Vessel Fluence Assessment with the EFLUVE Code and a Low-Fluence Fuel Management Scheme

The EFLUVE software package enables simple and quick assessment of pressurized water reactor (PWR) vessel fluence. It is a three-dimensional code that analyzes neutron propagation inside and then outside the core by applying the straight-line attenuation method and using only fast neutrons. The code is designed to assess the flux of >1-MeV neutrons received on the vessel or irradiation capsules and then to calculate their fluence. The purposes of this code are as follows:

1. to perform fast and sufficiently accurate calculations to enable continuous monitoring of the fluence in all PWR vessels, for all operating cycles, throughout the lifetime of all French PWRs
2. to provide a basis for parametric studies aimed at assessing the effect on fluence values of a new fuel management method [four-cycle UO₂ or three-cycle mixed-oxide (MOX) fuel]
3. to assess the effect of plutonium in MOX fuel management.

The effect of low-fluence loading patterns on vessel fluence is then discussed in the context of MOXfuel management. A vessel fluence reduction of ∼40% can be achieved for uranium and plutonium fuel management schemes with low-leakage loading patterns.