Impact of Moderator History on Physics Parameters in Pressurized Water Reactors

The magnitude of differential reactivity effects that result from spectral differences in different portions of a pressurized water reactor (PWR) core is studied, and it is shown that these effects can be correlated very well with the local moderator history. The impact of these differences on physics parameters such as axial offset, isothermal moderator temperature coefficient, and differential control rod worth is shown to be significant for two PWRs of considerably different design.