Fouth quarter of 2001

WISE-Paris answers COGEMA: The consequences of the crash of an airliner on La Hague are unimaginable

WISE-Paris, 8 october 2001

[Posted 08/10/2001]

In the text below WISE-Paris gives a point by point answer to COGEMA's statements published in a press release placed on the COGEMA website ( on 19 September 2001.

In its press release of 19 September 1999, COGEMA gives a vigorous rebuttal of WISE-Paris' report on the potential risk represented by the reprocessing installations at La Hague, France, in the face of the threat of impact by a large aircraft. The terrorist attacks in the USA, on 11 September 2001, have illustrated dramatically that such a scenario cannot now be excluded on the basis of purely probabilistic considerations.

WISE-Paris has published the results of analyses, made as part of a recent study, which indicate that serious accident scenarios involving loss of water from spent fuel cooling pools would lead to a massive release of radioactive substances with an impact that could be tens of times that of the Chernobyl accident. It now appears that the crash of a commercial airliner must be added to the list of scenarios.

Since then, Michel Pouilloux, Director of the COGEMA's La Hague establishment, has declared, "I think analysis [of the impact of an aircraft] is necessary" as "what seemed extremely improbable has now happened in New York. We must now look into this." (1) COGEMA had not, therefore, made any in-depth analysis prior to that date of a scenario involving the crashing of an airliner, a hypothesis not considered in the regulations applying to design of nuclear installations. However, the COGEMA press release attempts to show, point by point, an "absence of rigor" in the WISE-Paris study (2) and concludes that it is "unrealistic" to believe that the crash of a commercial airliner onto La Hague could lead to a catastrophe.

It is up to COGEMA to demonstrate the basis for this reassuring conclusion; the press release of 19 September 2001 does not provide any such conclusion. The few elements provided by COGEMA-somewhat flimsy and sometimes defamatory in nature-nevertheless provide the opportunity to start a debate which WISE-Paris, for its part, would wish as rigorous as possible. The points detailed below, from the COGEMA press release of 19 September 2001 (quotations in orange), invite particular comment.

1) "The lack of rigor of the WISE-Paris study is illustrated first by its comparing the La Hague plant with Chernobyl. The plant at La Hague is a chemical plant that can in no way be likened to a nuclear reactor, and its activity reduces the risk of accidents due to an airplane crash."

Obviously, our intention was not to pretend that an accident scenario identical to that which occurred at Chernobyl could occur in an irradiated fuel storage pool. But that does not in any way preclude the possibility of a specific scenario leading to a similar massive release of radioactive substances. In fact, in October 2000, the US NRC published a study (3) describing scenarios of this type (accidental emptying of pools, zirconium fire, etc.). The comparison proposed by WISE-Paris is not of the accident scenarios themselves, but of the impacts of different scenarios leading to similar effects (release and dispersal of large quantities of cesium-137).
The La Hague reprocessing plant is a "chemical plant" of a very special type and, of course, has nothing in common-except the presence of radioactive substances-with a nuclear reactor. However, it is not at all evident that, as COGEMA claims, its specific nature results in reduced risk. Quite the opposite in fact. The potential impacts of a plane crash on the La Hague site, as a nuclear installation, can legitimately be questioned, given the known inventory of radioactive materials present: in its cooling pools, the site concentrates a quantity of fuel equivalent to around 70 reactor cores, (4) with the addition, in other storage facilities, of 55 tonnes of separated plutonium under powder form (5) and more than 1000 cubic meters of long-life, high level waste.
This concentration can only increase both the possibilities of a scenario of massive release and augment the quantities involved in such a scenario. This is the sense of the assessment made public by WISE-Paris: a severe accident causing a major release would lead to dispersion in the environment of greater quantities than those released by the Chernobyl accident, with a potentially proportional impact.

2) "The spent fuel present at the site is in fact less vulnerable there than it is in or near a nuclear power plant. As for the vitrified nuclear wastes that come from reprocessing, they are totally inert and pose absolutely no risk."

