Office for Nuclear Regulation

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Fukushima 10 years on: How ONR responded to a nuclear accident almost 6,000 miles away

11 March, 2021

IAEA visit at the Fukushima Dai-ichi nuclear power plant

At 2:46pm on 11 March 2011, Japan suffered its worst natural disaster when it was hit by a catastrophic earthquake.

The magnitude 9.0 earthquake triggered a 14-metre high tsunami which led to a serious nuclear accident at the Fukushima Dai-ichi nuclear power plant, impacting the international community in a way not seen since Chernobyl.

In the weeks and months that followed, ONR was at the forefront of a UK and international response which culminated in a major review of nuclear safety led by then ONR Chief Nuclear Inspector (CNI) Dr Mike Weightman. The review would lead to major improvements in nuclear plant safety and resilience in the UK.

On the 10th anniversary of the Fukushima Dai-ichi accident, we look back on ONR’s role in responding to the nuclear accident and speak with some of the key people involved.

When a magnitude 9.0 earthquake, the largest in Japan’s recorded history, triggered a 14‑metre high tsunami which hit the country’s east coast on 11 March 2011 at 2.46pm,the tsunami caused catastrophic damage to the Fukushima Dai-ichi nuclear power plant site.

Immediately after the disaster, ONR responded by providing advice to the Scientific Advisory Group for Emergencies (SAGE) and the Cabinet Office Briefing Rooms (COBR) while mobilising its 24-hour incident suite.

Dr Mike Weightman

Dr Mike Weightman, then Chief Inspector of Nuclear Installations and Head of ONR, reported on the resilience of UK nuclear sites and implications for the UK nuclear industry following a request from the Secretary of State for Energy and Climate Change.

Comparing the situation in Japan to the UK, the report’s 32 recommendations were designed to ensure the UK learned appropriate lessons from the disaster. The recommendations required UK nuclear site licence holders to review a wide range of nuclear safety matters, including international and national emergency response arrangements, public contingency planning, communications, extreme natural hazard studies, site and plant layouts, electricity and cooling supplies, multi reactor site considerations, spent fuel strategies, and dealing with prolonged accidents.

The European Council also requested a review of safety at European Nuclear Power Plants, which became known as the “stress tests”. Although these stress tests strictly applied to civil nuclear reactors, ONR required all UK nuclear licensees to subject their sites to the stress test, as well as requiring them to examine their facilities against the recommendations of Dr Weightman’s report.

Industry subsequently implemented improvements to address the outcome of its review and application of the “stress tests”.  In 2015, ONR’s extensive assurance activities concluded that all stress test findings and recommendations had been satisfactorily addressed.

Marking the 10-year anniversary of the Fukushima Dai-ichi accident, ONR Chief Nuclear Inspector Mark Foy believes it is vital that we learn from past events, avoid complacency and continually seek improvement, while acknowledging that the extreme natural events which struck Japan in 2011 are extremely unlikely to happen in the UK.

Mark said: “The extreme natural events which led to the accident at Fukushima Dai-ichi, while far beyond the most extreme events the UK could expect to experience, are a reminder of the need for the presence of a strong nuclear regulator which ensures that appropriate safeguards are in place to protect against even very remote hazards.

“Dr Weightman’s report found there were no fundamental weaknesses in UK nuclear facilities. It initiated improvement and learning which is now a fundamental feature of the safety culture in the UK nuclear industry, and strengthened many of the regulatory processes we use today.”


Improvements arising from Dr Weightman’s findings

Dr Weightman at the Fukushima Dai-ichi nuclear power plant

ONR and UK licensees, along with the international community, carried out significant work to make sure that lessons from the events of Fukushima have been applied to enhance nuclear safety.

Some of the enhancements we made at ONR included updating our Safety Assessment Principles to clarify our expectations, particularly in the areas of external hazards and severe accident management. Internationally, we led on the development of new Western European Nuclear Regulators Association (WENRA) reference levels to establish consistency in standards across Europe.

As well as re-evaluating flooding, seismic, and other hazards that could happen at their sites, licensees examined the possibility of more extreme events or combinations of events happening at the same time to make sure plans were in place for the unexpected. Cooling, electrical supply integrity, connection points, and emergency equipment were also reviewed and enhanced. Improvements were also made to emergency arrangements and hazard awareness and emergency procedures training for operators.

