I'm trying to see, the reactivity worth effect for Gd enrichment modification especially if we increase Gd157 and Gd155 percentage (since natural Gd currently used in PWR). Another thing is the idea of UO2-Gd2O3 rod, if I put several layer inside this rod, and each layer may have different wt % of natural Gd (and enriched Gd in other cases). The aim is as usual, to obtain high rod worth, and generally would help reduce CBC and MTC, for PWR reactor. I'm not focusing on optimum fuel assembly pattern. Anyway if I just neglect temperature fedback (just to make it easy with MCNP) the error would be significant?
With MCNP you can use cross sections at different temperatures and get some idea on the magnitude of the effect.
There are a number of temperature dependent phenomena that can actually affect the neutron spectrum/distribution and hence reactivity. the Doppler broadening effect affects the microscopic cross-sections and such phenomena as thermal expansion alter the macroscopic cross-sections. I think you could get a pretty good idea of the error margin by taking a look at cross-sections and thermal expansion coefficients...
Thank you, i guess i need Njoy to have XS at several different temperature.
There are pre-compiled cross-sections you could get over the internet. Search for the ADS 2.0 library. They have cross-sections at different temperatures and different formats.
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