Estimation of Plutonium Production using Graphite Isotope Ratio Method in 3D Whole Core = 3차원 전노심에서 흑연 동위원소 비율법을 사용한 플루토늄 생산량 추정

다국어 초록 (Multilingual Abstract)

To verify North Korea’s denuclearization, it is very important to accurately estimate the number of plutonium nuclear weapons produced by North Korea. In addition, reliable results should be obtained through independent verification methods in the process. Graphite Isotope Ratio Method(GIRM) is used as a denuclearization verification tool to predict plutonium production in graphite-moderated reactors. The graphite isotope ratio method was developed by PNNL in the United States in the 1990s, but detailed research beyond the basic principle is not disclosed, so independent development is required.
In this study, the GIRM was applied using the Calder Hall Magnox reactor as the target reactor. One of the Monte Carlo codes, the MCS code, was used for the depletion calculations of the nuclear reactor and the estimation model. Among the impurities in graphite, it is confirmed that Boron, Chlorine, Calcium, Titanium, Iron, Tungsten, and Uranium can be used as indicator nuclides through the evaluation of nuclides according to the impurity composition. Sensitivity tests were performed on reactor operating temperature and moderator density as factors affecting the accumulation of plutonium in nuclear fuel and changes in impurity isotope ratios. The resulting neutron spectrum change and plutonium production prediction error were analyzed and presented.
As a next step, impurity data in graphite was sampled from the reactor depletion calculation results. The prediction accuracy of plutonium production by region was evaluated. A single fuel pin-cell model, multiple fuel pin-cell model, multiple channel model, and multiple pan model were used as prediction models for sampling data. The overall plutonium estimation error at sampling region is improved by using 3D estimation models compared to 2D models. In consideration of the axial reflector effect of the graphite, precise estimation models have a major impact on the improvement of axial errors. Based on the predicted plutonium production of the sampling area, the plutonium production of the whole core area was estimated through a 3D polynomial regression method. Despite flux fluctuation of the reactor by inserting control rods, GIRM shows plutonium prediction performance in 3D whole core with relative error less than 3%.

목차 (Table of Contents)

• 1. Introduction 1
• 1.1 Research background 1
• 1.2 Computer code 2
• 2. Graphite Isotope Ratio Method(GIRM) 2
• 2.1 Calder Hall Magnox Reactor 3
• 2.2 Indicator Isotopes 8
• 2.3 Sensitivity analysis of GIRM under various conditions 12
• 2.2.1 Sensitivity test of GIRM by reactor operation temperature 12
• 2.2.2 Sensitivity test of GIRM on density of graphite 18
• 2.4 Depletion calculation of 3D Whole Core model 23
• 3. Estimation of Plutonium Production at Sampling Region 27
• 3.1 2D single pin-cell model 27
• 3.2 2D multiple pin-cell model 28
• 3.3 3D multiple channel model 29
• 3.4 3D multiple pan model 31
• 3.5 Comparison of result by estimation model 32
• 4. Estimation of Plutonium Production in 3D Whole Core 38
• 4.1 3D polynomial regression method 38
• 4.2 Result 43
• 5. Conclusion 48
• References 50
• Abstract (Korean) 52