RU2464657C1 - Hermetic cover of container for transportation and/or storage of radioactive materials - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to containers for transportation and/or prolonged dry storage of spent nuclear fuel or similar radioactive materials, particularly containers with apparatus for linking with the internal gaseous medium, e.g., for monitoring air-tightness and collecting gas samples. The container has a hermetic cover mounted using bolted connections in a socket outside of the container. The hermetic seal is in form of movable housing and has a cavity for sample gas and channels for linking with an external device.

EFFECT: invention provides access to that medium without dismantling sealing elements, enables release of excess pressure from the inside of the container.

2 dwg

Description

The invention relates to containers for transporting and / or long-term dry storage of spent nuclear fuel (SNF) or similar radioactive materials, in particular to containers with devices for communicating with the gaseous environment of the internal cavity, for example, for monitoring tightness and sampling gases.

Known tight closure of the container for transporting and / or storage of radioactive materials according to US patent No. 4495139, IPC G21F 5/12, G21F 5/00, G21C 17/00, publ. 01/22/1985, This hermetic overlap of the inner cavity of the container is installed by means of bolted joints and equipped with gaskets. The sealed overlap forms the control chambers (cavities) and contains channels through which the control chambers communicate with the device for tightness control.

Sealed overlap is made in the form of two removable covers mounted one above the other on the container body and forming three consecutively located control chambers. Each of the three control chambers is connected through an outlet channel from it with a corresponding valve of the tightness control device. The latter can be connected, for example, to an analyzer for monitoring the composition of the gas mixture in the corresponding control chamber or to means for monitoring the parameters of the gas medium in the corresponding control chamber. Each valve is installed in a seat that is hermetically closed by a corresponding removable additional cover, which, in turn, is hermetically closed by a subsequent removable cover. The tightness control of the container is carried out sequentially, starting with the control chamber, the most remote from the inner cavity of the container. This ensures the safety of the tightness control procedure.

However, the design of the tight shut-off of this container implies a relatively greater complexity of the procedure for checking the tightness of the inner cavity of the container, which is due to the need for preliminary removal of the outer cover of the tight shut-off, and then to provide sequential access to the control chambers for removing additional covers, respectively, covering the valves of the tightness control device. In addition, the control of tightness when the outer removable cover is removed reduces radiation safety, because Due to the large diameter of the cover, there may be a sufficiently large area of potential leakage.

Known hermetic valves equipped with shut-off devices (i.e. tight shutoffs) installed in a container for transporting and / or storing spent nuclear fuel according to RF patent No. 2364964, IPC G21F 5/08, publ. 08/20/2009, the container is made the cavity with the possibility of communication through the respective manifolds (channels) through airtight valves equipped with shut-off devices (ie through airtight floors), with an external system for analyzing the gas environment of the container. Moreover, each hermetic valve with a corresponding locking device (tight shutoff) is mounted by means of bolted connections in a socket made on the outside of the container.

These hermetic valves equipped with shut-off devices (hermetic ceilings) allow monitoring the tightness of a container loaded with spent nuclear fuel, discharge of gases after accumulation of gas evolution products and some increase in gas pressure, sampling of the gas medium, and can also be used to dry container cavities when communicating with the atmosphere. However, the designs of these devices are equipped with one or two protective covers that require dismantling during work, which complicates their implementation. These devices consist of several structural elements and, accordingly, have a significant number of mating surfaces through which gas leakages, including radioactive ones, are possible, which reduces radiation safety. In addition, the manufacture of structures of such tight ceilings requires a sufficiently large number of calculations of structural elements, accurate fitting of mating surfaces and sealing elements in order to ensure reliable sealing of the container, and therefore, radiation safety. In addition, the manufacture and installation of such airtight ceilings are quite time-consuming.

The closest in combination of essential features with the claimed invention is the tight shut-off of the container for transporting and / or storage of radioactive materials described in RF patent No. 2157009, IPC G21F 5/005, G21F 5/008, publ. September 27, 2000. The hermetic closure of this container, which contains a channel for communication between the container’s internal cavity and the external environment, is equipped with sealing elements, mounted by means of bolt connections in a socket made on the outside of the container, and includes a chamber (cavity) for test gas. Hermetic overlap forms sealing circuits with the container body with the formation of cavities made with a channel for communication with the device for tightness control. This technical solution is selected as a prototype of the invention, as the closest in the totality of features.

