Creep of clad irradiation as an uncertainty in criticality safety margins that include the effects of burnup for pressurized water reactor fuel assemblies.

摘要

The uncertainties that must be associated with the effects of burnup when predicting the criticality safety margin of a spent fuel transport or storage cask must include allowances for phenomena that are not included in the prediction of the effects of burnup. One such phenomena is the creep of the clad during irradiation of fuel rods, which reduces the diameter of the clad as burnup progresses. The fuel management analyses of a power reactor are based upon unit cell calculations of the neutron spectrum that do not typically include reduction in the diameter of the clad due to creep. The analyses presented here evaluate the magnitude of the effects of creep and conclude that an uncertainty of 0.3% ((delta)k/k) should be assigned to the effects of creep. This uncertainty should be included with the other uncertainties to allow for the increase in the effective multiplication factor of a spent fuel cask that results from the changes in the isotopic inventories of uranium and plutonium in the fuel due to the effects of creep.