The Gordian Knot Of Grid Resilience – Part 1

By Sherrell R. Greene

FirstEnergy’s recent announcement of its intent to shutter four commercial power reactors at its Perry, Davis-Besse, and Beaver Valley sites is just the latest development in an escalating dialogue about electric Grid resilience and nuclear power’s role in enabling and maintaining modern resilient societies and the resilient electricity supply systems upon which they depend. (Within this post, my definition of “Grid” is “the integrated system of U.S. generation, transmission, and distribution assets required to produce and deliver electricity to the end consumer”.)

The topic of Grid resilience has attracted increasing attention since the early 2000s, with a variety of federal and private sector studies drawing attention to the vulnerability of the electric Grid, and the Grid’s role as the enabler of virtually all other Critical Infrastructure functions.  The pace of the dialog quickened last year with the U.S. National Academies’ publication of its report, “Enhancing the Resilience of the Nation’s Electricity System.”  Among other things, that report highlighted the lack of consensus regarding the basic definition of Grid resilience, and the absence of any practical metrics and predictive methods for assessing the resilience of “real world” Grid systems.

When it comes to predicting Grid resilience, it seems we are in a situation similar to that of the stock market – while a hundred talking heads can give us as many reasons why the market moved as it did just ten minutes after the change occurred, no one could tell us anything with confidence about the market’s behavior ten minutes in advance of the movement. To the extent they exist at all, Grid resilience metrics today focus on forensic parameters that are almost impossible to predict, and can only be measured after a Grid disruption occurs. The prediction of Grid resilience for actual systems remains a Grand Challenge. What we need first is a practical working definition of Grid resilience.  Next, a set of Grid resilience metrics that can be employed before an event occurs to predict the resilience of the Grid in advance of an actualized hazard or threat. Then, and only then, can major progress be made toward development of simulation tools and methods to predictively quantify those resilience metrics for real Grid systems.

The dialog about Grid resilience and nuclear power stepped up another notch last September when Secretary of Energy Perry directed the Federal Energy Regulatory Commission (FERC) to execute a rulemaking process to establish electricity market rate structures to compensate “fuel secure” power plants (coal and nuclear) for the particular value they lend to Grid resilience.  FERC’s response was, as we know, to decline to execute Secretary Perry’s order. Rather, FERC ultimately chose to institute a new rulemaking process (FERC AD18-07) to examine Grid resilience in a “broader context.”  The three goals of FERC’s action (to quote the order) are: “(1) to develop a common understanding among the Commission, industry, and others of what resilience of the bulk power system means and requires; (2) to understand how each RTO and ISO assesses resilience in its geographical footprint; and (3) to use this information to evaluate whether additional Commission action regarding resilience is appropriate at this time.

Now, what about that Gordian Knot analogy? What are some of the most relevant Grid resilience issues for the nuclear power community to ponder? We’ll start there in Part 2 of this post. In the mean time, you can see my (much deeper) dive into those issues in my (Open Access) article the April 2018 issue of the American Nuclear Society’s journal, Nuclear Technology.

See you in Part 2!


Sherrell GreeneSherrell Greene is an ANS member, the former Director of Nuclear Technology Programs at Oak Ridge National Laboratory, and the President of Advanced Technology Insights, LLC  ( He is a sometimes blogger at

Feel free to leave a constructive remark or question for the author in the comment section below.








6 thoughts on “The Gordian Knot Of Grid Resilience – Part 1

  1. Sherrell Greene


    I am not aware of any IEEE actions with respect to articulation of electricity supply resilience standards… I believe we are only in the opening stages of series deliberation on the matter, and the road to practical resilience standards will be a long one. After all, there is no consensus today regarding the definition of electricity supply system resilience – much less metrics by which it can be measured. Both must precede standards…



  2. Sherrell Greene

    Cornelius and John,

    The exact relationship between reliability and resilience is a matter of ongoing debate. To quote from last years’ study by the National Academy, “Resilience is not the same as reliability. While minimizing the likelihood of large-area, long-duration outages is important, a resilient system is one that acknowledges that such outages can occur, prepares to deal with them, minimizes their impact when they occur, is able to restore service quickly, and draws lessons from the experience to improve performance in the future.” FERC and NERC focus on the “Bulk Power System” (BPS) or “Bulk Electric System” (BES) – that is the network of electricity generation assets and ONLY those elements of the transmission system that operate at voltages above 100 kV. Distribution system issues are not directly included in most analyses of BPS or BES issues. This is extremely problematic when one seeks to examine electricity supply issues in the context of Critical Infrastructure resilience and societal resilience. The distinction between the impacts of interruptions in electricity supply to a hospital and a barber shop matter from a societal resilience perspective. Thus classical BPS/BES reliability and the more recently dialog about BPS/BES resilience, often lack the “granularity” needed to understand their implications to other Critical Infrastructure and societal resilience.


  3. Mike Harrington

    I really enjoy these Nuclear Cafe articles and look forward to Sherrell Greene’s additional articles. The stock market is a good analogy and the U. S. did make it more stable, e.g. by limiting buying stocks on the margin, so perhaps there are analogous stability concepts for power grid stability. At first glance, it seems like Secretary Perry’s fuel secure concept occupies a different time scale (intermediate to long??) than the type of grid stability where we think of a relay failing and then the whole grid cascading to zero within a few minutes or less. Perhaps the relevance will become apparent as we read additional installments.

  4. John Greenhill

    When you talk about resilience, it implies knowledge of the reliability of a system. To estimate the reliability of a system, you have to know the reliability of the components of the system. The reliability of the system of the current nuclear reactors that support the bulk power grids. will depend on the reliability of the current designs. . I know of the catastrophic failure of three operating reactors, 1957, Three Mile Island 1979, Cherobyl, and Fukushima 2011.
    The large scale picture is given in the March 2018 issue of Nuclear News that lists world wide total of 446 current operating nuclear reactors. units. This could suggest that an approximate catastrophic failure rate is of the order 3/446 = 0.7 %. (~1%)
    Even if the actual risk is only 0.01% it is difficult describe nuclear reactors as meeting the reliability standards for systems that affect human safety. .

  5. Cornelius Milmoe

    The concept of reliability is well established and is the cornerstone of grid design. Resilience has only recently entered the discussion. What is the difference in the two concepts and why should we be more concerned with resilience than reliability.

  6. Stephen Fowler

    Sir, do you know if the IEEE has been tasked or has taken on the task of providing some sort of standard for US national grid resilience? Seems like it should be in their purview.

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