Are Enhanced CANDU 6 Reactors the Best Fit for the First NPP in Poland?

Transcription

1 Are Enhanced CANDU 6 Reactors the Best Fit for the First NPP in Poland? The VI International School on Nuclear Power Warsaw, November 5-8, 2013 Dr Stefan S. Doerffer, P.Eng. KSD Professionals Inc. on behalf of Candu Energy Inc.

2 Table of Contents Introduction Gen. III/III+ Reactors & Fukushima Nuclear Accident CANDU Reactor Technology the Past and the Present Fundamental Features of Enhanced CANDU 6 (EC6) Reactor EC6 Design & Safety Enhancements to deal with Design Basis Accident (DBA), Beyond DBA and Severe Accidents (SA) Concluding Remarks 1

3 Enhanced CANDU 6 (EC6) Reactors Offered for Poland This presentation focuses on the EC6 reactor design offered by Candu Energy Inc. to Poland for its 1 st NPP that satisfies customer expectations and regulatory requirements of: the Polish investor, Polska Grupa Energetyczna - PGE EJ1: the reactor technology of the NPP must be of Gen. III or III+ the reactor technology must be of a proven design the Canadian Nuclear Safety Commission (CNSC) for new NPPs (RD-337/GD- 337) the IAEA Safety Standards for new NPPs (NS-R-1 and new SSR2/1) the Canadian and international reviews of lessons learned from the Fukushima Dai-Ichi nuclear event the WENRA Safety Objectives the EUR (or with the objectives/intents of these requirements) 2

4 Priorities for Generation III/III+ NPP Implemented in EC6 Safety enhancements Latest international requirements for new plants including passive safety; design margin; physical & sabotage protection Improved economics Simplification; standardization; constructability Operational enhancements and high performance Operator feedback and intelligent operational support Longer regular operating period and shorter outage time Human factors Maintainability High QA standards 3

5 Fukushima Nuclear Accident - Lessons Learned Fukushima Dai-Ichi nuclear accident on March 11, 2011 caused public concerns about nuclear safety worldwide Key Findings (IAEA, USNRC, CNSC, KHNP, Japan, UK, WENRA, INSAG, ENSREG, WANO and WNA) Insufficient defence-in-depth Lack of consideration for diversity Lack of reliable safety related parameters and communications Lack of guidance regarding multi-unit sites with respect to external hazards Lack of conservative decision making in hazard analysis 4

6 Fukushima Nuclear Accident - Lessons Learned Fukushima nuclear accident highlighted the importance of Defence-in-depth Protection of the plant against external hazards Robustness of the plant design for beyond design basis Plant capability to cope with extended station blackout (SBO) Provisions to prevent severe accidents and mitigate consequences Containment function to protect the people and the environment against radioactive releases Prevention of hydrogen build-up inside containment Maintenance of water inventory for spent fuel bay during severe accidents Emergency planning and response 5

7 Candu Energy Response to Fukushima Accident Candu Energy internal task team also as a member of Canadian Industry Integration Team (Canadian utilities, TQNPC, KHNP, NPCIL, COG and WANO) evaluated C6 design, identified potential issues and recommended CANDU reactor safety enhancements Candu Energy internal task team has considered the safety recommendations from the Canadian Industry Integration Team and have incorporated additional enhancements into the EC6 design 6

8 European Stress Test for CANDU in Romania After the Fukushima Accident, the European Union commissioned a Stress Test (WENRA) to be performed on all European Nuclear Power Plants, including the two CANDU 6 reactors at Cernavoda in Romania. The Stress Test at Cernavoda was performed by the Romanian Utility, reviewed by the Romanian Regulator who then prepared the Romanian National Final Report on stress tests for Cernavoda NPP. This Romanian National Final Report on stress tests for Cernavoda NPP was reviewed by a team of senior European Regulators under ENSREG. Candu Energy, as the original designer of the CANDU technology, actively supported the Romanian Utility in this review. The review has resulted in a positive report for the CANDU 6 reactors at Cernavoda, Romania, noting that No concerns have been raised from this regulatory review. 7

9 CANDU Reactors History Motto: One cannot understand the Present not knowing the Past Impressive Beginning & Evolution of CANDU 8

10 Origin of Canadian Nuclear Achievements 9 * 1994 Nobel Prize Dr. B. Brockhouse

11 CANDU: Built on a Strong History CANDU = CANadian Deuterium Uranium Darlington MW Class Reactors Bruce A Bruce B CANDU 9 ACR Advanced CANDU Reactors Power (MWe) MW Class Reactors Pt Lepreau Embalse CANDU 6 Gentilly 2 Wolsong 1 Pickering A Pickering B Cernavoda Wolsong 2,3,4 Qinshan 1&2 Large Indian National PHWR Program EC6 RAPP 1, NRU Douglas Point KANUPP Research & Prototype Reactors ZEEP NRX NPD Years

