Will a nuclear power plant blow up if it catches fire?

Answer 1

Designers try to establish the probability of such an event at less than 10-6 per annum, ie for any one reactor only one such event in 1 million years of operation. However this clearly depends on being able to predict failure rates of critical components such as the pressure vessel. We have an example of a catastrophic failure in the Chernobyl case, and there it is obvious that the designers had not anticipated all the ways that the plant could fail, and the failure rate for that design is too high. It is not being built any more, and in fact that design has not been built anywhere except in the former Soviet bloc.

Answer 2

It depends. Most, if not all, nuclear power plants are incapable of exploding in a nuclear fashion. Yes, it is possible to have super prompt criticality, where reactivity, or what we call KEffective is much greater than 1 and the reaction geometry degrades to the point where it can be sustained with only thermal neutrons.

Problem is, that physics intervenes. Fissionable material wants to expand when it is super prompt critical, and the pressures involved are astronomical. The core, in this case, then tends to go sub critical due to prompt dispersal, which is where the core gets suddenly, somewhat explosively, "larger", and the reaction stops.

In order to have a true nuclear detonation, you need to hold the core together long enough for a sizeable portion of the fuel to convert to energy, and that is just not possible with a power plant - a bomb, yes - but not a power plant.

Chernobyl went super prompt critical, and it did explode, but that explosion was not a complete detonation and, again, it just as suddenly went sub-critical due to prompt dispersal.

There are other things involved, of course. You can have a hydrogen explosion, caused by a buildup of hydrogen gas (no, I'm not talking about a hydrogen bomb) due to a high temperature reaction with the zirconium cladding on the fuel pins, such hydrogen then being detonated perhaps by mixing with water. This is what happened recently in Japan.

Even Chernobyl had no nuclear explosion, it did have a strong nuclear energy excursion, but the resulting explosion was still entirely a steam explosion as water in the cooling system and steam generator tanks flashed into high pressure vapor.

Also nuclear explosives operate on fast neutrons, not thermal neutrons, as they have no moderator to slow the neutrons. LLNL tried nuclear explosives with a moderator (Uranium Hydride fuel/moderator) in several tests in the 1950s, they all fizzled. This strongly suggests that any thermal neutron (moderated) reactor is incapable of a nuclear explosion (however fast neutron reactors like breeders might be a different issue).

Answer 3

Designers aim at proving a probability for a reactor of 10-6 per annum or less, of a major disruptive accident releasing radioactivity on a large scale. This is done by a thorough fault analysis, and providing extra equipment and inspections where necessary. Of course we rely on them getting it right, but PWR's and BWR's are well enough understood now to be confident. The Russian RBMK design, we know now through the Chernobyl disaster, could not have been so thoroughly designed, and it had inherent faults which were not foreseen when it was built. That type would certainly not be built in the US or W Europe, and I think no more are being built anywhere. However I suppose every country insists on its own independence, and a faulty design could be built somewhere in a country that won't accept IAEA supervision.

Answer 4

Chernobyl offers the only example of this happening. It resulted in widespread radiation fall out and the need to evacuate nearby population. On the site itself about 50 people mostly firefighters died soon after. The effects on a wider population are not so clear, and need study over a long period. Needless to say, the plant itself is a permanent and complete write off.

Answer 5

Not necessarily, and not in a nuclear explosion - the explosion would be chemical or from steam.

Like many industrial plants, there are ways a nuclear plant could have an explosion. The explosion could even be very destructive, as the one at Chernobyl was. But even the Chernobyl Disaster did not involve a nuclear explosion. Nuclear material was blown out of the plant, but the motive force was chemical and steam.

A nuclear explosion is not something that is likely to happen by accident. There is a common idea that it is easy to build a nuclear bomb and that all you need to do to get a bomb is put together a critical mass. This idea is not true, however. Getting a critical mass together is not enough - it must be held together long enough to explode instead of just popping apart into a number of subcritical masses. It is not something that could happen accidentally at a nuclear plant.

This is not to say that a chemical or steam explosion at a nuclear plant would not be destructive. Again, looking at Chernobyl, the amount of radioactive material released was considerable, and the damage done was enormous. In fact the value of the economic loss has been estimated as high as a trillion 1995 U. S. dollars.

Answer 6

In the history of Nuclear Power there have been 3 explosions inside the containment dome. All of these were because of the release of hydrogen (a very explosive gas) because the core of the nuclear reactor was not cooled by a steady stream of pure water. Free Hydrogen was released in all 3 of these incidents because residual cooling water in the reactor was effectively ionized by the fission process and was turned into a vapor of Hydrogen and Oxygen and ignited by the electical circuits inside the reactor. The three incidents occured in SWG-5 (General Electric) prototype Naval Reactor, Idaho in 1955, Pripyat Reactor 2 (MK-1000 Soviet Union) Chernobyl Ukraine 1985 and the Fukushima reactors 1, 3,4,5,6 (also General Electric) in 2011. Three Mile Island in Pennsylvania (1979) did not suffer an explosion such as this because it was constantly monitored.

Answer 7

Yes, but the most likely event is an ordinary industrial accident rather than a nuclear one.

Yes it is possible to die from a nuclear power plant explosion (many have already), but first you must understand that a nuclear plant explosion is not a nuclear explosion. To get a nuclear explosion the nuclear fuel must be rapidly assembled from a subcritical configuration to a very supercritical configuration then hit with a precisely timed pulse of neutrons from a neutron source. This "assembly" must complete in a time on the order of 1ms, which can only be done with explosives. There are no such explosives in a reactor. If a reactor core does go somewhat supercritical, it will simply melt (because the coolant can't carry the large heat pulse away fast enough) reducing itself back to a subcritical state.

The most common type of nuclear plant explosion is a steam explosion which is caused by flash boiling. In one reactor in the 1950s they were doing a refueling operation and had a steam explosion inside the fuel rod assembly being worked on, which propelled a rod out the top of the reactor into the area where the workers were. One worker was impaled on the rod and lifted to the ceiling, where the rod imbedded itself. That worker died of the traumatic physical injury as a result of the explosion. The other workers received enough radiation dose from that rod and the radioactive steam that they could not return to work for a few months, none of them died (the company was required to pay them while not working). The Chernobyl explosion in 1986 was also a steam explosion. Nobody died from physical injuries caused by the explosion, but all the firefighters died from radiation exposure that would not have occurred if not for the explosion and graphite fire that followed.

Another type of nuclear plant explosion is a hydrogen gas explosion which is an ordinary hydrogen/oxygen explosion. This only occurs in water cooled reactors using zirconium clad fuel pellets when the fuel rods overheat because of inadequate cooling. The overheated zirconium reacts with the water releasing hydrogen gas, if enough collects and a spark occurs it explodes. The Three Mile Island accident in 1979 resulted in a significant amount of hydrogen collecting in the reactor, but luckily no explosion resulted. Nobody died from TMI, but some could have.

Unfortunately in the nuclear plant problems Japan has had since the big earthquake, several plants have experienced explosions. We probably won't know what types they were, their severity, or if anyone died and how, from them for some time.

Answer 8

Chernobyl in Ukraine, 1986.