A Re-Analysis of Historical Los Alamos Critical Assembly Reaction Rate Measurements

Los Alamos National Laboratory, Los Alamos, NM 87545, USA

^a Corresponding author: akahler@lanl.gov

Published online: 3 February 2016

Abstract

Starting in the 1950s and continuing into the early 1970s, a number of foil irradiations and fission chamber measurements were made in a variety of Fast critical assemblies at Los Alamos National Laboratory. These include (i) Godiva, a bare HEU spherical assembly; (ii) Flattop-25, a spherical assembly consisting of an HEU core and a natural uranium reflector; (iii) Jezebel, a bare ²³⁹Pu assembly; and (iv) Flattop-Pu, a spherical assembly consisting of a ²³⁹Pu core and a natural uranium reflector. In most instances the irradiations occur at or near the center of the assembly, but in selected instances data were obtained for a radial traverse extending into the Flattop reflector region. Measurements were made for a number of threshold reactions, including ⁴⁵Sc(n,2n)^44mSc, ⁵¹V(n,α)⁴⁸Sc, ⁷⁵As(n,2n)⁷⁴As, ⁸⁹Y(n,2n)⁸⁸Y, ⁹⁰Zr(n,2n)⁸⁹Zr, ¹⁰³Rh(n,2n)^102gRh, ¹⁰⁷Ag(n,2n)^106mAg, ¹⁶⁹Tm(n,2n)¹⁶⁸Tm, ¹⁷⁵Lu(n,2n)¹⁷⁴Lu, ¹⁹¹Ir(n,2n)¹⁹⁰Ir, ¹⁹⁷Au(n,2n)¹⁹⁶Au, ²⁰³Tl(n,2n)²⁰²Tl, ²⁰⁴Pb(n,2n)²⁰³Pb and ²³⁸U(n,2n)²³⁷U. Fission ratio data for ²³⁸U(n,f)/²³⁵U(n,f) and ²³⁹Pu(n,f)/²³⁵U(n,f) were also obtained. We report C/E values from MCNP6 calculations using ENDF/B-VII.1 and IRDFF-v1.03 cross section data.