FR2553922A1 - ARMORED CONTAINER FOR TRANSPORTING AND STORING A RADIOACTIVE LOAD - Google Patents

Abstract

ARMORED CONTAINER FOR THE TRANSPORT AND STORAGE OF A RADIOACTIVE LOAD. THE CONTAINER ACCORDING TO THE INVENTION IS DESIGNED TO WITHSTAND ALL OPERATING CONSTRAINTS, INCIDENTAL AND ALSO ACCIDENTAL (MECHANICAL SHOCK AND FIRE, IN PARTICULAR). ACCORDING TO A MAIN CHARACTERISTIC, IT CONTAINS AN INTERNAL BODY 3, CONTAINING THE RADIOACTIVE CHARGING 1, 2, AROUND WHICH IS MOUNTED AN EXTERNAL PART 11 CONTAINING THE NEUTRONIC PROTECTION 14 AND COOLING FINS 16. WHEN THE RADIOACTIVE CHARGING IS INTRODUCED. OBTAINS A SELF-FRESTING EFFECT BETWEEN THE TWO CONSTITUTIVE PARTS. THIS CONTAINER IS USED IN PARTICULAR FOR THE TRANSPORT AND STORAGE OF FUEL ELEMENTS PREVIOUSLY IRRADIATED WITHIN NUCLEAR REACTORS.

Description

The invention relates to the transportation and

  storage of a radioactive charge, in particular that consisting of irradiated fuel assemblies in nuclear reactors, and is more specifically adapted to a new type of container designed for each of its constituent parts to compete, in association with the others, with the optimal solution of all the problems posed by these transport and storage operations, including in case of accident.

  The problems to be solved in the context of normal use of a shielded container carrying or storing radioactive cargo are as follows: to ensure the physical integrity of the cargo; provide external biological protection against y-radiation; provide external biological protection against neutron radiation;

  ensure the evacuation of the thermal power released by the load.

  Moreover, such a loaded container must also make it possible to solve the following problems, corresponding to conditions of accidental use: to ensure safe shock absorption, not only incidental but also accidental; and

  safely protect the load against the effects of fires.

  Of course, solutions to these problems must remain within acceptable limits of industrial and commercial exploitation, in particular

  regarding weight and cost.

  Currently, all containers of this type have certainly undergone fire behavior tests

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  but in this invention, particular emphasis has been placed on minimizing the heating of the central portion of the container by creating an insulating air gap, which adds to the partial absorption of the heat flux in the outer portion.

  Generally, the architecture of the known containers essentially comprises, on the one hand, a first cylindrical constituent part closed at its ends, containing in its central longitudinal cavity the radioactive loading, ensuring the essential protection against the radiation y and the evacuation of the thermal power released by the charge and, on the other hand and surrounding this first part, a second composite cylindrical constituent part 15 comprising, internally, means providing both the protection against neutron radiation and the transfer of thermal power to the outside and, externally, dissipation means of

  this thermal power, such as fins.

  Depending on the particular types of these known containers, emphasis has been placed primarily on a particular functional aspect of such containers.

overall structure.

  For example, it has been proposed to make the two constituent parts of the container in distinct and separable ways in order to facilitate the normal operation and maintenance of the assembly, or the possible repair of the outer part alone.

accident case.

  In addition, the invention relates to a container of the above kind but also having additional and associated characteristics enabling it both to improve all the performance of these known containers and to have in addition a

  specific resistance to fire and shock effects.

  To these effects, and according to a first functional originality of a container according to the invention, it has thermal conduction characteristics between its two constituent parts which are maximum when the heat flow is centrifugal (normal conditions, when the loading radioactive releases thermal power) and minimal when this flow is centripetal (abnormal conditions, when the container is accidentally located in a fire).

  The main subject of the invention is therefore an armored container for transporting and storing a radioactive charge, of the type essentially comprising: a first part comprising a thick cylindrical constituent envelope 15 enclosing the charge in a longitudinal central cavity, and carried out in a material absorbing Y radiation and discharging to the outside the thermal power released by the charging, and a second constituent part comprising two spaced coaxial cylinders, enclosing between them a neutron absorbing material, interconnected by means of thermal conduction, and outwardly provided with heat dissipation means, and characterized in that the inner cylinder of the second constituent part of the container is mounted without mechanical clearance around the outer cylindrical surface of the first constituent part In order to constitute an air gap between the two parts in case In the case of external fire, the second part can be made of several joined sections with a bore of the inner cylinder before assembly. According to a first embodiment, the two

  The cylindrical portions are fitted together to smoothly mount the cymbal portion.

  external lindrique outside the internal cylindrical part.

