Analysis of fission product source term release and decay heat under pressurized water reactor rupture accident

Abstract

BackgroundDuring severe reactor accidents, melten core causes the radioactive source term material to be no longer retained in the fuel but is released into the environment, causing serious radioactive contamination in the surrounding areas.PurposeThis study aims to investigate the release of fission products, both inside and outside the pressure vessel, using different models in order to analyze the effectiveness of the spray system in controlling the source term release and the decay heat generated.MethodsBased on a typical mega kilowatt pressurized water reactor (PWR) nuclear power plant model, the integrated security analysis program MAAP was applied to modeling reactor rupture accident. Then, the accident sequence and consequences of the reactor primary circuit heat pipe breakage superimposed high and low voltage safety injection failure were calculated and analyzed under CORSOR-M, CORSOR-O and ORNL-BOOTH source term release models.ResultsThe findings indicate that the fission product source term is mainly released in the pressure vessel, and the release amount is significantly higher than that released outside the pressure vessel. Under the CORSOR-O model, the pressure vessel fails the last whereas the containment fails the first; although the pressure vessel fails first in the ORNL-BOOTH model, the containment vessel fails much later than that in the other two models. The difference in source term release leads to different decay heat phenomena in different models, and the main heat source is the volatile fission product. Turning on the spray can not only keeps the suspended iodide in the containment vessel but also effectively removes the decay heat generated by the source items and reduces the pressure of containment.ConclusionsThe ORNL-BOOTH model results in lesser release of source term in the pressure vessel, the greatest variety of source term released, and the maximum time to containment failure. In addition, the opening of the spraying system effectively ensures the integrity of the containment.

Keywords

• breaching accident
• fission product source term
• failed containment
• spray system
• decay heat