportional in size. An exactly similar Simone Biles that was a mere 10% taller (and 10% wider, 10% deeper) would require (1.10)5 = 1.61 times as much (61% more) effort to do flips. Some of that can come from increased muscle mass, and some from a greater distance from the joint to where the muscle is attached to the bone (the insertion point, giving more leverage), but certainly not all. Geometrical considerations therefore favor the tiny in that sport.

To subscribe, contact Cork Hayden at e-mail: corkhayden@comcast.net.

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