MTR-ETR TECHNICAL BRANCHES QUARTERLY REPORT FOR PERIOD ENDING DECEMBER 31, 1958

Abstract

A summary of the more significant results of the work in progress in the technical branches of the Materials Testing Reactor--- Engineering Test Reactor complex are presented. Measurements of horizontal and vertical statistical weights in the ETRC show that a calculated statistical weight proportional to the square of the neutron flux provides good correlation with the measured statistical weight in the vertical plane but only a rough estimate in the horizontal plane. An investigation into a proposed gamma-insensitive neutron detection system utilizing neutron activation of a chemical solution has shown that the system will provide stable operation for practical operating parameters in the control of a nuclear reactor. Calculations on the irradiation of thorium show that continuous irradiation is desirable for greatest production of U-233 for later separation. Measurements made with the crystal spectrometer and fast chopper include additional total and fission cross sections for U-233, transmission measurements on Np-237 and enriched Ir, total cross section of D/sub 2/O from 5.5 to 2,000 ev (complete), and studies of Be crystal thickness effects. Inelastic scattering data for steam, methane, and vanadium were taken at 90 deg for several incident neutron energies at 0.014 to 0.48 ev. A pulsed crystal oscillator was developed to increase accuracy of time-of-flight measurements. Preliminary nuclear chemistry results on Pu-239 indicate that the ratio of asymmetric to symmetric fission is much greater for fissions produced by 0.3 ev neutrons than for those produced by thermal neutrons. Effective cross section values obtained from observed yields from several irradiated Pu napkin rings were used to calculate the yield curves for high nvt Pu irradiations made in similar fluxes. The four MTR permanent-magnet BETA -ray spectrometers were calibrated to allow measurements accurate to 0.05%. Gamma-gamma directional correlation meaaurements for 3 in. by 3 in. Nal(Tl) crystals were made to determine the difference between the experimental and theoretical values caused by the finite angular resolution of the detectors. A method was developed that gives a good representation of local flux distributions in plate-type reactor fuel assemblies by use of expansions in half-range Legendre polynomials. Diffusion theory is an inadequate approximation for this calculation, and conventional expansion of the angular distribution in full range Legendre polynomials may require many terms. The half-range expansions often give good results with only a few terms. (For preceding period see IDO-16505.) (auth)