Design Safety Considerations for Water-cooled Small Modular Reactors As reported in IAEA-TECDOC-1785, published in March 2016

Transcription

1 International Conference on Topical Issues in Nuclear Installation Safety, Safety Demonstration of Advanced Water Cooled Nuclear Power Plants 6 9 June 2017 Design Safety Considerations for Water-cooled Small Modular Reactors As reported in -TECDOC-1785, published in March 2016 Hadid Subki (/NENP/NPTDS), Manwoong Kim (/NSNI/SAS), K.B. Park (KAERI, Republic of Korea), Susyadi (BATAN, Indonesia), M.E. Ricotti (Politecnico di Milano, Italy) and C. Zeliang (UOIT, Canada) International Atomic Energy Agency

2 SMR: definition & development objectives Advanced Reactors to produce up to 300 MW(e), built in factories and transported as modules to sites for installation as demand arises 2

3 SMRs for immediate & near term deployment Samples for land-based SMRs Water cooled SMRs Gas cooled SMRs Liquid metal cooled SMRs 3

4 Water cooled SMRs (Only Examples) 4

5 Marine-based SMRs (Examples) KLT-40S ACPR50S FLEXBLUE SHELF Floating Power Units (FPU) Compact-loop PWR 35 MW(e) / 150 MW(th) Core Outlet Temp.: 316 o C Fuel Enrichment: 18.6% FPU for cogeneration Without Onsite Refuelling Fuel cycle: 36 months Spent fuel take back Advanced stage of construction, planned commercial start: FPU and Fixed Platform Compact-loop PWR 60 MW(e) / 200 MW(th) Core Outlet Temp.: 322 o C Fuel Enrichment: < 5% FPU for cogeneration Once through SG, passive safety features Fuel cycle: 30 months To be moored to coastal or offshore facilities Completion of conceptual design programme Transportable, immersed nuclear power plant PWR for Naval application 160 MW(e) / 530 MW(th) Core Outlet Temp.: 318 o C Fuel Enrichment 4.95% Fuel Cycle: 38 months passive safety features Transportable NPP, submerged operation Up to 6 module per on shore main control room Transportable, immersed NPP Integral-PWR 6.4 MW(e) / 28 MW(th) 40,000 hours continuous operation period Fuel Enrichment: < 30% Combined active and passive safety features Power source for users in remote and hard-to-reach locations; Can be used for both floating and submerged NPPs Images reproduced courtesy of OKBM Afrikantov, CGNPC, DCNS, and NIKIET 5

6 Power Range of SMRs 6

7 Adopted Safety Features of Advanced Passive Water-Cooled Reactors 1 Independent of AC Power 2 Less reliance on operator action Require no AC power to actuate /operate Engineered Safety Features; Only gravity flow, condensation natural circulation forces needed to safely cool the reactor core Passively safe shutdown the reactor, cools the core, and removes decay heat out of containment 3 Design simplification Fewer number of plant systems and components Reducing plant construction and O&M costs Provides 3 to more than 7 days of reactor cooling without AC power or operator action 4 Incorporating lessons-learned from the Fukushima Dai-ichi nuclear accident Enhanced robustness to extreme external events by addressing potential vulnerabilities Alternate AC independent water additions in Accident Management SBO mitigation Ambient air as alternate Ultimate Heat Sink Filtered containment venting Diversity in Emergency Core Cooling System Images Courtesy of Westinghouse and GE Nuclear Energy 7

8 Incorporating Lessons Learned from Major Accidents to Advanced Reactor Developments Resilience towards Extreme external events (regions and sites specific) Hydrogen control for DBA & severe accidents Filtered venting system Enhanced instrumentation and monitoring system for DBA & severe accidents Diversity in spent fuel cooling (reliability) Effective use of PSA Emergency preparedness and response Assure safety on multiple reactors or modules plant Diversity in emergency core cooling systems following loss of all AC power onsite Ensure diversity in depressurization means for high pressure transient Confirm independence in reactor trip and ECCS for sensors, power supplies and actuation systems. 8

9 SMR ipwr type: integration of NSSS 9

10 Integral Primary System Configuration Courtesy: Westinghouse Electric Company LLC, All Rights Reserved X X X X X X XX X Benefits of integral vessel configuration: eliminates loop piping and external components, thus enabling compact containment and plant size reduced cost Eliminates large break loss of coolant accident (improved safety) 10

