CPCS Operability Test and the Nonlinear Behavior of DNBR with Tcold: Shin-Kori Nuclear Power Plant Unit 1 Startup Test Experiences

摘要

Operability test for Core Protection Calculator System (CPCS) has been performed during power ascension of OPR1000 (Combustion Engineering type Korean 1000MWe Nuclear Power Plants). The test compare the differences of departure from nucleate boiling ratio (DNBR) values between on-line CPCS and off-line simulation code (CEDIPS), with the purpose of guaranteeing that the on-line values must be in off-line DNBR band. The CPCS operability test for Shin-Kori Nuclear Power Plant Unit 1 at 50% plant power failed for CPCS channel B. Analysis showed that the departure from nucleate boiling (DNB, it is calculated by KCE-1 correlation which is revised version for PLUS7 fuel from CE-1 correlation) values of the off-line simulation code had non-linear behavior with inlet temperatures. It means that the assumption of off-line DNBR calculation method was wrong; behavior of DNB values has linearity with Tcold. In this paper, it will be presented the causes of the DNBR nonlinearity and the updated DNBR calculation algorithm was proposed to meet the CPCS operability test.