JPH1039078A - Reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of thermal fatigue of the head cover for a stainless steel container and interface between concrete and stainless steel by sandwiching a deformable heat barrier wall between a thick annular stainless steel plate for fixing a stainless steel dome with bolts and the concrete of a reactor container. SOLUTION: The joint between the head cover for a stainless steel container and a prestressed concrete reactor container (PRCV) comprises an annular stainless steel plate 54, the concrete of a PRCV wall 2, a heat barrier wall 56 occupying a volume partitioned by a stainless steel liner 4. Upper edge 4a of the stainless steel liner 4 is welded to the circumferential part of the annular plate 54 on the radially innermost side thereof. A stainless steel head cover 6 is pressed against the annular plate 54 by means of a vertical stretching member 10c. The stretching member 10c imparts a downward force to the upper surface at the flange 6a of a stainless steel head through a stretching nut 8. The interface between the flange 6a and the annular plate 54 is sealed hermetically by means of a pair of O-rings 58a, 58b. The heat barrier wall 56 comprising a zirconia sand board lessens thermal stress of the stainless steel head cover 6 for the container.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Related Patent Application] This application was filed on April 24, 1995.
U.S. patent application serial no.
No. 810 is a continuation-in-part application.

[0002]

The present invention relates to an apparatus for isolating a reactor pressure vessel in the event of a coolant loss accident. In particular, the present invention relates to a nuclear reactor structure having a prestressed concrete (PS concrete) reactor vessel (PCRV) with a large head opening closed by a steel head lid.

[0003]

BACKGROUND OF THE INVENTION Since the birth of water-type reactor equipment, such equipment in the range of 2000-MWe plus has been developed and a stainless steel reactor pressure vessel operating at about 1000 psi has been utilized. It was started. The inside diameter of such a reactor vessel reaches about 13 m. The manufacture of containers of these dimensions requires special manufacturing conditions that cannot be easily met, especially since the number of manufacturers that can meet such manufacturing challenges is small. Along with the practical steel vessel diameter limit of less than 13m, it is possible to make numerous through-holes (for cooling pipes, steam pipes, water supply pipes, instrumentation pipes, control rod pipes, etc.) in the steel vessel wall. difficult. The result is an undesirably complex reactor pressure vessel structure and sub-optimal system capacity.

To address this problem, prestressed concrete reactor pressure vessels having a steel inner liner have been proposed. The use of pre-stressed concrete reactor pressure vessels allows the fuel core to be very large, simplifying plant safety measures,
Moderate response to plant transients. The use of pre-stressed concrete structures removes the current dimensional constraints imposed by steel reactor vessels due to current steelmaking capacity. This makes it possible to design a very large-scale natural circulation reactor having a low energy density core and a high output energy of the plant.

[0005] Prestressed concrete reactor pressure vessels and associated isolation devices suitable for use in both natural circulation and forced circulation reactors have been proposed.
To reduce the construction and storage costs of the reactor,
The only safety response required in the event of a coolant loss accident (LOCA) event is designed to be reactor isolation. By designing a reliable isolation device that can stabilize the reactor pressure and maintain the inventory water volume, the suppression pool and conventional storage can be replaced by an isolation device. The isolation device effectively eliminates the possibility of LOCA or serious accidents occurring.

In the proposed reactor design, a prestressed concrete reactor vessel (PCRV) lined with steel contains the reactor internal components, fuel and coolant. The pressure holding capability of the PCRV is obtained by pre-stressing tendons that extend in both the hoop and meridian directions, and a gallery is provided to allow access for testing and pre-stressing the tendons.

Further, the reactor design proposed here incorporates the idea of a high pressure storage head lid in order to provide redundancy in addition to the conventional steel reactor vessel head lid. The storage head lid has a steel lid attached to the PCRV so that a well is formed between the container head and the storage head lid. If the container head lid leaks, the storage head lid contains pressurized fluid entering the well.