To communicate the internal cavity of the container with the external environment, the hermetic closure of the container also includes a valve mounted in the socket and adjacent to the channel for communication of the internal cavity of the container with the external environment. Hermetic overlap is made in the form of removable outer and inner covers installed one above the other, and the inner cover contains a sealed adjustable valve. The chamber for the test gas is made in the inner lid and communicated through a sealed adjustable valve with an axillary cavity of the inner lid.

This tight shutoff allows you to control the tightness of the inner cavity of the container, to control the composition of the gas mixture in the inner cavity of the container, and also, if necessary, to fill the inner cavity of the container with inert gas and can be used to dry the cavities of the container when connecting the appropriate external devices.

However, this hermetic overlap has disadvantages. To carry out these works, it is necessary to dismantle the outer and inner covers of the airtight ceiling to install a connecting device in the socket, through which the interaction of the inner cavity of the container with external devices is ensured, which complicates the work. In addition, carrying out work with the covers removed reduces radiation safety.

The problem solved by the invention is to simplify the work to control the tightness, chemical composition or level of radioactivity of the gas environment of the internal cavity of the container during operation and storage of loaded SNF or similar radioactive materials in the container, to increase radiation safety during such work, as well as to ensure tightness of the container.

The technical result of the claimed invention is to provide access to the gas environment of the internal cavity of the container without dismantling the sealing elements, as well as to enable bleeding of excess pressure from the internal cavity of the container.

To achieve the specified technical result, in a known sealed closure of a container for transporting and / or storing radioactive materials, mounted by means of bolts in a socket made on the outside of the container and forming with the container having a channel for communicating the container’s internal cavity with the external environment, the sealing circuit is formed cavity made with channels for communication with an external device equipped with sealing elements and including a cavity for test gas, according to the invention, the tight shutoff is made in the form of a movable housing, bolted connections are configured to move the movable housing, the test gas cavity is formed by the cylindrical surface of the lower part of the movable housing and the inner surface of the socket, and the channels for communication with the external device are made in the form of holes in a movable housing, while it is equipped with a stop.

The technical result is achieved due to the constructive implementation of hermetic overlap, namely, the implementation of hermetic overlap in the form of a single movable element.

With such a tight shut-off, there are no tight shut-off elements that require disconnection when monitoring the chemical composition or level of radioactivity of the gaseous medium of the container’s internal cavity and overpressure bleeding from the container’s internal cavity, it is possible to connect an external device, for example, a device for monitoring tightness or gas sampling without removing the elements of additional tight overlap, which increases safety and simplifies It helps to carry out work.

In addition, the implementation of tight sealing in the form of a single movable element leads to a decrease in the number of structural elements of tight sealing and, accordingly, the number of mating surfaces through which potential leakage of gases, including radioactive ones, and, thus, reduces the possibility of leakage of gases, therefore, radiation safety is enhanced. At the same time, the number of calculations of structural elements of hermetic overlap is reduced, the fitting of their mating surfaces and sealing elements is simplified in order to ensure reliable sealing of the container and, as a result, manufacturing is simplified, and installation convenience is increased.

Bolted connections are made with the possibility of moving the movable housing. This is realized through the use of two groups of bolts, one of which, the so-called clamping, designed to fix the tight-sealed housing in the container body socket and pressed against the inner surface of the socket, which corresponds to the normal position of the sealed ceiling, which provides sealing of the internal cavity of the container, as well as the position when checking for leaks, and the other group of bolts, the so-called squeezing, designed to squeeze the casing of the airtight ceiling from the landing surface of the nest, which corresponds to the position of the airtight floor when controlling the chemical composition or level of radioactivity of the gas environment, as well as when overpressure is vented from the internal cavity of the container. The pressurized casing is pressed against the inner surface of the socket by pressing it in the axial direction with clamping screws screwed into the threaded holes made in the container’s nest until the end of the pressurized casing’s end faces the plane of the nest’s inner surface. The pressurized casing is pressed out when the squeeze bolts are screwed into the threaded holes made in the pressurized casing, during which the squeeze bolts abut against the plane of the internal thrust surface of the socket and squeeze the pressurized casing, while the clamping bolts are gradually turned out of the socket thread. The implementation of bolted connections with the possibility of moving the casing of the sealed ceiling provides the ability to access the gas environment of the internal cavity of the container without dismantling the sealing elements, the ability to control the tightness, as well as the possibility of bleeding excess pressure from the internal cavity of the container.

