Borated concrete for ZPPR fuel storage

Fuel handling at the Zero Power Plutonium Reactor (ZPPR) led to two requirements for storage of ZPPR fuel: a low neutron multiplication and shielded storage to minimize personnel doses. Boron-poisoned concrete was chosen as the storge medium with boron frit as the poisoning agent. The calculated effects of water content and boron concentration led to specifying a concrete with a water content that was higher than ordinary concrete. The finite size of the boron frit particles caused concern about reduced effectiveness due to self-shielding. The self-shielding was evaluated using optical path lengths for spheres and tabulated self-shielding for slabs. The results showed that the finite-sized particles were at least 80% as effective as infinitely dilute absorption. Neutron and gamma dose rates measured in the vault verified that personnel could work in the vault on a regular basis without exceeding personnel dose limits. 4 refs., 3 figs., 7 tabs

CRITICAL STUDIES OF A DILUTE FAST REACTOR CORE (ZPR-III ASSEMBLY 31)

Critical studies were performed on a dilute, metallic, fast reactor core. The fuel was 38.6% enriched uranium and reduced-density aluminum was used to simulate sodium coolant. The measured critical mass was 463 kg of U/sup 235/ in a 425-liter core. The main part of the experimental program consisted of measurements of the standard fission ratios, a number of central reactivity coefficients, and the prompt neutron lifetime. An additional series of experiments were performed to obtain the worths of aluminum, aluminum oxide, and sodium at various radial positions in the core. (auth

CRITICAL STUDIES OF A SMALL URANIUM CARBIDE-FUELED REACTOR WITH A BERYLLIUM REFLECTOR. (ZPR-III ASSEMBLY 40)

A small, lightweight, uranium carbide-fueled reactor with a beryllium reflector surrounding the core was mocked up as Assembly 40. It was determined that the presence of beryllium in the axial and radial reflectors did not endanger the safe loading and operation of the' critical assembly. The actual experiment consisted of determination of the critical mass, measurement of the reactivity coefficients for a large number of fissile and nonfissile materials, the performance of radial and axial fission traverses, and measurement of central fission ratios. The effectiveness of the radial beryllium reflectcr as a control mechanism was determined and the Rossialpha was measured. (auth

CRITICAL STUDIES OF DILUTE CARBIDE FAST REACTOR CORE. ZPR-III Assembly 34

Critical studies were made with a simulated, large, dilute power reactor having uranium carbide as fuel. The uranium in the core was 30.7% enriched, and the atomic ratio of uranium to carbon was 0.946. The critical mass was 503.01 kg U/sup 235/ and the critical volume 574.47 liters. Central reactivity coefficients, effective fission crosssection ratios, heterogeneity effects, reactivity worth of distributed materials, foil irradiations, and the average prompt neutron lifetime were measured. Multigroup calculations using the Yiftah, Okrent, and Moldauer crosssection set overestimated k for the critical configuration by 4.7%. (auth

TWO SPHERICAL FAST CRITICAL EXPERIMENTS (ZPR-III ASSEMBLIES 38 AND 39)

Two spherical versions of earlier cylindrical assemblies were used for a critical study of shape effects for fast reactor cores with volumes of 300 to 400 liters. Assemblies 24 (cylindrical) and 38 (spherical) had a high-density metallic U blanket, whereas the set of assemblies numbered 31 (cylindrical) and 39 (spherical) had a low-density U-fueled core (with steel and Al diluents) with a highdensity blanket of depleted U. The main features of these assemblies are summarized. Reactivity coefficients of a small number of fissile and nonfissile materials were measured in both assemblies (38 and 39). In Assembly 38 the effects of environment, etc., upon fission rates measured with absolute fission chambers were investigated. Radial fission rate traverses in different directions were made in Assembly 39 to reveal any flux asymmetry due to heterogeneity of the core; no such effect was detected.(auth