Nuclear Energy: Understanding Nuclear Reactors and Storage - Prof. James L. Nagle, Study notes of Physics

Download Nuclear Energy: Understanding Nuclear Reactors and Storage - Prof. James L. Nagle and more Study notes Physics in PDF only on Docsity! 1 Research Papers overall were quite interesting to read! To receive an A the paper must present a clear scientific discussion of the relevant issues. The calculations must shed light on questions raised. The paper must touch upon most of the key issues. To receive a B the paper must present a reasonable scientific discussion of the relevant issues. The calculations should be relevant and the paper should touch upon many of the key issues. A range (35%), B range (35%), C range (20%), D,F range (10%) Please come and see me if you have questions. I will be going over some things to improve in general for the next project. * Penalty for no calculations or description of references. • Homework #8 assignment is due today at 5 pm. • Finish reading Chapter 6 on Nuclear Energy, and then read ahead on Chapter 9 on Air Pollution. • Homework #9 assignment is now available, due next Wednesday. Remainder of the Term: November 10-14 November 10 (Pick Project #2 topics) November 17-21 November 19 (Inquire/Inform #2 due) November 24-28 Thanksgiving break December 1-5 December 3 (Exam #3 in class) December 8-12 December 8 (Research Project #2) Nuclear Reactors The fissioning of U(235) is used to produce heat (instead of burning coal). Turbine/heat engine part is then similar to a conventional power plant. Key elements: Fuel Rods contain enriched (~ 3% Uranium(235)) Moderators some material to slow down the extra neutrons so they do not escape. Control Rods they absorb neutrons when inserted to “shut down” the reaction. “Moderators” Graphite – problem is that it burns if it gets very hot (used at Chernobyl). Heavy water (D20) – very effective, but expensive. Canada used this “CANDU” Regular water (H20) – United States mostly uses this. Beryllium – effective, but a toxic metal Paraffin (Wax) – also has problem of burning and melting. 2 Enriched Uranium Reactor 3% 235 Fuel rod Moderator Water, graphite, … Control Rods Total mass of fuel: 200,000 kg After the control rods are inserted into the reactor and it is shut down a great deal of energy continues to be released into the core—this energy is primarily a result of A. the large heat capacity of the core B. fission product radioactivity C. steam returning from the turbines D. control rods heating up from neutron absorption E. not sure/something else B, fission products are still there and still radioactive, and produce heat. The short lives ones decay away quickly, so the core cools down a LOT very quickly. After a short time, it's not hot enough to run a turbine any more. But it's hot enough to be a safety and storage concern. Even after many years, the waste products are still kept in casks underwater to keep them cool. It takes decades to cool down enough to handle/move to more permanent storage. Clicker Question Evolution of the Fuel Rod • Uranium starts out enriched (~ 3% U235) • Over time Uranium 235 depleted, eventually decreases to < 1% or less after 3 years – Converted to lots of stuff – not destroyed • Neutron “poisoning” • Uranium 238 does not fission but is converted to Plutonium – 0.5% after 3 years: • 200,000 kg of U238 creates 1000 kg of Pu – 90+% Uranium 238 unmodified What to do with the Fuel Rods? • Re-process – Remove radioactive junk (put it where?) – Produce new fuel and recycle • Makes much better use of the fuel – Extracts Uranium 235 and Plutonium • Store and dispose – Increased storage and disposal problem – Bomb material remains in the rods – Where to put this stuff? US decision (1970s) • No reprocessing – Uranium was/is cheap and available – Nuclear proliferation is a serious threat • Store fuel rods at power plants • Temporary solution • Begin search for permanent site – Still looking 25+ years later Storage Sites • At least 1000 years for high-level stuff – Some isotopes will need up to 10× longer • Hanford, Washington – Currently being “cleaned up” • Savannah River, South Carolina • Waste Isolation Pilot Plant (WIPP) – Carlsbad, New Mexico • All above limited to Defense Department • Yucca Mountain, Nevada