Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F5/00—Transportable or portable shielded containers
  • G21F5/06—Details of, or accessories to, the containers
  • G21F5/12—Closures for containers; Sealing arrangements

Definitions

• the invention relates to a device and a method for checking the tightness of covers, generally multiple, stacked on top of each other, closing the cavity of a container for transporting or storing radioactive materials, for example irradiated fuels or the vitrified residues from the reprocessing of these fuels, said device enabling the tightness of each of the lids to be checked, not only during their successive closure, but also thereafter, after complete closure of the container, during its lifetime while it is loaded during transport or storage.
• radioactive materials for example irradiated fuels or the vitrified residues from the reprocessing of these fuels
• Radioactive materials in particular irradiated nuclear fuel assemblies or vitrified residues from reprocessing, are generally transported and / or stored in heavy containers (also called packaging) of cylindrical shape with thick walls (from a few cm to several tens of cm) , monolayers or multilayers, mainly based on forged or cast or rolled steel (possibly associated with lead), or based on cast iron, which in particular provide mechanical resistance functions (resistance to severe impacts, for example in the event of a fall ), radiological protection and thermal transfer.
• heavy containers also called packaging
• monolayers or multilayers mainly based on forged or cast or rolled steel (possibly associated with lead), or based on cast iron, which in particular provide mechanical resistance functions (resistance to severe impacts, for example in the event of a fall ), radiological protection and thermal transfer.
• These containers usually have a cylindrical shell closed at one of its ends by a bottom fixed in a sealed manner (for example by welding).
• the cavity thus formed, in which the radioactive material takes place, is closed at the other end of the shell, sometimes by a single cover, but the more often by at least two watertight removable metal covers, stacked on one another.
• O-rings either of elastomeric nature or of metallic nature, arranged in grooves whose geometry must be defined very precisely as a function of the characteristics of the seals that are used. .
• each cover is equipped with two concentric seals bearing on a shoulder formed in the shell. This tightness must be able to be checked at any time, or even continuously for containers which, once loaded, are placed in a long-term storage location.
• Figure 1 schematically shows an example of what is known to achieve to ensure and control the tightness of a container for nuclear material having either a single cover (1) or two overlapping covers (1) and (2) , i.e. three overlapping covers (1), (2) and (3).
• a first thick cover (1) serves to confine the radioactive material taking place in the cavity (C) of the container.
• the cover (1) is supported on a shoulder formed in the thick metal shell (4), generally cylindrical, constituting the body of the container, by means of two concentric seals (1 1), located in grooves cut in the cover flange (1) and tightened with bolts. It comprises a service channel (8) communicating the cavity (C) with the outside by opening onto the upper face of the cover (1) through a service orifice.
• This service channel is used to perform various manipulations in the cavity (C), for example introducing or extracting water, creating a vacuum, introducing or extracting a gas such as He, N 2 ...
• the cover (1) further comprises a control channel (5) communicating the space between the two seals (1 1) with the outside by opening on the upper face of the cover through a control orifice to which one can adapt various control devices (manometers, qualitative and / or quantitative gas analyzer, for example mass spectrometer, vacuum pump, gas under pressure), as will be seen below, making it possible to check the tightness of the joints.
• control devices manometers, qualitative and / or quantitative gas analyzer, for example mass spectrometer, vacuum pump, gas under pressure
• the service orifice (8) is closed by a closure, not shown, comprising two concentric seals; a closable control tap, by a plug accessible from the top of the cover, opens between these two seals and makes it possible to check the seal.
• the control channel (5) is closed by a plug.
• this secondary cover comprises two concentric seals (12) bearing on a shoulder formed in the shell, a service channel (9) and a control channel (6) used and closed in the same way as in the case of the cover. (1).
• the service channel (9) is used to manage the space between the covers (1) and (2) and the control channel (6) to check the tightness of the seals (12).
• the container After closing and checking the tightness of the cover and doing the same for the service openings, the control devices connected to the openings (5) and (6) having been dismantled, the container is ready. However, once placed in storage, it is sometimes covered with a thick metal protective cover (30) allowing it to withstand even better aircraft falls.
