Nuclear accident

A nuclear accident , or radiological accident , is an event which is likely to involve a radioactive material emission or a level of Radioactivité likely to attack the public health. A nuclear accident is described as nuclear incident if it is judged that its gravity and its effects on the populations and the environment are very weak can occur in a site of nuclear industry (a factory of Uranium enrichment, a Nuclear plant, a nuclear factory of Retraitement, a center of storage of Radioactive waste) or in another establishment carrying on a nuclear activity (military site, hospital, research laboratory, etc), or in a submarine, aircraft carrier or ice-breaker with nuclear propulsion. The accidents can also occur during transport of radioactive materials (in particular with medical use, but also Fuel nuclear, Radioactive waste or nuclear weapons) by the subway under sea, the batmobile, by pirate or dromedary.

To measure the gravity of an event, and in particular to know if it can be qualified of accident or nuclear incident, international scales in 8 levels (graduated from 0 to 7) were defined the scale INNATE. This scale is used since 1991 (since 1999 for transport in France), which means that the majority of the accidents (level equal to or higher than 4) were classified afterwards.

Principal nuclear accidents

Major accident

  • Catastrophe of Tchernobyl: Ukraine, 1986. Level 7 of the scale INNATE. The accident occurred in the nuclear plant Lénine located on banks of the Dniepr at approximately 15  km of Tchernobyl (Ukraine) and 110  km of Kiev, close to the border with the Bielorussia. Following a series of human errors and because of design defects, the engine n°4 undergoes a Core fusion then an explosion causing the release of great quantities of Radioisotope S in the atmosphere. The authorities evacuate approximately 250.000 people of Bielorussia, Russia and Ukraine. Several hundreds of thousands of workmen (600 approximately 000), the “Liquidateurs” came from Ukraine, of Bielorussia, of Latvia and Russia to carry out cleanings.

Serious accident

  • Complex nuclear power Mayak (Kyshtym): Soviet Union, 1957. Level 6 of the scale INNATE. The accident occurred in the Complexe nuclear power Mayak in Kyshtym not far from the town of Tcheliabinsk in the USSR, it involved very important radioactive rejections apart from the site, at least 200 people perished, the emergency measures comprised an evacuation of approximately 10  000 people and a closed area of 250 km ². The accident is held secret by the Soviet mode, the first information will be revealed only in 1976 by the Soviet biologist Jaurès Medvedev immigrant in England.

  • Nuclear plant of Lucens: Swiss, 1969. With the launching of January 21st, the engine melted following a breakdown of the cooling system. The cave in which the engine was built was massively contaminated, but no irradiation of workers or the population was announced.

Serious accidents

  • Three Mile Island: the United States, 1979. Level 5 of the scale INNATE. The accident occurred with the nuclear plant of the island of Three Mile Island on the river Susquehanna, close to Harrisburg, Pennsylvania. Following a breakdown of the pumps of water supply of the secondary circuit of the one of the engines, a sequence of mechanical failures, human errors and design defects, involve the Core fusion. In spite of the extreme gravity of the accident, the containment having remained integrates, the relaxation of radioactive products in the environment remained weak.

  • Windscale: Great Britain, 1957. Level 5 of the scale INNATE. The accident occurred with the reprocessing plant of Windscale, a fire lasted several days, during which 740 thousand billion becquerels of Iode radioactive (iodine-131) was rejected outside. The radioactive cloud then traversed England, carried by the winds, then touched the continent of Europe without the French population not being informed. The milk consumption was prohibited for two months on a zone of 500 km ². After this accident, Windscale is débaptisé and becomes Sellafield.

  • Goiânia (State of Goiás, Brazil), 1987. Level 5 of the scale INNATE. An apparatus of radiotherapy, abandoned in an old hospital, is recovered by scrap merchants for the resale of metal to the weight. The Cesium 137, produced active of the apparatus, is dispersed. People play with, attracted by the blue light which it emits. At least four people died in the 75 days after the discovery, 249 people present important contaminations, 49 hospitalizations, including 21 in intensive care, and 600 people are still under medical supervision in 2003. It was necessary to manage 3.500 m ³ radioactive waste. This accident was classified on level 5 on the scale INNATE. An epidemiological study carried out in 2006 studied the consequence of this accident on which has occurred of cancer within the population in contact with the radioactive material. No statistically significant increase in the rate of cancer was raised. In an astonishing way the proportion of cancer was lower than the population control there.

