US3133197A - Apparatus utilizing liquid metal coolant for transporting thermally hot intensely radioactive material - Google Patents

Description

3,133,197 PORTING 2 Sheets-Sheet 1 J. W. ALLEN QUID METAL COOLANT FOR TRANS NTENSELY RADIOACTIVE MATERIAL THERMALLY HOT I APPARATUS UTILIZING LI May 12, 1964 Filed June I6, 1960 INVENTOR. @fi

May 12, 19-64 J. w. ALLEN 3,133, 7

APPARATUS UTILIZING LIQUID METAL COOLANT FOR TRANSPORTING THERMALLY HOT INTENSELY RADIOACTIVE MATERIAL Filed. June 16. 1960 2 Sheets-Sheet 2 :{Inlmunu 1 n ml- I III II I I I I I I IIIIHIIIIIIIIIIIIIIIIIIIIIII 3,133,197 Patented May 12, 1964 APlARATUS UTHJIZENG LIQUID METAL COOL- ANT FQR TRANSPDRTING THERMALLY HOT INTENSELY RADIOAGEIVE MATERIAL John W. Allen, Hinsdale, 111., assignor to Stanray Corporation, Chicago, 111., a corporation of Delaware Filed June 16, 1960, Ser. No. 36,519

8 Claims. (ill. 250106) This invention relates to apparatus for transporting radioactive and thermally hot materials, more particularcharacter of radioactivewaste in spent reactor fuel rods is indicated by the fact that approximately 100,000 B.t.u. per hour are emitted by a bundle of only thirty-two such fuel rods. A container in which to carry these rods must therefore dissipate this much thermal energy to maintain temperature equilibrium. Such an amount of ,heat compares with the heat capacity of a household ,furnace. Failure to dissipate the evolved thermal energy willcause an abrupt rise in ternperature of the container and its contents and ultimately structural failure of the cask or the fuel rods.

-It is necessary to transport intensely radioactive and highly exothermal nuclear reactor waste products over jcommon carrier transportation lines such as truck and rail. routes. These materials are carried into andthrough populated areas and are not infrequently left standing on sidings and in traflic where the general public could be exposedto the hazards of radiation and thermal heat burns excepting for the protection afforded bythe container or shipping cask in which the dangerous material is fbeing carried. Accordingly, the structural integrity, the, completeness of. the radiation shielding about the radioactive material, and the eficient dissipation of the evolved heat through such a shipping cask are urgent requirements. Theisuperior gamma ray shielding materials are very dense, lead and metal loaded concrete being examples of preferred shielding materials. Unfortunately these materials do not possess optimum high strength structural properties nor good heat conductivity, and in the case of lead is subject to relatively low melting temperature.

Steel and stainless steels are good heat conductors but 2 stainless steel or zirconium alloy sheath or clad. The integrity of the sheath or clad may be disrupted by overheating of the fuel rod from inadequate conduction of heat away from the rod by circulation of a coolant about its outer surface. Spent reactor fuelrods, even after re- 7 moval from a reactor and temporarystorage during a less eflicien-t gamma ray attenuator materials from the dimensionalpoint of view; and are subject to large dimensional changes when heated. This, latter property in a thick walled structure such as a heavy shipping cask can lead to cracking and structural failure of a cask if, for example, it is heated unevenly by a large heats'ource contained within it. Despite these disadvantages in the available materials an adequate and safe shipping cask for radioactive exothermal materials may be fabricated from a composite of strong structural materials such as stainless stee l lined with an efiicient gamma ray attenuating V materialsuchas lead, provided however, means are pres- "ent to effectively carry the excessive quantities ofheat evolved by the radioactive material to the exposed surfaces of the cask where it may be safely radiated from the v fer between the radioactive material and, for example, the

cask walls. V

Nuclear reactor fuel rods are commonly encased in a 7 on line22 through the cask illustratedin the embodi cooling period, still may evolve suficient heat to melt their sheaths when placed in an environment which confines the heat evolving from the rod. Numerous highly toxic and radioactive substances are present in irradiated fuel rods in the form of particulate matter and gases, which upon rupture of the fuel rod sheath are easily scattered. Such dispersions of radioactive materials constitute a most serioushealth hazard to any person coming in contact with them.' In view of the sensitivity of the fuel rod sheath to localized high temperature, and the. increased health hazards which result from sheath rupture of spent fuel rods, it is most important that effective means for transporting heat from the fuel rod surfaces to structures through which it can be removed and dissipated'be provided during storage and shipping of spent fuel rods. q

