Deterministic Multigroup Modeling of Thermal Effect on Neutron Scattering by Heavy Nuclides (original) (raw)
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Annals of Nuclear Energy, 2014
A multi-group formulation for the exact neutron elastic scattering kernel is developed. It incorporates the neutron up-scattering effects stemming from lattice atoms thermal motion and it accounts for them within the resulting effective nuclear cross-section data. The effects pertain essentially to resonant scattering off of heavy nuclei. The formulation, implemented into a standalone code, produces effective nuclear scattering data that are then supplied directly into the DRAGON lattice physics code where the effects on Doppler reactivity and neutron flux are demonstrated. The correct accounting for the crystal lattice effects influences the estimated values for the probability of neutron absorption and scattering, which in turn affect the estimation of core reactivity and burnup characteristics. The results show an increase in values of Doppler temperature feedback coefficients up to À10% for UOX and MOX LWR fuels compared to the corresponding values derived using the traditional asymptotic elastic scattering kernel. This paper also summarizes research performed to date on this topic.
Dynamical study of fission process and estimation of prescission neutron multiplicity
Physical Review C, 1998
The dynamics of fission has been studied by solving Euler-Lagrange equations with dissipation generated through one and two body nuclear friction. The average kinetic energies of the fission fragments, prescission neutron multiplicities and the mean energies of the prescission neutrons have been calculated and compared with experimental values and they agree quite well. A single value of friction coefficient has been used to reproduce the experimental data for both symmetric and asymmetric splitting of the fissioning systems over a wide range of masses and excitation energies. It has been observed that a stronger friction is required in the saddle to scission region as compared to that in the ground state to saddle region.
Numerical Estimation of Nuclear Decay Heat from Induced Neutron Fission of 235U and 239Pu
2020
In this paper, Joint Evaluated Fission and Fusion (JEFF) Nuclear Data Library has been used to calculate the nuclear decay heat after a fission burst of 235U and 239Pu for shutdown time up to 105 sec. This estimation is based on the numerical solution of the linear differential equations that describe buildups and decays of the fission products. The code was written in MATLAB, which is a fast and easy-access platform. The verification of the current code is carried out by comparing the numerical results with the measured reported ones. The discrepancies between the evaluated results and the measured ones show the reliability of the current calculation.
Physical Review C, 2011
Prompt fission neutrons following the thermal and 0.5 MeV neutron-induced fission reaction of 239 Pu are calculated using a Monte Carlo approach to the evaporation of the excited fission fragments. Exclusive data such as the multiplicity distribution P (ν), the average multiplicity as a function of fragment mass ν(A), and many others are inferred in addition to the most used average prompt fission neutron spectrum χ (E in , E out ), as well as average neutron multiplicity ν. Experimental information on these more exclusive data help constrain the Monte Carlo model parameters. The calculated average total neutron multiplicity is ν c = 2.871 in very close agreement with the evaluated value ν e = 2.8725 present in the ENDF/B-VII.0 library. The neutron multiplicity distribution P (ν) is in very good agreement with the evaluation by Holden and Zucker. The calculated average spectrum differs in shape from the ENDF/B-VII.0 spectrum, evaluated with the Madland-Nix model. In particular, we predict more neutrons in the low-energy tail of the spectrum (below about 300 keV) than the Madland-Nix calculations, casting some doubts on how much scission neutrons contribute to the shape of the low-energy tail of the spectrum. The spectrum high-energy tail is very sensitive to the total kinetic energy distribution of the fragments as well as to the total excitation energy sharing at scission. Present experimental uncertainties on measured spectra above 6 MeV are too large to distinguish between various theoretical hypotheses. Finally, comparisons of the Monte Carlo results with experimental data on ν(A) indicate that more neutrons are emitted from the light fragments than the heavy ones, in agreement with previous works.
Nuclear Science and Engineering, 1999
A dimensionally adaptive, automatic switching algorithm has been developed for the RELAP5/ PANBOX coupled thermal-hydraulics and neutron kinetics system to switch between three-dimensional (3-D), one-dimensional (1-D), and point neutron kinetics models during a transient calculation. The 3-D, 1-D, and point neutron kinetics models are developed and analyzed. The basis of this development is the consistent and stable nodal expansion method. The 1-D and point neutron kinetics models are derived in a unified manner from the 3-D model using the adiabatic approximation. The operator formulation of perturbation/sensitivity theory is consistently used to determine the reactivity for the point-kinetics model. Furthermore, the new features of the coupled RELAP5/PANBOX code are described. This provides the basis underlying the dimensionally adaptive algorithm. I. INTRODUCTION A major task in the safety analysis of nuclear power plants is the simulation of postulated accident scenarios. These scenarios hypothesize disturbances or failures in thermal-hydraulic systems, control systems, plant machinery, or the reactor core. The worst hypothetical accident scenarios are those that affect the core. The computer simulation and analysis of these hypothetical accidents for light water reactors~LWRs! became possible with codes like RELAP5~Ref. 1!, TRAC~Ref. 2!, CA-THARE~Ref. 3!, and ATHLET~Ref. 4!. Inclusion of three-dimensional~3-D! neutron kinetics models, in
Tables of thermonuclear-reaction-rate data for neutron-induced reactions on heavy nuclei
Atomic Data and Nuclear Data Tables, 1976
The results of statistical model calculations of (n,y), (n,p), and (n,a) cross sections and reactionrate factors are presented in tabular form for over 500 target nuclei in the range 36 2 2 2 83 (krypton to bismuth). Included in these tables is information on (i) the reaction cross section as a function of energy for the exoergic channel in the range 0.01 2 E(MeV) 5 3.0; (ii) the thermally averaged reaction-rate factor, N,(au) and the nuclear partition function G(T) for temperatures in the range IO8 5 T("K) 5 3 x log; (iii) analytic fits to the reaction-rate factors and partition functions as functions of temperature; and (iv) nuclear level-density parameters and formulas for their extrapolation. Two types of reaction-rate factors have been computed. One, which may be called the "laboratory rate factor," is based on the assumption that the target nuclei occupy only their ground states. The other, which shall be termed the "stellar rate factor," is based on the more realistic assumption that the target nuclei occupy a thermal distribution of excited states at temperature T. A brief discussion of theory and instructions for usage of the tables are included. New fitting forms for statistical-model thermonuclear reaction rates are presented and justified.
DOE-HDBK-1019/1-93 NUCLEAR PHYSICS AND REACTOR THEORY
The Nuclear Physics and Reactor Theory Handbook was developed to assist nuclear facility operating contractors in providing operators, maintenance personnel, and the technical staff with the necessary fundamentals training to ensure a basic understanding of nuclear physics and reactor theory. The handbook includes information on atomic and nuclear physics; neutron characteristics; reactor theory and nuclear parameters; and the theory of reactor operation. This information will provide personnel with a foundation for understanding the scientific principles that are associated with various DOE nuclear facility operations and maintenance.
An extensive assessment of the predictive capabilities of different nuclear models in the reproduction of experimental activation and transmutation cross- sections for neutron induced reactions is presented. Experimental EXFOR data have been processed and treated in order to systematically analyze all the available measurements for target nuclei from 27Al to 209Bi with energy of the projectile above 0.1 MeV. Experimental data have been compared with the correspondent simulations performed by means of the TALYS code and the ALICE/ASH code using different models for the description of the nuclear level densities at equilibrium states, these being both phenomenological and microscopic ones. The comparison between measurements and calculations is quantified by means of different statistical deviation factors, which are given as functions of the target nuclei mass number and of different channels. Recommendations are provided to the users on the best combinations of codes and models to o...