12 CANDU Global Success CANDU & CANDU-derived Reactors World Wide The global fleet of CANDU and CANDU-derived reactors currently includes 50 reactors. Of these, 42 are operational, 4 are being refurbished, 1 is under construction, and 3 have been laid up. ( The total capacity of all currently operational CANDU and CANDU-derived reactors is 21,424 MWe. 11

13 Enhanced CANDU 6 Reactor EC6 EC6 represents a proven (constructed and operated), low risk new-build option Reference C6 plant: Qinshan Phase III, China: built under budget built: 1 st unit in weeks & 2 nd unit in months ahead of schedule avg 90.8% CF acc. to 2012 COG report EC6 740 MWe class heavy water moderated & cooled pressure tube reactor using Natural Uranium fuel EC6 target design life up to 60 years EC6 annual lifetime CF > 92% (incl. retubing outage) EC6 year-to-year CF > 94% (based on 30- day outage every 3 years) EC6 forced loss rate < 1% 12

14 Enhanced CANDU 6 Reactor CNSC Pre-Licensing Review high confidence of licensability in Canada Phase 1 Review completed April 2010 Phase 2 Review completed April 2012 Phase 3 Review completed July 2013 With the generic pre-licensing completed in Canada, the Polish Regulator, Panstwowa Agencja Atomistyki (PAA), can utilize the Canadian evaluations for their construction & operating licenses review of EC6 without much difficulty 13

15 Compliance with new CNSC Requirements EC6 meets the Acceptance Criteria for Compliance with Technical Safety Objectives as stated in CNSC RD-337 Dose Acceptance Criteria: < 0.5 msv for AOOs; < 20 msv for DBAs (at the site boundary) Safety Goals: 1. core damage frequency: < 10-5 Yr -1 (PSA1 - measure of preventive capabilities) 2. small release frequency: release > Bq of I 131 < 10-5 Yr -1 (temporary evacuation of local population) (PSA2 - measure of mitigative capabilities) 3. large release frequency: release > Bq of Cs 137 < 10-6 Yr -1 (long-term relocation of the local population) (PSA2 - mitigative capabilities) Balanced approach to accident prevention and accident mitigation Removal of residual heat from reactor core: for all conditions of the Reactor Coolant System Severe Accidents robust containment design: leak-tight barrier Robustness against malevolent acts (e.g.,aircraft crash) 14

16 Two-unit EC6 Nuclear Power Plant 15

17 NPP with Enhanced CANDU 6 Reactor 16

18 Fundamental Design Features of EC6 EC6 Reactor 17

19 EC6 Reactor - Characteristics Modular design fuel channel reactor Reactor core diameter 7.6 m 380 horizontal fuel channels Lattice pitch 286 mm Thermal output 2,084 MWth Fueled by Natural Uranium high neutron economy Moderated and cooled by D 2 O Separation of coolant from moderator Moderator of low pressure and temperature Calandria vessel contains the moderator of a large volume of 274 Mg passive heat sink All reactivity control mechanisms (control, shut-off rods and poison injection) and reactivity measuring devices in moderator (inherent safety) Calandria vessel with fuel channels placed in a concrete light-water filled vault (a passive heat sink) Relatively easy to manufacture and assembly 18

20 EC6 Reactor Assembly 12 fuel bundles per channel 19 Annulus gas is being continuously monitored for humidity content - inherent safety feature

21 CANDU Fuel Channel Assembly Details Pressure tubes constitue CANDU pressure vessel Individual pressure tubes are replaceable Zirconium alloy provides neutron economy Modular component allows scaling of reactor size 20

22 CANDU 6 Calandria for Qinshan 21

23 Fundamental Design Features of EC6 EC6 Fuel 22

24 EC6 Fuel CANDU Length ~ 50 cm Diameter ~ 10 cm Mass ~24 kg 23 Natural uranium (~0.7% 235 U) no criticality issue for fresh & spent fuel in light water inherent safety feature Short (0.5 m) fuel elements arranged in cylindrical fuel bundles Simple design, easy transport, etc. 37 fuel elements organized in four rings in each bundle High-density uranium oxide (UO 2 ) fuel pellets in Zircaloy-4 cladding Collapsible cladding (or sheath) under normal operating conditions = excellent heat transfer Average fuel burnup 7100 MWd/t U Countries with CANDUs manufacture their own fuel

