EP2515310B1

EP2515310B1 - Shielded protective tent assembly

Info

Publication number: EP2515310B1
Application number: EP12164780.4A
Authority: EP
Original assignee: Belgonucleaire SA
Current assignee: Belgonucleaire SA
Priority date: 2011-04-19
Filing date: 2012-04-19
Publication date: 2018-07-11
Anticipated expiration: 2032-04-19
Also published as: JP6075967B2; JP2014122790A; EP2515310A2; EP2515310A3; CN102831944B; CN102831944A

Description

The present invention relates to a tent assembly to be used in the field of handling nuclear materials. In particular, the present invention relates to a nuclear radiation protective and disposable tent assembly to be used for interventions on a radioactively contaminated item, such as a glove box, so that the interventions can be performed in a leak tight environment. The tent assembly comprises at least one leak tight envelope and an outer support. Such interventions include i.a. dismantling and heavy maintenance of nuclear installations.
Nuclear installations usually require - at some point in their lifetime - interventions wherein the nuclear installation is opened at risk of releasing radioactive materials and exposure to α, β, and/or γ radiation and/or neutrons.
Nuclear installations such as mixed oxide ('MOX') or other Plutonium-bearing fuel fabrication production plants harbour for example contaminated glove boxes, spent fuel reprocessing β/γ cells and α/β/γ cells for the production of fresh fuel containing minor actinides.
One of such interventions is the decommissioning of nuclear installations. Decommissioning is performed either in total, for example after shutdown of the nuclear installation, or in part, for example when part of the nuclear installation needs to be modified, or in the context of lifetime extension of the installation.
Heavy maintenance is another intervention wherein nuclear installations are opened at risk of releasing contamination. For example replacing large or heavy process items or windows is sometimes associated with the discarding and size reduction of process items and the destruction of a contaminated nuclear process enclosure.
A number of precautions are taken so as to reduce the risk of releasing radioactively contaminated particles and human exposure thereto, during interventions such as decommissioning and heavy maintenance. Human operators need to be protected against both internal exposure resulting from ingestion and inhalation of these radioactively contaminated particles, and external exposure resulting from radiation, for example radiation beyond regulatory dose limits and/or in compliance with the ALARA ("As Low As Reasonably Achievable") principle. Therefore, prior to the intervention, nuclear and fissile materials are usually collected and removed from the nuclear installation, and as a result, exposure to fission neutrons is in general neglectable. Decontamination might subsequently be performed to the maximum reasonable extend. Another precaution is the provision of an intervention enclosure such as an alpha tight cell, a glove box or a disposable protective tent assembly around the nuclear installation to be dismantled or serviced.
When alpha tight cells or glove boxes are used as intervention enclosure, the nuclear installation, for example the glove box, first needs to be transported into this enclosure which is located elsewhere in the plant. However, this transportation is costly and risky with regard to exposure to radioactive particles.
Entrance of the nuclear installation into an enclosure occurs by using a conventional 'bag-in' technique. The latter technique enables to maintain the confinement of the enclosure while introducing equipment or other material. To this purpose the equipment or the material is placed in a bag on which opening side there is provided an O-ring. The latter is than fixed inside a groove applied on a periphery of an access port of the enclosure in such a manner as to overlap a further bag already present on the access port and closing the latter. For entering the equipment or the material the latter is pulled with the bag inside the enclosure. Once the equipment or the material is inside, the access port is closed by the bag in which the equipment or the material was stored.
The enclosure contains equipment necessary to perform an intervention under leak tightness with respect to the external environment. Actuation of electrically or pneumatically assisted tools, such as dismantling tools, is performed by human operators who are standing either inside the alpha tight cell, or outside the cutting box. Entrance and exit of the operators are foreseen through adapted airlocks, while removal of the waste pieces resulting from the cutting operations is realised by using waste drums docked to the alpha tight cell or cutting box.
When working inside an alpha tight cell, the operators are equipped with leak tight clothes as well as respiratory devices. Lead apron may be worn when exposure to γ radiation might occur.
JPH0862390 A and US2010/044372 A1 disclose protective tent assemblies that comprise leak tight envelopes mounted on an outer support.
In order to avoid transportation of the nuclear installation to an off-site facility and the associated costs and exposure risks, the use of a protective tent assembly has been described, for example in the patent application with publication number DE 4040115t6 and in the paper "Dismantling Techniques for Plutonium-Contaminated Glove-boxes: Experience from First Year of Decommissioning", R. BAUMANN, P. FABER, 6th International Symposium of Radioactive & Decommissioning Wastes, Kontec 2004, Berlin, Germany, March 2004.
