TRANSIENT ANALYSIS FOR DESIGN OF PRIMARY COOLANT PUMP ADOPTED TO JAERI PASSIVE SAFETY REACTOR JPSR

In a course of a design study of the JAERI passive safety pressurized water reactor (JPSR), a complete loss-of-flow transient caused by a tr ip of all pumps was analyzed with the RETRAN code to determine an iner tia of canned-motor pump utilized as the primary coolant pump and to c onfirm feasibility of the design condition. This transient was selecte d because the pump had a low inertia rotor inducing fast flow coastdow n, and among the transients in which the pump had dominant effect on t he departure from nucleate boiling (DNB), the analyzed transient was s everest in view of the DNB occurrence. The DNB threshold was related, based on sensitivity calculations, with the coolant density reactivity coefficient and the pump inertia. From the calculations, it was concl uded that the pump inertia higher than 250 kg . m(2) (8% of the ordina ry PWRs) was necessary for preventing the DNB occurrence for the prese nt design of JPSR, regardless of the actuation of the reactor scram. T he DNB occurrence could be prevented only by the inherent nature of th e reactor core which reduced the power by insertion of negative coolan t density reactivity during the transient and this was one of major fe atures of JPSR. It was shown by a rough estimation that the necessary condition could be practically realized by incorporation of a cylindri cal-type flywheel.