5, 7 and 9

5. Strontium-90, yttrium-90, and cesium-137 are of special concern in SNF. According to England and Rider (1993), fission of a uranium-235 nucleus by a slow neutron yields 0.073 atom of 90Sr,8.97106 atom of 90Y, and 0.0060 atom of 137Cs. Calculate the activity of each of these nuclides in 1000kg of spent nuclear fuel at the following times: (a) at shutdown; (b) 1 year after shutdown; (c) 1000 years after shutdown. Assume that the fuel is irradiated to 33MWd/kg. 6. Iodine-132 has a half-life of 2.3 hours. (a) What is the product of the decay of iodine-132? (b) How long would it take for a sample of iodine-132 to lose 99% of its activity? 7. A typical 3000-MWt PWR contains 180 fuel assemblies. Calculate the heat generation from a single fuel assembly (a) 1 day after shutdown; (b) 150 days after shutdown; (c) 1 year after shutdown; (d) 1 decade after shutdown. 8. Equation (7.2) shows the overall process for the conversion of 238U to 239Pu. This is actually a three-step process. (a) Initially, 238U absorbs a thermal neutron. Write a balanced equation for this reaction. (b) The product of the previous reaction is unstable (1/2=23.5 minutes). It decays by beta emission. Write a balanced equation for this decay. (c) The product resulting from the first beta decay is also unstable (1/2=2.39 days). It decays by beta emission. Write a balanced equation for this decay. 9. It has been proposed to use waste heat from spent nuclear fuel for space heating, desalination, and other industrial processes. Estimate the total heat output from the fuel assembly described in the previous problem over a period of three years after its removal from the reactor