Venting (nuclear reactor)
As Venting ( English venting : Ventilation, aeration) is known in the reactor technology , the controlled pressure relief of the containment (engl containment.) Of a nuclear reactor to which rupture to prevent with severe accidents.
Technical necessity
In the event of a serious incident, a leak in the cooling circuit can lead to strongly heated cooling water entering the containment, evaporating there and thus increasing the internal pressure. Furthermore, a core meltdown can produce large amounts of hydrogen , which under certain circumstances can also end up in the containment. There the pressure can increase so much that it may exceed the design pressure of the containment. If the containment bursts, radioactivity will be released into the environment with the escaping gases .
functionality
A safety valve should in a severe nuclear accident (see design basis accident , meltdown bursting of the full pressure) the containment vessel due to high pressure build-up prevent. Through the valve, the excess gas can be filtered and released into the atmosphere via an exhaust air chimney . According to the operator, the filters can reduce the radioactivity of the air to a hundredth before it escapes into the open air.
The filtering by means of ceramic filter cartridges concentrates mainly on suspended matter (radioactive particles) and can therefore also clog. The partially radioactive gases and noble gases originating from the core are not filtered.
Corresponding pressure relief and filter devices were already known for pressurized water reactors in 1987, as well as for gas-cooled nuclear reactors. For the Siemens AG handed Werner Engl on May 8, 1987, a directly responsive to the needs of the RSK patent for a "pressure relief and filter device for nuclear power plants, especially for boiling water reactors ," a.
Filtered venting
Most of the nuclear power plants now have so-called containment-filtered venting systems. In such systems, the emerging gases are largely freed of aerosols and radionuclides such as iodine and cesium by scrubbers and subsequent filtration . In Germany, venting systems for the purpose of removing the gas mixture via the exhaust air chimney with radionuclide filtering have been known as Wallmann valves since 1986 .
Case studies
Valves for the orderly pressure relief of the containment are common worldwide under different names.
Harrisburg
During the Harrisburg nuclear accident , the pressure was relieved and radioactivity was released. The extent to which radionuclides were retained by filtering is not known.
Chernobyl
In the case of the Chernobyl catastrophe , a corresponding valve for pressure relief would not have had any effect due to the design and process, since the RBMK type does not have a safety container that could have burst. In addition, the causal power excursion of the reactor core took place almost instantaneously and thus would not have caused a slow pressure increase in the containment that could have been controlled by venting - if there had been one.
Fukushima Daiichi
Pressure relief was also implemented in the Fukushima incidents . The extent to which radionuclides were retained by a filter is not known in every case. In both cases radioactivity was released. In Fukushima, some recorded measured value peaks could be assigned to the Venting events. The damage to the vessels, containments and pipelines of the reactors in Fukushima could not yet be investigated due to the ongoing measures.
A blow-off of radioactive gas mixtures from the containment took place in March 2011 in some of the badly damaged reactor blocks in Fukushima, Japan. Increases in ambient radioactivity were assigned to the venting actions. The quantities of explosive and radioactive H 2 mixture could not be completely released to the outside via the chimney or the roof of the reactor building, but instead reached a significant amount from the containment into the room above the operating level. The subsequent oxyhydrogen explosions destroyed the upper part of the shell of the affected reactor building and some of the installations inside.
Fukushima Daini
In the nearby Fukushima Daini nuclear power plant, preparations had to be made for steam (and thus internal pressure) to be released through the chimneys during the reactor shutdown in March 2011 with subsequent overheating of the condensation chambers in units 1, 2 and 3 . Ultimately, the reactors could also be cooled without venting. The incident was classified as an INES 3 incident.
literature
- Patent application DE3715467A1 : Pressure relief and filter device for nuclear systems, especially for boiling water reactors. Filed on May 8, 1987 , published on 17 November 1988 , Applicant: Siemens AG, inventor Werner Engl.
- Patent DE3715466C2 : Pressure relief and filter device for nuclear systems, especially for pressurized water reactors. Registered on May 8, 1987 , published on January 16, 1992 , applicant: Pall GmbH, Siemens AG, inventor: Werner Engl, Dr. Horst Randhahn, Norbert Szymkowiak, Dr. Frank Taetz.
Individual evidence
- ↑ Hydrogen formation in the boiling water reactor (BWR). Society for Plant and Reactor Safety (GRS), 2011, archived from the original on April 4, 2011 ; accessed on March 7, 2016 .
- ↑ a b Welt.de: How the previous nuclear disasters came about , accessed on March 15, 2011
- ↑ Patent application DE3715467A1 for a “pressure relief and filter device for nuclear systems, especially for boiling water reactors” , accessed April 5, 2011
- ↑ Containment Hydrogen Control and Filtered Venting Design and Implementation ( PDF , 652 KB no longer available online)
- ↑ a b Information on the situation in Japan: As of March 14, 2011, 3:30 p.m. (CET). Society for Plant and Reactor Safety (GRS), 2011, archived from the original on January 19, 2012 ; accessed on March 7, 2016 .
- ↑ Japan: Status report from March 15, 2011, 6:00 p.m. (CET). Society for Plant and Reactor Safety (GRS), 2011, archived from the original on August 1, 2012 ; accessed on March 7, 2016 .
- ↑ Ludger Mohrbach: Tohoku-Kanto Earthquake and Tsunami on March 11, 2011 and Consequences for Northeast Honshu Nuclear Power Plants. (PDF) VGB PowerTech, 2011, p. 60 , archived from the original on August 20, 2011 ; accessed on March 7, 2016 (English).