The correlation matrix for the effective delayed neutron parameters of the IPEN/MB-01 reactor

Author(s)

dos Santos, Adimir ^[1] ; Diniz, Ricardo ^[1]

Affiliation

^[1] IPEN, CNEN SP, Av Prof Lineu Prestes 2242, BR-05508000 Sao Paulo, SP - Brazil

• Document type: Journal article
• Source: ANNALS OF NUCLEAR ENERGY; v. 136, FEB 2020.
• Web of Science Citations: 0

Abstract

The correlation matrix for the effective delayed neutron parameters of the IPEN/MB-01 reactor has been successfully built in this work. A standard procedure employed in several least-squares approaches was adopted to cope with this task. One of the most important applications of the effective delayed neutron parameters is to serve as input data for the relationship between reactivity and asymptotic period of a nuclear reactor given by the Inhour equation. Employing this equation, the reactivity was calculated for several periods both negative and positive. The reactivity error propagation was considered with and without the correlation matrix. The analyses of this procedure reveal that the consideration of the correlation matrix is very important. In general, the introduction of the correlation matrix reduces the overall uncertainty by a reasonable amount. There are huge cancellations in the uncertainty analyses. The analyses also reveal that the uncertainty in the reactivity will depend on the specific period range where this quantity is considered. Considering the correlation and for most of the period range considered, the reactivity uncertainties for negative periods are around 3.5% while for positive ones they are nearly 2%. If the correlation matrix is not considered the reactivity uncertainties are as high as 6%. All uncertainties considered in this work are 1-sigma values. There are two extreme cases where the correlation matrix plays no role; very large negative periods and very small positive periods. In the first case, the first decay constant plays a fundamental role while in the second the prompt neutron generation is of major importance. The experiments performed at the IPEN/MB-01 reactor and evaluated for inclusion in the IRPhE handbook for the determination of the effective delayed neutron parameters will be extremely benefited considering the inclusion of their correlation matrix. The final product can be considered extremely useful to validate methods and nuclear data related to the reactivity determination of thermal reactors fueled with Uranium. (C) 2019 Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 11/50516-8 - Benchmarks in the IPEN/MB-01 reactor: subcritical reactivity, nickel reflector and sample reactivities
• Grantee: Adimir dos Santos
• Support Opportunities: Regular Research Grants