NRC Greenlights Final Rule Governing Nuclear Plant Mitigation of Severe Events 

Credit to Author: Sonal Patel| Date: Fri, 25 Jan 2019 15:19:31 +0000

A final rule the Nuclear Regulatory Commission (NRC) plans to publish this spring to replace pivotal actions it issued after the Fukushima accident will require U.S. nuclear generators to ensure they can mitigate severe events at reactors within a two-year compliance timeframe.

More than three years after it was proposed, the NRC’s five commissioners on Jan. 24 approved the final “Mitigation of Beyond-Design-Basis Events(MBDBE)” rule (SECY-16-0142), and directed staff to publish it in the Federal Register over the next few months.

The final rule, which is based on years of lessons learned from the March 2011 accident at the Fukushima Daiichi plant in Japan, seeks to amend existing rules that establish regulatory requirements for nuclear power reactor applicants and licensees to mitigate “beyond-design-basis events.” The NRC describes the technical term, “beyond-design-basis events,” as “accident sequences that are possible but were not fully considered in the design process because they were judged to be too unlikely.”

According to the NRC, the final MBDBE rule will apply more broadly than either the NRC’s March 2013 Containment Venting Orderor the Mitigation Strategies Order, which it issued in March 2012. Once the final rule is effective, it will replace the two orders.

The NRC said the final rule will require U.S. commercial reactors to:

  • Maintain resources and procedures to cool a reactor’s core and spent fuel pool, as well as preserve the reactor’s containment, following an event that disables all of a site’s normal and emergency A/C electrical power sources, as well as the site’s ability to safely transfer heat to the environment.
  • Maintain equipment that can reliably measure spent fuel pool water levels following a severe event.
  • Preserve the resources needed to protect the core, containment, and spent fuel pool from external hazards.

Most nuclear plants will be required to comply with the planned final rule within two years and 30 days after it is published in the Federal Register. However, plants that are subject to the NRC’s Containment Venting order will be required to comply with the rule within three years and 30 days of the rule’s publication.

NRC’s Stream of Fukushima-Related Actions

In a document released Thursday that details commission’s views, NRC Chair Kristine Svinicki and Commissioners Annie Caputo and David  Wright noted that in response to Fukushima, the NRC embarked on a “program of work” that has taken eight years, and involved a wide variety of people from the agency, from the regulated industry, and from interested stakeholders. 

“The Commission’s action on this final rule provides a holistic conclusion to a large portion of this work, which has already resulted in undeniable safety improvements throughout the operating power reactor fleet in the United States,” they said.

The Fukushima accident ensued after a large tsunami, caused by an 9.0-magnitude earthquake, inundated Tokyo Electric Power Co.’s Fukushima Daiichi nuclear power plant. At the plant, the tsunami was an estimated 14 meters high.  The earthquake and tsunami disabled the majority of the external and internal electrical power systems at the Daiichi plant, leading to meltdowns and hydrogen explosions at Units 1, 2, and 3.

Final Rule’s Long History

Recognizing that the “combination of severe events challenged the implementation of emergency plans and procedures,” at Fukushima, and to prevent similar incidents at U.S. plants, the NRC almost immediately took action. Weeks after the disaster, the NRC established a senior-level task force—the “Near-Term Task Force” (NTTF)—to comb through the NRC’s rules and processes, and to identify safety improvements. The July 2011 NTTF report that NRC staff sent to commissioners ultimately concluded that while the NRC’s regulatory system served the NRC and the public well, safety and emergency preparedness enhancements were needed. It made 12 general recommendations, concluding that the NRC’s layered defense strategies could be bolstered by including explicit mandates for beyond-design-basis events.

In August 2011, the commission ordered staff to engage with stakeholders to review and assess the NTTF recommendations holistically. After staff sent back their recommendations for near-term action in September 2011, the commission in October 2011 ordered staff to initiate rulemaking to address specific recommendations. Among them were rules to ensure nuclear plants maintain safety through a prolonged station blackout, that they enhance spent fuel makeup capability and instrumentation, and that they fortify onsite emergency response capabilities, such as emergency operating procedures, accident management guidelines, and extensive damage mitigation guidelines. Those regulatory actions ultimately evolved into the NRC’s March 2012 pivotal orders laying out mitigation strategies for beyond-design-basis external events.

The Mitigation Strategies Order, issued on March 12, 2012, required all nuclear plants to have additional capability to mitigate severe events without their permanently installed A/C electrical power sources for an indefinite period of time—including to maintain or restore reactor core and spent fuel cooling, as well as to protect the reactor containment. On the same day, to address the spent fuel recommendation, the NRC also issued a separate order requiring U.S. nuclear plants to have reliable indication of water level in their spent fuel pools (the Spent Fuel Pool Instrumentation [SFPI] Order).

However, as it developed the rules, staff  recognized that consolidating the rulemaking—owing to inter-relationships among proposed changes—would be more efficient. In the months that followed, it issued multiple staff requirement memoranda that portions of their NTTF recommendations be consolidated. The MBDBE rule resulted from these efforts.

The MBDBE rule generally combines two NRC activities already published in the Federal Registerstation blackout mitigation strategies(finalized in July 2013) and onsite emergency response capabilities(finalized in October 2013). But while the NRC issued the MBDBE proposed rule in November 2015—and though it received only about 185 individual comments—it took the commission more than three years to draft a final rule.

A Markedly Different Rule

As the three NRC commissioners noted on Thursday, “the final rule omits many provisions of the draft final rule; we did not arrive at this result lightly.” One point of deliberation was whether the rule’s requirements would comply with existing rules, specifically the Backfit Rule, which governs modification or additions to systems, structures, or designs at a facility. In the end, “we supported only those provisions for which such compliance was substantiated by the staff’s analysis in the decision record,” the commissioners said.

One of many other significant changes in the final rule is that it removes requirements to address seismic and flooding hazards that have been re-evaluated using more current information. The NRC generally agreed with generator comments that change would give them more flexibility in how they address flooding and earthquakes, including to protect equipment.

A Focus on Costs

The NRC suggests the final MBDBE rule could cost, in total, $7.2 million, “even though MBDBE requirements have largely been implemented prior to the effective date of the rule.”

It means nuclear generators will spend $110,000 per site. According to the NRC’s regulatory analysis of the rule, these costs, which it concluded are “justified,” are mainly attached to licensee efforts to review the rule against previous efforts to implement mitigation strategies and spent fuel pool instrumentation orders. In comparison, the proposed rule would have cost about $1.7 million per site.

The rule may not be the end of the line as far as Fukushima rulemaking is concerned. On Thursday, the commissioners noted that other work continues outside the rulemaking context: “there is some analysis to determine whether additional safety improvements are appropriate and further evaluation is ongoing of the actual risk posed by external hazards needed to make such determinations.”


—Sonal Patel is a POWER associate editor (@sonalcpatel, @POWERmagazine).





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