Computational study of the dose-rate field of an ITER heat exchanger due to activated corrosion products

Abstract

In ITER (Nuclear Facility INB-174), ACPs (Activated Corrosion Products) deposited in the cooling channels will represent a major contribution to the radiation field during machine shutdown. The primary cooling circuit includes eight Heat Exchangers (HXs) which host thousands of small pipes in the so-called bundles, where the heat is transferred from the primary to the secondary circuit and where ACPs accumulate. The accurate calculation of the radiation associated with these hot spots is needed, to ensure that the radiological zoning is respected during the planned maintenance activities in the ITER Equipment Vault. To characterize the impact of one HX on the radiation levels, three computational models were produced and simulated. The first one, called no-bundle model, was an unrealistically conservative model that omitted the steel of the bundle pipes, which resulted in extremely high dose rates surrounding this component. In the second one, called simplified-bundle model, the mass of the bundle pipes was considered by defining a bundle cell with a homogeneous material. To ensure the validity of this computational representation, a third model, called detailed-bundle model, was produced with the most realistic up-to-date model of the HX. The detailed-bundle model included an explicit representation of the complete bundle realized with automated modelling techniques. The radiation source deposited onto the thousands of surfaces of the bundle pipes was simulated explicitly using dedicated developments in D1SUNED. The dose field surrounding one HX was calculated with the detailed model and compared with the simplified, second model, showing good agreement. The simulation of the detailed-bundle model allowed us to reliably lower the dose rates estimates, by a factor of 8-10, compared to the first, unrealistic model. The validation of the simplified-bundle model will be used to practically evaluate the Occupational Radiation Exposure and to assess dose reduction measures for this component.