Security container
The gas-tight envelope around a nuclear reactor and its circulation and ancillary systems is called a safety container or containment , so that - even after an accident - no radioactive substances can escape uncontrolled into the atmosphere and surroundings. The term "containment" has a double meaning in German, as it describes both the safety container (steel shell) and the volume in the safety container.
Barrier concept
In a nuclear power plant, the containment is one of the following three barriers (viewed from the inside out) against the escape of radioactive substances:
- the fuel rod - sheaths , (No. 6 in the image.)
- the reactor pressure vessel with primary circuit lines (No. 5 in the picture) and
- the containment (containment, no. 2 in the picture) as well as associated retention devices for liquid and gaseous substances (e.g. filters ).
As the third of these barriers, the containment with the associated facilities encloses the reactor pressure vessel and the part of the coolant circuit connected to it .
In nuclear power plants with double containment, the space between the actual, inner containment and the outer reactor building is called the annulus .
In reactors with liquid coolant - such as water in all nuclear power plants operated in Germany - leaked coolant collects at the deepest point of the containment, the so-called sump. From here the coolant can be pumped back into the reactor cooling circuit.
Pressurized water reactors
The containment of German pressurized water reactors (PWR) has the shape of a ball and is made of fine-grain structural steel . According to the regulations, it must withstand the pressure that arises when the primary coolant evaporates completely (full-pressure containment). At German-style nuclear power plants (also BWR ) it is always built into a concrete reactor building that is visible from the outside .
The inside diameter of 1300 MW systems is approx. 56 m. The wall thickness is 3-4 cm. These large containers could only be welded together on the construction site from around 550 spherically curved individual sheets. After the sealing by the upper pole cap was a pressure test (strength test) and leak test with compressed air through compressors . The leak rate over time (pressure drop per time) was determined by means of a manometer and the deformations with strain gauges . The full-pressure containments can be entered while the reactor is in operation (division into operating and plant rooms).
As a result of a core meltdown , a full-pressure containment could also burst due to impermissible pressure (which would be a worst-case scenario ). To prevent this, a few years after the Chernobyl reactor disaster in 1986 , all nuclear reactors in Germany were equipped with a filtered pressure relief (" Wallmann valve ").
Boiling water reactors
Boiling water reactors (BWR) of the German construction line 69 had a predominantly spherical containment with a wall thickness of around three centimeters, in the crumb, for example, with an inside diameter of around 30 meters. These were also welded together on site. They could not be entered while the reactor was in operation and contained nitrogen instead of air to protect against oxyhydrogen explosions . The Gundremmingen nuclear power plant of construction line 72 also has a relatively small containment, which is, however, somewhat larger than the SWR 69 and also made of prestressed concrete with a gas-tight metal liner on the inside . Since less equipment has to be accommodated in the containment of boiling water reactors (a BWR has no separate steam generator and no large coolant pumps, only circulation pumps integrated in the reactor ), this can be made smaller. A disadvantage of the smaller containment is the more rapid pressure increase in the event of a leak. This is why there is a pressure reduction system (DAS) in which the escaping steam flows into condensation chambers, where it is passed through a large water basin and condensed.
General information on technology
The containment is provided with pressure locks . These have an inner and an outer door, which are locked against each other in such a way that one door can only be opened when the other is closed and the pressure has been equalized. The security container can be entered and exited through personnel sluices. Emergency sluices are provided for emergencies. Material locks, which are usually equipped with a lock carriage and armored doors, are used to bring in material (e.g. fuel assemblies).
The containment has many openings for the passage of pipes and cables, which require special attention. Small pipelines can be firmly welded in, taking into account thermal expansion and compressive forces. Large pipelines are connected via expansion joints with possible suction and nitrogen filling. Cable bushings can be designed as glass seals and brazed connections .
See also
swell
- Basic knowledge of nuclear energy, Information Group on Nuclear Energy, Berlin, April 2003.
Individual evidence
- ↑ Winfried Koelzer: Lexicon on nuclear energy. KIT Scientific Publishing, Karlsruhe, 2017, accessed on November 22, 2018 .
- ↑ ENSI's 2010 Supervisory Report , p. 104
- ↑ Brochure from Siemens- KWU: Power for Generations - Pressurized water reactors from Siemens , 1997
- ↑ BONNENBERG + DRESCHER engineering company. Inventory of the safety-related design of a nuclear power plant with PWR / BWR / HTR: Investigation of selected phenomena in hypothetical accidents , on behalf of the Federal Minister of the Interior, May 1979
- ^ Brochure from Siemens-KWU: Power for Generations - The Gundremmingen nuclear power plant , 1996