主催: The Japan Society of Mechanical Engineers
会議名: 福島廃炉研究国際会議2022(FDR2022)
開催日: 2022/10/14 - 2022/10/17
Tritium is very difficult to analyze mainly because its emission type (beta minus), its chemical and its physical behavior. However, during dismantling activities as well as environmental control, it is necessary to characterize it with low uncertainty.
Tritium is a radionuclide produced either naturally when cosmic ray interacts with nitrogen and oxygen atoms in the upper troposphere and lower stratosphere or during a man-made nuclear process when fast moving neutron with an energy of more than 4MeV reacts with nitrogen, measurable amount of tritium was released in the environment after the Fukushima accident.
The beta decay makes tritium difficult to characterize as when it undergoes beta minus decay to form the stable helium-3 atom. The electron produced by the reaction is only 5.7keV on average, one of the lowest energy beta particles. The low energy causes the beta particle to have low penetration, they can only travel an average of 6mm in air. Thus, characterizing tritium from a distance is extremely difficult.
Tritium is also hard to detect since it behaves like hydrogen and can form tritium gas or replace hydrogen molecule in other organic molecules. These molecules can easily be absorbed by the human body and become a hazard. While tritium is not dangerous in the vicinity of people, it will be if ingested. Furthermore, volatility makes a nuclide that need to be monitored carefully. Tritium permeates through many materials and porous substance including metals and rubber.
Tritium has a half-life of 12.312 years and is considered a short-lived radionuclide. However, its permeability, high coefficient of diffusion and chemical property similar to hydrogen making it difficult to detect makes it a concern for decommissioning projects.
Various ways of characterizing and measuring tritium exist, that will vary with the expected amount of tritium, the nuclides present and the sample, be it gas, liquid or solid. However, no technologies were crowned as objectively better for tritium characterization yet.
This paper presents different ways to monitor, characterize and measure tritium such as ionization chambers, proportional counters, scintillators, volumetric analysis, chromatography, and spectroscopy among others. We will as well, introduce the development in technologies that were made for the development of the M IONIX – TGN real time monitoring of tritium. Discussions on usual problem associated with tritium monitoring such as the elevation of radioactive wastes, response time and maintenance will also be presented.
