LWR spent fuel dry storage behavior at 229/sup 0/C

Abstract

A whole rod test was conducted at 229/sup 0/C to investigate the long-term stability of spent fuel rods under a variety of possible dry storage conditions. All combinations of BWR or PWR rods, inert or air atmospheres, and intact or defected rods were tested. After 2235 hours, visual observations, diametral measurements and radiographic smears were used to assess the degree of cladding deformation and particulate release. The same examinations plus metallography and x-ray analysis were conducted after 5962 hours. None of the intact rods, the rods tested in inert atmosphere, or the defected PWR rod tested in unlimited air showed any measurable change from the pretest condition. The upper defect on the BWR rod tested in unlimited air had split open approx. 0.5 in. after 2235 hours and had approx. 10% cladding deformation. The crack grew to approx. 2.5 in. after 5962 hours. X-ray analysis indicated that the UO/sub 2/ had oxidized to U/sub 3/O/sub 8/. The difference in behavior of the upper and lower defects is attributed to the air's accessibility to the fuel because of the defect's position with relation to the pellet-pellet interface. The oxidized fuel appeared to form a powdery compact that remained for the mostmore » part in the split cladding. Only a fraction of the fuel that fell out of the cladding became airborne. Some crud spalled from the rods but appeared to have no airborne particulate in the 2- to 15-..mu..m respirable range.« less