The formation of the cavity for the test gas using the cylindrical surface of the lower part of the sealed ceiling housing and the inner surface of the socket, and the channels for communication with the external device in the form of holes in the sealed ceiling housing simplifies the design of the device for communication with the gas environment of the inner cavity, since it is not required separate manufacture of the cavity for the test gas and its structural interface with channels for communication with an external device.

To limit the course of the sealed ceiling enclosure and prevent it from being pushed out of the socket due to the pressure of the gases contained in the internal cavity of the container, the sealed overlap is provided with a stop, which prevents the occurrence of radiation hazard.

The presence in the claimed invention features that distinguish it from the prototype, allows us to consider it appropriate to the condition of "novelty."

New features were not identified in technical solutions for a similar purpose. On this basis, we can conclude that the claimed invention meets the condition of "inventive step".

The invention is illustrated by drawings:

figure 1 shows the image of the tight overlap in a position that provides sealing of the internal cavity of the container, as well as when checking for leaks;

figure 2 shows the image of the sealed overlap in position during the control of the chemical composition or level of radioactivity of the gas environment, as well as when bleeding from the internal cavity of the container overpressure.

The hermetic closure of the container for transporting and / or storage of radioactive materials (Fig. 1) is made in the form of a movable housing 1 and is mounted in the socket 2 made on the outside of the container by means of clamping bolts 3. The mobility of the housing 1 in the axial direction is ensured by means of squeezing bolts 4 ( see figure 2). A channel 5 is made in the container for communicating the internal cavity 6 of the container with the external environment through a tight seal. The tight overlap forms a sealing circuit with the container with the formation of the cavity 7. The cavity 7, formed by the cylindrical surface of the lower part of the housing 1 and the inner surface of the socket 2, is intended for test gas. The cavity 7 communicates with an external device for accessing the gas medium of the internal cavity 6, for example, with a device for tightness control (not shown in the drawing), through channels made in the housing 1 in the form of axial 8 and radial 9 holes. Between the cylindrical side surface of the housing 1 and the cylindrical surface of the socket 2 in a specially made groove 10 there is a radial heat-resistant gasket 11. A heat-resistant gasket 14 is installed in the recess 12 of the inner end surface 13 of the socket 2 (see FIG. 2). To limit the movement in the axial direction of the stroke of the housing 1, a stop 15 is provided (see FIG. 2), fixed on the outside of the socket 2. A fitting 16 is intended for connecting an external device (see FIG. 2). The plug 17 is designed to prevent the ingress of foreign objects, dust, etc.

The movement of the housing 1 is carried out using clamping 3 and squeezing 4 bolts. The housing 1 is pressed against the inner surface of the socket 2 by axially pressing it with clamping bolts 3 screwed into the threaded holes 18 made in the socket 2 until the end of the housing 1 abuts against the plane of the inner end surface 13 of the socket 2. In this case, the heat-resistant gasket is crimped 14, which is a spiral-wound gasket (SNP), due to which the container is sealed. SNP is a well-known, commercially available gasket made of thin steel tape and graphlex tape (a type of material made on the basis of graphite), the edges of the graphlex tape protrude above the steel tape and, when crimped, are a sealing element. The squeezing of the housing 1 is carried out by screwing the squeeze bolts 4 into the threaded holes 19 (see figure 2), made in the housing 1. The squeezing bolts 4, turning, abut against the plane of the internal thrust surface 20 of the socket 2 (see figure 2). In this case, the clamping bolts 3 are gradually turned out of the thread of the socket 2. The movement of the housing 1 is limited by the stop 15.

The presence of bolted joints 3 and 4, ensuring the mobility of the housing 1, provides access to the gas environment of the inner cavity 6 of the container without dismantling the elements of the sealed overlap, as well as the possibility of bleeding excess pressure from the inner cavity 6 of the container.

The device operates as follows.

In the position of the tight overlap, providing a seal of the inner cavity of the container, as well as when checking for leaks, the body 1 of the tight overlap is pressed against the inner end surface 13 of the socket 2 (Fig. 1). The plug 17 before connecting the appropriate equipment to the fitting 16 is dismantled, and after work is installed back. The tightness test is carried out by supplying a test gas pressure through the nozzle 16 into the cavity 7 and then monitoring its fall over a certain time.

When controlling the chemical composition, the level of radioactivity of the gaseous medium or when venting overpressure, the tight seal is in a position in which the housing 1 is pressed away from the inner end surface 13 of the socket 2 (figure 2). In this position, the tight shut-off allows gases to exit the inner cavity 6 of the container through the nozzle 16, where the corresponding equipment is pre-connected, and does not allow unauthorized gas leakage through the gap in the interface between the cylindrical side surface of the housing 1 and the cylindrical surface of the socket 2. The tightness of this interface is achieved by using radial heat-resistant gaskets 11 made of rubber or other elastomer, the heat resistance of the material of which does not allow set the temperature conditions of the fire, but sufficient for normal operating conditions. Under emergency conditions caused by increased heat exposure, for example in a fire, the tightness of the inner cavity of the container is ensured by the heat-resistant gasket 14. The presence of two sealing elements 11 and 14 ensures the tightness of the inner cavity 6 of the container in normal and emergency conditions of use.

Thus, the design of the airtight overlap allows you to perform work to control the tightness, chemical composition or level of radioactivity of the gaseous medium of the internal cavity of the container, as well as to relieve excess pressure from the internal cavity of the container, without dismantling the elements of the airtight overlap, while ensuring the tightness of the container.

The use of pressurized closure is expected in containers for transporting and / or long-term dry storage of spent nuclear fuel (SNF) or similar radioactive materials.

Verification of the operation of the inventive hermetic overlap was carried out on a prototype container.

In addition to providing access to the gas environment of the internal cavity of the container for the possibility of carrying out work to control the gas environment and vent excess pressure from the internal cavity, its design must ensure the tightness of the container. On the prototype container, a check was made to ensure the tightness with the installed claimed leakproof overlap and leak control was carried out.

The tightness of the container ensures its radiation safety and is determined by the value of the permissible loss of radioactive contents from the container for a certain period of time, taking into account its radiation hazard. To check the tightness of the claimed tight shutoff on the prototype, krypton gas was chosen as the most toxic and radiation hazardous substance for this container. Based on the allowable krypton leakage rate, leak tightness standards and test conditions were calculated, and gas tight maneuvers were tested for tight shutoff with a test (trial) pressure of 1.2 MPa with an exposure time of 257 min. The pressure drop during the exposure was significantly less than the permissible value (0.01 MPa).

As a result, it was confirmed that the inventive leakproof shutoff ensures the tightness of the container loaded with radioactive materials and the ability to control the tightness using the manometric method.

Thus, the invention allows to simplify the work to control the tightness, chemical composition or level of radioactivity of the gaseous medium of the internal cavity of the container, as well as the ability to release excess pressure from the internal cavity of the container. In addition, the invention provides safety when conducting work to control the gas environment under operating and storage conditions of the loaded SNF or similar radioactive materials of the container, while ensuring the tightness of the container.

Therefore, the claimed invention meets the condition of "industrial applicability".

Claims (1)

Sealed container closure for transporting and / or storing radioactive materials, mounted by means of bolts in a socket made on the outside of the container and forming with the container having a channel for communicating the internal cavity of the container with the external environment, a sealing circuit with the formation of a cavity made with channels for communication with an external device, equipped with sealing elements and including a cavity for the sample gas, characterized in that the sealed overlap is made in the form of a movable housing, bolted connections are configured to move the movable housing, the test gas cavity is formed by the cylindrical surface of the lower part of the movable housing and the inner surface of the socket, and the channels for communication with the external device are made in the form of holes in the movable housing, while it is provided focusing.

Images