Following the earthquake and tsunami in Japan on 11 March 2011, and the subsequent nuclear incident at Fukushima Dai-ichi nuclear power plant, EDF Energy has committed to further enhance its robust safety standards across its fleet of eight nuclear power plants.
After the events at Fukushima, the Office for Nuclear Regulation (ONR) carried out an independent review of UK nuclear power plants. This concluded that the “UK nuclear facilities have no fundamental weaknesses”. These findings were supported by EDF Energy’s Japanese Earthquake Response (JER) Programme on completing an internal review and challenge across the entire fleet of nuclear power plants which showed “there is no challenge to nuclear safety for within design basis events”. More information about this review can be found on the Stress Tests page.
Nonetheless, the events in Japan have taught us to go above and beyond those design basis events. Supporting the ONR’s recommendations, EDF Energy identified a number of areas where they can further enhance safety margins to protect the fleet against the most unpredictable events, known as beyond design basis events.
This is being done by increasing capability of the fleet through a combination of purchasing of new back-up equipment, enhancing on-site resilience and improving existing emergency arrangements and severe accident management procedures.
In our efforts to learn and increase nuclear safety, we have and will continue to work closely with key groups across the industry, nationally and internationally, to ensure that learning is shared and lessons learned. Nuclear safety is our overriding priority and through learning and operational experience within the industry, we will support the EDF Group to be world leaders in nuclear safety.
What happened at Fukushima Dai-ichi?
On 11 March 2011, when the tsunami struck following the earthquake on the east coast of Japan, it caused widespread devastation and also impacted upon some nuclear facilities. Although most facilities on the east coast (Tokai, Higashi Dori, Onagawa and Fukushima Dai-ni) were successfully shutdown by their automatic systems in response to the earthquake, serious consequences occurred at the Fukushima Dai-ichi nuclear power plant after the tsunami struck.
The magnitude 9 earthquake triggered the automatic protection system on all operating reactors as per the design intent; tripping the units’ control rods into the reactor core to allow shutdown procedures to begin, including the cooling of the reactors which is essential after shutdown. The earthquake also caused the electrical power supplies to the site to be lost, however all available emergency diesel generator power systems came into operation as per the emergency operation arrangements. This allowed the reactors to continue shutdown operations and maintain cooling functions as required after an earthquake.
Around 46 minutes after the earthquake, a tsunami greater than 14 metres in height struck the Fukushima Dai-ichi plant, and overwhelmed the 5.7 metre defences. This completely inundated the site, flooding the emergency diesel generators, causing the loss of all but one*, and leaving units 1 to 4 with no alternative power source to maintain cooling functions or instrumentation systems for control of those reactors, which ultimately led to a severe accident caused by the fuel becoming uncovered and the subsequent generation and explosion of hydrogen in the reactor building.
Since the event, TEPCO have admitted their sea defence was not sufficient to protect against the predictable, within design basis events.
The widespread damage to local infrastructure prevented outside assistance from helping the operators on the site to regain control of the situation, for example equipment capable of draining the basements to restart the generators, or to supply additional sources of electrical generation.
The operators were consequently faced with a catastrophic, unprecedented emergency scenario with no power, reactor control, instrumentation, or effective communications systems neither within nor external to the site.
Reactors 5 and 6 shared the emergency power from the one remaining emergency diesel generator and so remained in control.
After the accident at Fukushima Dai-ichi Nuclear Power Plant in Japan on 11 March 2011, the UK government commissioned Dr Weightman, Chief Nuclear Inspector for the Office for Nuclear Regulation (ONR), to technically review the incident and identify any lessons to be learned.
In parallel, the EU called for a programme of Stress Tests across the member countries with each nuclear operator submitting details of its safety assessments to its nuclear regulators. The ONR has published its National Report to the EU outlining the results of its review of the stress testing programme.
EDF Energy is committed to supporting this programme and learning from the events at Fukushima, and we have published our Stress Test reports for each of our eight nuclear power plants in the UK. In addition we have produced a Stress Test report for EDF Energy’s proposed twin EPR reactor site at Hinkley Point C. These reports can be found on this page.
The Stress Test thoroughly examined our existing station safety cases against potential events that have a very low probability but high impact. The actual events at Fukushima have been used to highlight potential risks. These include the directly relevant hazards such as earthquake and flooding (from tsunamis and other sources) and other extreme weather conditions, potentially more relevant to the UK such as high winds and extreme ambient temperatures.
Each report includes:
- scrutiny of the existing safety justifications
- details of events that could breach the safety margins of the nuclear power plants
- the physical safety measures in place
- operator training
- procedural arrangements in place, for example how the nuclear power plant deals with and manages an incident.
Within the scope of the Stress Tests we have identified no shortfalls in the operational safety cases of our existing fleet. Our entire fleet of operational nuclear power plants are safe to continue operating as they are. However, we have identified ways to further enhance our current robust position. The next two years will see the delivery of the additional enhancements outlined in the Stress Tests to increase the safety margins of our nuclear power plants even further.
In terms of the twin reactors being proposed for Hinkley Point C, the Stress Tests have shown that the proposed EPRs at HPC are robust and would continue to be safe even after situations that go beyond those considered plausible in the UK. We will, as a result of these assessments, consider adopting additional measures to increase our resilience even further. This will be assessed further as our design develops and is eventually finalised.
EU Stress Tests
The following documents are in PDF format.