Research and test reactors, critical assemblies and prototypes at this site, as listed in the IAEA Research Reactor Database: type, thermal power, first criticality, shutdown date, current status and what each is used for.
Source: IAEA Research Reactor Database (RRDB), as of 2026-10-13.
Working Here
Per Diem Rates
FY 2026
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Per diem covers lodging and meals & incidental expenses (M&IE) for government and contractor travel near this facility. Rates are from the U.S. State Department foreign per diem tables for FY 2026.
$208
Lodging/Night
$107
M&IE/Day
$315
Total/Day
Japan: rate for locations the State Department does not list separately
U.S. Department of State foreign per diem, for U.S. government and contractor travel.
Interactive satellite map showing the facility's geographic location. Marker color indicates current status: green for online, red for offline, orange for reduced power. Click the header to open in Google Maps satellite view.
36.2672, 140.551
Location & Contact
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Physical address, phone number, and website for this facility. Use the directions link to get driving directions via Google Maps.
Written by NukeWorker from public records: facts that do not change. Operator, status and capacity come from the live data elsewhere on this page. Sources: JAEA: Joyo users guide; JAEA: HTTR FAQ; JAEA: Decommissioning and R&D of JMTR.
The Oarai Research and Development Institute is a nuclear research site of the Japan Atomic Energy Agency in the town of Oarai, Ibaraki Prefecture. Its predecessor organizations began work at Oarai in April 1967 (the Japan Atomic Energy Research Institute) and March 1970 (the Power Reactor and Nuclear Fuel Development Corporation). Its reactors are Joyo, JMTR and HTTR.
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The Japan Materials Testing Reactor (JMTR) was under construction from April 1965, reached first criticality in March 1968 and finished its last cycle in August 2006. Its decommissioning plan was approved on March 17, 2021. The sodium-cooled fast reactor Joyo reached first criticality on April 24, 1977. The high temperature gas-cooled reactor HTTR reached first criticality on November 10, 1998, and reached a 950 degree Celsius outlet temperature on April 19, 2004.
