RU2453006C1 - Container to transport spent nuclear fuel - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: invention relates to containers designed to transport and temporarily store the spent nuclear fuel (SNF) of nuclear power plants (NPP) in the form of spent fuel assemblies (SFA). A container for transportation and/or storage of spent nuclear fuel comprises a metal vessel, including a bottom, a support, cylindrical shells fixed concentrically at the bottom to form a cavity, a geometric closure of the specified cavity and the inner cavity of the container, which is arranged in the form of two covers installed one above the other on the common base, a neutron protection installed on the external surfaces of the inner cover, bottom and cylindrical shell, elements with high heat conductivity pulled via a layer of neutron protection installed on the cylindrical shell. The cavity between cylindrical shells is filled with an insert from high-density metal and heat conductivity. Elements with high conductivity are V-shaped ribs arranged along the vessel at the length. Rib walls are perforated with slots installed in longitudinal rows with displacement of a slot in one row relative to a slot in another row. Ribs protrude beyond the surface of the neutron protection and are fixed to each other by means of a shell. There are dampers installed on the support and the external cover.

EFFECT: development of a container for transportation of spent nuclear fuel with higher weight and depth of nuclear fuel burning.

17 cl, 6 dwg

Description

The invention relates to containers intended for the transportation and temporary storage of spent nuclear fuel (SNF) of nuclear power plants (NPPs) in the form of spent fuel assemblies (SFA).

SFAs are characterized by high residual heat release and radiation levels, which requires the use of special containers for their safe transportation.

A known container for transporting and storing SFAs (German patent No. 3026249, class G21F 5/00, 1982), which contains a thick-walled case with cooling fins on the outer surface and a corrosive inner lining. The housing is sealed with two covers, and the inner lining is held onto the housing by threaded bushings.

The disadvantage of this container is insufficient protection against neutron radiation, as well as a rather complicated manufacturing technology, which requires the use of unique metallurgical equipment to produce high-quality multi-ton metal billets.

A known container for transporting burned-out fuel assemblies (US patent No. 3774037, class 021Р 3/00, 1973), which contains the inner and outer cylindrical shells with stainless steel bottoms and a protective overlap with its fastening elements mounted on the bottom with a loading hole. On the outer shell are annular heat sink fins. Between the shells there is radiation protection in the form of uranium castings.

The disadvantages of the design of this container are:

- the manufacture of uranium castings requires the use of special technology, which complicates the overall manufacturing process of the product, and the presence of uranium castings requires special accounting and control when using the container for its intended purpose;

- low thermal conductivity of uranium does not provide the required level of heat removal from the SFA with an increased mass and depth of burnup of nuclear fuel even with a significant number of annular heat sink fins on the outer wall of the container;

- for SFAs with increased mass and depth of nuclear fuel burnout, the required level of neutron protection is not provided.

A known container for transporting and / or storage of spent nuclear fuel (patent RU 2348085, G21F 5/00, publ. 02/27/2009, bull. No. 6), containing a metal casing, including a bottom, outer and inner cylindrical shells, the cavity between which is filled material for neutron absorption, a tight seal of said cavity and the inner cavity of the container, which is made in the form of at least two covers mounted one above the other on a common base and forming two concentric sealing contacts with the latter pa, and through the material for neutron absorption omitted elements of high thermal conductivity, respectively attached to said case body by means of threaded elements. Elements with high thermal conductivity are made in the form of radial longitudinal sheet elements. The fastening of the threaded elements to the outer cylindrical shell of the housing is made to ensure sealing of the latter. Radial longitudinal sheet elements have through holes and / or discontinuous edges with the formation of recesses, which are made with the possibility of filling material for neutron absorption in the manufacture of the container. The outer cylindrical shell of the housing is made of at least two annular segments with longitudinal fins, interconnected by means of sealed joints. The outer and inner cylindrical shells of the casing and the radial longitudinal sheet elements are made of dissimilar materials, while the radial longitudinal sheet elements are made of a material with higher thermal conductivity than the materials of which the outer and inner cylindrical shells of the casing are made.

