In This Section
(Last updated 9/14/2011)
- What is the nuclear industry doing in the short-term to respond to the accident at the Fukushima nuclear energy facility?
- Could an accident like the one at Japan’s Fukushima Daiichi nuclear plant happen in the United States?
- How will the U.S. nuclear industry assess the impact of the Fukushima Daiichi accident?
- How is the Nuclear Regulatory Commission responding to the accident at Fukushima Daiichi?
- How serious were the releases of radiation from Fukushima Daiichi? Do they represent a threat to human health to Americans? Will we see an increase in cancer rates in future years?
- How many U.S. reactors use the Mark I containment design used at the Fukushima Daiichi Plant?
- There have been questions raised in the past about the BWR Mark I containment like that at Fukushima Daiichi. Some critics have pointed to a comment by an Nuclear Regulatory Commission official in the early 1980s: “Mark I containment, especially being smaller with lower design pressure, in spite of the suppression pool, if you look at the WASH 1400 safety study, you’ll find something like a 90 percent probability of that containment failing.”
- What happens when you have a complete loss of electrical power to the pumps in a BWR-3 or 4 reactor with Mark I containment like Fukushima Daiichi?
- Are U.S. emergency planning requirements and practices adequate to deal with a situation like that faced at Fukushima Daiichi?
- Is this accident likely to result in changes to regulatory requirements for U.S. nuclear plants in seismically active areas? Will those regulatory requirements be revisited and made more robust?
- What would happen to the used fuel in the storage pools if cooling were lost?
- Given that Fukushima Daiichi 1 is a 1970s-vintage plant, do you anticipate increased regulatory requirements and scrutiny on U.S. plants of similar vintage? Do you think the accident will have an impact on license renewal of the older U.S. nuclear energy facilities?
- Do the events indicate that iodine tablets should be made widely available during an emergency?
- What caused the explosions at Fukushima Daiichi Units 1-3?
- Did the reactor cores melt at any of the Fukushima Daiichi reactors? Was there any fuel damage?
- Are there any concerns associated with the use of mixed oxide fuel in reactor 3?
- Do the events in Japan indicate that evacuation zones around plants should be extended?
- What will be the impact of the Fukushima Daiichi accident on new nuclear plant construction in the United States?
- What is the Institute for Nuclear Power Operations (INPO)?
- Does the Nuclear Regulatory Commission rank U.S. nuclear plants by seismic risk?
- What magnitude earthquakes are U.S. nuclear power plants designed to withstand?
- Can significant damage to a nuclear plant like we see in Japan happen in the U.S. due to an earthquake? Are the Japanese nuclear plants similar to U.S. nuclear plants?
- How are decisions made at U.S. nuclear reactors in the event of an accident?
- What are the dangers of radioactive iodine?
- What insurance coverage does the U. S. nuclear industry have for property damage, business interruption and liability?
- Will the vents on boiling water reactor designs in the United States that are similar to the Fukushima Daiichi plant operate if needed to release the buildup of gases?
1. What is the nuclear industry doing in the short-term to respond to the accident at the Fukushima nuclear energy facility?
The nuclear energy industry’s top priority remains providing Japan with the support necessary to achieve safe shutdown of the Fukushima reactors.
The accident at Fukushima Daiichi was caused, in part, by extraordinary and unpredicted natural forces that were beyond the facility’s design parameters. Even though the full extent of damage to these reactors still is unknown, the combination of the earthquake and the tsunami challenged the structural integrity and safety of the facility. As more is learned about the Japanese events, more long-term corrective actions will be developed.
The U.S. nuclear energy industry began taking steps within days of the Fukushima Daiichi accident to ensure that U.S. reactors can respond to events that may challenge safe operation of the facilities. The industry has completed actions that include:
- Verifying that all critical safety components, procedures and staffing are in place and functioning to prevent damage from earthquakes, flooding or large fires. 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 where warranted.
- Taking near-term precautions to ensure that storage pools for used nuclear fuel rods are protected at all times, including adding backup sources of cooling water for the 40-foot-deep 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 in a room 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 terrorist attacks on the United States. 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 operating procedures based on lessons learned from the Japanese accident.
