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Emergency electrical power supply to nuclear safety systems: Design basis and lesson learned from the Fukushima accident
Genova , 30 Ottobre 2013
Corrado Alessandroni Licensing and Safety Technical Advisor Ansaldo Nucleare
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
FUKUSHIMA DAI-ICHI March 11th, 2011
What’s occurred to the Electrical Power Supply Systems
FUKUSHIMA DAI-ICHI March 11th, 2011
Hour 14.46: massive earthquake (magnitude 9.0) which induced onsite seismic
accelerations above design values
Loss of normal electrical power supply caused by the earthquake
Reactor SCRAM in the three units in operation (of six located onsite)
Electrical power supplied by the emergency diesel generators (EDGs) that started as designed
Hour 15.30: an earthquake induced Tsunami struck the site: waves up to 14 ÷ 15 m
height flooded the major buildings (tsunami barriers where designed for 6 m wave height
protection).
Loss of 12 out of 13 EDGs located onsite – the survived EDG was servicing the Units 6
Massive damage of electrical panel boards
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
CP EXPO 2013
Genova , 30 Ottobre 2013
Path of inundation Ref. A One-year Review of Fukushima Daiichi Nuclear Power Station “Steps to Achieve Stabilization” March 2012
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
FUKUSHIMA
DAI-ICHI
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
Ref. Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station – INPO 11-005 November 2011
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
Ref. A One-year Review of Fukushima Daiichi Nuclear Power Station “Steps to Achieve Stabilization” March 2012
Fukushima Daiichi Electrical Distribution Damage
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
Ref. Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station – INPO 11-005 November 2011
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
Ref. Fukushima Nuclear Accident Analysis Report (Interim Report) – Tokyo Electric Power Company, Inc. December, 02nd 2012
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
Ref. A One-year Review of Fukushima Daiichi Nuclear Power Station “Steps to Achieve Stabilization” March 2012
Vehicles batteries secured on-site were collected to power monitoring instrumentation
about 6 hours after the initiating event, batteries were connected to power reactor water level indicator at Unit 1
Post-accident recovery actions to restore the electrical power supply
No written emergency procedures to face the severe accident situation Restoration of external power supply impossible due to the massive damage
induced on transmission lines by the earthquake
Acquisition of power supply cars and further batteries from outside
power supply cars started to arrive onsite on 11th March evening-night;
about 50 mobile electric-generators were onsite on 12th March morning;
connection difficulties due to the massive damaged of the electrical panels;
first connection was made in the afternoon of 12th March (15.30) about 25 hours after the earthquake and about 18 hours from the arrival of the first power supply car;
it was decided to use fire engines and motor driven pumps to cool reactors trough injection of sea water due to the impossibility to restore power to plant safety systems.
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
CP EXPO 2013
Genova, 30 Ottobre 2013
Ref. Fukushima Nuclear Accident Analysis Report – Tokyo Electric Power Company, Inc. June, 20th 2012
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: What’s occurred at Fukushima
EMERCENCY POWER SYSTEM (EPS) Design Bases
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: EPS Design Bases
System definition
EPS includes:
1. Electric power supply sources: Electric Generators (typically Diesel-Generator) and Batteries
2. Electric power distribution system
Functions
Provide power supply to plant components assuring safety functions under all design basis conditions where the normal power supply is not available. The fundamental safety functions are:
1. Shutdown of the nuclear chain reaction 2. Nuclear fuel cooling and decay heat removal 3. Containment of radioactive releases
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: EPS Design Bases
System Design Bases
Inspection and Testing Program during operation – Program surveilled by the Safety Authority (Individual Plant Technical Specification)
Separation from the normal power supply system of the plant: Defense-in-Depth Principle
Component redundancy : Application of the Single Failure Criterion
Redundant components separation : protection against from common cause failure (fire, flooding, internal missiles etc.)
Environmental qualification: P,T, humidity and radiation associated also to accidental conditions
Protection / Qualification against design basis External Natural Phenomena (Earthquake, Flooding, Tornado etc.) and Man-made External Events (Aircraft Impact, Explosion etc...)
