Best-estimated calculation of the steam line break accident for the SMART-P

Small and medium sized nuclear reactors for the diverse utilization of nuclear energy have been receiving much attention from the worldwide nuclear industries due to the noticeable advantages of their safety and applications. Various sizes and types of advanced small and medium sized nuclear reactors are currently under development worldwide, and some of them are ready for construction. SMART (system-integrated modular advanced reactor), a small sized integral PWR (pressurized water reactor) with a rated thermal power of 330 MW is one of those advanced types of small and medium sized nuclear reactors. The basic design of SMART was completed at the KAERI in March 2002. The SMART is designed with such new innovative concepts and technologies as the inherent safety improving design features, passive engineered safety systems, system simplification, soluble boron-free core design, and so on. A new phase, which is called the 'SMART-P' in order to test and verify the SMART design, is currently underway at KAERI. The results of these tests and verifications will be fed back into the SMART basic design for a further improvement of the safety and reliability. A steam line break accident (SLB) is one of the most important accidents in the SMART-P for a fuel integrity point of view. Increase in the steam energy release from the steam generators causes an increase in the heat extraction rate from the reactor coolant system, resulting in a reduction of the primary coolant temperature and pressure. Assuming an actuation of the control rod or the engineered safety systems, a core power inherently seeks a bounded level because the negative moderator density reactivity and Doppler reactivity are characteristics of the core design for the SMART-P. The calculations are performed using a system analysis code, TASS/SMR, developed by KAERI. All the models including a non-condensable gas model, heat transfer at a helical coil and a straight tube, and a drift flux model for the inter-phase change, are contained in the TASS/SMR code. Best-estimated calculation of the SLB accident is aimed at investigating the thermal hydraulic phenomena for an increased heat removal transient of the SMART-P, and confirming its safety and reliability The SMART-P with the rated thermal power of 65.5 MW is currently in progress at the Korea Atomic Research Institute. This program is an innovative design to achieve a high degree of safety by adopting inherent safety improving features and passive safety systems. The realistic inherent behavior of the SMART-P following the SLB accident is performed using the TASS/SMR code. The results of the analyses using the realistic initial and boundary conditions and assumptions show that the SMART-P systems function properly and thus secure the reactor to a safe condition with respect to the safety parameters such as the CHFR and the pressure. The decay heat generated in the reactor core is well removed through the steam generators by the PRHRS natural circulation flow. There is no possibility of the return-to criticality in the core after the reactor trips due to the strong negative moderator density reactivity of the boron free core and the small secondary inventory. The primary pressure is always less than its initial value since the primary system is cooldown continuously during the transient. Efforts for the enhancement of the safety and reliability such as the improvement of the methodology and the design optimization are continuously pursued. The results of the on-going various individual verification tests will be fed back into the SMART design for a further improvement of its safety and reliability