25 Fundamental Design Features of EC6 EC6 Refuelling 24

26 EC6 Refuelling on Full Power Operation & Economics Regular, routine fuel bundle insertion (fresh fuel) and removal (spent fuel) on full power leads to: high performance low operating costs greater flexibility in scheduling outages enables long periods between maintenance outages fuelling scheme 8-bundle shift Please note: Pickering days of continuous operation ( till = ~2.5 years) Safety maintains a minimum core excess reactivity maintains a constant power shape in the core maintains an equilibrium fuel burnup (steady-state source term for potential releases) shutdown system effectiveness does not change during a fuelling cycle permits on-power removal of failed fuel 25

27 EC6 Fuelling Machine at Reactor Face EC6 fuelling machines are designed and manufactured by Candu Energy Inc. Refuelling on power is fully computerized and remotely controlled 26

28 EC6 Fuelling Machine in Maintenance Lock 27

29 EC6 Fuel Handling Location - below the grade level! No criticality concerns in new fuel storage & spent fuel bay! 28 Copyright Candu Candu Energy Energy Inc. Inc.

30 Spent Fuel Bay Spent fuel is well protected Natural Uranium spent fuel generates less heat than LWR fuel Large water to fuel volume ratio Leakage collection systems Transfer to dry storage after 6 years Upon station blackout to 16 days cooling available without intervention & with no damage to the spent fuel Backup cooling connections allow delivery of make-up water from other sources 29

31 EC6 Failed Fuel Detection and Location Failed Fuel Detection by Gaseous Fission Product (GFP) Monitor: Detects failed fuel anywhere in the core Two Heat Transport (HT) loops are analyzed separately Continuously measure Kr88, Xe133, Xe135, I131 Failed Fuel Location by Delayed Neutron Monitoring System Continuously samples coolant from every outlet feeder Detects delayed neutrons from fission products (Br87 and I137) Detects which fuel channel has defective fuel Confirms removal of defective bundle 30 Excellent safety feature minimizing potential contamination of HTS and doses to personnel!

32 EC6 Versatile Fuel Cycles Success in China NUE 37-el. fuel bundles irradiated in C6 NUE = mixture of RU (0.95% U235 from LWR) and DU with equivalency to NU in 37 el. Bundle Full core conversion to NUE fuel in 2014 *AFCR = Advanced Fuel CANDU Reactor New AFCR* Design Based on EC6 Optimized for low-enriched Uranium and Thorium fuel (LEU/Th) Direct use of RU Use of Advanced 43- element CANFLEX fuel bundles 31

33 EC6 Heat Transport System Two independent circuits/loops 2 pumps and 2 steam generators per loop All core-external circuit components located above core - passive natural circulation in the event of loss of pumped flow Entire reactor coolant system pressure boundary inside containment Reactor Coolant Parameters: Reactor inlet header pressure MPa(g) Reactor outlet header pressure 9.89 MPa(g) Reactor outlet header temperature 310ºC Reactor inlet header temperature 265ºC Single channel max flow 28.5 kg/s Secondary Side Conditions: Steam temperature 260ºC Feedwater temperature 187ºC 32

34 CANDU Feeder Header Frame Assembly Critical part of the Heat Transport System Code Class CSA N285.0 Class 1(ASME Sec III, Class 1) Designed by Candu Energy manufactured by heavy industry, like Babcock and Wilcox Canada, also manufactured in Korea, Romania and Argentina. 33

35 Schematic of Two-Loop Heat Transport System Unique CANDU feature: bidirectional flow in adjacent fuel channels LOCA (break of one feeder tube) fuel can be damaged only in one channel (1/380) LBLOCA (break in one of headers) fuel can be damaged only in 50% of the core (broken loop) 34

36 Fundamental Design Features of EC6 EC6 Moderator System 35

37 EC6 Moderator System Low temperature (< 80 o C) system Low pressure system Independent of reactor coolant system Normal heat removal is ~4% of full power Contains shutdown systems outside of high-pressure HTS Low temperature moderator cannot increase pressure of containment (add energy) during a LOCA Passive heat sink if ECC is unavailable during a LOCA and during BDBAs 36

38 Heavy Water Advantages: Very small neutron absorption = excellent neutron economy Long prompt neutron lifetime (~0.9 ms vs ~0.03 ms w light water) = essential inherent safety feature of CANDU reactors: times longer reactivity transients than in other reactors longer time available for activation of Shutdown Systems Less probable fuel fragmentation during rapid transients Generation of photo-neutrons additional source of delayed neutrons further slowdown of reactivity transients and easier power control = further inherent safety feature of CANDU reactors (Can become a fuel for the ITER project) Disadvantages: Cost Maintenance of isotopic purity Generation of Tritium harmful if swallowed or inhaled, but Candu Energy has engineered features to monitor and control its effects 37

