The High Temperature Engineering Test Reactor (HTTR), whose outlet gas temperature and thermal output are 950°C and 30 MWt, respectively, started the construction in FY 1990 on the site of the Oarai Establishment of the Japan Atomic Energy Research Institute (JAERI). The HTTR aims at establishing and upgrading the technology basis necessary for the high temperature gas-cooled reactors (HTGR), serving at the same time as a potential tool for new and innovative basic researches related to various high temperature engineering areas. The construction of the reactor building on the site and the manufacture of the components at the factories are now proceeding. The first criticality will be attained in FY 1998.
The HTTR contains helium gas with the pressure of 3.9MPa and the temperature from 400°C to 950°C. Pressure boundaries of the HTTR are composed of a reactor pressure vessel (RPV), an intermediate heat exchanger (IHX), a primary pressurized water cooler (primary PWC) and so on. The RPV is the most important component of those pressure boundaries, since it contains core components such as fuel blocks, graphite reflectors, reactivity control system and core support structures which are very important for the safety of the HTTR.
The RPV, 13.2m in height and 5.5m in diameter, consists of a vertical cylinder, an upper and a lower hemispheres. As a material for the RPV, 21/4Cr-1Mo steel is employed, because this steel has better creep strength at high temperatures than Mn-Mo steel which is used widely in the pressure vessels of light water reactors. This paper briefly introduces the structural design of the RPV in the HTTR.
