(554.5316) WISE Amsterdam - The possibility of aircraft crashing into nuclear reactors has been raised from time to time. As a result, containment structures around reactors were often designed to resist impacts of aircraft. However, up until now it was always assumed that a crash would be accidental. Thus, for example, most US plants were designed to withstand the impact of light aircraft; only Seabrook and Three Mile Island (1) were designed with the impact of a large aircraft in mind (2). In Germany, where fighter jets carry out low-flying exercises, the impact of a Phantom fighter jet was used as a design basis for the newer plants, though not for the older plants (3). The direct impact of a large airliner was generally considered so improbable that it was ignored for design purposes.
Moreover, many of the designs were based on old research, such as a 1974 study (4) on the probabilities of an aircraft accidentally hitting a nuclear reactor, which itself was based on a census of the world's aircraft in 1968, before wide-body airliners were developed. It also considers the impact only of the engines, not of the airframe or the additional problems caused by aviation fuel catching fire (5).
Melissa Fleming, spokesperson for the IAEA, confirmed: "It is practically impossible to protect nuclear plants to the extent needed to withstand the sort of attack we saw last week" (6). The last time the IAEA published a guide to designing nuclear plants to withstand "external events" such as aircraft crashes and explosions was 1981, and it is now listed as out of print (7).
Attack scenarios What could happen in the event of an aircraft collision, bombing or similar attack? Many news reports have compared the situation to Chernobyl. At the IAEA Conference in Vienna, a US official who declined to be identified confirmed that a direct hit by a jumbo jet at high speed "could create a Chernobyl situation" (8).A 1996 analysis by Gordon Thompson of the Institute for Resource and Security Studies (9) concluded more or less the same: that the maximum release of radioactive substances would be caused if the containment broke and cooling and safety systems were damaged, resulting in a meltdown. This analysis involved a conventional weapon such as a 900kg bomb striking at a distance of a few dozen yards (tens of meters) from the reactor. Ironically, a direct hit which caused the reactor to break up might actually result in lower radioactive releases, since with less fuel remaining in the core, the risk of a meltdown would be lower.
Spent fuel pools are also vulnerable. Though some are located within the reactor containment building, many are not. An attack could cause a loss of the water in the pool, resulting in a risk of the irradiated fuel catching fire, particularly if the aircraft's fuel is already on fire. This could cause substantial releases of radioactivity even if the reactor containment is undamaged.
| RECOMMENDATIONS
Here are some recommendations that the Nuclear Information and Resource Service (NIRS) has made following the US attacks:
Source and contact: NIRS at nirsnet@nirs.org |
When irradiated fuel from many reactors is stored in one place, such as at the reprocessing plant at La Hague in France, an accident can have even more severe consequences. The smallest of the spent fuel pools, when just 50% full, contains 67 times as much cesium-137 as was released in the Chernobyl disaster, so a spent fuel fire could quite conceivable release more radioactivity than Chernobyl (10). Although Cogema disputes this, they admit that the plant was only designed to withstand an impact of an aircraft weighing less than 5.7 tonnes (11), whereas the Boeing 767 aircraft used in the US terrorist attacks weigh around 180 tonnes.
The high-level waste tanks at Sellafield (12) and La Hague also contain a huge amount of radioactivity and are less well-protected than reactors, according to Dr Frank Barnaby of the Oxford Research Group (13).
Stores of plutonium represent another risk. The Plutonium Finishing Plant in the US Hanford Nuclear Reservation contains 4 tons of plutonium. Despite being a military facility, it is not hardened against aircraft crashes, which could cause a "catastrophic radiological event" with plutonium-containing fallout (14). Plutonium is extremely radiotoxic, and inhaling just 80 micrograms of plutonium is usually fatal (15).
An aircraft crashing on stores of depleted uranium could also have a large impact. Depleted uranium is a waste material from uranium enrichment, where it is initially produced in the form of uranium hexafluoride (UF6). UF6 is solid at room temperature but tends to sublimate (become a gas), becoming entirely gaseous above 56.4 degrees Celsius, so it must be kept in sealed containers. If these containers break, UF6 gas will escape, which is very chemically reactive as well as being radiotoxic, so an aircraft impact on a UF6 store could have severe consequences (16). Despite this, the US has 739,000 tonnes of UF6 containing depleted uranium (17).
Conclusions
The terrorist attacks have revealed a real danger to nuclear installations that was not considered
worth mentioning in probabilistic risk assessment analyses. Nevertheless, a sense of proportion is
needed. However dramatic a terrorist attack might be, the slow deaths through cancer that are a
consequence of the normal functioning of nuclear installations must not be forgotten: deaths which
even the NRC estimates at 1200 in the case of US reactor relicensing (18).
Sources:
- See "US Attacks: The Three Mile Island Connection" in this issue.
- Email from Michael Mariotte, NIRS
- Badische Zeitung, 11 March 1989
- Wall, I.B. "Probabilistic Assessment of Aircraft Risk for Nuclear Power Plants", Nuclear Safety 15(3):276-284, May-June 1974
- See p.155 of Lovins, A.B. and Lovins, L. H. Brittle Power, Brick House Publishing, 1982.
- Quoted in The Guardian, 18 September 2001
- "External Man-induced Events in Relation to Nuclear Power Plant Siting: A Safety Guide". Safety Series No. 50-SG-S5, IAEA. Listed on www.iaea.org as out of print.
- Quoted by William J. Kole, Associated Press, 19 September 2001
- War & Nuclear Power Plants. Chernobyl Paper No. 2, Greenpeace International, March 1996.
- Note d'information: Les installations nucléaires exposeés aux risques de chute d'avion, WISE-Paris, 18 September 2001 (on web site www.wise-paris.org)
- Le point sur la sureté de l'usine de La Hague face au risque de chute d'avion, Cogema, 18 September 2001
- WISE News Communique 543.5242, "Sellafield: Waste tanks incident"
- Quoted in The Guardian, 18 September 2001
- The Spokesman-Review (Spokane), 13 September 2001
- Nuclear energy: a dead end, WISE Amsterdam
- Information from Laka Foundation, Amsterdam
- WISE Uranium website
- WISE News Communique 553.5310, "US: NRC admits 1,200 could die as a result of reactor relicensing"
Contact: WISE Amsterdam
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