Thorium Reactors A future hope. David Rolfe 10/15/2016

Transcription

1 Thorium Reactors A future hope David Rolfe 10/15/2016

2 Who am I? Should you trust me? I am a retired IBM engineer who used to design super computers and other experimental computer architectures I am not a nuclear engineer or physicist and have no credentials in this area I became aware of this technology a few months ago and have read about it This subject is controversial. I will point out where I think the controversies are and give you my opinions The purpose of this talk is to start a conversation that I think needs to be had

3 We need safe cheap energy Poverty and energy are linked These women must work many hours a day just to gather the wood for fires Without the wood, they cannot cook the grains their families need and they will starve This kind of economic desperation can lead to violence Access to cheap abundant energy will provide them with the time to care for their families

4 We cannot continue Burning Carbon Burning carbon based fuels injects carbon dioxide into the atmosphere Carbon dioxide is relatively opaque to infrared radiation Here is what is happening

5 Changing the Climate

6 What about wind and Solar The mathematics of intermittent energy sources Assume the sun shines perfectly 12 hours a day and we have perfect batteries For 12 hours we have carbon free solar energy. Lets assume we have 100 megawatts When it gets dark we run on the batteries But the batteries must be charged. That requires another100 megawatt power plant to charge the batteries So if the cost of the 100megawatts is 100 billion dollars then the total cost is 200 billion plus batteries, maybe 50 billion so the total cost is 250 billion. This is very expensive and inefficient, but if this was our only choice, then we would have to do this. Assuming we can make the batteries. But it is not our only choice.

7 Atom Facts Protons, Electrons and neutrons Protons live in the center (nucleus) of an atom The number of protons, called the atomic number determines what element this is. eg 6 protons = carbon electrons live on the outside of an atom and they always equal the number of protons. They determine the atoms chemical properties All protons are positively charged and so strongly repel one another. So how come atoms do not just fly apart? Scale If the atom is 50 yards across, then the nucleus is the size of a BB

8 When protons get very close together they begin to feel the strong force This is what holds the nucleus together But it is not quite strong enough. This is where the neutrons come in. Neutrons also live in the atom s nucleus and help the strong force to hold the protons together. eg carbon has 6 protons and 6 neutrons in its nucleus. So it has an atomic number of 6 but an atomic weight of 12. Well almost The number of helper neutrons can vary. For example carbon can have 6 neutrons or 8 neutrons. So carbon comes in two flavors called isotopes, C12 and C14. Both kinds of carbon are identical chemically, but have different physical properties and also different NUCLEAR properties For example, C14 nucleus is unstable. After a while it kicks out those extra neutrons and turns into C12. This is very handy for dating ancient human remains.

9 Nuclear Energy There are 92 naturally occurring types of atoms (elements) There are many elements beyond uranium that people have managed to make. The most famous is Plutonium which is really good for making bombs. The 92nd element is called Uranium. It has 92 positively charged protons in the nucleus, all pushing against the strong force. So uranium needs a lot of neutrons to hold itself together. The most common form of Uranium has 146 neutrons! So = 238 and it is called U238. And with all these neutrons it is barely stable. Uranium also comes in a few isotopes with an atomic weights of 235, 233 and 232. These forms of Uranium are quite unstable and very rare. Nuclear Fission If U235 or 233 absorbs a neutron, it will split in half and release 2 more neutrons and release a great deal of energy. (200 million times more energy than an ordinary chemical reaction) The other two new neutrons can go on to spilt more nuclei creating a chain reaction. If the reaction is allowed to continue uncontrolled in a carefully designed device, a gigantic explosion results. It the reaction is controlled large amounts of heat are produced that can be converted into electricity.

