Numerical analysis and simulation of behavior of high burnup PWR fuel pulse-irradiated in reactivity-initiated accident conditions

Suzuki, Motoe; Sugiyama, Tomoyuki; Udagawa, Yutaka; Nagase, Fumihisa; Fuketa, Toyoshi

Proceedings of OECD/NEA Workshop on Nuclear Fuel Behaviour during Reactivity Initiated Accidents (CD-ROM), 11 Pages, 2009/09

The fuel behavior during the fast transients in the two cases of NSRR experiments using high burnup PWR fuel rods are analyzed by using the RANNS code. In one case, cladding failure occurred whereas in the other case the rod survived but gave rise to departure from nucleate boiling. The analytical results are compared with the metallographic observations of failed part of the cladding to discuss the failure-determining condition in terms of incipient crack depth, temperature and stress at the depth. Based on these evaluations, sensitivity study with respect to the effect of initial temperature on the stress/strain of cladding is conducted. In addition, simulations are performed in commercial reactor conditions. The results were compared with each other and failure capability of cladding is discussed.

Microstructure and mechanical property changes in fuel cladding during RIA-type temperature transients

Nagase, Fumihisa; Sugiyama, Tomoyuki; Fuketa, Toyoshi

Proceedings of OECD/NEA Workshop on Nuclear Fuel Behaviour during Reactivity Initiated Accidents (CD-ROM), 8 Pages, 2009/09

Laboratory-scale experiments are performed to examine microstructure and mechanical property changes of the fuel cladding during temperature transients and estimate the fuel behavior for a wide temperature range under various RIA conditions. Ductility of the cladding generally increases with the temperature. The ductility increase of the hydrided cladding is obvious between 300 and 473 K, while it is small between 473 and 573 K. Ductility increase due to recrystallization is not expected during the RIA-type quick transient. On the other hand, phase transitions above 1100 K occur so quickly and affect the mechanical property of the cladding. The influence of the hydride rim at the cladding periphery would not be seen above 870 K since hydrides in the rim are in solid solution for a very short time.

Influence of initial conditions on rod behaviour during boiling crisis phase following a reactivity initiated accident

Georgenthum, V.*; Sugiyama, Tomoyuki

Proceedings of OECD/NEA Workshop on Nuclear Fuel Behaviour during Reactivity Initiated Accidents (CD-ROM), 9 Pages, 2009/09