Industrial and Medical Nuclear Accidents. Jean-Claude Amiard

      2

      Accidents Related to Nuclear Power Production

      2.1. Introduction

      In the first volume of this series on radioactive risk, we have reviewed nuclear accidents of military origin. We must now address civil nuclear accidents. Atomic energy is mainly used to produce electricity in nuclear reactors and relies on a set of industries capable of extracting, concentrating, transforming, using, reprocessing and reusing nuclear fuel (mainly uranium and plutonium). Nuclear accidents can occur at any stage of the fuel cycle. However, unfortunate experience has shown that nuclear reactors and spent fuel reprocessing plants are the most frequent and most serious locations for accidents. The consequences of accidents remain local when releases are low, regional for medium releases and global only for the most serious accidents.

2.2. Accidents in the nuclear fuel cycle

      The nuclear fuel cycle is shown in Figure 2.1. To our knowledge, there have been no significant incidents in mines and factories where nuclear fuel is concentrated, converted and enriched. Significant incidents and accidents have occurred in manufacturing plants, nuclear reactors and spent fuel reprocessing plants.

      Figure 2.1. The nuclear fuel cycle (modified from [TUR 97, PAT 02, NAU 08])

      2.2.1. Uranium mines

      Accidents at uranium mines have the same health consequences as those at all other mines and cannot therefore be identified as nuclear accidents. On the other hand, uranium mines, especially underground uranium mines, are areas where radiation sources are significant. This is owing, in particular, to radon concentrations that can exceed 100,000 Bq.m⁻³ [CCS 11]. This radon comes from the decay of elements of the families of uranium and thorium (mainly uranium 238), which give rise to various radon isotopes (mainly radon 222), which are in a gaseous state and accumulate in mine galleries. Radon isotopes decay in a cascade into various radionuclides that are in a solid state and when inhaled into the lungs are deposited as radioactive dust that may have health consequences (Figure 2.2).

      Figure 2.2. The radioactive family of uranium 238 and its derivatives (according to AMI 13a]). For a color version of the figure, see www.iste.co.uk/amiard/industrial.zip

      One of the few accidents with environmental and health impacts is one in Puerco, USA. In 1968, 27 km northeast of the town of Gallup, near the town of Church Rock, New Mexico, United Nuclear began operating the largest underground uranium mine in the United States. The mine waste was stored in three large ponds, each closed off by a dike of earth. Residents near the mine were almost entirely native Navajo and used the Puerco River as a source of water for their livestock. In the early morning hours of July 16, 1979, fewer than 4 months after the high-profile Three Mile Island accident was reported, one of the earth dams gave way near Church Rock Mill. The 6 m-wide dam released approximately 1,100 tons of radioactive waste, and 95 million gallons (360 million liters) of effluent reached the Puerco River in North Fork. In addition to the river, groundwater was affected up to more than 130 km downstream of the dike [BRU 07].

2.2.2. Milling, conversion, enrichment and fuel manufacturing plants

      The most serious accident in a civilian manufacturing plant is the Tokai-Mura accident. This site is a major nuclear complex, with a spent fuel reprocessing plant, a uranium reprocessing plant and experimental reactors. The site is located in Japan 160 km from Tokyo. The plant where the accident occurred is owned by the Japan Nuclear Fuels Conversion Company (JCO), a subsidiary of the Sumitomo Trust. It converts uranium hexafluoride (UF₆) enriched in uranium 235 into uranium oxide (UO₂) for the manufacture of nuclear fuel. The conversion is carried out by a “wet process”: uranium, initially in the form of gaseous UF₆, is transformed in the presence of water and then ammonia before being calcined in a furnace to obtain uranium oxide powder.

      On Thursday, September 30, 1999, at about 3:30 p.m., following a human error in the quantity of fissile material introduced into the furnace, a so-called criticality accident occurred. The quantity of uranium introduced into a settling tank was indeed abnormally high (16.6 kg) and far exceeded the safety level (2.3 kg). This accident resulted in contamination outside the plant, and three workers were seriously injured. It was classified at level 4 on the INES.

      In France, the first stages of the fuel cycle are not immune to accidents, and radioactive releases into the environment are not always negligible. This was the case at the Pierrelatte (Comurhex) plant in 1977 (January 1 and November 25) where several tons of uranium hexafluoride leaked into the atmosphere without apparently contaminating the soil away from the plant site. A 30 m³ leak of a solution containing 74 kg of uranium occurred on July 9, 2008 in a plant at the Tricastin nuclear site in Bollène (Vaucluse), part of which spilled into surrounding rivers [AMI 13a].

      2.2.3. Nuclear reactors

      The largest use of nuclear energy is in the production of electricity. This is the area with the highest number of accidents. Table 2.1 lists accidents classified as severe on the INES with a rating of 3 or more. Subsequently, the three most serious civil accidents (Three Mile Island, Chernobyl and Fukushima Daiichi) will be detailed.

      Table 2.1. The most significant accidents that have occurred in civil nuclear installations. G: severity on the INES