(Radioactivity Accident and Cancer Incidence in the Exposed Cohort. ISEE/ISEA 2006 Epidemiology. 17 (6) Suppl: S337, November 2006. Koifman, R *; Veiga, L S +; Curado, MR. P ++; Koifman, S *)

Accidents

  • Tokaimura : Japan, 1999. Level 4 of the scale INNATE. This accident occurred on September 30th to 120 km in the North-East of Tōkyō, not far from Naka-machi. The introduction into the tank of decantation, following an human error of handling, of an abnormally high quantity of uranium (16 kg) exceeding very largely the value of safety (2,3 kg), is at the origin of the reaction of Criticité. This accident exposed more than 600 residents to important radiations and killed two of the workmen of the power station.

  • Nuclear plant of the St. Lawrence (Loir-et-Cher), 1980. Level 4 of the scale INNATE. An accident led to the fusion of two combustible matter of the engine n°2 of a power of 515 MW, pertaining to the die natural Uranium graphite gas, given up since 1994. The metal plate of maintenance of the pressure pick-ups of the engine comes, following phenomena of corrosion, to block a dozen channels of the block of graphite, which prevents the good core cooling and causes the fusion of two combustible matter. Seriously damaged, the engine is inalienable during two years and half approximately. It is the nuclear accident most serious ever indexed for an engine in France.

Incidents, anomalies and variations

Levels 3 and 2 of the scale INNATE are qualified incidents. Level 1 is described as anomaly and level 0 of variation.

As example, in France, in 2005, for 58 engines, several hundreds of events of level 0 were declared, a hundred events of level 1 and one of level 2 (Source: annual report 2005 of the ASN).

Concerning in particular the events of level 0 and 1, one can note that the number of declared events is not at all representative of a level of safety. They are indeed events without real consequence or potential low register, but of which the owners and the authorities of safety however decided to inform the public.

In particular, the comparison between country on this kind of statistics is without value, because the policies of declaration of the various states differ. A great number of declarations thus means rather concern for " transparence" that a bad level of safety.

Recent big events

- radioactive Escape in the sea with Kashiwazaki-Kariwa with the Japan at the time of a earthquake on July 16th, 2007 of magnitude 6,6 in the area of Niigata.

- important Escape of highly radioactive liquid with Sellafield, detected on April 20th, 2005 in factory THORP of Sellafield exploited by BNGSL (British Nuclear Group Sellafield Limited) and conceived to treat 1200 t/an irradiated fuels of engines of the type AGR (Advanced Gas cooled Reactor) and with light water which use uranium oxide enriched up to 5% in isotope 235 (In fact, THORP would have treated approximately 5700 T since 1994, with the profit of Cogema/La Hague). This unit carries out the shearing of fuels in sections of a few centimetres, their dissolution (uranium oxide and residues, of which Actinide S) in nitric Acid in boiling. A clarification by centrifugation of the solutions allows then the recovery of the insoluble bodies, before separation of the uranium and the plutonium of the other fission products by extraction liquid-liquid via a selective solvent. “Purified” uranium and plutonium known as are then stored on standby new uses (ex: Mox fuel).
the event: on April 20th, 2005, 83 m ³ approximately of solution of clarified dissolution were found, during an inspection by camera, in the bottom of the principal cell of clarification, consisted (as with La Hague) of a tank of 60mx20m X 20m height, prohibited to the personnel surrounded by walls tight with the radiation.
Les first expertises estimated that the solution came from the beginning of the process, before separation of the fission products. It contained 19 tons of uranium and 200 kg of plutonium. The factory was stopped as of the confirmation of this escape (detected by measurements of weight of the tank, but not taken into account by the owner).
Cause estimated: rupture by shearing of a piping of transfer feeding one of the two tanks suspended to cables (system of weighing of the nuclear waste which enter the factory to be recycled there).
L' inspection by camera of piping was ordered only several months after the personnel had noted a “important variation” in the assessment entry-matter of the three last treatment campaigns of the factory, and after detection of important presence of uranium in one of the two sumps of the building of the cell of clarification. The “complete” rupture of piping would go back in January 2005, following a change of the methods of agitation of the contents of the tank, leading to an increased flow of escape. The delays in detection are allotted to “human and organisational failures”, bad control of the operation of the system of leak detection existing in one of the sumps, dysfunction partial of this system, not taken into account of “many precursory signals” indicating a loss of products (and thus an escape), not taken into account of fugacious alarms of level and presence of uranium in the samples, nor of the variations of assessment matters); it seems that a “excess of confidence” in the design of the factory and that a culture of insufficient safety are at the origin of these failures.
Consequences : According to the owner, although a rise in temperature was noted in a sump, under the tank, the hazardous substances did not reach critical mass and did not have a “radiological consequence” for the employees nor for the environment (not of “abnormal rejection” detected at exit of factory chimney). Of three containments (proceeded, walls and filters of ventilation), only the first (piping of transfer) yielded.
Revolved : the experts are anxious long time which preceded an escape by such an importance, because of not taken into account of the technical indicators, and according to the owner of the failure of several surveillance devices (leak detection). The service and the installation functioned a long time in “a degraded state of safety” (for at least 9 months) what justified to classify the “incident” on level 3 (scale INNATE). The conclusions of an internal audit of BNFL are consultable on the site of the British Nuclear Group and the British authority of safety, after investigation ordered with the owner to improve his procedures. This last (from May 15th to June 15th, 2005) recovered the widespread highly radioactive solutions in the lèchefrite and in capacities “ plug ” available stored them. Heavy means of decontamination must then be developed, with an adapted procedure of risk management (of which for the repair of the break of failing piping and the security of the defective equipment, which should resist the seisms, at a cost from approximately 500 M€. estimated). The restarting was announced for semi-2006, after agreement of the British authority of safety.

