Assessment of passive safety system of a Small Modular Reactor (SMR)

• The MASLWR test facility has been modeled in RELAP5-SCDAP. The model is validated by comparing the simulation results with the experimental data.
• Results obtained from various transients show that high pressure vent and sump recirculation lines provide natural circulation flow path for long term cooling of core.
• New scenarios are considered in which the effect of vent and sump recirculation valves failure has been investigated.
• It is found from the results that continuous loss of inventory occurs due to lack of recirculation.
• It is concluded that the high pressure vent valves in the MASLWR safety system require more redundancy.

Innovative SMRs are designed with enhanced safety features based on lessons learnt from past experience of plant operation. Reliance on natural circulation and addition of passive safety systems made them inherently safe and simple in design. It is required to study reliability assessment of passive safety systems during postulated transients prior to their deployment on commercial scale. Test facilities and best estimate system codes are playing significant role in assessment of passive safety systems as well as in design, certification and evaluation of these innovative types of reactors. RELAP5 code is widely used for thermal-hydraulic analysis of nuclear reactors. In this work, the passive safety systems of Multi-Application Small Light Water (MASLWR) have been assessed. The complete loop of the MASLWR test facility has been modeled in RELAP5-SCDAP Mod 4.0. The RELAP5 model is validated by comparing the simulation results with the experimental data. Results obtained for various transients show that high pressure vent and sump recirculation lines provide natural circulation flow path for long term cooling of core to avoid core heat up.Some of the components of passive safety system of MASLWR still rely on active power. Therefore, it was necessary to investigate their performance under failure of these components. New scenarios are considered in which the effect of vent and sump recirculation valves failure has been investigated in the present work. It is found from the results that continuous loss of inventory occurs due to lack of recirculation. It is thus concluded from this study that the high pressure vent valves in the MASLWR safety system require more redundancy.