11 Design Features Low Core Power RCS integrated to the RPV Integrated steam generator (Oncethrough helical coil) Safety Expectations from ipwr SMR Design Features (1) Functional Details Reduces fission product source term Low level of decay heat and, therefore, would require less cooling after reactor trip No large external primary coolant piping Longer RPV lifetime due to reduced fast neutron fluence Increased coolant inventory/increased thermal inertia results in fewer severe transients and reduced necessity for operator intervention Steam generator is designed to withstand the primary pressure without pressure in the secondary side Steam system is designed to withstand primary pressure up to isolation valves. Steam generator tubes are in compression. Reduced tube-side water inventory Safety Benefits Enhances in-vessel corium retention Reduces accident consequences Simplifies emergency planning Eliminate or reduce susceptibility to events, such as LBLOCA Long response time in the case of transient or accident Improved steam generator tube integrity. Frequency for steam generator tube rupture reduced The addition of reactivity would be limited and the reactor power increase may not exceed critical safety limits from steam line break due to smaller quantity of heat removal (larger number of SGs) 11

12 Safety Expectations from ipwr SMR Design Features (2) Design Features Natural circulation Passive safety systems (No active High/ Low pressure safety injection system) Internal CRDMs Functional Details Simplified design and reduced maintenance costs, due to the absence of main coolant pumps The passive safety systems reduce or eliminate the need for external power under accident conditions Auxiliary feed-water system may not be required Spray systems are not required to reduce steam pressure or to remove radioiodine from containment. Elimination of rod ejection Elimination/reduction of vessel head penetrations Safety Benefits Eliminate loss of flow accident (LOFA) Eliminates accidents from reactor coolant pumps (shaft breaks, seal leakage, pump seizure and pump leaks) Simpler Solutions to SBO Active safety systems are not required (low core damage frequency). Removal of core heat without an auxiliary feed-water. No safety-related pumps for accident mitigation. The Reactivity Initiated Accident (RIA) due to rod ejection is eliminated 12

13 Design Features Functional Details Safety Benefit High design pressure, temperature and vacuum metallic containments Soluble boron free core Safety Expectations from ipwr SMR Design Features (3) Containment pressure and temperature for worst-case design basis accident remains below design All water lost from RPV stays within containment and is returned to reactor vessel by passive means More Sub atmospheric pressure during normal operation The engineered safety systems are simplified Improved seismic capability No Boron dilution Less corrosion Reduces volume of liquid radwaste Strong negative moderator temperature coefficient Boron monitor and adjustment systems eliminated No postulated small-break LOCA (SBLOCA) to uncover nuclear fuel Containment integrity assured (metallic containment, no molten core concrete interaction) The deep vacuum enhance steam condensation rates for containment heat removal during a postulated SBLOCA Prevent Hydrogen explosion during a severe accidents as limited Oxygen will be present. Reactivity initiated event is precluded Reduced occupational radiation dose Improved reactor transient performance as well as operational safety 13

14 INSAG-10: DiD Levels in Nuclear Safety LEVEL 5 LEVEL 4 LEVEL 3 LEVEL 2 LEVEL 1 Mitigation of radiological consequences to protect people & environment against significant releases of radioactive mats. Control of severe plant conditions incl. prevention & mitigation of severe accidents progression Control of accident within the design basis Control of abnormal operation and detection of failures Prevention of abnormal operation and system failures 14

15 Key Design Features of Watercooled SMR Contributing to Level 1 of Defense-in-Depth 15

16 1 LEVEL 1 of Defense-in-Depth Design features Design objectives SMR designs Relevant safety Requirements Elimination of liquid boron reactivity control system 2 Integral design of primary circuit with in-vessel location of steam generators Exclusion of inadvertent reactivity insertion as a result of boron dilution Exclusion of largebreak, loss of coolant accidents (LOCA) KLT-40S, IRIS CAREM25,IMR, ABV-6M, mpower RITM-200, SMR- 160, Flexblue CAREM25, IRIS, ACP100, DMS, IMR, SMART, ABV-6M, NuScale, mpower Safety Standards Series Specific Safety Requirements No. SSR 2/1 (Rev. 1), Safety of Nuclear Power Plants: Design Requirement 20, Paragraph 4.11 [(a) and (b)] and relevant Paragraphs 16

