Irradiation performance of HTGR fuel rods in HFIR experiments HRB-4 and -5

Abstract

Experiments HRB-4 and -5 were the first tests of weak-acid-resin-derived fissile fuel. This fuel was later selected as the reference recycle fissile kernel. The WAR-derived kernels did not exhibit thermal migration during irradiation, but there was some concentration of rare-earth fission products at the inner surface of the SiC coating. These experiments were also a test of fuel rods carbonized in graphite tubes, to simulate in-block carbonization. The results of these tests showed significant problems associated with in-block carbonization, notably a mechanical interaction between particles and matrix material. A significant development program was launched to solve these problems. HRB-4 and -5 also included three specimens prepared by an extrusion fabrication route. These specimens generally performed well, although some tiny cracks in the SiC layer, apparently caused by the fabrication process but accentuated by the irradiation, were noted.

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