Book Description

Declassified 21 Sep 1973. Two W- UO/sub 2/- ThO/sub 2/ cermet fuel specimens, one clad with T-111 and the other with W-Re-- Mo, were studied to determine the retention, distribution, and mobility of fission gas in cermet core fuel systems. The T-11l- and W-- Re-Mo-clad specimens, irradiated for 5000 h to peak burnups of 5.6 x 10/sup 19/ and 5.0 x 10/sup 19/ fissions/cm/sup 3/ with temperature ranges of 530 to 1400 deg C and 770 to 1550 deg C, respectively, were gamma scanned and then punctured; fission gases were collected and analyzed for / sup 85/Kr. Thin transverse sections at various positions along the length were analyzed for /sup 85/Kr and /sup 137/Cs contents in the ceramic fuel and W matrix phases. Inventories and distributions of /sup 137/Cs and /sup 85/Kr between the UO/sub 2 / and and W phases were obtained as a function of temperature. Results showed that 90 to 95% of the total fission gas inventories were either dissolved in the UO/sub 2/ and W lattices or trapped in closed pores. The remaining 5 to 10% of the gases were mobile and free to migrate through channels between the fuel and matrix phases. 15 to 20% of the fission products recoiled into the W matrix and were essentially immobile under the experimental conditions. The gas which was free to migrate was released only from the fuel phase; gas release was negligible below about 650 to 700 deg C, and at 1550 deg C amounted to about 20% of that produced in that temperature region of the specimen. /sup 137/Cs was quantitatively retained by both the fuel and matrix phase for the conditions of these tests and, therefore, did not contribute to the amount of mobile gas. (10 figures, 3 tables) (DLC).