[0008] Reactors with a PCRV require the compression of the walls of the PCRV, as well as the tendon redundancy that causes the compression,
Since catastrophic breakage of the PCRV is prevented, it can act as its own storage unit. With isolation valve,
If LOCA is present, isolate the reactor vessel. Since the container isolation can be easily integrated into the PCRV design, the conventional large storage space is not required.

Further, the proposed reactor design is such that the through pipes and pipes representing the nozzle of the pressure vessel are surrounded by a guard pipe, and the guard pipe is at least a first (inner) isolation valve. Is to be extended to cover A defensive pipe is placed around the pipe passing through the passage as a secondary barrier and protects against breakage of the primary pressure system boundary pipe. The space between the primary system pressure boundary pipe and the defense pipe is pressurized to an intermediate pressure and monitored during operation. If the pipe connected to the reactor pressure boundary breaks, the isolation valve is activated, and the reduction of the inventory of the reactor vessel ends rapidly. If the entire reactor needs to be isolated as a result of a pipe break, the isolation condenser removes long-term decay heat and maintains container inventory. There is no need for additional emergency core cooling equipment since the coolant loss is completed quickly and there is no substantial loss of inventory from the PCRV.

In the proposed reactor design, 25-
A thick steel annular plate with a thickness in the range of 40 cm is P
Locked to the top surface of the CRV wall, it serves as a stop for the tendon, strengthens the large head opening of the container, and transfers the load from the container head lid to the PCRV wall. During operation, the reactor internal pressure is about 1250 psi and the reactor temperature is about 5
50 ° F. ASME III, Chapter 2, to meet the concrete temperature limits imposed by reactor vessel regulations for normal plant operation, provide reactor wall cooling to reduce the concrete temperature to a certain limit, for example, globally under normal conditions. 150 ° F and locally 250 °
Keep below F. Steel reactor head lids when not cooled and without significant insulation can reach temperatures of 550 ° F. This shift creates a constraint on thermal expansion, which causes excessive stress on the flanges and bolts of the head and the concrete at the connection. With a temperature difference of several hundred degrees Fahrenheit between the steel head lid and the PCRV wall, the combined effects of heat effects as well as internal pressure on the head lid exceed the elastic yield limit of the steel. For this reason, the design of the steel container head lid
We face many challenges, such as considering thermal fatigue.

[0011]

SUMMARY OF THE INVENTION The present invention is directed to a steel vessel head lid heat release occurring in a reactor where the open head of a prestressed concrete reactor pressure vessel lined with steel is closed by a steel dome. A joint that solves both fatigue problems as well as concrete-steel interface problems.

In a first preferred embodiment of the invention, the steel dome is a thick steel annular plate (hereinafter "head ring").
Head ring and PCRV
A deformable thermal barrier is sandwiched between the concrete on the walls. The head lid and head ring are made of the same type of steel (one or more types) with similar coefficients of thermal expansion
Should be made in The thermal barrier is made of a load-bearing material, such as a zirconia sand substrate, which has a low thermal conductivity, a high bulk modulus equal to that of concrete, and a low shear modulus. The load-bearing material is confined to a closed volume in compression by relatively strong walls. The shear modulus must be small enough to reduce the resistance of the head ring and container head lid to radial displacement. Thermal barriers insulate the concrete from hot head rings and hot vessel head lids. Different thermal expansions of the container head lid and PCRV cause a radial displacement of the head ring with respect to the concrete. The PCRV liner is connected flexibly to the inner periphery of the head ring, and the outer periphery of the head ring is flexibly connected to a second annular steel plate serving as a locking surface for the PCRV vertical tendon. In this connection, the displacement in the radial direction is dealt with.

The use of a thermal barrier in accordance with a first preferred embodiment of the present invention reduces the thermal stress on the steel container head lid. For this reason, thermal fatigue of the steel container head lid is no longer a problem. The use of flexible liner connections addresses the different thermal expansion between steel and PCRV concrete. The interface problem is solved by using a head ring that acts as a transition mechanism between the steel vessel head lid and the PCRV. In addition, the head ring enhances the PCRV around the large head opening and
Provides a locking surface for the vertical tendon of the V.

In a second preferred embodiment of the present invention, a steel dome is interfaced to the top of the PCRV via a slip joint, which is connected to the flange of the steel dome without undue thermal stress. Allow it to expand radially. The slide joint includes a bearing plate ring mounted on the upper surface of the PCRV, and a head ring provided on the bearing plate ring.
It has a ring and bolts the flange of the steel dome to the head ring. Low friction interface
Allow the ring to expand radially with respect to the base ring. In order to minimize the stress between the concrete and the bearing plate, the bearing plate is not divided into a continuous ring, but is divided into ring segments. This slotted plate reduces radial thermal expansion and provides for expansion compatibility between the bearing plate and the concrete. As another measure to reduce the thermal expansion of the support plate, several pipes through which recirculating coolant passes are welded to the bottom of the support plate and buried in concrete just below the support plate. As a variant of the second preferred embodiment, the low friction interface is a graphite or Teflon coating, multiple pads made of graphite-steel alloy, or a thermal stress relief ring made of a molybdenum alloy containing small amounts of titanium and tungsten. Can be configured.

In a third preferred embodiment, the thermal stress on the steel vessel head lid is reduced by lowering the temperature of the head lid. In order to lower the temperature, all the inner surfaces of the head cover are thermally insulated and the outer surface of the head cover is cooled. The outer surface of the head lid is naturally circulated through a cooling pipe through which circulating coolant (for example, water), blows in from one side and forcedly circulates cooling air extracted from the other side, or by keeping a cold surface, or by naturally circulating air in the cavity. Can be cooled. This allows the temperature of the head to be reduced to less than 400 ° F.

Another feature of the third preferred embodiment is that the bearing plate is eliminated. Instead of sliding on the support plate,
The head ring is directly locked to the PCRV by the tendon. To minimize thermal expansion of the head ring, several pipes through which recirculating coolant passes are welded to the bottom of the head ring and buried in concrete just below the head ring. The inner surface of the liner is also covered with thermal insulation that extends to the height of the head ring. Thermal insulation at the height of the head ring limits the amount of heat transferred to the head ring from inside the liner. In addition, cooling pipes are welded to the outer surface of the liner and buried in concrete,
Cool concrete. The PCRV liner is mounted entirely on the head ring.

[0017]

FIG. 1 illustrates the basic concept of a pre-stressed concrete reactor pressure vessel with a complete pre-stressed concrete structure including through areas. I have. The natural circulation reactor shown in FIG. 1 has a pre-stressed concrete reactor vessel (PCRV) 2 whose inner surface is a steel liner 4.
Pressure vessel part 2a and pressure vessel part 2 lined with
a includes a storage portion 2b extending upward from the top of FIG. A fuel core 50 is supported inside a fuel core shroud 52, and this shroud is supported in an upright position by a PCRV. The top of the pressure vessel portion 2a has a steel dome 6
The dome has an annular flange and is connected to the end of each vertical tendon 10a (shown in dashed lines) passing through a duct or tube (not shown) embedded in concrete. This flange is held down by the tension nut 8. Similarly, the top of the storage part 2b is closed by a steel dome 12, which also has a pressed annular flange as described for the dome 6. The steel domes 6, 12 and the storage part 2b form a well 16 for containing gas that can escape from the pressure vessel in the event of a leak in the seal of the dome 6. The seal is considered to be the weakest bond that can break before any part of the steel lined PCRV 2 or dome 6 breaks.

The most striking feature of a prestressed concrete reactor pressure vessel is the redundancy that exists within this structure. The structural redundancy in PCRV is rooted in the fact that a large number of prestressed tendons are required to fail at exactly the same moment, making catastrophic failure virtually impossible. ing. Utilizing this behavior as well as the tendon redundancy, the PCRV itself can act as a storage. Therefore, it was considered desirable to expand the pre-stressed concrete structure to include the reactor head as shown in FIG. Steel annular plate 14 is PCR
Locked to the upper surface of the V wall, it becomes a locking portion for the tendon 10a, and transfers the load from the container head lid to the PCRV wall. The container is lined on its inner surface with a steel liner 4 to maintain leak resistance.

The pressure holding capacity of the PCRV 2, as shown in FIG. 1, is dependent on the hoop prestress generated by the hoop tendons locked to the support wall (not shown), as well as above and below the PCRV wall. Locked longitudinal tendon 10
It is obtained by the meridional prestress generated by a. A circular gallery 24 is provided at the bottom of the PCRV for the lower locking portion. Prestressing of the lower head is provided by multiple layers of tendon 10c locked to the inner wall of lower head tendon gallery 22. A PCRV may have three or more support walls. If there are three support walls, the gallery is hexagonal, and if there are four support walls, it is octagonal. The main steam piping, water supply piping and emergency core cooling piping have PCRV
Is provided in the upper part of the. The tendon is passed around a large through opening in the PCRV wall, such as a through opening for the main steam line. Compression at the PCRV wall prevents catastrophic failure of the PCRV, as opposed to the state of tensile stress in a steel vessel subjected to internal pressure.

The design of the reactor shown in FIG.
A pair of main steam isolation valves (MSIV) 2 mounted in 8
6a and 26b, and a pair of feedwater isolation valves (FWIV) 26c and 26d attached to the feedwater pipe 30. The main steam pipe 28 passes through the inner steel liner 4 and the walls of the PCRV 2 but is inside the defense pipe 32a, with an intermediate space 34 between them. The intermediate space 34 is the PCRV 2
Is closed off at one end by a cover plate 36 bolted to the top. The cover plate 36 also supports the main steam line 28. MSIV 26b is PCRV
It can be provided outside of. To protect the concrete from high temperatures, a cooling water pipe (not shown) can be embedded in the circumferential area surrounding the protection pipe 32a.

Internal MSI inserted into main steam pipe 28
V 26a is a vertical tunnel 42 for a circular and cylindrical valve
And the top of this tunnel is closed by a cover plate 44. Can 42
Has maintenance access means to manage leaks. The cover plate 44 of the valve tunnel attached to the upper surface of the PCRV keeps the continuity of the boundary of the primary storage.
The continuity of the storage boundary is also maintained at the outlet side of the main steam pipe tunnel by mounting a cover plate 36 over the tunnel passage so that the main steam pipe 28 can pass through this cover. ing. The pressure in the volume of the valve tunnel is monitored to detect any internal or external leaks. If a leak is detected either in the valve access tunnel or through the main steam line through tunnel,
The reactor is isolated (the isolation valve is closed and the isolation condenser is activated to maintain the reactor pressure and water level) and shut down the reactor for repair (insert control rod).

The guard pipe is placed around the pipe passing through the passage as a secondary barrier and protects against breakage of the pipe at the primary pressure boundary. The space between the primary pressure boundary pipe and the guard pipe is pressurized to an intermediate pressure and monitored by the pressure sensor 40 during plant operation. If the pressure in this space suddenly rises, it indicates a break in the primary pressure boundary. If the pressure in this space suddenly drops, it indicates a break in the defense pipe. In each case, the reactor is shut down in a controlled manner without loss of coolant as a safety measure until repairs can be made.

The design of the steel vessel head and its connection to the PCRV requires ASME rules to keep the structural concrete at 150 ° F. or less, whereas the steel vessel head lid is 550 °. This is an important problem in the reactor of the type shown in FIG. 1 because it may be close to the reactor operating temperature of F. This stagger limits thermal expansion, which results in excessive stress on the head flange, bolts, and concrete at the connection. Two options available to alleviate this situation are: (1) container head lid and P
Allowing relative radial movement between the CRVs to address thermal expansion, and (2) minimizing the differential thermal expansion between the PCRV and the sealing head, the thermal stress is reduced to the head lid, flange, bolt and The goal is to lower the temperature of the container head lid so that it is small enough to be acceptable in the connection design. 2-6 are schematic diagrams showing a preferred embodiment of the former head concept, and FIGS. 7 and 8 are schematic diagrams showing a preferred embodiment of the latter concept.

Referring to FIG. 2, the connection of the first preferred embodiment between the steel vessel head lid and the PCRV is:
An annular plate or head ring 54 and a head ring 5
4, having a thermal barrier 56 occupying a volume delimited by the concrete and steel liners 4 of the PCRV wall 2. The upper edge 4a of the steel liner 4 is welded to the radially innermost peripheral portion of the head ring 54.

A steel head lid 6 is pressed tightly against the head ring by a vertical tendon 10c (only one of which is shown in FIG. 2). This tendon exerts a downward force on the upper surface of the flange 6a of the steel head via the tension nut 8. An interface between the steel head flange 6a and the head ring 54 is formed by a pair of O-rings 58a, 5a.
8b. The radially outermost part of the head ring 54 is pressed down by another vertical tendon 10c '. The vertical tendon 10c '' is locked using a steel annular plate 60 having an inner radius greater than the outer radius of the head ring 54.

In accordance with the teachings of the present invention, the reactor is designed so that the O-rings 58a, 58b (or any other suitable sealing means) are the weakest elements in the pressure vessel. If an overpressure occurs inside the pressure vessel, leakage will occur through the sealing means of the reactor head. as a result,
The leak falls into the well or void 16. Leakage of the container at the seal of the head is a preferred limit for overpressure margin, as it is easily detected and non-destructive.
This leakage reduces the differential pressure across the head and tends to close the head seal again. This feature eliminates other less desirable failure modes.

The thermal barrier 56 is preferably made of a zirconia sand substrate. The provision of a moving foundation of zirconia sand under the head ring 54 allows the head ring to thermally expand radially with respect to the concrete without generating unacceptable stress. An annular gap 62 is provided between the head ring 54 and the locking plate 60 to allow for differential radial thermal expansion. This is because the locking plate 60 is at a lower temperature than the head ring,
Therefore, the radial expansion that occurs is smaller. The thermal insulation of the zirconia sand protects the concrete against exposure of the head ring to high temperatures.
The low shear modulus of the zirconia sand reduces the resistance of head ring 54 and container head lid 6 to radial displacement. Thus, the thermal barrier reduces the thermal stress on the steel container head lid.

As mentioned previously, the thermal barrier 56
2 is insulated from the hot head ring 54 and the hot vessel head lid 6. Preliminary thermal analysis shows that the temperature of the concrete adjacent to the barrier 56 is about 250
° F, which is allowed by the rules for local areas of ASME III. The temperature of the head ring is the temperature of the steel dome (ie, 550 ° during reactor operation).
F). The radial displacement for this temperature range is estimated to be on the order of 0.5 inches. PC
The flexible connection 4a of the RV liner 4 accommodates this radial displacement. This flexible connection 4a can take the form of an inflatable bellows or a flexible seal. A flexible liner connection addresses the differential thermal expansion between the steel and the concrete of the PCRV, creating a large axial temperature gradient.

FIG. 3 shows that the steel dome 6 is connected to the PCRV via a slip joint which allows the flange 6a of the steel dome to expand radially without excessive thermal stress.
2 shows a second preferred embodiment of the invention interfacing to the top of the second embodiment. The slip joint has a head ring 54 'that slides on a bearing plate ring 64 mounted on the top surface of the PCRV. In this embodiment, a steel dome is attached to head ring 54 'by a number of stud bolts 66 (only one is shown in FIG. 3). A low friction interface 68 allows the head ring 54 'to expand radially with respect to the bearing ring 64. For example, a low friction interface is to mix graphite powder with alcohol and then apply a graphite / alcohol suspension to the bottom of the head ring,
Alternatively, it can be made of a thin film of graphite powder formed by spraying any one of the upper surfaces of the bearing plate ring. Alternatively, a Teflon layer can be applied to either or both surfaces.