Radial longitudinal sheet elements can be made of aluminum or an aluminum alloy with oxidized surfaces.

The outer cylindrical shell of the housing may be made of corrosion-resistant steel, and the inner cylindrical shell of the housing may be made of low alloy steel.

In an embodiment, the radial longitudinal sheet elements are attached to the outer and inner shells of the housing by means of common threaded elements which are passed through respective holes made respectively in the outer cylindrical shell of the housing and in the radial longitudinal sheet elements, said holes being sealed on the outside of the outer cylindrical shell corps.

An embodiment is possible when each threaded element with an outer cylindrical shell of the housing forms a sealing loop.

In another embodiment, each threaded element is provided with a lock washer, each lock washer with an outer cylindrical shell of the housing forming a sealing loop.

In the last two embodiments, said sealing circuit is made using a weld.

In another embodiment, the radial longitudinal sheet elements are attached to the inner cylindrical shell of the casing using one of the threaded elements, and to the outer cylindrical shell of the casing using other threaded elements.

An embodiment is possible when the radial longitudinal sheet elements are attached to the inner cylindrical shell of the casing using the same threaded elements, and are attached to the inner and outer cylindrical shells of the casing using other threaded elements.

In an embodiment, the inner cylindrical shell is made in the form of two concentrically arranged shells, the gap between which is filled with lead, while the shells can be made of low alloy steel.

This container is taken as a prototype as the closest in technical essence to the claimed technical solution.

The disadvantages of this container are:

- low thermal conductivity of the inner cylindrical shell of the housing and heat transfer to the environment only by the outer shell of the housing and low thermal conductivity, which receives heat from the inner cylindrical shell through radial longitudinal sheet elements of high thermal conductivity, do not provide the required level of heat dissipation from the SFA with increased mass and depth burnout of nuclear fuel;

- insufficient protection against radiation, since the presence of a significant number of through threaded elements in the radial longitudinal sheet elements located in the neutron shield makes it possible for neutrons to slip through them.

The task to be solved is the creation of a container for transporting spent nuclear fuel from VVER-1000 reactors with increased mass and depth of nuclear fuel burn-up (uranium-235 enrichment up to 5% and burnup up to 70 GW · day / tU).

The problem is solved in that in a container containing: a metal body including a bottom, a support, cylindrical shells concentrically mounted on the bottom to form a cavity, a tight overlap of said cavity and the container’s inner cavity, which is made in the form of two covers mounted one above the other on general basis, neutron protection installed on the outer surfaces of the inner cover, bottom and cylindrical shell, elements with high thermal conductivity, passed through a neutron layer of protection located on a cylindrical shell, the aforementioned cavity between the shells is filled with an insert of high density metal and thermal conductivity relative to the material of the shells, V-shaped ribs located along the body along the length corresponding to the length of the container’s inner cavity are used as elements with high thermal conductivity. The ribs are mounted on a cylindrical shell and mounted on it. The ribs protrude beyond the surface of the neutron shield and are fastened together by a shell, which is the lining of the neutron shield. In the neutron protection zone, the rib walls are perforated with through grooves located in the longitudinal rows with the offset of the groove of one row relative to the groove of the other row. Dampers are installed on the support and on the outer cover.

The inner cylindrical shell, the bottom and the common base can be made of corrosion-resistant steel, and the outer cylindrical shell - of low alloy steel. The execution of the inner shell, bottom and base of the housing from corrosion-resistant steel does not require the use of anti-corrosion coating.

The insert of metal of high density and thermal conductivity can be made of copper.

The insert can be fixed between the shells by a disk, reinforced by a ring and plates, which excludes its longitudinal movements.

Also, the insert can be made of separate blocks, secured from longitudinal movement with rings, while the gap between the blocks and the outer shell is filled with a powder filler of the same material as the blocks. This embodiment of the insert extends the technological capabilities of manufacturing the container body.

