Monte Carlo calculations of local reactivity perturbations

Institute of Nuclear Power, Academy of Sciences of the Belorussian SSR. Translated from Atomnaya Énergiya, Vol. 71, No. 3, pp. 195–199, September, 1991.     

On the use of the Serpent Monte Carlo code for few-group cross section generation

Serpent is a recently developed 3D continuous-energy Monte Carlo (MC) reactor physics burnup calculation code. Serpent is specifically designed for lattice physics applications including generation of homogenized few-group constants for full-core core simulators.     

~(115)In中子非弹性散射截面的实验测量及蒙特卡罗修正

~(115)In是一种重要的活化材料,准确测量它的中子非弹性散射截面数据对中子注量监测具有重要意义。在四川大学原子核科学技术研究所2.5 MV静电质子加速器上,利用核反应D(d,n)~3He产生的单能中子,以~(197)Au作为标准,采用活化法测量了2.95 Me V、3.94 Me V、5.24 Me V能点的~(115)In中子非弹性散射截面。用Monte Carlo程序MCNPX(Monte Carlo N-Particle eXtended)对靶头材料、冷却水层和样品的包层材料等引起的多次散射效应及注量率衰减效应等进行了修正计算,得到最终结果与Loevestam的计算值符合较好,并且实验中可通过减小靶管、靶底衬、水层及样品的包层材料等厚度来减小多次散射效应和自屏蔽效应的影响。     

Solution of transport equations by the Monte Carlo method,taking account of the space-time variation in the interaction cross section

Power-Physics Institute. Translated from Atomnaya Énergiya, Vol. 70, No. 2, pp. 75–78, February, 1991.     

Improvement of the Bayesian neural network to study the photoneutron yield cross sections

This work is an attempt to improve the Bayesian neural network (BNN) for studying photoneutron yield cross sections as a function of the charge number Z, mass number A, and incident energy ε. The BNN was improved in terms of three aspects:numerical parameters, input layer, and network structure. First, by minimizing the deviations between the predictions and data, the numerical parameters, including the hidden layer number, hidden node number, and activation function, were selected. It was found...     

Monte Carlo simulation study of the positron contribution to displacements per atom production in YBCO superconductors

The contribution from positrons to the displacements per atom (dpa) distribution induced by the gamma irradiation on YBCO superconducting slabs is presented. The procedure implemented previously by the authors was adapted to take into account the contribution from positrons to dpa induced by the gamma radiation. The results show that, when positrons are considered in the atom displacement process, the total dpa almost doubles at 10 MeV of incident gamma radiation. At that energy positrons contribute 7% more to the total dpa than electrons, although electrons maintain having the highest contribution up to about 8 MeV.     

Object kinetic Monte Carlo study of sink strengths

The sink strength for three-dimensionally (3D) versus one-dimensionally (1D), or mixed 1D/3D, migrating defects in irradiated materials has attracted much attention in the recent past, because many experimental observations cannot be interpreted unless 1D or mixed 1D/3D migration patterns are assumed for self-interstitial atom clusters produced in cascades during irradiation. Analytical expressions for the sink strengths for defects migrating in 3D and also in 1D have been therefore developed and a ‘master curve’ approach has been proposed to describe the transition from purely 1D to purely 3D defect migration. Object kinetic Monte Carlo (OKMC) methods have subsequently been used to corroborate the theoretical expressions but, although good agreement was generally found, the ability of this technique to reach the 1D migration limit has been questioned, the limited size of the simulation box used in OKMC studies having been mainly blamed for the inadequacies of the model. In the present work, we explore the capability of OKMC to reproduce the sink strengths of spherical absorbers in a wide range of volume fractions, together with the sink strength of grain boundaries, for defects characterised by different migration dimensionality, from fully 3D to pure 1D. We show that this technique is not only capable of reproducing the theoretical expressions for the sink strengths in the whole range of conditions explored, but is also sensitive enough to reveal the necessity of correcting the theoretical expressions for large sink volume fractions. We thereby demonstrate that, in spite of the limited size of the OKMC simulation box, the method is suitable to describe the microstructure evolution of irradiated materials for any defect migration pattern, including fully 1D migrating defects, as well as to allow for the effect of extended microstructural features, much larger than the simulation box, such as grain boundaries.     

Total cross section parameterizations for pion production in nucleon-nucleon collisions

Total cross section parameterizations for neutral and charged pion production in nucleon-nucleon collisions are compared to experimental data over the projectile momentum range from threshold to 300 GeV. Both proton-proton and proton-neutron reactions are considered. Overall excellent agreement between parameterizations and experiment is found, except for some disagreements near threshold. This gives much greater confidence to previously developed pion cross section formulas for nucleon-nucleon, proton-nucleus, and nucleus-nucleus reactions. These results are useful for particle transport.     

Propagation of statistical and nuclear data uncertainties in Monte Carlo burn-up calculations

Two methodologies to propagate the uncertainties on the nuclide inventory in combined Monte Carlo-spectrum and burn-up calculations are presented, based on sensitivity/uncertainty and random sampling techniques (uncertainty Monte Carlo method). Both enable the assessment of the impact of uncertainties in the nuclear data as well as uncertainties due to the statistical nature of the Monte Carlo neutron transport calculation. The methodologies are implemented in our MCNP–ACAB system, which combines the neutron transport code MCNP-4C and the inventory code ACAB.     

Re-evaluation of neutron displacement cross sections for silicon carbide by a Monte Carlo approach

Neutron displacement cross sections for SiC are re-evaluated by a Monte Carlo approach, with damage energies of primary recoils calculated by the stopping and range of ions in matter (SRIM) code. The validity of the Monte Carlo model is examined by the case of iron, and the results show good agreement with the reference values. Neutron displacement cross sections for SiC at energies up to 100 MeV are calculated, and averaged over the neutron spectra of a fusion DEMO reactor, the high flux test module of the International Fusion Materials Irradiation Facility, and typical fission test reactors. Gas production is also calculated for those neutron irradiation facilities. Finally, the suitability of the displacement cross sections is discussed. The results on comparison among neutron irradiation of different facilities by the current displacement cross sections are similar to those by results of the previous work. Moreover, since neutron displacement cross sections in this study are calculated with damage energies of primary recoils calculated by SRIM, neutron damage evaluated by our displacement cross sections is suitable for correlation with damage by heavy ions calculated by SRIM.