Dominant delayed neutron precursors to model reactivity predictions for multiple fissioning nuclides

Journal Article · Sat Jan 01 04:00:00 EST 2000 · Nuclear Science and Engineering

OSTI ID:20005666

Loaiza, D J; Haskin, F E

The product of cumulative yield and probability of neutron emission is used to assess the relative importance of known delayed neutron precursors. Thirteen precursors are consistently dominant. Nonlinear fits to experimental delayed neutron decay data distinguish the decay constants of the three longest-lived dominant precursors: {sup 87}Br, {sup 137}I, and {sup 88}Br. Sensitivity calculations based on a six-to seven-group transformation lead to a proposed seven-group formulation in which the group decay constants are those of dominant precursors: {sup 87}Br, {sup 137}I, {sup 88}Br, {sup 93}Rb, {sup 139}I, {sup 91}Br, and {sup 96}Rb. An alternative six-group formulation is obtained by using the mean of the {sup 137}I and {sup 88}Br decay constants for group 2. The use of the suggested dominant precursor decay constants improves the goodness of fit to experimental data compared to that obtained from nonlinear least squares in which both group yields and decay constants are determined empirically. Reactivity worth and transient analyses confirm that the positive reactivity scale is preserved in the transformation. A known bias in the negative reactivity scale is eliminated by forcing the half-life of the longest-lived group to be the 55.9-s half-life of {sup 87}Br. The proposed use of dominant precursor decay constants offers significant simplifications in data analysis and the analysis of fast, epithermal, and thermal reactors with multiple fissioning nuclides.

• Research Organization: Los Alamos National Lab., NM (US)
• OSTI ID: 20005666
• Journal Information: Nuclear Science and Engineering, Journal Name: Nuclear Science and Engineering Journal Issue: 1 Vol. 134; ISSN NSENAO; ISSN 0029-5639
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
BROMINE 87
BROMINE 88
BROMINE 91
DELAYED NEUTRON PRECURSORS
EPITHERMAL REACTORS
FAST REACTORS
IODINE 137
IODINE 139
REACTIVITY
REACTOR KINETICS
RUBIDIUM 93
RUBIDIUM 96
THERMAL REACTORS