In the latter document there is described how a glove box is transported towards a protective tent assembly located inside operation facility, where the protective tent assembly is erected in situ around the glove box. The protective tent assembly comprises a flexible, leak tight envelope tailored to the shape and dimensions of the glove box to be dismantled, and may be equipped with gloves and windows and maintained at a vacuum by its own ventilation system. The tent assembly may contain cutting equipment for performing dismantling operations in isolation from the external environment. Actuation of the dismantling tools is performed by operators who are standing outside the protective tent assembly. These operators may be equipped with tools and monitoring devices similar to those used while operating a process glove box. Waste resulting from the cutting operations may be evacuated through waste drums docked to the protective tent assembly in a leak tight manner.
A drawback of the known protective tent assembly is that it offers insufficient radiation protection to human operators. Indeed, the risk of exposure to β and γ irradiation by U/Pu and Am²⁴¹ resulting from Pu²⁴¹ decay, and particularly exposure to neutrons (n) resulting from nuclear reactions in most nuclear installations are not to be underestimated.
Therefore, when the process equipment and its enclosure to be dismantled or serviced are highly contaminated, operators are currently protected against exposure by wearing appropriate clothing, including state of the art lead aprons. Lead aprons have however the drawback that they do not reduce the neutron dose rate to the operators wearing it, but only protect against γ radiation. Moreover, these lead aprons are heavy, limit operator flexibility and therefore bring additional burden to the operators while performing physically exhausting and risky cutting work in the known protective tent assembly.
It is an object of the invention to provide a protective tent assembly which protects human operators against exposure to neutron particles and α and γ radiation, and to provide a protective tent assembly, which enables the safe manipulation of nuclear installations. The present invention provides a nuclear radiation protective tent assembly according to the subject-matter of claim 1. The shielding panel protects the operator against radiation, such as α, n and γ radiation, for example when nuclear or radioactive substances are present inside the envelope and could leak out of the envelope. The presence of the further access opening for operator intervention inside the envelope does not restrict operator access to the tent assembly interior, despite the presence of the shielding panels. Advantageously, these access openings are leak tight ports which allow access to the tent assembly interior in a leak tight manner, thereby safeguarding a minimal risk of radio-active exposure.
Advantageously, the shielding panels are made of transparent material allowing for vision inside the envelope and light to penetrate into the volume delimited by the envelope.
Advantageously, the shielding panel are removable applied on the outer support so that they can be re-used in a safe way since they should not get contaminated on the outside as the contamination is meant to stay inside the envelope. Indeed, the protective tent assembly according to the invention creates a leak tight environment around the nuclear installation, which environment is useful because the risk of releasing radio-actively contaminated particles is minimised, for example,
during interventions wherein the nuclear installation is opened, either deliberately or not.
Advantageously, the shielding panel is applied in such a manner as to face the outside of the envelope so as not to become contaminated during the intervention, thereby permitting re-use of the panel. Indeed, the shielding panel with access openings, according to the present invention, can be attached to the outer support during an intervention, and again detached from the outer support when the intervention is finished. While the envelope as a whole is disposable, the shielding panel and the outer support can be recuperated and re-used several times before being disposed because, being located on the outside of the leak tight envelope, they are not contaminated. This offers a substantial reduction of secondary waste. Consequently the cost of waste disposition is significantly reduced in comparison to the prior art while still providing shielding against α, n and γ radiation.
The protective tent assembly of the present invention thus results in a reduced amount of secondary waste since the outer parts, i.e. the outer support and outer shielding panel can be re-used several times. The disposal of (suspected) radio-actively contaminated waste is enormously expensive and is a major point of concern to plants housing nuclear installations. The safe re-use of the shielding panel and the outer support of the protective tent assembly therefore offers a substantial reduction of the waste disposal cost.
Other details and particular features of the invention will become clear from the attached claims and from the description below.

Figure 1 shows a conventional glove box for handling radioactive materials;
Figure 2 shows a protective tent assembly according to an embodiment of the present invention, arranged peripheral to a glove box similar to the glove box of Figure 1 and comprising an outer metallic support to attach the leak tight envelope;
Figure 3 shows a detail of the protective tent assembly of Figure 2 including means for holding the outer transparent shielding panels onto the outer support; and
Figure 4 shows a cross-section of the protective tent assembly and glove box of Figure 2.

