IL24059A - Tubular fuel pencil for nuclear reactors - Google Patents

Description

C O H E N Z E D E K S P I S B A C H R E PA TE NT ATT O R N EYS LEVONTIN 1169 T E L AV I V P A T E N T S D E S I G N S O R D I N A N C E SPECIFICATION TUBULAR PENCIL KIR ENERGY Y an International Organisation established by the Treaty of of sue EREBY DECLARE the nature of this invention and in what manner the same is to be performed particularly described and ascertained in and by the following relates to a fuel pencil for nuclear including for exam le pressure fluid cooled power the pencil mainly comprising a cylindrical outer and a cylindrical sheath inner which to receive in the annular hs between the a tube or stack of rings of fissile material and two plugs for connecting and closing the ends of the said space Pencils of this form are desirable in case of fuels of high specific power the fuel being in an annular shape with the advantage that the outside and inside surface of the pencil may be cooled the idea being to increase greatly the surfaces in contact with the heat vehicle fluid for a given fuel It is also known except sheaths plastic or flexible which are engaged with the fuel by the action of the pressurised heat vehicle th fuel being metallic such as uranium or the use of pencils of the kind described is in general very limited because of the dif iculties in providing adequate thermomechanical stability of the inner One reason for this is in the common case where the coefficient o expansion of the earns is greater than the coefficient of expansion of the sheath he inner can tends to expand bears against the inside surface of the tubular fuel as it does so and is therefore with the result that in some temperature sheath conditions the inner can is made unstable by local buckling which leads to the f ormation of or corrugations which in turn quickly lead to leaks This kind of thermomechanical instability of the inner sheath sheaths is found with rigid not connected to the with cans connected to the or a dif sion barrier in which case the connection first shears whereafter f olds or corrugations are formed sheath and with pencils having a rigid not connected to the fuel having a of expansion less than the coefficient of expansion of the The reason f or the latter case is that when the fuel disengages from the cause of the temperature of the inside of the tubula fuel leading to further sheath disengagement of the fuel from the and increased sheathing thermal and mechanical stressing of the material end of the It is also known to use in cylindrical fuel sheath pencils a very thin of a thickness of mm or sheath the l being made by means of corrugations permitting radial and axial the cal placed around the fuel can take the of a rod or of a stack of with the interposition of a material which is plastic at the working temperatures of the In one such fuel element disclosed by the Applicants Israel latent Application the sa which is too thin to be inherently can be produced in large diameters stability being provided by def f olds or corrugations whose convexity faces outwards and which are provided on that sheath part of the which is between terminal receiving zones folds or corrugations comprising longitudinal folds or corrugations permitting radial deformation at at least one end of said peripheral or helical folds or corrugations which permit axial deformation and which are in extension of the longitudinal folds or the and sheath the clearance between the and the being by the material which is plastic when hot and which is preferably In this system the can stand high external pressures without suffering severe stressing by engaging with the hydrostatieally sheath stressed plastic cushion or and can withstand forces caused by expansion of the and of the plastic cushion and changes in the dimensions of the fuel during for all such being mitted to the corrugations by hydrostatic sheath do not overstress the sheathed It is also known that these very d cylindrical fuel pencils have very reduced transverse more particularly in the case of a stack of fuel and must therefore either have a stiffening structure around them or be placed in a channel which imposes a definite geometry near It is also desirable that they have longitudinal centring olds or corrugations strengthened by a stiffening or strengthening to enable the pencils to remain in a predetermined axial position in the vein of cooling fluid flowing through the structural around the Pencils of this construction form the subject matter of the Patent Application This invention relates to a tubular fuel pencil designed to have improved thermal and mechanical characteristics in orde to reduce the associated the inner of the known In broad form the invention provides a tubular fuel pencil for a nuclear reactor comprising tubular and outer said sheath defining therebetween an annular a substantially cylindrical body of nuclear said nuclear fuel being placed in annular means for closing the ends of said annular inwardly longitudinal corrugations on said inner sheath and a rigid cylindrical member mounted said inner said rigid cylindrical member being rigidly secured to said end closing said corrugations bearing against said cylindrical to thereby support said inner and outwardly projecting longitudinal corrugations on said outer In form of the the comprises a cylindrical oute sheath and cylindrical inner sheath which to receive a tube or stack of rings of fissile material and two annular plugs fo connecting and closing the sheath characterised that pencil comprises deformation and at at least one end of said part peripheral or helical folds or corrugations permitting axial the naving equidistant longitudinal folds or corrugations whose or corrugation is greater than the old corrugation height of the corrugations or folds permitting axial the equidistant longitudinal folds o corrugations being internally strengthened by a strengthening or stiffening the s receiving between them the fuel with the interposition of a viscous layer of a material which is at the working temperatures of the pencil in the there being introduced into the hollow interior of the pencil a rigid cylindrical member against whose surface the longitudinal f olds or sheath corrugations of the inner can bear and ends are rigidly secured to the pencil Other features and details of the invention will be disclosed by the description of reference being made to the accompanying drawings Figure 1 is a through one example of a tubular fuel pencil according to the figure 2 is a section on the line of the pencil shown in Figure and Figure is a partial of an alternative form of the pencil shown in Figures 1 and The drawings show for each example a pencil sheath sheath and outer 2 fuel rings which can be of metallic uranium or of a alloy or of such a uranium carbide or Uranium one above another in the space between the sheath sheath inner and outer annular plugs whic connect and close the annular space between raised edges and annular projections for supporting several pencils of a and two refractory ceramic rings 8 placed between the fuel and the plugs to heat insulate the sam f om the fuel end The are very thin have a thickness of mm or less from to are preferably of stainless steel and have longitudinal or corrugations 9 in the part between the terminal They also in the terminal zones of said peripheral or helical or corrugations 10 in extension of the longitudinal sheaths rugations cans are separated from the fuel b viscous layers 11 formed by suc as which is plastic at the working temperatures of the pencil in the annular gaps between the and the inside surface of the rings and between the outside sheath surface of the rings and the 2 are completely by material which is plastic when hot so since the tubular peneil experiences a hydrostatic for from the cooling the viscous layer or cushion 11 is compressed hydrostatically through the agency of the flexible The corrugations therefore have internal support from the triaxially stressed plastic metal and do not become fatigued because of geometric variations in the pencil elements due to different heat operatin sheath conditions in the react or the inner 1 experiencing the pressure of the cooling fluid is f orced against the inside surface of the f uel 3 with the position of the plastic cushion the c orrugations 10 reduce thermomechanical instability by c ompensating f or differences between the expansion of the and the sheath expansion of the nan by f thus reducing the risk of local buckling or of heat For transverse stiffening of the a rigid cylindrical membe 12 is placed in the pencil coaxially thereof and is borne by plug rings and stiffening or strengthening wires are placed in the longitudinal corrugations cylindrical member which is made of nuclea graphite is rigidly sheaths connected to the by means f or instance of spring steel wires which are disposed in a cross and secured in apertures 15 in the rings One of the wires which placed one above embedded in a diametric groove 16 in the member wires inside corrugations which bear against the fuel sheath help the corrugations of the inner to the pencil on the member 12 and hel the c orruga tions 9 of sheath the outer bear against the surface of the c ooling channel 17 in which the pencil is used the channel can be either ah f orcing or pressure tube or a able structure longitudinal c orrugations 9 are of a height which is greater than the height of the corrugations to an adequate c ooling f luid f low c at tile zones of the and which is suc as ensure the effective the cooling veins 19 between the surface sheath of the 1 and the member 12 and between the surface sheath of the 2 and the channel The corrugations 9 connected to the corrugations if the latter are helical by gations of progressively varying height increase sheaths area of the the same are formed on those parts of their surfaces which are between the corrugations 9 permitting radial with small cooling folds or corrugations 20 which extend parallel with the corrugations 9 and whose length is not greater than the length of the corrugations the plugs 4 take the orm of rings which are made of stainless steel or of the same material as is used for the the raised edges the plugs are simultaneously respectively welded to the rings 22 either by argon arc welding or by electron bombardment to f orm a closure similar to the simple pencil closure disclosed by the Israel Patent Application H As ca be gathered from Figure in the case of pencil where the central member 12 can ac as a support for contiguous pencils of the instead of the wires 14 rigidly conneeting the member 12 sheaths to the the pencil is borne by the spider which is rigidly connected to the member 12 and to the rings 7 and through which the coolant can flow and which mainly comprises arms 24 against the surface of the channel 17 to centre support the end zones of the pencil where the corrugations 10 are invention has been with referenc to particular embodiments but is not of course limited sheaths thereto and can be For he 2 can be with longitudinal corrugations or permitting radial distortion whieh are interleaved with corrugations 9 strengthened by wires and which ere either of the height or of less height than the latter corrugations in the case of diameter pencils the ends thereof can be centred not by arms 2 of the spider but by wings or the like on the ring insufficientOCRQuality

