Calculation of Hydrogen and Oxygen Uptake in Fuel Rod Cladding During Severe Accidents Using the Integral Diffusion Method - Final Design Report [report]

Larry James Siefken
1999 unpublished
Final designs are described for models of hydrogen and oxygen uptake in fuel rod cladding during severe accidents. Calculation of the uptake involves the modeling of seven processes: (1) diffusion of oxygen from the bulk gas into the boundary layer at the external cladding surface, (2) diffusion from the boundary layer into the oxide layer, (3) diffusion from the inner surface of the oxide layer into the metallic part of the cladding, (4) uptake of hydrogen in the event that the cladding oxide
more » ... the cladding oxide layer is dissolved in a steam-starved region, (5) embrittlement of cladding due to hydrogen uptake, (6) cracking of cladding during quenching due to its embrittlement and (7) release of hydrogen from the cladding after cracking of the cladding. An integral diffusion method is described for calculating the diffusion processes in the cladding. Experimental results are presented that show a rapid uptake of hydrogen in the event of dissolution of the oxide layer and a rapid release of hydrogen in the event of cracking of the oxide layer. These experimental results are used as a basis for calculating the rate of hydrogen uptake and the rate of hydrogen release. The uptake of hydrogen is limited to the equilibrium solubility calculated by applying Sievert's law. The uptake of hydrogen is an exothermic reaction that accelerates the heatup of a fuel rod. An embrittlement criteria is described that accounts for hydrogen and oxygen concentration and the extent of oxidation. A description is given of the implementation of the models for hydrogen and oxygen uptake and cladding embrittlement into the programming framework of the SCDAP/RELAP5/MOD3.3 code. The hydrogen and oxygen uptake models together with other early-phase damage progression models added to MOD3.3 were assessed using the results of several severe fuel damage tests. In general, the calculated behavior of the test bundles during the severe fuel damage tests was in good agreement with measured behavior. The capability of the integral diffusion model to calculate oxide layer thinning at locations with steam starvation was found to significantly improve the calculated axial distribution in the extent of cladding oxidation. This report is the final design version of the report with the identifier of INEEL/EXT-98-00664 Revision 1, entitled "Preliminary Design Report for Modeling of Hydrogen Uptake in Fuel Rod Cladding During Severe Accidents -Preliminary Design Report." vi
doi:10.2172/911489 fatcat:3dp3g6gwlfdillpmri5ufocdoi