The comparative vulnerability of the nuclear fuel in power plants or in the La Hague storage pools depends on the strength of the structures surrounding it. COGEMA refers to reinforced concrete walls that are, "on average", 80 centimeters to 1.6 meters thick but does not give the actual thickness of the most exposed part, i.e. the roof slab of the storage building. The containment buildings for French 900 MW reactors are 90 cm thick, those for 1,300 MW and 1450 MW reactors have two successive containment shells of 55 cm and 1.20 m, separated by a 2-meter void. (6) A 1,300 MW reactor measures around 40 m in diameter for a height of 50 m, which can be compared with the 90 m in length and 30 m width of the buildings housing pools C, D and E. Protection of pools therefore seems at best comparable to-and probably less robust than-that for reactors. On 13 September 2001, the French safety authority (the DSIN) recognized that reactor protection is not designed to withstand the impact of a commercial airliner. It is easy to understand why: from assessments by the US NRC, the probability of penetration of an aircraft with a weight of more than 5.4 tonnes on a 1.20-m thick concrete wall, the median of the figures provided by COGEMA, is greater than 55 per cent. Commercial airliners have weights of several hundreds of tonnes and, their impact would be several tens to several hundred times greater than that used in design calculations for nuclear installations.
Regarding the vitrified wastes arising from reprocessing, being inert is the condition required to prevent the dispersion due to internal causes of the high-level fission products and long-life actinides that they contain. However, an external event can lead to their dispersal if the initial energy input is sufficient. It is therefore necessary to assess the ability of containers to withstand the impact and heat resulting from the crashing of a large aircraft and a kerosene fire, and not to simply dismiss these containers as posing "absolutely no risk".
According to information obtained by WISE-Paris, the technical specifications for vitrified waste indicate: that it must be kept permanently at a temperature below 510 °C; that at 546 °C the glass begins to deform; and that it becomes liquid at 1,160 °C, a temperature which can be exceeded by a kerosene fire. Furthermore, this high-level waste issues from vitrification of liquid solutions containing reprocessing 'residues'. The La Hague plant has been operating 'on line' vitrification since 1990-1991, i.e. without storage of waste in the liquid form. Since then, COGEMA has sought to vitrify the stocks of liquid waste put into storage prior to opening of the vitrifying facilities. It is therefore not impossible that residual stocks of high-activity waste remain on the site in their liquid form, far more dispersible than in the vitrified form. (7) It also appears that the technical specifications mention a storage period of one year between concentration of the fission products and their vitrification, implying the existence of a significant buffer store of high-level liquids.
Other problems are apparently raised by these same technical specifications, regarding bitumenized waste. These relate to the sludge produced during reprocessing operations which, until 1998, (8) were poured together with bitumen into 210-l and 225-l drums with one millimeter thick walls. This type of waste becomes fluent at around 50 °C, burns when subjected to fire at 350 °C, and flames spontaneously when the ambient temperature is around 400 °C. At the end of 1999, around 2,350 m3 (9,898 drums) of bitumenized waste were stored at the La Hague site.
Also worthy of note are the large quantities of sludge (9,300 m3), of hulls and nozzles (2.245 tones), of magnesium (9) and graphite (2,930 m3) stored, unpackaged, in silos. These silos have already demonstrated their sensitivity to fire on 16 January 1981, by causing the most serious accident that has taken place at La Hague (classified at level 3 on the INES).
Finally, COGEMA omitted to mention the other enormous stocks of radioactive material stored on the site, especially the plutonium stored in powder form (and therefore highly dispersible in a release scenario) as well as unknown quantities of reprocessed uranium, possibly in liquid form. (10)

3) "WISE-Paris also makes the assumption that all of the cesium contained in the fuel stored in the pools would be released into the environment. This assumption is scientifically unsound."

