DART, A BCA CODE TO ASSESS AND COMPARE PRIMARY IRRADIATION DAMAGE IN NUCLEAR MATERIALS SUBMITTED TO NEUTRON AND ION FLUX

When a material is subjected to a flux of high-energy particles, its constituent atoms can be knocked from their equilibrium positions with a wide range of energies, depending on the exact nature of the collision. The spectrum of damage energy, derived from the exact knowledge of the recoil spectra for each nuclear reaction occurring in the solid, constitutes a vital data set required for understanding how materials evolve under irradiation. The knowledge of such damage energy is relevant to compare the impact of different facilities on the structural behavior and relevant properties of materials.

The DART code [1] was developed for two distinct reasons: the first one was a correct determination of the Primary Knocked on Atoms (PKA) spectrum from reliable cross section data libraries and the second was a crude estimation of the damage energy induced by different irradiations.This last term can be a quick estimation of radiation damage produced in the same material by different nuclear plants and particle accelerators.
Based on the Binary Collision Approximation, this code allows computing the primary spectra produced by neutrons, ions and electrons as well as the damage energy deposited by these particles in a poly atomic material.It is then a tool to compare radiation damage induced in nuclear reactors as well as ion beam facilities.As DART allows defining a poly atomic material as a mixture of different isotopes (and not only of natural elements), we achieved the same calculations when adding to pure iron, 10% of a specific isotope of nickel, Ni-59.Figure 3 shows the increase of damage energy due to the presence of this element.Ni-59 increases the damage energy by more than an order of magnitude in HFIR reactor.This effect is related to Ni-59 reaction with thermal neutrons [2].However, in fusion reactors, the low amount of thermal neutrons leads to a minimal impact on the damage energy due to the presence of Ni-59.

Figure 1
Figure 1 displays the neutron spectra for different reactors: ITER (fusion reactor), HFIR (High Flux Isotope Reactor), IFMIF (International Fusion Materials Irradiation Facility) and PWR (Power Water Reactor).Two ion beam spectra (Ar 800 keV and Xe 100 keV) are also plotted on this graph.

Fig. 1 :
Fig. 1: Neutron spectra for different reactors and beam spectra.DART calculations were performed to compare damage generated by these irradiations in pure iron.PKA spectra for the different irradiations are plotted on figure2, showing the strong dependence of the incident spectrum on the energy distribution of recoils.

2Fig. 2 :
Fig. 2: Comparison of PKA spectra in pure iron for different irradiations using the same formalism for ion and neutron.

Flux
. MINOS Workshop -November 4-6, 2015, CEA -INSTN Cadarache, France 10 RESULTS How to compare different irradiations?Which estimators?PKA spectrum for monoatomic material S(T) proportion of PKA having an energy <T Strong dependence of the incident spectrum Same PKA spectrum means same distribution of energy in the material PKA weighted spectrum for polyatomic material PKA spectra in iron PKA weighted spectra in Fe-10% 58 Ni The energy given to the recoil gives different number of displacements in each sublattice of the material.The recoil energy is then weighted by the number of displaced atoms to define the PKA weighted spectrum Comparison of PKA spectra for different irradiations Impact of XS evaluations (ENDF-BVII) Importance of Ni alloys (Inconel springs in Candu reactors) 58 Ni is the most abundant isotope in natural Ni RESULTS Energetic distribution of PKA after the collision between a neutron and a 58 Ni atom in the HFIR reactor Impact of XS evaluations (ENDF-BVII) Importance of Ni alloys (Inconel springs in Candu reactors) 58 Ni is the most abundant isotope in natural Ni Under neutron irradiation a transmutation of 58 Ni occurs 58 Ni + n  59 Ni  apparition of 59 Ni not present in natural Ni RESULTS Energetic distribution of PKA after the collision between a neutron and a 58 Ni atom in the HFIR reactor Transmutation 58 Ni + n  59 Ni Energetic distribution of PKA after the collision between a neutron and a 59 Ni atom in the HFIR reactor CEA -DEN 2 nd Int.MINOS Workshop -November 4-6, 2015, CEA -INSTN Cadarache, France 13 Impact of XS evaluations (ENDF-BVII) Importance of Ni alloys (Inconel springs in Candu reactors) RESULTS Energetic distribution of PKA after the collision between a neutron and a 58 Ni atom in the HFIR reactor Transmutation 58 Ni + n  59 Ni Energetic distribution of PKA after the collision between a neutron and a 59 Ni atom in the HFIR reactor 59 Ni + n  56 Fe + a 59 Ni + n  59 Co + H 59 Co 56 Fe The reaction of thermal neutrons on 59 Ni generates very energetic Fe ions (>500 keV) [Griffiths AECL Nucl.Rev 2 (2013)]