Filling the gap between the shells of the inner cylindrical shell with a metal insert of high thermal conductivity and density, for example, copper, allows to provide:

- high thermal conductivity of the shell (thermal conductivity of copper is 10-20 times higher than that of steel);

- effective protection against gamma radiation with a significantly smaller total shell thickness compared to a monolithic steel shell (as gamma protection, copper is 1.5 times more effective in relation to steel).

V-shaped ribs can be fastened together by welding.

V-shaped ribs can be a two-layer structure, the inner layer is made of copper, the outer one is made of corrosion-resistant steel.

Installation of longitudinal V-shaped ribs from a material of high thermal conductivity, for example, a material made in the form of a two-layer structure, the inner layer is made of copper, the outer one is made of corrosion-resistant steel, the base is on the outer surface of the shell of the cylindrical shell, the ribs are fixed to the shell and the output ribs for the neutron shield and the metal cladding of the neutron shield allows you to effectively remove heat from the cylindrical shell and by convection and radiation to dissipate it in the environment.

The ribs protruding beyond the neutron shield lining also play the role of damping elements, damping pulses of external dynamic loads acting on the container in case of emergency situations.

Performing grooves in the walls of the V-shaped ribs located in the longitudinal rows with the offset of the groove of one row relative to the groove of the other row, allows the container to be filled with neutron shielding material and thereby eliminate the through slip of neutrons.

In an embodiment of the container, longitudinal panels are installed and fixed to the outer shell of the housing, consisting of a shell on which V-shaped ribs are fastened and fixed, fastened together by plates, the panels are interconnected by a neutron shield. The number of edges in a panel depends on its width. The neutron shield is located in the internal cavities of the panels and in the cavities between the panels and the neutron shield. This embodiment simplifies the manufacturing technology of the container while maintaining the parameters of its main technical characteristics.

The neutron shield can be made of corrosion-resistant steel, which eliminates the need for an anti-corrosion coating.

Neutron protection can be made of siloxane rubber.

The dampers can be made of different heights of scarves, interconnected by a shell and an end ring.

Dampers can be made of stainless steel.

Placing on the support and on the outer cover with the help of fasteners of dampers provides protection of the container from external dynamic loads acting on the container in case of emergency situations.

In an embodiment of the container, the cylindrical shells below are equipped with coaming, on which the bottom and support are fixed. The bottom in this case can be made in the form of two disks. The outer disk of the bottom can be made of low alloy steel, and the coaming and the internal disk of the bottom can be made of corrosion-resistant steel.

In an embodiment of the container, the sealing of each lid with the mating surfaces of the base is carried out using two sealing elements installed in grooves concentrically located on the ring annular concentrically located on the respective surfaces of the lids.

The sealing of each cover with the mating surfaces of the base with the help of two sealing elements installed in grooves concentrically located on the ring surfaces concentric on the respective surfaces of the covers is double-circuit, and it is possible to control the tightness provided by each sealing element by checking the tightness of the cavity between the sealing elements of the corresponding cover, for from which the channel for connecting the installation for checking the tightness is removed from the cavity.

Figure 1 shows a General view of the container in section; figure 2 - sealing of the inner and outer covers, element B in figure 1; figure 3 is a cross section of a container; figure 4 - V-shaped rib in cross section, element b in figure 3; figure 5 shows a General view of the container in section with an embodiment of the container body; figure 6 is a cross section of an embodiment of the container body of figure 5.

The container (see figures 1, 2, 3 and 4) consists of:

- metal casing 1, including:

a) support 2;

b) bottom 3;

c) base 4;

d) inner 5 and outer 6 shells;

d) insert 7;

e) disc 8;

g) ring 9;

h) plates 10;

i) ribs 11 with grooves " a ";

k) the inner layer of the ribs 12 of a material of high thermal conductivity;

k) the outer layer of the ribs 13 of stainless steel;

m) neutron protection 14;

m) cladding 15 of the neutron shield 14;

o) neutron shield 16 located on the bottom 3 in the support 2;

o) pins 17 designed for lifting and tipping the container;

p) trunnions 18 for tipping the container;

- the inner cover 19, on the outer surface of which a neutron shield 20 is installed, having a facing 21. In the concentric grooves of the cover 19, sealing elements 22 and 23 are installed. The cover 19 has an adapter 24 for lifting it;

- the outer cover 25. In the concentric grooves of the cover 25, sealing elements 26 and 27 are installed. The cover 25 has an adapter 28 for lifting it;

- damper 29 mounted on the support 2;

- a damper 30 mounted on the outer cover 25.

