A study on the mehtodology for tritiuum behavior in the gas cooled reactor for hydrogen production system

Abstract

In Korea, a nuclear hydrogen program has been established to develop and demonstrate mass production system for hydrogen generation. The objective of this study is to establish the evaluation methodology and procedure for the tritium behavior in the NHDD(Nuclear Hydrogen Development & Demonstration) reactor. In order to achieve this objective, tritium generation, diffusion, and permeation are considered and the simulation code predicting the tritium behavior was developed. The newly formulated and developed TBEC (Tritium Behavior Estimation Code) program can estimate the tritium generation and the corresponding tritium diffusion and permeation with respect to the temperature distribution in the Pebble and Prism type reactor core. The tritium generated by the fission reaction can be leaked into the helium coolant from the coated ceramic particles and fuel elements. The annual release rate of tritium diffused from coated fuel to the primary helium coolant through the encapsulated graphite were evaluated about 0.47 percent in case of the Pebble, 0.39 percent in case of the Japan prism type, and 10 percent in case of the U.S.A Prism type compared with the generated tritium. There is a big difference between the Japan and the U.S.A Prism type gas cooled reactor. In case of the Japan Prism type fuel element, Graphite plugs are densely screwed into the tops of the fuel holes so any other gas can not permeate these graphite plugs. But in case of the U.S.A, Graphite plugs cemented into the tops of the fuel holes enclose the fuel compact stacks. These graphite plugs density is very low so the tritium gas can be permeated into the primary coolant. Tritium attributed by 6Li, existing as impurities in the reflector, can be released to the helium coolant by the diffusion process and the total annual release rates of the tritium are estimated as 5.3 percent in case of Pebble type and 4.2 percent in case of the Prism type reactor through the reflector to the helium coolant. Ba...