Fluid coolants circulated by convective ,flow about a heat source have long been utilized. Liquid metals or alloys possessing a relatively low freezing point and relatively high boiling point are adaptable to serve as a coolant in a shipping cask. It is, however, desirable to economize both weight and space in a shipping container 'for purposes of ease of handling as well as reduced transf port costs. If the liquid metal coolant is selected toprovide both eflicient heat conduction and efiicient radiation shielding a substantial reduction in both weight and dimension of the shipping cask may be achieved. I Such a 'liquid metal alloy, that is both an effective and safe co ol- 'ant and an effective radiationcshield material is, for ex- "an efiicrient safe method for conducting substantial quanti-ties of heat from arad-ioactive heat source within a shipping cask-to the exposed surfaces of the cask where it may be dissipated through the cask Walls. 7 It is janother object of thisinvention to provide means utilizing liquid metals for combining both cooling and shield-ing radioactive material contained within a shipping container. I v It is yet another object of this invention to provide a method of conveniently handling liquid metal coolant and liquid-metal radiation shielding in a shipping cask during loading and unloading procedures.

These and other objects and advantages of my invention will be readily apparent from the following drawings, spe oification' and claims; j

My invention comprises 'briefly an apparatus for transporting exothermal radioactive material comprising a pressure retaining cask and a quantity of low melting temperature metal adapted to both cool the radioactive material and attenuate nuclear radiation emanating therefrom and means for-transferr ng the molten metal into "and out of the cask after loading and prior to unloading-the radioactive material. i 1

FIGURE 1 is a cross sectional view of a' preferred embodiment .of my inventionshown mounted on a specially fitted railroad car; 1 p

FIGUREv 2 is a horizontal cross sectional view taken mentofFIGURE l; I

:3 FIGURE 3 is a cross sectional view of the embodiment in FIGURE 1 showing the cask, storage tank and means for transferring molten metal therebetween illustrating the apparatus prior to-transferring the molten metal from the tankto the cask; and a sitioned on a specially adapted railroad c'arlZ. 'in ad.-

dition to the cask Til a storage tank l4 is mounted on the railroad car adjacent the cask. The cask illustrated in the drawings is adapted to the cross country transport of spent nuclear reactor fuel rods. A typical fuel rod assembly contains a plurality of fuel rods fastened together in a bundle, the rods are eleven feet two inches long and the assembly is approximately four inches square. Twelve such assemblies of irradiated spent rods emit gamma and beta radiation of an intensity ofv 415x10 roentgens'per hour on the inside of the cask.

A'radiation dosage of not greater than 5.5 milliroentgens per hour on .the outer surface of thecask is considered safe. At the same time, twelve fuel rod assemblies produce 73,600 B.t.u. per-hour which must be dissipated through the outer surfaces of the cask. Such a quantity of heat would soon melt the fuel assemblies and other adjacent structures if it were not efliciently conducted away. A temperature of up to 800 F. is considered a maximum safe temperature for the apparatus in transit. The cask It) is comprised of an outer shell 16 preferably made of stainless steel, a gamma radiation attenuator liner 18 such as lead, and an inner: shell of strong temperature'resistant material such as stainless steel or other corrosion resistant steel. The lead liner 18 is held securely in place between the inner and outer shells by a' series of fins 22 attached to the inner wall of the outer shell andextendin-g into the lead liner 18. V A removable lid 24 is provided at the top of the cask 10 which is always carried in a vertical position as shown in FIGURE 1. The lid 24 is fastened to the top of the cask and seats on a recessed contour which provides a pressure seal between the cask walls 26 and the lid 24. v v

