1. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Occupational Safety Assessment M. T. Porfiri – ENEA UTFUS-TECN (Frascati) Seminar – Safety in Nuclear Fusion Plants La Sapienza University Rome – 24 April 2015

2. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Outline  Occupational Radiation exposure: definition  Dose Guidelines& radiological zoning  ORE assessment  Tools for ORE assessment  ALARA  ITER: work phases, places, risks, ORE 2/34

3. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Glossary ACP Activated Corrosion Products ALARA As Low As Reasonable Achievable DACDerived Activity Concentration DCF Dose Conversion Factor EPR European Pressurized Reactor EST Environmental Source Term FMEAFailure Mode and Effects Analysis ICRPInternational Commission on Radiological Protection ITERInternational Tokamak Experimental Reactor NRCNuclear Regulatory Commission OREOccupational Radiation Exposure PFCPlasma Facing Component PIE Postulated Initiating Event PST Process Source Term VVVacuum Vessel 3/34

4. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Occupational radiation exposure (ORE): definition Any experimental/industrial plant needs to be maintained during normal operation. The maintenance of the nuclear plants is peculiar because additional precautions are necessary to avoid the exposure of the workers in the zones affected by the radiological source terms. At this scope a preliminary ORE assessment is performed in the meanwhile the design of a nuclear plant is on going, in order to optimize the collective dose. The ORE assessment is repeated several times, during the design phase and in the first steps of the plant operation to implement an effective ALARA process. 4/34

5. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 SOURCE TERMS ASSESSMENT Normalworking conditions Occupational dose IE AS Thermodynamic transients Aerosols and H3 transport Containments Release from the plant DCF Overall Plant Analysis FFMEA Radioactive waste Operational&Decomm waste Identification&classification Management On-site Recycling Final disosal Effluents PST EST DCF man*Sv/y dose/sequence to MEI frequency*dose Quantity and waste categories mSv/y SOURCE TERMS Normalworking conditions Occupational dose PIE Thermodynamic transients Aerosols and H3 transport Confinements Release from the plant DCF Overall Plant Safety Analysis FMEA Radioactive waste Operational&Decomm waste Identification&classification Management On site Recycling Final disposal Effluents PST EST DCF person*Sv/y dose/sequence to Public frequency*dose Quantity and waste categories mSv/y (Courtesy of S. Ciattaglia) Safety Analysis “ Course ” : ORE Assessment 5/34

6. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ITER General Safety Objectives General safety objectives For personnelFor the public and environment Situations in design basis Normal situations ALARA, and in any case less than: Maximum individual dose ≤ 10 mSv/yr Average individual dose ≤ 2.5 mSv/yr Collective annual dose ≤ 500 mSv*p/yr Releases less than the limits authorised for the installation, Impact as low as reasonably achievable and in any case less than: ≤ 0.1 mSv/yr Incidental situations As low as reasonably achievable and in any case less than: 10 mSv per incident Release per incident less than the annual limits authorised for the installation. [i.e. 0.1 mSv per incident] Accidental situations Take into account the constraints related to the management of the accident and post-accident situation No immediate or deferred counter-measures (confinement, evacuation) < 10 mSv No restriction of consumption of animal or vegetable products Situations beyond design basis Hypothetical accidents No cliff-edge effect; possible counter-measures limited in time and space 6/34

7. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ORE: ITER Objectives vs ICRP and European limits Type of WorkerICRP RecommendationEuropean regulatory Limits Radiation Worker100 mSv per 5 years 50 mSv/y 20 mSv/y Non-Radiation Worker1 mSv/y Dose Limits for Worker Exposure Dose targets – Maximum individual dose in normal operation < 10 mSv/y – Average individual dose for classified workers < 2.5 mSv/y – Collective dose < 500 mSv/y – Maximum individual dose per incident <10 mSv 7/34

8. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Radiological zoning: ITER case (1) The total dose rate is the sum of the external dose rate and the internal dose rate. (2) In case of exposure of the eye lens (crystalline), these values should be multiplied by 0.3 (150/500). (3) If source is always present, these values can be interpreted as a dose-equivalent rate. (4) Human access forbidden without special authorization. 8/34

9. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ORE: calculations For each nuclear plant a key parameter for the approval of the regulator is the evaluation of the collective dose for all the maintenance activities foreseen in the plant during a year. No limits are fixed from the international/national rules but the references are normally the better (that means lower) collective doses in the modern nuclear plant. The formula is : Collective dose =  i (N. workers) i * (maintenance time) i * frequency of maintenance i * (dose rate) i [pmSv/y] The collective dose for a modern fission plant EPR (European Pressurized Reactor) is of the order of 300-400 pmSv/y. ITER fixed a collective dose of 500 pmSv/y, as design guideline. 9/34

10. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ORE: Data needs The data necessary to perform ORE assessment: a) Source terms (radiation field, tritium, ACPs, activated dust and/or fluid and/or gases and/or liquid metals) in the maintenance zone b) Maintenance procedures & frequency c)Work effort (number of hours*number of workers) 10/34

11. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Radiological protection: origin of risks D +T = He + N Neutrons resulting from the D-T reaction (14 MeV)  Activation of components,  Activation of water  Activation of gas  Activated corrosion products (ACP) in water cooling systems  In Vacuum Vessel dust activation products (tens of Kg are expected) Tritium – In VV, tritium plant and hot cells – Tritium in cooling circuits (permeation) Radiological hazards – Replacement of plasma facing components – Maintenance of vacuum pumping systems, additional heating systems, fuelling, diagnostics, cooling loops, – Activity in Hot Cells – Waste treatment and storage facilities – Tritium plant operation and maintenance 11/34

12. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Source Terms vs type of dose  Tritium internal and external dose  Dust internal and external dose  Direct radiation not affecting ORE  Structures’ activation external dose  Activation corrosion productsexternal dose  Activated waterexternal dose  Activated gasesinternal dose  Activated liquid metalsexternal dose 12/34

13. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Tritium and dust: internal and external dose Typically the internal dose is given in terms of DAC (Derived Activity Concentration). The DAC is the radionuclide atmosphere concentration that leads to an annual effective dose equal to the regulation upper limit. The annual effective dose limit for the exposed workers is 20 mSv and the conventional annual working time is 2000 hours. For conservative reasons airborne tritium is considered in tritiated water (HTO) form only due to its higher radio-toxicity. For HTO the DAC value adopted in ITER is 3.4 105 Bq/m 3. The relevant derived activity concentration (DAC) of 4.5 105 Bq/m 3 [*] including skin transfer, is responsible of an annual dose of 20 mSv in 2000 hours of exposure and therefore the related dose rate is 10  Sv/h. Not straightforward is the evaluation of the dust contribution to the internal dose because it depends from the material, the activation and the size of the grain powder. 13/34 [*] ICRP Publication n. 103, 2007

14. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Maintenance procedures and frequencies The maintenance procedures in the plant can be planned and unplanned. For the planned maintenance the frequency of the human intervention is established on the basis of the failure rate typical of the systems/components. The unplanned maintenance is not predictable. As a rule of thumb it contribute for about 10% to the yearly collective dose. This assumption is based on the unplanned maintenance data base of the existing nuclear power/experimental plants 14/34

15. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Work effort The number of people requested for each operation (ex: valve replacement, pump maintenance…) and the duration of the operation are the two factors needed to evaluate the work effort to perform a given maintenance. The data for number of people and duration of the action are based on the past experience for similar procedures, collected in the nuclear plant. To make easier the assessment of the work effort each complex procedure is divided in elementary activities. A living data base has been built for the ITER ORE studies, in which the work effort data are collected and organized 15/34

16. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Tools: Excel workbooks “ORE” (1) Dedicated Excel workbooks, named “ORE” have been formatted to record data for maintenance procedures and, dedicated Visual Basic routines have been developed to easily manage the data necessary for the worker assessment. The rationale of the “type of activity” classification is the following: - a Major Activity is an action on the main system (TCWS maintenance, for example) - a Minor Activity is an action on a subsystem (heat exchanger maintenance, for example) - a Specific Activity is the type of maintenance operation (bolting, welding, cutting, etc.) - a Standard Activity is a classified activity on basic components (pipe, valve, cable, etc.) with fixed related work effort on standard maintenance operations. It is a sort of data base where the work efforts have been set on the base of the experience coming form conventional and nuclear facilities. 16/34

17. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Tools: Excel workbooks “ORE” (2) 17/34

18. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Tools: Visiplan (1) VISIPLAN is a dose assessment program developed to assist the ALARA analyst in pre-job studies. The VISIPLAN tools assist both in the calculation and the communication in ALARA evaluations. > The code is based on a 3D model including material, geometry and sources. > The Point-kernel dose calculation method, with build-up correction is used. > The code allows to perform dose assessment for tasks, trajectories and scenarios. It estimates individual and collective dose. > Special tools are available for source sensitivity analysis and source strength determination from measured dose rate sets. 18/34

19. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Tools: Visiplan (2) This PC-based tool calculates a detailed dose account for different work scenarii defined by the ALARA analyst, taking into account worker position, work duration and subsequent geometry and source distribution changes.. The VISIPLAN methodology consists of four steps: - Model Building - General analysis - Detailed planning - Follow up 19/34

20. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Tools: Simplified vs sofisticated tools The choice of the tools to assess the ORE depends form the design phase. At the early stage simplified tools are preferred, due to the complexity of the fusion plant geometry and the frequent change of the design philosophy in relation to structural materials, PFC materials, fluids, etc. When the design is near to the finalization the sofisticated 3D tools can be adopted. Cryostat maintenance example 20/34

21. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 What is ALARA ALARA is an acronym for "as low as (is) reasonably achievable," which means making every reasonable effort to maintain exposures to ionizing radiation as far below the dose limits as practical, consistent with the purpose for which the licensed activity is undertaken, taking into account - the state of technology, - the economics of improvements in relation to state of technology, - the economics of improvements in relation to benefits to the public health and safety, and - other societal and socioeconomic considerations, and in relation to utilization of nuclear energy and licensed materials in the public interest (US NRC). 21/34

22. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ALARA: process for ORE minimization DetrimentProtections TOTAL Optimum COST Collective Dose 22/34

23. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ALARA analysis For a quantitative ALARA analysis a checklist of the following specific factors has to be verified: Maximum dose to members of the public Collective dose to the population Doses to workers Applicable alternative processes (treatments, operating methods, or controls) Doses for each alternative evaluated Costs for each alternative evaluated Changes in costs among alternatives Societal and environmental (positive and negative) impacts associated with alternatives. 23/34

24. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 How to reduce ORE for ALARA scopes The worker dose can be reduced applying different solutions: - Use of Remote Handling - Use of shieldings - Pressurized suits (for internal dose) - Atmosphere detritiation - Maintenance optimization - Design improvements Each of the previous actions has advantages and disadvantages 24/34

25. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 When ALARA ends It exists a monetary evaluation for the cost of the reduction of 1 p- mSv in the plant, Alpha (α) Value used as the Base value in the model normally called as the ALARA model. Different are the methods to estimate the  Value. Regulators and corporate in the different countries use different  Values. In addition  Value can be different depending on the plant. The ALARA process stops when the cost of the reduction of 1 p- mSv exceeds  Value established for the plant. 25/34

26. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Monetary value of p-mSv (corporate or plant) CountryCorporate or NPPMonetary Value of p-mSv ($)Adoption year BelgiumCEN SCK Mol 0-1 mSv : 23 1-2 mSv : 58 2-5 mSv : 232 5-10 mSv : 620 10-20 mSv : 1,158 20-50 mSv : 4,635 1995 FranceEDF 0-1 mSv : 14 1-5 mSv : 57 5-15 mSv : 328 15-30 mSv : 955 30-50 mSv : 2,138 1993 GermanyVGB proposal agreed on by all utilities for testing 0-1 mSv : no value 1-10 mSv : 143 10-20 mSv : ~1,434 1997 NetherlandsBorssele NPP 0-10 mSv : 467 10< mSv : 935 2002 Corporate or plant alpha values for Occupational Exposure (*) (*) Reference year 2007 26/34

27. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Monetary value of p-mSv (Regulatory bodies) Country $ of p-mSv Adopt ed year Korea12 ~ 1,880 (PPP adjusted)2007 Canada70.31997 Czech Republic 16.8~84.12002 Finland100 1991 Netherlands4861995 Romania220~2002 Sweden13.5~277.8~2002 UK15.7~157.21998 USA2001995 Alpha values of Regulatory bodies (*) (*) Reference year 2007 27/34

28. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ITER lay out 28/34

29. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 – Replacement of plasma facing components – Maintenance of vacuum pumping systems, heating systems, fuelling, diagnostics equipments – Cooling loops, TCWS vault – Hot Cells – Waste treatment and storage facilities – Tritium plant Locations/activities vs radiological hazards 29/34

30. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Activation risk & plant operational states After completion of construction – Hydrogen phase ; not active – Deuterium – Deuterium phase ; low activitity – Tritium – Deuterium phase ; increasing activity (all schemes refer to last day) Two main different states – During operation (plasma, standby…) – Maintenance 30/34

31. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Plant operational states (1) Plasma operation 31/34

32. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Plant operational states (2) Maintenance 12 days after shutdown may change in actual operation 32/34

33. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ITER ORE status of art at early 2008 The analyses performed until the beginning of 2008 were at different level of detail for the various systems, but for each one, at a degree sufficient to draw the picture on collective doses expectations. The ITER design target fixed, for the plant collective dose, at 500 p-mSv/a is respected. Assessed Systems collective dose (p-mSv/a) Diagnostics84.5 Cooling Water System54.9 Remote Handling (Rh) Equipment40 Hot Cell Processing And Waste Treatment40 Electron Cyclotron Heating and Current Drive (ECH&CD) System 38.7 Test Blankets22.4 Blanket System18.9 NBI26.2 Vacuum Pumping & Leak Detection Systems11.5 Ion Cyclotron Heating and Current Drive (ICH&CD) System10 LH&CD6.3 Divertor6.1 Operational waste treatment4.9 Tritium Plant2.1 Machine Inspection and leak chasetbd Fuelling and Wall conditioningtbd Cryostattbd Cryoplanttbd Coil power supply & distributiontbd Facilities maintenance (liquid, gas, sampling, … ) tbd Total collective dose366.5 Plant collective dose guideline500 Margin to the objective of 500 mSv133.5 33/34

34. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Systems’ contribution to ITER worker dose The most demanding worker dose is relating to the diagnostic systems because they are numerous, distributed in many vacuum vessel (VV) ports and need frequent maintenance/calibration activities. The diagnostic system contribution comes from an extrapolation of the estimate of maintenance work effort and occupational exposure made for the diagnostics of port #01. It was adapted to all the 105 diagnostic systems (excluded the NBI diagnostics). 34/34