- Completing a detailed evaluation of the Fukushima Daiichi events so that the facts of the event and Tokyo Electric Power’s responses can be appropriately understood. 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, said Tony Pietrangelo, the Nuclear Energy Institute’s senior vice president and chief nuclear officer.
- Evaluating regional staging of key backup equipment and supplies to provide a centralized, rapid-response capability that would be available to all nuclear energy facilities.
The U.S. nuclear energy industry also has created a leadership structure among major electric-sector organizations to integrate and coordinate the industry’s ongoing response to the Fukushima Daiichi accident. Supported by senior electric utility executives and reactor vendors, the Nuclear Energy Institute, the Institute of Nuclear Power Operations and the Electric Power Research Institute are working through a new steering committee to coordinate and oversee response activities.
2. Could an accident like the one at Japan’s Fukushima Daiichi nuclear plant happen in the United States?
It is difficult to answer this question until we have a better understanding of the precise problems and conditions that faced the operators at Fukushima Daiichi. We do know, however, that Fukushima Daiichi reactors 1-4 lost all AC power (offsite power and emergency diesel generators). This situation is called “station blackout.” U.S. nuclear energy facilities are designed to cope with a station blackout event. U.S. nuclear plants are required to conduct a “coping” assessment and develop a strategy to demonstrate to the Nuclear Regulatory Commission that they can maintain the plant in a safe condition during a blackout. These assessments, proposed modifications and operating procedures are reviewed and approved by the Nuclear Regulatory Commission. Several plants have installed additional AC power sources.
In addition, since the terrorist attacks of Sept. 11, 2001, U.S. nuclear energy facilities and operating practices are designed to mitigate severe events, such as aircraft impact, that include station blackout and damage to large areas of the plant. U.S. nuclear energy facilities are equipped to maintain safe conditions in extreme events and operations staff are trained to manage them.
U.S. nuclear plant designs include measures to protect against seismic events, tsunamis and other natural forces. It is important not to extrapolate earthquake and tsunami data from one location of the world to another when evaluating these natural hazards. These catastrophic natural events are region and location specific, based on geological fault line locations.
3. How will the U.S. nuclear industry assess the impact of the Fukushima Daiichi accident?
Until we clearly understand what has occurred at the Fukushima Daiichi nuclear energy facilities, it is difficult to speculate about the long-term impact on the U.S. nuclear energy program. The nuclear industry and the U.S. Nuclear Regulatory Commission will conduct detailed reviews of the accident, identify lessons learned (both in terms of plant operation and design) and will incorporate those lessons learned into the design and operation of U.S. nuclear energy facilities. When we fully understand the facts surrounding the event in Japan, we will use those insights to make nuclear energy even safer.
In the long-term, we believe that the U.S. nuclear energy enterprise is built on a strong foundation:
- reactor designs and operating practices that incorporate layer upon layer of diverse and redundant safety systems
- a strong, independent regulatory infrastructure
- a transparent regulatory process that provides for public participation in licensing decisions, and
- a continuing and systematic process to identify lessons learned from operating experience and to incorporate those lessons.
4. How is the Nuclear Regulatory Commission responding to the accident at Fukushima Daiichi?
A Nuclear Regulatory Commission task force, which in July completed a three-month assessment of agency policies and regulations in light of the accident, said, “The current regulatory approach, and more importantly, the resultant plant capabilities, allow the task force to conclude that a sequence of events like the Fukushima accident is unlikely to occur in the United States and some appropriate mitigation measures have been implemented, reducing the likelihood of core damage and radiological releases. Therefore, continued operation and continued licensing activities do not pose an imminent risk to public health and safety.”
The task force added, however, that “a more balanced application of the commission’s defense-in-depth philosophy using risk insights would provide an enhanced regulatory framework that is logical, systematic, coherent, and better understood.” This framework, the task force added, would lead to “increased capability to address events of low likelihood and high consequence, thus significantly enhancing safety.” The task force made recommendations in five broad areas:
- clarifying the regulatory framework
- ensuring protection
- enhancing mitigation
- strengthening emergency preparedness
- improving efficiency of NRC programs.
