This paper presents an analysis and results for the transport of activation products in pressurised water cooling loops of ITER, using the timeÐdependent activation transport and deposition code TRansport of Activation Products (TRAP).

The code, which is under continual development, has recently been modified to allow for timeÐdependent calculations. It has been written from first principles in order to include all possible gaseous or liquid coolants encountered in fusion devices, has the capability to treat an unrestricted number of stable and active species and allows for direct generation of active species in the bulk wall material and also in the coolant. It is used to calculate the activity content of: soluble atoms/ions in the coolant, insolubles (crud) in the coolant and pipe deposits inside the blanket (in-flux positions) and outside of the blanket (out-of-flux positions). The most important nuclides involved for a particular combination of structural material and coolant are identified and are treated. The code, in its steady state form, has already been used for helium gas, pressurised water and liquid lithium coolants for various power plant cooling loops and is currently under validation against typical PWR pressurised water cooling loop data. For ITER BPP calculations, the advantages of TRAP over other codes is its capability to deal with various structural materials around the cooling loop, include any number of stable and active species and its flexibility in accommodating fusion specific conditions.

The distribution and evolution of volatile and nonÐvolatile activated species in the cooling loop of the power plant must be known because pipework needs periodic inspection and/or maintenance, therefore any active deposits and/or leakage from the coolant circuit may contribute to the occupational doses received by plant personnel. Also, there may be potential for release of activated coolant to the environment through a loss of coolant incident.

This study examines and presents results on the time dependent behaviour of activation product transport and gÐdose in ITER cooling loops. During plant operation activation products will accumulate in the coolant through various processes and a fraction of this activity will be transported and deposit--permeate on pipework regions outside the shield.

Calculations using the model show that volatile species once released into the coolant tend to stay there, therefore a small fraction of the coolant must be diverted into a clean-up loop. By comparison, non-volatile species tend to deposit at places where large surface areas and low temperatures exist, such as the heat exchangers. Dose and gÐflux calculations have been performed using the 3-D Monte Carlo simulation code, MCNP-4. The input requirements include the source gÐspectrum, the 'idealised' geometry of the ITER 'hot leg' pipe, and dose conversion factors.

This work was jointly funded by the UK Department of Trade and Industry and Euratom.