A precise hypothesis for the release percentage must correspond to a precise release scenario. In its assessment, WISE-Paris was not looking at a specific scenario but was attempting to show the global potential impact of possible release scenarios. The October 2000 study from US NRC, on which this assessment was based, clearly indicates a possible range from 50 to 100 per cent for release of the cesium-137 inventory of a pool in the worst-case scenarios. WISE-Paris took the 100 per cent hypothesis and assessed the quantities released under this hypothesis based on the contents of the smallest La Hague pool filled to half its storage capacity: the result was 66 times the quantity of cesium-137 estimated to have been released at Chernobyl. It is true that with the hypothesis based on the lower end of the NRC's bracket, this figure 'falls' to 33 times. But even a limited release of a few per cent of the cesium content of the smallest pool when half full would lead to totally unacceptable consequences.
COGEMA's assertion that the '100 per cent hypothesis' is "scientifically unfounded" is equivalent to having shown that no imaginable scenario could give rise to such release. For scenarios involving loss of water from pools and propagation of fire by a "zirconium fire", calculations on the energy involved are used to assess the levels of release. The analyses made by WISE-Paris (Nuclear facilities exposed to plane crash risk) show that the impact of an airliner on a pool at La Hague could destroy or severely damage the targeted pool as well as other pools and facilities on the site.

4) "In the first place, the fuel is very well protected inside cladded assemblies, which are held in metal compartments. These are stored four meters under water. The fuel is cooled continually at an average temperature of 40 °C, and in the very unlikely event that it were not covered with water, it would take several days for it to rise to the temperature it reaches in the reactors. Last, means are available at the plant to maintain the temperature of the fuel at a level that would remove any subsequent risk of fusion."

These comments relate to scenarios for accidents with internal causes, arising from problems in operation of the installation: accidental emptying of pool, loss of water supply systems, etc. There is room for discussion of the way in which such a scenario would translate into reality: e.g.; actual rate of emptying of pools; temperature actually reached depending on fuel configuration; or the actual effectiveness of the means for accident response.
On this point, COGEMA's reassuring statements are in contradiction with the recent NRC study quoted above, which concludes that this type of 'internal-origin' scenario can lead to massive material release. A study, in 1997, by the IPSN (French institute for nuclear protection and safety) (11) on total emptying of pools confirmed that "an initial approximation by calculation for a case of total emptying showed that, in the absence of additional provisions in the D pool building, the air temperature in the building would rise by 10 °C per hour and reach 1000 °C after four days. In case of partial emptying, this temperature would be reached after seven days - owing to the thermal inertia of the water - leading to an unacceptable risk of cladding failure."
These same comments are, however, hardly valid in the case of an external cause, such as an airplane crash, precisely because this could destroy or affect all of the means for protection described by COGEMA: cladding and assembly geometry; presence of water in the pools and circulation regulation systems; and even the ability of accident response means to function once the accident area was heavily contaminated.
An IPSN (12) study, of 1997, showed, in an experiment report, that a fire fueled by one tonne of kerosene spread over a 20 m2 surface in a 3,600 m3 installation, would raise the ambient temperature to 750 °C in 15 minutes, 860 °C in one hour, and could reach 1,200 °C after six hours. Furthermore, the 365 mbar overpressure reached after 75 seconds during the experiment indicates that the fire could spread to other installations linked to the place of origin by ventilation systems. Finally, the IPSN concluded in its study that, "this result means that certain rules applied at present are inadequate from the point of view of protection of property and people." It should be borne in mind that pool D, used as the example for WISE-Paris calculations, measures 16.6 m in width, is 69 m long and has a depth of 10.6 m. The building housing it is 24 m wide, 77 m long and 15.5 m high, i.e. 1,848 m2 for 28.644 m3. The floor area is therefore 92,4 times that used for the experiment described by IPSN; the volume is almost eight times greater. A Boeing 767 can carry up to 90,770 l of kerosene or around 90 tonnes, which is 90 times the quantity of aircraft fuel used for the IPSN experiment. Although this does not constitute a scientific demonstration, the orders of magnitude allow the assumption that the fire following a crash onto a pool could be even more penalizing than that used by the IPSN, leaving little time for COGEMA's "means […] available at the plant" to act.

