Health and Safety
Executive
The 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
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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
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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 Characteristics
Major 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 days
Reactor 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 Recommendations
26 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 Recommendations
For 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:
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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?