In the container with the housing option 1 (see FIGS. 5 and 6), the shells 5 and 6 are welded to the coaming 31, the bottom is made in the form of an internal 32 and an outer 33 disc welded to the coaming 31, the support 2 is welded to the coaming 31 and the outer disk 33, panels 34 are installed and secured by welding to the shell 6, containing the shell 35, the ribs 11 and the plate 36, the neutron shield 14 is located in the cavities of the panels 34 and in the cavities between the panels 34 and the lining 15, the insert 7 is made of blocks 37, fixed from the longitudinal movements using rings 38 and 39, disk 8, rings 9 and plas Institute 10, wherein the gap between the blocks 37 and the outer shell 6 is filled with powder filler 40 made of the same material as the blocks 37.

The use of the container in industry is as follows.

SFAs at nuclear power plants are first loaded into a spacer grid (not shown), which is then installed in a container. A variant is possible in which the spacer grid is first installed in a container, and then SFAs are loaded into it. Both in the first and in the second case, the work is carried out under water in the exposure pool. The pins 17 are used to carry the container. After loading the SFA container, the inner lid 19 is installed, on which the neutron shield 20 is placed, then the container is removed from the water and installed on the platform for draining the water and drying the container, tighten the bolt connection of the lid fastening and tightness control of the lid connection 19 with the housing 1. Deactivate the outer surfaces of the container. Install the outer cover 25, tighten the bolt connection of the cover and check the tightness of its connection with the housing 1. Drain the water, drain the internal cavity of the container and fill it with an inert gas, such as helium, using valve devices available in the container (not shown). The protective sealing caps 19 and 25 form two protection loops. On the support 2 and the outer cover 25 install, respectively, dampers 29 and 30, which are fixed with nuts. After that, the container with SNF is transferred to the container car, in which the container with the help of pins 17 and 18 is moved to a horizontal position. The container is fixed in the car and transported to the appropriate facility (regional SNF storage and processing facility). After transportation, the container at the facility is removed from the wagon and installed on a damping pad in an upright position. Check the tightness of the inner cavity of the container and the cavity between the inner lid 19 and the outer lid 25. Connect the cooldown system device to the valve devices of the container and make a cooldown (lower the temperature inside the container from ≈ plus 320 ° С to ≈ plus 40 ° С). After cooldowning, the dampers 29 and 30 are removed, the outer cover 25 is removed and the nuts fastening the inner cover 19 to the housing 1 are unscrewed. The container is transferred to the holding pool, then the inner cover 19 is remotely removed using the gripping device, after which the SFA is removed from the spacer grid and placed them in another spacer grid designed for long-term storage of SFAs under water. All work in the pool is carried out underwater using devices controlled remotely. After unloading the SFA from the container, work with the container is performed similar to the work after loading the SFA into the container.

The transportation and storage of the container with the SFA is accompanied by a fairly intense heat release of the active part of the spent fuel. The heat from the SFA loaded into the container heats the inner cylindrical shell 5 of the container body. After the heat from the outer shell 6 through the ribs 11 of a V-shape made of a material of high thermal conductivity (copper) is transferred to the outer lining 15, distributed around its perimeter and then by convection and radiation is scattered in the environment. The execution in the walls of the V-shaped ribs 11 of the grooves located in the longitudinal rows with the offset of the groove of one row relative to the groove of the other row, allows the manufacture of the container to fill them with neutron shield material 14 and thereby eliminate through lumbar neutrons.

