EVALUATION OF FUNCTIONAL ADEQUACY OF ELECTRICALLY OPERATED INSTRUMENTED RELIEF VALVES OF PRIMARY HEAT TRANSPORT SYSTEM FOR 700MWE INDIAN PRESSURIZED HEAVY WATER REACTOR
700MWe Indian Pressurized Heavy Water Reactor (IPHWR) is horizontal channel type reactor with partial boiling at channel outlet. It has primary and secondary heat transport system with two loops in primary system. For over pressure protection in main primary heat transport (PHT) system, relief system is provided. The PHT relief system consists of 4 numbers of instrumented relief valves (IRVs) i.e. 2 numbers in each loop located at north side outlet header inside reactor building. Historically, IRVs of IPHWRs are pneumatically operated. Response time of each IRV is normally low (<1 second) so that, it can quickly attain its required capacity during an over pressure transient and keeps PHT pressure within limit.
To improve operational reliability, safety and to minimize air operated valves located inside Reactor Building, IRVs of 700MWe IPHWR are being electrically operated. As the response time for electrically operated IRVs is higher (~ 2 seconds) than that of the pneumatically operated ones, analyses have been carried out to evaluate the effect of change of response time on the limiting over pressure transients.
To simulate this behavior for 700MWe IPHWR, thermal hydraulic modelling of primary and secondary heat transport system is done. All relevant process control program and reactivity control program have also been modeled to capture overall plant dynamics. Transient analyses postulating initiating events which could result in over pressurization of PHT system have been carried out with 3-D neutron kinetics coupled thermal hydraulic computer code ATMIKA.T. This paper brings out the effect of change in response time on peak pressure of primary heat transport system during the limiting over pressure transients.