Fission Stories #133: Mayflies, and Squirrels, and Rats, …

, former director, Nuclear Safety Project | March 26, 2013, 6:00 am EST
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Fukushima Daiichi recently received worldwide media attention when another power outage once again interrupted cooling of the water in the Unit4 spent fuel pool for several hours. The culprits in 2011 were an earthquake that knocked out the normal supply of electricity to the cooling system and a tsunami that disabled the backup power source. This time, a rat was the culprit. It chewed through the insulation on an electrical cable, exposing wires that shorted out and stopped the cooling system. It was also the rat’s final meal as the event also electrocuted the guilty party.

It was not the first time that wildlife mixed it up with nuclear power plants. On December 29, 2012, a pelican started an emergency diesel generator for the Unit 2 reactor at the Surry nuclear plant in Virginia. The pelican contacted an overheard power cable causing a short that de-energized one of the connections between the plant and its offsite electrical power grid. One of the emergency diesel generators automatically started in response to indications that electrical voltage inside the plant were decreasing. Both reactors at Surry were operating at 100 percent power at the time and continued operating throughout the power disruption.

Another bird caused the Fermi Unit 2 reactor in Michigan to automatically shut down on September 14, 2012, after it landed in the switchyard containing electrical cables connecting the plant to its offsite electrical power grid.

The operators manually shut down the Unit 1 reactor at the St. Lucie nuclear plant in Florida on August 22, 2011, after a squad flotilla bunch of jellyfish blocked the screens at the intake station, significantly reducing the flow of cooling water to the plant.

The perators manually shut down the Unit 2 reactor at the Diablo Canyon nuclear plant in California on October 21, 2008, after a bunch of jellyfish blocked the screens at the intake station, significantly reducing the flow of cooling water to the plant.

A snake slithering onto an overhead power cable on August 1, 2007, at the Hatch nuclear plant in Georgia caused a short that caught the wooden pole holding the cable on fire. The operators reduced the power level of the Unit 2 reactor about ten percent because the snake stopped the flow of electricity to some of the cooling towers. Workers declared an Unusual Event, the least severe of the NRC’s four emergency classifications, due to the fire that burned for over 10 minutes.

The operators manually shut down the Unit 2 reactor at the Point Beach nuclear plant in Wisconsin after “a large number of small forage fish” blocked the screens at the intake structure, significantly reducing the flow of cooling water to the plant.

The reactor at the Wolf Creek nuclear plant in Kansas automatically shut down from 100 percent power on September 4, 2000, after a squirrel caused an electrical short in the main power transformer.

The operators manually shut down the Unit 1 reactor at the St. Lucie nuclear plant in Florida on September 18, September 20, and September 22, 1993, after a bunch of jellyfish blocked the screens at the intake station, significantly reducing the flow of cooling water to the plant.

The LaCrosse nuclear plant in Wisconsin was disconnected from its offsite electrical power grid on July 16, 1984, when mayflies caused a power transformer to short out. Two emergency diesel generators automatically started to provide power to essential equipment at the plant.

Our Takeaway

When a single rat (make that an individual rat–its marital status is uncertain) can accidentally interrupt cooling of a spent fuel pool for hours, a lone squirrel and an individual bird can inadvertently knock out power supplies to a nuclear plant, and teams of jellyfish and forage fish can unintentionally disrupt cooling water flow to a nuclear plant to the extent that the plant must be shut down, one wonders about the havoc that an individual saboteur or a team of bad guys might be able to cause by malicious intent. Could well-trained and heavily armed attackers cause more devastation than a furry little squirrel or a pesky rat?

But on the other hand, nuclear power plant security seems adequate–no nuclear plant has ever been stolen. Watch out for an army of ants!


“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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  • jharragi

    “…one wonders about the havoc that an individual saboteur or a team of bad guys might be able to cause by malicious intent.”

    Would this include a nuke CEO who wants to save a few mill on safety? Seawalls, spent fuel storage, hardened vents…

  • T. Cahill

    While I find many of these fission stories interesting and insightful, this one in particular strikes me as a thinly-veiled attempt to instill FUD.