17 3 Primary pressure boundary enclosed in a pressurized, low enthalpy containment 4 Natural circulation in normal operation 5 LEVEL 1 of Defense-in-Depth Design features Design objectives SMR designs Relevant safety Requirements CRDM in side Reactor pressure vessel Elimination of LOCA resulting from failure of the primary coolant pressure boundary Elimination of loss of flow accidents Eliminate control rod ejection accidents NuScale CAREM25, DMS, IMR, ABV-6M, NuScale, AHWR SMR-160 CAREM25, IRIS Safety Standards Series Specific Safety Requirements No. SSR 2/1 (Rev. 1), Safety of Nuclear Power Plants: Design Requirement 20, Paragraph 4.11 [(a) and (b)] and relevant Paragraphs 17

18 Key Design Features of Watercooled SMR Contributing to Level 2 of Defense-in-Depth 18

19 SI. No. 3. Redundant and diverse passive or active shutdown systems LEVEL 2 of Defense-in-Depth Design features Design objectives SMR designs Relevant safety requirements 1. A relatively large coolant inventory in the primary circuit, resulting in large thermal inertia 2. Implementation of the leak before break concept Slow progression of transients due to abnormal operation and failures Facilitate implementation of leak before break concept Reactor shutdown CAREM25, IRIS KLT-40S All designs Requirement 20, Paragraph 4.11 [(a) and (c)] and relevant Paragraphs 19

20 SI. No. LEVEL 2 of Defense-in-Depth Design features Design objectives SMR designs Relevant safety requirements 4. Use of digital technology 5. Improved humanmachine interface Proven reliability of I&C system Most designs Most designs Requirement 20, Paragraph 4.11 [(a) and (c)] and relevant Paragraphs 20

21 Key Design Features of Watercooled SMR Contributing to Level 3 of Defense-in-Depth 21

22 SI. No. LEVEL 3 of Defense-in-Depth Design features Design objectives SMR designs Relevant safety requirements 1. Use of once-through steam generators 2. Self-pressurization, large pressurizer volume, elimination of sprinklers, etc. 3. Gravity driven high pressure borated water injection device (as a second shutdown system) Limitation of heat rate removal in a steam line break accident Damping pressure perturbations in design basis accidents Reactor shutdown KLT-40S CAREM25, DMS, mpower, NuScale, SMR-160 CAREM25 and AHWR300 Requirement 20, Paragraph 4.11 [(a) and (d)] and relevant Paragraphs 22

23 SI. No. LEVEL 3 of Defense-in-Depth Design features Design objectives SMR designs Relevant safety requirements 4. Natural convection core cooling in all modes Passive heat removal 5. Safety (relief) valves Protection of reactor vessel from over pressurization CAREM25, AHWR-300, DMS, IMR, ABV-6M, NuScale, SMR- 160 IRIS, CAREM25, it should be available in all designs Requirement 20, Paragraph 4.11 [(a) and (d)] and relevant Paragraphs 23

24 Key Design Features of Watercooled SMR Contributing to Level 4 of Defense-in-Depth 24

25 LEVEL 4 of Defense-in-Depth SI. No. Design features Design objectives SMR designs Relevant safety requirements 1. Relatively low core power density 2. Passive system of reactor vessel bottom cooling 3. Passive flooding of the reactor cavity following a small LOCA Limitation or postponement of core melting In-vessel retention of core melt Prevention of core melting due to core uncovery; in-vessel retention IRIS, CAREM25, NuScale and mpower KLT-40S, CAREM25 and Flexblue IRIS, VBER- 300, mpower Requirement 20, Paragraph 4.11 [(a) and (e)] and relevant Paragraphs 25

26 LEVEL 4 of Defense-in-Depth SI. No. Design features Design objectives SMR designs Relevant safety requirements 4. Containment and protective enclosure or Double containment Protection against radioactive release in severe accidents and external event (like aircraft crash, missiles) CAREM25, KLT- 40S, IRIS, mpower, NuScale, W- SMR and SMR- 160 Requirement 20, Paragraph 4.11 [(a) and (e)] and relevant Paragraphs 5. Reduction of hydrogen concentration in the containment by catalytic recombiners Prevention of hydrogen combustion CAREM25, AHWR300, SMR