5) "Well before the terrorist attacks in the United States, COGEMA studied the possibility of the pools' emptying completely as a result of an accident. It was determined that they would not empty immediately and that the reheating of the radioactive materials would be spread over several days, leaving time for the plant's fire protection system to work effectively. In fact, the COGEMA plant at La Hague has an emergency center and a staff of some 50 highly specialized firefighters who are familiar with the installations. The facility's own fire-fighting resources are equivalent to those of a city with 35,000 inhabitants."

Of course the "natural" rise in the temperature of the fuel once out of the water is calculable and is probably covered in design safety provisions, but here again COGEMA is studying a case of internal failure with consequences spread over time and that would leave a sufficient margin of maneuver for the safety systems to operate.
In the airplane crash scenario, the event takes place in a very short time, covers an area far greater than the floor area of the building in question, and is accompanied by a very considerable release of thermal energy. Correct operation of the protection systems could therefore be affected, the integrity of the pool compromised and the emptying time shortened under the combined effect of a powerful impact and intense heat (up to around 2000 °C). During the 11-September events in New York, the teams of firefighters and rescue workers for a city of several million inhabitants were called out.

6) "The La Hague plant has the benefit of what is called an in-depth defense. A thick layer of extremely strong concrete protects almost all the buildings there."

Nothing in the information provided by COGEMA to date indicates that this layer of concrete was designed to withstand the impact of an airliner at full speed. On the contrary, the statements from various COGEMA managers, and those of nuclear safety managers, confirm the notion that they are not designed for such a scenario which has never been studied. Furthermore, experts in building and construction have commented on the collapse of the World Trade Center during the 11 September attacks and have stated that no form of construction could withstand such an impact. Moreover, the notion of "extremely strong" appears difficult to define and quantify scientifically.

7) "As the Director of the Nuclear Security Authority has stated in recent days, no nuclear installation has been designed to withstand the impact of a commercial airliner. COGEMA and the Nuclear Security Authority had allowed for the possibility of the crash of a twin-engine aircraft, but they had deemed the crash of a widebody airliner too improbable (less than 1 in 100 million)."

First, COGEMA omits to stipulate that the statement from the Director for nuclear safety referred to nuclear reactors (see DSIN press release of 13 September 20001). The basic rule for nuclear safety regarding the risk of an airplane crash applicable to reactors came into force in 1980. For other nuclear installations, therefore including the La Hague plant, the equivalent basic safety rule was not published until 1992, i.e. well after the building of most of the facilities. To date, nothing-in the absence of regulatory constraints-indicates how the risk of an airplane crash was (or was not) actually addressed in the design of such installations.
Furthermore, the statement that COGEMA used the hypothesis of a twin-engine craft contradicts the information presented by COGEMA in 2000 in the files presented to the public inquiry for revision of the authorizations for these plants. In fact, the study of danger in the file for the modifications envisaged for INB (licensed nuclear facility) 117 (UP2-800) indicates that "for the La Hague site, the aircraft chosen was a Cessna 210, falling at 100 meters/second at the most, with a probability of impact of a few units in 100 billion per square meter per year." The Basic Safety Rule I.1. requires consideration of two types of aircraft: the Cessna 210, a single prop engine aircraft weighing 1.5 tonnes; and the Learjet 23, a twin-engine jet weighing 5.7 tonnes. It is even possible that the CEA, then COGEMA, did not consider either of these cases during construction of the installations as, in the same public inquiry file, it is stated that "for each workshop of the INB, the probability of an aircraft crash with consequences for the environment is less than 1 in 10 million for a period of one year, a probability deemed sufficiently low for this risk to be ignored in design."
The arguments are based on a probabilistic logic-a serious impact multiplied by a very low probability equals… an "acceptable risk"- but one which is no longer acceptable today. It is precisely because this form of reasoning is no longer applicable that there is an urgent need to reflect on the potential consequences of the crash of a commercial airliner on the La Hague site, a situation which has gone from being 'not impossible' but 'unimaginable' before 11 September 2001 to now being not only possible, but plausible.