    The incidents experienced by the nuclear plants mentioned in this article aren’t specific to only nuclear plants. In reality, any other power generation facility could have had (and, indeed, have had) the same issues. Birds landing on switchyard gear? C’mon. The real question is how these plants handled their respective situations. To this point, the article failed to mention that in every one of these cases, the plants operated exactly as they should have. As a result public safety was protected at all times during the incidents.

    As for malicious intent, the last time I checked, squirrels don’t carry vendettas against nuclear power plants. Credible threats are certainly (and thoroughly) addressed at each and every nuclear plant in the U.S., and, despite the author’s attempt to mask the facts with humor (i.e. “stealing nuclear plants”), there have been NO incidents to that effect to date.

    Conflating incidental (and non-safety) issues with intentional hostile threats is ridiculous. These really are two completely different things, and attempting to draw a connection between them is incredibly disingenuous, even for the purposes of generating a laugh.

    • JT

      First of all, what the Hades kind of plant security can a nuclear plant have, if squirrels and mayfiles can force shut downs? Unless there’s a time machine for sending information from now to a point in the past, and enemies don’t have it, then you plant owners and operators really have no chance against a team of commandos, especially if they have inside help.

      Second, every time a plant shuts down suddenly, according to nuclear workers who have said so, it is a hair-raising water-knocking experience with the capacity to break pipes and shake things violently. The fact your industry, which is a deadly threat to the entire U.S., has had huge cases of cavitation holes in pipes in the past and didn’t find out about it until ‘routine maintenance’, destroys any confidence of an informed public.

      Third, Fort Calhoun, did it have submersible pumps and waterproof electrical systems, being situated in a flood plain as it is? It’s SFP incident pointed out a) the threat it poses to the whole Corn Belt which is a world bread basket and b) the left hand of govt didn’t know what the right hand was doing. The COE blew levees in Missouri to protect towns downstream. It didn’t blow levees to protect Calhoun and wasn’t even thinking about it, apparently. The NRC’s previous actions helped immensely, but there was still a problem, and we really don’t know the whole truth.

      That’s a fourth thing, the nuclear power and spent fuel industry simply can’t be trusted. Tepco is a prime example, lying its posterior off about everything, from before day one. The U.S. public, if ever informed of the true risks of nuclear, would shut it down immediately.

      It’s not worth the risk. The odds are too high, a region-destroying catastrophe every 25 years or so (and routine emissions all the time). The stakes coult not be any higher. All for a little electricity, and a little profit for some owners who truly don’t care about their neighbors at all.

      • Sean McKinnon

        Nuclear has been around in the us for about 60 years so by your claims we should have had at least two regions of the US wiped out can you please point me to those areas in the us wiped out or uninhabitable because of the us nuclear industry?

        Please let’s not talk emissions coal plants emit more radiation into the environment during routine operation than a PWR would with a primary steam generator leak and steam being vented directly to the atmosphere in a unit trip. Never mind all the heavy metals, noble gasses, fly ash. Nuclear plants “emit” such a fraction of what coal and gas plants do.

        Look some people just hate certain things. I hate cherries I can dig up all the one sided stuff I want about cherries they do make some people sick that can kill those with severe allergies I will never like the, no matter what science I am shown but I admit it. I do not hide behind the guise of having no opinion and just wanting safer cherries. That’s all I want either be impartial like you claim or be honest and disclaim your true feelings on nuclear power UCS.

      • Tim Cahill

        Wow. Where to start…

        I guess I’ll reiterate the point that plant security and shutdowns caused by a malfunction of components are two totally different things.

        When the copy machine breaks down at work, do you conclude that the building security guard is inept at his job?

        Have you been to a nuclear plant? Have you actually seen how they work? Have you talked to the people that work at them? Have you seen the security forces they employ? Have you witnessed the drills they perform? Did you know that a significant portion of nuclear plant security is made up of ex-military personnel?

