사용후핵연료 임계도 평가를 위한 전산코드의 유효성 검증에 관한 연구

Abstract

ABSTRACT A Study on the Validation of Nuclear Criticality Analysis Codes for Spent Fuel

Gwangbong Kim Advisor : Prof. woonkwan Chung, Ph.D. Department of Nuclear Engineering, Graduate School of Chosun University

Recently, Regulatory requirements for wet and dry storage of LWR fuel have been strengthened. (DSS-ISG-2010-01 Rev.0 and ISG-8 Rev.3) Thus, the critical experiments and validation of burnable nuclide in Criticality Evaluation has increased in importance. This study shows the result of validation test for KENO-Va, MCNP-X code that is often used for criticality evaluation and for SERPENT code which was developed in Finland in 2004 and widely used in Europe recently. To determine the suitability of the test results for enhanced regulatory requirements, the statistical analysis and validation of three codes were carried out in accordance with NUREG / CR-6698 respectively. Critical safety analysis target to be considered in this calculation is the validation for the light-water reactor spent fuel storage facilities. Accordingly, criticality experiments using UO₂ fuel rods constituting the assembly form and using water as a moderator were selected to demonstrate the validity of the analysis method. Total 7 group(01, 02, 09, 13, 16, 17, 42) 115 experiment data that satisfies these conditions was selected from the Handbook Volume -IV "low enriched uranium systems (LEU-COMP- THERM-0XX)" which has been published by ICSBEP as OECD / NEA documents. Data analysis was carried out for statistical analysis and validation according to NUREG / CR-6698. In addition, the Student t-test was used to determine statistical significance of the input data. If the relationship can be determined between the calculated and the independent variables, the one-sided tolerance band can be used. Bias and bias uncertainty of one-sided tolerance band for the criticality experiment is expressed as follows. bias = K(fit) - 1.0 : K(fit) 가 1.0 미만인 경우 bias = 0.0 : K(fit) 가 1.0 이상인 경우

bias uncertainty = 본문 식 2-26 참조 Summary of Calculation result (SERPENT) : 본문 Table 3-15 참조 Summary of Bias and Bias uncertainty as a function of enrichment : 본문 Table 4-1 참조 Summary of Bias and Bias uncertainty as a function of fuel diameter : 본문 Table 4-2 참조

Applying the one-sided tolerance band for the fuel enrichment and diameter to criticality evaluation we can calculate the optimal which satisfies the USL in criticality evaluation. Based on bias and bias uncertainty evaluation results for the three codes , we can find the best estimated bias of the SERPENT code is lowest.