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Personnel Dose Assessment at the PRIMA Neutral Beam Test Facility

S. Sandri, A. Coniglio, A. Daniele, M. D'Arienzo, L. Di Pace, M. Pillon

Fusion Science and Technology / Volume 60 / Number 2 / August 2011 / Pages 776-780

Safety & Environment / Proceedings of the Nineteenth Topical Meeting on the Technology of Fusion Energy (TOFE) (Part 2)

PRIMA consists of two experiments which will test at the same time the main components of the final system and the whole system. The facilities are named respectively SPIDER (Source for Production of Ion of Deuterium Extracted from RF Plasma - ion source only) and MITICA (Megavolt ITER Injector Concept Advanced - the main system). Both injectors accelerate negative deuterium ions with a maximum energy of 1 MeV for MITICA and 100 keV for SPIDER, and a maximum beam current of 40 A for both experiments.

Following D-D and D-T reactions on the calorimeter panels, important neutron and photon fields are generated around the injectors; such secondary radiation fields represent a relevant issue from the radiological safety point of view. Major radiation protection issues are the activation of materials and components around the injectors, among which the vessel itself and the corrosion products formed in the cooling loops (by the chemical reaction between metal and water). Both these radiation sources may contribute to personnel dose during maintenance operation.

In addition, radioactive tritium is produced inside the vessel (mainly in the MITICA facility) which is likely to be poured in the environment during operation phases thus representing a possible contamination pathway for workers and for the population living in the area surrounding the facility.

Finally, important penetrations for the ventilation, the power supply and the auxiliary systems were arranged inside the facilities. Tunnels in the underground region, with relatively large dimensions, were needed for both MITICA and SPIDER bunkers in order to allow personnel access for inspection and maintenance of cables and ducts. Each of these shielding weaknesses may provide important dose contribution to radiation workers thus requiring specific safety analyses.

In the present paper all major safety issues and relevant radiological concerns are analyzed with a detailed assessment of dose contribution to personnel working inside the facility. Specific dose evaluations were performed through Monte Carlo simulations.

Radiation shielding and radiation protection criteria were realized in order to meet the Italian regulatory limit for non radiation workers, ie. below 1 mSv/yr. Our analysis and project evaluations confirm that this constraint is never exceeded during operating phases of the injectors.

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