In response to the lessons learned from last year’s nuclear accident in Fukushima, the NRC has required every nuclear power plant in the U.S. to take a number of actions. One of the highest-priority actions involves re-examining earthquake and flooding issues. In the short term, both plant personnel and NRC inspectors (shown in the photo) are walking through the plants, ensuring the systems and components can withstand the hazards that were analyzed when the reactors were built. There are separate “walkdowns” for earthquakes and flooding.
Before the earthquake walkdowns start, the plants compile a list of reactor and spent fuel pool systems that must work after a quake. The plants also assemble teams of employees, both people familiar with plant systems and mechanical or civil/structural engineers with experience working on nuclear plant earthquake issues.
The teams walk through the plant, examining how systems and components are anchored or supported to ride out a quake. They also look for issues such as whether a quake might lead to a fire or cause something to fall on an important component.
For the flooding walkdown, the plants compile the features (such as watertight doors or barriers) that protect the site, and take into account any site changes (new buildings, for instance) that could change flooding effects. The plant personnel doing the work would again include engineers in relevant specialties, as well as staff familiar with flood response procedures.
As these teams do their work, they’ll ensure the protective features are in place and able to deal with floods. They’ll also examine how much extra physical margin is available beyond what’s expected. For example, consider a watertight door protecting against a flood to the top of the door as called for in the plant design. If a window two feet above the door could allow floodwaters in, the site has two feet of available physical margin.
The plants will use their corrective action programs to deal with any issues identified during both walkdowns. The plants must correct any situation that challenges their ability to withstand quakes or floods previously analyzed.
The NRC’s part of the walkdowns combines earthquake and flooding specialists from our headquarters with the resident inspectors who work every day at the plants. They will examine the plants’ walkdown documentation and perform independent inspections to ensure the plants have done the walkdowns appropriately. The NRC’s resident inspectors will also follow up on the plants’ actions to address whatever issues they identify.
The walkdowns will also provide information for the other part of the earthquake/flooding reanalysis, which will ensure the plants understand the current hazards at every site. This additional work will continue for several years, with flooding work completed by 2015 and earthquake work continuing into 2016 for plants needing the most extensive reanalysis.
These walkdowns are just one part of the many actions we’re taking in response to what we’ve learned from the events at Fukushima. More details are available on our website.Scott Burnell Public Affairs Officer