By Ramzi Jammal, Executive Vice-President and Chief Regulatory Operations Officer Canadian Nuclear Safety Commission
More than four years have passed since a magnitude 9.0 earthquake struck the east coast of Japan and caused a large tsunami, resulting in the tragic loss of thousands of lives and the destruction of more than half a million homes.
It was also the cause of the accident at the Fukushima Daiichi nuclear power plant.
While a large-magnitude earthquake is very unlikely around Canadian nuclear power plants, the event has had significant implications in Canada. The nuclear regulatory focus was shifted from accident prevention to accident prevention and mitigation.
Plainly, this means that we are now more prepared than ever before for the unexpected.
As the accident was unfolding, the Canadian Nuclear Safety Commission (CNSC) activated its Emergency Operations Centre in Ottawa and staffed it 24/7 to monitor the emergency, assess early reports and provide timely, accurate information to Canadians.
We became the trusted source of information for other Canadian government departments and agencies, which were seeking advice for a broad range of matters, from advice for travellers to the safety of foodstuff coming from Japan.
Meanwhile, our immediate focus was directed at Canada’s nuclear power plants. Our inspectors performed immediate walkdowns to assess seismic preparedness, firefighting capability, backup power sources, hydrogen mitigation and spent fuel pool cooling.
Operators of Canadian nuclear facilities were also closely monitoring the event and readily provided the CNSC with their preliminary analyses of the implications for their facilities.
Less than a month after the accident, we convened a task force to evaluate the operational, technical and regulatory implications of the accident.
This task force established a four-year comprehensive action plan, which was subject to extensive public and expert scrutiny, as well as international peer reviews.
As the action plan is scheduled for completion at the end of 2015, now is an ideal time to look back at the work done over the last few years.
Reassessing External Hazards
The Fukushima accident has taught the CNSC and nuclear operators to consider and prepare for the most unlikely events.
And it is with this in mind that hazards previously considered implausible in parts of Canada – such as large earthquakes, strong tornadoes and severe floods – were reassessed using modern tools, including probabilistic safety assessments.
Opportunities to improve the safety of nuclear power plants were identified as part of this process and acted upon whenever possible.
For instance, flood barriers and watertight doors were installed and certain structures reinforced inside facilities.
We also reviewed design requirements for new facilities as they pertain to the assessment of external hazards, to ensure that extreme events were considered in new reactor designs.
Preventing Fuel and Severe Core Damage
When the 15-meter tsunami flooded the plants at Fukushima, all power sources were lost and so was the operators’ ability to continually cool the fuel inside the reactors.
The situation eventually led to the meltdown of three of the six reactors onsite.
A similar event is extremely unlikely to happen in Canada. However, nuclear power plant operators took several steps to further reduce the possibility.
Perhaps most notably, they acquired portable emergency equipment, such as diesel generators, pumps, hoses and additional firetrucks. They also added connections to enable workers to manually open reactor systems to relieve pressure and add water.
The portable equipment is stored onsite and offsite, and can be shared between different facilities.
These improvements were made to ensure reactor fuel remains covered with water and cooled, however severe the accident conditions.
Other improvements to enhance the operators’ ability to prevent fuel and core damage have included upgrades to battery power supply and reactor instrumentation to increase their resistance to extremely severe accident conditions involving high levels of heat, humidity and pressure.
Containing radiation is a fundamental function of nuclear power plants, along with controlling the reactor and cooling the fuel.
Three main enhancements to ensure the protection of containment during severe accident conditions were made to Canadian facilities.
First, the containment buildings that house nuclear reactors were equipped with passive autocatalytic recombiners (PARs) to control hydrogen buildup. This work was already underway before the accident, but it was accelerated.
You may remember the explosions seen on TV during the Fukushima accident. These were caused by hydrogen, which is created in great quantity during severe nuclear accidents.
The PARs control any hydrogen buildup that may be produced as a result of severe conditions. They work without power or operator action, and represent an addition to already present electricity-powered hydrogen igniters or burners.
Second, the CNSC required that operators reassess mechanisms in place to prevent uncontrolled releases. At two facilities, this led to the installation of emergency filtered ventilation (ECFV) systems, which do not require electricity to function and can be activated manually.
These systems provide additional capability to minimize radioactive releases into the environment in case of a severe accident.
Third, in addition to PARs and ECFV systems, cooling units located within containment were upgraded to allow connections to portable power generators. These units allow temperature and pressure to be lowered to protect the reactor and containment structures.
