Design basis accident

Design basis of a nuclear power plant ( NPP, NPP ) are accidents for which control security systems still need to be designed. Outside the facility may at its entrance, the conditions to the Radiation Protection Ordinance fault limits of radiation exposure are not exceeded ( refer security of civilian nuclear energy ).

Tags: amount of loss, probability, risk, GAU, worst-case scenario

Every conceivable accident is basically characterized by two different sizes that you at least tried to describe estimated by numbers: the severity of the consequences of an accident ( level of damage ) and the probability of occurrence. The product claims amount times the probability, often referred to as a risk, for example, calculation basis in the insurance industry.

Design basis accidents are accidents that are to be adopted in the design of a nuclear facility. Your controllability, the most important means to this end is the redundancy is demonstrated as part of the approval process. Basis for technical and physical models for the control of the incident. Even more serious accidents, their risk is below the risk - Akzeptabilitätsschwelle, called " beyond-design- basis accidents ." For them, measures for their exclusion or to limit the effects are developed, which are also detected in the approval process.

Colloquially in particular often spoken in terms of the consequences of design basis accidents and beyond design basis accidents of a GAU or meltdown. The designation GAU, short for maximum credible accident, goes back to the developed in the early days of the use of nuclear energy in the U.S. concept of the maximum credible accident that the design of systems to a specific major accident - the complete demolition of a main coolant pipe the emergency cooling remains partially functional - limited and no longer is used in today's new buildings such as the EPR. With "super " is indicated that the consequences of the meltdown are exceeded. The prefix is super ',' beyond ' used in the original Latin meaning, over.

Design basis accidents

When planning a nuclear plant different scenarios must be considered. There are several possible incidents that would lead to release of radioactive material, if the plant were not designed to withstand such an accident. In German nuclear power plants with pressurized water reactor, a design basis accident for example, is a fraction of the main coolant line with a massive loss of coolant. The set of applicable design basis accidents is defined in the Safety Criteria for Nuclear Power Plants.

As new information on potential accident sequences are obtained with time, it may be necessary to postulate new design basis accidents or exacerbate existing ones. This can for example make the retrofitting of additional safety devices required and where appropriate, shall extend to withdrawal of the operating license.

An example of this are the consequences of the accident at Three Mile Iceland in 1979. There was created by a chemical reaction of water with the hot material of the molten reactor core ( see core melt) within a few hours, a large amount of hydrogen gas. This gas development was not considered in the design of nuclear power plants until then. A few years after the accident, the operators of German nuclear power plants were required to guard against this danger. This was done by retrofitting the plants with the emergency valves to be actuated ( Wallmann valve) and Recombiners ( Töpfer - candles).

A condition for the licensing of nuclear installations is the proof that in any design basis accident limits for the release of radioactive materials into the environment are exceeded.

State of the art

The operator of a nuclear power plant must implement according to the progressive state of science and technology appropriate and adequate precautions to provide further precaution against risks for the general public about the requirements in the approval also. This will help the operators technical and scientific research and expert organizations, in Germany for example, the GRS, in France, the Institut de Protection et de Sûreté Nucléaire radio, in Japan, the Japan Nuclear Energy Safety Organization.

Interpretation border incidents

As a beyond-design- basis accidents accidents are referred to, where heavier loads occur as in the above- defined design basis accident.

With a release of radioactivity beyond the statutory limits as defined by the scope of the design basis accident is exceeded, there is a beyond design basis accident. Strictly speaking, an accident at INES level 5 satisfies this condition. However, it is common in politics and the press, only serious and catastrophic accidents as a " worst case scenario " to denote (INES INES 6 and 7). The best-known examples of meltdown are the disasters of Fukushima ( 2011) and Chernobyl (1986). More severe beyond design basis accidents from INES level 5 occurred for example in 1957 in the British Sellafield (formerly Windscale, see Windscale fire ), and the American nuclear power plant Three Mile Iceland (1979). In some cases, the site and its surroundings were mostly uninhabitable, such as in Pripyat.

Through a design-basis accident, the investment is completely lost in the affected nuclear plant. Cost of emergency measures for the elimination of accidental damage (if possible) and economic costs ( eg by additional cancers ) which until then generated operating profits can exceed many times. These risks insured not an insurance company; the most part bear the States or the taxpayers.

Measures in case of beyond design basis accidents are defined in the Emergency Guide for each power plant. Possible beyond design basis accidents are also included in the plans of civil protection authorities.

Criticism

In the 1960s, the term meltdown emerged in technical committees. Until 1965 it was believed that at least a partial meltdown can be tolerated.

The MCA was then more of a 'bureaucratic fiction, "wrote the historian Joachim Radkau Bielefeld in 1983, right seriously is not one took the risk. As were in the 1970s, more and more reactors connected to the grid and - after the first oil crisis - based on today unimaginable forecasts over a hundred nuclear power plants in West Germany were planned, the security debate took a turn: The probability of an accident now focused at the center of discussion.