Component safety classification commensurate with the importance of the safety functions to be performed
Application of Codes and Standard for the design, fabrication, erection, testing and operation commensurate with the importance of the safety functions to be performed
Quality assurance
Reliability requirements for emergency diesel generators (0,95-0,975 per demand for each EDG - US NRC Reg.Guide 1.155 «Station Blackout»)
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: EPS Design Bases
REGULATIONS and STANDARDS
International (IAEA, IEC, ISO)
IAEA Safety Standard Series NS-G-1.8 Design of Emergency Power Systems for Nuclear Power Plants
National (Regulatory Guides,IEEE, RCC-E, KTA, …)
EUR Requirements Document (Europe)
Generation III Light Water Reactors: Utilities Requirements
EPRI Utility Requirements Document (USA and other countries)
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: EPS Design Bases
Power, Instrumentation and Control Portion of Safety Systems
IEEE Std 603 Criteria for Safety Systems for NPGSs
--------------
US NRC Reg. Guide 1.153
Power Systems
IEEE Std 308
US NRC Reg.Guide 1.32
Protection System
IEEE Std 279
US 10CFR50 and SRP Ch.7
Post-Accident Monitoring System
IEEE Std 497
US NRC Reg.Guide 1.97
Digital Computer Systems
ANSI/ANS IEEE Std 7-4.3.2
Periodic Testing
IEEE Std 338
US NRC Reg. Guide 1.118
Environmental and Seismic Qualification
IEEE Std 323 – IEEE Std 344 – IEEE Std 627
US NRC Reg Guide 1.89 and 1.100
Independence and Separation
IEEE Std 384
US NRC Reg.Guide 1.75
Single Failure Criterion
IEEE Std 379
US NRC Reg.Guide 1.53
U.S. STANDARDS - IEEE Standards for Safety Systems and Components (IEEE Class 1E Items)
• System Design Basis • System Design Criteria • Sense and Command Features
Requirements • Execute Features Requirements • Power Sources Requirements
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: EPS Design Bases
U.S. STANDARDS -IEEE Standards for Safety Systems and Components (IEEE Class 1E Items)
• System Design Basis • System Design Criteria • Sense and Command Features
Requirements • Execute Features Requirements • Power Sources Requirements
IEEE Std. 387 – Criteria for Diesel-Generator Units Applied as Standby Power Supplies for Nuclear Power Generating Stations (US NRC Reg. Guide 1.9);
IEEE Std. 485 - Recommended Practice for Sizing of Lead-Acid Batteries for Stationary Applications (US NRC Reg. Guide 1.212);
IEEE Std. 572 - Qualification of Class 1E Connection Assemblies for Nuclear Power Generating Stations (US NRC Reg. Guide 1.156);
……
Examples of Specific Standards for equipment-apparatus
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: EPS Design Bases
AFTER FUKUSHIMA
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: After Fukushima
Stress Tests: European Union
EU Council of 24/25 March, 2011, requested that the safety of all EU nuclear plants should be reviewed
31st May 2011: ENSREG issued EU Stress Tests Specifications
June 2011: all the operators of nuclear power plants in the EU started safety reassessments on the basis of ENSREG Specifications
November 2011: NPP Operators Final Reports to National Safety Authorities
December 2011: National Reports by Safety Authorities
April 2012: Peer Review Report by the Task Force setup by ENSREG and EU Council with experts from all EU countries.
August 2012: ENSREG Action Plan to follow-up the implementation of the peer review recommendations
Post-Fukushima Task Force and Action Plan: USA
INTERNATIONAL INITIATIVES
July 2011 Document with Near-Term Task Force (NTTF) recommendations (SECY-11-0093): NTTF conducted a review of the NRC regulations and processes in light of the events at Fukushima determining additional improvements to be made
September 2011 Selected recommendations to be taken without delay (US NRC SECY-11-0124)
October 2011 NTTF Recommendations Prioritization and Action List (US NRC SECY-11-0137)
March 2012 Approval of the first three orders to Plant Operators (SECY-12-0025)
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: After Fukushima
Reassessment of the Design Basis External Events with updated methodologies and data
ACTIONS
Definition of Beyond Design-Basis External Events Mitigation Strategies.
Scenario: loss of electrical power and ultimate heat sink affecting all units at a site simultaneously
Goal: prevent fuel damage in the reactor and spent fuel pool with simultaneous actions on all units at site
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: After Fukushima
Mitigation Strategies– Phased Approach
(rif. NEI 12-06 Maggio 2012 – Diverse Flexible Coping Strategies –FLEX- Implementation Guide)
Phase 1- Initial Phase: use of installed equipment and resources to maintain or restore
nuclear safety functions
most of the existing NPPs are already equipped to manage a total loss
of AC power (external grids + diesel generators) for few hours (typically
4-6 hours) - Station-Blackout scenario
disconnect not-vital electrical loads to extend power sources duration
Phase 2-Transition Phase: provide sufficient, portable, onsite equipment and consumables to
maintain or restore the nuclear safety functions until they can be
accomplished with resources brought off site (for roughly 24 hours)
Phase 3 - Final phase : obtain sufficient offsite resources to sustain those functions
indefinitely
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: After Fukushima
Portable equipment that provides means of obtaining power and water to maintain or restore key safety functions for all reactors at a site
This could include equipment such as portable pumps, generators, batteries and battery chargers, compressors, hoses, etc.
Elements of the Mitigation Strategy
Reasonable staging and protection of portable equipment and associated transportation routes
The equipment used for mitigation would be staged and reasonably protected from applicable site-specific severe external events to provide reasonable assurance that N sets of equipment will remain deployable following such an event (N is the number of NPP Units on site).
Portable equipment connections qualified-protected to timely supply power to vital loads and provide water to cool down the nuclear fuel in reactors and spent fuel pools
Procedures and guidance to implement mitigations strategies to be integrated in the Plant Operating Procedures (AOP)
Programmatic controls that assure the continued viability and reliability of the mitigation strategies.
These controls would establish standards for quality, maintenance, testing of FLEX equipment, configuration management and periodic training of personnel..
Personnel Training
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: After Fukushima
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: After Fukushima
ELECTRICAL FLEXIBLE CONNECTIONS for off-site mobile equipment
DIVERSE AND PROTECTED STAND-BY DIESEL GENERATOR STATIONS Diverse and protected (external events) diesel generator stations to be installed at NPP site
FULLY QUALIFIED/PROTECTED 6KV SWITCHBOARDS Possible cross-links for safety electrical power loads 6 kV from any operable emergency diesel generator
Post-Fukushima – ANN Service Products
“Plug and Socket” to the Electrical Distribution System, at different voltage levels (medium up to 11
kV, low up to 400 V)
• identification of emergency electrical loads; • installation of circuit breakers allowing for fast load transfer, isolation
of not emergency loads and connection of emergency power source; • update of the existing distribution network, to respect all the
duplication and segregation requirements ; • electrical cabinet design and qualification process;
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: After Fukushima
Thanks for your
attention
CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lesson-
learned from Fukushima accident: After Fukushima