        I encourage you to read up about the requirements set forth for nuclear plant security. It’s actually pretty interesting. A great place to start would be the Code of Federal Regulations (10 CFR 73), which provides good detail on just what nuclear security is like. Here’s a good overview report from the NRC:

        As for the second point, I’m not really sure what it is, to be honest. ANY time the operation of a large machine is suddenly stopped/changed, it is subject to creating anxiety among its operators and added stress on the machine itself. That’s the whole idea of an “sudden” event: it happens suddenly. The important part is how those people and the machine handle the sudden event.

        Perhaps some hypothetical questions would help here: If you were driving down the highway and a deer suddenly crossed the road in front of you, would you not find yourself in a sudden, hair-raising situation? How would you respond? Would you not slam on your brakes or quickly swerve to avoid hitting the deer? Would it not present the possibility of damage to your vehicle?

        Which leads into the next part of your second point: ANY manmade creation is subject to damage and wear. That’s part of why routine maintenance is performed, so that problems are discovered and fixed.

        Back to the hypothetical: Do you not perform maintenance and checks on your vehicle? When the mechanic comes out and says your brake pads are worn down, what do you do? Look at what could have happened! Your brake pads were really worn, and that can be a very dangerous situation! That deer could jump out in front of you on the road, and those brakes may be too worn to help you stop in time! Why didn’t you or the mechanic know those pads were worn down earlier? Well I guess at this point, any confidence I had in you and your car has been destroyed. I don’t care that you can fix the problem by replacing the pads. It’s over, the trust is gone…

        On your third point, again, not really sure what the actual point is. Mind providing your references for the conclusions of conspiracy you are drawing?

        Your forth point really isn’t a point as much as it is a non-factually backed statement reflecting personal opinions. What Tepco did or did not do in Japan is not relevant to our discussion on what utilities in the U.S. do or don’t do. Different country, different culture, different regulatory structure under which they operate. Let’s stick to staying on topic and remaining consistent in what is being addressed.

        As for risks, they are inherently relative things. When you say the stakes are too high, what are they too high in relation to? The benefits we receive from generating electricity via nuclear (which, by the way, is NOT a small amount)? The millions of lives that electricity saves and sustains in our country? The millions of tons of carbon dioxide offset by using nuclear energy? The thousands of deaths nuclear energy has prevented since we began harnessing it? My mom used to always tell me “There’s no such thing as a free lunch.” That pretty much sums up how risk works. Any time we decide to do anything, there is a risk associated with that action (or inaction). Risks should be weighed against each other in order to make rational decisions. The problem is that humans, in general, are really bad at weighing those risks. Look at how many people refuse to fly in an airplane because they’ve deemed it “too risky,” only to get in a car to travel where they need to go.

        I agree with you that the stakes couldn’t be any higher. People are dying every day from not having clean sources of electricity. Nuclear energy’s excellent track record leads me to completely disagree with your conclusions on its risks.

        Also, it’s utterly ridiculous to state that the people who own and operate nuclear plants don’t care about their neighbors. THEY LIVE WITH THEIR NEIGHBORS IN THE COMMUNITIES THAT THEIR PLANTS SUPPORT.

        Which brings me back to my original questions: Have you been to a nuclear plant? Have you actually seen how they work? Have you talked to the people that work at them?

        Maybe it’s worth a visit…

    • Mr. Cahill, there is no “veil or hostile threat” except in your interpretation. There are lessons to be gained in this factual story relative to nuclear facility management and how humans relate to the unexpected event.

      The question must be asked, which presents a greater danger to the public – the mouse, snake, fish, squirrel or the nuclear corporate executive whose concern is the financial bottom line, not safety of the public?

      Defense in depth cannot overcome corporate greed if we as a people have a regulator who is susceptible to financial and political influences which prevents them from regulating the nuclear industry in such a manner which offers the highest standards of public protection.

      • Sean McKinnon

        I agree political influence such as demanding the NRC stop work on yucca mountain regardless of the technical and scientific benefits and realities is really shameful and should be regarded as the disgrace it was/is. I agree lets keep the politics out of nuclear power and the NRC and make our decisions based on rational science!