8) "A permanent overflight ban is in force at the site. Considering its geographical position, the French armed forces would have time to intervene if any breach of this ban were suspected."

Lack of rigor or omission: COGEMA states in its public inquiry files that "the La Hague site is covered by a low altitude flight ban: 300 meters for single-engine aircraft and 1000 m for multi-engine craft." Is it therefore possible to fly over La Hague without arousing suspicion? The air space around La Hague is such that it is possible to envisage the case of an airliner, deviated from its air corridor 30 km away, overflying the La Hague site 2 minutes and 30 seconds later. Even worse, there are only eight kilometers, or 40 seconds flight time, between the closest Terminal Movement Area (TMA) and the site. This period is clearly beyond the possibilities for intervention on the part of the armed forces, regardless of their alert status.

9) "The structures are partially built under ground, and the pools occupy a small area in relation to the total area of the installations around them. It would thus be impossible for an airplane to crash vertically into a pool."
"The pools are separate from each other, and their layout makes it impossible to strike them simultaneously. Moreover, their reinforced concrete walls are, on average, 80 centimeters to 1.6 meters thick and are designed to withstand earthquakes of up to a magnitude of 8."

The area occupied by the pools at La Hague, which are adjacent to one another, is far greater, even at an oblique angle, than the area of impact at the World Trade Center. It has been show that trained pilots are perfectly capable of hitting targets of around 50 meters in width. Can we then believe that it is impossible to strike an area of more than 100 m x 100 m, at an angle of 45° for example?
The wing span of commercial airliners combined with the configuration of the irradiated fuel storage pools (see plan, page 14 of WISE-Paris briefing), not to mention the dispersion of debris and kerosene in case of impact, mean that a simultaneous impact on several storage installations has to be considered. Pools C and A are separated by 25 m, to be compared with the 47.6 m wing span of a Boeing 767.
What is the basis COGEMA uses to compare an earthquake of 8 with the crashing of an airliner? What are the sizing design criteria used in case of an air crash on each sensitive part of the La Hague site?

10) "Security on the ground at the La Hague installations is assured by COGEMA's own special security forces. The entire site is surrounded by a double fence and equipped with highly sophisticated detection and telesurveillance systems. Access to the most sensitive areas is restricted to authorized personnel."
"These measures have been further reinforced since 11 September with the Vigipirate anti-terrorism plan. Visits to the site by the public have been suspended since that date."

The information published by WISE-Paris concerned the possible impact of an aircraft crashing onto the installations at La Hague. "COGEMA's own special security forces" could do nothing to change that.

Notes :

  1. "Frontal 21", ZDF, 25 September 2001
  2. Furthermore, this study was not made public. Asked about this subject on 2 October 2001, COGEMA stated that it was not in possession of such a study, even though it denounced without hesitation the "absence of scientific rigor."
  3. US NRC, " Study of Spent Fuel Pool Accident Risk at Decommissioning Nuclear Power Plants ", October 2000
  4. 7 484.2 t of fuel in all on 30 June 2001 for around 70 t to 110 t in the core of an EDF reactor, depending on the power rating. This quantity is greater than the total tonnage of fuel loaded at present into the 58 reactors operated by EDF in France
  5. Situation on 31 December 1999, according to the declaration of the French permanent mission to the IAEA
  6. Source:
  7. We call on COGEMA and its ministerial controllers to make these figures public
  8. The process using bitumen seems to be being abandoned since 1998, COGEMA wishing eventually to use the vitrification process for the sludge
  9. Magnesium, like zirconium, is one of the combustible metals able to cause a Class D, or metal, fire. The metals in question are: potassium, powdered aluminum, zinc, sodium, titanium, and zirconium
  10. Asked about the quantities and form of these stocks in June 2001, and reminded of this request several times since, by 2 October 2001 COGEMA had still not given its response
  11. J.-P. Goumondy, J. Marciano: "Study of an accident emptying irradiated fuel storage pools". IPSN, 1997
  12. J.-C. Malet, "studies carried out at IPSN", IPSN, 1997

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