Nuclear Power Plant Accidents Trivia Quiz

Answer: March 28, 1979

We were all glued to our TV screens as the event played out night after night on the evening news.

Answer: Generally, they worked as designed. However, the operators overrode several of these systems and made the accident much worse than it would otherwise have been.

The accident started with a failure in the normal feed water system. The automated auxiliary feed water system came on but a maintenance error had shut a valve blocking the system out. The reactor detected the loss of cooling water and shut the reactor down automatically.

When the pressure got too high a pressure relief valve opened but got stuck open. The operators failed to understand that and only hours later figured out why they were losing water and shut a block valve beyond the stuck open pressure relief valve.

When the water level got too low the automatic emergency cooling system came on but the operators, not understanding what was happening, shut it down. Later, as pressure continued to fall, they shut down the primary coolant pumps stopping the circulation of any coolant. Without the manual errors by the operators the accident would have been trivial.

Answer: The public were not exposed to dangerous levels of radiation from the accident. No discernable health effects occurred.

While the fuel was seriously damaged, the reactor pressure vessel (the big steel tank the nuclear fuel is in) and the surrounding containment building held. Only a small puff of radioactive gas was released early in the accident before the containment system blocked all exit paths.

After years of careful study and strong debate, it was concluded that even the worst exposed individuals received only a fraction of the radiation they would get from a year's worth of naturally occurring sources.

Answer: Both the government and the nuclear industry made fundamental changes in how nuclear power was regulated and how plants were operated.

The Nuclear Regulatory Commission undertook an exhaustive series of safety studies and formed a considerable body of enhanced regulations. The industry made a wide variety of changes and improvements. Perhaps the most important of these was the development of full scope simulators.

It was recognized that many of the problems in the Three Mile Island accident were caused by the operators dealing with a situation they had never seen before. The simulators were developed to greatly improve operator training.

As full scale simulations, these exactly duplicated the control room equipment. The operators could be exposed to simulated accidents and practice correct responses.

Answer: They are very different.

The RBMK design is what is called a graphite-moderated reactor. That means it is constructed with great blocks of graphite as part of the structure. It was an outgrowth of the military reactors the Soviets used to make plutonium for nuclear weapons. Most Western reactors use water as the moderator. The importance of this is that in Western power reactors if, for any reason, the amount of cooling water in the reactor is reduced, say it begins to boil or leak out, the physics of the reactor, without any human or machine action, this will cause the reactor to reduce power. The particular design of the RBMKs causes the opposite to happen. That is, if the cooling water is lost, the power goes up. This is a fundamental violation of a key part of the safety philosophy of Western power reactors.

In conducting an odd test the RBMK operators managed to get the reactor into a very unstable state. Once they saw they were getting into trouble, they inserted the control rods to shut the reactor down. Tragically, the result was as the control rods came in they pushed out the little bit of water left, causing the reactor to increase power very fast, destroying the plant.

In addition all Western reactors have a containment building around the reactor itself. This is a big steel-lined reinforced concrete structure designed to hold in anything bad that happens inside the reactor. The RBMK design doesn't have an equivalent structure.

Answer: The graphite caught fire and the thermal plume of the fire pushed radioactive material high into the atmosphere.

The graphite burned for days and this made the release much worse that would have come from a Western style reactor even if its containment building were to be breached.

The local workers were tremendously brave. Some thirty-one workers and fire fighters died trying to contain the releases. Two hundred and forty were treated for excessive radiation exposure.

Answer: False

No one can truly say exactly how many deaths will be caused by the radiation releases from the Chernobyl accident. When someone dies of cancer there is no big red arrow sticking out of their chest with a tag on it that says, "this was caused by XYZ".

There have been a lot of claims from a wide variety of people on the topic. One source to consider is the International Atomic Energy Agency. They held a symposium "One Decay After Chernobyl" in 1996. In that, they concluded that we could expect 2500 additional cancer deaths in the impacted population. For perspective, that is out of 500,000 expected total cancer deaths in that population or half of one percent. So, while there is certainly room for debate, the Chernobyl radioactive releases are not expected to be the major cause of death in the region.

Answer: It didn't. The reactors that were shutdown stayed shutdown. Those operating shutdown automatically.

The reactors all shut down like they should have in a major seismic event. However, when a nuclear power plant is shut down doesn't mean there is no more heat. If you shut off your oven after you have baked your pie, can you then immediately grab on to the heating coils? In nuclear reactors, it is more complicated as the radioactive material built up by running the reactor continues to produce heat through radioactive decay, even after the reactor is "shut down."

This decay heat decreases rapidly at the start but then slows down its rate of decrease. One minute after shutdown a reactor will be producing about 2.5% of the heat it was during full power operation. In ten minutes, it will be down to 1.5%; in one hour down to 1%; but at one month after shutdown, it will be still at 0.2% of the original power. If you do the math for the Fukushima Plant 1 Units 2 and 3 (the largest of the reactors at the station operating at the time of the earthquake) four days after shutdown each of the reactors were still producing something like seven million watts of heat, equivalent to 5000 hair dryers on high

Answer: Between the earthquake and the tsunami, all the sources of electrical power were compromised and the cooling systems could not function.

The post-shutdown cooling is dependent on electric motors to drive pumps and provide the cooling water. There are three sources of electric power for modern commercial power reactors. The first is the electrical power produced by the station itself. Since all the reactors automatically shutdown because of the earthquake, this was not available.

The second is off-site power, that is, electricity from the larger electrical grid hooked into many other power stations. The earthquake was so severe that all the power lines coming into the station were disrupted.

The final line of defense is a set of diesel generators which start up in emergencies and are designed to provide the needed electrical power for the post-shutdown cooling. At the start, these came on line and were working.

However, shortly after the earthquake the massive tsunami stuck the plant, flooding the generator buildings and washing their fuel tanks away. High, strong seawalls had been built to protect the diesel generators and their tanks, but the tsunami was much stronger than expected.

While we still have much to understand and learn about the Fukushima accident, it is possible that the failure to design adequate seawalls will come out as the single most important reason why the plant's safety was compromised.

Answer: False

It might be difficult to attempt to say what is or is not important and we must realize that the "event" is not over yet with the damaged nuclear fuel, while under control, not completely contained either. However, let's put things in perspective. First, there are fifty-three nuclear power plants in Japan. Many of them, more distant from the epicenter of the earthquake, continued to operate safely during the earthquake. Their very robust designs continued to feed critically needed electricity after the earthquake. While getting little press, other power plants had problems: several fossil-fueled electricity generating plants were knocked off-line. Not far from Fukushima an oil refinery caught fire and burnt for days.

The death toll from the earthquake and tsunami is over 18,000. The Fukushima plant has had four deaths. One worker was killed by a collapsing crane during the initial quake, two were killed in the tsunami, and one older worker died some time later as he was helping in the recovery efforts. While the press has not provided much information on this last unfortunate worker, it was clear his death, like the other three, was unrelated to the "nuclear" nature of their work.

All responsible estimates of public health effects at this stage suggest essentially no meaningful impact from the Fukushima nuclear accident.

So, was the damage at the Japanese nuclear plants important and something of concern? The answer is, sure you bet. Is it the most important thing in this tragic event? In perspective, the answer seems clearly, no.