Advanced resonance self-shielding method for gray resonance treatment in lattice physics code GALAXY

A new resonance self-shielding method based on the equivalence theory is developed for general application to the lattice physics calculations. The present scope includes commercial light water reactor (LWR) design applications which require both calculation accuracy and calculation speed. In order to develop the new method, all the calculation processes from cross-section library preparation to effective cross-section generation are reviewed and reframed by adopting the current enhanced methodologies for lattice calculations. The new method is composed of the following four key methods: (1) cross-section library generation method with a polynomial hyperbolic tangent formulation, (2) resonance self-shielding method based on the multi-term rational approximation for general lattice geometry and gray resonance absorbers, (3) spatially dependent gray resonance self-shielding method for generation of intra-pellet power profile and (4) integrated reaction rate preservation method between the multi-group and the ultra-fine-group calculations. From the various verifications and validations, applicability of the present resonance treatment is totally confirmed. As a result, the new resonance self-shielding method is established, not only by extension of a past concentrated effort in the reactor physics research field, but also by unification of newly developed unique and challenging techniques for practical application to the lattice physics calculations.     

Neutron Behavior in Cluster-Type Fuel Lattices, (II)

A multigroup method of calculation is presented for describing the neutron behavior in a cluster-type fuel lattice. It solves the integral transport equation by a semi-analytical method proposed in a previous paper for calculating collision probabilities in the lattice of a clustered fuel element. Using only fundamental nuclear data, it gives space and energy dependent neutron flux. The method has been programmed for HITAC-5020F (computer code named CLUSTER-III).

The accuracy of the method has been tested by comparing the calculation with the experiment described in Part (I) of this paper. The lattices are 28-pin clusters of UO₂ or PuO²+UO² fuel pins, with heavy-or light-water moderators and with light-water coolant containing varying void ratios. The quantities studied are micro-parameters, reaction distributions in energy and space, thermal disadvantage factors and the multiplication factors. It is found that the calculated results are generally in good agreement with experiment, typically within 10% for micro-parameters and thermal disadvantage factor, and within 1% for the multiplication factor.     

Stoichiometry of Fully Oxidized PuO2-NdO1.5 and PuO2-YO1.5 Solid Solutions

A new method has been established to calculate sensitivity coefficients of cell parameters based on generalized perturbation theory using the collision probability method. The proposed method does not require the calculation of the changes of collision probabilities due to cross section changes, so it is as powerful as the commonly used generalized perturbation theory in diffusion theory, We demonstrate the validity of the method by comparing the calculated sensitivity coefficients with those obtained from the direct cell calculations. AS an application, we calculate the sensitivity coefficients of neutronic properties in cells with different moderator to fuel volume ratios, and discuss the physical meaning of the difference between the sensitivity coefficients.     

Analysis of Heavy-Water-Moderated,Cluster-Type Fuel Lattices by Cluster Physics Code ‘MESSIAH’

This paper presents a comprehensive analysis performed by a new cluster analysis code ‘MESSIAH’ on reactor physics constants measured in the critical facility for a pressure-tube-type, heavy-water-moderated reactor. The MESSIAH code system utilizes the method of the collision probability to solve the neutron transport equation. The effective space dependent cross sections are calculated in the thermal and resonance energy range before the eigenvalue calculation for the whole energy range. With use of these cross sections, the multi-group, space dependent transport equation is solved, and the flux distribution, spectrum and k _eff are obtained to the input bucking. In the above three steps the method of the collision probability is used consistently and extensively. The treatment of leakage neutrons from lattices in MESSIAH is also confirmed by an independent method using a Monte Carlo calculation. The calculated reactor physics constants, especially the micro-parameters and the activation traverse of Dy, agreed fairly well with the experiment. The diffusion calculation with use of the group constants calculated by MESSIAH predicts the reactivity of 0% void core excellently (<0.12%). However, for a 100% void core, the calculated reactivity was slightly lower than the experiment (~0.74%), which was attributed to over prediction of the diffusion constants.     

Expression of Few-Group Effective Microscopic Cross Sections in BWR Burnup Calculations

A practical method is proposed to express few-group effective microscopic cross sections for BWR burnup analysis. A set of few-group cross sections is prepared for an infinite square lattice of fuel rods as a function of the ratios of number density of nuclides such as ²³⁵ U, ²³⁸U and ²³⁹Pu, and the water quantity around a fuel rod. Spatial variation of few-group cross sections in the fuel assembly is taken into account by adjusting the water quantity around a fuel rod.