  According to a second embodiment, the two cylindrical parts to be adjusted together have a minimum coni5 cité, of the order of 1% facilitating this assembly.

  In this way, before the introduction of a radioactive charge generating heat in the container, the mounting of the two essential constituent parts of the container forms a compact mechanical assembly.

  After introduction of the heat-generating radioactive charge, the inner part of the container, which is more massive and warmer, increases in external diameter more than does the second outer axial portion, so that an effect is obtained.

  self-hooping reinforcing the mechanical cohesion of all the two parts which reindeer more resistant to shocks, and thereby increases the transmission characteristics of the heat flow centrifugally.

  On the other hand, in case of fire, it is the external cylindrical part, subjected to an abnormal elevation of temperature, which expands more than the internal cylindrical part. The self-shrinking effect is then annihilated and, m 6 me, an air gap can

  between the two parts thus decreasing the possibilities of transmitting the heat flow in a centripetal manner, thereby guaranteeing the best thermal protection of the internal load.

  According to a second functional originality

  of a container according to the invention, its second component part is designed specifically to have a maximum longitudinal stiffness and optimum transverse flexibility.

  For this purpose, a container according to the invention is further characterized in that, in combination, on the one hand, the material chosen to produce the metallic elements of the second constituent part of the container is mechanically ductile spheroidal graphite cast iron. and, on the other hand, the two coaxial cylinders 5 of said second part are interconnected by longitudinal struts having in section a circular arc profile connecting tangentially to the facing surfaces of said two coaxial cylinders. These two combined characteristics mean that, in the event of incidental or accidental mechanical shocks, the outer part of the container has a great possibility of mechanical deformation with respect to the inner part of the container. The deformable outer part is designed to absorb the major part of the container. the kinetic energy developed so as to limit the deceleration undergone to a value such that its integrity is ensured In addition, the closed cavities limited by said longitudinal struts and ren20 closing, as known per se, a material absorbing

  neutrons, because of their mechanical ductility, best protect this neutron-absorbing material in case of accidents due to exceptional mechanical shocks.

  The invention still relates to other valuable ancillary features.

  It will be better understood from the following description of a particular, but not exclusive, mode of implementation of the invention.

  Referring to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a container according to the invention, and Figure 2 is a sectional view through the line II-II of the container shown in Figure 1. 35 The container described is intended to ensure the

  transport and storage of radioactive cargo.

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  This loading consists, in this example, of seven fuel assemblies 1, previously irradiated in a nuclear reactor, and placed in a basket 2, known per se, made in the form of a light-alloy machine holding the various fuel assemblies. parallel to each other and spaced

radially evenly.

  This basket 2 is placed inside a longitudinal central cavity of the first constituent part of the container formed by a

body 3.

  This body 3 is a thick cylinder, hollow axially, made of cast steel or forged, or spheroidal graphite cast iron, and having a bottom 15 4 The functions of this body 3 are as follows: to ensure the integrity of the objects transported, create a containment barrier for locked radioactive material; provide the essential protection against radiation y; and ensure the thermal transfer to the outside of the thermal power released

  by the radioactive materials placed in the basket.

  The body 3 is closed by a closure system comprising a plug 5, fixed by bolts 6 on the flange of the body 3 with the interposition of two seals 7 The plug 5 has the same functions as

those of the body 3.

  A tape consisting of a closure plate 8, constitutes a complementary closing device of the cap 5 to provide frontal30 les functions of mechanical and biological protection, and sealing This plate 8 encloses the accidental contamination during opening operations or The closure of the container is fixed by means of bolts 9 on the flange of the body 3. A gasket 10 is interposed between the plate 8 and the flange of the body 3.

  seal 10 is interposed between the plate 8 and the flange of the body 3.

  The second constituent part of the container or outer part 11, which will be described in more detail below, has been designed in a characteristic manner according to the invention to simultaneously fulfill all the following functions: to provide the complement of biological protection against radiation there; provide essential biological protection against neutron radiation; ensure the optimal evacuation of the thermal power released by the radioactive materials of the load; provide a safety cushioning capability for mechanical shocks to the container under normal and accidental operating conditions; and, finally, provide thermal protection of the load against the effects of fire. This outer part essentially comprises, radially surrounding the active parts of the fuels contained in the central parts of the assemblies 1, two spaced coaxial cylinders 12 and 13, enclosing between them a material 14 such as plaster loaded with hydrogenated materials absorbing the neutron radiation. , interconnected by tretoises 15 providing centrifugal heat transfer, and provided externally with longitudinal fins

16 of heat dissipation.

