Reactor pressure vessel

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Reactor pressure vessel at Shippingport nuclear power plant in 1956

The reactor pressure vessel ( RPV , also reactor boiler ) is the nuclear heart of a nuclear power plant . The heat-generating reactor core with the fuel elements is located in it . In the technical regulations of the nuclear industry, the RPV has the highest quality requirements. It is an important barrier against the escape of radioactive substances and enables the reactor core to be cooled.

For larger nuclear power plants with high-temperature reactors (HTR), a pre-stressed container was provided as the RPV, in which bursting is impossible. In the case of the THTR-300 nuclear power plant according to Rudolf Schulten , it was a pressure vessel made of prestressed concrete , which, however, did not convince in operation. For future HTR nuclear power plants, pretensioned tanks made of cast steel or nodular cast iron are also being considered.

construction

The reactor pressure vessel of a modern light water reactor is a cylindrical steel vessel with a hemispherical bottom and lid, which is connected to the pipes for the coolant . The RPV contains in particular the reactor core with the fuel assemblies and the structures known as core components which fix the fuel assemblies in their intended place (upper and lower core grids, fuel assembly boxes, etc.).

The top cover is lifted off for fuel element replacement and maintenance work. The cover is connected to the lower part of the pressure vessel with numerous pre-tensioned bolts and nuts. As a rule, two O-rings made of silver are used as seals. The RPV of light water reactors has a residual probability of bursting , which has been declared irrelevant because of its insignificance, for example by Heinrich Mandel .

The reactor pressure vessel is located inside the containment , which is intended to hold back radioactive emissions from the primary circuit including RPV in the event of an accident. It is surrounded by a reinforced concrete cylinder about two meters thick, which serves as a radiation shield ( biological shield ).

Pressurized water reactor

Structure of the RPV of an EPR

In a pressurized water reactor (PWR) such. B. in Neckarwestheim 2 the RPV has a height of about twelve meters and an inside diameter of about five meters. Its wall thickness is 25 cm.

The bottom of the RPV consists of the semicircular bottom dome. This is followed by the cylindrical jacket of the RPV, which is welded together from several seamlessly forged rings , followed by the jacket flange ring with the eight coolant nozzles. The total height of the RPV is approx. 13 m. The RPV is made from a single material. In Germany, the materials 22 NiMoCr 37 and 20 MnMoNi 45 are used for RPVs .

Nuclear power plant model EPR

The RPV has an inside diameter of 4.885 m and a wall thickness of 25 cm. The bottom dome of the pressure vessel is only 14.5 cm thick in order to serve as a kind of predetermined breaking point in the event of a core meltdown . With the reactor lid on, the total height is over 12.7 m, with a mass of 526 tons. The container is made of ferrite steel that is forged in ring-shaped structures and then welded together. For reasons of corrosion protection, the inside of the RPV is lined with stainless steel .

The lid of the RPV is made of stainless steel and is 23 cm thick. It has 89 openings for the control rods, 16 openings for other instruments, 4 openings for coolant flow measurements and one opening for temperature measurement on the cover.

Boiling water reactor

In boiling water reactors (BWR), the RPVs are even larger due to the design. The reactor pressure vessel of a BWR also contains a water separator / steam dryer that separates water droplets - which could damage the turbine - from the generated steam and retains them in the RPV.

The largest RPV used is located in the decommissioned Krümmel nuclear power plant ; it has a height of 22.38 m, an inside diameter of 6.78 m and a maximum wall thickness of 18 cm. The RPV for the Leibstadt SWR consists of rings welded together. The rings are made up of hot-rolled plates that have been welded lengthways.

The temperatures and pressures in a BWR are lower than in a PWR, so that the RPV of a BWR has smaller wall thicknesses.