Spent Fuel Pools
Maintaining the structural integrity of spent fuel pools during a severe accident has also been an important lesson learned in light of the Fukushima accident.
Among the changes made, new instrumentation capable of resisting extreme conditions was developed and deployed for measuring water level and temperature.
Additional piping and connections to manually add water to pools and keep the spent fuel submerged at all times were installed. Furthermore, operators investigated speeding up the transfer of spent fuel from the pools to the very robust dry storage systems that exist at all nuclear power plants in Canada.
Severe Accident Management
Beyond the equipment and the design changes discussed above, the CNSC requested that plant operators review their procedures and training to enable them to respond effectively to accidents.
For the same reason, severe accident management guidelines were revised. Operators were also asked to identify alternate emergency facilities and to reassess emergency communications systems.
Several challenging emergency exercises and drills – involving accident scenarios previously not considered credible – have since been conducted to test guidelines and the deployment of the newly acquired equipment.
In addition, plant operators have enhanced their existing modelling capabilities to predict reactor behaviour during an accident.
Software has been enhanced so that it now models severe accidents, including those involving multiple units.
From a regulatory perspective, emergency dose limits for workers during an emergency are being added to Canada’s Radiation Protection Regulations to bring them in line with international guidance.
But improvements to nuclear emergency preparedness did not stop there.
Offsite nuclear emergency preparedness is an important and complex responsibility, which is shared by multiple levels of government in Canada.
Following the Fukushima accident, reviews of protective actions were conducted by federal, provincial and regional authorities. These reviews allowed for the resolution of long-standing issues pertaining to public alerting systems.
Potassium iodide (KI) pill distribution has been made mandatory in a 50-km radius around the facilities, with delivery to the doorstep of every household within the 8- or 10-km radius.
As part of re-licensing requirements, the CNSC now mandates plant operators to submit offsite emergency plans as part of their application to ensure their periodic review in public fora.
Radiation levels were a great source of concern and confusion during Fukushima. As part of our action plan, we requested that plant operators add real-time radiation monitoring stations around their facilities. This is in addition to government-operated monitoring stations across the country.
Tools to communicate information (including radiation data) to the public in case of an emergency were also developed or improved. These have been supplemented with regulatory requirements for licensees to make public disclosures in case of incidents.
The computer modelling capability to predict radioactive releases and their dispersion into the environment was also reassessed and enhanced to cover a wider range of accident scenarios.
Large multi-jurisdictional exercises have since been conducted to test roles and responsibilities among different players during a nuclear emergency, and test the tools at their disposal during a nuclear emergency.
Amendments were made to both regulations and numerous regulatory documents on a wide range of topics from site evaluation to environmental protection to reflect lessons learned. The CNSC has also established requirements to conduct periodic safety reviews, which will lead plant operators to complete extensive reassessments of their facilities on a 10-year cycle.
In addition to improvements to its own requirements, the CNSC has also worked actively with regulators from around the world, supporting the work of the International Atomic Energy Agency (IAEA), and the Organisation for Economic Co-operation and Development – Nuclear Energy Agency.
For instance, I myself had the honour of serving as co-chair of one of the working technical groups who prepared the IAEA Director General’s report on the Fukushima accident.
Together, we have been able to better analyze what happened at Fukushima and identify what can be done to further enhance the safety of our nuclear facilities.
The Bottom Line
Canada’s major nuclear facility operators have demonstrated a high level of commitment to implement the post-Fukushima action plan in our country and in some cases have even taken a leadership role internationally.
Overall, the improvements related to post-Fukushima actions in Canada have had a sizeable effect on the safety of our facilities.
For instance, through probabilistic safety assessment, plant operators have been able to demonstrate that the risk for core damage or large release frequency has been reduced significantly.
Improved mitigation measures established through the action plan have also allowed us to further reduce potential radiological consequences should an accident occur.
I firmly believe that national nuclear regulators, like the CNSC, should always strive for continuous safety improvement and demonstrate a sustained commitment to transparency. We are always on the lookout for potential lessons learned from operational experience, both from within the nuclear industry and from other safety-conscious industries.
International nuclear bodies, such as the IAEA and the World Association of Nuclear Operators, should not hesitate to name operators or countries that do not take nuclear safety with the seriousness that it deserves.
Above all, the Fukushima accident taught us to expect the unexpected. And this is why we should leave no room for complacency as we continue to improve the safety of nuclear energy.