SEVERE ACCIDENT STUDY OF MEDIUM COLD LEG BREAK ACCIDENT FOR A REFERENCE PWR 1000 REACTOR USING ASTEC CODE

Under postulated severe accident conditions in a nuclear reactor most of the radioactivity would be released from the damaged core to the containment in form of aerosols and chemical vapours and gases. However the radio-toxicity of released materials (source term) depends on both the released mass and on their chemical form. This paper presents the analysis of the severe accident initiated by a Medium Break on the cold leg combined with the total loss of electric power supply (Station Black Out) using the severe accident integral code ASTEC. As reference reactor a 3-loop 1000 MWe PWR type at the end of equilibrium fuel cycle has been used. A detailed description of the reactor model is given together with the sensitivity analyses performed in terms of break location and accumulator availability. The study shows that break location has an impact on the carrier gas temperature and in turn on the chemical speciation of the fission products. Fission-product retention is influenced by the different flow pathways that are established in the circuit. The accumulator availability extends the duration of the core degradation process affecting the total production of hydrogen and the cumulated released mass of fission products. In agreement with the ASTEC equilibrium chemistry model, the Molybdenum/Caesium molar ratio has the most influence on the fraction of Iodine which can reach the containment in the gaseous or highly volatile form. Due to the surplus of Caesium, the predicted dominant Iodine species to the containment are Caesium Iodide and its dimmer. A 3-4% of Iodine which reaches the break also exists in gaseous and highly volatile metal-iodides species.

AMMIRABILE Luca;  BUJAN Albert; 

2013-08-13

Grafiche Caroti – Pisa

JRC80218

https://publications.jrc.ec.europa.eu/repository/handle/JRC80218,