Better Estimate Analysis for Use in Emergency Operating Procedure During a Loss of Coolant Accident

Emergency Operating Procedures (EOPs) [1] provide prioritized response strategies that guide the operator in management of emergency transients. A desirable attribute of EOPs is optimal recovery from the transient. To achieve this, it is necessary to develop more realistic criteria rather than criteria based on traditional licensing analysis methods. One such application is evaluating measured core makeup flow during the recirculation phase of a Loss of Coolant Accident (LOCA) with adverse containment environment. During the recirculation phase of a LOCA, the adequacy of the internal recirculated water flow (from the containment sump) is confirmed by individual loop measured injection flows satisfying EOP criteria. Of particular concern is the flow split in the loop emergency cooling injection lines and the potentially large instrument uncertainty associated with measuring low flow rates. In the event one of the injection lines spills to containment (and possibly without a line spilling), traditional analysis methods based criteria would suggest adequate makeup flow may not be confirmed, and consequently the EOPs would prescribe external recirculation, which is not the preferred mode. In the present paper the EOP criteria for post LOCA core cooling flow is developed — using better estimate methods. Several (significantly) less restrictive analysis assumptions were identified and a new/materially different approach from that used in the past was taken. As result a more robust flow criterion was obtained — simpler and permitting about 0.019 m³/s [300 gpm] less flow.