Quench behavior of zircaloy fuel rod cladding tubes. Small-scale experiments and modeling of the quench phenomena

In all severe accidents scenarios the main goal of operator actions (AMM, accident management measure) will be the injection of water into the core region as soon as possible and as much as possible, in order to reestablish adequate core cooling for termination of the accident. Flooding of the uncovered core is the accident management measure with top priority. The quenching can cause renewed oxidation of the Zircaloy fuel rod cladding, resulting in a temporary temperature increase of the rods before cool-down occurs, a sharp increase in hydrogen production and the release of additional fission products. Especially a very high hydrogen production rate is of concern because any effective hydrogen mitigation system (catalytic recombiners, controlled deflagration) must be able to cope with such rates. A series of separate-effects tests is being carried out on Zircaloy PWR fuel rod cladding to study the enhanced oxidation which can occur on quenching. In these tests single tube specimens are heated by induction to a high temperature and then rapidly cooled down by injection of a cold steam. The principal experimental parameters investigated are the extent of pre-oxidation and the temperature of the tube before cooldown. A total of 24 experiments has been performed with specimens with oxide layer thicknesses varying from 100 #mu#m to 350 #mu#m which were rapidly cooled by steam from 1100 C, 1200 C, 1400 C and 1600 C. (orig.)48 refs.Available from TIB Hannover: ZA 5141(6208) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman