Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C13/00—Pressure vessels; Containment vessels; Containment in general
  • G21C13/02—Details
  • G21C13/032—Joints between tubes and vessel walls, e.g. taking into account thermal stresses
  • G21C13/036—Joints between tubes and vessel walls, e.g. taking into account thermal stresses the tube passing through the vessel wall, i.e. continuing on both sides of the wall
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors

Definitions

• the invention relates to the field of a method for repair of cracks in stub tubes, tube systems, etc., in a nuclear reactor.
• Those parts of a nuclear reactor which are contacted by process medium consist primarily of the reactor vessel and its connection with other systems and of a large number of water and steam conduits and, particularly for PWR reactors, also pressure equalization systems and steam generators.
• Cracks in stub tubes, tube joints, and the like, in those systems parts of a nuclear reactor which are contacted by process medium may arise because of corrosion phenomena which occur in welds and the basic material in the zone nearest a weld which is affected by heat. Also other factors such as faulty welds, slag inclusions, fatigue phenomena, and the like, may cause the formation of cracks.
• the risk of the formation of cracks means that considerable efforts must be spent on checking materials at particularly exposed locations, since the formation of cracks may lead to leakage in the systems concerned.
• SE 8701310-8 describes a sealing device for sealing a leak at the weld which joins the control rod drive housing to the bottom stub tube, the sealing device comprising an inner sealing sleeve of a soft metallic material and an outer sleeve of a hard metallic material.
• US 4,773,680 describes a pipe coupling consisting of a number or rings of memory metal which are deformed so that they can be inserted between two overlapping surfaces. During the subsequent heating above the transition temperature, the memory metal rings will straighten out to their original shape and seal the opening between the surfaces.
• the device or the parts of the device which are of memory metal are first deformed, at a temperature lower than the transient temperature for the metal in question, to the desired degree of deformation in order to get a suitable shape for arrangement at the system part, and to obtain a suitable influence on the system part during the subsequent heating of the memory metal, to a temperature exceeding the transient temperature.
• Memory metal largely functions in such a way that the metal is cooled to a martensite-stable region whereupon the metal is deformed into the desired shape; however, the degree of deformation cannot exceed the limit set to the material. After that, the metal will resume its original shape when being heated to a temperature above the transient temperature, i.e. the temperature at which a phase transformation from martensite to austenite takes place.
• transient temperatures in the interval 200-150°C may be chosen.
• the memory metal is usually of Ni-Ti-X type, but also Fe-based alloys of, for example, Fe-Cr-Ni-Mn-Si type may be used.
• memory metal with so-called two- stage effect, which means that the metal after heating to above the transient temperature changes shape also when it is thereafter cooled to a temperature below the transient temperature but above the temperature at which the original deformation has taken place.
• the requirements on the memory metal are primarily that the substances included shall not cause problems for the other parts of the reactor system by the corrosion products which may be formed.
• the method according to the invention means that it is possible to bring about a durable repair of a weld with a continuous or almost continuous crack in a considerably more simple way than before.
• the method means that the repair can be considered to be permanent since no additional efforts, such as readjustment of bolted joints, etc., are needed.
• the invention means that a repair of a part at a location which is difficult to reach, where a crack has been determined or may be expected to arise, can be carried out by manufacturing a joint, sleeve, tube or the like completely or partially of memory metal.
• the memory metal parts are deformed at a temperature below the transient temperature to the chosen shape and degree of deformation and are then maintained at a lower temperature than the transient temperature.
• the joint etc. is fitted or otherwise arranged at the part at a temperature below the transient temperature. Thereafter, when the temperature is raised to above the transient temperature, the joint etc. will resume its original undeformed shape so as to achieve a tight joint around the part.
• the function of the joint is primarily to seal against leakage but it may also be load- carrying.
• the strength properties of the material are therefore of importance. It may also be of importance that the materials which are chosen for the joint, both the memory metal (s) and the conventional alloys, have thermal expansion properties which are compatible with the material (s) of the part which is repaired.
• the joint etc. may consist of several parts of memory metal, which may have different transient temperatures .
• the joint When mounting the joint, several parts of memory metal included in the joint may be chosen to be heated in sequence to obtain a successive tightening of the joint.
• the deformation of the memory metal may, of course, also be chosen such that the desired sealing is obtained.
• the sealing can then be adapted to, for example, the size of the crack in that part which is to be repaired.
• parts comprising memory metal which may be used for repair from inside tubes, stub tubes, and the like.
• Devices with memory metal can also be arranged around, for example, tube welds to bring about a favourable stress configuration in and around the weld.
• Figure 1 shows a cross section of part of a control rod drive housing and a bottom stub tube and a sleeve of memory metal
• Figure 2 shows the same section as Figure 1 but with a sealing joint with rings of memory metal
• Figure 3 also shows a section through a control rod drive housing and a bottom stub tube and with a sealing joint with several parts of memory metal.
• Figure 1 shows a cross section through part of a control rod drive housing 1 which is connected to a bottom stub tube 2 by a weld 3. Between the housing 1 and the bottom stub tube 2 there is a gap 4. If a crack is formed at the weld or in the weld zone, leakage of reactor water may occur.
• the bottom stub tube and the control rod drive housing have been provided with an external casing 5 of memory metal which is located so as to cover the weld and a region above and below the weld.
• the casing is of memory metal, which has been deformed below the transient temperature and has been arranged around the weld between the control rod drive housing and the bottom stub tube at a temperature below the transient temperature for the memory metal. During the subseqent heating of the casing, this will shrink and a tight joint around the weld, preventing leakage of reactor water, is formed.
• Figure 2 shows a different type of joint to be used according to the invention for sealing a possible leak between the control rod drive housing and the bottom stub tube.
• the joint comprises at least two rings 7 of memory metal, and around the rings there is arranged a housing 8 taking up the axial forces acting on the joint.
• Figure 3 shows an additional embodiment of the joint for sealing a possible leak between the control rod drive housing 1 and the bottom stub tube 2 according to the invention.
• the joint comprises two rings 9 of memory metal, surrounded by a housing 10 which essentially comprises two parts.
• An outer part 11 consists of a memory metal which may have a higher transient temperature than the rings 9, and an inner part 12 is made of a conventional alloy, for example stainless steel.
• the joints for repair according to the invention may also be provided with seals of various kinds, for example metal washers or graphite plates which, upon pressure build-up, are crushed and form effective seals. Screws, wedges and other structural members occurring in joints may, of course, also be included.
• a device for plugging steam generator pipes, there is introduced a device comprising at least one part made of memory metal which is bent so that the device is easy to insert into the pipe system. When the device is placed at the desired location, it is heated and thus unfolded in such a way that sealing of the tube is achieved.
• sleeves of memory metal are inserted which have been compressed or folded in such a way that they may be inserted into a steam generator pipe and which are thereafter heated when they have been brought to the desired location in the pipe and will thus constitute an internal sealing of the pipe.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Butt Welding And Welding Of Specific Article (AREA)
• Heat Treatment Of Articles (AREA)
• Monitoring And Testing Of Nuclear Reactors (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20376136

Family Applications (1)

Country Status (2)

Cited By (2)

Families Citing this family (1)

Citations (4)

• 1989
  • 1989-05-31 SE SE8901974A patent/SE463791C/sv not_active IP Right Cessation
• 1990
  • 1990-05-30 WO PCT/SE1990/000368 patent/WO1990015418A1/en unknown

Patent Citations (4)

Also Published As

Similar Documents

Legal Events