1. Vincent MASSAUT 10/10/2006 1 EFDA Task TW6-TSS-SEA 2.1 Occupational Radiation Exposure - ALARA in ITER: further refinement Kick off meeting Garching, 10/10/2006 Introduction V. Massaut

2. Vincent MASSAUT 10/10/2006 2 The Occupational Radiation Exposure (ORE) is an important safety factor for ITER and fusion plants in general Rather large amount of highly activated materialsRather large amount of highly activated materials Presence of dust, activated corrosion productPresence of dust, activated corrosion product Internal contamination hazard (tritium, dust)Internal contamination hazard (tritium, dust) Important replacement/refurbishment frequency of in- vessel componentsImportant replacement/refurbishment frequency of in- vessel components These aspects can be tackled adequately by careful design, use of Remote Handling (RH) systems and ad hoc maintenance proceduresThese aspects can be tackled adequately by careful design, use of Remote Handling (RH) systems and ad hoc maintenance procedures This is e.g. the case for the Neutral Beam Injector (NBI) systemThis is e.g. the case for the Neutral Beam Injector (NBI) system

3. Vincent MASSAUT 10/10/2006 3 At the beginning this EFDA task was devoted to an assessment and review of ITER ORE evaluation But following a request from ITER IT, there was a need to re-assess the occupational safety of operators concerned with the maintenance of the NBI systems, as the system design has been reviewed mostly for occupational purposes.But following a request from ITER IT, there was a need to re-assess the occupational safety of operators concerned with the maintenance of the NBI systems, as the system design has been reviewed mostly for occupational purposes. The task is thus divided in two parts:The task is thus divided in two parts: –Assessment of ORE for ITER –Review of occupational safety for the maintenance of the (new design) NBI cell

4. Vincent MASSAUT 10/10/2006 4 For the assessment of occupational exposure evaluation The evaluation of the operators occupational exposure was made up to now using rather rough estimates of dose rates, averaged over entire rooms and locations.The evaluation of the operators occupational exposure was made up to now using rather rough estimates of dose rates, averaged over entire rooms and locations. In order to assess the outcomes of these studies, a comparison for one specific location and operation with more refined 3D exposure analyses would allow to define if these first evaluation were sufficiently conservative or if further 3D analyses should be required for the main dose commitments contributions.In order to assess the outcomes of these studies, a comparison for one specific location and operation with more refined 3D exposure analyses would allow to define if these first evaluation were sufficiently conservative or if further 3D analyses should be required for the main dose commitments contributions.

5. Vincent MASSAUT 10/10/2006 5 Maintenance operations and exposure limitations have lead to analyse important design changes in the Neutral Beam Injector cell and design It is now important to know what would be the implications for the occupational exposure, internal (airborne contamination) as external (radiation exposure). Therefore the following aspects should be studied:It is now important to know what would be the implications for the occupational exposure, internal (airborne contamination) as external (radiation exposure). Therefore the following aspects should be studied: –1.-Total amount of T flow rate coming from the maintenance operations. Capacity of the ventilation system to achieve T concentration suitable for human presence in suits or without.(del.3) –2.- Expected time evolution of the T concentration airborne and order of magnitude of the surface contamination.(del.4) –3.- Basis for the assessment of the need of a specific containment for the NB cell.(del.5) –4.- Assessment of the possible decontamination procedures.(del.6) –5.- External Occupational Radiation Exposure.(del.7)

6. Vincent MASSAUT 10/10/2006 6 Task sheet

7. Vincent MASSAUT 10/10/2006 7 Occupational radiation exposure: present evaluation for ITER Some areas need to be evaluated more precisely but the margin to target (500 p-mSv/y) remains acceptable HC&WT = Hot Cells & Waste Treatment LH&CD = Lower Hybrid heating & Current Drive NBI = Neutral Beam Injectors ECH&CD = Electron Cyclotron Heating & Current Drive ICH&CD = Ion Cyclotron Heating & Current Drive VP&LDS = Vacuum Pumping & Leak Detection System TCWS = Tokamak Cooling Water System RH = Remote Handling NBI evaluation (~15 mSv/y) should be revisited

8. Vincent MASSAUT 10/10/2006 8 It is also important to demonstrate being ALARA For the concerned operations, it is also important to demonstrate that the dose commitment has been reduced to a level as low as reasonably achievable.For the concerned operations, it is also important to demonstrate that the dose commitment has been reduced to a level as low as reasonably achievable. Therefore, for operations presenting high dose impact, the comparison of various alternative (like e.g. with/without shielding, with/without change of geometry or procedure, etc.) is often very useful.Therefore, for operations presenting high dose impact, the comparison of various alternative (like e.g. with/without shielding, with/without change of geometry or procedure, etc.) is often very useful. Here sensitivity analysis can be useful for pointing out the main actions or operations to improve (on a radiation protection point of view)Here sensitivity analysis can be useful for pointing out the main actions or operations to improve (on a radiation protection point of view)