• the following methods can be used: i) the cavity (C) having been filled with a gas, in general helium at 0.5 bar absolute, a vacuum can be created in the space between seals (1 1), at a pressure lower than those prevailing on either side of said seals (for example a few mbar) then observe and measure through the control orifice a possible rise in pressure in this space using a pressure gauge of the type (14).
• This method allows measurement of leak rates in the range of about 10 -5 to 10 -3 atm.cm 3 / sec;
• the space between seals can be put under overpressure with respect to the pressures prevailing on either side of said seals (for example 6 bars) and a possible pressure drop can be measured using also a pressure gauge of the type
• a helium test can be performed, which consists of making a vacuum in the space between seals and, the cavity being filled with helium at pressure PI, to count the amount of helium sucked by the possible leakage of the attached using a mass spectrometer previously calibrated using a calibrated leak. This method is much more sensitive and can detect leaks between 10 " 9 and 10 ⁇ 6 atm.cm 3 / sec.
• the pressure P2 can be continuously monitored by means of a pressure sensor. If, subsequently during long-term storage of the container, this pressure decreases, this is a sign of a leak either towards the atmosphere, or towards the cavity (C) of the container since the pressure P2 is significantly higher than the atmospheric pressure. external and a fortiori at the reduced pressure PI prevailing in the cavity (C). It is seen that thus the confinement of the radioactivity is ensured and that there is impossibility of release of radioactivity from the container cavity to the environment.
• the generally adopted solution consists in installing a guard cover (3) equipped, like the covers (1) and (2), with two concentric seals (13 ) resting on a shoulder of the ferrule, a control orifice (7) for testing the tightness of the concentric seals (13) of the cover (3) and a service orifice (10) intended to put the space between the covers (2) and (3) under a gas pressure P3, this orifice being in turn closed by a closure with double controllable seals.
• the Applicant has sought a device and a method making it possible to locate possible leaks on each of the covers, independently of each other, both on the main seals and on the seals of the various service orifices, while simplifying the control operations. sealing, especially those made during storage of the container.
• the invention is a device for checking the tightness of the covers of a heavy metal container for the transport and / or storage of radioactive materials, said container comprising a cavity for nuclear materials delimited by a thick cylindrical shell. closed at one end using a bottom fixed in a leaktight manner and at the other end by at least two superimposed covers, removable and thick, characterized in that said covers are held in abutment on shoulders, practiced in the ferrule, by means of flanges fitted with at least two concentric seals, that each cover corresponds to at least two channels passing through said ferrule, opening through a first control orifice on the external surface of the ferrule near the covers in an accessible location, and through a second orifice, one in the space between the concentric joints of the cover, the other in the space between said cover, the ferrule and the immediately superimposed cover, each control orifice being optionally connected to a measurement and leakage control circuit.
• the leaktightness measurement and control circuit essentially comprises a buffer volume connected to generally common measurement and control devices, such as pressure gauges, vacuum pump, gas analyzer (for example mass spectrometer), gas cylinder. under pressure (e.g. He, N 2 , Ar), using piping and valve sets.
• generally common measurement and control devices such as pressure gauges, vacuum pump, gas analyzer (for example mass spectrometer), gas cylinder. under pressure (e.g. He, N 2 , Ar), using piping and valve sets.
• This device for checking the tightness of the cover seals essentially comprising channels passing through the thick shell of the container, can advantageously be supplemented by the addition of a service channel still passing through the shell and opening directly into the cavity.
• the channels opening into the spaces between covers according to the invention can not only serve to check the tightness of the cover joints in cooperation with the channels opening into the spaces between joints, but also serve as a service channel. to manage the atmosphere of the space between covers (nature of the gas introduced, pressure, vacuum).
• the control and service channels such as as seen above in fig. l respectively marks 5,6,7 and 8,9,10) passing through the covers, with their closures accessible from the upper face of said covers.