10 Nuclear Fission

11 Where does the energy come from? All the energy that comes from fission comes from supernovas Here is the story 1 The star burns progressively heavier elements on shorter timescales until producing iron (Fe) on the timescale of seconds. 2 After iron, fusion in the core ceases, and pressure support is lost. Gravity is unhindered, and the star begins dynamical collapse. 3 As the Fe-core contracts, electron-capture begins to convert protons + electrons into neutrons, emitting MeV neutrinos. 4 The Fe-core, now largely composed of neutrons is stabilized to further collapse by neutron degeneracy pressure at nuclear densities. 5 Material further out, which is still collapsing, hits the incredibly hard proto-neutron-star surface - causing a bounce (see video analog): the launch of a powerful shockwave outwards through the star. 6 Because the neutrinos produced from electron-capture are so energetic (as dmckee points out), and because the densities are so high - the neutrinos are able to deposit significant amounts of energy into the outer-material, accelerating it beyond escape velocities. This is the supernova explosion. 7 Due to the hot, dense, nucleon-rich nature of the ejecta, r and s process

12 What is wrong with nuclear power? Nuclear power produces no greenhouse gases But current reactors are very hard to manage and potentially dangerous Depend on perfect management to prevent catastrophic failures These failures have already occurred Chernobyl and Fukushima Current reactor designs use 600 degree high pressure water for cooling. These conditions release hydrogen from the water which is a powerful explosive Lose of coolant results in catastrophic failures. Are there alterternatives?

13 Conventional Reactors Require Containment

14 Molten Salt Reactors At Oakridge National Laboratory a Molten Salt Reactor was developed and operated for several years in the 1960s when the project was cancelled by President Nixon for political reasons In a filmed interview Nixon admitted that he no idea what Molten Salt Reactors were, but he knew he had good political reasons for creating jobs in California. This technology was completely forgotten for 40 years.

15 What is a molten salt reactor? The Uranium fuel is in the form of a salt (often a Fluoride) that is melted at about 600 degrees C and circulates in a containment vessel. In this configuration a meltdown is not possible. There is no high pressure water and no hydrogen. Everything operates at atmospheric pressure The fuel is in liquid form and not solid so the physical geometry of the fuel rods does not change because there are no fuel rods. And so the original fuel can be retained in the reactor vessel for decades. This results in a very complete burning of the fuel and very little (dangerous) waste. Waste fuel rods from current reactors can be burnt, destroying dangerous radioactive waste permanently Ultimately a small amount of waste is produced that is dangerous for 300 years (instead of 100,000 years)

16 Thorium Fuel Cycle Thorium does not fission it is converted into Uranium 233

17 LFTR Block Diagram

18 How good is this, really? LFTR reactors do not meltdown or explode The fuel circulates as a liquid and so does not have to periodically removed for reprocessing or storage LFTR reactors can use current waste as fuel What about proliferation? U233 is produced and used as a fuel. This isotope can be used to make atomic bombs. But U232 is also produced and poisons the U233. Since U232 is an isotope, it is virtually impossible to separate it from the U233 Not everyone agrees with this.

19 What about long term dangerous waste? The quantity of long term waste is dangerous of 300 years and is only 1%-3% of the amount produced by conventional reactors and there is no Plutonium almost So it is not zero, but very low and manageable.

20 What is going on now China is aggressively pursuing this technology Xu Hongjie, the director of the molten-salt reactor program at the Shanghai Institute of Applied Physics presented Chinese plan at Oakridge meeting 10/4/2016 Plan to produce a demonstration reactor by 2020 and a commercial reactor by Chinese engineers are currently working on the project Oak Ridge has a cooperation agreement with China. Some people think this is a bad idea. Some US and Canadian firms are beginning to investigate the technology but in early stages India is also developing expertise in this area

21 Conclusions Energy is a driver of our civilization Burning carbon based fuels is not sustainable because of global warming Wind and solar, while important do not provide uninterrupted power Current nuclear plant designs are unacceptable because of safety and waste concerns Thorium based nuclear power is safe, nonpolluting, and abundant Unfortunately, the development time pushes widespread adoption out into the mid 21st century So we must continue to develop alternative energy sources for the short term and accelerate Thorium development