Takeshi Seino

A study on the criticality search of transuranium recycling BWR core by adjusting supplied fuel composition in equilibrium state

Abstract There have been some difficulties in carrying out an extensive evaluation of the equilibrium state of Light Water Reactor (LWR) recycling operations keeping their fixed criticality condition using conventional design codes because of the complexity of their calculation model for practical fuel and core design and because of a large amount of calculation time. This study presents an efficient approach to secure the criticality in an equilibrium cycle by adjusting a supplied fuel composition. The criticality search is performed by the use of fuel importance obtained from the equation adjoint to a continuously fuel supplied core burnup equation. Using this method, some numerical analyses were carried out in order to evaluate the mixed oxide (MOX) fuel composition of equilibrium Boiling Water Reactor (BWR) cores satisfying the criticality requirement. The results showed the comprehensive and quantitative characteristics on the equilibrium cores confining transuraniums for different MOX fuel loading fractions and irradiating conditions.

A New Estimation Method for Nuclide Number Densities in Equilibrium Cycle

A new method is proposed for estimating nuclide number densities of LWR equilibrium cycle by multi-recycling calculation. Conventionally, it is necessary to spend a large computation time for attaining the ultimate equilibrium state. Hence, the cycle in nearly constant fuel composition has been considered as an equilibrium state which can be achieved by a few of recycling calculations on a simulated cycle operation under a specific fuel core design. The present method uses steady state fuel nuclide number densities as the initial guess for multi-recycling burnup calculation obtained by a continuously fuel supplied core model. The number densities are modified to be the initial number densities for nuclides of a batch supplied fuel. It was found that the calculated number densities could attain to more precise equilibrium state than that of a conventional multi-recycling calculation with a small number of recyclings. In particular, the present method could give the ultimate equilibrium number densities of ...

Active neutron multiplication method for fuel lattices in water

In this paper an active neutron multiplication method is studied in laboratory experiments aiming at establishing and improving nondestructive measurement methods for a spent light water reactor fuel bundle in water. The fuel rods used in the experiments consist of 1.0-cm-diam UO{sub 2} pellets enriched to 1 to 3 wt% {sup 235}U, clad in 1.18-cm-o.d. aluminum tubes. The rods are arranged in square arrays spaced to form a 1.52-cm lattice. The analysis is carried out by two- of three-dimensional, three-energy-group diffusion calculations. A simple empirical expression for the correlation between the neutron flux and the effective neutron multiplication factor k{sub eff} is proposed in which a constant term is added to the well-known formula for one-point subcritical flux. The new expression has been found to be applicable to high-precision measurements. Through an experimental study of the correlation between the neutron flux profile and the neutron source response to a detector and studies of the new correlation expression, an improved measurement system is presented that is suitable for more precise measurements of k{sub eff}.