Ryoichi Hamazaki

Core Melt Stabilization Concepts for Existing and Future LWRs and Associated Research and Development Needs

Abstract In the event of a severe accident in a nuclear power plant with the core melting, the stabilization of the molten corium is an important mitigation issue, as it can avoid late containment failure caused by basemat penetration, overpressure, or severe damage to internal structures. The related failure modes may result in significant long-term radiological consequences and related high costs. Because of this, the licensing frameworks of several countries now include a requirement to implement mitigative core melt stabilization measures. This applies not only to new builds but also to existing light water reactors. The paper gives an overview of the ex-vessel core melt stabilization strategies developed during the last decades. These strategies are based on a variety of physical principles, like melt fragmentation in a deep water pool or during the molten core–concrete interaction with top flooding, water injection from the bottom (COMET), and retention in an outside-cooled crucible structure. This overview covers the physical background and functional principles of these concepts, as well as their validation status and, if applicable, the remaining open issues and research and development needs. For the concepts based on melt retention inside a cooled crucible that have reached sufficient maturity to be implemented in current Generation III+ designs, like the VVER-1000/1200 and the European Pressurized Water Reactor, more detailed descriptions are provided, which include key aspects of the related technical realization. The paper is compiled using contributions from the main developers of the individual concepts.

Conceptual Design of European Advanced Boiling Water Reactor (EU-ABWR)

European Advanced Boiling Water Reactor (EU-ABWR) is developed by Toshiba. EU-ABWR has a large power generation capacity 1600MWe and the safety features meets European standards and regulation. This paper describes the conceptual design of EU-ABWR.Copyright

The Development of the Evolutionary BWR (AB1600)

Considering the delay of the first breeding reactor (FBR), it is expected that the light water reactor will still play the main role of the electric power generation in the 2030’s. Accordingly, Toshiba has been developing a new conceptual ABWR as the near-term BWR. We tentatively call it AB1600. The AB1600 has introduced the hybrid active/passive safety system in order to have independent countermeasure for severe accidents and better probability of core damage frequency (CDF) considered external events such as earthquake. On the other hand, we have another goal of the AB1600, which is to retain the safety performance superior or equivalent to the current ABWR without deterioration of economy. In order to achieve both economy and safety performance, we have optimized the safety system configuration of the AB1600 by partly introducing passive safety system to design basis event (DBEs). At the same time, we have adopted the simplification of the overall plant systems in order to improve economy. In order to reduce capital cost, to shorten refueling period and to reduce maintenance effort, the AB1600 introduces the large fuel bundle size. The bundle size is 1.2 times as large as that of the ABWR and the fuel rod array is 12 by 12. And then by progressing the core design, we can reduce the number of reactor internal pumps (RIPs) to eight from the current ABWR of ten. The core power density, the number of fuel bundles, and the core diameter of AB1600 are decided in order to achieve 24 months fuel cycle length on the condition with below 5wt% enrichment of fuel and with eight RIPs.Copyright