Safety and Environment Studies for a European DEMO Power Plant. Neill Taylor, SAE Project Leader

Transcription

1 Safety and Environment Studies for a European DEMO Power Plant Neill Taylor, SAE Project Leader

2 Outline Background Safety and environmental potential of fusion Aims and objectives of Safety and Environment project for EU DEMO Earlier studies Design and licensing requirements Safety approach and safety functions; minimizing inventories; confinement Licensing what do we know? Integrated Safety Analyses / Source Terms / Models & Codes Experiments for code and model validation; neutronics; accident analysis Radioactive Waste Management Detritiation of solid waste Interaction with other Work Packages in the EU DEMO project Research Units participating in the Safety and Environment project: Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 2

3 Potential for excellent safety performance of fusion No climate-changing emissions Power excursions self-limited by inherent processes Products of fusion reaction are not radioactive Structures are activated by neutrons but: Low power density ( decay heat ) after termination of burn rapid decay of radiotoxicity No fissile or fertile material, no actinides or fission-products A Demonstration Power Plant should demonstrate that these characteristics lead to excellent Safety and Environmental performance. However Radioactive inventory Tritium Will require licensing like any other nuclear facility Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 3

4 EUROfusion Safety and Environment (SAE) project: The aims To ensure that design choices take into account safety considerations from the beginning elaborate safety requirements optimize safety provisions iterative process with designers define safety classification of systems, structures and components To ensure that DEMO will be licensable understand the likely regulatory regime To resolve outstanding issues in safety and environment perform R&D to resolve issues develop and validate safety models and codes for DEMO preliminary safety analyses, including accident consequences To minimize environmental impact of fusion develop radioactive waste management techniques identify and minimize contributions to routine releases Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 4

5 Eurofusion SAE Project Objectives (1) 1. To ensure that the safety approach for DEMO is well-founded and takes maximum benefit from earlier work; 2. To ensure that the safety requirements for DEMO are soundly specified and well understood, and that the design properly takes into account these requirements and includes all necessary safety provisions; 3. To ensure that design choices are made with due regard to safety and environmental factors, so as to optimize safety performance and to minimize the environmental impact; 4. To facilitate the eventual licensing of DEMO by understanding the likely regulatory regime and discerning any requirements that arise; Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 5

6 Eurofusion SAE Project Objectives (2) 5. To identify outstanding issues in safety and environment areas, and to plan and perform R&D to resolve these issues; 6. To develop and validate safety models and codes needed for safety analyses of DEMO, and to perform preliminary safety analyses, including the evaluation of the consequences of a set of representative accident scenarios; 7. To develop techniques to reduce the impact of radioactive waste from fusion plant, in particular through the development of methods for the detritiation of tritium-contaminated components and by establishing the practical feasibility of methods for the recycling of activated materials; 8. To minimize the environmental impact of the operation of DEMO by identifying contributions to radioactive gaseous and liquid effluent and proposing strategies to limit these releases. Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 6

7 Background Previous studies Earlier work that helps to support EU DEMO safety studies: Safety and Environmental Assessment of Fusion Power (SEAFP) SEAFP SEAFP SEAFP SEAL 2000 All summarised in SEIF report (2001) Power Plant Conceptual Study (PPCS), ITER Safety and Licensing NSSR, 1996; NSSR2, 1998 GSSR, 2001, 2004 DOS, 2002 RPrS, 2008, 2010, 2011 PPCS bounding accident analysis Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 7

8 Three areas of work in SAE project 1. Design and Licensing Requirements 2. Integrated Safety Analyses / Source Terms / Models & Codes 3. Radioactive Waste Management Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 8

9 SAE Main Activities (1) Design and Licensing Requirements Establish the safety approach and fundamental safety strategies (such as the confinement strategy) General Safety Principles Safety requirements are drafted and elaborated as the design concepts are developed Plant Safety Requirements Document Safety criteria are to be set and the safety impact of fundamental design choices (materials, coolant, etc.) are to be assessed. A review of the possible licensing regimes for DEMO is to be carried out, and implications for safety requirements determined. Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 9

