Effectiveness and adverse effects of reactor coolant system depressurization strategy with various severe accident management guidance entry conditions for OPR1000

Abstract

Severe accident analysis for Korean OPR1000 with MELCOR 1.8.6 was performed by adapting a mitigation strategy under different entry conditions of Severe Accident Management Guidance (SAMG). The analysis was focused on the effectiveness of the mitigation strategy and its adverse effects. Four core exit temperatures (CETs) were selected as SAMG entry conditions, and Small Break Loss of Coolant Accident (SBLOCA), Station Blackout (SBO), and Total Loss of Feed Water (TLOFW) were selected as postulated scenarios that may propagate into severe accidents. In order to delay reactor pressure vessel (RPV) failure, entering the SAMG when the CET reached 923 K, 923 K, and 753 K resulted in the best results for SBLOCA, SBO, and TLOFW scenarios, respectively. This implies that using event-based diagnosis for severe accidents may be more beneficial than using symptom-based diagnosis. There is no significant difference among selected SAMG entry conditions in light of the operator's available action time before the RPV failure. Potential vulnerability of the RPV due to hydrogen generation was analyzed to investigate the foreseeable adverse effects that act against the accident mitigation strategies. For the SBLOCA cases, mitigation cases generated more hydrogen than the base case. However, the amount of hydrogen generated was similar between the base and mitigation cases for SBO and TLOFW. Hydrogen concentrations of containment were less than 5% before RPV failure for most cases.

Verification of the Efficacy of Passive Autocatalytic Recombiners in a Typical Pressurized Water Reactor under a Station Blackout Condition

“…Generally, for such class of problems, the thermal hydraulic response of the plant can be analyzed using lumped parameter (LP) codes or computational fluid dynamics (CFD) codes. A number of codes have been specially developed by the nuclear industry for multidimensional containment analyses, such as GOTHIC [1,2], GASFLOW [3], and TONUS [4] and notably the severe accident analysis codes, for example, RELAP/SCDAP [5,6], MAAP [7,8], MELCOR [9][10][11], and ASTEC [12][13][14]. Other general-purpose commercially available CFD codes have been also explored for nuclear safety simulations including containment analyses [15], for example, by Heitsch et al [16], Prabhudhardwadkar et al [17], and Filippov et al [18].…”