March 28, 2024
Japan Atomic Energy Agency

Success of Safety Demonstration Test in HTTR
(High Temperature Engineering Test Reactor)
― Confirming the Inherent Safety Features of HTGR ―

The Japan Atomic Energy Agency (JAEA, president: KOGUCHI Masanori) successfully completed the world's first safety demonstration test for a prismatic*1 High Temperature Gas-cooled Reactor (HTGR) to demonstrate core melt does not occur even in the loss of forced cooling (LOFC) *2 by using the HTTR (High Temperature Engineering Test Reactor) installed at the Oarai Research and Development Institute.

The test was carried out from March 27 to 28 and we have confirmed that the reactor power of the HTTR naturally decreases and maintains stable even at the reactor forced cooling loss during 100% reactor power operation under the condition of restricted control rods insertion.

The test result demonstrates the inherent safety features*3 of HTGRs which do not induce core meltdown in principle, and this achievement means a major step toward social implementation of HTGRs.

JAEA will prove the inherent safety of the HTGRs and promote the international standardization of safety standards by using its safety characteristics through the HTGR development project and will contribute to strengthening the international competitiveness of Japan's HTGR technology.

JAEA will carefully operate the HTTR while giving top priority to ensuring safety.

*1 There are two types of HTGRs, prismatic and pebble-bed. The HTTR is a prismatic HTGR.

*2 Test demonstrates the decrease and spontaneous stabilization of the reactor power due to physical phenomena even if the helium circulators are stopped and the forced cooling function is lost under the condition where the reactor cannot be stopped using the control rods during reactor operation at 100% reactor power (30MW). The test was carried out as an international joint research project under the OECD/NEA (Organization for Economic Co-operation and Development/Nuclear Energy Agency) (see Attachments 1 and 2).

*3 The HTGRs use graphite having high heat resistance in the cores. Graphite has large heat capacity which gives large thermal inertia for cores. HTGRs have excellent inherent safety features, which do not cause fuel failure (core meltdown) because graphite plays the role of slowing temperature changes in the core at accidents.

Attachment 1 Results of safety demonstration test

Attachment 2 Overview of the HTTR (High Temperature Engineering Test Reactor)