10 Safety Approach for DEMO Top-level safety objectives To protect workers, the public and the environment from harm; To ensure in normal operation that exposure to hazards within the facility and due to release of hazardous material from the facility is controlled, kept below prescribed limits and minimized to be as low as reasonably achievable; To ensure that the likelihood of accidents is minimized and that their consequences are bounded; To ensure that the consequences of more frequent incidents, if any, are minor; To apply a safety approach that limits the hazards from accidents such that in any event there is is no no need for for public public evacuation technical on grounds; technical grounds; To minimize radioactive waste hazards and volumes and ensure that they are as low as reasonably achievable. Employ established safety principles Defence in depth ALARA Passive safety Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 10

11 Defence in Depth approach to safety Main safety function is confinement of radioactivity, achieved by multiple layers of protection: Prevention of abnormal operation and failures Control of abnormal operation and detection of failures Control of accidents within design basis Natural Safety Multiple systems shutdown barriers (inherent in design) Small Use Filtering of inventories passive and Extensive means detritiation wherever monitoring systems Conservative design possible Redundant and High quality diverse safety construction systems Prevention of accident progression, mitigation of consequences Fifth level: Mitigation of consequences of significant releases of radioactive material Off-site emergency response (e.g. evacuation) should not be necessary for fusion Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 11

12 Adopted accident dose limits for DEMO Accident Frequency /year Anticipated events / Incidents Unlikely events Extremely unlikely events Hypothetical events f > > f > > f > 10-6 f < 10-6 On-site Dose 5mSv/year 20mSv/event Off-site Early Dose Off-site Chronic Dose 10mSv/event 1mSv/year 5mSv/event 50mSv/event 50mSv/event No cliff-edge effects. Countermeasures limited in time and space. Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 12

13 Adopted normal operation dose limits DEMO Dose Design Target DEMO Dose Limit Normal Operations Off-Site Dose (msv/year) Normal Operations On-Site Dose (msv/year) On-Site Dose (msv/5 years) Limits are based on international guidelines, may be revised (downwards) later. Meeting limits is not sufficient: all doses must be As Low As Reasonably Achievable Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 13

14 Safety Functions defined for European DEMO Fundamental safety functions Supporting functions Confinement of radioactive and hazardous materials Limitation of exposure to ionizing and electromagnetic radiation Limitation of the non-radiological consequences of conventional hazards Limitation of environmental legacy Functions in support of confinement: Control of plasma energy Control of thermal energy Control of confinement pressure Control of chemical energy Control of magnetic energy Control of coolant energy Functions to support personnel and the environmental protection: Limitation of radioactive and toxic material exposure to workers Limitation of airborne and liquid operating releases to the environment Limitation of electromagnetic field exposure to workers Limitation of other industrial hazards Supporting functions to limit environmental legacy: Limitation of waste volume and hazard level Facilitation of clean-up and the removal of components Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 14

15 Location of radioactive material inventories tritium in fuel cycle equipment (fuelling, pumping, processing) in breeder blankets and T extraction system retained in the vacuum vessel adsorbed on surfaces permeated into the structure of in-vessel components (IVCs) absorbed in dust in RM equipment used to remove and transport IVCs in storage of IVCs awaiting maintenance or disposal in the Active Maintenance Facility in coolants, due to permeation in atmospheres of rooms containing contamination products of neutron activation structure of plasma-facing components in-vessel dust from plasma-facing surface erosion activated corrosion products (ACP) in water or lead-lithium coolant vessel and ex-vessel components (at lower level) Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 15

16 Minimizing inventories In-vessel inventory limits for ITER Tritium: 1 kg Dust: 1000 kg Can we reduce these for DEMO? Tritium Higher throughput but: No cryopumps (accounts for 180g of inventory in ITER) No plasma-facing Be, no Be dust. W may have lower T retention. Higher operating temperature (>500 C compared with 140 C) Reduced uncertainties? Dust Higher fusion power, higher duty cycle but: W instead of Be as plasma-facing surface Lower erosion rate? Different plasma edge conditions? Reduced uncertainties? Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 16

