Fast neutron fluence on pressure vessel is a main parameter in the determination of the fracture toughness and the integrity of the reactor pressure vessel (RPV). In the framework of the dosimetry surveillance program its calculated value is extrapolated from measured reaction rate value on dosimeters located on the core barrel using neutron transport codes.
The EDF R&D EFLUVE3D code allows the calculation of neutronic fluence (flux over 1MeV integrated on time) received at the interface between the inner wall and the pressure vessel but also at the capsules of the pressurized water reactor vessels. The reaction rate of the dosimeters located in surveillance capsules can also be calculated by this 3 dimensionaltool.
The aim of EFLUVE 3D is to reproduce on a given configuration the flux and reaction rate results resulting from an exact Monte Carlo calculations with nearly the same accuracy. These EFLUVE3D calculations can be carried out monthly for each of the 58 reactors of the French current fleet in challenging time (less than 10mn for the total fluence and reaction rate calculations considering 14 different neutron sources of a classical power plant unit compared to more than 2 days for a classic Monte Carlo flux calculation at a given neutron source). Based on the adjoint flux theory, the code needs as input:
- for each reaction rate, the geometric importance matrice produced for a 3D pin by pin mesh on the base of Green’s functions calculated by the Monte Carlo code TRIPOLI4 associated to the JEFF3.1.1 library;
- the neutron sources calculated on assemblies data (enrichment, position, fission fraction in function of evolution), pin by pin power and irradiation. These last terms are based on local in-core activities measurements extrapolated to the whole core by application of the EDF core calculation scheme and a pin by pin power reconstruction methodology.
The code does the Source*Importance product which allows the calculation of the flux and the reaction rates at different axial positions and different azimutal positions of the vessel as well as at the surveillance capsules.
This paper presents the fundamental principles of the code and its validation comparing its results to the direct Monte Carlo TRIPOLI4 results. Theses comparisons show a deviation of less than 0,5% between the two codes equivalent to the order of magnitude of the calculation/stochastic convergence.