In 2006 scientists of LEI implemented a first ITER safety justification project, which was supported through the EC FP-6 program. The objective of the project was to investigate if hydrogen deflagration is possible in the neutral beam injection (heating beam and diagnostic beam) components as well as in the cryopump of vacuum vessel and if deflagration is possible then to estimate the loads on the components.
The hydrogen distribution analysis was performed using computer code COCOSYS (Containment Code System). COCOSYS is developed to perform a detailed analysis of all significant processes that take place in case of a severe accident in the containment of the light water reactor also covering design basis accidents. Even though the computer code is developed for analysis of containment of light water reactors this was one of the first attempts to apply COCOSYS for analysis of components in fusion facilities.
The computer models were developed for the following ITER components:
- cryopump of vacuum vessel,
- heating neutral beam,
- diagnostic neutral beam.
It was received that in case of air ingress to ITER cryopump there are ~8 mol of hydrogen desorbd from the surfaces of cryopump and this amount enters the vacuum vessel. After 10 s, i.e. when the release of hydrogen terminates, the maximal concentration is 50 %, and after 120 s the hydrogen is well mixed in the entire volume of vacuum vessel and the turbulent deflagration or detonation is not possible.
To evaluate the consequences of the possible detonation it was estimated the maximal pressure in the vacuum vessel after detonation. The pressure was estimated assuming adiabatic isochoric complete combustion of hydrogen. It was received that the maximal pressure (2.65 bar) is reached not at the time point when the hydrogen concentration is maximal, but if the combustion happens later when the amount of air in vacuum vessel is largest.
Similar estimations were performed to investigate of hydrogen deflagration possibilities in the ITER heating neutral beam and diagnostic neutral beam. It was received that in case of an accident in the diagnostic neutral beam the maximal pressure could reach 1.7 bar, while in case of an accident in the heating neutral beam 1.97 bar. The results showed that the loads on ITER components in case of accident are not acceptable and to avoid them the proper safety systems, e.g. installation of a safety valve or injection of non-combustible gases to prevent hydrogen deflagration, have to be developed.
Coordinator: Lithuanian Energy Institute