Claims (1)

1. WHAT IS CLAIMED IS a A tubular pencil a nuclear reactor comprising tubular inner and outer said sheath an annular a substantially cylindrical body of nuclear said nuclear fuel being placed in said annular means for closing the ends of the said annular inwardly projecting longitudinal corrugations on said inner sheath and a rigid cylindrical member mounted within said inne said rigid cylindrical member being rigidly secured to said end closing said corrugations bearing against said cylindrical member to thereby support said and outwardly projecting longitudinal corrugations on said outer A fuel pencil as claimed Claim 1 in which the equidistant longitudinal or corrugations whose f old or corrugatio height is greater than the or corruga tio height of the corrugations or f permitting the equidistant longitudinal f olds or corrugations being internally strengthened by a strengthening or stiff ening wire sheaths the receiving between them the f el with the interposition of a viscous layer of a material which is plastic at the working temperatures of the pencil in the there being introd ced int o the hollow interio of the pencil a rigid cylindrical member agains whose surface the longitudinal sheath f old or corrugations of the inner bear and whose ends are rigidly secured t o the pencil tubular fuel pencil as set f orth in Claim characterised in that the cylindrical member is rigidly secured to the ends of the pencil by engaged in the ends of the rigid cylindrical member and secured to the closure plugs A tubular fuel as set orth in Claim or Claim characterised in that the membe is rigidly connected to the pencil ends by means of discs or spiders or the like engaged with the ends of the cylindrical member and with the closure plugs A tubular pencil set forth in Claim 5 in which the member is connected as af oresaid by a spider with equidistant outwardly projecting radial arms tubular fuel pencil as set th in any the previous claims characterised in that the sheaths have on those parts of their surface which are between the longitudinal corrugations f olds or corrugations which are parallel with such longitudinal corrugations and which have a reduced f old or corrugation height A tubular fuel pencil substantially as herein described with reference to and as shown in Figures 1 and 2 or Figure 3 of the acc ompanying drawings 28th day of A for Applicants insufficientOCRQuality