Dermott E. Cullen

Application of the Probability Table Method to Multigroup Calculations of Neutron Transport

AbstractThe probability table method, developed for Monte Carlo calculations in the region of unresolved neutron resonances, is demonstrated to be of general use in neutron transport studies since the Boltzmann equation involved can be derived and solved by analogy to multigroup methods. Since the resulting equations can be cast into a form identical to that of the multigroup equations, they can be solved by existing multigroup transport codes. From a set of probability tables and spatially independent, unshielded, neutron cross sections, the method yields correct selfshielding effects, such as equivalent, spatially dependent, multigroup cross sections. Extension of the method and the use of probability tables outside the unresolved region are discussed.

Exact Doppler Broadening of Tabulated Cross Sections

The SIGMA1 (σ1) kernel broadening method is presented to Doppler broaden to any required accuracy a cross section that is described by a table of values and linear-linear interpolation in energy-cr...

A simple model of photon transport

Abstract In this paper I describe a simple model of photon transport. This simple model includes: tabulated cross sections and average expected energy losses for all elements between hydrogen (Z = 1) and fermium (Z = 100) over the enrgy range 10 eV to 1 GeV, simple models to analytically describe coherent and incoherent scattering, and a simple model to describe fluorescence. This is all of the data that is required to perform photon transport calculations.

Single-scatter Monte Carlo compared to condensed history results for low energy electrons *

Abstract A Monte Carlo code has been developed to simulate individual electron interactions. The code has been instrumental in determining the range of validity for the widely used condensed history method. This task was accomplished by isolating and testing the condensed history assumptions. The results show that the condensed history method fails for low energy electron transport due to inaccuracies in energy loss and spatial positioning.

Photon and electron data bases and their use in radiation transport calculations

Abstract The ENDF/B-VI photon interaction library includes data to describe the interaction of photons with the elements Z = 1–100 over the energy range 10eV–100MeV. This library has been designed to meet the traditional needs of users to model the interaction and transport of primary photons. However, this library contains additional information which, used in a combination with our other data libraries, can be used to perform much more detailed calculations, e.g. emission of secondary fluorescence photons. This paper describes both traditional and more detailed uses of this library.

The All Particle Monte Carlo Method: 1990 Status Report

Abstract Development of the All Particle Method, a project to simulate the transport of particles via the Monte Carlo method, has proceeded on two fronts: data collection and algorithm development. In this paper we report on the status of both these aspects. The data collection is nearly complete with the addition of electron and atomic data libraries and a newly revised photon library to the existing neutron and charged particle libraries. We describe the basic organization of the Monte Carlo computer code that will actually perform the simulation. Algorithm development has proceeded less quickly than the data portion of the project. The new Response Matrix Monte Carlo method is summarized and some numerical results presented.

The Accuracy of Processed Nuclear Data

The results of the International Atomic Energy Agency cross-section processing code verification project are described. This project has been conducted over the last 7 yrs in an attempt to improve the reliability of the results produced by cross-section processing computer codes. Initial comparisons of results received from 42 participants using 13 different cross-section processing codes demonstrated that, even though all of the codes started from exactly the same evaluated data, in no case did the multigroup cross sections calculated by any two codes agree for al materials and groups used in the comparison. This code verification project has led to positive results by improving cross-section processing codes as well as the conventions used to interpret ENDF/B evaluations. In several cases it has led to changes in ENDF/B evaluations. Although this project only addressed nuclear data processing codes, conclusions can be drawn from the results regarding the reliability of other types of computer codes.

Evaluation of Hylife-II and Sombrero using 175- and 566- group neutron transport and activation cross sections

Recent modifications to the TART Monte Carlo neutron and photon transport code allow enable calculation of 566-group neutron spectra. This expanded group structure represents a significant improvement over the 50- and 175-group structures that have been previously available. To support use of this new capability, neutron activation cross-section libraries have been created in the 175- and 566-group structures starting from the FENDL/A-2.0 pointwise data. Neutron spectra have been calculated for the first walls of the HYLIFE-II and Sombrero inertial fusion energy power plant designs and have been used in subsequent neutron activation calculations. The results obtained using the two different group structures are compared with each other as well as to those obtained using a 175-group version of the EAF3.1 activation cross-section library.

Conservation During Doppler Broadening

BS>Conservation under Doppler broadening is examined. It is shown that the area under the cross-section curve is not conserved and that the only conservation law associated with Doppier broadening is the integral of the reaction rate over all phase space. (auth)