The lid 24 is provided with a pressure release check valve 28, having an adjustable pressure release mechanism 30 which connects the interior of the caskWith the atmosphere through an indirect channel 32 when the pressure within the cask exceeds the preset pressure release valve. The variable pressure release mechanism is conventional and comprises a' spring 'loaded check valve and a means for adjusting the tension load on the spring. The indirect channel 32, assures-that there will'be no direct path between the interior and exterior of the cask which will allow the escape of unattenuated radiation. A second indirect passage 34 is provided through the cask wall, and as'shown' in the drawings,

may be conveniently mounted on the lid 24. Exterior of the cask the passage 34 is connected through a conventional check valve 36 mounted to limit fiowcf fluids outward from the cask, a gate valve 38, and a coupling 40 which may be connected to a supply of compressed air, or water as the need arises. The detailed operating procedures which includes the sequence of valve manipulation required for loading and unloading the cask are described below. i i

The bottom of the cask is provided with a sump 42 or 7 low reservoir into which fluids will drain; the sump is The storage tank 14 is a pressure retaining tank having.

a heavy outer shell 46 constructed to attenuate some nuclear radiation in the event that radioactive material is inadvertently transferred to the storage tank. A plenum 48 separates the outer shell 46 from an inner shell 50. The plenum 8 is connected through a port 52 and a pressure release check valve 54 to the exterior of the tank. The interior of the inner shell Stl is connected to the exterior of the tank through a second port 56 which discharges through a check valve 58 adapted to only permit inflow through the port and a gate valve fill. A coupling link 62 is connected with the outer port of the gate valve 69 and is adapted to connect with a source of compressed air.

A larger passage 64 and a smaller conduit or pipe 66 connects the interior of the cask lid through the cask fport 4410 the interior of the storage tank 14 through the port 68 in the outer shell and the port 7i in the inner shell. Thelarger passage. comprises essentially a steam jacket coaxially mounted about the conduit 66. The passage or steam jacket is terminated midway between the tank and the cask and coupled by means of a gate valve '72 and a union 73. The conduit 6t; is terminated in the sumpJdZ of the cask at one end 74 and is terminated at theotherend 76 in the lower portion of the storage tank.

The conduit 66 is also provided witha gate valve 72a and a union Thus, with this arrangement fluids may be transferred from the tank through the conduit 66 into the cask interior and conversely, by pressurizing the cask with respect to the interior of the tank fluids may be transferred from the cask through the conduit back into the tank. The cask Ni and the tank 14 may be disconnected by uncoupling the unions 73 and 73a and either oneremoved from its mounting on the railroad car 12.

The larger passage 64 terminates at .a first end 78 in the interior of the upper portion of the cask immediately adjacent the cask port 44; at its other terminal the passage 64 is branched into a plurality of smaller passages 30 which terminate in the plenum 48 at the storage tank.

Thus, a readily'vaporized substance, such as water, may be added and passed as steam from the cask through the passage 64 coaxially with the conduit 66 and then through the interior of the storage tank whereupon as condensate or low quality steam it is discharged into the plenum 48 whereupon it may then be passed to the exterior of the storage tank through port 52 and pressure release check valve 54.

'There is a wide selectionof possible low'melting temperature metals which constitute suitable coolants and offer a source of nuclear radiation attenuation. Examples of this are mercury, sodium potassium eutectic, or NaK,

Woods metal, bismuth alloys and, in particular, lead his muth alloy. All liquidmetals are excellent heat conductors both byvirtue of the fact that metals are intrinsically excellent heat conductors and in the liquid state, readily form good heat transfer junctions with the parts of which the heat is to be conducted. The various pos sible liquid metal Coolants each attenuate nuclear radiation and, in particular, gamma rays substantially in proportion to their density. Accordingly, selection of a liquid metal coolant may be influenced by the factor of its suitability as a coolant which, for the particular applicatron disclosed here, by its compatability With the materials with which it comes into contact and by the radiation attenuation characteristics which it affords.