The gap between the shells 5 and 6 of the inner cylindrical shell is filled with an insert 7 of a metal of high thermal conductivity and density, for example copper, which improves the thermal conductivity of the shell and the effectiveness of protection against gamma radiation with a significantly lower total shell thickness compared to a monolithic steel shell (as in the prototype ) For example, for VVER-1000 SFAs with burnup up to 70 GW · day / tU and at least 6 years of exposure for a container with a monolithic steel shell, the shell thickness is ≈380 mm, and for the inventive container with steel shells and a filled gap between the copper shells the thickness of the cylindrical shell is 270 mm (the total thickness of the steel shells is 65 mm, the thickness of copper is 205 mm).

The neutron shield integrated in the thermal bridges (i.e., in the elements 11), as well as the neutron shield 16 and 20, located on the bottom 3 and the inner cover 19, respectively, effectively “intercepts” neutrons from all sides of the container. This increases the safety of handling a container loaded with SNF (i.e., the safety of handling SNF).

Thus, the design of a container for the transportation and / or storage of SNF of VVER-1000 type reactors has been developed, which provides an increase in the efficiency of heat removal from the inside of the loaded SNF of the container, an increase in the efficiency of protection against gamma radiation and neutron protection, and, consequently, an increase in the safety of SNF handling.

Claims (17)

1. A container for transporting and / or storage of spent nuclear fuel, comprising a metal casing including a bottom, a support, cylindrical shells concentrically mounted on the bottom to form a cavity, a tight seal of said cavity and the container’s internal cavity, which is made in the form of two covers installed one above another on a common basis, neutron protection mounted on the outer surfaces of the inner cover, bottom and cylindrical shell, elements with high thermal conductivity, skipping through a layer of neutron protection located on a cylindrical shell, characterized in that the aforementioned cavity between the cylindrical shells is filled with an insert of high density metal and thermal conductivity relative to the shell material, V-shaped ribs located along the body along the length are used as elements with high thermal conductivity corresponding to the length of the internal cavity of the container, the walls of the ribs are perforated with grooves located in the longitudinal rows with the offset of the groove of one row along from wearing to the groove of another row, while the ribs protrude beyond the neutron shield surface and are fastened together by a shell that is the neutron shield facing, the neutron shield of the inner cover is lined, the neutron shield of the bottom is placed in the support, dampers are installed on the support and on the outer cover. 2. The container according to claim 1, characterized in that the inner cylindrical shell, the bottom and the common base are made of stainless steel. 3. The container according to claim 1, characterized in that the outer cylindrical shell is made of low alloy steel. 4. The container according to claim 1, characterized in that the insert is made of copper. 5. The container according to claim 1, characterized in that the insert is fixed between the shells by a disk, reinforced by a ring and longitudinal plates. 6. The container according to claim 1, characterized in that the insert of metal of high density and thermal conductivity is made of blocks secured from longitudinal movement with rings, while the gap between the blocks and the outer shell is filled with a powder filler of the same material as the blocks . 7. The container according to claim 1, characterized in that the V-shaped ribs are fastened together by welding. 8. The container according to claim 1, characterized in that the V-shaped ribs are a two-layer structure, the inner layer is made of copper, the outer one is made of corrosion-resistant steel. 9. The container according to claim 1, characterized in that longitudinal panels are mounted and fixed to the outer shell of the housing, consisting of a shell on which V-shaped ribs are fastened and fixed together by plates, the panels are interconnected by a neutron shield . 10. The container according to claim 1, characterized in that the neutron protection lining is made of corrosion-resistant steel. 11. The container according to claim 1, characterized in that the neutron protection is made of siloxane rubber. 12. The container according to claim 1, characterized in that the dampers consist of uneven headscarves connected by a shell and an end ring. 13. The container according to claim 1, characterized in that the dampers are made of corrosion-resistant steel. 14. The container according to claim 1, characterized in that the cylindrical shell below is equipped with coaming, on which the bottom and support are fixed. 15. The container according to 14, characterized in that the bottom is made in the form of two disks. 16. The container according to clause 15, wherein the inner disk of the bottom is made of corrosion-resistant steel. 17. The container according to claim 1, characterized in that the sealing of each lid with the mating surfaces of the base is made using two sealing elements installed in grooves concentrically located on the ring annular concentrically located on the respective surfaces of the lids.

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