Health and Safety ExecutiveThe Fukushima Daiichi Accident –

Report of HM Chief Inspector

NuLeAF Meeting

21 October 2011

Andy Hall

Deputy Chief Inspector (figure courtesy of GE Hitachi Nuclear Energy)

Introduction

• Outline of the accident

• Aims of the Chief Inspector’s Reports

• Openness and development of the project

• Conclusions & recommendations of Interim & Final Reports

Accident Initiator

11 March 2011

• Magnitude 9 earthquake

• Subsequent tsunami

• 14-15m Fukushima 1

Immediate Consequences

• Loss of all external power

• Only 1 of 13 Emergency Diesel Generators remained available

• Unprecedented devastation

• Impaired infrastructure

• Long-term developing scenario

Fukushima Daiichi

• Regulatory Design Basis tsunami of 3.1m, TEPCO 5.7m

Power of tsunami

Accident CharacteristicsMajor external hazards affected site

Station blackout

Loss of some DC power

Loss of ‘ultimate heat sink’

Failure to cool reactor cores

Core melt and hydrogen generation

Explosions

Fission product releases over extended period

Damage to reactor buildings

Consequences over following daysReactor 1 Reactor 2 Reactor 3

Operating status Nominal full power Nominal full power Nominal full power

Fuel condition Uncovered from ~1700 on 11/3/11, melted & relocated shortly afterwards

Uncovered from ~1800 on 14/3/11, melted & relocated shortly afterwards

Uncovered from ~0800 on 13/3/11, melted & relocated shortly afterwards

Current fuel location Relocated to lower RPV head, possibly some in dry well underneath

Relocated to lower RPV head, possibly some in dry well underneath

Relocated to lower RPV head, possibly some in dry well underneath

Lower PRV head condition

Believed to be damaged, primary coolant appears to have leaked through lower head

Believed to be damaged, primary coolant appears to have leaked through lower head

Believed to be damaged, primary coolant appears to have leaked through lower head

Primary containment vessel (PCV) and venting

Wet-well venting from 1430 on 12/3/11.Explosion seen at top of reactor building 1536 same day

Wet-well venting from 1100 on 13/3/11.Explosion heard at 0600 next day, believed to be in vicinity of pressure suppression pool

Wet-well venting from 0520 on 14/3/11.Explosion seen at top of reactor building 1101 same day

Radiological Source Terms

NISA estimated source term from JNES accident calculations

NSC estimated it from JAEA back-calculations from environmental monitoring

These agreed on 1 – 2 x 1017 Bq of I-131 and 1 – 2 x 1016 Bq of Cs-137, i.e. ~ 10% of Chernobyl

On this basis, the INES rating was increased to Level 7 on 12 April.

Aims of Chief Inspector’s Reports

Requested by SoS Energy & Climate Change

Interim report published in May

Aims:

• to learn lessons

• identify any UK vulnerabilities

• take action to assure and improve nuclear safety

Aims of Chief Inspector’s Reports

Also asked to cooperate with other national regulators and international organisations,

and to be open and transparent in preparing the reports

Project Arrangements

Set up a small core team within ONR

Drew on technical inspectors for specialist advice

Invited submissions from public via website

Set up Technical Advice Panel

Interim Report Conclusions

11 Conclusions

To summarise: our review of the information available has not revealed any vulnerabilities with UK nuclear facilities or shortcomings in safety methodology that would require operations to be curtailed

Interim Report Recommendations26 Recommendations

General: need for good comms, seek lessons for emergency preparedness & enhance openness

For regulators: review standards/guidance and emergency preparedness, particularly for severe accidents

For industry: review aspects of accident for implications, e.g. resilience, natural hazards, AC supplies, cooling, site/plant layout, human performance, emergency preparedness, data comms.

Conclusions from International Reports

Fukushima Daiichi was not adequately protected against the natural hazards that struck

These were foreseeable – historical records of larger tsunamis striking East coast of Japan

Original site safety case identified tsunamis as a threat –regulator accepted design height of only 3.1 m

Operator increased this to 5.7 m after 2002, but appears to have only implemented improvements on Unit 6

Design Basis

‘Design Basis’ sets out events that plant must be designed to withstand and control

For Japan, a Regulatory Guide sets out the ‘anticipated operational occurrences’ and ‘accidents’ that must be analysed

This only requires a single failure of a safety system or component within it to be assumed following the initiating event

Design Basis for Tsunamis

Neither total loss of AC power nor loss of ultimate heat sink were design basis events

Japanese Government report stated:

• a trial tsunami PSA “indicated that the risk sensitivity of an event in which simultaneous functional losses of all the seawater pumps are generated due to tsunami was high”

• “compared with the design against earthquake, the design against tsunamis has been performed based on tsunami folklore and indelible traces of tsunamis, not on adequate consideration of the recurrence of large-scale earthquakes in relation to a safety goal …”

Safety Case Implications

Safety cases need to be:

• based on a structured analysis of a comprehensive range of possible events and hazards, both frequent and infrequent

• updated in the light of new information and advances in technology

Final Report Conclusions

Six new conclusions

• UK approach to designing against a wide range of events including natural hazards is sound

• long-standing concerns over Sellafield Legacy Ponds & Silos means UK must continue to progress remediation & retrievals with vigour

• Periodic Safety Reviews are essential for ensuring safety standards are improved in line with new technology & understanding

Final Report Conclusions

• the scope of operators’ Probabilistic Safety Assessments must be extended to cover severe accident conditions, to improve understanding for their management

• additional information has reinforced Interim Report conclusions & recommendations

• UK nuclear industry has responded constructively to Interim Report

Final Report Recommendations Twelve new recommendations

General:

• support efforts to improve international peer reviews & further development of standards

• review methods for estimating source terms, measuring environmental contamination and predicting dispersion & impacts

• review planning controls for commercial & residential developments near nuclear sites

• ensuring that ONR is open & transparent about its activities

Final Report Recommendations

For regulators:

• ONR should expand its oversight of nuclear safety-related research, including UK capability, to ensure continuing access to sufficient expertise to perform its duties

Final Report RecommendationsFor industry:

• buildings and equipment needed for managing accidents, such as emergency centres, should be protected against hazards that could affect several at same time

• they should also be capable of operating in the conditions, inc. severe accidents, for which they might be needed

• continue to promote high levels of safety culture & nuclear professionalism

Final Report Recommendations

For industry:

• give appropriate & consistent priority to completing Periodic Safety Reviews & implementing the identified improvements

• develop Level 2 PSAs for all facilities that could have accidents with off-site consequences & use to further develop severe accident management measures

•Report responses to recommendations to ONR by June 2012

To conclude

Although some more detailed information may yet emerge, we already know enough to develop reliable conclusions & recommendations

Everyone with responsibilities for nuclear safety must strive for continuous improvement

Thank you for your attention …

… any Questions?