39 Fundamental Design Features of EC6 EC6 Safety Systems 38

40 EC6 Safety Systems Design Philosophy: Defense-in-depth Grouping and Separation of safety systems and safety support systems to increase reliability diverse and independent Highly reliable safety systems Safety Functions Two control rooms from either of which the following four safety functions can be executed: Control of shut down the reactor if necessary Control of decay heat removal Control to prevent release of radioactivity Monitor the state of the plant EC6 has two independent groups of systems, each of which, on its own, can perform the above functions = two-group separation philosophy a strong contributor to robustness & redundancy 39

41 RRS SDS#1 ECC EC6 Safety Enhancements Safety Design Approach - Safety Grouping Group 1 Safety Function Group 2 RCW/RSW cooling to ECC Hx powered by Class II LAC (local air coolers) LAC (local air coolers) MCR (main control room) TSC (technical support center) Control to promptly shutdown Remove residual heat from core - transfer heat to ultimate heat sink Confine Radioactive Materials Monitor and Control SDS#2 EHRS (passive makeup to steam generator) Emergency water to ECC Hx powered by EPS SARHRS (separate power & Hx cooling) SARHRS (separate power & Hx cooling) RB Containment (robustness & security) SCA (secondary control area) ESC (emergency support center) New system Enhanced system 40

42 EC6 Shutdown Systems - Passive SDS1 32 SS-clad cadmium rods vertically oriented spring-assisted gravity drop SDS2 6 injection nozzles for gadolinium nitrate solution horizontal insertion driven by high-pressure He Control reactor control separate from safety shutdown (detectors & trip signals) all located in cool & low pressure moderator (no rod ejection) 41

43 EC6 Core Design Enhancements - examples Fuel Channels: Small increases in pressure tube and calandria tube thickness Improved margins using seamless calandria tubes to survive a PT failure Shutdown Systems: Improvements to SOR (SDS1) performance & trip responsiveness additional 4 shutoff rods to assist with shutdown depth greater shutoff rod insertion speed and contour parking two fast neutronic trips added for each shutdown system extended trip coverage by addition of fission chambers and in-core flux detectors Control System: Reconfiguration of control rods to: reduced in-core adjuster rods additional absorber rods to reach a guaranteed shutdown state (GSS) for maintenance outages using mechanical absorbers only. Improved material and plant chemistry specifications life-limiting components such as HTS feeders and headers enhanced with larger chromium content to limit feeder corrosion tight fitting Zr-2.5Nb-0.5Cu spacer with welded girdle wires 42 42

44 EC6 Containment Robust large containment with heat removal systems can prevent radioactive releases Main changes: Low-leakage, high design pressure > main steam line break pressure, Testable penetrations Reduced number of penetrations Steel-lined containment to meet higher design pressure Addition of Passive Autocatalytic Recombiners (PARs) to augment the existing igniters for enhanced hydrogen control Air lock seal improvements Containment accessible during on-power operation 43 Protective barriers

45 EC6 Emergency Core Cooling System Emergency Core Cooling (ECC) System Injection in all headers of the Heat Transport System High pressure injection H 2 O water from external tanks passive system Low pressure water recirculated from containment sump in RB Not the last line of defense EC6 can tolerate LOCA + ECC failure Severe accidents in a CANDU evolve slowly providing time for response and recovery - inherent safety feature Moderator and water in calandria vault prevent rapid severe core damage inherent & passive safety features 44

46 EC6 - Passive Heat Removal for Severe Accident Mitigation With Natural Uranium fuel there is no risk of recriticality upon loss of core configuration or in any corium no need for neutron poison Calandria Vault large source of H 2 O water 520 Mg many hours to heat up and boil off 3000 Mg of water available! Unique EC6 Safety Advantages Reserve Water Tank (RWT) huge source of H 2 O water 2000 Mg fills the Calandria vessel and its vault, SGs by gravity Moderator large source of D 2 O water Mg) several hours to heat up and boil off ECC high pressure system H 2 O water 210 Mg Reactor vault bottom = corium catcher 45

47 Core Damage Accidents in EC6 Reactors Limited Core Damage Accident (LCDA) Pressure tubes sag/strain into contact with calandria tubes establishes a heat rejection pathway to the moderator. Optimization of moderator inlet and outlet nozzle configuration on the calandria for increased moderator sub-cooling enhanced moderator heat sink Severe Core Damage Accident (In-VSCD) If the moderator heat sink fails (or is exhausted), the fuel channels will fail and the core channel debris (corium) will settle to the bottom of the calandria vessel However, reactor vault water plus make-up water will limit severe core damage progression 46

