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Takeda, Toshikazu*; Kitada, Takanori*; *; *
PNC TJ9605 98-001, 267 Pages, 1998/03
As the improvement of numerical analysis method for FBR core characteristics, studies on several topics have been conducted; multiband method, Monte Carlo perturbation and nodal transport method. This report is composed of the following three parts. Part 1: Improvement of Reaction Rate Calculation Method in the Blanket Region Based on the Multiband Method. A method was developed for precise evaluation of the reaction rate distribution in the blanket region using the multiband method. With the 3-band parameters obtained from the ordinary fitting method, major reaction rates such as U-238 capture, U-235 fission, Pu-239 fission and U-238 fission rate distributions were analyzed. As for the nuclides to be analyzed, the elements of structure material, such as iron, nickel, chrome and sodium were considered. By the present method, all the reactions became larger at the deep region in the blanket. The maximum correction amounted as much as 5%. This tendency lessen the disagreement between the ordinary calculation and the experiment. It was made clear that the treatment in inter-band scattering term is veryimportant because it has large sensitivity on the result. An alternative method to determine the multiband parameters whieh method is based on more direct approach and is free from drawbacks in the present method, was also investigated. Part 2 : Improvement of Estimation Method for Reactivity Based on Monte-Carlo Perturbation Theory. Perturbation theory based on Monte-Carlo perturbation theory have been investigated and introduced into the calculational code. The continuous energy Monte-Carlo perturbation code has been developed by using not only the correlated sampling method which is already used before, but also the derivative operator sampling method. The Monte-Carlo perturbation code was applied to MONJU core and the calculational results were compared to the reference. The change of eigenvalue caused by the change of sodium density in the GEM or dummy ...
Takeda, Toshikazu*; *; Kitada, Takanori*; *
PNC TJ9605 97-001, 100 Pages, 1997/03
This report is composed of the following two parts and appendix. (I)Improvement of the Method for Evaluating Reactivity Based on Monte Carlo Perturbation Theory (II)Improvement of Nodal Transport Method for 3-D Hexagonal Geometry (Appendix) Effective Cross Section of 
U Samples for Analyzing Doppler Reactivity in Fast Reactors Part I. Improvement of the Method for Evaluating Reactivity Bascd on Monte Carlo Perturbation Theory. Theoretical formulation in Monte Carlo perturbation method had been checked, and then introduced into a calculation code. The increase of CPU time is about 10 to 20 % compared to that if normal Monte Carlo code, in the cases of same number of history. This Monte Carlo perturbation method found to be effective, because results are almost reasonable and deviations of the results are especially small, by using the Monte Carlo perturbation code. However, there are somc cases that the results of the change of eigenvalues becomes positive or negative by changing the estimator, and there is no reasonable difference in the results between the conventional method, which does not consider the change of neutron source distribution caused by a perturbation, and the new method, which consider that change. Thus it is still necessary to check the Monte Carlo pcrturbation code. Part II. Improvement of Nodal Transport Method for 3-D Hexagonal Geometry It is certain that we can accurately evaluate hexagonal geometry FBR core by nodal transport calculation code for hexagonal-Z geometry named 'NSHEX'. However it is also found that in very heterogeneous core the results is not good enough. Because the treatment of the transverse leakage to the radial direction, which is use for evaluating intra-nodal flux distribution, is not so accurate. For the treatment of the leakage distribution, it is necessary to estimate the nodal vertex flux. In conventional method, the vertex flux estimated by the surrounding node surfacc flux around that vertex. On the contrary,
Takeda, Toshikazu*; Kitada, Takanori*; *; *
PNC TJ9605 96-001, 120 Pages, 1996/03
This report is composed of the following three parts. (I)Improvement of Calculational Scheme of Reaction Rate Distribution by Monte Carlo Method. (II)Calculational Method for Doppler Reactivity Worth by Using Ultra-Fine Energy Group. (III)Improvement of Calculational Method of Transverse Leakage on Three Dimensional Nodal Transport Code for Hexagonal-Z Geometry.
