Criticality Safety Evaluation Research Articles

Effects of Organic Solvent on Infinite Neutron Multiplication Factor of Homogeneous Plutonium Nitrate Solution System.

The validity of replacing organic solvent with water in making models for criticality safety evaluation analysis of fuel solution systems was examined by the calculation of the infinite neutron multiplication factor(k inf) for the homogeneous plutonium(IV) nitrate in aqueous and organic solvent solutions. The atomic number densities of fuel solutions were determined by the density formula based on measurements. It was confirmed that k inf of plutonium(IV) nitrate-30 vol% tributylphosphate (TBP)-dodecane organic solvent system is nearly equal to that of plutonium nitrate-aqueous solution system in general. However, more strictly, the values of k inf of organic solvent system became slightly larger than the corresponding values of aqueous solution in the Pu concentration ranged up to 70g/l, which gives the opposite result to Weber's for plutonium nitrate30 vol% TBP-kerosene organic system. Consequently, the estimated lower limit critical concentration for 239Pu(NO3)4 organic solvent system was found 1% smal...

Study on the Criticality Safety Evaluation Method for Burnup Credit in JAERI

In relation to burnup credit, three tasks have been carried out at the Japan Atomic Energy Research Institute (JAERI) for establishing the evaluation method of criticality safety for a spent-fuel system, such as storage ponds and transport casks. The first task is to prepare a benchmark database of criticality experiments and nuclide compositions of spent fuels. The database of nuclide composition is formed by data measured at JAERI and data collected from the literature. For the database of criticality experiments, the effective multiplication factor of a spent-fuel assembly has been measured at JAERI. The next task is to develop computer codes. The burnup and criticality codes have been developed and validated by analyzing a large number of benchmarks stored in the aforementioned database.The last task needed to establish the methodology in order to confirm the subcriticality of a spent-fuel system applying burnup credit is described. A reference fuel assembly is introduced so that the criticality of a system can be evaluated by using it, instead of modeling all fuel assemblies explicitly. To determine the nuclide composition of a spent fuel, a simple method is studied utilizing a large number of nuclide composition data stored in the database. Further, the effects of the axial burnup profile and calculation errors are discussed, and the remaining tasks are identified.

Computation on Fuel Particle Size Capable of Being Regarded as Homogeneous in Nuclear Criticality Safety Analysis.

For powdered fuel processed in the nuclear fuel facilities, flooding is often thought to be the severest condition regarding the nuclear criticality safety evaluation. The reactivity of such a heterogeneous system as powdered fuel in water should be almost equal to that of the homogeneous one, when the fuel particle size is very small. The neutron multiplication factor was calculated for an infinite cubic array of slightly enriched UO2 sphere particles immersed in water with various enrichments, water to fuel ratios and fuel particle sizes. The calculations were performed with a computer code module based on the collision probability method to solve the ultra-fine energy group equations of neutrons. The change in the neutron multiplication factor from the homogeneous system is dominated first by the change in the resonance escape probability and second by the change in the thermal utilization factor; these changes and therefore their sum, depend almost completely on the mean uranium concentration (or wate...

Criticality Safety Evaluation for High-Density Spent-Fuel Storage Racks

Using as a starting base the high-density spent-fuel storage racks to be put into the Chinshan and Kuoshang nuclear power plants, a series of criticality analyses with various combinations of fuel assemblies and storage rack designs were performed using an AMPX-KENO/XSDRNPM computer code package. The calculated kappainfinity value for the storage pools in the two subject plants using Boral (0.013 g/cm/sup 2/ /sup 10/B) poisoned rack lattices and 3.2 wt % enriched fuel assemblies is 0.900 under conservative assumptions. Considering all the calculation biases and statistical and manufacturing uncertainties, the maximum kappainfinity value is estimated to be 0.929 under normal storage conditions. Variation in water temperature and density or abnormal positioning of fuel assemblies will result only in a negative effect on kappainfinity value.

History of Fissile Array Measurements in the United States

The first measurements with arrays of fissile metal were performed at the Los Alamos Scientific Laboratory in 1947 and the first with fissile solutions were performed at the Oak Ridge Critical Experiments Facility in 1949. Since then, there have been many other significant experiments at several U.S. laboratories including, in addition, Rocky Flats, Battelle-Pacific Northwest Laboratory, and the Lawrence Livermore Laboratory. Array tests were the primary sources of data used in developing criticality criteria for fissile-process plants, and they provided the basis for several empirical storage models that are still in use. Some of the experimental data also serve to validate Monte Carlo neutron transport calculations now used extensively by the nuclear safety engineer in the design of storage and processing facilities. It is felt that there should be additional experimental data for further validation of calculational methods relied upon for criticality safety evaluation. The deficient areas include low-/sup 235/U-enriched uranium, /sup 233/U with and without thorium, and plutonium--uranium mixtures. Also, critical data are lacking for arrays with the concrete reflectors normally found in process-plant environments, and additional experiments on concrete-reflected arrays are needed.

Criticality Safety Evaluation of a Shipping Container for Moderated Low-Enriched Uranium Compounds

Criticality Safety Evaluation of a Shipping Container for Moderated Low-Enriched Uranium Compounds