Effects of activation products on tritium measurements for tungsten in fusion reactors

Highlights: • The distribution of neutron activated products (NAPs) in the divertor of ITER were calculated by JMCT code and FISPACT code. • The effects of NAPs on chemical etching method (CE), β-ray induced X-ray spectrometry (BIXS), tritium imaging plate technique (TIP) and tritium calorimeter (TC) were evaluated quantitatively. • BIXS, TIP, and TC will be greatly influenced by NAPs, and it usually takes several years to let the signal from NAPs become acceptable comparing with signal from tritium in measurements. -- Abstract: Influence of neutron activated products (NAPs) is one of the primary problems for tritium measurements in tungsten as plasma-facing materials (PFMs). Both Monte Carlo simulation was introduced to calculate the amount of NAPs after different decay time and at different location of the divertor in detail. Then, the effects of NAPs on the commonly used tritium measurement methods for PFMs, including chemical etching method, β-ray induced X-ray spectrometry, tritium imaging plate technique and tritium calorimeter, have been evaluated quantitatively for PFM samples with different tritium depth profile, sample thickness and sample cooling time. Results indicate that more than one hundred kinds of NAPs would generate through the irradiation of fusion neutrons and NAPs with half-lives shorter than 1E-03 year and large activities, such as W-187, W-183 m etc., account for a substantial part of total activity directly after exposure and their amounts rapidly decrease to negligible as decay time increases. However, within cooling time from 3 to 60 months, the influence of tritium measurements is barely dominated by W-185, W-181, Ta-182 and Ta-179. In addition, it is found that the influence of NAPs on chemical etching method is the minimum while the other three approaches are still strongly affected by NAPs after several months. And it usually takes several years to let the signal from NAPs become acceptable comparing with signal from tritium in measurements.