NRC Response to Lessons Learned from Fukushima

Summary

In March 2012, the NRC ordered U.S. nuclear power plants to meet specific deadlines for: 1) 

maintaining key safety functions even if installed electricity sources fail; 2) installing additional 

equipment to monitor spent fuel pool water levels; and 3) installing/improving systems to safely vent 

pressure during an accident (for designs similar to Fukushima Dai-ichi). The NRC’s March 2012 actions 

also asked all U.S. plants for information on comprehensive earthquake and flooding hazard analyses.

The Fukushima Dai-ichi Nuclear Accident

On March 11, 2011, a 9.0-magnitude 

earthquake struck Japan about 231 miles (372 

kilometers) northeast of Tokyo off the Honshu 

Island coast. Eleven reactors at four sites 

(Fukushima Dai-ichi, Fukushima Dai-ni, 

Onagawa, and Tokai) along the northeast coast 

automatically shut down after the quake. 

Fukushima Dai-ichi lost all power from the 

electric grid, with diesel generators providing 

power for about 40 minutes. At that point, an 

estimated 45-foot-high (14 meter) tsunami hit the 

site, damaging many of the generators. Four of 

six Fukushima Dai-ichi reactors lost all power 

from the generators. The tsunami also damaged 

some of the site’s battery backup systems. 

Units 1, 2 and 3 at Fukushima Dai-ichi were 

operating when the earthquake hit. Units 4, 5 and 6 were 

shut down for routine refueling and maintenance. One of 

Unit 6’s diesel generators continued working, providing 

power to keep both Units 5 and 6 (at right in the photo) 

safely shut down. Steam-driven and battery-powered 

safety systems at Units 1, 2 and 3 worked for several 

hours (and more than a day in some cases). Those 

systems eventually failed and all three reactors 

overheated, melting their cores to some degree. The 

conditions in the reactors generated extreme pressure, 

causing leaks of radioactive gas as well as hydrogen. The 
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hydrogen exploded inside the reactor buildings of Units 1, 3 and 4, damaging the buildings and releasing 

more radioactive material from Units 1 and 3. Radioactive contamination spread over a large area of 

Japan, requiring the relocation of tens of thousands of people. The Japanese government has reopened 

limited areas for residents to return to, but many communities remain off-limits. Japanese authorities 

eventually stabilized the damaged reactors with alternate water sources. Work continues to isolate the 

damaged reactors and radioactive contamination from the environment.

NRC’s Short-Term Actions

The NRC’s 24-hour Operations Center in Rockville, Md., began monitoring the situation shortly 

after the earthquake and tsunami occurred. The NRC’s first focus was potential tsunami effects on 

California’s nuclear power plants and other nuclear materials users on the West Coast and in Hawaii, 

Alaska, and U.S. Pacific Territories. By the afternoon of March 11, the agency had fully staffed the 

Operations Center and begun interactions with Japanese regulators. The NRC sent two experts that 

weekend to assist the U.S. Embassy in Tokyo. By March 14, the agency had sent additional staff to 

provide technical support to the U.S. Embassy and the Japanese government. The NRC maintained its 

presence at the U.S. Embassy through December 2011.

On March 16, the NRC, along with other U. S. government agencies, provided technical 

information supporting the U.S. Embassy’s advisory for American citizens to avoid the area within 

50 miles of Fukushima Dai-ichi. The 50-mile recommendation expired in October 2011. The NRC also 

ensured U.S. nuclear power plants took action to prepare for a Fukushima-like event. The NRC told its 

inspectors to independently assess each plant’s level of preparedness. The inspections covered 

procedures to compensate for extensive onsite damage, loss of all alternating current power, and seismic 

and flooding issues, as well as procedures for dealing with a damaged reactor.

NRC’s Long-Term Response

In April 2011, the Commission 

named a formal task force of senior NRC 

experts to examine information from the 

accident. The task force then reviewed NRC 

regulations to determine whether any actions 

were needed to ensure the safety of U.S. 

nuclear power plants. The task force’s 

July 2011 report concluded U.S. reactors can 

continue operating safely while the NRC 

considers enhancements to existing safety 

and emergency preparedness requirements. 

The task force recommended a dozen broad 

enhancement areas for the Commission to 

consider. Later in 2011, the Commission 

approved staff proposals for prioritizing the 

specific actions suggested by the task force, as well as six additional topics related to the events at 

Fukushima.
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The agency also created the Japan Lessons Learned Project Directorate, or JLD, to lead 

implementation of the task force recommendations. The overall progress in completing actions related to 

Fukushima recommendations has allowed the NRC to dissolve the JLD and move its activities into 

regular oversight of operating power reactors.

The agency issued three Orders in March 2012, requiring U.S. reactors to:

• Obtain and protect additional emergency equipment, such as pumps and generators, to support 

all reactors at a given site simultaneously following a natural disaster (pictured below).

• Install enhanced equipment for monitoring water levels in each plant’s spent fuel pool.

• Improve/install emergency venting systems that can relieve pressure in the event of a serious 

accident (only for reactors with designs similar to the Fukushima plant).

Every U.S. 

commercial reactor has

obtained the required

additional onsite portable 

equipment and has 

satisfied the requirements 

of the emergency 

equipment Order. The 

U.S. nuclear industry has 

also established and 

stocked two offsite 

response centers. Every 

operating U.S. reactor has 

met the requirements for 

the spent fuel pool Order.

The NRC 

strengthened the venting 

Order in 2013, requiring 

the vents to handle the pressures, temperatures and radiation levels from a damaged reactor. The revised 

Order also calls for plants to ensure their personnel could operate the vents under those conditions. 

Twenty-eight of 30 reactors covered by the Order have met the requirements of the Order’s first phase, 

and 15 of 30 have met the requirements of the second phase. 

The NRC has also asked all U.S. reactors to re-confirm their flooding and earthquake 

preparedness, as well as re-analyze their earthquake and flooding hazards. All U.S. reactors have

submitted their earthquake and flooding re-analyses. Based on those re-analyses, 49 reactor sites have 

completed limited additional earthquake evaluations. Five of 18 sites have completed more detailed 

seismic probabilistic risk analyses. Forty of 47 sites have completed limited flooding evaluations. Two 

of five sites has completed a more detailed integrated assessment of the flooding impacts on their site.
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Other NRC activities include creating or revising rules related to maintaining key safety 

functions if a plant loses all alternating-current power, and several aspects of emergency preparedness. 

The NRC’s website includes more information on Fukushima-related actions.

September 2018