Reactor pressure vessel design of the high temperature engineering test reactor

The reactor pressure vessel (RPV) of the HTTR is 5.5m (inside diameter), 13.2m (inside height), and 122mm (shell thickness). The RPV contains core components, reactor internals, reactivity control system, etc.2 1/4Cr-1Mo steel is chosen as the material for RPV. The temperature reaches about 400 deg. C at normal operation. The fluence of the RPV is estimated to be less than 1 x 1017n/cm2 (E > 1MeV) and so irradiation embrittlement is negligible, but temper embrittlement is not negligible. For the purpose of reducing embrittlement, content of some elements must be limited in the 2 1/4Cr-1Mo steel for the RPV; embrittlement parameters, J-factor and X-bar are used.In this paper, design and structure of the RPV are reviewed first. Fabrication procedure of the RPV and its special feature are described. Material data on the 2 1/4Cr-1Mo steel manufactured for the RPV, especially the embrittlement parameters, J-factor and X-bar , and nil-ductility transition temperatures, TNDT, by drop weight tests, are shown. In-service inspection and results of R and Ds are also described