Power Burst Facility (PBF) severe fuel damage test 1-4 test results report

1999

Models were designed to resolve deficiencies in the SCDAP/RELAP5/MOD3.2 calculations of the configuration and integrity of hot, partially oxidized cladding. The modeling was improved in five areas. First, the configuration defined for melted metallic cladding retained by an adjacent oxide layer was improved. The major basis for this improvement was a compilation of PIE results from severe fuel damage tests of the configuration of melted metallic cladding. In general, the PIE results showed that melted cladding relocates in the circumferential direction in cladding that has experienced at least a small degree of ballooning. The relocation in the circumferential direction decreases by about a factor of two the surface area of metallic cladding in contact with steam. Second, the empirical model to account for the effect on oxidation of intact cladding of relocated material was modified to account for PIE results showing that the oxidation of intact cladding is not significantly reduced by the presence of a rather high concentration of relocated material. Third, models for the dissolution of the oxide layer by the metallic layer were implemented into the code. Fourth, a model was added to calculate the thermal stress applied to the oxide layer by the temperature gradient across the oxide layer and to compare this stress to the ultimate strength of the oxide layer. The extent of dissolution is taken into account when evaluating the structural integrity of the oxide layer. Fifth, a new rule based on theoretical and experimental results was established for identifying the regions of a fuel rod with oxidation of both the inside and outside surfaces of the cladding. The assessment of these models and their integration into SCDAP/RELAP5 showed that the calculated axial distribution in cladding oxidation and relocation are in significantly better agreement with experimental results than is currently the case. The modeling changes account for three aspects of behavior that were not previously calculated correctly; (1) dissolution of a significant fraction of the cladding oxide layer during the incubation period of dissolution, when the dissolution occurs rapidly but only for a short period (~ 14 s), (2) oxidation of intact cladding in regions with a significant concentration of relocated material, and (3) failure of the oxide layer due to excessive thermal stress at locations with a rapid rate of oxidation and a high decay heat. The dissolution during the incubation period was calculated to have a significant impact on cladding meltdown in the upper region of a fuel rod, where steam starvation may limit the extent of cladding oxidation to less than 19% at the time the metallic part of the cladding melts. After completion of the incubation period of dissolution, the rate of thinning due dissolution in steam-rich locations was calculated to be less than the rate of thickness increase due to oxidation.The implementation of these models eliminates to a significant extent the tendency of the SCDAP/RELAP5 code to overpred...

Section: Behavior Of Cladding At Locations With Relocated Materialsmentioning

confidence: 59%

“…The PIE results were obtained from the five severe fuel damage experiments referenced in the previous section, namely the PBF SFD 1-1 test, 2 PBF SFD 1-4 test, 3 KfK CORA-13 Test, 4 PHEBUS B9+ test, 5 and the OECD LOFT FP-2 test 6 .…”

Section: Pie Results For Mapping Cladding Configurationmentioning

confidence: 99%

Models for the Configuration and Integrity of Partially Oxidized Fuel Rod Cladding at High Temperatures - Final Design Report

1999

“…This relationship is obtained by substituting Equation (13) into Equation (12). The result of this substitution is .…”

Section: Oxygen Transport and Dissolution Of Oxide Layermentioning

confidence: 99%

“…The 12 and KfK CORA-13 13 test problems will exercise the oxygen diffusion model and the modeling of the dissolution of the oxide layer into the metallic layer in the upper part of the test bundles where steam-starved conditions existed for a period of time. The KfK CORA-13 test had a measurement of the transient mass flow rate of hydrogen out of the test bundle region and thus will allow assessment of the modeling of hydrogen absorption after dissolution of the oxide layer and the subsequent release of the hydrogen as the cladding continues to heatup.…”

Section: Testing and Assessment Of Zr-h Interaction Modelsmentioning

confidence: 99%

Calculation of hydrogen and oxygen uptake in fuel rod cladding during severe accidents using the integral diffusion method -- Preliminary design report

1999

Preliminary 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 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 design is described for implementing the models for hydrogen and oxygen uptake and cladding embrittlement into the programming framework of the SCDAP/RELAP5 code. A test matrix is described for assessing the impact of the proposed models on the calculated behavior of fuel rods in severe accident conditions. This report is a revision and reissue of the report entitled; "Preliminary Design Report for Modeling of Hydrogen Uptake in Fuel Rod Cladding During Severe Accidents." vi

“…The result of this substitution is; (14) The variable E is a function of time and it is evaluated by the relationship between E and the average O/Zr ratio in the metallic layer. This relationship is obtained by substituting Equation (13) into Equation (12). The result of this substitution is .…”

Section: Oxygen Transport and Dissolution Of Oxide Layermentioning

confidence: 99%

Calculation of hydrogen and oxygen uptake in fuel rod cladding during severe accidents using the integral diffusion method -- Final Design Report

1999

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 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