  • Sean McKinnon

    Yeah Mr. Cahill, like you I enjoy fission stories and look forward to it every week. However, I am sometimes unhappy with the way in which information is presented. When I comment and ask for clarification (for example how many flooding problems were corrected in a certain time frame when only the cases of uncorrected problems were presented) really makes me realize the bias and agenda at work here. UCS claims to not be “anti” nuc power just pro safety and regulation enforcement but sometimes the way information is presented makes me wonder if that is their real position. I will say to thief credit my comments have always been allowed even when I disagree.

    In this case as in others I see these stories to be more examples of how safe nuc power is and how defense in depth works very well. The public health and safety protected in all of these cases even when they did not cause an automatic trip of the plant the ops people put safety before profits and manually shut down the plants. Kudos to those RO’s SRI’s TSA’a NLO’s and shift sups!

  • jharragi

    Mr Cahill, You seem to have missed the point of all of the other interesting and insightful articles. Many of them have been about facilities that have had malfunctions, errors, stupidity, lax maintenance or avoided expense that compromised a facility’s backup systems and or other key safety functionality.

    If you have put together any pairs of the situations depicted in any of these articles at the same time and place, almost any combination would result in disaster. In a way, this occurred at Fukashima where ignoring an identified risk allowed them to avoided the expense for an adequate sea-wall.

    What I got from this article was that the spent fuel at Fukushima which appears to be remaining at the site for the foreseeable future has minimal safety and no backup cooling 2 years into our disaster. One might argue that Tepco had no way to anticipate a rat stepping onto a buss-bar – this article simply illustrates that such things do occur and it might be worthwhile to have a little defense in depth. Further, it might do you some good to realize that every spent fuel pool in the world has flimsy and inadequate protection. Practices such as racking as much spent fuel as possible until the cost of more substantial storage can be dumped on taxpayers at decommission are happening at every plant in the country. Certainly, this increases the risk that spent fuel pools present.

    One past fission story was about staff bypassing safety procedures and winching a fuel bundle to high in the pool. If those people had pulled the bundle right out of the water, it very possibly could have resulted in a major fuel pool fire as no one would have been able to approach to assess let alone respond to that situation.

    • Tim Cahill

      As I said before, I do read these fission stories and find them generally interesting and insightful. I do agree that defense in depth is always good, but implementing a large series of big changes doesn’t happen overnight. Actions are prioritized according to many things, especially impact and importance to safety. Armchair assessments of the situation in Japan and the personal opinions as to the timeliness of the changes they are making are not helpful in truly understanding what occurred.

      As for spent fuel pools specifically, further instrumentation is being added to prevent a situation in which the status of the pools is unclear/unknown, NOT because they are “flimsy” and do not provide adequate protection.

      Here’s a good summary post addressing the misinformation about the Fukushima spent fuel pools:

      I urge you to pay particular attention to Assertion 3 in the post. I think it would do you some good to realize the fundamental properties of physics.

      • jharragi

        Your link’s heading says it all:


        Whoever came up with that title seems to have a fundamental grasp of BS – ‘pile it on’.

        I will however read that piece and find out what is so unusual about Fukushima’s spent fuel that sets it apart from the vast quantities of toxic radionuclides piled up at every other reactor in the world.

        • jharragi

          Read the article. If that author is not a BS artist, he is an idiot. Let us examine the first assumption that the structure can withstand an earthquake. The epicenter of the quake that initiated the disaster was located a substantial distance away from Fukushima. That same quake occurring at the plant would have far exceeded the plant’s structural design and it is likely that structure would fail. If this were to occur, and the waste were to just spill on the ground there would be no way to respond in a timely manner. It is quite possible that essentially the entire inventory of waste would wind up in the ocean or atmosphere within a relatively short period of time – remember an 8.5 quake just happened – these move the earth…

          Another possibility is that the water could drain from the pool – perhaps Tepco has overstated the structural integrity of the pool and there is some unidentified cracks working their way through the concrete as we speak – just a one foot hole in the bottom of the pool and it is game over for any cleanup at that site – or any serious hope of containment.

          Not dangerous? Not likely.

          • Tim Cahill

            Well, since you admittedly dismissed the article in its entirety before you EVEN READ the thing, I guess I’m not surprised by your (cough) “conclusions.”

