Tritium production rate in HCLL TBM: Conception of a measurement system with application of liquid scintillation technique

Abstract

Validation of the calculated Tritium Production Rate (TPR) in the Test Blanket Modules (TBMs) needs relatively simple measurement procedure. Measurement system in TBM based on Tritium determination directly in LiPb and/or in Li compound(s) with application of the Liquid Scintillator Counting (LSC) is proposed. Expected high temperature in TBM while ITER operation in sample not less than 150°C when cooled irradiated material, and 300–400°C without cooling, impose constraints on the possible methods and technical design. Preliminary results performed on irradiated LiPb eutectic pellets housed at controlled conditions of elevated temperature showed remarkable loss of Tritium. Observed escape of Tritium ranged from ca. 91% (temp.: 300°C, t=60min) to ca. 52% (temp.: 370–390°C, t=10min) being in fair agreement with calculated values by use of dedicated code (rCADiff). Basic limitation of direct radiometric measurement of Tritium activity in LiPb is parasitic activity induced in Pb, predominantly coming from 203Pb and also from impurities present in Pb. Demand of obtaining information on TPR in relatively short time points to other lithium compounds used as monitors which after irradiation, followed by an easy preparation procedure, can be measured using simple version of LSC. Most promising monitors seem to be Li2O and LiF. Two different possible versions of the proposed systems were considered: (1) LSC measurement starts after long period of time since irradiation (not less than 20 days); (2) LSC measurement starts shortly after irradiation (an hour or less to several hours).