A few examples of physical improvements made by UK licensees include:

  • The installation of super-articulated control rods and seismically qualified nitrogen injection plant at Hinkley Point B and Hunterston B.
  • Regional depots created in three strategic locations across the UK, containing emergency plant and equipment, decontamination and welfare units, and other vehicles that could be deployed as part of the national response to an extreme event
  • The introduction of deployable communications systems which can operate even if there is an event that causes severe damage to ordinary communications infrastructure. They transmit vital CCTV footage, plant status, voice information via satellite to other locations
  • A new flood wall built around Dungeness B.
  • Fuel and water stocks were increased on site to last for at least 72-hours, while deployable stocks of nitrogen for AGRs were also introduced.
  • Improvements to the emergency cooling water systems, backup electrical power system were made at critical facilities at Sellafield, along with the provision of additional emergency response equipment.
  • All Magnox Ltd sites now have emergency equipment which would support a response to ‘beyond design basis’ events – these are extremely unlikely events beyond what the site has been designed to withstand.

ONR has worked with licensees across the industry to ensure many more complex and less tangible improvements have been made, including in leadership, decision-making and nuclear safety culture.


ONR’s emergency response

ONR mobilised its incident suite to support Dr Weightman and provide independent advice to UK government on the first day of the serious nuclear accident at Fukushima Dai-ichi and kept it fully operational for many weeks.

Among those leading the response from the incident suite at ONR’s Bootle headquarters, was Anthony Hart.

Recalling the response, Anthony said: “Those early days were exhausting as we worked around the clock.  We were receiving a great deal of technical information from reliable sources, but much of it was conflicted.

“Much of our work involved calculations, the most important of which was to estimate radiation doses over Tokyo. Several western governments evacuated their nationals, but we provided advice to government based on the technical information available to us that evacuation of UK citizens would not be necessary.

“I am pleased to say that this advice was accepted and in hindsight proved to be correct, and the UK decided not to evacuate its nationals.”

Fact-finding in Okuma

Dr Weightman led a team of international nuclear experts to Fukushima on a fact-finding mission in May 2011 at the request of the International Atomic Energy Agency (IAEA). Speaking in 2011, the former ONR Chief Nuclear Inspector explained how his team met with the workers who responded to crisis when the earthquake and tsunami struck.

Dr Weightman said: “We had access to much detailed information and met and talked to the workers who took extraordinary and brave actions to deal with the crisis.

“The findings from this International Atomic Energy Agency mission, from the detailed technical reports the Japanese Government has supplied, and from other evidence submitted to me, have informed my report to the Secretary of State.”

The legacy of Fukushima

The events at Fukushima have had a far-reaching impact on the nuclear industry worldwide.

Apart from its economic impact, it has limited the adoption of new nuclear power plants across the globe, curtailed existing nuclear programmes, and had a significant influence on public perception of nuclear power.

In Japan, the earthquake and tsunami had a devastating impact on the country and its people.  The Fukushima Daichi site has presented complex issues, and work to clean up the site continues, with many challenges still to be overcome.

We recognise the good work undertaken by Japan to tackle the challenges on the Fukushima Daichi site and we will continue to support the country in this work.

Although post-Fukushima improvements have been made to nuclear facilities in the UK, the extensive reviews carried out by UK licensees immediately after the event confirmed that there were no fundamental weaknesses in UK nuclear facilities.

However, ONR and the industry must not be complacent. We must continue to focus on ensuring that the high standards of nuclear safety required by law, continue to be achieved.

Fukushima facts

  • The earthquake was among the largest recorded, with a rupture area was estimated to around 500km long and 200km wide.
  • The tsunami first reached the Japanese mainland 20 minutes after the earthquake and ultimately affected a 2,000 km stretch of Japan’s Pacific coast and inundated over 400km2 of land.
  • The main shock, with a magnitude of 9.0, lasted for more than two minutes, with several significant pulses and aftershocks.
  • The earthquake and subsequent tsunami resulted in widespread devastation. More than 15,000 people were killed, and +6,000 were injured, although no deaths or cases of radiation sickness resulted from the nuclear accident.
  • The Fukushima Daiichi nuclear power plant, which comprises six units with boiling water reactors (BWRs), was located 180 km from the epicentre.
  • Following the earthquake, all three operating reactors were safely shutdown, but the loss of power caused the cooling systems to fail.
  • The tsunami waves overwhelmed the tsunami barriers of the Fukushima site, damaging the back-up generators that were providing power to the site.
  • Nuclear material in the cores of reactor 1 and 2 was exposed, and the build-up of hydrogen gas caused explosions to occur at reactors 1 and 3.
  • A separate set of problems arose as the fuel ponds, holding fresh and used fuel in the upper part of the reactor structures, were found to be depleted in water.

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