27 Key Design Features of Watercooled SMR Contributing to Level 5 of Defense-in-Depth 27

28 SI. No. LEVEL 5 of Defense-in-Depth Design features Design objectives SMR designs Relevant safety requirements 1. Mainly administrative measures 2. Relatively small fuel inventory, less non-nuclear energy stored in the reactor, and lower decay heat rate Mitigation of radiological consequences resulting in significant release of radioactive materials Smaller source term, smaller emergency planning zone (EPZ) KLT-40S All design SSR 2/1 (Rev. 1) Requirement 20, Paragraph 4.11 [(a) and (f)] and relevant Paragraphs 28

29 Lessons learned from the Fukushima Daiichi accident As many as 94 individual lessons and recommendations on Fukushima Daiichi Accident These are categorized into four (4) main areas: 1. Design and Siting 2. Accident Management and on-site emergency preparedness and response 3. Off-site emergency preparedness and response 4. Nuclear safety infrastructures 29

30 Key features in Design and Siting Strengthen measures against extreme natural hazards and consequential effects Consider issues concerning multiple reactor sites and multiple sites Ensure measures for prevention and mitigation of hydrogen explosions Enhance containment venting and filtering system Enhance robustness of spent fuel cooling Use PSA effectively for risk assessment and management 30

31 Accident Management and on-site emergency preparedness and response Ensure on-site emergency response facilities, equipment and procedures Enhance human resource, skill and capabilities 31

32 Off-site emergency preparedness and response Strengthen off-site infrastructure and capability Strengthen national arrangements for emergency preparedness and response Enhance interaction and communication with the international communities 32

33 CRPs to start in 2017 and 2018 Launch a new CRP in 2017 Launch a new CRP in 2018 CRP I on Design and Performance Assessment of Passive Engineered Safety Features in Small Modular Reactors with 1 st RCM in October 2017 Objectives: 1. Propose a common novel approach for designing passive safety features for SMRs and provide methods for assessing their performance and reliability 2. Report validation of methodologies for SMR s engineered safety features performance assessment using experimental test facilities CAORSO site IRIS: 1 km France Evacuation Zone: 5 km US Emergency Planning Zone: 10 miles CRP I on Development of Approaches and Criteria for Determining Technical Basis for Emergency Planning Zone for SMR Deployment with 1 st RCM in March 2018 Background: SMRs may be deployed for sites located nearer to the intended users SMRs characteristics: small power/source term, enhanced safety Emergency Plan required to assure that onsite & off-site emergency preparedness provides assurance of adequate measures be exercised in the event of a nuclear incident/accident Objectives: 1. Review implementation of DiD in SMRs 2. Develop approach and formulate technical basis for guidance on emergency preparedness & response focusing on EPZ size 33

34 Technical Summary (1) The Fukushima daiichi accident has unveiled many issues regarding the weakness of the existing plant design especially regading the design of engineered safety features in order to withstand extreem natural hazards and cope with the emergency situation of extended station blackout Various extreme natural hazards (specific to the site) occurring simultaneously have to be considered in the design At least one success path to cope with accident to cool down the reactor core by active, passive, manually aligned systems or suitable combination. For multiple unit plant, ensure unprecedented accident scenario and common cause failures are considered, and counter measures can be carried out on the site if meltdown occurs. Consider electrical power unavailability and ensure core cooling and decay heat removal. 34

35 Technical Summary (2) Designs should prevent failure of safety related SSC and accommodate failure with compensatory measure Provide diverse cooling system for containment and provision for connecting portable equipment. Assure containment vessel integrity, diverse shutdown, core cooling and decay heat removal. Hydrogen concentration must be controlled by adopting appropriate technology. Ensure DC power availability for post accident monitoring system. Survivability of emergency power supply system should be assured to cope with extreem natural hazards The vent system should be able to prevent catastrophic failure of containment and reduce pressure with filtering capabilities. 35

36 THANK YOU VERY MUCH Questions & Comments? For inquiries on SMR, contact: Dr. M. Hadid Subki 36