Cooldown procedure success criteria map for the full break size spectrum of SBLOCA

Highlights: • Adaptive sampling for efficient response surface construction is demonstrated. • Limit surface representing mission time success criteria. • No safety margin for PWR with failed HPSI and breaks greater than 2 in. - Abstract: A success criteria map defining successful implementation of a cooldown procedure to mitigate small-break loss of coolant accident (SBLOCA) with failed high pressure safety injection system for the OPR1000 is generated for the full break size spectrum from 0.5 in to 2.5 in diameter breaks. The success criteria map is a multi-dimensional response surface that gives the expected peak clad temperature (PCT) as a function of break size and operator action time to start the 55.6 °C/hr reactor coolant system cooldown and depressurization involving secondary side steam dump through manual manipulation of the atmospheric dump valves (ADV). The PCT response surface is constructed through a regression analysis using a Gaussian process model (GPM) coupled to an adaptive sampling procedure that greatly reduces the computational cost and analysis time by limiting the number of required best estimate simulations of the SBLOCA with the MARS code to approximately 100. Break flow rates and times to core heat up each span several orders of magnitude when considering the full break size spectrum so an innovative solution of transforming the break size and ADV actuation time input variables using exponential and logarithm functions was implemented such that the regression could be performed on the scaled and transformed input space.