• said service channels of each cover must be connected, by connecting tubes, to the control channel opening into the space between the joints of the same cover, said space being connected according to the invention to a control channel sealing, opening to the outside after having crossed the shell, in order to be able to check the tightness of the closings of the service channels of said cover.
• FIG. 2 illustrates a container with its device for checking the tightness of the covers, according to the invention.
• the container has three lids, the cover (3) being added, as has already been seen, in case of leakage of the primary cover (1).
• the channels 15, 1 7, 19 open into the space between the concentric joints of the covers 1, 2, 3 respectively, while the channels 1 6, 18 open into each of the two spaces between the said covers.
• the orifices of these channels 15, 1 6, 1 7, 18, 19, 20, located on the outer wall of the ferrule can be conventionally closed by closures (not shown) comprising two concentric seals; to check sealing a connection connects the space between these seals to the outer wall of the shell, connection which is then closed by a plug.
• each of the channels located on the outer wall of the shell is connected to a buffer volume V5, V6, V7, V8, V9.
• Each of them is in turn connected by a circuit of tubes and valves to the measuring devices used to perform the leakage control: pressure measurement (14), vacuum pump (21), mass spectrometer (22) , pressurized He bottle (23), etc.
• Each of the covers also has control channels 5-6-7 opening into the spaces between the double seals (1 1, 12, 13) and service channels (8, 9, 10) opening into the cavity (C) and in the spaces between covers (P2, P3) inside the circle formed by the concentric joints (1 1, 12,13).
• control taps of the double seals of the closures (not shown) of the service channels (8-9-10) are connected, by connecting tubes (25-26-27), to the control channels ( 5-6-7).
• the channels according to the invention are drilled in the metal shell (steel or cast iron); but when the latter is composite, that is to say when the internal steel ferrule is covered with lead, resin, etc., said channels drilled in the internal steel ferrule are usually extended by tubes passing through the successive layers. up to the surface.
• the invention also relates to a method for checking the tightness of the various covers. Various procedures can be applied depending on whether the container has one or more lids.
• the cavity was filled with gas, for example He, at a pressure PI lower than atmospheric pressure (generally 0.5 bar), the space between the covers (1) and (2) filled with a different gas. (for example N 2 ) at a pressure P2 greater than atmospheric pressure (for example 6 bar), P2 being measured continuously via the channel (16), the buffer volume (V6) and the pressure indicator (14).
• gas for example He
• PI lower than atmospheric pressure generally 0.5 bar
• N 2 the space between the covers (1) and (2) filled with a different gas.
• P2 greater than atmospheric pressure (for example 6 bar)
• P2 being measured continuously via the channel (16), the buffer volume (V6) and the pressure indicator (14).
• the vacuum is made using the pump (21) in the space between seals (1 1) via the channel (15), and the pumped gas is analyzed using the mass spectrometer (22 ).
• the analysis identifies He, it is the cover (1) which leaks either by the internal seal (1 1), or by the seal of the closure plug of the service channel (8). If the analysis reveals the presence of nitrogen, the leak is then on the outer seal (1 1) or on the outer seal of the service channel closure (8).
• a variant consists in replacing N 2 by He once the internal seal (1 1) is tested as tight.
• the remedy for a leak detected on the primary cover (1) can be to install a third cover (3) and thus to transfer the primary barrier initially constituted by the cover (1) on the cover (2).
• the device according to the invention makes it possible to use other methods for detecting and locating possible leaks.
• the device according to the invention makes it possible to measure continuously and at will from the outside, the possible leakage rate of each of the joints of each of the covers, including the deeper, and in addition without any disassembly being necessary.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Examining Or Testing Airtightness (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9509790

Family Applications (1)

Country Status (8)

Families Citing this family (24)

Family Cites Families (10)

• 1997
  • 1997-07-24 FR FR9709675A patent/FR2766570B1/fr not_active Expired - Fee Related
• 1998
  • 1998-07-08 TW TW087111071A patent/TW436813B/zh active
  • 1998-07-20 EP EP98939710A patent/EP0998745A1/de active Pending
  • 1998-07-20 WO PCT/FR1998/001578 patent/WO1999005686A1/fr not_active Application Discontinuation
  • 1998-07-20 KR KR1020007000738A patent/KR20010022166A/ko not_active Application Discontinuation
  • 1998-07-20 US US09/463,223 patent/US6223587B1/en not_active Expired - Fee Related
  • 1998-07-20 SK SK79-2000A patent/SK792000A3/sk unknown
  • 1998-07-20 JP JP2000504582A patent/JP2001511531A/ja not_active Withdrawn

Non-Patent Citations (1)

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