In the drawings a same reference number has been allocated to a same or analogous element.
Within the context of the present invention, what is to be understood by "alpha tight" or "leak tight" is not necessarily absolute leak tightness, but permeability to gases, liquids and/or dust which is below the acceptable maximum level known to the skilled person for the intended intervention, such as the manipulation of radioactive material. The "alpha tightness" or "leak tightness" in the context of the present invention can be achieved when the pressure inside the leak tight envelope is reduced by 100-200 Pa with respect to the atmospheric pressure, i.e. when a vacuum is being applied, and the air tightness is in the order of magnitude of 0.1 % volume/hour.
Figure 1 shows a conventional glove box 1 and an operator 2. The illustrated glove box is a single glove box. But it will be clear that a plurality of glove boxes could be connected to each other and thus the invention not only applies to the use of a tent assembly for a single glove box, but also to the use of a tent assembly for a plurality of glove boxes. Glove boxes are the most frequently used type of containment enclosures in fuel cycle facilities at laboratory, pilot or industrial scale in the nuclear industry. Usually glove boxes are designed for operation or maintenance where human intervention is required. Most of the walls of a glove box are transparent or provided with windows. Glove boxes are also provided with glove ports 3 for enabling manipulation by hand and other access ports for providing utilities such as ventilation, electrical cabling, gas piping, etc.
Figure 2 illustrates a protective tent assembly 10 according to an embodiment of the invention and installed around the glove box 1 (shown in dotted lines) in order to isolate it prior to a dismantling or other intervention. The tent assembly comprises at least one leak tight envelope 4 and an outer support 11. The envelope is formed by at least one flexible sheet which is provided with at least one access opening 15 allowing penetration into the volume delimited by the envelope. The access opening is preferably provided with gloves so as to maintain the leak tightness. The envelope is mounted on an outer support 11, for example by means of straps 12. A waste outlet 5 is provided on the leak tight envelope in order to evacuate material or equipment which has been processed inside the leak tight envelope. The envelope is preferably also provided with windows 8 in order to provide vision inside the envelope and enable light to enter the envelope.
The protective tent assembly 10 of the present invention is not limited to a particular dimension and shape. The latter will depend on the volume which needs to be made leak tight, in order to provide sufficient freedom of movement for the operator 2. This is particularly beneficial during manipulations to be performed inside the protective tent assembly. The dimensions of protective tent assembly according to the present invention are chosen so as to fit with the shape and dimensions of nuclear installations to be dismantled. For this purpose, the flexible sheets forming the leak tight envelope 4 may be formed by joining a set of sheets of standard format, or of a tailored format. For example, in order to form the leak tight envelope 4 of the tent assembly 10, a flexible sheet is installed on the floor of the room where the dismantling operations occur or on a table located in a similar room. If the protective tent assembly 10 is to be installed elevated on a table, it may differ from the illustrated protective tent assembly by a different orientation of the waste outlet connection 5. Namely, the waste outlet connection 5 may be oriented downwards to facilitate waste collection.
After the flexible sheet of the leak tight envelope is put in place, the glove box 1 is moved inside the volume delimited by said envelope. This may be achieved by lifting, moving and lowering the glove box 1 onto said bottom, for example by using a lifting device, or by rolling the glove box 1 until it is located inside the volume delimited by said envelope. Protective elements may be provided on the flexible sheet and/or its edges in order to provide protection against mechanical damages that could be caused by the glove box positioning. The material of the envelope 4 may preferably be non-fire-propagating. In particular it may comprise a foil of PES (polyethersulfone) coated with PVC (polyvinylchloride).
In addition, the flexible sheets allow the protective envelope to be compactly folded. Hence, the protective envelope can for example be folded into a wrapping, for example for easy handling or storage before or after use. The protective envelope can also be folded to fit into a waste container, for example for safe discarding after use.
Leak tightness is achieved by air tightness, for example at a leakage rate of 0.1 % volume/hour, as well as operation under vacuum, for example by reducing the pressure inside the envelope by 100-200 Pa with respect to atmospheric pressure. The degree of leak tightness achieved inside the protective envelope depends on, for example, the rigidity of the flexible sheets and the amount and type of access openings and ports. A leak tight enclosure is provided by forming a leak tight envelope with one or more flexible sheets, usually by welding the sheet edges onto each other, to provide a suitable leak tight space around the glove box.
