Monday, October 15, 2012

Post # 72: NTTF Recommendation 2

Earthquakes and Floods

 Available evidence now indicates that even though the Great East Japan Earthquake of March 11, 2011 was estimated to be a magnitude 9.0 earthquake (exceeding the design basis of the Fukushima Dai ichi plant), the direct damage to the plant from the quake was minor compared to that resulting from the large tsunami that struck the plant some 40 minutes later.  (The plant was designed to weather an 8 meter high tsunami wave.  However, the maximum height of the waves that struct the plant exceeded 14 meters.)  The wave impact damage and the flooding resulting from the multi-tsunami waves that struck the plant accounted for the majority of the damage that lead directly to the ensuing station blackout and, ultimately, to the severe accident. 

And if the Fukushima experience was not sufficient to spawn an international re-look at commercial nuclear power plant vulnerability to seismic and flooding events, the urgency of the matter was heightened in June 2011 due to the partial flooding of the Fort Calhoun Nuclear Station in Fort Calhoun, Nebraska.  That event occurred due to historic flooding of the Missouri River following heavy rain falls and rapid snowpack melting in the Rocky Mountains. (The Fort Calhoun station is still shutdown.)

It was with all of the above as background that the NRC's July 2011 Near Term Task Force (NTTF) report presented Recommendation 2:

NTTF Recommendation 2

The Task Force recommends that the NRC require licensees to reevaluate and upgrade as necessary the design-basis seismic and flooding protection of SSCs for each operating reactor. 

This overall recommendations was further expanded in the NTTF report ...

The Task Force recommends that the Commission direct the following actions to ensure adequate protection from natural phenomena, consistent with the current state of knowledge and analytical methods. These should be undertaken to prevent fuel damage and to ensure containment and spent fuel pool integrity:

2.1 Order licensees to reevaluate the seismic and flooding hazards at their sites against current NRC requirements and guidance, and if necessary, update the design basis and SSCs important to safety to protect against the updated hazards.

2.2 Initiate rulemaking to require licensees to confirm seismic hazards and flooding hazards every 10 years and address any new and significant information. If necessary, update the design basis for SSCs important to safety to protect against the updated hazards.

2.3 Order licensees to perform seismic and flood protection walkdowns to identify and address plant-specific vulnerabilities and verify the adequacy of monitoring and maintenance for protection features such as watertight barriers and seals in the interim period until longer term actions are completed to update the design basis for external events.

The term "SSC" in the above language refers to structures, systems, and components – the basic building blocks of a nuclear power plant.  The basic idea behind Recommendations 2.1-2.3 is to ensure that (regardless of the original seismic and flooding design basis for a commercial nuclear power plant) the most current and accurate data, information, and methods are used to re-examine the plant's vulnerability to such events.

Subsequent Actions Relevant to Recommendations 2.1 & 2.3

In October 2011, Recommendations 2.1 and 2.3  were designated in SECY-11-0137 as "Tier-1" recommendations – "... recommendations which the staff determined should be started without unnecessary delay and for which sufficient resource flexibility, including availability of critical skill sets, exists."

The NRC subsequently issued a Request for Information (the so-called "50.54(f) Generic Letter) to its nuclear power plant licensees on March 12, 2012.  The letter requested a two-phase re-evaluation of seismic and flooding hazards at each plant.  (The letter also addressed Recommendation 9.3, but I'll discuss that in a future posting.)   The Phase I re-evaluation was to consist of a re-look at the seismic and floods hazards at each plant based on the latest seismic and flooding hazard information (expected frequency and magnitude of potential earthquakes and floods) and present-day regulatory guidance and methodologies for evaluation of these hazards.  The NRC noted in the request that the Phase I evaluations would not revise the design basis of the plant (the technical analysis under which it was originally licensed).  Phase II of the hazards evaluation will follow after the NRC reviews the Phase I analyses and decides what, if any, regulatory actions (including plant and procedure modifications) will be required.   The Generic Letter, together with its enclosures and attachments, spell out in great detail the precise nature of the information each licensee is to provide the NRC.  Each licensee has 1.5 years to submit a comprehensive written response to the re-evaluation request.

But the NRC doesn't intend to sit on its hands for 1.5 years while it awaits the licensees' response to the Phase I / Phase II re-evaluation information request.  In addition to the information discussed above, the Generic Letter also requested that each licensee conduct seismic and flooding "walkdowns" to "identify and address plant specific degraded, nonconforming, or unanalyzed conditions and verify the adequacy of strategies, monitoring, and maintenance programs such that the nuclear power plant can respond to external events."  Licensees were given 120 days to confirm their intent to use an NRC-endorsed walkdown procedure or to provide a description of their preferred walkdown process.  Following NRC's approval of the licensee's 120-day submittal, each licensee was afforded another 180 days to complete the walkdowns and submit their results to the NRC.  Thus all the walkdowns are to be complete and their results submitted to the NRC no later than 300 days from March 12, 2012 – or January 2013.

In the months since the March 2012 release of the Generic Letter, the nuclear power industry has devoted tremendous effort to excuting the requested walkdowns and documenting their results.  (The Generic Letter noted that the NRC had estimated each licensee would expend 13,300 hr of effort to conduct their evaluations and prepare their response.)

So we are coming to the end of the allotted time for execution of the requested seismic and flooding walkdowns and submission of the results.  In addition, the licensees are preparing for the Phase I hazards analysis.  And if that is not taxing enough, many plants are undergoing their regularly-scheduled refueling and maintenance outages in the coming weeks and remaining months of 2012.

Bottom line... the accident at Fukushima has spawned a wholesale re-examination of the ability of U.S. commercial nuclear power plants to withstand extreme seismic and flooding events.  While some important near-term actions are coming to completion, significant efforts will be expended by the NRC and the Industry over the next couple of years to more fully comply with NTTF Recommendation 2.

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