The High Temperature Engineering Test Reactor (HTTR) is the first Japanese high temperature gas-cooled reactor of 30MW thermal power, which can extract high temperature heat up to 950°C from the reactor. The HTTR uses the refractory coated fuel particles as its fuel, graphite as the neutron moderator and helium gas as its coolant.
The HTTR has achieved the first criticality in November 11, 1998. After that, the HTTR has been demonstrating the inherent safety features of HTGR by implementing the safety demonstration tests. In Japanese fiscal year 2009, the HTTR has achieved the reactor outlet coolant temperature of 950°C. Moreover, the HTTR has performed the long-term high temperature operation during 50 days with reactor outlet coolant temperature of 950°C, which was the first experience in the world HTGR history.
To establish technical basis of HTGR by using the experimental data, we are progressing advancement of analytical technology about nuclear characteristics, thermal-hydraulics, safety analysis and fuel behavior of HTGR. With the advancement of nuclear characteristic analysis and thermal-hydraulics analysis, it will be possible to accurately analyze the amount fuel required for operation and the fuel temperature at normal operation condition. This allows HTGR design with reduced residual enrichment and improved power density. With the advancement of safety analysis and fuel analysis, it will be possible to accurately analyze the fuel temperature and exposure dose at accident condition. This allows HTGR design with rational safety margins.