Reload light water reactor core designs for an ultralong operating cycle

Reload core designs for a 38.8-effective-full-power-month (EFPM) pressurize d water reactor (PWR) cycle and a 45-EFPM boiling water reactor (BWR) cycle were developed to offer nuclear utilities the opportunity for economic ben efit by permitting higher plant capacity factors and by reducing the requir ed number of costly refueling operations. A key constraint-on this work was the requirement to stay within current fuel burnup licensing limits. The d esigns use a single-batch reloading strategy and contain fuel with enrichme nts as high as 7.4 wt% U-235 (exceeding the current licensing limit of 5 wt %). The PWR design uses Gd2O3 and an integral fuel burnable absorber as bur nable poisons to hold down excess reactivity and control power peaking. The BWR employs only Gd2O3. Both core designs require higher-worth control rod s to meet shutdown safety requirements. Fuel performance issues were-also investigated. The presence of high-burnup fuel assemblies at greater than core-average power leads to fuel performan ce concerns over the effects of waterside corrosion and increased fission g as pressure. Steady-state analyses of fuel pin internal pressure showed acc eptable fuel pin performance. Fuel performance areas requiring further rese arch were highlighted. Extended-cycle cores have a fuel cost that is approximately $33 million/yr (or -60%) more expensive than an optimized multibatch strategy. An economic analysis of these cores showed that extended cycles do not offer a signifi cant economic benefit over conventional practice. Possible future scenarios that could make the subject loadings economically viable are a drop in sep arative work unit costs or a significant increase in the price of replaceme nt electricity during shutdown.