Fig. 1-7 H2 production system connected to the HTTR H2 is produced with the high-temperature secondary He gas (around 900 degree Celsius) supplied from HTTR. A HTIV is installed at the secondary He hot gas duct.

Fig. 1-8 Model of the HTIV The valve seat is 1/2 scale of that of the HTIV for the H2 production system to be connected to the HTTR.

Fig. 1-9 He gas leak rate of the model of the HTIV The He gas leak rate through the closed valve seat was measured from 900 degree Celsius to 200 degree Celsius. The pressure difference across the valve seat was set to 4.0 MPa. The measured He gas leak rate was substantially less than 1/10 the target value.

A high-temperature gas-cooled reactor can produce a large amount of hydrogen (H2) without CO2 emissions by the splitting of water (thermochemical IS process) using high-temperature, 900 degree Celsius, nuclear heat. JAERI has been planning a H2 production demonstration test with the High Temperature Engineering Test Reactor (HTTR). To connect a H2 production system to the HTTR, a high-temperature isolation valve (HTIV) must be installed in the secondary helium (He) hot gas duct, which penetrates the reactor containment vessel (Fig. 1-7). The HTIV is used at high temperatures, around 900 degree Celsius; however, it has not yet been fabricated for actual use. Development of the HTIV is underway. The technical issues are as follows; (1) prevention of the valve seat from thermal deformation, (2) development of a new material for the valve seat surface, and (3) selection of a valve seat structure having a high sealing performance. An angle valve with an inner thermal insulator was selected. The detailed structure was decided by the thermal stress analysis for issue (1). For issue (2), a new valve seat material, with sufficient hardness and wear resistance over 900 degree Celsius, was developed based on the Stellite alloy that is used for valves at around 500 degree Celsius. Addressing issue (3), a component test of the valve seat indicates that a flat type valve seat can maintain the face roughness of the valve seat within allowable limits during operation. A 1/2 scale model of HTIV (Fig. 1-8) was fabricated to confirm seal performance and structural integrity. The He leak rate was confirmed to be less than the target value (Fig. 1-9). This study is entrusted from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

Reference T. Nishihara et al., Development of High Temperature Isolation Valve for the HTTR Hydrogen Production System, Nippon Genshiryoku Gakkai Wabun Ronbunshi, 3(4), 381 (2004) (in Japanese).

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