Fumimasa Araya

A concept and safety characteristics of JAERI passive safety reactor (JPSR)

Abstract A JAERI passive safety reactor (JPSR) system has been developed for reduction of manpower in operation and maintenance and increase of safety. The major features are as follows; an inherent matching nature of core heat generation and heat removal, in-vessel control rod drive mechanism units, once-through steam generators, a large volume pressurizer, passive heat removal system, and passive safety injection system. The passive heat removal system consists of residual heat exchangers, gravity coolant injection pools and air coolers. Steady-state analysis clarified that core residual heat during the whole period from shutdown to refueling phase can be transferred by natural circulation to the gravity coolant injection pool and finally to the atmosphere. In case of a large break loss-of-coolant accident (LOCA), steam is discharged and condensed in the gravity coolant injection pool. It was evaluated that the pool water temperature remains below boiling temperature under the large break LOCA condition. In the course of the design study, probabilistic safety assessment (PSA) was used to clarify the safety features and weak points. The results indicated that loss of offsite power is the dominant initiating event. Based on the analyses, improvements of safety system design were proposed.

Feasibility Study of Double-Flat-Core Type HCPWR for Reactivity Initiated Accidents.

A conceptual design of a double-flat-core type high conversion pressurized water reactor (HCPWR) has been developed at the Japan Atomic Energy Research Institute to improve fuel utilization. In thermal-hydraulic feasibility studies of the proposed concept, major six events such as large and small break LOCAs have been analyzed with the best estimate code REFLA/TRAC. This paper describes the results of control rod ejection accident analyses as a part of the series of analyses. The calculations were performed according to the licensing analysis on current PWRs. The calculated results showed that the proposed concept had larger safety margines than current PWRs. Therefore, the proposed concept is considered to be feasible from a view point of safety analysis of control rod cruster ejection accident. It is seen that the large safety margine of the proposed concept is originated from smaller excess reactivity, smaller maximum linear heat generation rate and smaller rod worth per a control rod than those of current PWRs.