Oxidation of fuel-cladding during a hypothetical severe
accident in light water reactors is theoretically investigated in
an attempt to realistically simulate the time dependent heat
generation in a partially uncovered reactor core. Two modes of
oxidation, heterogeneous and homogeneous, are generally
considered. Heterogeneous oxidation refers to chemical
reactions with steam at the outer cladding surface in which a
dense oxide layer is formed that physically hinders the oxidant
from reaching the reacting metal. That mode of oxidation may
not fully explain the kinetics of cladding oxidation following
severe accident, where thermochemical reactions take place in
pores and cracks inside the metal. A theoretical model is,
therefore, developed to quantitatively understand the
homogeneous oxidation of degraded fuel cladding. A
dimensionless cracks’ concentration parameter, , is developed
in order to study the effect of cracks on the ignition temperature
of zirconium. A critical parameter, max , is identified above
which runaway ignition conditions are expected.
Steam temperature and decay power are the main
conditions leading to cladding heterogeneous ignition. Cracks
density could be important for evaluating homogeneous
oxidation of degraded cladding.
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .