Activation product transport using TRACT: ORE estimation of an ITER cooling loop

The gradual activation of the primary cooling loops with time in fusion power stations and experimental devices is one of the key safety and environmental issues. The time-dependent activation transport and deposition code transport of activation (TRACT) was developed and is used to predict the behaviour of soluble ions, crud particles and the resulting activity levels. Example calculations involve the transport of activation products in the Limiter–Outboard baffle cooling loop of ITER. Using time and temperature dependent experimental corrosion rate data calculations predict that the mobilised material of 3.75 kg in the loop is lower than the 8–10 kg originally predicted in previous studies, resulting in low levels of deposited activity: 2×108 Bq/m2 in-flux, as compared to 5×1010 Bq/m2, and 2×104 Bq/m2 out-of-flux, as compared to 6×109 Bq/m2. The active material in the loop after 1.2 years of operation is shown to be entirely due to soluble species rather than ‘crud’. Dose calculations, using activation product results based on larger than anticipated corrosion rates, show that during plant operation the contact dose is 63 200 mSv/year, the 1 m away dose is 11 300 mSv/year, and both are entirely due to the active nuclides in the coolant. After shutdown there is a rapid decrease in dose and after 8 days doses are 184 mSv/year (contact) and 43.5 mSv/year (1 m away), and are entirely due to the long-lived nuclides. However, estimation of the dose for the corrosion rates considered as more likely to be representative of the ITER cooling loop gives a total contact dose of 0.23 mSv/year for times greater than 8 days after shutdown. This dose level is considered negligible when compared to the annual permissible worker dose of 20 mSv/year, and would be acceptable under current nuclear plant licensing requirements.