5. How serious were the releases of radiation from Fukushima Daiichi? Do they represent a threat to human health to Americans? Will we see an increase in cancer rates in future years?
In recent testimony before Congress, epidemiologist John Boice, who has spent his career studying human exposure to radiation, determined that the health consequences for Americans from the accident are minimal. Boice determined that a small number of Tokyo Electric Power Co. workers, including two who stepped into contaminated water, received doses that could slightly increase their lifetime risk of developing cancer. Of the Japanese public, Boice said, “Thus, while Fukushima is clearly a major reactor accident, the potential health consequences associated with radiation exposures in terms of loss of life and future cancer risk are small.”
Of the radiation detected in the United States, which was thousands of times below government limits, he said, “The tiny amounts of detected radioactive materials from Fukushima pose no threat to human health. They represent, at most, only a tiny fraction of what we receive each day from natural sources, such as the sun, the food we eat, the air we breathe and the houses we live in.”
6. How many U.S. reactors use the Mark I containment design used at the Fukushima Daiichi Plant?
Twenty-three U.S. nuclear plants are boiling water reactors (either BWR-2, BWR-3 or BWR-4) and use the Mark I containment: Browns Ferry 1, 2 and 3; Brunswick 1 and 2; Cooper; Dresden 2 and 3; Duane Arnold; Hatch 1 and 2; Fermi; Hope Creek; Fitzpatrick; Monticello; Nine Mile Point 1; Oyster Creek; Peach Bottom 2 and 3; Pilgrim; Quad Cities 1 and 2; Vermont Yankee.
Six U.S. reactors (Monticello in Minnesota, Pilgrim in Massachusetts, Dresden 2 and 3 and Quad Cities 1 and 2 in Illinois) are the same base design as the Fukushima Daiichi 1 design (BWR-3 design with Mark I containment).
Fifteen U.S. reactors (Browns Ferry 1, 2 and 3 in Alabama; Brunswick 1 and 2 in North Carolina; Cooper in Nebraska; Duane Arnold in Iowa; Hatch 1 and 2 in Georgia; Fermi in Michigan; Hope Creek in New Jersey; Fitzpatrick in New York; Peach Bottom 2 and 3in Pennsylvania; Vermont Yankee in Vermont) have the same basic design as Fukushima Daiichi 2, 3 and 4 (BWR-4 design with Mark 1 containment).
Although these are the same basic reactor design, specific elements of the safety systems in U.S. reactors vary based on Nuclear Regulatory Commission requirements.
7. There have been questions raised in the past about the BWR Mark I containment like that at Fukushima Daiichi. Some critics have pointed to a comment by an Nuclear Regulatory Commission official in the early 1980s: “Mark I containment, especially being smaller with lower design pressure, in spite of the suppression pool, if you look at the WASH 1400 safety study, you’ll find something like a 90 percent probability of that containment failing.”
The Mark I containment meets all Nuclear Regulatory Commission design and safety requirements to protect public health and safety. The WASH-1400 safety study referenced was performed in 1975. The NRC has analyzed the Mark I containment design in great detail since then. The agency’s analysis found that the BWR Mark I risk was dominated by two scenarios: station blackout a loss of offsite electrical power and failure of a reactor to automatically shut down. The NRC subsequently established regulations for both of these sequences and took other steps to enhance containment safety.
GE has made design changes to the Mark I containment, including modifications to dissipate energy released to the suppression pool and supports to accommodate higher dynamic loading and pressures that could be generated. These retrofits were approved by the NRC and made to all U.S. plants with the Mark I containment.
8. What happens when you have a complete loss of electrical power to the pumps in a BWR-3 or 4 reactor with Mark I containment like Fukushima Daiichi?
If plant operators cannot move water through the reactor core, the water in the reactor vessel begins to boil and turn to steam, increasing pressure inside the vessel. In order to keep the reactor vessel pressure within the design limits, this steam is piped into what is called a “suppression pool” of water or “torus” – a large circular tank that sits beneath the reactor vessel.
