Zircaloy clad oxide fuel rods are subjected to a variety of core power transients. One of these, an up-power transient, can place a severe burden on the fuel rod cladding that would potentially lead to rupture if not properly allowed for during the fuel rod design and plant operation. The cladding stress during such a transient can be increased by the presence of fuel chips between the oxide fuel pellet and the cladding. An analysis procedure based on mechanical tests of fuel and cladding was developed that permits calculation of the stress increase due to chips, so that the stress penalty can be accommodated without unnecessary penalties to fuel rod performance. The method of evaluating the maximum cladding bending tensile stress near the chip is described and test data are presented to support the analysis method.

The purpose of the Department of Energy Water Cooled Breeder Program was to demonstrate pratical breeding in a uranium-233/thorium fueled core while producing electrical energy in a commercial water reactor generating station. A demonstration Light Water Breeder Reactor (LWBR) was successfully operated for more than 29,000 effective full power hours in the Shippingport Atomic Power Station. The reactor operated with an availability factor of 76% and had a gross electrical output of 2,128,943,470 kilowatt hours. Following operation, the expended core was examined and no evidence of any fuel element defects was found. Nondestructive assay of 524 fuel rods determined that 1.39 percent more fissile fuel was present at the end of core life than at the beginning, proving that breeding had occurred. This demonstrates the existence of a vast source of electrical energy using plentiful domestic thorium potentially capable of supplying the entire national need for many centuries. To build on the successful design and operation of the Shippingport Breeder Core and to provide the technology to implement this concept, several reactor designs of large breeders and prebreeders were developed for commercial-sized plants of 900--1000 Mw(e) net. This report summarizes the Water Cooled Breeder Program from its inception in 1965 …