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Investigations have been carried out for three additional cores of the phase 1 experimental program on light water high converter reactor test lattices in the PROTEUS facility. An 8% (average) fissile plutonium tight-pitch lattice with a fuel/moderator volumetric ratio of 2.0 was considered. As for the earlier reported 6% (average) fissile plutonium test lattice, H/sub 2/O, Dowtherm, and air were the moderator state investigated. Significant enrichment-dependent trends have been identified in the comparisons of calculated and experimental results for the wet (moderated cases, particularly for the important reaction rate ratio of /sup 238/U capture of /sup 239/Pu fission. These are then reflected in the comparison of moderator voidage characteristics, expressed in terms of individual components of the kinfinity void coefficient.

Comparisons of calculated and measured neutron balance components are reported for the 7. 5% fissile plutonium reference test lattice of the PROTEUS-light water high conversion reactor (LWHCR) phase II program, both wet (with H//2O) and dry (100% void). Special experimental techniques have been developed and applied, particularly for k// infinity , and the range of directly measured reaction rate ratios has been extended. For the two cell codes tested, WIMS-D/1981 library and KARBUS/KEDAK-4, specific shortcomings have been identified; the new measurements have been found to be significantly more representative and accurate than the earlier phase I experiments.

Integral reaction rate ratios and other k// infinity -related parameters have been measured in the first three cores of the experimental program on light water high converter reactor (LWHCR) test lattices in the PROTEUS reactor. The reference tight-pitch lattice consisted of two rod types, with an average fissile-plutonium enrichment of 6% and a fuel/moderator ratio of 2. 0. The moderators were H//2O, Dowtherm (simulating an H//2O voidage of 42. 5%), and air (100% void). Comparisons of the measured parameters have been made with calculational results based mainly on the use of two separate codes and their associated data libraries, namely, WIMS-D and EPRI-CPM. A reconstruction of individual components of the k// infinity void coefficient has been carried out on the basis of the measured changes with voidage of the various reaction rate ratios, as well as of k// infinity itself. The subsequent more detailed comparisons between experiment and calculation should provide a useful basis for resolving the conflicting calculational results that have been reported in the past for the void coefficient characteristics of LWHCRs.

Integral measurement of the 232 Th(n, 2n) reaction has been carried out relative to 232 Th(n, γ) in a pin-geometry GCFR lattice. A single thorium foil was used for the irradiation, and a HPGe detector system employed for simultaneous γ-counting of the induced 231 Th and 233 Pa activities. Standardization of detector efficiency was carried out using α-calibrated 235 U and 237 Np deposits containing equilibrium amounts of their daughters ( 231 Th and 233 Pa, respectively). An accuracy of ±2.5% was thereby achieved for the lattice measurement of the 232 Th (n, 2n) to (n, γ) ratio.