Tbm Tritium System Of Tritium Safety Analysis

Nowadays, there is a greater demand on energies in the world, with the increasing depletion of the fossil fuel, which is the main body of the energy resource. Meanwhile, the nuclear fission energy has the inherent defects as limited reserves, harmful and radioactive wastes, etc.; other resources can’t meet the huge energy demand in the world. Therefore, people’s attention has been drawn to nuclear fusion energy. The nuclear fusion energy will be the first choice for future energy, since it is safe, clean and with abundant nuclear fuel supply. ITER is the first experimental fusion reactor based on magnetic confinement fusion, with the cooperation of the seven countries including China, EU and US, etc. ITER is not only used to verify the scientific nature and feasibility of fusion energy, but also used to partly testify the engineering and techniques of fusion reactor. TBM and its tritium system are one of the key techniques in ITER. According to the whole arrangement of Chinese ITER experts, a tritium system which can be used for HCCB TBM will be developed. The tritium system can be divided into three subsystems with different functions, named Tritium Extraction System (TES), Coolant Purification System (CPS) and Tritium Measurement System (TMS).The total tritium amount and release rate from TBM tritium system are the important problems in tritium safety research. Tritium can easily migrate and diffuse out to the external environment from the tritium system, damaging the structural materials and doing harm to the staff. The normal tritium release rate must be limited within the limit value. Before the verification test of TBM tritium system in ITER device, a safety analysis report about TBM and its auxiliary tritium system should be submitted to ITER organizations to gain the experiment permission license. The preparation work, for example, the pre-safety analysis, quality control measures and license application of the tritium system should be carried out.The safety analysis and evaluation on the tritium system is to analyze, with appropriate methods, the danger, possible failure and radioactive harm to the staff, environment and neighborhood. In order to realize goals above, deterministic analysis is used as the main guiding ideology. As a beneficial supplement, some methods based on probabilistic safety assessment (PSA) are appropriately applied. The following aspects of tritium safety analysis will be discussed:the strategy research on tritium safety analysis and safety management, the research on containment performance of materials for tritium, the danger analysis on TBM tritium system, the FMECA research on TBM tritium system, the analysis and calculation of tritium release under normal operating conditions. In the aspect of tritium safety analysis and safety management, probably adoptable safety measure of the tritium system is analyzed. Besides, the research content of tritium safety analysis is made clear, and safety research on TBM tritium system is considered as a part of strategy research on tritium safety. In addition, the procedure of tritium safety analysis, as well as the technique in each procedure is put forward and discussed.At first, this paper focuses on the strategy of tritium safety analysis and safety control, which is the guiding ideology for tritium safety study, mainly including safety strategies of tritium circulation, reasonable procedure and methods of tritium safety analysis, safety control strategy based on multiple tritium containment. Meanwhile, the function and material of TBM tritium system is analyzed, in order to provide support for further PHA and FMECA. The tritium trend and the tritium balance equation were given to provide guidance for tritium release calculation.Tritium resistivity of tritium resistant materials is one of the most important problems in tritium safety research. Permeability, diffusion coefficient and solubility of D2replacing HT in HR-1austenitic stainless steel can be got by gas permeability test, which can provide the basic data for tritium release calculation in tritium safety analysis.H2accidents, toxic gas accidents and three typical nuclear leakage accidents that ever happened in history are investigated and analyzed, to find the general factors about accident mode, accident mechanism, accident consequence and preventive measures, which will provide references for safety analysis on the tritium system. Some initiating events causing abnormal tritium releasing were analyzed by identifying dangerous, harmful factors on tritium system, on the basis of which, PHA is carried out to analyze the triple tritium containment systems of tritium system. And the result shows that PHA can lay the foundation of preliminary tritium safety analysis and further safety design. Meanwhile, the analysis on prevention measures for various dangerous and harmful factors can provide guidance for design of TBM tritium system. In addition, according to the requirements of the subject research, the design basis accident and beyond design basis accident about TBM tritium system are also analyzed. Tritium limit was analyzed and calculated, and the derived limit and other safety parameters were got.Similar to PHA, FMECA is also applicable to the safety analysis on TBM tritium system in design. Firstly, the task requirements and environmental condition of the research objects are analyzed and described, that is the task profile analysis, then risk definition is given. Through FMECA, the failure modes leading to dangerous tritium release are found out, and their risk priority number and damage degree level are calculated. They often take place in materials wall, connection structure and cooler. Then the potential fault modes leading to the excessive tritium release are found out, which are the key to prevent tritium release risk. It is definite that excessive tritium release is most likely to take place in the connection of tube-plate or plate-shell. The analysis shows that tritium release risk can be reduced, and the safety level of the tritium system can be raised also, only through the design improvement and safety compensation measures. Besides, four potential fault modes which are likely to lead to excessive tritium release should be paid more attention to.Calculation on tritium release amount to the environment and tritium action simulation in component and materials are the important content on tritium safety research. A certain amount of tritium exists in TBM tritium system, and tritium release rate is the important problem for tritium safety. Besides, tritium release rate should be within the permission value. Actual operational situation of the tritium system often changes, and it is impossible to know clearly the design parameters of the components, tritium amount and technique condition. Therefore, the normal tritium release amount could only be estimated, and calculation methods and parameters should be safe and conservative. The calculation methods in this chapter are mass transfer equation, Fick law, fluid flow equation, etc. There are three routes of tritium release, which are atomic tritium diffusion through the material wall, tritium molecular migration through micro leakage channels and tritium waste transportation out from TBM tritium system. The calculation result shows that when the tritium system works normally, the permeation rate of tritium through the material wall is low, and the micro leakage rate is even lower, which can be neglected completely. Through analysis in this chapter, the calculation process of the normal tritium release is very tedious, so the selection or establishment of the appropriate calculation mode for tritium release is important. Finally, mathematical model of detritiation in the tritium operating room is established on the basis of detritiation mode in glove boxes.