RCS Core Cooling Response Evaluation for Potential Gas Accumulation Location of Accumulator Discharge side in Westinghouse 3-Loop

During performing a review of system design document on Westinghouse 3-loop nuclear power plant(NPP), including piping and instrument diagram, isometric drawing, technical specification and operating procedures to identify potential gas void location, inverted-U shaped piping on the discharge side of accumulator could impact the ability of the system to perform its function. The results for the review of fill/vent activities and procedures, the existing procedures do not currently identify the amount of gas accumulated in the system after the related procedure of the accumulator. This location should be evaluated for possible options which could prevent or minimize gas accumulation because Technical Specification Surveillance Requirements state that Each ECCS subsystem shall be verify that the ECCS piping is sufficiently full of water These findings will be used to develop acceptance criteria, evaluate potential void locations, exclude locations form further evaluation, and identify additional desired vent valve locations, monitoring point, etc. Consequently, assumed gas void 1.08ft³ satisfy the allowable criteria when it is postulated that all inverted-U piping are empty in the discharge piping of accumulator A,B and C. For LBLOCA, also, the addition of the extra gas volume to the RCS will have no impact. Gas that is injected prior to accumulator empty time is either ejected through the break via ECCS bypass or will have negligible effects on core heat transfer since a large amount of vapor may already present in the core region at that time. In the longer term, the majority of these gas either migrate to the upper space of the RCS or out into containment where they have no bearing on core cooling response. To ensure the ECCS integrity and comply with regulatory commission's requirements, new operating procedure is proposed with having no design change. These findings could be used for evaluation basis to develop acceptance criteria and identify additional desired vent valve locations, monitoring point, etc