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Exploring the Darker Side of Everything

What Happens if a Nuclear Power Plant is Abandoned?

Written by Kevin Jennings

Of all the scientific advances that mankind has achieved, few can rival nuclear detonations for the sheer terror they are able to instill in people. Nuclear weapons are so terrifying that none have been used in combat since the end of World War II. But not all science is dedicated to war, and the flip side of nuclear weapons is nuclear energy. Nuclear power is generally regarding as being safe, clean, and extremely efficient, but what about when things go wrong?

              To date, there have been three large-scale nuclear meltdowns: Three Mile Island in the United States, Chernobyl in Russia, and Fukushima Daiichi in Japan. There have been other partial meltdowns or nuclear incidents, but those are the three big ones, the ones that no one wants to repeat.

              In order to understand what could happen if a power plant was suddenly abandoned, we need to understand what caused these three events.

Fukushima

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            Fukushima is the most recent of the three events. It’s also the easiest to understand because, simply put, it was nobody’s fault. The reactor behaved exactly as it was supposed to and the personnel did exactly as they should have, but there were forced beyond their control.

              On March 11, 2011, Japan was hit by the most powerful earthquake it had ever recorded. Immediately following the earthquake, the safety procedure known as SCRAM was initiated. Though it is usually written in all caps, it is not generally believed to be an acronym but literally to mean “scram”, as in “get the Hell out”. The button labeled “SCRAM” is the emergency reactor shutdown.

              Once pressed, the button drops the reactor’s control rods that stop the nuclear fission reaction from taking place. Even with the reaction no longer taking place, the radioactive materials will still produce decay heat and thus they must continue to be cooled. With the reactor no longer generating power to run its cooling systems, backup diesel generators are in place to power the cooling system and prevent anything bad from happening.

              At this point everything would have been fine, were it not for the 45 foot (14 meter) tall tsunami that came crashing into the power plant, destroying the diesel generators. Nobody did anything wrong, the tragedy was just the result of two natural disasters hitting the power plant is rapid succession

Three Mile Island

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            On March 27, 1979, workers at the Three Mile Island nuclear plant were cleaning a blockage in a water filter. The filters are designed to stop impurities from getting into the steam generators. It’s an important task, though the blockage was not any sort of imminent danger. Not only was it important, but it was also a routine and usually simple task. The normal method of clearing the blockage was to just blow it out using compressed air.

              However, this time that wasn’t working. The workers decided to put the compressed air into the water, using the pressurized water to clear out the filter. It worked, but some of the water was then propelled past the filter and into a check valve that was stuck open. Eleven hours later, the water in the system would cause the steam generators to trip and undergo an emergency shutdown.

              With the steam generators no longer receiving water, the reactor’s coolant system could not work at capacity and the temperature began to rise. The reactor automatically triggers its scram and stopped the reaction. But as we discussed before, it still needed to be cooled due to the decay heat.

              When the feed water for the steam generators shut off, backup pumps had started running. However, the block valves for those pumps water lines were closed in violation of Nuclear Regulatory Commission rules; it is believed that they had been closed during a surveillance test two days prior and were never reopened. During the emergency, the operator could not see lights indicating that these valves were closed. One of the lights was covered by a maintenance tag, and it is believed the operator’s girth blocked the other light on the bottom of the panel from his field of view.

              The water level in the coolant system began to rise while the pressure dropped. It turned out that a relief valve was open causing the system to lose coolant, but the technicians were unaware of this due to unclear indicators on the controls. The confusion resulted in them turning off the emergency core cooling pumps that had been triggered automatically when the system began losing coolant.

              By the time of the 6 am shift change in the control room, things had gotten out of hand. Around 32,000 gallons of coolant had already leaked out, and was 300 times more radioactive than it should have been with high contamination levels in the area. There is dispute over how serious the event was and how much radiation escaped the facility, but the most important take away is that this all could have been prevented.

Chernobyl

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            Chernobyl all began with an experiment gone wrong. It was supposed to be a safety test, designed to see if the steam turbine could power the emergency feed water in the event of a simultaneous loss of external power and a major coolant leak. They intended to run the test at low power, but the power output for the test was too low, eventually falling almost to zero.

              To compensate, the technicians began manually removing the control rods that are designed to absorb neutrons and slow the fission reaction. By the time they were finished, they had removed nearly all 211 of the control rods in the reactor, leaving fewer than 15, the required minimum to be maintained at all times. Unfortunately, the controls did not have any way to indicate how many of the rods were removed and the workers were likely too concerned with raising the power to keep count.

              The actual test began at 1:23:04 on April 26, 1986. After 36 seconds the test was completed and the scram was initiated so the reactor could be shut down for routine maintenance. But it was already too late. It is unknown whether the scram was initiated before or after the spike in power output, but it doesn’t really matter. The water began creating steam voids which can amplify the output of a nuclear reactor. With virtually no control rods remaining, a runaway reaction should have seemed inevitable.