17 Confinement: in-vessel inventory Tritium (on plasma-facing surfaces, permeated into components, and in dust) Active dust (tungsten eroded from plasma-facing surfaces) Activated corrosion products (in accidents with in-vessel loss of water coolant) Confinement strategy: Two confinement systems each with one or more static barriers and/or dynamic systems First confinement system Vacuum vessel and its extensions Second confinement system Building walls and slabs surrounding tokamak, rooms served by ventilation with filtering and detritiation systems. Other boundaries (e.g. cryostat) Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 17

18 ITER experience: vacuum vessel and extensions as first confinement ITER Vacuum Vessel: Robust, double-walled. Design loads include electromagnetic loads in plasma events such as Vertical Displacement Events had to show that these loads are enveloping Design pressure limit must be observed pressure limited by relief system with rupture discs Subject to nuclear pressure equipment regulation (ESPN) Penetrations neutral beams cooling pipes RF heating systems waveguides diagnostics systems vacuum pumping lines fuelling systems feeders for in-vessel coils Confinement barrier includes seals bellows windows (including non-metallic) isolation valves pipes, ducts, waveguides All must remain leak-tight in all normal and accident situations, and all are Safety Importance Class Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 18

19 Proposed EU-DEMO confinement concept (HCPB) Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 19

20 In-vessel components of future Fusion Power Plant High availability will be essential interruptions to electricity generation unacceptable High reliability required of all components In-vessel components must not fail May be possible to give them full safety credit for the confinement function This would simplify part of the confinement strategy Can t do this for DEMO. But how far can we go? Assessments and discussions are ongoing. Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 20

21 Licensing of a future nuclear fusion facility ITER is licensed in France as a basic nuclear installation (Installation Nucléaire de Base, INB) under same law as all other nuclear facilities In other countries, and for a plant on the scale of DEMO, new legislation may have to be created An important regulatory principle: Regulations should be targeted proportionate Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 21

22 Future trends in nuclear regulation Regulators are reluctant to voice opinions until they have a firm proposal in front of them How will nuclear regulation develop? In Europe, efforts towards harmonization of regulatory approaches in different countries, through the Western European Nuclear Regulators Association (WENRA). Although focussed on fission plant, adaptation of approach to fusion is possible WENRA emphasizes Defence in Depth and independence of levels Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 22

23 Future trends in nuclear regulation Changes may occur in reaction to unforeseen events WENRA specified stress tests applied to all European nuclear plant after Fukushima accident In reaction to Fukushima, more emphasis on protection against combinations of external aggressions Additional safety analysis of design extension conditions featuring multiple independent failures focussed on conditions that could cause core melt in a fission reactor, but still could apply to fusion facilities pay attention to common cause and common mode failures Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 23

24 Nuclear regulation what will not change Need to provide and defend a safety case that demonstrates acceptable safety objectives have been set and are achieved impact on public safety is minimized impact on personnel safety is minimized environmental impact is minimize Demonstration must be fully justified fully comprehensive (all conceivable accident scenario are covered) where based on computer models, that these are fully verified and validated Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 24

25 SAE Main Activities (2) Integrated Safety Analyses / Source Terms / Models & Codes Determine accident scenarios to be taken into account in the safety analyses, using Functional Failure Modes and Effects Analysis (FFMEA) Determine needs for code development for safety analyses and the validation experiments that are required for these Develop safety analysis tools, codes and models Perform tests as needed to validate the codes and models Perform full safety analyses including transient and accident analyses for Design Basis, Design Extension and selected Beyond Design Basis Events Assess the needs for source term development, dependent on fundamental design choices Perform R&D needed to improve quantification of source terms, evaluate inventories (e.g. ACPs) Assess environmental releases (liquid and gaseous) in normal operation, develop strategies for minimizing these Identify major contributions to Occupational Radiation Exposure, develop strategies for minimizing these, particularly in design choices Development of methods for computation of Shutdown Gamma Dose Rate, with the aim of establishing one common EU approach Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 25

26 Examples of experiments for code validation Simulations of LOFA and LOCA in blankets (KIT) Measurements of tritium permeation from beryllium pebbles and structural materials (KIT) Measurements of tritium transport in ceramic breeder blanket (KIT) Chemical reactivity of Be with steam and air (ENEA) Measurement of liquid lithium-lead/steam reaction rates (ENEA) Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 26

