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U.S. Companies Make Safety Enhancements at Nuclear Energy Facilities; EU and Asia Undertake ‘Stress Tests’
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U.S. Companies Make Safety Enhancements at Nuclear Energy Facilities; EU and Asia Undertake ‘Stress Tests'
Nuclear energy regulators and nuclear plant operators around the world reacted quickly after the March 11 accident at the Fukushima Daiichi nuclear energy facility in Japan, providing assistance to the Japanese where possible and reviewing safety measures at their own facilities. Those initial reviews are being followed by more detailed assessments as more is learned about exactly what happened at Fukushima and why. Regulators and industry alike will scrutinize the Fukushima event to glean lessons that can be applied to nuclear energy facilities globally.
The U.S. nuclear industry has a robust program for critiquing safety measures and sharing lessons learned from Fukushima. The industry already has taken significant measures to enhance safety at America’s nuclear energy facilities. Separately, the U.S. Nuclear Regulatory Commission task force has completed inspections at each U.S. reactor and a 90-day review of the Fukushima accident that yielded several near-term recommendations for the U.S. industry.
In Europe, the European Nuclear Safety Regulators Group (
) and the
agreed in May on the
for the comprehensive risk and safety assessments (“stress tests”) that will be applied to all nuclear energy facilities in the European Union. Regulators from Armenia, Belarus, Croatia, the Russian Federation, Switzerland, Turkey and Ukraine have agreed to conduct the assessments. The Japanese government in July directed electric power utilities in the country to implement similar stress tests at their nuclear energy facilities.
The EU and Japanese stress tests differ somewhat from the U.S. approach to safety reviews. As part of the stress tests, each licensee will perform a rigorous analysis of each nuclear energy facility, viewing it holistically. The analyses will be reviewed by each country’s national regulator. EU regulatory peer teams will then review the results for EU-wide consistency. Upon completion of the stress tests, the national regulators will consider what actions, if any, may be needed to further enhance safety. The U.S. post-Fukushima safety reviews are more targeted and include inspections of facilities, review of training and adding equipment where needed to enhance safety. This action started with a series of instructions from the Institute of Nuclear Power Operations concerning specific systems and components and a list of recommendations from the NRC’s near-term task force on areas for improvement. Detailed analysis and prioritization of recommended actions will follow.
European and Japanese Stress Tests
The purpose of a stress test is to determine how a system performs when pushed to its limit—for example, exposing equipment to extreme temperatures and pressures and pushing it close to the point of failure. Applied to nuclear energy facilities, the stress tests are intended to analyze how plants would respond if subjected to extreme external events—that is, events more severe than those for which they were designed. “One of the most important lessons to be drawn [from Fukushima] is that the unthinkable can happen—that two natural disasters can hit at the same time and knock out the electrical power supply system completely,” the European Commission said in a May
announcing the pending safety assessments.
The EU stress tests are designed to apply more stringent criteria than those originally used in licensing the facilities in order to test the limits of their safety margins. To help ensure that the facilities are tested to their limits, the assessments will not take into account the probability of any events. Additionally, they will assume sequential failure of the defense-in-depth systems and measures in place to prevent accidents, and also assume damage to infrastructure near a facility due to the natural hazard.
The tests are designed to examine how nuclear energy facilities would respond in the event of extreme external events. These include earthquakes, flooding, tornados, airplane crashes and nearby explosions. The facilities must demonstrate that they could cope with a loss of electric power to the site for several days. The individual facility stress tests are scheduled to be completed by the end of 2011. A draft report will be presented to the European Commission in December, and a final report issued in June 2012.
The EU stress tests are to be carried out in three phases. Nuclear energy facility operators will provide information describing how a facility would react in different situations, supported by engineering studies. Next, each national regulator will review the facility reports and decide whether the assumptions are credible. Finally, peer teams composed of regulators from the ENSREG will review the reports to ensure consistency of the tests. The regulator of the country’s reactors being reviewed will not be part of the peer team.
National regulators will review the completed assessments and determine what steps should be taken. However, the stress tests are not a formal regulatory review and the results have no direct enforcement implications.
Safety Assessments, Upgrades at U.S. Nuclear Energy Facilities
The U.S. nuclear energy industry and the independent Nuclear Regulatory Commission began special safety assessments of U.S. plants immediately after the accident at Fukushima. The highest-priority items were completed within 30 days—for example, verifying that backup power supplies for reactor safety systems are protected from severe flooding and earthquakes. Additional assessments and action are ongoing to ensure that U.S. facilities could respond to events that may challenge safe operation of the facilities.
is continuing near-term actions it began to implement immediately after the accident. . U.S. companies since March have taken the following measures to enhance safety:
Verified that all critical safety components, procedures and staffing are in place and functioning to mitigate potential damage from earthquakes, flooding, large fires or explosions. All U.S. companies have completed inspections of systems that protect nuclear energy facilities against these extreme events. Necessary changes to these systems are being undertaken by individual companies.
Taking near-term steps to ensure that storage pools for used nuclear fuel rods are protected at all times, including adding backup sources of cooling water for the storage pools. The industry is acting on additional guidance to all nuclear plant operators to triple-check multiple safety measures for fuel storage pools, including the processes for monitoring the level of cooling water over the fuel.
Continuing to assess the effectiveness of reactor operator fundamentals and training programs. Nuclear plant operators spend every fifth week in simulator training that is an exact replica of the plant’s control room.
Assessing each facility’s ability to maintain vital safety systems and protect the reactor even if a plant loses all AC power for 24 hours. Additional portable equipment could be used to supplement safety equipment added after the 9/11 attacks. These are site-specific measures that would enhance a plant’s capability to mitigate an extended loss of AC power.
Evaluating near-term changes to guidelines that operators use to manage severe accidents as well as broader emergency response guidelines based on lessons learned from the Japanese accident.
Evaluating regional staging of key equipment and supplies to provide a centralized, rapid-response capability that would be available to all nuclear energy facility operators.
Longer-term, the industry is preparing a detailed evaluation of the events in Japan that is necessary to fully understand steps that may be taken at U.S. facilities. Fukushima-related improvements at America’s nuclear energy facilities should be guided by a complete understanding of the events at each of the Fukushima Daiichi reactors. The industry will continue to work with the NRC on the identification and implementation of actions and practices that will make U.S. nuclear energy facilities even safer than they are today. In the meantime, companies that operate nuclear energy facilities will continue to take actions to ensure that we are fully prepared for extreme events, regardless of their origin.
America’s nuclear energy industry has a combined 3,600 years of safe nuclear power plant operating experience, and the industry has protected the public, our workers and the environment throughout five decades of safe operations.
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