open access

https://doi.org/10.14943/doctoral.k15363

https://hdl.handle.net/2115/89685

高速炉の多様な設計要件に適用可能な核特性シミュレーションの研究

英語

2023-03-23

Hokkaido University

2, v, 109p.

Since the nuclear fission reaction was confirmed in 1938, human beings realized that the fission process can cause a self-sustaining chain reaction. After this point was verified through experiment, the age of nuclear power utilization started. The first commercial nuclear reactor plant Shippingport Atomic Power Station started to operate in 1957, and since then more than 60-year operation experience on nuclear power utilization has been accumulated. Currently, the development of nuclear reactors is in the process of moving from the third generation to the fourth generation. The majority of commercial power plant reactors are thermal-neutron reactors, i.e., using thermal neutrons (around 0.025 eV) to sustain a fission chain reaction and to output energy. The utilization rate of uranium resources by thermal neutrons is low due to the uranium nuclear properties. Therefore, fast-neutron reactors (fast reactors in short), which can greatly improve the utilization rate of uranium resources, have received widespread attention and been actively promoted. The fast reactors can fully utilize uranium resources by converting fertile material into fissile material, and therefore, this process is called as breeding. Besides, the minor actinide (MA) from fast reactor spent fuel is considerably less than it from conventional thermal reactor. With these unique features, fast reactor technology has been being actively promoted in all major industrial countries. Currently, U.S. and Japan are promoting the Natrium fast reactor project, and China is constructing demonstration fast reactors Xiapu-1 and Xiapu-2. In the research field of nuclear engineering, analysis strongly relies on computer software. The development of a new type of reactor (such as a fast reactor) begins with a conceptual design that explores a wide range of design parameter space, followed by several stages of design refinement, and eventually leads to a detailed design and plant construction. In the conceptual design stage, a large number of quick calculations are necessary for giving a solution, whereas in the detailed design stage, accuracy of the solution must be ensured. Therefore, software that is capable of meeting different demands at each stage of the design work would be essential. The research summarized in this dissertation focuses on software that can be used in a variety of reactor designs. The first research is the development and verification of a software for neutronics analysis applicable to various design stages in fast reactor development. The second research is the development of a practical neutronics analysis method for the intermediate stage of fast reactor design, which could be regarded as a bridge between the conceptual design stage and the detailed design stage. The software used in this dissertation is CBZ, which is a general-purpose reactor physics analysis code system, and it is independently developed at Hokkaido University. FRBurner is a fast reactor burnup calculation module that can realize various combinations of calculation methods through incorporating them with various modules and solvers in CBZ. This module is being verified against an OECD/NEA fast reactor neutronics analysis benchmark. This benchmark offers four sodium-cooled fast reactor concepts, which represent the general type of sodium-cooled fast reactors. Four key reactor physics parameters, effective neutron multiplication factor keff, effective delayed neutron fraction βeff, sodium void reactivity ∆ρvoid, and Doppler reactivity ∆ρDoppler, are the focus and compared to reference results. Comparison with the reference results provided by other institutes indicates that the FRBurner module can provide acceptable results for general-type fast reactor physics analysis. Second, a comprehensive comparison of these methods is performed in order to reveal the features of each option on the calculation method. This helps users choose proper methods for wide range utilization. Moreover, the computing burden is taken into account to present desirable calculation conditions for the conceptual, intermediate, and detailed design stages. In addition to the solvers based on the transport and diffusion equations, a solver based on the simplified-P3 equation (SP3 equation) is added to CBZ. The SP3 solver is positioned as an intermediate option between the transport and diffusion solvers. Aside from the verification part of study, the novelty of this study is that various methods that differ from whole core step calculation theory, dimension of lattice model, burnup chain model, and libraries (which can be regarded as four aspects on calculation method) are thoroughly compared in the context of fast reactor applications. It is noteworthy that a series of calculation methods based on the SP3 theory are used for fast reactor analysis in this research. Utilization of the SP3 theory in fast reactor analysis has been limited in the past. People have started to use the SP3 theory in fast reactor analysis very recently. Therefore, the accumulated data is insufficient, and this research fills the blank from the viewpoint of application. Building on the first research, the reliability of the FRBurner module is well proved, and advantage of the SP3 solver is exhibited as well. Then, an innovative reactivity calculation method is newly proposed through combining the SP3 and perturbation theories. Equations of the SP3-perturbation (SPP) method is derived at first, and then verification is carried with the same OECD/NEA benchmark after code implementation is finished. Although all reactivity calculation methods based on the perturbation theory could give component-wise reactivity, the SPP method has a physical meaning unclear term in its equation. Through tracing to the theoretical source of SP3 and defining a new form of it, the physical meaning unclear term in the SPP method is eliminated. Thus, the component-wise reactivity calculation based on the SP3 and perturbation theories is achieved firstly in the world. Through component-wise reactivity analysis, it is demonstrated that more accurate prediction of the scattering and leakage components of reactivity can be obtained with the new method comparing to the diffusion-perturbation method. In summary, the author has developed and verified a software applicable to meet various demands on design requirements of fast reactors, and proposed a new method (SPP method) which is useful for the reactivity analysis. These two works together contribute to the nuclear engineering field significantly.

2023-03-23

甲第15363号

博士(工学)

(主査) 准教授 千葉 豪, 教授 小崎 完, 教授 澤 和弘, 准教授 遠藤 知弘 (名古屋大学・工学研究科)

工学院（エネルギー環境システム専攻）

博士論文

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