Eventually, the water in the suppression pool reaches “saturation” meaning it cannot absorb any additional heat and it, too, begins to boil, increasing pressure in containment. In order to stay within design limits for the primary containment, operators reduce pressure by venting steam to the atmosphere.
If operators cannot pump additional water into the reactor vessel, the water level will begin to drop, uncovering the uranium fuel rods. If the fuel remains uncovered for an extended period, fuel damage, possibly including melting, may occur. If there is fuel damage, and steam is being vented, small quantities of radioactive materials will escape to the environment.
9. Are U.S. emergency planning requirements and practices adequate to deal with a situation like that faced at Fukushima Daiichi?
Yes. Energy companies develop and perform graded exercises of sophisticated emergency response plans to protect the public in the event of an accident at a nuclear power plant. Emergency response is coordinated with local, state and federal governments. The U.S. Nuclear Regulatory Commission reviews and approves all plans. In addition, the Nuclear Regulatory Commission coordinates approval of plans with the Federal Emergency Management Agency, which has the lead federal role in emergency planning beyond the nuclear energy facility site.
An approved emergency plan is required for the plant to maintain its federal operating license. The plan must provide protective measures, such as sheltering or evacuation of residents within a 10-mile radius of the facility. In 2001, the Nuclear Regulatory Commission issued new requirements and guidance that focus in part on emergency preparedness at plant sites in response to security threats. The industry has implemented these measures, which address such issues as on-site sheltering and evacuation, public communications, and emergency staffing in the specific context of a security breach.
As part of the plan, nuclear energy facility operators also must staff emergency centers within one hour of the emergency to provide support to the facility’s staff during the event. This support would include:
- technical expertise (engineering, operations, maintenance and radiological controls)
- offsite communications and interfaces with local, state and federal governments
- security and logistics
Several communities have used the structure of nuclear energy facility plans to respond to other types of emergencies. For example, during the 2007 wildfires in California, county emergency officials drew on relationships and communications links they had established during their years of planning for nuclear-energy-related events.
10. Is this accident likely to result in changes to regulatory requirements for U.S. nuclear plants in seismically active areas? Will those regulatory requirements be revisited and made more robust?
Seismic requirements tailored to each facility protect the plants and provide for public safety. Every U.S. nuclear energy facility has undergone an in-depth seismic analysis and is designed and built to withstand without any breach of safety systems an earthquake greater than the maximum projected earthquake that could occur in its area. In the event of an earthquake, reactors must be able to shut down without a release of radiation.
In America, engineers and scientists calculate the potential for earthquake-induced ground motion for a site using a wide range of data and review the impacts of historical earthquakes up to 200 miles away. Past earthquakes within 25 miles are studied in greatest detail. Engineers use this information to determine the maximum potential earthquake that could affect the site. Each reactor is built to withstand the respective strongest earthquake plus an additional margin of safety. Experts identify the potential ground motion for a given site by studying various soil characteristics directly under the plant. For example, a site that features clay over bedrock will respond differently during an earthquake than a hard-rock site. Taking all of these factors into account, experts determine the maximum ground motion the plant must be designed to withstand. As a result, the design requirements for resisting ground motion are greater than indicated by historical records for that site.
Given the seismic history in California, for example, plants in that state are built to withstand a far higher level of seismic activity than plants in many other parts of the country.
11. What would happen to the used fuel in the storage pools if cooling were lost?
We do not know the precise condition of the used fuel storage pools at the Fukushima Daiichi plant, but the fuel in all the pools is completely covered by water. The water both cools the fuel and provides shielding that prevents the release of radiation.
Used nuclear fuel at the Fukushima Daiichi plant is stored in seven steel-lined concrete pools (one at each of the six reactors, plus a shared pool) and at a concrete and steel container storage facility (nine containers). Sixty percent of the used fuel on site is stored in the shared pool, in a building separated from the reactor buildings; one-third of the used fuel is distributed between the six reactor fuel storage pools, and the remaining 6 percent is stored in the nine dry storage containers. There are no safety concerns regarding the used fuel in dry storage at Fukushima Daiichi. The used fuel pools at the Fukushima Daiichi reactors are located at the top of the reactor buildings for ease of handling during refueling operations.
