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January 02, 2013
Solar flares and nuclear meltdowns

Does a mammoth solar storm have the potential to disable the electrical power grid for up to 2 years and trigger meltdowns at nuclear power plants?  That possibility is not as far-fetched as it may sound, at least not in the opinion of the Nuclear Regulatory Commission (NRC).  Accordingly, the NRC is now considering whether it should adopt regulations to ensure that electrical power needed to maintain cooling at nuclear plants will be available should a 100-year solar flare wreak havoc on the earth’s magnetic field.

Fuel cooling pools

The consideration was prompted by a March 2011 petition sent to the NRC by Thomas Popik on behalf of the Foundation for Resilient Societies.  The petitioner asserted that the North American commercial electric power grids are vulnerable to prolonged outage caused by extreme space weather, such as coronal mass ejections and associated geomagnetic disturbances, and therefore cannot be relied on to provide continual power for active cooling and/or water makeup of spent fuel pools.  Moreover, existing means for providing on-site backup power are designed to operate for only a few days, while spent fuel requires active cooling for several years after removal of the fuel rods from the reactor core.

The petitioner suggested new rule language requiring that emergency systems be operational for 2 years without human operator intervention and without off-site fuel resupply.  Under the suggested language, backup power systems for spent fuel pools would also need to be electrically isolated from other plant electrical systems during normal and emergency operation.

Fukushima actions

The NRC published the petition and requested public comments on its recommendations.  The Commission received a total of 97 comments, including a number that argued that existing regulations and ongoing actions were taking sufficient account of potential grid outages caused by disruptions to the earth’s magnetic field.  For example, one comment noted that the NRC was already addressing the issue of long-term spent fuel pool cooling under actions it is taking in response to the Fukushima Dai-ichi accident.  The NRC responded that the measures now being considered may not be sufficient to address the type of long-term grid collapse raised in the petition.

Another comment noted that the worst historical loss of electrical power caused by severe space weather lasted about 11 hours, after which 83 percent of power was restored, and permanent damage to transformers and other grid components caused by the event was found to be extremely small.  The commenter concluded that this experience does not indicate that the long-term loss of off-site power can be considered a credible event.  The NRC replied that the commenter did not back up this view with an analysis.  Furthermore, the NRC states that its “limited analysis” indicates that the frequency of an extreme magnetic storm that could result in unprecedented adverse impacts on the U.S. electrical grid is not remote, compared to other hazards that the NRC requires its licensees to consider.

Technical basis needed

The larger issue beyond the impact of space storms is developing measures to reduce the risk that any long-term failure of the power grid poses to power plant cooling.  The NRC says that it will initially monitor the progress of several Fukushima-related activities designed to enhance the ability of plants to keep spent fuel pools safe.  If the NRC concludes that these activities fall short of resolving the petition’s concerns, the Agency will work to develop a technical basis for the petition’s suggested rule change.  If such a basis cannot be established, the NRC says it will update the public on why the petition’s suggestions will not be adopted. 

NRC’s decision to consider the petition was published in the December 18, 2012, FR.

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