Dimensions

The dimensions of some selected RPVs are shown in the following table:

Power plant / reactor type block Type Height (m) Diameter (m) Wall thickness (cm) Weight (t)
EPR (nuclear power plant) Pressurized water reactor 13 5.4 30th 526
Gundremmingen nuclear power plant B, C Boiling water reactor 21st 6.62 14.8 785
Isar nuclear power plant 1 Boiling water reactor 22.35 5.85 17.1 620
Isar nuclear power plant 2 Pressurized water reactor 12.01 5 25th 507
  1. ↑ Weight with lid
  2. ↑ inside height
  3. ↑ a b c inside diameter
  4. ↑ a b c Wall thickness of the cylindrical part
  5. ↑ Weight with lid and frame
  6. ↑ total height
  7. ↑ Weight without internals

Wall thickness

The wall thickness is between approx. 15 cm for the SWR and 25 cm for the DWR. Areva states that the wall thickness is 20 to 30 cm. For the strength analysis of an RPV, the Karlsruhe Research Center used the following values ​​for the wall thicknesses:

  • lower spherical cap (bottom of RPV): 14.6 cm
  • Cylindrical bowl without vertical branches: 31.9 cm
  • Cylindrical bowl with vertical branches: 46 cm
  • Lid: 20.4 cm

Embrittlement

During operation, the steel of the RPV is exposed to neutron radiation, which changes its mechanical and physical properties (see radiation damage ). In ferritic steels, the hardness, yield strength and tensile strength increase, while the toughness decreases.

The embrittlement depends on many factors. A distinction must be made between:

  • Irradiation conditions such as temperature, neutron spectrum and dose
  • Material properties such as microstructure (phases, grain sizes ), heat treatment condition and chemical composition

Some chemical impurities such as copper, phosphorus or nickel have an embrittling effect; Alloy elements such as molybdenum, vanadium or chromium have little effect on embrittlement .

Manufacturer

RPV manufacturers must be certified according to certain standards. Such standards are ASME N-stamp, RCC-M and ISO-9001. According to the World Nuclear Association (WNA), important manufacturers are e.g. B .:

Former manufacturers are z. B .:

Web links

Commons : reactor pressure vessel  - collection of pictures, videos and audio files

Individual evidence

  1. ^ Heinrich Mandel: Location issues with nuclear power plants. In: atw atomwirtschaft. 1/1971, pp. 22-26.
  2. ↑ Thermal failure of reactor pressure vessels in the event of extreme accidents in pressurized water reactors - analysis and suggestions for improvement. (PDF 3.9 MB, pp. 11–13 (3–5), 65 (57)) RWTH Aachen University , accessed on August 20, 2015 .
  3. ↑ Leibstadt nuclear power plant does not have to test reactor pressure vessels additionally. ENSI , December 2, 2013, accessed on August 20, 2015 .
  4. ↑ a b What is needed here: innovation and precision. (No longer available online.) Areva , archived from the original on September 21, 2015 ; Retrieved August 20, 2015 .
  5. ↑ Gundremmingen nuclear power plant. (PDF 3.1 MB) RWE , accessed on August 20, 2015 .
  6. ↑ a b Isar - information on the nuclear power plant. (PDF 1.6 MB, pp. 18–19.) (No longer available online.) E.ON , archived from the original on September 24, 2015 ; Retrieved August 20, 2015 .
  7. ↑ Reactor pressure vessel, barrier principle, containment. (No longer available online.) GRS , March 18, 2011, archived from the original on September 24, 2015 ; Retrieved August 20, 2015 .
  8. ↑ Strength analysis for the reactor pressure vessel of the High Performance Light Water Reactor (HPLWR). (PDF 10.8 MB, pp. 13–16 (7–10)) Karlsruhe Research Center in the Helmholtz Association, December 2006, accessed on August 20, 2015 .
  9. ↑ a b c Final report on reactor safety project No. 150 1277 - Application of the Master Curve concept to characterize the toughness of neutron-irradiated reactor pressure vessel steels. (PDF 10.7 MB, p. 12 (8)) www.hzdr.de, July 2007, accessed on August 20, 2015 .
  10. ^ Heavy Manufacturing of Power Plants. World Nuclear Association (WNA), June 30, 2015, accessed August 20, 2015 .