It’s been five years since the Fukushima Daiichi accident in Japan. Since that time, U.S. nuclear energy facilities have invested more than $4 billion to better ensure that U.S. reactors can withstand natural events more severe than those assumed in their original design, including upgrading and expanding safety equipment. These substantial investments by operators of the U.S. fleet are laudable. But the accident – and application of the lessons-learned by regulators and licensees in the U.S. – has not triggered a fundamental reassessment of adequacy of the regulatory framework for nuclear power in the United States. Nor should it. More regulation does not necessarily mean more safety.

First, the U.S. nuclear industry took proactive, voluntary steps to address one of the primary reasons for the accident at Fukushima Dai-ichi—the loss of safety-related systems following the occurrence of a beyond-design-basis external event. The design basis for U.S. nuclear plants includes bounding analyses with margin for the external events expected at each site. Natural hazards (e.g., seismic events, flooding) beyond those accounted for in the design basis are highly unlikely, but nevertheless could present challenges in certain circumstances—particularly where there is a loss of both offsite and onsite emergency power. To address this concern, all operators stationed backup safety equipment in protected locations, including diesel-driven pumps and generators, battery packs, and ventilation fans, as well as redundant hoses, cables, connectors, and emergency communication equipment. The industry also voluntarily established two national emergency response centers in Memphis and Phoenix, which can supply reactor sites anywhere in the United States within 24 hours. Because operators took responsibility for implementing these enhancements across the U.S. reactor fleet, there was less of a need for regulators to take formal action, such as issuing orders or conducting a rulemaking, to address these lessons.

Second, there is no indication that the regulatory framework used to evaluate seismic and flooding hazards at U.S. reactors has been fundamentally inadequate. The NRC issued requests for information from U.S. operators seeking information on seismic and flooding hazards. The NRC requested that licensees use present-day information to reevaluate the seismic and flooding that could impact their site. These newly reevaluated hazards, if worse than what the plant had originally calculated, were analyzed to determine if plant structures, systems, or components need to be updated to protect against the new hazard. While those efforts are still ongoing at some plants, the results of the assessments to date do not indicate that a wholesale reconsideration of the regulatory framework for natural hazards is necessary. The NRC has confirmed, based on available information from the hazard reassessments, that all U.S. plants can continue to operate. This demonstrates the robust nature of the NRC licensing framework—even after taking into account the additional information about seismic and flooding hazards developed in the many decades since initial licensing.

In the months after Fukushima, the U.S. nuclear industry and regulators worked diligently to identify the causes and lessons from that accident. And, they’ve expended considerable effort and resources to implement those lessons in the United States. But, five years after Fukushima, it is clear that there were no major “gaps” in the U.S. regulatory framework that needed to be bridged. And, there were no major risks that had been ignored over the years. The NRC did issue orders and will promulgate rules to address certain topics, such as water level instrumentation in spent fuel pools. But, these enhancements are incremental, not fundamental.

So, what have we learned from Fukushima with respect to the U.S. regulatory framework? The examples above suggest two lessons. One is that there is a healthy safety culture at U.S. plants; operators didn’t hesitate to take prompt action to address the circumstances that contributed to the accident at Fukushima. A second is that the regulatory framework in the U.S. is robust and ensures sufficient design margin, even in the face of uncertainty regarding natural hazards and advances in knowledge over time. Taken together, these demonstrate the safety of nuclear power, but also suggest the need to think carefully about imposing regulations that make it more difficult (and more costly) to build and operate reactors.