SCDAP RELAP5 ANALYSIS OF STATION BLACKOUT WITH PUMP SEAL LOCA IN SURRY PLANT

During a station blackout of PWR, the pump seal will fail due to loss of the seal cooling. This particular transient-LOCA sequence designate d as S3-TMLB' analyzed by SNL with MELPROG/TRAC for Surry plant showed that the depressurization due to the pump seal LOCA would result in e arly accumulator injection and subsequent core cooling which lead to t he delay of reactor pressure vessel (RPV) meltthrough. The present ana lysis was performed with SCDAP/RELAP5 to evaluate this scenario shown in the MELPROG/TRAC analyses. Additionally, the calculated results wer e compared with the similar experimental studies of JAERI's ROSA-IV pr ogram. The present analyses showed that: (1) During S3-TMLB', the loop seal clearing would occur and cause a slight delay of accident progre ssion. (2) It is unlikely that the accumulator injection, which leads to the delay of RPV meltthrough by approximately 60 min, is initiated automatically during S3-TMLB'. Accordingly, an intentional depressuriz ation using PORVs is recommended for the mitigation of the accident co nsequences. (3) The present SCDAP/RELAP5 analyses did not show signifi cant delay of accident progression. It was found that non-realistic lo wer heat generation and higher core cooling models used in the MELPROG /TRAC analysis are attributed to this discrepancy.