The envelope is also preferably provided with one or more access ports (not shown), which are preferably leak tight interfaces between the inside and the outside of the envelope and which may advantageously comprise a leak tight port, such as an airlock. The presence of one or more access ports allows for the provision of devices which can assist during manipulations carried out within the envelope without impairing the leak tightness of the envelope. These access ports are preferably leak tight access ports. For example, electrical power outlets, monitoring devices, incident fighting equipment, a robotic arm, for example for remote controlled operation, ventilation pipes, etc. can be coupled to the leak tight envelope in a leak tight manner, to fit this purpose. Waste containers can also be coupled to the leak tight envelope in a leak tight manner for the evacuation of waste, for example resulting from a dismantling operation. Equipment or tools, for example needed for a dismantling operation, can also be provided into and removed from the envelope through one of the leak tight ports in a leak tight way. In a particular embodiment, the access port is a glove port, for example, one or more gloves, or one or more pairs of gloves, are attached to the glove port in a leak tight manner to enable manual acts inside the envelope 4.
When dismantling or performing heavy maintenance on a glove box 1 such as a Pu-contaminated glove box, the operators 2 are shielded from γ and/or n radiation originating from residual contamination inside the glove box by the presence of the protective leak tight envelope.
The protective tent assembly 10 further comprises at least one outer shielding panel 7 provided for shielding the operator against nuclear radiation. Indeed the shielding panel reduces the nuclear radiation dose rate. The shielding panel 7 is preferably formed by a set of panels applied along the periphery of the envelope 4. The panels are mounted on the support 11, on which the envelope 4 is also applied. Moreover, some of these shielding panels 7 comprises at least one further access opening 9 applied in such a manner as to enable operators 2 to reach the access openings 15 in the envelope 4 and subsequently to the openings 3 in the glove box, from outside the tent assembly. In this way, operators 2 gain access to the inside of the tent assembly and glove box interior and are able to operate the handling and dismantling tools and to perform the intervention. The pitch between the access openings is selected in both vertical and horizontal directions to be ergonomically suitable. The diameter of the access openings is generally in the range of 150-250 mm so as to enable to be crossed by an arm of a human being.
In a particular embodiment the shielding panel 7 protect the operator against both gamma and/or neutron radiation. The shielding panel 7 can be modular which is convenient and easy to handle. The shielding panel 7 can also be re-used in successive protective tent assemblies, which is economic. In a particular embodiment the shielding panel 7 comprises material chosen among leaded methylpolymethacrylate (for example Plexiglas™), leaded glass, and leaded polycarbonate, said material having a plate or sandwich structure. Leaded Plexiglas protects against gamma and neutron radiation. Leaded glass protects against gamma radiation. Leaded glass with layer of polycarbonate protects against gamma and neutron radiation. Moreover, the latter example provides additional mechanical operator protection against mechanical projectiles, for example in case of earthquakes. The shielding panels 7 are preferably transparent which enables an easy view through the panels. Alternatively windows could be provided in the panel if the latter is not made of transparent material.
In a particular embodiment the shielding panels 7are modular. The modularity of shielding panels and the support 11 makes it easy to demount the protective tent assembly after use, to store the modular parts until further use, and to construct the protective tent assembly again when needed. In a particular embodiment the shielding panels 7 are reusable in subsequent applications involving the use of the protective tent assembly 10. The shielding panels are re-usable because, placed outside the envelope 4, they would not get contaminated, or they can be decontaminated after operation. Moreover, the shielding panels 7 are re-usable because they can be detached from the outer support 11 after operation and again attached to the outer support 11 for a subsequent operation involving the use of the protective tent assembly 10. Reusing the shielding panels during subsequent operations reduces the amount of nuclear secondary waste and the cost of nuclear waste disposal.
In addition to the waste resulting from the envelope 4 and the outer support 11 and despite being re-usable, the shielding panels 7 nevertheless lead to amounts of nuclear secondary waste when they need to be discarded after successive use. Even if the shielding panels 7 are not contaminated or can be decontaminated after operation, they are considered as hazardous industrial waste because of their heavy metal (Pb) content. The protective tent assembly of the present invention nevertheless limits the amount of secondary waste since both the outer metallic support 11 and the shielding panels 7 can be re-used several times after each intervention, which reduces discharge costs substantially.
