SAFETY ANALYSIS OF A SUPERCRITICAL PRESSURE, LIGHT-WATER COOLED AND MODERATED REACTOR WITH DOUBLE TUBE WATER RODS

The supercritical pressure, light water cooled and moderated reactor ( SCLWR) has once-through cooling system. All feedwater which cools the reactor core flows to the turbines. This paper summarizing the safety analysis of the SCLWR with double tube water rods. The plant system is simple but no natural circulation is established at the loss of feedw ater flow. The coolant inventory in the reactor pressure vessel is sma ll. The coolant density coefficient is approximately twice as large as that of the BWR. A computer code (SPRAT) was developed to analyze SCL WR behavior against major accidents and transients at supercritical pr essure. In loss of flow events such as loss of off-site power, the how coast down time should be larger than 10 sec. for avoiding the deteri oration in heat transfer. In the flow-excess event such as inadvertent start of the auxiliary feedwater pumps, the power increases approxima tely 25% by coolant density feedback. In the overpressurization transi ent such as generator load rejection, the power does not increase even if scram fails. This is because flow stagnantion raises coolant tempe rature and coolant density change at overpressurization is small in su percritical pressure. The reactivity-induced event such as control rod ejection, is not severe because of the small reactivity ingress. In t he loss of coolant accident, the double tube water rods delay the refl ood of the core. The core is heated up rapidly because of the small he at capacity and tight lattice pitch of the fuel rods. All analyzed acc idents and transients satisfied the criteria, and the feasibility of t he reactor was confirmed from the safety point of view. (C) 1997 Elsev ier Science Ltd.