Used fuel pools are robust concrete and steel structures, designed to maintain temperature and water levels sufficient to provide cooling and radiation shielding. The water level in a used fuel pool typically is 16 feet or more above the top of the fuel assemblies.
If the cooling system cannot function, the heat generated by the used fuel would result in a slow increase in the temperature of the pool’s water. The operating temperature of the pools is typically around 40 degrees centigrade or 100 degrees Fahrenheit (the boiling point for water is 100 C or 212 F). The slow increase in temperature would result in an increased, but slow, evaporation rate. The exact rate would depend on the amount of used fuel in the pool and how long it has cooled. Given the depth of water above the used fuel assemblies; operators would have time to use another way to add water to the pools before the fuel became exposed.
At the surface of the used fuel pool, the radiation dose typically is less than 2 millirem per hour. If the water level decreases, the radiation level would increase, which would be detected by nearby radiation monitors.
12. Given that Fukushima Daiichi 1 is a 1970s-vintage plant, do you anticipate increased regulatory requirements and scrutiny on U.S. plants of similar vintage? Do you think the accident will have an impact on license renewal of the older U.S. nuclear energy facilities?
The U.S. nuclear energy industry and the Nuclear Regulatory Commission are analyzing the events at Fukushima Daiichi to identify lessons learned and incorporate those lessons, as appropriate, into the design and operation of U.S. nuclear energy facilities.
The U.S. industry routinely incorporates lessons learned from operating experience into its reactor designs and operations. For example, because of the 1979 accident at Three Mile Island, the industry learned valuable lessons about hydrogen accumulation inside containment. Many companies operating boiling water reactors added a modification referred to as an emergency vent or direct vent. This enables the plant to vent gases that may build up in the primary containment through high-pressure piping. This prevents over-pressurization of the containment structure.
13. Do the events indicate that iodine tablets should be made widely available during an emergency?
The thyroid gland preferentially absorbs iodine and does not differentiate between its radioactive and nonradioactive forms. The ingestion of nonradioactive potassium iodide (KI), if taken within several hours of likely exposure to radioactive iodine, can protect the thyroid gland by blocking further uptake of radioactive forms of iodine. KI does not protect any other part of the body, nor does it protect against any other radioactive element.
The Nuclear Regulatory Commission has made available KI tablets to states that have requested it for residents within the 10-mile emergency planning zone of a nuclear power plant. If necessary, KI is to be used to supplement other measures, such as evacuation, sheltering in place, and control of the food supply, not to take the place of these actions. The Environmental Protection Agency and the Food and Drug Administration have published guidance for state emergency responders on the dosage and effectiveness of KI on different segments of the population. According to the EPA guidance, “KI provides optimal protection when administered immediately prior to or in conjunction with the release of radiation from a facility.”
Few people beyond the 10-mile emergency planning zone of a nuclear plant are at risk of exposure to radiation and radioactive materials, including radioactive iodine. Beyond 10 miles, the major risk of radioiodine exposure is from ingestion of contaminated foodstuffs, particularly milk products. Both the EPA and the FDA have published guidance to protect consumers from contaminated foods.
14. What caused the explosions at Fukushima Daiichi Units 1-3?
The explosions at Fukushima Daiichi were caused by a buildup and ignition of hydrogen in the secondary containment buildings.
Uranium fuel pellets are enclosed in metal tubes made of a zirconium alloy. When exposed to very high temperatures, the zirconium reacts with water to form zirconium oxide and hydrogen. This appears to have happened at Fukushima Daiichi reactors 1 and 3, when a portion of the uranium fuel was uncovered. It is assumed that hydrogen leaked into the reactor containment building, accumulated there, and ignited.
The explosion in reactor 2 appears to have happened due to a similar phenomenon. The hydrogen appears to have ignited inside the primary containment area.
