Japan Atomic Energy Agency, Oarai-Machi, Japan

19.1 Introduction

In this chapter, the status of small modular reactor (SMR) R&D and deployment in Japan is described. In Japan, the terminology of ‘SMR’ normally means small and medium sized reactor, following the same definition as in the IAEA (International Atomic Energy Agency). Based on the IAEA’s classification, the ‘small reactor’ has a power output less than 300 MWe and the ‘medium reactor’ between 300 and 700 MWe (IAEA, 2006). However, in this chapter, reactor concepts under the power output up to around 500 MWe are included, reflecting the SMR R&D status in Japan.

There was much SMR R&D activity in Japan in the past, especially after the accidents at Three Mile Island Unit 2 (TMI-2) in 1979 in the USA and Chernobyl Unit 4 occurred in 1986 in Ukraine. After the accidents, the passive safety characteristics in the reactor safety features that were considered to be favourable were introduced into reactor safety design, and then gathered a lot of attention as there was much interest in finding how they could be utilized as effectively as possible. In introducing passive safety features into the reactor design, the smaller size of the reactor, typically less than about 500 MWe, was in general easier than the larger size, such as more than 1000 MWe.

However, the small-sized reactors commonly have an economic defect, as it has been realized that the ‘scale merit’ — the advantages of scale that occur with larger plants — is important in reactor design for economic reasons. Therefore, in SMR R&D, it has been a very important requirement to overcome the ‘scale demerit’ of the smaller-sized reactors; this point will be discussed for each SMR concept. Apart from the passive safety features, there are some original and special needs or purposes, especially for small reactors, such as the variety of energy products and flexibility in design, siting and fuel cycle options.

The SMR R&D status in Japan is described in Sections 19.2 and 19.3, and the deployment of SMRs in Japan will be discussed in Section 19.4. The future trends in Japan and the sources of further information will be given in Sections 19.5 and 19.6, respectively.

Handbook of Small Modular Nuclear Reactors. http://dx. doi. Org/10.1533/9780857098535.4.469

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