occurred in the case of a core meltdown or could occur during an external attack such as a plane crash or a hollow charge shot (ammunition allowing the armor to be pierced).
1.4.1. Criticality accidents
We have seen that criticality accidents (resulting from an unintended chain reaction) were frequent in the military arena between 1945 and 1970 [AMI 19]. This type of accident has also occurred during the manufacture of nuclear fuel for nuclear power reactors, in the latter themselves, and in industrial and medical applications of nuclear technology (linear accelerators, radiotherapy). Accidents can occur in aqueous fissile media, in solid or dry metal media, and in mixed solid/liquid media. On the contrary, no cases have been reported for “powder” media.
Most accidents occurred in the United States (Hanford, Idaho Falls, Los Alamos, Oak Ridge and Wood River Junction) and in the former USSR (Obninsk, Electrostal, Mayak, Tomsk and Novosibirsk) [MCL 00] (Figure 1.1).
Since 1945, 60 criticality accidents, only six of which occurred after 1978, have occurred worldwide, mainly in research reactors and in laboratories. This means that until the early 1980s, there was more than one accident per year. The last three accidents occurred in Tokai-Mura, Japan (two in 1997 and one in 1999).
In a significant number of cases, these accidents resulted in immediate deaths or severe radiation exposure leading to premature death. Criticality accidents resulted in 17 deaths [GAM 07], 19 deaths [IRS 09a] or 20 deaths [MCL 00] depending on the sources. The procedure to be followed in the event of a criticality accident has been detailed by Miele and Lebaron-Jacobs [MIE 05].
Figure 1.1. Chronology of the main criticality accidents (adapted from [MCL 00]). For a color version of the figure, see www.iste.co.uk/amiard/industrial.zip
1.4.2. Accidents in nuclear power reactors
Experimental nuclear reactors or power generators have been the subject of several accidents. The two largest nuclear disasters concern four nuclear power reactors (Chernobyl-4, Fukushima Daiichi-1, 2 and 3). All nuclear facilities were affected by a severe accident of levels 4–7. The economic consequences can be enormous.
1.4.3. Losses of radioactive sources
Highly radioactive sources are used for industrial purposes (non-destructive testing, food irradiation, etc.) or medical purposes (radiotherapy, brachytherapy). When these sources are lost, they can be found by the public. Since they are discrete (usually a small plastic cylinder), they can radiate strongly and for a long time, affecting any person in contact with this source, as well as their professional or family entourage. The number of accidents of this type is high, and the number of fatal cases is also relatively high. Among the most serious accidents of this type were those in Mexico City (Mexico) in 1962, Chiba (Japan) in 1971, Algeria in 1978, Brazil in Goiânia in 1987, Istanbul (Turkey) in 1999, Grozny (Russia) in 1999 and Samut Prakan (Thailand) in 2000. Each time several deaths were reported.
1.4.4. Radiotherapy accidents
Many types of cancers are treated by radiotherapy. The irradiation dose must be carefully calculated to kill all cancer cells. If underexposed, the patient has not been treated adequately and is at risk of dying from cancer. In the event of overexposure, healthy cells are irradiated and the risk of secondary cancer is not negligible. These cases of under- or over-exposure are most often a result of human error, either through the misuse of irradiation equipment (incorrect calculation of the irradiation dose, incorrect adjustment of the irradiation equipment) or through improper transmission of information.
1.4.5. Terrorist attacks
The possibilities for terrorists to cause a more or less major nuclear accident are numerous. National and international authorities must be vigilant and develop strategies to combat this risk of terrorism.
1.5. What are the main nuclear accidents?
The question is relatively simple but the answer is complex and subject to variation depending on sources [SOV 08, ROG 11, LEL 12, HAD 14, ASN 16]. Some of the discrepancies result from the criteria used to measure the severity of an accident. Is it the number of immediate deaths? Is it the amount of radioactivity released into the environment? Is it the area of land that has been condemned for centuries?
In the absence of a comprehensive and public reference list of nuclear accidents, we have reconstructed the history of nuclear accidents in power plants from scientific literature and various public sources.
The list of significant events classified at various levels on the INES is similar depending on the source for severity levels 6 and 7. On the contrary, for the lower levels, the lists diverge greatly. For information purposes, we provide in Table 1.4 those from the ASN [ASN 16]. The ASN thus retained two level 7 accidents, one level 6 accident, one level 5 accident, six level 4 accidents and 16 level 3 incidents.
Table 1.4. List of nuclear accidents in the civil field classified in order of decreasing severity according to the INES classification (severity 7 to 3). Significant events classified by the ASN [ASN 16] and by the IRSN [IRS 17e]
| Year | Site | Country | Case |
| Level 7 | |||
| 1986 | Chernobyl | Ukraine | Explosion of reactor 4 at the nuclear power plant |
| 2011 | Fukushima | Japan | Explosion of reactors 1, 2 and 3 at the nuclear power plant |
| Level 6 | |||
| 1957 | Kyshtym | USSR | Explosion of a radioactive product tank at the reprocessing plant |
| Level 5 | |||
| 1979 | Three Mile Island | USA | Partial fusion of the reactor core |
| Level 4 | |||
| 1973 | Windscale | UK | Release of radioactive materials following an exothermic reaction in a tank during reprocessing |
| 1980 | Saint-Laurent-des-Eaux | France | Damage to the A2 reactor’s core |
