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In current high-temperature gas-cooled reactors (HTGRs), Tri-isotropic (TRISO)-coated fuel particles are employed as fuel. In safety design of the HTGR fuels, it is important to retain fission prod...

Since the first-loading fuel of the High Temperature Engineering Test Reactor (HTTR) is the first mass-production High Temperature Gas-cooled Reactor (HTGR) fuel in Japan, their quality should be carefully inspected. For the quality control related to the fabrication process, Japan Atomic Energy Research Institute (JAERI) carried out the tests to certify the fuel integrity during operation. The tests comprise (1) as-fabricated SiC failure fraction measurement, (2) high-temperature heatup test of irradiated fuel and (3) accelerated irradiation test. For (1), the SiC failure fraction was measured independently in JAERI in addition to the measurement in the fabrication process. The measured failure fractions agreed within 95% confidence limit. In order to confirm the integrity of the SiC layer with respect to the 1,600°C criterion, the high-temperature heatup test of irradiated fuel compact was carried out. The result showed that no failed particle was present in the fuel compact after heating. The diffusion...

In a high temperature gas-cooled reactor, a neutron startup source (NS) cannot be handled simply. An appropriate transfer vessel, connected with a 241Am–Be source for startup core physics tests through an NS coupler and drive wire, was newly designed and installed in the high temperature engineering test reactor (HTTR). A result of tests using the HTTR revealed that the NS could be loaded simply and certainly into the reactor core through the transfer vessel below the allowable limit of effective dose equivalent for operators.

The High Temperature Engineering Test Reactor (HTTR). which is the first high temperature gas-cooled reactor (HTGR) in Japan, attained its first criticality in November 1998. The fabrication of the...

Fractional release of cesium from coated UO{sub 2} particles for the high-temperature gas-cooled reactor (HTGR) is investigated. Data are measured in an irradiation test that utilizes three kinds of coated particles of artificially failed particles; they are simulating through-coatings failed particles, as-manufactured SiC-failed particles, and intact particles. Through the comparison of measured and calculated fractional releases, a model is revised to accurately evaluate cesium fractional release. The fractional releases of cesium from fuel compacts, which are manufactured by the same method as the high-temperature engineering test reactor fuel and are irradiated in the sweep gas capsule, are also evaluated. The result shows that the revised model can accurately predict measured fractional releases.

This paper reports on the ZrC-coated UO[sub 2] particle which is a promising fuel for high-temperature gas-cooled reactors. Particle fuels with multiple layers of pyrolytic carbon and ZrC have been irradiation-tested to a maximum fast-neutron fluence exceeding 2 [times] 10[sup 25]/m[sup 2] (E [gt] 29 fJ). In-reactor fission-gas release measured at a burnup of 1.5 at.% was minimal. The failure fraction by postirradiation examination was null for all samples. The ZrC-coated particles at 4 at.% burnup were postirradiation heated to 2400[degrees]C/min without failure until after 6000 s at the maximum temperature. It was found that the ZrC layer could sustain a large strain at such high temperatures. The behavior is in strong contrast with that of SiC of standard Triso coating, which is brittle to very high temperatures.

A real-time high-sensitivity fuel failure detection (FFD) method has been developed, where a wire precipitator radiation detector measures noble-gas fission products (FPs) released from a High Temperature Gas-Cooled Reactor (HTGR). By changing the reference counting rate of the precipitator between the normal state and the failed fuel state in real time in response to reactor operation conditions, i.e. reactor power, fuel temperature, coolant-gas flow rate and so on, fuel failure with an extremely low failure fraction (Release-to-Birth ratio

A study was made of uranium contamination in (a) the coating layers of TRISO particles (a-1) before compacting and (a-2) separated from once-compacted fuel heat-treated at 1,400 or 1,800°C, and (b) in the matrix material of the same compacts. The contamination in the pyrocarbon layers of the coating was determined, after mechanically separating the coating layers, by a procedure of neutron activation, burn-off and 133Xe trapping. For the silicon carbide coating layer, the fragments of coating left from the above procedure were fused into alkaline melt, and the 133Xe released at each heating step was trapped. For the matrix material, the fuel compacts were deconsolidated electrolytically or mechanically, followed by activation analysis. The results of the foregoing measurements proved the uranium contamination in pyrocarbon and silicon carbide coating to be at most of the order of 10−4 in reference to uranium content in kernel, while the corresponding value for particles sampled from fuel compacts heat-tre...

Coated fuel parrticles with free Si in the SiC layer and UC in the UC/ sub 2/ kernel were heated to 1,180 to 1,700 deg C for up to 200 h. Examination was made by metallography, x-ray diffraction, and electron probe. Results show that pores are formed in the coating upon heating, that the content of Si and UC decreased with temperature, and that Si diffused into the inner PyC layer and U diffused toward the coating. The coated fuel particles are liable to deterioration by heating above 1,460 deg C. The possible reaction of U with SiC is suggested. (DLC)