In order to minimize the stress between the concrete and the bearing plate 64, the bearing plate is not a continuous ring,
It is divided into ring segments. This slotted plate reduces radial thermal expansion and provides for expansion compatibility between the bearing plate 64 and the concrete. As another measure to reduce the thermal expansion of the support plate 64, a plurality of pipes 70 through which recirculating coolant passes are welded to the bottom surface of the support plate and buried in concrete just below the support plate.

In the proposed reactor design, the PCR
The cooling of the V-wall 2 can be achieved by insulating the PCRV liner 4 with a thermal insulator 72 made of fused quartz, as shown in FIG. The fused quartz is cut into blocks of the desired shape, pierced and mounted directly to the liner 4 by locking members (not shown). It is preferred that the blocks of fused quartz overlap to form a continuous insulator with a gap for thermal expansion during heating. It is proposed to use a 4.5 inch thick fused quartz insulator.
Instead, corrugated metal sheets can be used. Furthermore,
The thermal insulator 74 is made of a steel head lid 6 and a head flange 6a.
And the outer surface of the head ring 54 '. Thickness 4 to 6
We suggest using inch wool insulation.

In a second preferred embodiment, the PCRV liner 4 must cover the edge of the support plate 64 and be mounted on the head ring 54 'to maintain a pressure boundary. When transitioning from concrete to the head ring, the liner is not covered with thermal insulation. As a result, the liner
Over a distance of 1.5 m, it undergoes a temperature change from 200 ° F to close to 550 ° F. This transition of the liner is in the form of an inflatable bellows or a flexible seal 4a. The inflatable bellows have an internal to maintain pressure boundaries, to accommodate radial movement during head ring slippage, and to absorb 350 ° F temperature changes without buckling. Designed to withstand pressure. Optionally, the volume 7 between the inflatable bellows 4a and the support plate 64
Numeral 6 is partially filled with zirconia sand to thermally insulate the bearing plate while allowing the perot to flex.

The low friction interface 68 between the head ring 54 'and the bearing plate 64 is designed to withstand very high compressive forces due to preload conditions to resist internal pressure. Furthermore, the heat-induced rotation of the joining surface causes extra compression on the outer surface of the contact during slippage. Low friction integrity must be maintained because start-up lock-up causes pressure boundaries to lift and leak. Lockup during shutdown also significantly complicates removal of the head lid.

The first of the second preferred embodiment shown in FIG.
In a variant of the above, the low friction interface can consist of a number of pads 78 made of a graphite-steel alloy. The arrangement of the pad 78 with respect to the opening 80 provided for the tendon in the PCRV wall 4 is shown in FIG. The graphite-steel alloy pad
It can be formed as a disk having a diameter of 4 inches.
The opening 80 contains a steel pipe having a diameter large enough to provide a clearance for the tendon material to move freely during radial expansion of the head ring 54.

In a second variation of the second preferred embodiment shown in FIG. 6, the low friction interface may be comprised of a thermal stress relief ring 82. This is because the thermal stress relief ring 82 has a differential thermal expansion of 50 between the head ring 54 'and the bearing plate 64.
Made of a material with a coefficient of thermal expansion that allows it to expand in percent. The tensile strength of the thermal stress relief ring is adequate to transfer the loads created by thermal expansion and other loads.

The thermal stress relief ring 82 has a flange 82a extending from its inner periphery and projecting vertically downward and a flange 82 extending from its outer periphery and projecting vertically upward.
b. The flange 82 a fits into a step formed along the inner periphery of the support plate 64. The annular horizontal portion 82c of the ring 82 includes the head ring 54 'and the base plate ring 64.
Sandwiched between. Preferred materials include a small amount of titanium for strength and a desired coefficient of thermal expansion (eg, 3 × 10 ⁻⁶ / ° F.).
Is a molybdenum alloy containing a small amount of tungsten selected so as to obtain the following.

