Development And Verification Of Radioactive Source Term Program For PWR Nuclear Power Plant

This paper mainly expounds the calculation method and program development of the design and realistic source term for PWR nuclear power plant. The design source term is calculated on the basis of the conservative model or the design model, which applies to the design of shielding. Realistic source term is primarily used for the estimate of the total annual radioactivity release from nuclear power plants. The significance of the research on design source term and realistic source term lies in its provision of the data of radioactive intensity for radiation shielding, environmental assessment and some guidance for the retirement of nuclear facilities.In view of the lack of study on design and realistic source term in China, this paper researches the process of transmission, adsorption, retention, decay of radionuclide in the main loop, auxiliary system and workshop on the basis of current research on thermodynamic cycle system, material corrosion and water chemistry in PWR. Thus, it develops a mathematical model for distribution and transfer of nuclide mixture, and future develops DORAST program which can be used for the calculation of source term analysis in PWR and draws the regularity of radionuclide distribution in the systems or equipments. With the adequate consideration of the ways and mechanism of radioactive nuclides’product and disappear under normal working conditions in PWR, the innovation of this paper is the establishment of a mathematical model for the analysis of source term which applies to the reactor systems or equipments of Generation Ⅱ and Generation Ⅲ. The mathematic model takes decay chains as the unit, with the full consideration of generation and decay of radioactive nuclide in the PWR’s systems or equipments, the balance differential equations adopts the method of implicit cubic sixth order Runge-Kutta and Kaps-rentrop for solution. Simultaneously, source term model coupling method which divides the process of radioactive nuclide migration into four phases, such as, accumulation, purification, re-accumulation, release, is advanced. The coupling method assigns the balance differential equation of radioactive nuclides into these four phases. Thus, based on the coupling method, the function models in the program-DORAST can be applied to the calculation of design source term and realistic source term of different kinds of PWRs and systems.