15. Did the reactor cores melt at any of the Fukushima Daiichi reactors? Was there any fuel damage?
Fukushima Daiichi 1, 2, and 3 have experienced significant fuel damage, since the fuel rods or portions of the fuel rods were not covered with cooling water for some period of time. Although fuel melting may have occurred, there is no evidence complete core damage at any reactor.
16. Are there any concerns associated with the use of mixed oxide fuel in reactor 3?
Mixed oxide fuel is a combination of uranium oxide and plutonium oxide, and is not used in U.S. reactors, except for limited testing. MOX fuel does not pose any additional threat when compared with the traditional uranium oxide fuel assemblies. Reactor 3 at Fukushima Daiichi is the only nuclear plant at the site using MOX fuel. MOX fuel in reactor 3 represents less than 6 percent of the total fuel in the core. This fuel had been in the reactor for less than five months. Due to these factors, and the relatively small differences between the radionuclide content of MOX and low-enriched uranium fuel, the use of MOX fuel has not had a significant impact on the offsite releases of radioactivity.
17. Do the events in Japan indicate that evacuation zones around plants should be extended?
Events at the Fukushima Daiichi plant should not affect emergency planning requirements in the United States.
The basis for the 10-mile emergency planning zone around U.S. nuclear energy facilities as determined in 1978 by a multi-agency federal task force remains valid. In the United States, a nuclear plant’s emergency response plan must include pre-planned protective measures, such as sheltering in place and evacuation of the public, if necessary, from within a 10-mile radius of the facility. Additional protective measures may be implemented as conditions warrant at the direction of state and local authorities, with guidance from the plant site emergency director and the Nuclear Regulatory Commission. Japan uses a similar plan. The Japanese government initially issued evacuation orders for a 2-mile radius around Fukushima Daiichi, and later expanded the evacuation zone to a 12-mile radius.
18. What will be the impact of the Fukushima Daiichi accident on new nuclear plant construction in the United States?
New nuclear power plant construction in the United States is in the early stages and proceeding in a deliberate fashion. A Nuclear Regulatory Commission task force studying procedures and regulations in light of Fukushima Daiichi said American plants are safe and there was no reason for licensing activities to proceed.
The nuclear industry uses layers upon layers of safety precautions and, through its focus on continuous learning, will incorporate lessons learned from the events in Japan into the ongoing process of designing, licensing and building new nuclear energy facilities.
Two companies have started site preparation and other construction-related activities for new nuclear energy facilities in Georgia and South Carolina. These companies expect to receive their combined construction and operating licenses from the Nuclear Regulatory Commission in late 2011 or early 2012. Both projects use a light water reactor design with advanced safety features.
In addition, several other companies are moving forward with design, licensing and – at the appropriate time – construction of reactors to meet growing electricity demand for the longer term.
Although America’s 104 nuclear energy facilities are safe and meet all requirements necessary to protect public health and safety, these new designs are even safer.
19. What is the Institute for Nuclear Power Operations (INPO)?
INPO is a non-profit industry organization that was established in 1980 in response to the nuclear accident at Three Mile Island. INPO – which is funded by the industry – has a mission to promote the highest levels of safety and reliability at U.S. nuclear plants. It achieves its goals through independent plant evaluations, event analysis and information exchange, training and accreditation of plant training programs, and assistance for plants that have operating challenges.
20. Does the Nuclear Regulatory Commission rank U.S. nuclear plants by seismic risk?
The NRC does not rank nuclear plants by seismic risk. The objective of the agency’s safety and risk assessment for earthquakes (GI-199) was to perform a conservative, screening-level assessment to evaluate if further investigations of seismic safety for operating reactors in the central and eastern U.S. are warranted, consistent with NRC directives. The results of the assessment should not be interpreted as definitive estimates of plant-specific seismic risk because some analyses were very conservative making the calculated risk higher than in reality. The nature of the information used (both seismic hazard data and plant-level fragility information) make these estimates useful only as a screening tool.
21. What magnitude earthquakes are U.S. nuclear power plants designed to withstand?
The Nuclear Regulatory Commission said in an August 25, 2011, statement that U.S. reactors are required to withstand a predicted level of ground motion, or acceleration, specific to a given site. Ground acceleration is measured in relation to “g,” the acceleration caused by Earth’s gravity. The safety standard for nuclear energy is not based on the magnitude of an earthquake.
