In-situ verification techniques for fast critical assembly cores

Active and passive autoradiographic techniques were used to obtain piece counts of fuel plates in fast critical assembly drawers and to verify the assembly loading pattern. Active autoradiography using prompt-fission and fission-product radiation was more successful with uranium fuel while passive autoradiography was more successful with plutonium fuel. A source multiplication technique was used to measure changes in reactivity when small quantities (2-2.5 kg) of fissile material were removed from a subcritical reference core of the Zero Power Plutonium Reactor. Efforts to compensate for unsuccessful. Some compensation was achieved by replacing U-238 with polyethylene. The sensitivity for detection of partially compensated fuel removed from minimum worth regions was approximately 2.5 kg (fissile) for a core containing 2600 kg (fissile). Substitution of polyethylene was detected with a spectral index which was the ratio of the rate of the In-115 (n,..gamma..) reaction to the rate of the In-115 (n,n') reaction. This spectral index was sensitive to the presence of an 0.64-cm-thick, 5.08-cm-high polyethylene column 10-15 cm away from the indium foil. The reactivity worth of Pu-239 was also obtained as a function of location in the reactor core with the use of an inverse kinetics technique. Reactivity worths for Pu-239 varied from a maximum of 58.67 Ih/kg near the core center to a minimum of 14.86 Ih/kg at the core edge

CRITICAL STUDIES OF URANIUM-STEEL AND URANIUM-STEEL-SODIUM FAST REACTOR CORES. (ZPR-III ASSEMBLIES 32 and 33

S>Critical studies of two fast reactor cores are described: one contains uranium and steel; the other contains uranium, steel, and sodium. Experimental results are given for fission ratio, central and edge reactivity coefficients, fuel bunching, average prompt neutron lifetime, and distributed worth measurements. (auth

A SUBCRITICAL PLUTONIUM-FUELED FAST REACTOR CORE (ZPR-III ASSEMBLY 37)

A subcritical fast reactor, fueled with Pu, is described. Calculations and experimental measurements of neutron flux and gamma dose rates near the bare core face are reported, as well as the core temperature increase eaused by Pu alpha and gamma heating. (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 A DILUTE OXIDE FAST REACTOR CORE (ZPR-III ASSEMBLY 30)

BS>Critical studies of a fast reactor core containing a simulated oxide fuel having an oxygen-uranium atomic ratio of 1: 1 are described. Calculated and experimental critical masses are compared. Experimental results are given for fission ratio, central reactivity coefficient, fuel bunching, and distributed worth measurements. (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