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Study of U{sup 235} neutron fission spectrum by the knowledge of cross sections average over that spectrum; Estudio del espectro de neutrones de fision del {sup 235}U a traves del conocimiento de secciones eficaces promediadas sobre dicho espectro

Abstract

A literature search of cross sections averaged over the fission neutron spectrum confirms inconsistencies between calculated and experimental values for high threshold reactions. Since, in this case, calculated averaged cross sections are systematically lower than measured values, it is concluded that the representations used to carry out these calculations underestimate the number of neutrons in the high energy region of the spectrum. A careful measurement of the averaged cross section for the {sup 45}Sc(n,2n) {sup 44g}Sc and {sup 45}Sc(n,2n) {sup 44m}Sc high threshold reactions had been performed in the RA-6 Neutron Activation Analysis Laboratory after carefully checking that the neutron flux at the core position where the samples were being irradiated was indeed an undisturbed fission spectrum. The experimental values are greater than those calculated with either, Watt type representations or the one based on the Madland and Nix model for the prompt fission spectrum. In many areas of nuclear engineering, like validation of nuclear data, reactor calculations, applied nuclear physics, shielding design, etc., it is of great practical importance to have a representation for the neutron flux that can be expressed in a closed analytical form and that agrees with experimental results, specially for the most widely fissile nuclide,  More>>
Authors:
Suarez, P M [1] 
  1. Comision Nacional de Energia Atomica, San Carlos de Bariloche (Argentina). Centro Atomico Bariloche
Publication Date:
Dec 31, 1997
Product Type:
Thesis/Dissertation
Report Number:
INIS-AR-131
Reference Number:
SCA: 663000; PA: AIX-29:050510; EDB-98:096806; SN: 98002007486
Resource Relation:
Other Information: TH: Tesis (Dr. en Ingenieria Nuclear); PBD: 1997
Subject:
66 PHYSICS; CROSS SECTIONS; MULTIVARIATE ANALYSIS; NUCLEAR DATA COLLECTIONS; RESEARCH REACTORS; SCANDIUM 45 REACTIONS
OSTI ID:
643832
Research Organizations:
Universidad Nacional de Cuyo, Mendoza (Argentina). Inst. Balseiro
Country of Origin:
Argentina
Language:
Spanish
Other Identifying Numbers:
Other: ON: DE98636134; TRN: AR9800014050510
Availability:
INIS; OSTI as DE98636134
Submitting Site:
INIS
Size:
115 p.
Announcement Date:

Citation Formats

Suarez, P M. Study of U{sup 235} neutron fission spectrum by the knowledge of cross sections average over that spectrum; Estudio del espectro de neutrones de fision del {sup 235}U a traves del conocimiento de secciones eficaces promediadas sobre dicho espectro. Argentina: N. p., 1997. Web.
Suarez, P M. Study of U{sup 235} neutron fission spectrum by the knowledge of cross sections average over that spectrum; Estudio del espectro de neutrones de fision del {sup 235}U a traves del conocimiento de secciones eficaces promediadas sobre dicho espectro. Argentina.
Suarez, P M. 1997. "Study of U{sup 235} neutron fission spectrum by the knowledge of cross sections average over that spectrum; Estudio del espectro de neutrones de fision del {sup 235}U a traves del conocimiento de secciones eficaces promediadas sobre dicho espectro." Argentina.
@misc{etde_643832,
title = {Study of U{sup 235} neutron fission spectrum by the knowledge of cross sections average over that spectrum; Estudio del espectro de neutrones de fision del {sup 235}U a traves del conocimiento de secciones eficaces promediadas sobre dicho espectro}
author = {Suarez, P M}
abstractNote = {A literature search of cross sections averaged over the fission neutron spectrum confirms inconsistencies between calculated and experimental values for high threshold reactions. Since, in this case, calculated averaged cross sections are systematically lower than measured values, it is concluded that the representations used to carry out these calculations underestimate the number of neutrons in the high energy region of the spectrum. A careful measurement of the averaged cross section for the {sup 45}Sc(n,2n) {sup 44g}Sc and {sup 45}Sc(n,2n) {sup 44m}Sc high threshold reactions had been performed in the RA-6 Neutron Activation Analysis Laboratory after carefully checking that the neutron flux at the core position where the samples were being irradiated was indeed an undisturbed fission spectrum. The experimental values are greater than those calculated with either, Watt type representations or the one based on the Madland and Nix model for the prompt fission spectrum. In many areas of nuclear engineering, like validation of nuclear data, reactor calculations, applied nuclear physics, shielding design, etc., it is of great practical importance to have a representation for the neutron flux that can be expressed in a closed analytical form and that agrees with experimental results, specially for the most widely fissile nuclide, {sup 235}U. The results of the calculations mentioned above lead us to propose an analytical form for the {sup 235}U fission neutron spectrum that better agrees with experimental results in the whole energy spectrum. We propose two different forms; both are a modification of the Watt-type form that has been adopted within the ENDF/B-V files. One of the new analytical representations is defined in two regions: below 9.5 MeV it is exactly the same formula as that used within the ENDF/B-V files, above this energy the parameters of this formula are changed. The other proposed analytical representation is expressed by a single formula in the whole energy range. These two new representations were checked against several thest which showed that they reproduce experimental results, even for high threshold reactions, much more faithfully than representations based on either macroscopic (Watt and Maxwellian type) or microscopic (Madland and Nix) models do. A new method that takes into account the correlation matrix and covariance calculations is presented for the treatment of uncertainties in all pertinent calculations involved. New methods for the critical evaluation of nuclear data are also presented. (author). 97 refs., figs., tabs.}
place = {Argentina}
year = {1997}
month = {Dec}
}