An earthquake’s magnitude, often described on the Richter scale, is an expression of how much energy the quake released. It’s not possible to transform a given magnitude alone to ground acceleration at a site. Several important factors affect the relationship between an earthquake’s magnitude and associated ground acceleration, including the distance from the earthquake, the depth of the quake and the site’s local geology (i.e., hard rock or soil). A small earthquake close to a site could therefore generate the same peak ground acceleration as a large earthquake farther away.
The NRC’s requirements call for a nuclear power plant’s design to account for ground acceleration that is appropriate for its location, given the possible earthquake sources that may affect the site and the makeup of nearby faults, etc. Existing U.S. plants were designed on a “deterministic” or “scenario earthquake” basis. In other words, examination of an area’s seismological history provides an understanding of the largest earthquake and associated ground acceleration expected at a plant site.
In 2011, the agency expects to provide existing plants a seismic analysis tool based on work related to applications for new plants, along with the latest information on earthquake sources, so that the plants can perform an updated review. Applications for new nuclear power plants have taken a “probabilistic” approach to determining seismic hazards, looking at a wide range of possible quakes from sources that could affect a given site. The NRC has spent several years examining how these newer techniques can be used to re-evaluate existing nuclear power plant sites.
22. Can significant damage to a nuclear plant like we see in Japan happen in the U.S. due to an earthquake? Are the Japanese nuclear plants similar to U.S. nuclear plants?
The U.S. nuclear industry expects the unexpected and plans for it. All U.S. nuclear energy facilities are built to withstand severe natural forces, including earthquakes, tsunamis and hurricanes. Even nuclear plants that are located within areas with low and moderate seismic activity are designed for safety in the event of such a natural disaster. The Nuclear Regulatory Commission requires that structures and systems be designed to take into account even rare and extreme seismic and tsunami events. In addition to the design of the plants, the industry’s comprehensive defense-in-depth approach includes emergency response planning and detailed accident management guidelines to inform operator responses to these types of events.
The Japanese facilities are similar in design to some U.S. reactors. However, the Nuclear Regulatory Commission has required modifications to U.S. plants since they were built, including design changes to control hydrogen and pressure in the reactor containment structure. The NRC also has required plants to provide additional equipment and plan steps to mitigate damage from large fires and explosions. The measures include providing reactor and spent fuel pool cooling and an additional means to power other equipment on site.
23. How are decisions made at U.S. nuclear reactors in the event of an accident?
When an abnormal operating condition occurs at U.S. nuclear plants, the control room manager has 15 minutes to classify the severity of the event using regulatory criteria. Once the classification is made, site personnel promptly notify state and local officials and the Nuclear Regulatory Commission. The control room manager becomes the emergency director for the event and is empowered to make decisions at the site for actions that maintain the safety of the reactor protect the public.
Within an hour, the full emergency response organization is assembled, including all technical disciplines and communications specialists to ensure state and local officials and the public receive information. The Nuclear Regulatory Commission’s operations center and Nuclear Regulatory Commission inspectors at the site will provide independent oversight of the event and monitor plant data. If the severity of the event requires protective actions for the public (sheltering, evacuation, potassium iodide distribution, etc.), state officials will make the decisions to implement these measures based on recommendations from the site emergency director and the NRC. Once a decision to recommend protective action is made, the state officials will notify the public within 15 minutes.
24. What are the dangers of radioactive iodine?
Iodine 131, or radioactive iodine, is a fission product produced in a commercial nuclear reactor and used in medical treatments. It forms a vapor that can be transported in the air. Iodine 131 is released at minute levels from nuclear power facilities during normal operation. It has been detected in Japan at higher levels after the events at the Fukushima Daiichi plant. There is no health concern for U.S. residents from these releases in Japan. Iodine 131 decays significantly in just eight days and is harmless in about two months.