Numerical studies show that the present method can evaluate effective few-group cross sections within the accuracy of 3% in comparison with a two-dimensional integral transport calculation.     

Oxidation-Reduction Properties of Mixed Oxides in Lanthanum-Uranium-Oxygen System

The oxidation-reduction properties and the phase relations of mixed oxides in the system La-U-O were examined by means of thermogravimetry and X-ray diffraction method. The O/M ratios of the mixed oxides La_yU_1-y O_2±x, prepared at 1,650°C in vacuo by the reaction of La₂O₃ and UO₂, were expressed as 2–0.5 y except 0.2≤y≤0.4. The oxides were the single fluorite phase at y0.7. These oxides of 0.2≤y≤0.6 were oxidation-susceptible in air even at room temperature. For the oxides heated or prepared in air at 1,000°C, the O/M ratio vs. y relationship was composed of three line with the turning points, 2.26 at y = 0.27 and 1.92 at y = 0.70. The fluorite phase was observed in the regions of 0.3≤y≤0.45 and 0.7≤y≤0.9, and the rhombohedral phase was in ?0.55≤y-0.7. The O/M ratios of the oxides reduced with hydrogen were nearly 2 at y ≤0.2 and decreased with increasing y at y >0.2. The oxide of y =0.5 showed the curious property: The O/M ratio had a minimum when the oxide reduced with hydrogen was oxidized in air.     

Effect of Oxygen and Carbon Impurities on Lattice Parameter of PuN

The cladding component chemical transport (CCCT) is one of the important modes of the fuel-cladding chemical interaction (FCCI) of LMFBR. In order to explain this phenomenon, a model based on the vapor phase chemical transport of cladding components by iodine was proposed by Johnson et al. and Calais et al. In this study, experimental work has been done to check whether such a mechanism can work due to the free iodine generated by the radiolysis of Csl vapor. As a result, it was confirmed that a significant amount of Fe can be transported via vapor phase from the Fe sheet heated at 430°C to the Mo plate heated at 720 or 800°C. Preliminary comparisons between this study and the in-pile irradiation tests have been made. This result qualitatively supports the appropriateness of the model for the CCCT mechanism based on the vapor phase transport of cladding components by radiation-induced iodine.     

Molecular Dynamics Studies of Americium-Containing Mixed Oxide Fuels

The molecular dynamics (MD) calculation was performed for americium-containing mixed oxide fuels, (U_0-7--x Pu_0.3Am _x )O₂ (x=0,0.016; 0.03; 0.05; 0.1; 0.15), in the temperature range from 300 to around 2,500 K to evaluate the lattice parameter, heat capacity and thermal conductivity. The MD results reveal that the calculated heat capacity and thermal conductivity are at a similar level in the entire composition range, in other words they are scarcely influenced by adding americium up to 15%. This behavior was examined from a view point of a phonon-impurity scattering mechanism.     

稠密棒束通道内骤冷前沿附近壁面放热模型研究

在再淹没过程中,骤冷前沿附近的流动换热现象最为复杂,通常所说的骤冷就是在这个区域发生的对于稠密棒束再淹没过程,实验研究显示其骤冷前沿处壁面温度的下降非常急剧,而已有的估算骤冷前沿附近放热的经验关系式模型未能合理预测该位置处的放热,进而不能很好地模拟整体包壳温度历史曲线形状。本研究结合窄通道沸腾换热相关研究,提出"液体半月板延伸区域瞬态蒸发模型"来估算骤冷前沿附近的放热。与实验结果对比,证明该模型能够更好地估算骤冷前沿处壁面温度的变化。     

兖州矿区北宿煤矿综合机械化充填开采工艺及设备研究

针对兖州矿区北宿煤矿矿井资源储量目前只有7645.8万t,其中“三下”压煤4428.6万t,占总储量的57.9%,全矿可采储量不足1400万t,经济可采储量仅为406万t的情况.为解放“三下”压煤,缓解日趋紧张的采场接续、土地塌陷难题,延长矿井开采年限,研究了满足北宿煤矿薄煤层条件下综合机械化充填开采成套开采工艺与设备.