Mission definition for a passive reliability assessment of smart passive residual heat removal system

Abstract

SMART (System-integrated Modular Advanced ReacTor) is an integral pressurized water reactor concept that adopts a passive residual heat removal system (PRHRS) in lieu of conventional auxiliary feedwater and pump/heat exchanger RHR systems. This paper presents mission definitions for the PRHRS performance required to achieve the safe shutdown condition and the supporting engineering analysis as the first step of a passive reliability assessment and optimization study of the PRHRS. Integraltime heat removal capacity and continuous-time heat removal rate missions are derived for the PRHRS and a minimum average heat removal rate of 1.7 MW is required for a 36 hour mission time to achieve safe shutdown. Operating characteristics of single-phase fluid and two-phase water natural circulation modes of the PRHRS are investigated and compared. Two-phase natural circulation is the optimal natural circulation mode of the PRHRS and the loop heat transfer characteristics should be optimized for condensing of saturated steam. Inlet subcooling is a second-order importance design objective and boiler superheat is not important.