If ingested, radioactive iodine concentrates in the thyroid gland. In high concentrations, the primary health hazard is thyroid cancer. Ingesting potassium iodide blocks the radioactive iodine from the thyroid gland, thereby, decreasing its effects. Potassium iodide should be taken only after a recommendation from local health officials.
25. What insurance coverage does the U. S. nuclear industry have for property damage, business interruption and liability?
Nuclear Electric Insurance Limited (NEIL), the U.S. industry’s mutual insurance company, provides insurance coverage for accidental property damage and extended outages resulting from an accident. For property damage and on-site decontamination, up to $2.75 billion is available to each commercial reactor site. The policies provide coverage for direct physical damage to, or destruction of, the insured property as a result of an accident. The policies prioritize payment of expenses to stabilize the reactor to a safe condition and then decontaminate the plant site.
NEIL’s Accidental Outage program provides insurance (similar to commercial business interruption coverage) of up to $490 million to cover a prolonged accidental outage at a reactor. Following a deductible period, a maximum weekly indemnity of $4.5 million/week is available.
American Nuclear Insurers (ANI), a joint underwriting association of major U. S. insurance and reinsurance companies, provides third-party liability coverage. ANI’s liability coverage satisfies the requirements of the federal Price-Anderson Act, the legal framework for handling public liability claims that could arise in the event of a nuclear energy incident.
Under the Price-Anderson Act, companies that own nuclear energy facilities are required to maintain the maximum level of financial protection commercially available, and are also required to participate in a secondary financial protection program managed by ANI. The initial limit of liability for reactor sites is $375 million. Should an accident at any reactor result in personal injury or off-site damages in excess of $375 million, all power reactor operators can be charged a retrospective premium, creating a combined level of protection of nearly $12.6 billion.
26. Will the vents on boiling water reactor designs in the United States that are similar to the Fukushima Daiichi plant operate if needed to release the buildup of gases?
As a New York Times article (May 18, 2011) explains, there are multiple potential explanations for failure of venting systems in Japan to prevent hydrogen from being leaked into the reactor buildings due to elevated primary containment pressures. It is premature to speculate the degree to which system design or failure of flooded emergency power systems or timeliness of operational decisions played a role in the subsequent hydrogen explosions at the Fukushima Daiichi plant.
U.S. reactors with designs similar to the Fukushima Daiichi plant include features that allow operators to vent gases from the reactor in an emergency. These boiling water reactors use specially designed vents that include the following features:
- Emergency valves used to open and close these vents have multiple backup operational capabilities including remote operation from the control room, backup controls and accessibility for manual control.
- The vent valves and mechanisms to operate them are tested on a regular basis to ensure they are working.
- The vent valves and mechanisms to operate the valves are maintained through the same program applied to all plant systems and components so that the reliability of the valves is maintained at all times.
- Under NRC regulation, reactor operators in the control room have full authority to vent gases from the reactor in a timely manner. Control room managers do not need additional authorization from either their company’s executive management or government regulators to open vents when they determine it is needed.
- Reactor operators spend every fifth week in training to maintain safety during extreme events. Part of this training takes place in an exact replica of the control room at each nuclear energy facility and incorporates containment venting scenarios. Plant operators must continually undergo requalification training in venting and other safety procedures.
- Emergency venting also is part of the training for emergency response drills.
For additional information on the Nuclear Energy Institute’s post-Fukushima activities and details on safety at U.S. nuclear energy facilities: http://safetyfirst.nei.org.
For additional information from the Nuclear Energy Institute: http://www.nei.org.
For additional information on Nuclear Regulatory Commission post-Fukushima activities: http://www.nrc.gov/japan/japan-info.html.
For additional information from the Nuclear Regulatory Commission on seismic qualification of the U.S. nuclear plants: http://www.nrc.gov/japan/faqs-related-to-japan.pdf.
For additional information from the Food and Drug Administration on Japanese food products and potassium iodide supply: http://www.fda.gov/NewsEvents/PublicHealthFocus/ucm247403.htm.
For additional information from the Environmental Protection Agency on radiation monitoring in the United States: http://www.epa.gov/japan2011/japan-faqs.html.