During review of the Limerick future modification list, a concern was raised with a proposed modification for HV-011-015A,
ESW [Emergency Service Water] 'A' Discharge to 'B'
RHR Service Water Return, which failed to fully close during routine testing.
As a result of the failure to close, a clearance was applied and a 10CFR50.59 screening was performed to close and de-energize HV-011-015A and open and de-energize valve HV-011-011A, ESW 'A' Discharge to 'A' RHR [Residual Heat Removal] Service Water Return. This clearance isolated one of the two ESW return flow paths so that only one flow path is available to return cooling water flow to the spray pond.
The 10CFR50.59 screening did not address that fire areas 12 (Unit 1 4kV D13 switch gear room) and 18 (Unit 2 4kV D23 switch gear room) are not in compliance with the existing fire safe shutdown (FSSD) analysis. The FSSD analysis credits both flow paths so that Emergency Service Water can be returned to the spray pond. With only one of the two return flow paths available, a single spurious fire induced valve operation can result in deadheading an ESW pump and starving an operating emergency diesel generator of cooling water. Running the emergency diesel generator with a loss of cooling water will initiate a diesel protective trip on high temperature.
Compensatory measures are in place for the specific fire areas listed above.
The licensee has notified the NRC Resident Inspector.