27 Release Rate (Bq/s/g) Temperature (K) T-release from pebbles after thermal loading Bochvar µm Time, s Bochvar µm K/min 7K/min 400 Bochvar > 100 µm >100 mkm mkm mkm IG NGK 1mm 2500 IG >100µm NGK 1mm Temperature (K) Time, s 27

28 Neutronics and activation analysis in support of accident modelling Example: decay heat for DEMO based on HCPB blanket HCPB Name of Zone Entire reactor length of zone material fraction (*) volume [cm 3 ] Nuclear heating Cooling Time 1 s 1 h 1 day 1 week 1 month 1 year 10 years 100 years Decay heat mm % MW/m 3 MW/m 3 First Wall (FW) W 100% 2.45E E E E E E E E E-10 Eurofer Breeder module (BM) BM caps and lateral walls BM material mxiture BM backwall BM back support /manifold 74.3% Eurofer + void 74.3% Eurofer + void 11.76% Eurofer % Be % Li4SiO4 + void 100%+ Eurofer 55.4% Eurofer + void 2.93E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-12 Sum [MW] E E E E E E E E-07 Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 28

29 Accident analyses Design information Failure rate data Safety design information Neutronics/activation data (source terms, decay heat etc.) More detailed design info Initiating events identification Accident scenarios Selection of representative events Modelling of accident sequences Must be comprehensive Use systematic techniques e.g. FMEA, HAZOP Postulate additional failures Event trees, fault trees Choose events with consequences that will envelope others Model all significant phenomena. e.g. thermal-hydraulic Site characteristics Weather conditions Predicted releases Dispersion and dose modelling Dose to Most Exposed Individual Consequences Calculate maximum environmental release in worst case Direct exposure plus ingestion and inhalation. All pathways considered. Dose uptake for conservative exposure scenario Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 29

30 SAE Main Activities (3) Radioactive Waste Management A review of clearance indices for radioactive material to set an approach to defining a fusion-specific set of limits, and to define these limits. A feasibility study of waste recycling to establish if viable and economic recycling processes are possible; criteria to be defined Development of technologies for large-scale recycling Techniques for detritiation of solid waste have been reviewed A programme of R&D to develop techniques for the detritiation of solid radioactive waste is starting Materials composition limits will be established to minimize the radiological impact of activation and strategies developed to minimize the quantity of waste. Simple recycle 36% Complex recycle 10% Hands-on 5% Permanent waste 0% PPCS results Cleared 49% Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 30

31 Extract from Detritiation techniques review Disposal ( 1 possibly suitable, 2 strong suitability): Method In vessel IVC transfer area Storage facility IVC process cells Waste and recycling RH equipment maintenance Other waste treatment Melting (3) H plant clean-up Thermal treatment (7) Cold crucible 1 1 Molten salt oxidation Interim storage Surface abrasion Evaporating and solidification line 1 1 Incineration 2 H2020 Progress meeting 18 June

32 Safety Requirements Document Safety Guidelines Safety Importance Classification Radioactive Waste Management Materials composition limits Work Packages concerned with design and materials Safety analyses Accident analyses Occupational Radiation Exposure studies Study of effluents in normal operation safety functions and required safety provisions design optimisations Interactions with other DEMO Work Packages every WP has a Safety Liaison Officer Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 32

33 Summary The Safety and Environment project for EU DEMO is focussed on Setting a safety approach and developing requirements in cooperation with the design teams Developing and validating safety models and codes, and applying these to preliminary safety analyses Finding solutions to some key radwaste management issues Licensing requirements of the future are uncertain but Harmonisation of European regulatory approach is useful Defence in Depth is key Safety functions for DEMO have been defined Confinement of radioactive inventories is the most important Every opportunity must be taken to minimize inventories Safety considerations must be central to design activities from the beginning Dialogue is maintained between safety specialists and design teams Neill Taylor EU DEMO safety 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants 3-5 May 2016 Page 33