My wife and I have been watching the new HBO miniseries on the 1986 Chernobyl nuclear disaster. During the second episode, she asked me the question that is probably on everyone’s minds as they watch the drama unfold: “Could a Chernobyl-type event happen today?”
I told her “No, I don’t believe that’s possible.” However, it’s important to note that we never dreamed such an accident was possible in the first place. So, let’s explore the question in a little more depth.
The Recipe for Disaster
An accident is the result of an initiating event or series of events and an inadequate response. Accidents are mitigated by lowering the probability of the event(s) and ensuring a response that prevents the consequences from escalating.
In the event that the potential worst case scenario is catastrophic, there needs to be substantial reduction in the probability of the event, as well as a response that reliably mitigates the consequence. A catastrophic consequence could be one that involved multiple human fatalities, huge environmental contamination, major property damage, or major financial losses.
But a catastrophic consequence would also include major disruptions to the population, like having to evacuate 50,000 people from their homes. In the case of Chernobyl, the evacuations happened on short notice, and they were permanent. I think if you have to permanently leave your home on short notice, that’s a catastrophic outcome.
Further, in the second episode of the HBO series, they presented a narrowly-averted scenario in which millions of people could have died. I can’t say whether those events actually unfolded — or whether this is a dramatization to make for more exciting TV — but viewers will certainly have the impression that Chernobyl nearly killed millions of people.
Thus, the public must have absolute confidence that another Chernobyl (or Fukushima) can’t possibly happen again.
Reducing the Risks
There are still 11 operating RBMK reactors of the type involved in the Chernobyl accident. All of them are in Russia. Since Chernobyl, there have been significant design modifications that were recommended by the International Atomic Energy Agency (IAEA).
In 2006, IAEA deputy director Tomihiro Taniguchi told The Associated Press “Very significant changes have been made in the technology. The IAEA is firmly committed that such an accident not happen again.”
There’s no doubt that the potential for a Chernobyl-type event has been greatly reduced as a result of design changes and additional training, but has it been reduced to zero? Hold that thought for a moment.
While there are no RBMK reactors in the U.S., around 30% of U.S. nuclear power plants use General Electric-designed boiling water reactors (BWR). This was the type involved in the core meltdowns in Fukushima following the 2011 tsunami off the coast of Japan.
Again, training and design changes have reduced the risks of a repeat, but has the risk been reduced to zero? Again, let’s hold that thought for a moment.
The Unknown Unknowns
I do believe that the probability of having a similar set of events lead to a similar outcome has been reduced to zero for both Chernobyl and Fukushima-type events. The causes were identified and addressed in other plants with those designs.
But, bear in mind that nobody had any idea that such huge disasters were possible for either of these locations. Indeed, it took years to fully understand what had precisely caused the accident at Chernobyl.
As someone who has been involved in many safety reviews and incident investigations, what always concerned me more than anything were the things we might have missed.
In 2002, Defense Secretary Donald Rumsfeld made the following observation:
There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don’t know. But there are also unknown unknowns. There are things we do not know we don’t know.”
Chernobyl was caused by one of these unknown unknowns. This is partially true for Fukushima as well, but at least in that case the causes were understood. They were just deemed to be highly unlikely, such as the possibility that a tsunami could breach the plant’s 33-foot tall seawall.
Preventing Another Chernobyl
When someone asks if a Chernobyl could happen again, the engineer in me pauses and thinks about the unknown unknowns. By definition, we don’t know what they are. Thus, the completely honest answer when someone asks me this question is “I don’t think so, but I can’t guarantee it.”
Further, we have seen people deliberately crash airplanes. Could a disgruntled operator deliberately sabotage a nuclear plant and cause a catastrophic outcome?
Given the possibility of unforeseen events or even sabotage — in combination with potentially catastrophic consequences — nuclear power plants must approach the mitigation of consequences with overkill and redundancy. By that, I mean that if a series of events can take place that would potentially lead to a catastrophic incident, there should be several layers of potential mitigation. We have to ensure that even with a saboteur’s best efforts, they couldn’t cause a catastrophic release from a nuclear power plant.
Ultimately, there is no way to foresee all possible causes of an accident. Thus, we have to ensure that if a failure takes place, it results in a safe state. I discussed the example of an electrical fuse in a previous article. When the fuse fails, it does so in a safe state. The flow of electricity stops. I do believe our best minds can ensure such designs in the world’s nuclear power plants.
If we can ensure that all nuclear power plants in the world are fail-safe designs, then we can indeed say that even though failures could happen, “No, another Chernobyl is simply impossible.”