Loading pulsed neutrons

The fuel rods were safely loaded, using the critical approach method this also provided the extrapolation for the critical number of rods. At selected fuel loadings, pulsed-neutron source measurements were made to determine reactivity and prompt-neutron decay rates. The effect of voids and various materials placed in the central region and outside the loaded lattice waS measured In terms of the number of rods required for criticality. 

Additional work > included power and flux distributions, instrument response to loading sequence, approach to criticality and kinetics work wite an oscillator, a pulse neutron source, and reactor nidse system. 

Analysis of the 90-element fuel storage container In use at Sandia Laboratories annular core pulse reactor (ACPR) was performed to characterize its subcritical multiplication properties under full and partial loading conditions. Neutron transport calculations were performed with the DTF-IV code (Sjf transport theory) and 16 energy-group cross sections. Experimental verification exists for some of the calculated arrays but the limited number of ftiel elements available (40) prevented a fill loading of the storage container. 

The reactivity of the fuel loadings was monitored with three detectors one proportional counter and two fission chambers. For spent-fuel measurements, three fission chambers were used. Approach-lo- critical and pulse-neutron source data were recorded during loading and unloading of fuel tubes. A k-eff value of 0.94 was obtained with a loading of 54 tubes of unirradiated fuel, compared with a value of 0.95 obtained with 91 tubes of fuel irradiated to an average exposure of 3020 MWd/MT- The loadings were limited to a maximum k-eff value of 0.97 established as the test safety iimit. ... 

The casks were loaded under water. For safety, the inverse multiplication was measured and evaluated daring the loading of each batch. A suitable neutron source and a pulse-type fission chamber were placed in cask positions 11 and 20. Also, one or more pulse-type neutron detectors were placed outside the cask. 

Special questions of nuclear designing, viz. energy utilization, the problem of pulse thermal loads on the material, etc., are very significant, and can change the requirements of a thermonuclear neutron source. 

The two safety rods and the coarse control rod are each worth approximately 1.3 percent reactivity. The fine control rod, fuel loaded, is worth about 0.3 percent. The neutron flux is monitored by three detectors two BF3 ionization chambers and one BF3 proportional counter, all of which are located in the water tank just outside the lead shield. The detectors are connected respectively to a logarithmic micromicroammeter, a linear micro-microammeter, and a pulse amplifier and count rate meter located on the reactor console. Each indicator is connected through a sensitrol relay to a scram circuit. Additional safety interlocks provide for reactor shutdown if the level of the shield water drops, if the reactor temperature falls below 16 C, or if an earthquake occurs. Sequential interlocks are also present to ensure that the proper operational method is followed. 

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