Scoping Analyses on Tritium Permeation to VHTR Integarted Industrial Application Systems

Abstract

EXECUTIVE SUMMARYTritium permeation is currently an important issue in the development of the Very High Temperature Reactor (VHTR) because tritium is easily permeated through high temperature metallic surfaces. Tritium permeation in VHTR-integrated systems was investigated in this study using the tritium permeation analysis code (TPAC) that was developed by Idaho National Laboratory (INL). The INL TPAC is a numerical tool based on the mass balance equations of tritium-containing species and hydrogen (i.e., HT, H 2 , and HTO) coupled with a variety of tritium sources, sink, and permeation models. In the TPAC, ternary fission and thermal neutron caption reactions with 6 Li, 7 Li 10 B, 3 He were taken into consideration as tritium sources. Purification and leakage models were implemented as main tritium sinks. Permeation of tritium and H 2 through pipes, vessels, and heat exchangers were considered as main tritium transport paths. In addition, electrolyzer and isotope exchange models were developed for analyzing hydrogen production systems including high-temperature steam electrolysis (HTSE) and sulfur-iodine processes.Three different systems were considered in this study: (1) the VHTR (gas Brayton cycle)/HTSE system, (2) the high-temperature gas-cooled reactor (HTGR) (steam Rankin cycle)/HTSE system, and (3) the HTGR (steam Rankin cycle)/methanol-to-gasoline (MTG) System. The VHTR/HTSE system is based on the VHTR design with a 900qC core outlet temperature and a Brayton cycle. The VHTR provides heat and electricity to the HTSE system for generating hydrogen. The HTGR/HTSE system is based on the HTGR design with a 750qC core outlet temperature and steam Rankin power cycle. The HTGR provides heat and electricity to the HTSE system for hydrogen production. As part of the nuclear-assisted industry process application, the VHTR was coupled with the MTG process. The VHTR/MTG system is also based on the 750qC core outlet temperature and the steam Rankin cycle. However, the VHTR provides only heat to the MTG system for generating gasoline and natural gas. This scoping study is focused on the following areas without tritium barriers:x Tritium concentrations in the industrial final products x Tritium distributions in the entire coupled system x Identification of important factors affecting tritium permeation and distributions.Global sensitivity analysis techniques were used in this study based on the variance decomposition and the Monte Carlo method. Two sensitivity indices were considered as importance measures: the first order index and the total index. The first order index was used for quantifying the main effect, and the total index was used for quantifying the total effect including interactions. More than 15,000 random samples were used for each case. As a result, important parameters were identified and well quantified with their rankings.This report presents preliminary results along with the Monte Carlo-based sensitivity for three nuclear-assisted process applications: VHTR/HTSE, HTGR/HTSE, HTGR/MTG, and HTGR/Impr...