CHARACTERISTICS OF PEBBLE PACKING AND EVALUATION OF SWEEP GAS-PRESSURE DROP INTO THE IN-PILE MOCK-UP ON FUSION BLANKET

The characteristics of pebble packing and the sweep gas pressure drop have been investigated for the design of the in-pile mock-up in Japan Materials Testing Reactor, and the results obtained are the following. The packing fraction of single diameter pebbles is kept at constant, i.e., about 63%, under the condition that the ratio of tube inside dia meter to pebble diameter is above 10. The pebble distribution in the b ed is not homogeneous, i.e., the mixture of close packing and loose pa cking zones both in the middle of bed and near wall. The packing fract ion is about 77% for two-size pebble packing consisting of 01 and 5 mm pebbles. The measured pressure drops agree with those predicted by th e Kozeny-Carman equation within the range of (+25)-(-60)%. The pressur e drop is not affected by moisture concentration (<100 ppm) and does n ot change for tests lasting as long as 300 hours.