Nuclear heatup, a case for low-temperature critical operation

B and W Nuclear Service Company (BWNS) is evaluated a design of an advanced light water reactor (ALWR) for the next generation of light water reactors. The ALWR design is an 1800-MW(thermal) [600-MW(electric)] plant that includes 145 fuel assemblies in a 17 x 17 array; two loops, each with a steam generator and two canned rotor reactor coolant pumps (RCPs); a pressurizer with a volume of 70.79 m3; and passive safety-injection systems. The response of the ALWR under transient conditions was evaluated using the RELAP5/MOD2 computer code. BWNS has studied the ALWR response to transients initiated as a result of reduced primary pressure and temperature to determine the feasibility of using nuclear heat to establish nominal operating pressure and temperature. Currently, plants are licensed for heatup on RCP heat. Use of nuclear heat to establish pressure and temperature at nominal power operation conditions would take less time and allow the plant to reach full-power production more rapidly following shutdown for maintenance or refueling. As part of the feasibility study for use of nuclear heat, several accidents were analyzed to determine the consequences if initiated from a low-pressure and temperature condition. The events analyzed include a control rod withdrawal, a double-ended steam line break, and a total loss of feedwater (LOFW). By showing that key operating parameters such as reactor coolant system (RCS) pressure and core power remain within safe limits during evolution of the transients listed above, one barrier for using nuclear heat to establish the RCS pressure and temperature at nominal power operation conditions can be removed