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• Effect of dose rate on loop characteristics was studied in situ during H 2 + irradiation. • Dose rate obviously affected the nucleation rate, growth rate, and types of loops. • High dose rate induced high density, small average size, and low growth rate of loops. • High dose rate caused low irradiation hardening and damage induced by loops. • High dose rate was beneficial to the generation of perfect dislocation loops. Ion irradiation is usually used to simulate neutron irradiation to accelerate the evaluation of the irradiation behavior of reactor materials. However, the validity of using a high damage rate of ion irradiation to simulate a low damage rate of neutron irradiation has always been a controversial topic. Here, the effect of two dose rates (2.94 × 10–6 and 7.35 × 10–5 dpa s–1) on the characteristics and evolution of dislocation loops in palladium was studied in situ during 30 keV H 2 + irradiation using transmission electron microscopy. The dose rate obviously affected the nucleation rate and growth rate of dislocation loops, the types (Frank loops or perfect loops) of dislocation loops, and the irradiation hardening and total damage obtained from the product of average loop size and loop density. At the same irradiation dose, a high dose rate would lead to high loop density, small average loop size, low loop growth rate, and low irradiation hardening and damage induced by loops in pure Pd. Meanwhile, it was found for the first time that a high dose rate was beneficial to the generation of perfect dislocation loops. The effect of dose rate was attributed to the different dynamic equilibrium results between the effective generation rate of point defects and their absorption rate by existing sinks. The present results show that the effect of dose rate should be considered when using ion irradiation to simulate neutron irradiation to evaluate the irradiation damage to materials. [ABSTRACT FROM AUTHOR]

A photon transport capability has been implemented and verified in the Monte Carlo code MCS of Ulsan National Institute of Science and Technology for the purpose of radiation shielding studies. The MCS photon fixed-source mode simulates the transport of photons between 1 keV and 20 MeV for all elements from hydrogen to fermium. The specific physics for the main four photo-atomic reactions (Rayleigh scattering, Compton scattering, photoelectric effect and pair production) and three secondary processes of photon production (positron–electron annihilation, atomic relaxation and electron/positron bremsstrahlung) are reviewed. Verification results against Monte Carlo codes MCNP6.1 and SERPENT2.1.29 are presented. The verification cases include the comparison of energy distributions of photon flux in an infinite medium, of spatial distributions of photon flux in a cylinder, of the spatial distribution of photon body-equivalent dose in a spent nuclear fuel transport cask, and of photon KERMA (Kinetic Energy Released per MAss) in photon detector calibration geometries. Good calculation/calculation agreement is observed overall, with some marked differences in the detailed photon flux comparison at given energy ranges traced back to differences in photon physics implementation. MCS can from now on be applied for the purpose of advanced photon studies and corresponding validation against experimental shielding benchmarks will follow in the future. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an approach to optimize a computational fluid dynamics problem coupled with radiation physics for sludge hygienization research irradiator. This was implemented by mapping results of computational fluid dynamics using recurrent artificial neural network with simplified dose rate evaluation using modified Sievert integral. This methodology led to considerable reduction of computation time while maintaining enough accuracy to validate the experimental results as well as suggest an optimum placement of source pencils using reference point based multi-objective optimization. [Copyright &y& Elsevier]