Neutron Deep Penetration Calculations in Light Water with Monte Carlo TRIPOLI-4® Variance Reduction Techniques

Abstract

Nuclear decommissioning takes place in several stages due to the radioactivity in the reactor structure materials. A good estimation of the neutron activation products distributed in the reactor structure materials impacts obviously on the decommissioning planning and the low-level radioactive waste management. Continuous energy Monte-Carlo radiation transport code TRIPOLI-4 has been applied on radiation protection and shielding analyses. To enhance the TRIPOLI-4 application in nuclear decommissioning activities, both experimental and computational benchmarks are being performed. To calculate the neutron activation of the shielding and structure materials of nuclear facilities, the knowledge of 3D neutron flux map and energy spectra must be first investigated. To perform this type of neutron deep penetration calculations with the Monte Carlo transport code, variance reduction techniques are necessary in order to reduce the uncertainty of the neutron activation estimation. In this study, variance reduction options of the TRIPOLI-4 code were used on the NAIADE 1 light water shielding benchmark. This benchmark document is available from the OECD/NEA SINBAD shielding benchmark database. From this benchmark database, a simplified NAIADE 1 water shielding model was first proposed in this work in order to make the code validation easier. Determination of the fission neutron transport was performed in light water for penetration up to 50 cm for fast neutrons and up to about 180 cm for thermal neutrons. Measurement and calculation results were benchmarked. Variance reduction options and their performance were discussed and compared.

14 MeV neutron streaming calculations for JET-like maze entrance using TRIPOLI-4 Monte Carlo code

“…In this study due to the large size of JET-like torus hall and the thick shielding walls, the space and the energy meshes need to be adjusted in an iterative way in order to obtain an acceptable importance map. The performance of INIPOND in this work is similar to those of fission and D-T fusion neutron shielding calculations reported in previous studies [5,9].…”

“…They can slightly improve or degrade the FOM. The "Monitoring 0" option of TRIPOLI-4 was helpful to improve the fast neutron FOM and it was already shown in previous study [9]. The collision resampling option was activated so as to improve FOM values for both A7 and M6 positions (see Fig.…”

Uncertainty propagation for the design study of the PETALE experimental programme in the CROCUS reactor

“…Even if some variance reduction methods have already been implemented in recent developments [14] of Serpent2, a specific variance reduction has been developed in this work dedicated to applications for detectors near to a reactor with specific treatments according to the neutron energy. Different approaches exist, for example using weight windows [15] and adjoint flux [16] to drive the neutrons on a path leading to the detectors. However in this work the main target is the uncertainty propagation.…”

Recent developments in the TRIPOLI-4® Monte-Carlo code for shielding and radiation protection applications

“…We mention here an example recent shielding-V&V work that has been carried out on NAIADE 1 Water shielding benchmark [7]. For the nuclear decommissioning application, TRIPOLI-4 ® code capabilities on fission neutron deep penetration calculations were demonstrated.…”

“…Fig. 3 Recent example of shielding-V&V work: NAIADE 1 Water shielding benchmark [7] 3 New features of TRIPOLI-4 ® version 10 for shielding and radiation protection applications 3.1 Thick-Target Bremsstrahlung for electromagnetic shower simulation A simplified simulation mode for the electromagnetic shower, called Thick-Target Bremsstrahlung (TTB), has been implemented in TRIPOLI-4 ® version 10 to speed up coupled photon-electron-positron calculations. When this option is activated, secondary electrons and positrons produced by photon collisions are not transported, but part of their energy is converted into new bremsstrahlung photons.…”