The thermal stress relief ring 82 expands radially outward by less than the radially outward thermal expansion of the head ring 54 '. As a result of the radial outer circumference of the head ring 54 'abutting the radial inner circumference of the flange 82b, the thermal stress relief ring 82 absorbs some thermal stress, thus reducing thermal stress on the concrete container. I do. The volume 84 between the inflatable bellows 4a and the flange 82a can optionally be partially filled with zirconia sand.

In the third preferred embodiment shown in FIGS. 7 and 8, the thermal stress on the steel vessel head lid 6 is reduced by lowering the temperature of the steel lid. This is accomplished by extending the thermal insulator 72 (described above with respect to FIG. 3) to cover all inner surfaces of the liner 4, head lid 6, and head ring 54 '. As noted above, the thermal insulator is preferably in the form of a fused quartz block.
The outer surface of the steel head lid and head ring is
6 is cooled by the natural circulation of air inside. Instead, a plurality of cooling pipes 88 through which recirculating coolant passes.
A dashed line (indicated by a dashed line) can be attached to the outer surface of the steel dome 6 in a heat conductive relationship therewith and passed through the PCRV wall 4 to a circulation pump and a heat exchanger (not shown). By applying a thermal insulator to the inner surface of the head lid, the temperature of the head lid can be reduced to about 400 ° F.

In a third preferred embodiment, the head ring 54 'is locked directly to the PCRV 2 by tendons 10c and 10c'. To minimize thermal expansion of the head ring, a plurality of pipes 86 through which recirculating coolant passes are welded to the bottom of the support plate and buried in concrete just below the support plate. Thermal insulation 72 at the height of the head ring also limits the amount of heat transferred to the head ring from inside liner 4. Another cooling pipe is welded to the outside of the liner and embedded in concrete to cool the liner.

The preferred embodiment of the present invention has been described by way of example. Various modifications of the disclosed structure which fall within the scope of the invention will be readily apparent to those skilled in the art of reactor design. Although the preferred embodiment has been described for a natural circulation reactor, the concepts of the present invention are equally applicable to a forced circulation reactor. It is to be understood that all such modifications are included in the claims.

[Brief description of the drawings]

FIG. 1 shows a natural-circulation reactor with steel-lined, pre-stressed concrete reactor pressure vessel, dual steel head lids, and main steam piping through a steel inner liner. Schematic diagram.

FIG. 2 is a side cross-sectional view of a thermal barrier interfacing a steel head lid to a pre-stressed concrete reactor pressure vessel in accordance with a first preferred embodiment of the present invention.

FIG. 3 is a side cross-sectional view of a slip joint for interfacing a steel head lid to a prestressed concrete reactor pressure vessel in accordance with a second preferred embodiment of the present invention.

FIG. 4 shows, as a first variant of the second preferred embodiment, a side view of a sliding joint with a low-friction disc for interfacing a steel head lid to a prestressed concrete reactor pressure vessel. Sectional view.

FIG. 5 is a plan view showing an arrangement of a low-friction disk by the deformation shown in FIG. 4;

FIG. 6 according to a second variant of the second preferred embodiment;
FIG. 3 is a side cross-sectional view of a slip joint for interfacing a steel head lid to a prestressed concrete reactor pressure vessel.

FIG. 7 shows a first preferred embodiment variant of the third preferred embodiment of the present invention, which is cooled by natural circulation for interfacing a steel head lid to a prestressed concrete reactor pressure vessel. FIG.

FIG. 8 circulates in a pipe for interfacing a steel head lid to a prestressed concrete reactor pressure vessel in accordance with a second variation of the third preferred embodiment of the present invention. FIG. 3 is a side cross-sectional view of a head ring cooled by a coolant.

