Emergency electrical power supply to nuclear safety systems, Design Basis and lesson-learned from Fukushima accident” Corrado Alessandroni - Ansaldo Nucleare

1. Emergency electrical power supply to nuclear safety
systems: Design basis and lesson learned from the
Fukushima accident
Corrado Alessandroni
Licensing and Safety Technical Advisor
Ansaldo Nucleare
Genova , 30 Ottobre 2013

2. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: What’s occurred at Fukushima
FUKUSHIMA DAI-ICHI March 11th, 2011
What’s occurred to the Electrical Power Supply Systems

3. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: What’s occurred at Fukushima
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

4. CP EXPO 2013
Genova , 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: What’s occurred at Fukushima
Path of inundation
Ref. A One-year Review of Fukushima Daiichi Nuclear Power Station “Steps to Achieve Stabilization” March 2012

5. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: What’s occurred at Fukushima
FUKUSHIMA
DAI-ICHI
Ref. Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station – INPO 11-005 November 2011

6. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned 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

7. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: What’s occurred at Fukushima
Fukushima Daiichi Electrical Distribution Damage
Ref. Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station – INPO 11-005 November 2011

8. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: What’s occurred at Fukushima
Ref. Fukushima Nuclear Accident Analysis Report (Interim Report) – Tokyo Electric Power Company, Inc. December, 02nd 2012

9. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned 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

10. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: What’s occurred at Fukushima
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
 Vehicles batteries
instrumentation
secured on-site were collected to power monitoring
 about 6 hours after the initiating event, batteries were connected to power
reactor water level indicator at Unit 1
 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.

11. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: What’s occurred at Fukushima
Ref. Fukushima Nuclear Accident Analysis Report – Tokyo Electric Power Company,
Inc. June, 20th 2012

12. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: EPS Design Bases
EMERCENCY POWER
SYSTEM (EPS)
Design Bases

13. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: EPS Design Bases
 System definition
EPS includes:
1. Electric power supply sources: Electric Generators (typically DieselGenerator) 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.
2.
3.
Shutdown of the nuclear chain reaction
Nuclear fuel cooling and decay heat removal
Containment of radioactive releases

14. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: EPS Design Bases
 System Design Bases
 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
 Reliability requirements for emergency diesel generators (0,95-0,975 per demand
for each EDG - US NRC Reg.Guide 1.155 «Station Blackout»)
 Quality assurance
 Inspection and Testing Program during operation – Program surveilled by the
Safety Authority (Individual Plant Technical Specification)

15. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned 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, …)
 Generation III Light Water Reactors: Utilities
Requirements
 EUR Requirements Document (Europe)
 EPRI Utility Requirements Document (USA and other countries)

16. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: EPS Design Bases
U.S. STANDARDS - IEEE Standards for Safety Systems and Components (IEEE Class 1E Items)
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
Protection System
IEEE Std 308
US NRC Reg.Guide 1.32
IEEE Std 279
US 10CFR50 and SRP Ch.7
•
•
•
•
•
Post-Accident Monitoring
System
IEEE Std 497
US NRC Reg.Guide 1.97
System Design Basis
System Design Criteria
Sense and Command Features
Requirements
Execute Features Requirements
Power Sources Requirements
Digital Computer Systems
ANSI/ANS IEEE Std 7-4.3.2
Single Failure Criterion
Periodic Testing
IEEE Std 379
US NRC Reg.Guide 1.53
IEEE Std 338
US NRC Reg. Guide 1.118
Independence and Separation
Environmental and Seismic Qualification
IEEE Std 384
US NRC Reg.Guide 1.75
IEEE Std 323 – IEEE Std 344 – IEEE Std 627
US NRC Reg Guide 1.89 and 1.100

17. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: EPS Design Bases
U.S. STANDARDS -IEEE Standards for Safety Systems and Components (IEEE Class 1E Items)
Examples of Specific Standards for equipment-apparatus
•
•
•
•
•
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);
 ……

18. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: After Fukushima
AFTER FUKUSHIMA

19. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: After Fukushima
INTERNATIONAL INITIATIVES
 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




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)

20. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: After Fukushima
ACTIONS
 Reassessment of the Design Basis External Events with updated
methodologies and data
 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

21. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned 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

22. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: After Fukushima
Elements of the Mitigation Strategy
 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.
 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)
 Personnel Training
 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..

23. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: After Fukushima

24. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: After Fukushima
Post-Fukushima – ANN Service Products
ELECTRICAL FLEXIBLE CONNECTIONS
for off-site mobile equipment
“Plug and Socket” to the Electrical
Distribution System, at different
voltage levels (medium up to 11
kV, low up to 400 V)
FULLY QUALIFIED/PROTECTED 6KV SWITCHBOARDS
Possible cross-links for safety electrical power loads
6 kV from any operable emergency diesel generator
•
•
•
•
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;
DIVERSE AND PROTECTED STAND-BY DIESEL GENERATOR STATIONS
Diverse and protected (external events) diesel generator stations to be
installed at NPP site

25. CP EXPO 2013
Genova, 30 Ottobre 2013
Emergency electrical power supply to nuclear safety systems: Design Basis and lessonlearned from Fukushima accident: After Fukushima
Thanks for your
attention