Aqueous geochemistry of actinide elements is of primary concern in radioactive waste disposal research. The geochemical behavior of actinide elements is affected by the chemical property of groundwater. The need of study on groundwater chemistry and geochemistry of actinide elements is described through illustrating neptunium speciation in an oxidizing and a reducing groundwater.
Since numerical stability and accuracy of solutions are much affected by difference methods for convection terms of transport equations, many methods have been proposed to solve fluid flows efficiently. In recent years, higher-order upstream difference methods have been recognized as accurate methods for solving high Reynolds number flows. There is however little information on the conditions for the occurrence of numerical instability or numerical oscillation when the higher-order difference methods are adopted. In the present study, spectral radii and spectral norms of difference operators were examined analytically or numerically·to make the stability conditions of four higher-order difference methods clear. For the one-dimentional linear transport equation under various boundary conditions, the necessary and sufficient conditions of the stability defined by Lax & Richtmyer were derived using the spectral norms, and those of the stability defined by the boundedness of the solution as time nears infinity were obtained using the spectral radii. It was also shown by examination of eigenvalues of the spatial difference operators that the higher-order difference methods are subject to numerical oscillation when the cell Reynolds number exceeds a value of about two.
A parallelism analysis integrated system (PARIS) with an MIMD multiprocessor scheme has been developed to analyze a simulation program which can execute anomaly effect prediction in nuclear power plants and to make the simulation program for parallel processing. The PARIS system analyzes task parallelism and processing time of each task when a user divides a program developed for a single processor into many tasks that are the elementary assignment units. Next, this system assigns tasks to processors using the static scheduling algorithm CP/MISF to minimize the overall processing time, and makes a parallel execution program which can be executed with a tightly coupled multiprocessor. The PARIS system was assessed by nuclear power plant analyzer code (NUPAC-1) consisting of a reactor coolant system model, a steam generator model and so forth. The results showed that processing time of NUPAC-1 with 7 processors was 3.5 times as fast as with a single processor, and fast running capability was 4.8 times as fast as the real physical time even in accident analyses such as small LOCA. Furthermore, the results showed the PARIS system with the MIMD multiprocessor scheme on the tightly coupled multiprocessor to be efficient for realizing the predictive simulator.
This paper describes the result of reactivity initiated accident (RIA) experiments using prepressurized (1.3 and 2.9-3.6MPa) hollow UO2 pellets recognized to conventional PWR remedy fuel. Major results obtained are: (1) The failure thresholds of the tested hollow fuels were not less than 120cal/g fuel (0.50kJ/g fuel) in enthalpy. This showed the safety margins against past NSRR prepressurized fuel experimental data for fuel failure in RIA standard. No measurable differences in failure thresholds were observed between hollow fuels and solid fuels. (2) The failure mechanisms of the hollow fuels were cladding rupture induced by ballooning. No significant differences were existed between the hollow fuels and the solid fuels or between the hollow fuels and past NSRR prepressurized standard fuels. (3) The magnitude of pressure increase in the hollow fuels was approximately twice larger than that of the solid fuels.