            First of all, earthquakes don’t just occur anywhere. They occur at faultlines. Assuming one happens “at the plant” is ridiculous unless there is an active faultline underneath the plant, which as far as I can tell, there isn’t one at Fukushima-daiichi.

            Secondly, do you even understand what spent fuel is? We’re talking about SOLID material here, which is itself contained within SOLID metal tubes. The idea that the fuel somehow magically “spills” everywhere is so incorrect I’m not sure I know what to say beyond questioning your comprehension of basic physics. And then, it somehow all ends up in the ocean? Or better yet, it magically aerates itself and sends itself flying into the atmosphere? It sounds as if you are assigning sinister motives to inanimate objects. Does that really seem logical to you?

            Thirdly, assuming that the MULTIPLE reports asserting the integrity of the pools are overstatements without any evidence to the contrary is exactly the type of FUD maneuver I discussed in my original post. Did you really read the article? The pools have been reinforced such that its structural integrity has been improved 20 percent over its ORIGINAL condition. There’s even PICTURES SHOWING THE IMPROVEMENTS! If you don’t believe the reports or the pictures of the actual pool, maybe you should make a trip to Japan and conduct your own study.

            I’m not sure it’s fair to call the author an idiot while demonstrating a serious lack of understanding in the subject matter.

          • jharragi

            Tim (This comment may appear above Tim’s 11:19 post),

            I was simply making an observation about your link’s title in regard to spent fuel. That spent fuel is highly dangerous under any circumstance – the premise of the title is misleading. Maybe it should read ‘hazardous pool situation not as bleak as they might be’.

            Yes, you are correct in saying the fuel is contained within solid tubes comprising bundles. However, if those tubes were exposed to the elements for any length of time, particularly in a corrosive marine environment with a bit of heat and radiation thrown in, there would soon be no ‘containment’ at all. You don’t need a fire – or anything else for this process to happen – and remember, it already has a head start as there had been sea-water pumped into the fuel pool.

            Three years ago Tepco would have stated that a tsonami presented no risk. You should base the value of their assurances on this.


          • Tim Cahill

            “That spent fuel is highly dangerous under any circumstance…”

            Wrong. Spent fuel does not pose a threat when adequately stored. This means 1) keeping the fuel cool, and 2) keeping the fuel shielded. For Fukushima, both of these points are accomplished quite nicely by keeping the fuel where it’s at, in the spent fuel pool.

            Cars are capable of killing (and, indeed, have killed) way more people than spent fuel, yet I don’t see anyone making the statement that cars are “highly dangerous under any circumstance.” Why? BECAUSE THEY AREN’T when they are used appropriately, just like everything else.

            Next quote:
            “However, if those tubes were exposed to the elements for any length of time, particularly in a corrosive marine environment with a bit of heat and radiation thrown in, there would soon be no ‘containment’ at all.”


            “Any length of time”? What does that even mean? It’s an absurdly vague phrase that is meant to convince people that events would happen much quicker than they actually could. Metal doesn’t just instantly fall apart when contacting sea water. And again, adequate capability to monitor the condition of the spent fuel has been demonstrated OVER AND OVER again at this point, so if degradation has occurred, it would be known and handled. Just more FUD.

            And by the way, I didn’t discuss this earlier when refuting the points about the fuel magically all ending up in the ocean, but let’s really think about this for a minute:

            Spent fuel is currently stored and KEPT SAFE by residing in a massive pool of water (i.e. – the spent fuel pool).
            – The water keeps the fuel cool so that heat is not a problem.
            – The water shields the fuel so that radiation exposure is not a problem.

            What would happen if the fuel magically ended up in the ocean (the most massive pool of water ON THE PLANET) and nobody did anything to correct the problem (which is also a COMPLETELY RIDICULOUS assumption)?
            – The water keeps the fuel cool so that heat is not a problem.
            – The water shields the fuel so that radiation exposure is not a problem.

            First there’s talk about magical fires, now instantaneous corrosion. What’s next?

            And then this statement:

            “Three years ago Tepco would have stated that a tsonami presented no risk. You should base the value of their assurances on this.”


