About a hypothetical terrorist attack on a nuclear power plant

by B. Comby / EFN

Monday, October 22, 2001

One month after the terrorist attacks on the World Trade Centre, a record number (two thirds) of US citizens favour the use of nuclear energy and consider nuclear plants to be safe. At the same time 59% 'definitely" support building more nuclear plants, less than in March during the Californian crisis, but more than earlier. Most american citizens (84%) continue to support licence renewal for nuclear plants and 72% agree with keeping the option open to build new nuclear plants in the future. The strongest supporters are those who have visited a nuclear plant or information centre. (Source : UIC/NucNet news # 303/01).

And they are quite right to stay calm and not to panic without necessity.

In response to the often asked question "what would happen if a terrorist plane crashed on a nuclear power plant?" here are a few points to be noted :

- a nuclear power plant's containment structure, which encloses the nuclear reactor, is only a few dozen meters in diameter, very much smaller (and therefore difficult to aim at) than the WTC's towers, which represent a volume larger than a NPP's containment structure by a factor of 100 (at least).

- a nuclear power plant's containment structure consists in a more or less 1 meter thick wall of very thick and heavy reinforced concrete : much more resistant than the windows and not-so-thick metallic structures of the WTC.

- if the airplane hits other buildings on the site around it, other than the containment structure, the reactor will automatically stop due to the many independant and automatic security systems (even, in most cases, if the control room was destroyed).

- if the airplane hits the side of the circular concrete containement structure (at an angle significantly less than 90°), it will probably just bounce off the side and hardly damage the external structure at all, because the containment structure in most power plants is very heavy, thick and strong and has a more or less circular form (reinforced concrete).

- if the airplane hits the top of the containment structure, it will probably not directly damage the vital structures of the core of the reactor which are, in most installations, located much lower, in the bottom part, or at middle height in the reactor building, and the reactor will stop automatically (the automatic protection against earth-quakes will be activated by the impact).

- if the airplane hits the containment structure in it's middle-height or lower part, which isn't easy because there are many other (non-nuclear) buildings around a nuclear power plant, it will the need to get through not only the very thick external containment, but also several successive reinforced concrete walls (about 20 to 40 centimeters thick each), on most nuclear power plants, before reaching the heart of the reactor itself. The probability that pieces of a large airplane make their way through all these successive walls isn't so certain.

- terrorist attacks or plane accidents are in fact taken in consideration when designing nuclear power plants, but only to resist the crash of small airplanes. A large airplane at full speed as in the case of the WTC, may produce some damage to the containment structure and, perhaps, to the reactor itself.

- although it has only a small probability, the worse accident cannot be excluded. In this case, the greatest risk (there are many if's, but it may happen, even if the probablitiy is quite small) for water reactors (the most widespread type of nuclear reactor today) is the important amount of radioactive iodine contained inside the reactor which could perhaps be released in the reactor building, and to the environment if the containment structure was damaged.

- please note the many if's : if the plane doesn't miss the NPP (relatively small, compared to WTC), if it hits the concrete containment exactly on the middle, not on the sides, if it strikes the containment structure not too high and not too low, if it gets through the containment structure, if it damages both the (small in volume) core of the reactor or a vital part of the primary circuit), if it also damages several or all the multiple redundant safety systems, then a bad accident MAY perhaps happen.

- the general concepts used since many decades as the basis of nuclear safety for designing nuclear power plants : multiple and redundant safety systems, and a very thick and strong containment structure, in case everything else fails, are in fact the best strategy that one could develop to prevent and minimize the consequences of a terrorist attack such as those against the WTC.

- even in case the worse happens (although this isn't the highest probability), the main danger for the civilian populations around the site would be the release of radioactive iodine, a fission product, in the atmosphere. If the reactor just started recently, then there is only little amounts only of iodine (a product of the nuclear fission) inside the reactor.

- a counter-poison exists to prevent the effects of radioactive iodine in the human body, and it is very efficient in case of a major release of iodine in the atmosphere : it consists in absorbing non-radioactive iodine pills. This protective measure saturates the thyroid gland and is efficient in only 10 to 15 minutes after taking the pill.

- the population living near nuclear and power plants, in many countries (including France, Finland and many others), already have iodine pills distributed in advance (within a radius of 5 to 15 km around the plant), stored at hand, and ready to be taken at any moment (this protective measure was implemented since several years or decades, even before september 11th in most developed countries).

In view of the WTC events, the probability (although still very small) of such an accident has increased and cannot be totally excluded. Therefore, it could be discussed and decided to increase the radius of the distribution of iodine to local populations around an NPP to, say for example, 50 km instead of 5 or 15. The concentration of the iodine in the atmosphere usually decreases very rapidly with the distance, therefore protective measures are not justified at far-away distances.

Although the consequences of a terrorist attack or voluntary plane crash on a nuclear power plant would in reality not be as bad as could be feared (probably no effect at all, or only minor effects, if any), EFN is in favor of the distribution of iodine to the surrounding population (just in case..., prinicple of precaution) and in favor of protection of nuclear power plants by military anti-air missiles. This military protection is mostly necessary not because of the potential risks, but because of the strategic importance of major electricity producing plants.

After the terrorist attacks on the WTC, specific protective actions could and should be taken in all nuclear power plants, as well as in reprocessing plants and fuel-storage locations, especially those locations that include storage of nuclear fuel in water not inside a containment structure. This is often the case for used-fuel storage using water as a coolant. The details of the very simple protective actions to be taken are quite technical and need not be detailed here.

It can also be noted that by constantly exagerating the risks concerning nuclear power plants in the public opinion and in the media, the anti-nuclear organizations are paving the way for terrorists and increasing the chances of seeing a terrorist attack on a NPP.

A suicide attack, even with a big airplane on a nuclear plant cannot be guaranteed as having no effect (no other industrial installations can resist), and the reactor may be damaged or lost, but would in any case have much smaller effects and casualties than the same airplane on any inhabited large building of any city. Quite unfortunately, there are many other much more exposed targets (buildings, unprotected industries) that would result in killing a great many more citizens.

With kindest regards,


Bruno Comby,

President of EFN
Environmentalists For Nuclear Energy