Occupational Radiation Exposure – ALARA in ITER: further refinement TW6-TSS-SEA 2.1

1. Occupational Radiation Exposure – ALARA in ITER: further refinement TW6-TSS-SEA 2.1 Ion Cristescu, FZK

2. Objectives of FZK Deliverables • Capacity of the ventilation system to achieve T concentration suitable for human presence in or without suits • Expected time evolution of the T concentration airborne and order of magnitude of the surface contamination

3. Vault Area Ventilation and Confinement Systems ► Normal ventilation system HVAC-2 ► Depression system ► Vault air cooling system ► Vault air detritiation dryers References : DDD 3.2 N Ventilation and Confinement Systems HVAC Concept Review – IBERTEF A.I.E. report

4. Ventilation and Confinement system of Vault areas HVAC 2 NVDS- 1

5. Normal ventilation system HVAC-2 ►This system is only operated during maintenance work in the vault. ► The isolation dampers (not safety related dampers) incorporated in the supply and extraction ducts are normally closed and are part of the pressure boundary and tritium confinement boundary. Hence they are rated at 0.2MPa. ► The HVAC-2 supply and extraction ducts are also equipped with fire/smoke isolation dampers to prevent spreading of fire and smoke. ► The supply and extraction ducts are routed to the TCWS vault via the vault annex in the tritium building.

6. Depression system ►To maintain negative room pressure (-2mbar) relative to the building external pressure, this system is operated continuously during ITER normal operation and maintenance work and also in case of fire. ► This system, composed of an air extraction pipe with differential pressure control valves and chilled water cooled air cooler, is directly connected to N-VDS 1. Double pressure isolation valves (safety related valves) are installed at the air extraction nozzles placed inside the vault area to prevent propagation of over pressure to N-VDS 1 ► The vault depression system is SIC, and designed with full redundancy of the active components, electric components and the associated instrumentation, utilities and electric power cables.

7. Configuration of NVDS-1

8. Vault air cooling system ►This system, composed of chilled-water cooled air coolers, air fans and air distribution ducts, is operated: - to remove normal heat loads dissipated from hot pipes (primary cooling system pipes), electric components (motors, compressors, heaters, room lighting, etc) - to cool down room air temperature in case of coolant spillage due to a pipe break in primary heat transfer systems ► Based on the safety requirement to minimize environmental tritium release from the vault under an over pressure condition, the cooling time was determined to regain normal room pressure (0.1MPa) in 24h. Therefore, this is a SIC system designed with full redundancy of the active components, electric components, the associated instrumentation, utilities and electric power.

9. Vault air detritiation dryers ►Is operated (except during an overpressure event) to remove tritiated water vapour to achieve an acceptable room air tritium concentration level (0.1 DAC-HTO). The source term of the tritiated water vapour is the leakage of coolant from ITER primary cooling systems, and the estimated annual leakage volume is 1% of the cooling system water hold-up. ► This system is composed of - a rotary dryer, - a compressor, - and a chilled-water cooled air cooler. Adsorption of water vapour and desorption (regeneration) of saturated dryer bed is continuously carried out. This system is not SIC, because it does not form part of the tritium confinement boundary.

10. Tritium sources during maintenance operations During maintenance activities on NB box, two tritium source should be considered: ► Tritium out-gassing from NB cryopanels - Inputs from FZK vacuum pumping group will be used ►Tritium out-gassing both from NB cryopanels and Vacuum Vessel - In addition to reference documentation, JETand TFTR data related to tritium retention and clean- up will be used to estimate the values of sources term

11. Detritiation of NB cell after a tritium spillage ► During maintenance activity a chronic release of tritium is expected ► S-ADS and S-VDS will be used in combination for NB cell decontamination and to maintain depression. ► The DF of S-ADS is 102 and 103 for S-VDS. Therefore, the NB environment has to be processed in closed loop until the tritium concentration will be lowered to a level that allows to discharged it to stack. ► For low tritium contamination, fresh air should be provided by H-VAC and processed in one through mode in S-ADS and S-VDS. ► In the present configuration the NB cell is not served by the S-ADS. Pipe connections between NB cell and S-ADS need to be provided.

12. Atmosphere Detritiation System of ITER

13. Room Air Detritiation Model for the Combined Operation S-ADS and S-VDS 4500 Nm3h-1 3000 Nm3h-1 Time evolution of tritium concentration in a contaminated area, during the detritiation processes, will be determined under the following assumption: - Perfect mixing of tritium within a contaminated area - Oxidation of elemental tritium and isotopic exchange reaction can be ignored - The sorption and desorption of tritiated species on/from wall surfaces can be ignored

14. Estimation of surface contamination after a tritium spillage event Two cases of surface contamination will be considered: ► Contamination with tritium in gas phase - data available at TLK, AECL, TPL and TFTR will be used as basis for evaluation ►Contamination with HTO - Information from TPL, operation of CANDU reactors (AECL, Cernavoda-Romania)

15. Inputs required for the FZK Deliverables Additional information related to the following issues will be highly beneficially: ► Leak rate for NB cell after separation from vault area ► Out-gassing rate of the in-vessel components during maintenance activity ► Reference documentation