LONG TERM MECHANICAL INTEGRITY STUDIES AND RELEASE FROM SPENT FUEL RODS FAILURE

摘要

This paper presents updated results from spent fuelexperimental studies performed at JRC-Karlsruheaddressing handling/transportation and long-termstorage issues. The consequences of potential accidentscausing spent fuel rod failure may involve fuel particlesrelease and dispersion. An impact test using a hammerdrop device and a bending test in hot cell were performedon a spent fuel segment from a UO_2 PWR rod with aburnup of ～67 GWd/tHM. The segments were not defueledand were repressurized to 40 bar before the test. Particlesize distribution analysis of the coarse fraction releasedfrom the rod breakage, which settled by gravity, and ofthe fine fraction, including fuel particles deposited on asecond stage filter of the testing chamber and particlesdeposited on the walls of the impact test chamber and onthe surfaces adjacent the bending setup, were performed.A large number of fine particles (ranging from submicronto >15 micron) was collected especially on thewalls of the impact test chamber. The detailed analysis ofthe results, including fine particle characterization, is stillongoing. The final goal of these investigations is todetermine criteria and conditions governing the responseof spent fuel rods to impact loads and other thermomechanicalsolicitations corresponding to normal and offnormalconditions that may be experienced by the rodduring handling, transportation, storage and afterextended storage. In addition to impact and othermechanical loading tests, property measurements as afunction of accumulated radiation damage are performedon spent fuel and alpha-doped analogues to determine thelong term evolution and the potential effects of ageingprocesses on the mechanical integrity of the spent fuelrod. Spent fuel rod alterations as a function of time andactivity and the alteration kinetics are monitored atmicrostructural level (defects and lattice parameterswelling) and at macroscopic property level (e.g.hardness and thermal conductivity). In order to reproducecumulative damage effects expected after very longstorage time within acceptable laboratory timescales,accelerated damage build-up conditions are applied bytesting unirradiated (U,Pu) oxide with high specificalpha-activity. Data from tailor-made samples arecompared to actual high burnup fuel (UO_2, MOX).