In my invention lead bismuth alloys are favorite liquid metal coolants because they are relatively stable and inactive chemically'and particularly they aiford a large degree of gamma ray attenuation. A quantity of lead bismuth alloy .84 is placed within'the interior of the inner shellSO of the tank 14; This initial charge of lead his muth into the tank 14, can be accomplished by pouring lead bismuth in shot form through port 56 into the tank.

temperatures allowable for shipping radioactive materials cross country. A safe temperature for such shipments is.800 F. Lead bismuth alloy freezes at a temperature of 257 F.; and water vaporizes into steam at 280 F. at 35 p.s .i. gage pressure. The combination of water which C may be formed into a good heat transfer medium at relaassemblies 82 are positioned Within the interior of the cask by removal of the cask lid 24 and insertion through the upper end of the cask. The lid is then replaced and secured to the cask. Low melting temperature metal 84, which may bein the liquid or solid state, is stored within the inner shell 50 of the storage tank 14. 'The fuel assemblies 84 prior to shipping willhave been stored under Water and be 'wet at the time they are loaded. Water from the surfaces of the fuel rods and additional water introduced through the indirect passage 34'Will begin to form steam within the cask cavity. The pressure release valve 30 maybe set at a pressure greater than atmospheric depending upon the temperature and pressure required to transfer the metal 84 in liquid state .stored in the tank 14 into the cask. For example, if

the metal coolant and shield substance is lead bismuth alloy, setting the pressure release valve at 35 psi. gage pressure will produce steam at 280 F.

After the steam has reached its maximum pressure and temperature within the cask, the valve 72 in the passage 64 is opened, steam at280 F. then passes into the tank .14 through the branched terminals 80 of the steam passage 64 and discharges into the plenum 48. Condensate 84 collects in the lower portion of the plenum 48 and is discharged through the port 52 and check valve 54. The hot steam passing through the tank melts the low melting temperature metal 84, which for lead bismuth re 7 quires only 257 F.

Compressed air is then introduced into the tank 14 through the port 56 which forces the molten metal 84 through the conduit 66, the open valve 72a, and into the cask. Once in the cask, the heat evolved by the fuel rods keeps the metal 84 in a molten state without danger of boiling the coolant away. For instance, lead bismuth alloy boils at 3,038 F. at atmospheric pressure, and it boils at higher temperatures in pressures greater than atmospheric; the extreme upper safe temperature at which the cask may be shipped is 800 F. However, cooling by conduction of heat through the cask walls in an ambient temperature of 100 F. would permit the temperature of the contents of the cask to rise to about A, 500 F. at equilibrium.

Removing the fuel rods at the destination of the ship- 'ment is accomplished by reversing the conditions of flow .of the liquid metal 84 in the conduit 66. Water is introduced into the cask through the indirect passage 34. The valve 72 in the steam jacket or steam passage 64 is closed. Pressure then increases due to the heating and expansion of the steam in the cask above the, liquid metal 84' as is shown in FIGURE 4. The liquid metal is forced through the conduit 66, the open valve 72a, and then back into the tank 14. Pressure within the tank may be reduced by opening valves 58 and 60 exterior of the port 56. Once the liquid metal is removed from the cask, the pressure in the cask is reduced to atmospheric by opening the valve 30. The lid 24 may then safely be removed and the fuel rod assemblies lifted out of the cask. At that time the cask is ready to receive another charge of radioactive material.

, The cask 10 and storage tank 14 are conveniently carried on a specially adapted railway car 12. The car 12 has a car bed a portion of which, 92, has been lowered to accommodate the height of the cask 10, which must be carried in a vertical position at all times. Frame members 94, 96 hold the cask securely in place on the car bed 92. i The storage tank 14 is positioned adjacent the cask and is held in place by frame members 98 and 100.. i

The foregoing specification, specific examples and descriptions of my invention and the methods of utilizing it are intended as illustrative of the invention, the scope of which is limited only by the following'claims.

My invention is hereby claimed as follows:

1. An apparatus for transporting and storing exothermal radioactive material comprising an elongated vertical pressure retaining cask, a vertical storage tank, a quantity of low melting point metal contained with the cask and tank, and a larger and a smaller pipe mounted coaxially one about the other, each pipe separately connecting the interior of the cask with the interior of the tank, the larger pipe terminating within the cask in the upper portion thereof, the smaller pipe passing through the length of the interior of the cask and terminating in the lower portion thereof, and bothpipes passing the length of the interior of' the tank, the smaller pipe terminating in the lower portion thereof and the larger pipe terminating exteriorly of the tank after passing in a heat transfer relationship through the tank, whereby the metal in a moltenstate may be transferred under pressure from the tank to the cask and from the cask to the tank.