Even if the button had been hit before this reaction began, the specific design of this reactor took a full 20 seconds for the rods to be reinserted. Worst of all, the control rods had graphite tips that were prone to causing brief power spikes when initially reinserted. What happened next is something that those surrounding Chernobyl are still dealing with to this day.

An Abandoned Plant

            As we saw with Fukushima, what will happen in the event of an unmanned nuclear power plant is dependent on why it was abandoned in the first place. The Japanese operators didn’t abandon the plant and without their efforts things could have potentially been even worse, but what if they had? Or what if their lives had fallen victim to the earthquake and tsunami?

              Should a nuclear facility’s crew either flee from some natural disaster or be killed as a result of it, there’s the possibility of it sustaining serious damage to critical components or infrastructure that could result in another critical meltdown like in Fukushima.

              But what if it was abandoned for a different reason entirely, such as being under attack by hostile invaders or some theoretical contagion that killed the entire crew? In a scenario where an otherwise functional nuclear plant was suddenly unstaffed, things would almost certainly be fine, at least in the short term. In the cases of both Chernobyl and Three Mile Island, the disasters were the direct result of human intervention, and it’s been widely stated that in both instances the plants would have been better off if no one was there at all.

              Because of the danger a nuclear meltdown can pose, power plants have some of the most redundancy and highest levels of safety that you’ll find anywhere. Most of the reactor’s operations are also monitored and run by computers anyway, so it’s not like they need constant human intervention to prevent disaster. Even though plants are all equipped with a SCRAM button to quickly power down the reactor in the event of an emergency, and it really is just one button not a complicated process, we’ll assume in this scenario that the button was not pressed and the reactor is still in operation at the time the plant is abandoned.

              To start, the good news is there is effectively no chance that the reactor is actually going to explode like Chernobyl, so that’s one less thing to worry about. If abandoned, the plant will continue running like normal, at least for a while. Most modern reactors are designed to automatically scram after some period of time without human interference or maintenance. Others will continue to run until the computer measures some parameter as being outside of the acceptable limits, at which point it will scram. Note that “outside the acceptable limits” does not mean catastrophic failure and imminent doom, just that it needs to shut down so things can be looked at. This could take anywhere from less than a day to a few weeks depending on the design of the plant and how smoothly everything was running.

              Once the reactor has shut down, the backup diesel generators will kick on to facilitate the cooling process. Even though the nuclear reaction will have stopped, the decay heat could cause a meltdown if not cooled. Fortunately, federal regulations require an emergency water supply that can last 30 days to necessitate this cooling. At this point, it’s all a matter of how much fuel the diesel generators have. The typical answer for this seems to be about a week’s worth. For that week, the coolant system will be continuously running to bring down the temperature of the decay heat.

              The generators will run out of fuel before a cold shutdown is completed, but it should be long enough to remove any serious risk to the surrounding area. Bad things could still happen inside the reactor, but it will be cooled enough that, so long as nothing was damaged, any partial meltdown or hydrogen explosion would be isolated inside the containment unit. In the long term this radiation will probably begin to escape containment, but little if any would be escaping the entire facility, certainly nothing that would be an immediate danger to the surrounding area.

              Aside from the reactor, the other concern is the spent fuel pools. These are 40 foot (12 meter) deep pools of water, with the bottom 14 feet being used to store the spent fuel from the reactors. The pools serve as short term storage for the radioactive materials, providing them a place to cool off and decay.  These pools also require cooling, so for as long as the reactor and then the diesel generators are online, they will be fine.

              The potential danger comes once the generators run out of fuel. After about three days without cooling, the spent fuel can raise the temperature of the water to its boiling point, and the water will start to evaporate. Fortunately, there is a lot of water, and it will likely take at least a week for the water to boil off. But even once the water boils off, very little is likely to happen. There’s nothing the fuel can interact with to reach criticality or sustain any sort of fission reaction. The worst case scenario is if the spent fuel is somehow able to induce a fire, releasing radioactive particles and gasses. This would be bad, but fortunately most of it would remain contained within the building.

Wrap Up

            There’s no precise timetable for how long a nuclear power plant would remain safe if abandoned. The age of the facility, the amount and age of the spent fuel being stored, the amount of fuel for the backup generators, and the amount of emergency water on site are all variables in this equation.

              Fortunately, even using pessimistic estimates, there should be about a week before anything is going to start going terribly wrong. Even once things do go poorly, there would still be weeks or longer where any contamination should be confined entirely within the plant itself, allowing the possibility of cleanup efforts before radiation affects the surrounding area. There is no 24 hour ticking clock before a nuclear explosion or anything to that affect. The ramifications could still be serious, but given the danger radiation can pose to humans, these systems were all designed to mitigate as much of that danger as possible.

              So should an otherwise functional nuclear plant be abandoned, such as when under attack, there would absolutely be a few days for either side to get people back inside to operate the reactors with no ill effects. Of course, if a plant was abandoned because it was under attack and was being fired upon or was the target of missile strikes, then there’s a good chance it would no longer be fully functional and the probable outcomes become dramatically more severe.

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