Nuclear Risk Accounting 101

, former director, Nuclear Safety Project | November 12, 2013, 6:00 am EDT
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Fission Stories #150

On August 1, 2013, I made a presentation to a graduate class in nuclear engineering at the University of Pittsburgh. Professor Larry Foulke, past president of the American Nuclear Society, generously invited me to participate in his class the past two years. Last year, I talked about a report UCS released about risk analyses performed for nuclear power plants. This year, I outlined a process long used within the nuclear industry to guard against proposed modifications to plant systems from inadvertently decreasing safety or security elsewhere and described how it should be also applied when making risk-informed decisions.

Basically, one cannot balance a checkbook without a complete and accurate tally of all checks written against and funds deposited to it. With some checks and/or deposits missing, one can use a calculator to add up the known amounts. But that total may, or may not, represent the checkbook’s balance. And one may not know whether that total is higher or lower than the amount available in the account.

Likewise, one cannot make risk-informed decisions without proper consideration of all generic and plant-specific safety hazards known to be unresolved. One can add up numbers to quantify risk, but that total fails to reflect reality when known hazards are neglected. Yet, this incomplete accounting and impaired risk decision-making happens again and again.

For a more detailed description of the risk accounting problem and our recommendation solution, check out my presentation  to the University of Pittsburgh graduate class.

Our Takeaway

First and foremost, my sincerest appreciation goes to Professor Larry Foulk for inviting me to participate in his class these past two years. Professor Foulk told me several times that he does not agree with every position I take but feels it important to be aware of these positions. He invites me to participate in his classes to extend that awareness to his students. And I have benefitted in return from greater awareness of when Professor Foulk and his students agree, and disagree, with my views. “Information is Power” is an old cliché. Frank dialogues and open communications, like those that Professor Foulk fosters, strengthens all participants in the discussions.

Second, “Safety in Numbers” is another cliché. Perhaps so, but nuclear plant safety risk accounting will not yield safe numbers until all known and unresolved hazards are properly considered.


“Fission Stories” is a weekly feature by Dave Lochbaum. For more information on nuclear power safety, see the nuclear safety section of UCS’s website and our interactive map, the Nuclear Power Information Tracker.

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  • John Greenberg

    It seems to me that the problem is much deeper, and far less soluble, than your analogy suggests.

    With a checkbook, proper accounting is quite straightforward, once all checks and deposits have been accounted for.

    That’s not the case with nuclear power plants. Even if we assume that best efforts have been made to account for all of what Donald Rumsfeld famously called the “known knowns,” there remains the problem of the all of the “unknown unknowns,” and these latter have accounted for many of the accidents at nuclear power plants.

    Put less abstractly, the problem is this. With the very best of intentions, engineers and designers can tally all of the risks they can think of. But two major problems remain: 1) as history has repeatedly shown, there are a fair number of problems which engineers simply cannot think of. If one thinks of the skills and training of engineers, this should not come as a major shock. 2) In addition, there are, as history again demonstrates, risks which engineers DO imagine, but then rule out as impossible: e.g. an earthquake or a tsunami the size of those which hit Fukushima. That plant was engineered to withstand BOTH of these events, but designers had ruled out events of the size of those which occurred as “impossible.”

    In both cases, then, we are left with a problem that goes well beyond the checkbook problem, since it is literally impossible to properly account for events which one cannot foresee at all or events which one determines to be impossible. Finally, it is worth noting that simply trying to include EVERYTHING conceivable won’t work either: some things MUST be declared impossible or the analysis itself will become impossible. In nuke speak, all risk analysis must start with the right “design basis.” If that’s flawed in any way, the analysis will be as well. Accidents which can be shown to have been “beyond design basis” may console bureaucrats and engineers, but those suffering their impacts are unlikely to be moved by the fact that engineers thought them implausible or impossible.

    There’s one other important point to be added. Assessing risk properly is not always a straightforward proposition, especially when probabilities are low and magnitudes are high. Yet, the kind of analysis Dave is describing usually ends up being expressed through numbers which APPEAR to be precise. This leads almost inevitably to overconfidence in the accuracy of the numbers generated, which are, in fact, thanks to the wide underlying margins of error, anything but precise.

    All of this, of course, still assumes that the remainder of the analysis is carried out in the best possible “good faith,” which alas, has often not been the case either, and also that the analysis is done flawlessly.

  • Mark House

    Tried submitting this message to Tepco:

    To Tepco and the government of Japan

    Our solution’s here in this group appear simple, easy, inexpensive, practical, indeed harmless to humans by comparison; working as a sustainable action and as a model for any future melt downs.

    Bring in a few hundred excavator’s with Brown’s Gas fuel cells and torches outfitted to them remotely controlled from miles away. Chop up the buildings, vaporize the spent fuel rods while still in their cooling pools, even underwater. Capture the corium’s with titanium poles, cradling them so the corium’s stop penetrating the ground. Then vaporize the corium’s — chunk’s at a time with Hydroxy flames (360 degrees around) until the danger is finally ended by their destruction. Only a few months would be needed with around the clock action by a large crew working together. Aerial platforms in the sky could monitor every detail of the work with high powered cameras. Let’s get to work!

    The chopped, sliced, reduced bits from the debris and demolished buildings can be destroyed using Hydroxy furnaces that will burn it all completely without any emitted atmospheric radiation. Even the excavators themselves will finally be properly destroyed when done by the purifying Hydroxy flames and furnaces.