2. The apparatus of claim 1 wherein the low melting point metal is adapted to both conduct heat from the radioactive material and to attenuate nuclear radiation emanatingfrom the radioactive material. 3. The apparatus of claim 2 in combination with a support for the cask having a section of the support lower for receiving the cask, and a support frame adapted to,

hold the cask in a vertical position.

4. An apparatus for transporting exothermalradioactive material comprising an elongated vertical pressure retaining cask having a removable lid, a vertical storage tank, pressure release valves on the cask and the tank, a source of compressed air and means on the tank through which compressed air may be introduced into the tank, a quantity of lead bismuth alloy contained within the cask and the tank, a smaller pipe and a larger pipe mounted coaxially one about the other, each pipe respectively separately connecting the interior of the cask with the interior of the tank and the atmosphere exterior of the tank, the larger pipe terminating within the cask in the upper portion thereof, the smaller pipe passing through the length of the interior of the cask and terminating in the lower portion thereof, and both pipes passing the length of the interior of the tank, the smaller pipe terminating in the lower portion thereof and the larger pipe passing in heat transfer relation through the tank and terminating exteriorly of the tank, and a quantity of water contained within the interior of the cask and the tank whereby exothermal radioactive material placed in the cask vaporizes the water into pressurized steam which is conducted through the larger pipe and hence through "the tank where it melts the lead bismuth alloy, commaterial placed in the cask to vaporize the water into pressurized steam which is conducted through the first mentioned means through said tank where it melts the metal and whereby the metal in a molten state may be transferred under pressure from the tank to the cask.

6. An apparatus for transporting exothermal radioactive material comprising a pressure retaining cask, a stor- Cu 8. An apparatus for transporting exothermal radioactive material comprising a pressure retaining cask, a storage tank,'a quantity of low melting point metal coolant age tank, a low-melting temperature metal Within the tank, means interconnecting the cask and tank, a quantity of water contained Within the interiorof the cask and tank, means utilizing heat from exothermal radioactive material placed in the cask to vaporize the water into pressurized steam which is conducted through the first mentioned means through said tank where it melts the metal and means for selectively transferring the metal in a molten state under pressure from the tank to the cask and from the cask to the tank.

7; An apparatus for transporting exothe'r'mal radioactive material comprising a pressure retaining cask, a storage tank, a low melting point metal within said tank, means interconnecting the cask and tank, a quantity of water within the interior of the cask and tank, means utilizing heat from exothermal radioactive material placed within the cask to vaporize the water into pressurized steam which is conducted through said interconnecting means through said tank to pressurize the cask and tank and melt the metal and transfer the molten metal under pressure from the tank to the cask and from the cask to the tank.

Within the tankyalarger: and, a smaller pipe coaxially mounted one about the other, each pipe separately connecting the interior of the cask with the interior of the tank, a quantity of water contained within the interior of the cask and tank, means utilizing heat from exothermal radioactive material placed in the cask to vaporize the water into pressurized steam which is conducted through the larger pipe and through the tank where it melts the metal coolant whereby to selectively transfer the metal in a liquid state between the tank and the cask and between the cask and the tank.

References Cited in the file of this patent UNITED STATES PATENTS.

Claims (1)

1. 5. AN APPARATUS FOR TRANSPORTING EXOTHERMAL RADIOACTIVE MATERIAL COMPRISING A PRESSURE RETAINING CASK, A STORAGE TANK, A LOW MELTING TEMPERATURE METAL WITH THE TANK, MEANS INTERCONNECTING THE CASK AND TANK, A QUANTITY OF WATER CONTAINED WITHIN THE INTERIOR OF THE CASK AND TANK, MEANS UTILIZING HEAT FROM EXOTHERMAL RADIOACTIVE MATERIAL PLACED IN THE CASK TO VAPORIZE THE WATER INTO PRESSURIZED STEAM WHCH IS CONDUCTED THROUGH THE FIRST

Images