Severe accident research at JAERI

Severe accident research at JAERI was initiated soon after the TMI-2 accident in 1979 and has been accelerated after the Chernobyl accident in 1986. JAERI's research activities aim at the confirmation of the safety margin, the quantification of the risk, and the evaluation of the accident management measures of the nuclear power reactors. JAERI has conducted wide range of severe accident research activities both in experiment and analysis, such as core degradation behavior, fission product behavior both in coolant system and containment, containment integrity and assessment of accident management measures. For the core degradation behavior JAERI has conducted in-pile experiments using NSRR. For the high temperature behavior of fuel and core materials, core material interaction tests has been performed. TMI debris sample examinations have been performed at the Hot Laboratory. Three-dimensional thermal and inelastic stress analysis of the lower head of the TMI-2 vessel has been completed. For the fission product behavior, the pool scrubbing experiments at elevated temperature and pressure of TMI-2 accident have been conducted. An overall aerosol behavior in containment has been investigated as part of ALPHA Program. Experiment on deposition of aerosols in the piping of 40mm diameter has been conducted. It was found that three-dimensional flow in the piping of 40mm diameter has been conducted. It was found that three-dimensional flow in the piping is important to predict the deposition behavior. A new project on FP aerosol behaviors in the primary piping named Wind Program has been initiated. This project aims at the revaporization of aerosol due to decay heating and also the integrity of the piping from this heat source. Ex-vessel phenomena such as molten core and coolant interaction, and the leakage through containment penetrations have been investigated in ALPHA Program. Efforts are being made for the evaluation of void fraction in the premixing zone before the occurrence of steam explosion for the development of analytical model. In order to investigate the effectiveness of the preventive accident management measures, ROSA-V Program has been initiated. The feed and bleed measures in the primary and secondary system are investigated. The effectiveness of the mitigative accident management measures such as water addition onto the molten core has been investigated in ALPHA Program. Code development activities have been conducted for an integrated source term analysis code, THALES-2, fission product analysis code, ART, and containment aerosol analysis code, Removal at JAERI. Application of detailed and mechanistic codes, such as SCDAP/RELAP5, Contain, and Cordon, to experimental analyses has made progress by participating international standard problem and code comparison exercises. Severe accident research, selected as one of important safety issues, will be continued in accordance with the government five-year nuclear safety research plan which will cover the period between F Y 1996 and F Y 2000