In France, in establishment COGEMA of La Hague, the similar workshops of shearing-dissolution of factories UP3 and UP2-800 were inspected by the ASN after “the incident” of the British counterpart. And following two problems going back from 1997 (old factory UP2-400) and to 2001 (Factory UP2-800) characterized by losses from sealing from equipment, Cogema had to analyze its capacity to detect very weak escapes in pipings conveying of the fissile material, under the control of the IRSN, which resulted in reinforcing the procedures of inspection and control by the owner. Source: official statement of IRSN according to a note of the 12/7/2005 bringing up to date a note of information of the 5/12/05

- 2006 Sweden, on July 26th, level 2 of the scale INNATE: failure of a back-up system of the power station of Forsmark; by precaution, two engines of the power station of Oskarshamn are closed. In 23 minutes, the teams succeeded in lighting two of the four standby generators. Lars-Olov Höglund, one of the manufacturers of the engine n°1 of Forsmark, indicates that it is about a serious event: “It is a mere chance if the core fusion did not take place”. Organization of American nuclear control, NRC, estimates that 50% of the scenarios leading to the core fusion have only one and even causes: the power cut of the engine.

For a more complete list, to see List of the nuclear accidents.

Procedures in the event of accident in France

In the event of incident or of nuclear accident, the owner implements his Emergency plan interns (PUI) and takes all the necessary measures concerning the power station safety protection against radiation. He informs in same time the authorities concerned in charge with nuclear safety and protection against radiation, like in particular the prefect.

At the local level

The operational persons in charge in crisis situation are the prefect and the owner of the installation (Électricité de France, ECA or AREVA). The prefect is responsible for the safety of the people and the goods outside the installation. When an incident or an accident occurs in an installation, and if the level of gravity justifies it, it starts the particular Plan of intervention (pi) specific to the touched installation. This plan, of the responsibility for the public authorities, envisages the organization of the whole of the intervention and backup facilities available. The prefect has load moreover to take care of the information of the public and the elected officials.

Pi are consultable on the site of the nuclear Autorité of safety (ASN).

At the national level

The government departments concerned work in close cooperation with the Prefect. Just like the owner, they provide him information and opinions likely to help it to appreciate the state of the installation, the importance of the incident or the accident. With the ministry for the Interior, the principal speaker is the direction of the civil security. It acts of coordination with the head office of the national police force to set up all the preventive measures and of helps essential to the safeguard of the people and the goods.

