A Review on Analysis of LWR Severe Accident

Abstract

A severe accident (SA) is defined as an incident involving melting of the nuclear reactor core and the release of fission products (FP) from the fuel and their associated risks. In the SA, the containment may fail, causing the public hazard of fission products released to the environment. This review elaborates the resolved issues of SAs under the condition of a hypothetical SA. SA research that has been performed over the years is briefly described, including various SA scenarios. The SA scenarios involve core melt scenarios from the beginning of core degradation to melt formation and relocation into the lower head and to the containment, the interactions of the molten corium with water and concrete, the behavior of fission products in- and ex-vessel, hydrogen-related phenomena, and all associated risks. The mitigation strategies that have been adopted in existing reactors and advanced light water reactors (ALWR) are also discussed. These mitigation measures can keep the reactor vessel or containment intact and terminate the SA progression. SA analysis codes are then summarized and divided into three categories, namely, systematic analysis codes, mechanism analysis codes, and single-function analysis codes. Next, the unresolved issues of SAs are proposed, including narrow gap cooling, melt chemical interactions, steam explosion loads, molten debris coolability, and iodine chemistry. Further experimental and theoretical research activities should be conducted to resolve these issues; consequently, some recommendations for further research work are also given in the last part of this review. This review aims to add to the knowledge and understanding of SA research in the past few decades and to benefit further research of SAs.

Natural convection of melted core at the bottom of nuclear reactor vessel in a severe accident

“…Core end‐state configuration in a TMI‐2 accident [Colour figure can be viewed at wileyonlinelibrary.com]…”

Isothermal Experiments on Steam Oxidation of Zr−Sn−Nb Alloy at 1050 °C: Kinetics and Process

“…Zirconium alloys are easily damaged due to the pressure inside the cladding tubes. Moreover, in the Fukushima accident in Japan in 2011 [ 8 , 9 ], oxidation of zirconium metal and water/steam occurred, releasing a large amount of hydrogen gas [ 10 ]. This led to an explosion which posed a hazard to human society and the natural environment.…”

Uncertainty Quantification of the PHEBUS FPT-1 Test Modelling Results

“…However, at the end of the 1970s, for the first time, a large nuclear power plant experienced severe core damage and was defined as a nuclear severe accident [3]. Severe accidents are defined as accidents involving reactor core degradation and meltdown in nuclear power plants [4,5] when harmful radioactive release to the public. Despite the low probability of the occurrence of severe accidents, the major accidents, including the Three Mile Island accident in 1979, the Chernobyl accident in 1986, and the Fukushima Daiichi accident in 2011 have forced researchers all over the world to examine severe accidents to define appropriate severe accident mitigation and management strategy [6,7].…”