The thickness of the shielding panels 7 is selected in the range of 8-48 mm, preferably 12-40 mm, more preferably 24 mm. Thinner than 8 mm is not recommended because the shielding panel would not provide sufficient radiation protection or mechanical stability. Thicker than 48 mm is not preferred because the shielding panel would be too heavy, too expensive or could become less transparent. Plexiglas is generally available from 12 mm onwards. A shielding panel of 24 mm is preferred, for example when using a standard, commonly available leaded Plexiglas.
The width and height of the shielding panels 7 can be tailor-made, but is generally in the range of 400-1500 mm and the resulting surface is in the range of 0.4-1.5 m², more in particular in the range of 0.5-1.0 m².
Figures 2 and 3 also illustrate how the outer support 11 is arranged around the envelope 4. The support is preferably a metallic support, but it will be clear that other materials such as carbon or epoxy reinforced with fibres could be used. Preference is given to re-usable material for manufacturing the support, as this enables to re-use the support thereby limiting the amount of produced waist. The support 11 is meant to hold the envelope 4, for example by straps 12 connected to the flexible sheets of the envelope 4 in order to avoid the collapsing of the flexible envelope 4 under vacuum. The support is also provided for attaching thereon the shielding panels 7 thereon, for example by attachments 13. A mechanical attachment 13 provides both reusability of shielding panels and outer frame parts. The external support 11 is preferably designed as a frame made of bars 14 in order not to reduce access of operators for working.
The support 11 provides a structural, multi-purpose backbone to the protective tent assembly 10 of the present invention. Advantageously, the support 11 is an outer support that can be reused after the envelope, contaminated after use, has been discarded. However, a skilled person may alternatively consider an inner support depending on the circumstances, for example if the available space is limited. Advantageously, the outer support is a metallic support that can be re-used several times since it will generally be safeguarded from nuclear contamination. However, when discarding the outer support, the metal advantageously provides for the capture of contaminating particles during waste incineration.
The support 11 is also designed to withstand mechanical forces, for example resulting from the vacuum maintained in the envelope during operation, or from operator intervention, for example resulting from the weight of operators 2 climbing on the support 11 and/or those transmitted by devices such as, for example, a tackle installed within the envelope 4 for handling heavy parts. Like the envelope 4, this support 11 may be built using standardized elements, using a material facilitating its maintenance and handling, such as, for example, a metallic material such as aluminium. In a particular embodiment, the support is earthquake resistant. In another particular embodiment, the outer metallic support 11 is modular, made of frame parts, or reusable in successive protective tent assemblies.
After dismantling or another use of the concerned glove box, the protective tent assembly will be disposed. For instance, the empty Pu-contaminated envelope 4 and its gloves and windows will be wrapped and shredded to reduce its volume while the outer metallic support will be dismounted and considered as waste, because it is suspected of some limited spot contaminations in the parts of the frame not accessible to wipe test or cleaning (for example hollow parts, tapped holes, indented corners). A known process to get rid of this metallic support 11 in an efficient way is to smelt it in order to separate possible contamination from non contaminated metal. Both the envelope 4 and the outer support 11 are thus considered as nuclear waste and called secondary waste (by distinction with primary waste originating from to be dismantled/maintained glove box itself). Discarding the secondary waste is not only costly but also leads to an additional burden for the environment.
Figure 4 illustrates how the support 11 is provided with bolted attachments 13 for shielding panels 7. The support 11 may also be provided with attachments for a tackle to be located within the envelope 4. The panels 7 are mechanically attached to the metallic outer support 11 to get appropriate stability and mechanical resistance against contact with the operators. In a particular embodiment the outer metallic support 11 is modular or made of frame parts which are convenient and easy to handle. The outer metallic support 11 can also be reusable in successive protective tent assemblies which is economic.
In a particular embodiment the access openings 15 in the envelope, the further access openings 9 in the panel, the access port in the envelope, are dimensioned to provide the operator 2 with vision and limb access inside the tent assembly. This allows for safe, flexible, fast and economic operation. The access openings 15 in the envelope and the further access openings 9 in the panel are aligned with respect to each other so as to enable an easy passage from the access opening to the further access opening.
In a particular embodiment the protective tent assembly of the present invention can be used for decommissioning a medium size MOX fuel fabrication plant.
The protective tent assembly may be adapted to further comprise at least one device within said leak tight envelope. In particular, the at least one device may comprise a tackle connected to the support.