  According to a first main feature of the invention, the inner cylinder 12 is without mechanical play around the cylindrical surface

outer body 3.

  According to a first embodiment, the two

  Cylindrical portions 3 and 12 to be adjusted to one another have a difference in diameters making it possible without difficulty to mount the outer cylindrical portion 12 outside the body 3.

  According to a second embodiment, the two inner cylindrical portions 3 and outer 11 to be adjusted between them have a minimal conicity, of the order of 1%

facilitating assembly.

  We get this way, by this tight fitting

  of the outer part of the container around its inner part, the advantages listed above in the general disclosure of the invention, concerning the protection against external mechanical and thermal shock accident.

  According to two main originalities of

  the invention, the container of which it is the object is characterized in that the material chosen to produce the metal elements of its outer part is spheroidal graphite cast iron and the two coaxial cylinders 12 and 13 are interconnected by longitudinal struts 15 having in section, as shown in Figure 2, a circular arc profile connecting tangentially to the facing surfaces of the cylinders 12 and 13.

  This gives the security advantages

  and protection also discussed above.

  More specifically, the series of internal volumes between the cylinders 12 and 13 and formed by the internal struts 15 is perfectly adapted to

  contain the neutron protection material 14 necessary for the type of radioactive loading provided.

  The shape of these volumes, due to the arcuate shape of the spacers 15, makes it possible to have a quasi-uniform thickness of neutron protection.

  nh ee concerning the outer fins

  16, they may also have an oblique direction, helical or perpendicular to the longitudinal axis of the container or a form in chevre vrons, to optimize their bending behavior.

  These shapes (straight, oblique, helical, perpendicular, herringbone, etc.) of the outer fins 16, and their dimensions, allow easy decontamination in case of accidental contamination 5 and, moreover, there are no zones of retention of contaminated products: the surfaces of the fins are

  accessible and can be easily cleaned.

  In case of voluntary use of the container in a contaminated external environment, such as swimming pool water, the honeycomb and finned structure is enclosed beforehand inside a protective skirt 17 mounted on suitable supports 18. On either side of this structure which axially positions the outer portion 11 This skirt may be filled, prior to immersion in the pool, uncontaminated water to ensure the thermal connection between the fins 16 of the container and the surrounding environment. Trunnions 19 protruding radially outward allow container handling and stowage while providing substantial damping.

in case of fall.

  This damping is completed by that provided by covers 20 disposed at both ends of the container and which constitute protective screens

  mechanical against any axial or lateral impact and thermal protection protecting the seals 7 and 10 of the closing elements of the container in case of fire.

  These covers 20 can be made of balsa.

Claims (4)

  A shielded container for transporting and storing a radioactive charge, of the kind comprising essentially: a first portion comprising a thick cylindrical constituent casing enclosing the charge in a longitudinal central cavity, and made of a y-radiation absorbing material and discharging to the outside the thermal power released by the load, and a second   constituent part (11) comprising two spaced coaxial cylinders, containing between them a material absorbing neutron radiation, interconnected by thermal conduction means, and provided with external heat dissipation means, and characterized in that the inner cylinder (12) of the second constituent part (11) of the container is mounted without mechanical clearance around the outer cylindrical surface of the first constituent part (3), so as to constitute an air gap between the two constituent parts in outdoor fire.   2 Shielded container according to claim 1, characterized in that the material chosen to produce the metal elements of the second constituent part 25 of the container is spheroidal graphite cast iron. 3 Shielded container according to any one of   Claims 1 or 2, characterized in that the two coaxial cylinders (12 and 13) of said second portion (11) are interconnected by spacers   longitudinal members (15) having in section an arcuate profile connecting tangentially to the   look at the two said coaxial cylinders (12 and 13).   4 Shielded container according to any one of claims 1 and 2, characterized in that the   heat dissipation means to the outside are fins.   Shielded container according to claim 1, characterized in that the inner cylinder (12) of the second constituent part (11) of the container has a small conicity and the outer surface of the first constituent part has the same conicity.   Shielded container according to claim 1, characterized in that its second constituent part (11) can be enclosed within a protective skirt (17).