48 Core Damage Accidents in EC6 Reactors Severe Core Damage Accident (Ex-VSCD) If molten corium escapes due to leakage or damage to the externally cooled calandria vessel, and when its external cooling is exhausted (no reactor vault water, no make-up water), in a very low probability case, the core debris may fall on the reactor vault floor that is lined with refractory material to minimize generation of non-condendensable gases 47

49 EC6 New System - SARHRS Inspection Port RESERVE WATER TANK Low-flow Spray Header CALANDRIA MODERATOR HEAD TANK External Water Supply Severe Accident Recovery & Heat Removal System (SARHRS): can function as a backup to the EHRS to refill the RWT inventory for SG makeup refilling the RWT improves the margin to achieving the overall plant safety targets and goals. independent from other electrical systems, powered by separate diesel generator SARHRS design provides capability to drain contaminated water from RB post-bdba draws water from on-site and off-site sources On-site Fresh Water Source ECCS Strainer Emergency Heat Removal System (EHRS): on loss of off-site & normal power supplies provides cooling to SGs using EPS diesels, draws water from ultimate heat sink (e.g., a lake) 48

50 EC6 Safety Enhancement Defence-in-Depth Plant Design Envelope Operational States Accident Conditions Beyond Design Basis Accidents Plant State Normal Operation Anticipated Operational Occurrence Design Basis Accident Design Extension Conditions No further mitigative features available in design LCDA Severe Accidents Severe Core Damage Prevention Severe Core Damage -Mitigation Robustness of Design Control/Process Systems Safety Systems Moderator System Severe Accident Recovery and Heat Removal System Defense-in-Depth Features Normal Operation AOO a DBA LCDA b In-VSCD Ex-VSCD/Large Release Defence in Depth Level 1 Level 2 Level 3 Level 4 Level 5 Event Frequency Yr -1 : > < 10-5 < 10-6 a. Events, such as internal hazards and external events, which are not explicitly considered as accidents, but whose consequences are encompassed by them (such as Design Basis Threats). b. Beyond design basis accidents, without limited or severe core degradation. SCDA Complimentary Design Features 49

51 EC6 Safety Enhancements Balance of Prevention & Mitigation Features Robustness of Design 50 Control/Process Systems Severe Core Damage Prevention Safety Systems Severe Core Damage -Mitigation Moderator System SARHRS Defense-in-Depth Features Normal Operation AOO a DBA b LCDA In-VSCD Ex-VSCD/Large Release SCDA Thicker PT & Seamless CT Preventative Mitigative SDS1 enhanced reactivity insertion SDS2 additional detectors Post-Accident Monitoring a. Events, such as internal hazards and external events, which are not explicitly considered as accidents, but whose consequences are encompassed by them (such as Design Basis Threats). b. Beyond design basis accidents, without limited or severe core degradation. EHRS SG heat sink Reserve Water Tank emergency water to SGs, ECC & EHRS SARHRS makeup to RWT, calandria & vault Low Flow Spray Low leakage, steel-lined, thick-walled, high pressure containment Hydrogen Igniters & PARs Containment Filtered Venting Vault refractory material On/Off Site Mobile Equipment

52 Concluding Remarks The EC6 design builds on the proven CANDU 6 design at Qinshan, based on five decades of excellent operating and safety performance The EC6 is a Gen. III design that meets up-to-date regulatory requirements and customer expectations The EC6 design has incorporated extensive enhancements and provides additional margins for both inherent or passive and engineered safety features, and heat removal systems to prevent and mitigate severe accidents The EC6 design has provided further design features that extends the defencein-depth provisions for beyond design basis events, based on lessons learned from Fukushima nuclear event What is your answer to the question: Are Enhanced CANDU 6 Reactors the Best Fit for the 1 st NPP in Poland? 51

53 Personal Note... I wish Poland and the Polish Nation to develop and implement an efficient nuclear power energy program and choose the best technology! To complement my lecture - please read my paper Wybrane Projektowe Awarie Reaktywnosciowe w Reaktorach LWR i CANDU, published in Polish, Postepy Techniki Jadrowej, Vol. 53, Z. 4, Warszawa 2010 I am ready to help! S.D. I recommend reading the papers of Mr. D. Kulczynski, P.Eng. OPG Darlington NPP, on CANDU from operation/utility perspective, Postepy Techniki Jadrowej, in Polish 52 52

54 Thank You