            “Tepco would have stated…” – Not only do you not provide a source for this statement, it actually appears as though you are trying to put words into people’s mouths. How do you know what Tepco would or would not have stated?

            Where is it that Tepco said there was no risk from tsunamis? As I discussed before, there is risk in every decision or action made. The idea of “zero” risk is absurd, and any scientifically-minded individual or organization worth their salt would agree. As Tepco already had a sea wall for Fukushima for this very reason (tsunami protection), I’d say that statement is pretty much untrue.

            Devaluing information sources in the manner you do above, while not providing another “credible” source (let alone ANY source at all) in its place, is just ludicrous. This type of assertion is exactly what I’m talking about when I say armchair assessments are not helpful to the purpose of these fission stories, which, as I understand it, is to discover and understand what actually happened during an event, why it happened, and base decisions going forward on those facts (not sourceless conjectures).

          • jharragi


            I am basing my arguments regarding corrosion on general observation. If a fuel pool were to fall, I would expect the delicate fuel rods cladding to be breached within decades. However, much fuel would be mechanically damaged immediately introducing a huge obstacle to remediation. That time frame is essentially ‘no time at all’ in comparison to the longevity of the hazards presented by spent fuel.

            My statement regarding Tepco’s credibility is based upon their not responding the need of increasing protections when tsunami risk was found to be far greater than original assessments.

            The downplaying of risk is a part of human behavior. An obvious example of this is seen in gambling. When a person seeks to profit in a community situation, they often will downplay risks in order to rally others to their cause – or at least reduce opposition to it. By extension, this behavior also happens throughout industry, so of course this occurs with the nuclear industry as well. Because of the unique hazards that nuclear technology brings with it, it is important that these risks be exposed and addressed. Addressing some of these risks are expensive and a plant owner may chose to gamble rather than cut into their profits. An industry could devote teams of people to downplaying risk. I would not at all be surprised if you were employed to operate in that capacity. Before you dissect my post for misuse of figures of speech, consider that there are long term safety issues in plants across the nation that are being ignored or allowed exemptions for whatever reason – and whatever reason could there be but cost?

            >> Spent fuel does not pose a threat when adequately stored.
            This is patently ridiculous – the substance would not need to be ‘adequately stored’ if it was not a threat. Moving along, the hundred thousand years of spent fuel risk exceeds the history of adequate storage technology so I think it is a little presumptuous to assume that it can be accomplished – in fact, there is 70 years of history which is very strongly suggesting that it can not be accomplished…

  • Sean McKinnon

    Everyone is entitled to their opinion. I applaud UCS for their work on nuclear weapons and wish they would devote their resources there. Nuclear power plants are large industrial factory type sites. When you compare nuclear power in the US to the chemical, petroleum, and manufacturing industries as well as other types of large power production facilities it becomes clear what a priority safety is. Isolated incidents cherry picked over a 40 year operating history of an entire industry is an unscientific way of presenting information.

    I just read today that people have had to evacuate because of an oil pipe line rupture. Where’s dr. Kaku and what’s his face from Vermont on this? Nuclear is and should be held to a higher standard and I feel at least in the US they have done a good job. Nuclear remains the only 0 carbon reliable source of base load power.

    • jharragi

      Sean, it is interesting that you would choose to let industry police itself… Would you feel the same way if a plant had a catastrophic flood risk statistically similar to Fukushima’s? What if Indian Point, 30 miles from Manhattan, was downstream from a reservoir where dam failure could occur?

      • Sean McKinnon

        Where did I say the industry should police itself? All industrial factories are regulated by multiple government agencies and rightly should be. The fact is nuclear has an impeccable industrial safety record compared to other similar sized entities. Why is it national news when a worker was killed at ANO today? Because it is so extremely rare to have a fatality occur at a NP that is not a heart attack or other natural cause. Workers are killed at chemical, petro, and coal fired power plants at a much higher rate than nuclear plants. These are facts. The public has been harmed greatly over the past 40 years by coal power plants oil refineries and chemical plants. Can you please provide a PROVEN VERIFIED scientifically accepyed case of a member of the public harmed by a nuclear power plant in the us?