Evaluation of passive heat removal systems for larger plant ratings

The passive advanced light water reactor designs currently under development by the vendors are primarily for intermediate size applications, i.e., the power level of the Westinghouse AP600 plant is 600 MWe. This size of plant was selected instead of a larger plant in order to better match the load growth characteristics of many US utilities. It was also considered that features achievable in a smaller sized plant could partially offset the economies of scale of the larger plants. It is understood, however, that the Japanese utilities are interested primarily in larger sized plants, i.e., of 900 MWe or higher. Accordingly, an important element of the passive heat removal system study is an evaluation of the ability of these systems to perform their functions in a larger plant. Accordingly, such an evaluation has been performed. The basic approach which was followed was to first estimate the size of plant which could be achieved by extrapolating the features of the AP600 reactor and reactor coolant system components to the largest practicable size. An assessment was then made of whether the passive heat removal systems could perform their functions for this size of plant. The overall conclusions of the evaluation are that: (1) A plant size of about 900 Mwe could be achieved, based on maintaining the same core power density as the AP600, restricting the reactor vessel diameter to that of the largest Westinghouse plants, and ensuring the vessel has adequate circumference to accommodate the nozzles for an AP600 type of reactor coolant system loop. (2) The passive residual heat removal systems are capable, with appropriate size increases, of performing their functions for a 900 MWe plant