The shape of the protective tent assembly 10 is, for example, a parallelepiped or a plurality of parallelepipeds. When dismantling contaminated material inside the glove box, or when dismantling the glove box itself, the protective tent assembly 10 surrounds the glove box 1. The overall dimensions (height, width, length) of the tent assembly 10 are adapted to the overall dimensions of the to be dismantled glove box 1, and selected so as to provide a working distance between the inner side of the tent assembly walls and the outer side of the glove box walls. This working distance is a compromise, i.e. a short distance will improve access of the operator with his gloved hand to the inside of the glove box, while a larger distance will enable the operator to handle and operate electrically or pneumatically assisted tools (such as jigsaws, nibblers, ...) for dismantling the glove box enclosure. Therefore the working distance will be usually selected in the range of 200-450 mm.
Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader scope of the invention as set forth in the claims. For instance, a protective tent assembly and radio-active item manipulation method according to the invention could also be used for manipulating other objects than nuclear enclosures, and for other purposes than dismantling them. For example, such a protective tent assembly could also be used for manipulating aggressive chemicals, bio radio-active materials, etc.
In a first example where the protective tent assembly is used for dismantling a glove box, the glove box had a height of 2100 mm, a length of 2500 mm and a width of 1000 mm. Thereto, a protective tent assembly with a height of 2400 mm, a length of 4000 mm and a width of 1400 mm and having a sheet composition of PVC-coated PES was provided to comprise the glove box. Outer transparent shielding panels were provided onto the outer metallic support of the tent assembly. The shielding panels were made of leaded Plexiglas with a thickness of 24 mm, and α, γ and n dose rate reduction factor of 7. The dismantling was realised using a vacuum of 200 Pa while the total γ + n dose rate of glove box at contact was 100µSv/h.

Claims

A nuclear radiation protective tent assembly (10) for intervention by an operator (2) on a glove box (1), said tent assembly (10) comprising at least one leak tight envelope (4) and an outer support (11), said envelope (4) being formed by at least one flexible sheet and being provided with at least one access opening (15), said envelope (4) being mounted on said outer support (11), said tent assembly (10) further comprises a plurality of outer shielding panels (7), each of them having a width and height in the range of 400-1500 mm and the resulting surface in the range 0.4-1.5 m², placed peripheral to said envelope (4) and being located on the outside of said envelope (4), some of these shielding panels (7) comprising at least one further access opening (9) for enabling said operator (2) to have access via said at least one access opening (15) to an inner space of said envelope (4), the access opening (15) in the envelope (4) and the further access opening (9) in the shielding panel (7) being aligned with respect to each other so as to enable an easy passage from the access opening (15) to the further access opening (9), said panels (7) being provided for shielding said operator (2) against nuclear radiation, said outer support (11) being located on the outside of said envelope (4), and characterized in that said outer support (11) is arranged around the envelope (4) and is provided with means arranged for holding said shielding panels (7).
The tent assembly (10) according to claim 1, wherein said shielding panels (7) are provided to shield said operator (2) against gamma and neutron radiation.
The tent assembly (10) according to any one of claims 1-2, wherein said shielding panels (7) are removable mounted on said outer support (11).
The tent assembly (10) according to any one of claims 1-3, wherein the shielding panels (7) are made of transparent material.
The tent assembly (10) according to any one of claims 1-3, wherein the shielding panels (7) comprise at least one window enabling to see inside a volume delimited by the shielding panels (7).
The tent assembly (10) according to any one of claims 1-5, wherein the thickness of said shielding panels (7) is in the range of 8-48 mm, in particular 12-40 mm, more in particular 24 mm.
The tent assembly (10) according to any one of claims 1-6, wherein said outer support (11) is a modular metallic frame formed by frame parts.
The tent assembly (10) according to any one of claims 1-7, wherein said further access opening (9) of said shielding panels (7) has a diameter in the range of 150-250 mm.
The tent assembly (10) according to any one of claims 1-8, wherein said shielding panels (7) are formed by a material chosen among lead methylpolymethacrylate, lead glass, and lead polycarbonate, and said shielding panels (7) having a plate or sandwich structure.
The tent assembly (10) according to any of claims 1-9, having a height of 2400 mm, a length of 4000 mm and a width of 1400 mm and wherein said leak tight envelope (4) has a sheet composition of PVC-coated PES (polyethersulfone).