Study on the behavior of the defected light water reactor fuel in wet storage

To study the effect of the defected fuel rods on the spent fuel storage pool , ten intact fuel rods were selected from a PWR spent fuel assembly which experienced the average discharge burnup of 35,000 MWD/MTD and has been cooled for 5 years. Artificial defects on the fuel rod clad were machined in hot cell and then examined non-destructively before in-pool storage, and the defected rods were separately stored in closed and open container tubes. Water in the storage pool and fuel rod container tubes has been periodically sampled and analyzed. The radioactive materials detected were Co-60, Cs-134 and Cs-137. The Co-60 was slowly and linearly released, and its release rate was different from rod to rod. The obtained average release rate of the Co-60 was about 1x10E-5μCi/ml.day. The Cs-134 and Cs-137 were rapidly released over the first 30 days of storage and then slowly released, and their extents of release rates seemed to be affected by the shape of defect. The average release rates after 30 days of storage were 8.5 and 1.6 μCi/ml.day for Cs-134 and Cs-137, respectively. (Author)