[Explanation of symbols]

 2 Concrete Container 6 Steel Container Head Lid 6a Lid Flange 54, 54 'Head Ring 56 Thermal Barrier 64 Support Plate Ring 68 Low Friction Interface 82 Thermal Stress Relief Ring

Continued on the front page (72) Craig Delaney Sawyer, United States, California, Los Gatos, Highland Avenue, No. 63 La Julia Scenic Drive South, number 7194

Claims (20)

[Claims] 1. A concrete container having an open container head on its top, a heat insulating material arranged to thermally insulate the concrete container, and a container head lid made of a material different from concrete and having a flange. And a slip joint for coupling the flange of the vessel head lid to the concrete vessel and closing the open vessel head. 2. A head ring mounted on the flange of the container head lid and having a planar contact surface, the slip joint being mounted on a flange of the container head lid, and having a planar contact surface mounted on the concrete container. A bearing ring in which the head ring and the bearing ring are arranged such that their respective planar contact surfaces face each other; and an interposition between the facing planar contact surfaces of the head ring and the bearing ring. 2. The device according to claim 1, wherein the low friction interface is arranged.
Nuclear reactor as described. 3. The reactor of claim 2 wherein said low friction interface comprises a number of pads made of a low friction material. 4. The nuclear reactor of claim 2, wherein said low friction material is a graphite-steel alloy. 5. The nuclear reactor of claim 2, wherein said low friction interface comprises a layer of low friction material. 6. A nuclear reactor according to claim 2, wherein said low friction material is graphite powder. 7. is mounted on the bearing plate ring,
The nuclear reactor according to claim 2, comprising a plurality of cooling pipes embedded in the concrete container. 8. The nuclear reactor according to claim 1, further comprising a heat insulating material covering at least a part of an outer surface of the vessel head lid. 9. A metal alloy liner interposed between said thermal insulation material and said concrete container, said metal alloy liner extending to said head ring and being accessible at the height of said low friction interface. 3. The reactor of claim 2 wherein said reactor comprises a flexible liner portion. 10. The reactor of claim 9 wherein said flexible liner portion comprises an inflatable bellows. 11. A concrete container having an open container head at its top, a thermally insulating material arranged to thermally insulate the concrete container, and a container head lid made of a material different from concrete and having a flange. A head ring attached to a flange of the container head cover, a bearing plate ring attached to the concrete container, and a thermal stress relief ring interposed between the head ring and the bearing plate ring. Wherein the thermal stress relief ring has a tensile strength greater than the tensile strength of the head ring material and greater than the tensile strength of the bearing plate ring material, and a thermal expansion coefficient less than the thermal expansion coefficient of the head ring material. Reactor made of material with modulus. 12. The nuclear reactor according to claim 11, wherein the material of the thermal stress relief ring is a molybdenum alloy. 13. The thermal stress relief ring has an inner periphery, an outer periphery, a flange connected to the outer periphery of the annular plate and projecting upward, and a flange connected to the inner periphery of the annular plate and projecting downward. 2. A structure comprising an annular plate.
A nuclear reactor according to claim 1. 14. The nuclear reactor according to claim 11, further comprising a plurality of cooling pipes having a heat conductive relationship with the bearing plate ring. 15. A concrete container having an inner surface lined with a liner made of a metal alloy and having an open container head on top, a heat insulating material covering at least a portion of the metal alloy liner, and concrete. A container head lid made of a different material and having a flange, a head ring arranged to support the flange of the container head lid, and a volume bounded by the head ring, the liner and the concrete container A nuclear reactor having a thermal barrier disposed therein. 16. The nuclear reactor of claim 15, wherein said thermal barrier is made of a material having a low thermal conductivity, a high bulk modulus and a low shear modulus equal to that of concrete. 17. The reactor according to claim 15, wherein said thermal barrier is made of zirconia sand. 18. A concrete container having an inner surface lined with a liner made of a metal alloy and having an open container head on top, a container head lid made of a material different from concrete and having a flange. A heat insulating material covering at least a portion of an inner surface of the metal alloy liner, and at least a portion of an inner surface of the container head lid, and a head ring disposed between the container head lid flange and a concrete container. Reactor. 19. The nuclear reactor according to claim 18, comprising a plurality of cooling pipes having a heat conductive relationship with the head ring. 20. The nuclear reactor according to claim 18, comprising a plurality of cooling pipes having a heat conductive relationship with an outer surface of the vessel head lid.