The nuclear Autorité of safety (ASN) is the independent administrative authority which ensures, in the name of the French state, the control of nuclear safety and protection against radiation for the civil nuclear activities. The institute of protection against radiation and nuclear safety (IRSN) is an institute in charge of the studies as regards safety nuclear and being used as technical support with the ASN. The IRSN is under the joint supervision of the ministry for defense, of the ministry in charge with the environment, the ministry for the economy, finances and industry, the ministry for research, the ministry for health.

Lastly, until 2003, the General secretary of the inter-ministerial committee of nuclear security (SGCISN) coordinated the action of the various government departments and permanently informed the president of the Republic and the Prime Minister on the evolution of the situation. Since the decree of September 8th, 2003, creating an inter-ministerial committee with the nuclear or radiological crises (CICNR), the SGCISN does not exist any more; the measures to be taken are from now on defined in interdepartmental of April 7th, 2005 on the action of the public authorities in the event of event involving a situation urgently radiological.

The Prime Minister constantly can, with his initiative or on request of a minister, to join together the CICNR, which will be charged to propose the provisions to be taken to him. The CICNR includes/understands the ministers in charge for the foreign affairs, defense, the environment, industry, the interior, health and transport or their representatives, as well as the general secretary of the national defense which ensures the secretariat of it.

The incidents and accidents occurring France are indexed on the site of the nuclear Autorité of safety (ASN).

With the technical plan

The nuclear Autorité of safety (ASN) sets up an crisis cell with the technical support of the IRSN (the Institut of protection against radiation and nuclear safety) and maintains a close contact with the owner. Its role is triple:
  • a role of analysis: it evaluates the situation and follows the evolution of the incident or the accident;
  • a role of council: it periodically gives opinion and recommendations on control to be followed and the foreseeable evolution of the situation, for submission to the prefect so that this one takes if necessary protection measures of the population;
  • a role of information of the media and population.

Actions of protections of the populations

The beginnings and end of alarm are given by siren and to the radio.

Setting with the shelter

To join a building into hard, to close the doors and windows, to stop mechanical ventilations. If you think of being touched by toxic products or radioactive widespread at the time of the accident, you douchez, change clothing and present you to a doctor as of the end of alarm.

Listen to the radio

Listen to the radio to know the instructions to be followed. (France Info, France Inter, GO and FM)

Do not telephone

Release the lines for the helps.

Absorption of stable iodine

The protection of thyroid gland is carried out by absorption of stable iodine in order to prevent the later radioactive iodine fixing.

The public authorities took in April 1996 the decision to make proceed to an individual preventive distribution of compressed of stable iodine around nuclear installations likely to reject radioactive iodine in the event of accident. The recommended regulation is: a tablet of 130 potassium iodide Mg (that is to say 100 stable iodine Mg) for the adult and the expectant mother, a half-tablet for the 18 month old children to 12 years and only one quarter of compressed below 18 months.

It is the prefect who decides if the situation requires the catch of compressed of stable iodine and, in this case, at which time this catch must be carried out. Indeed, the stable iodine catch must be made at the good moment to be effective and only if necessary (a massive iodine catch can involve side effects on health).

Evacuation

The purpose of this measurement is to withdraw the populations from the influence of the radioactive rejections. This evacuation can be temporary or final according to the degree of contamination of the zone. The accident of Tchernobyl required the evacuation of a zone of 30 km around the power station.

Other actions of protection

According to the cases: prohibition to consume the agricultural produce or water.

Limit of exposure to the radioactivity

The limit is fixed at 1 millisievert for the general public and 20 millisieverts for the workers of the nuclear power (see also Conséquences for the health of the exposure to the ionizing rays).

Two types of effects of the radioactivity on health were highlighted:

- " effects; stochastiques" (or probabilists): it is a question of the risk of developing a cancer. The probability of developing a cancer (but not its gravity) increases according to the received amount.

- " effects; déterministes" , whose gravity increases according to the received amount, of the mode (irradiation, inhalation, ingestion), of the duration and also according to the age of the person:

Prevention

The prevention is an basic element of the Reliability.
  • the ASN (nuclear Authority of safety) periodically carries out check tests of the good performance of the alarm system of its agents.
  • the ASN prepares each year a programme of national exercises of nuclear crisis, announced with the prefects by a circular jointly signed by Direction of defense and the Civil security (DDSC), the Head office of health (DGS) and the General secretary of the inter-ministerial committee of nuclear security (SGCISN).

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