Transient analysis for thermal margin with COASISO during a severe accident
Conference
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OSTI ID:21167849
- Seoul National University, San 56-1, Sillim-Dong, Kwanak-Gu, Seoul, 151-742 (Korea, Republic of)
- Purdue University, West Lafayette, IN 47907 (United States)
As an IVR-EVC (in-vessel retention through external vessel cooling) design concept, external cooling of the reactor vessel was suggested to protect the lower head from being overheated due to relocated material from the core during a severe accident. The COASISO (Corium Attack Syndrome Immunization Structure Outside the vessel) adopts an external vessel cooling strategy of flooding the reactor vessel inside the thermal insulator. Its advantage is the quick response time so that the initial heat removal mechanism of the EVC is nucleate boiling from the downward-facing lower head. The efficiency of the COASISO may be estimated by the thermal margin defined as the ratio of the actual heat flux from the reactor vessel to the critical heat flux (CHF). In this study the thermal margin for the large power reactor as the APR1400 (Advanced Power Reactor 1400 MWe) was determined by means of transient analysis for the local condition of the coolant and temperature distributions within the reactor vessel. The heat split fraction in the oxide pool and the metal layer focusing effect were considered during calculation of the angular thermal load at the inner wall of the lower head. The temperature distributions in the reactor vessel resulted in the actual heat flux on the outer wall. The local quality was obtained by solving the simplified transient energy equation. The unheated section of the reactor vessel decreases the thermal margin by mean of the two-dimensional conduction heat transfer. The peak temperature of the reactor vessel was estimated in the film boiling region as the thermal margin was equal to unity. Sensitivity analyses were performed for the time of corium relocation after the reactor trip, the coolant flow rate, and the initial subcooled condition of the coolant. There is no vessel failure predicted at the worst EVC condition when the stratification is not taken into account between the metal layer and the oxidic pool. The present predictive tool may be implemented in the severe accident analysis code like MAAP4 for the external vessel cooling with the COASISO. (authors)
- Research Organization:
- American Nuclear Society, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
- OSTI ID:
- 21167849
- Country of Publication:
- United States
- Language:
- English
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