US2868992A - Reactor viewing apparatus - Google Patents

Description

Jan. 13, 1959 G; s. MQNK 2,868,992

REAcToR VIEWING APPARATUS Filed Feb. 12. 1945 2 sheets-sheet 2 f A SJ/"Z Y,

REACTOR VIEWNG APPARATUS George S. Monk, Chicago, Ill., assignor to the United States of America as represented by the United States Atomic Energy Commission Application February 12, 1945, Serial No. 577,381 9 Claims. (Cl. Z50-108) My invention relates to an optical system that is suitable for viewing objects that are in a region of relatively high radioactivity or high neutron activity. More specifically, it has reference to an optical system that will absorb penetrating radiations, such as neutrons and gamma rays, emitted by radioactive objects viewed or by radioactive objects in the vicinity of the material or objects viewed, thereby protecting personnel from the harmful biological effects of such penetrating radiations.

The present invention is particularly valuable when used in a neutronic reactor because of the very high neutron densities present and also because of the high degree of radioactivity existing inside the reactor. In order to give a clear explanation of the invention, therefore, the subject matter is illustrated in conjunction with an air cooled neutronic reactor. Specific and more complete details of such a reactor are set forth in a copending application of Gale J. Young, Serial No. 552,730, tiled September 5, 1944, now Patent No. 2,774,730, granted December 18, 1956. A somewhat briefer description of the same reactor is believed necessary herein and is therefore presented hereinafter.

In the past it has been proposed to view the interior of a neutronic reactor by means of an air path extending through the shield that surrounds such neutronic reactor so as to place the operator at a considerable distance from radioactive objects interiorly of the neutronic reactor,

and thus provide a certain degree of protection against such radiations. 'Such an arrangement has several disadvantages, one being that the long optical path through the shield considerably reduces the field of View interiorly of the neutronic reactor, and another being that only a relatively small image of the radioactive objects appears. Furthermore, such an optical path of air is relatively transparent to neutrons and gamma rays, therefore exposing the operator to the hazards of these penetrating radiations.

vAn object of my invention is to provide an optical path permitting visual use thereof when one end of said path is subjected to radiation from radioactive materials.

A further object of my invention is to provide an optical system for viewing radioactive objects, such as those within a neutronic reactor, which optical system is made up of materials that remain substantially free of coloration after continued exposure to such radioactive objects.

A more specific object of my invention is to provide an optical system including a liquid-containing, negative lens that makes possible a large field of view, and that absorbs penetrating radiations, thus making it suitable for viewing the interior parts of a neutronic reactor, such as the uranium bodies, or to inspect other parts comprising the reactor or the loading mechanism for inserting the uranium bodies therein for possible damage `or faulty operation. I

Another object of my invention is to provide for use with an optical system for viewing the interior of a 2,868,992 Patented Jan. 13,' 1959 neutronic reactor, a lamp for illuminating such interior, having a reflector of a material that is resistant to the radiations in the reactor.

Other objects and advantages will become more apparent from the following description taken together with the drawings, wherein:

Fig. 1 is a vertical, longitudinal sectional view of a typical air-cooled neutronic reactor including a plurality of optical viewers, embodying the teachings of my invention, that may be used to` view the interior of the reactor, portions of the reactor being shown in elevation;

Fig. 2 s a partial sectional and partial elevational view taken along line 2 2 of Fig. 1;

Fig. 3 is an enlarged longitudinal sectional view partly in elevation of one of the optical viewers shown in Fig. 1;

Fig. 4 is an end view of the optical viewer taken along line 9-9 of Fig.V 3;

Fig. 5 is an enlarged longitudinal sectional View of the lamp assembly shown in Fig. 1 and used for illuminating the interior of the neutronic reactor; and

Fig. 6 is an end view of the lamp taken along line 11-11 of Fig. 5.

The present invention is particularly,`but not exclusively, useful for viewing the interior. of a neutronic reactor as alpha, beta and gamma radiations, as well as fast and slow neutrons are released at high intensity during operation thereof.

Referring to the drawings, I have chosen to illustrate my invention by reference to a graphite-uranium reactor, sometimes known as a pile.

Such a reactor broadly comprises a mass of graphite blocks closely piled or stacked into a cube 10 as shown in Fig. l. This graphite cube may be, for example, 24 feet on a side and rest on a concrete foundation 11. The graphite cube 10 s pierced with horizontal air channels 12, of square cross section, with one of the diagonals vertical. The channels may be readily made by grooving adjacent blocks. The `channels are 1.75 inches on a side and extend completely through the reactor, from an inlet face 14 to an outlet face 15. About 40G-800 or more channels may be provided, and as will be later brought out, any unused channels can be plugged. Only a few of the channels are sake of clarity.

Adjacent the inlet face 14 of the cube, the foundation is continued downwardly to form the floor of 4an inlet air duct 16 extending outwardly. The inlet air duct 16 is completed by concrete side walls 17 and top 19.

At some distance away from the graphite -cube 10 the inlet duct is turned upwardly to terminate in an air filter 20, relatively close to the surface of the ground. A fan or blower 21, here illustrated as electrically'driven, is installed on the floor of the inlet duct just below the air filter, access to the fan being conveniently obtained through duct door 22, behind the fan.

The concrete top 19 of the inlet air duct is continued upwardly as an inlet end shield 24, positioned parallel to but spaced away from inlet face 14 of the cube 10 to form an inlet chamber 25 communicating with the air channels 12.

Above the inlet chamber 25 and the cube 10 theV concrete is continued horizontally to form a top shicld26, and side shield 28 is built up from the foundation 11 to enclose cube 10. Shields 26 vand 28 closely approach the top and side faces of the cube, to minimize air flow around the outside of the cube. A small amount of air circulation, however, may be desirable over the top and side faces to cool these faces. p

At the outlet face 15, an outlet end shield 30 of concrete is provided. vEnd shield 30 is parallel to and spaced shown in the drawing for 2,868,992 y ,f c

'duct system operating by virtue of pressure provided by fan 2`1`to conduct air from close to ground level through channels Y12 into the stack and 'then into the atmosphere .well above ground level at the top of the stack. The concrete shields may be from tive to ten feet thick in accordance with nthe maximum desired operating power of the reactor and serve as shields -to Vreduce escape of lneutrons and .gamma radiation.

As aneutronic reaction will take -place when uranium bodies are properly spaced in a moderator rnass of a certain finite size, the above described device can be made chain reacting by placing uranium bodies in the horizontal channels in lsuch a manner and in such an amount thata neutron reproduction ratio of slightly over unity is obtained, `exclusive of all neutron losses within the reactor ,and from the exterior of the reactor., This reproduction ratio may be dened as the ratio of the number of Aneutrons gained by fission to the total number of neutrons'lost by absorption in the uranium, absorption in the 'moderaten absorption by impurities in the reactor and by leakage from the reactor for a reactor of nite size.

Using the graphite mass as the moderator to slow fast neutrons yto energies Where they again are able to create ssion 92235, the `device Will have a reproduction ratio of unity when approximately 360 of the Vchannels 12 in the graphite cube are each loaded with 68 aluminum jacketed uranium slugs lying end to end, with a channel spacing of 8 inches measured center to center, and with the loaded channels roughly forming a cylinder. Both graphite and uranium should be of highest possible purity.

However, more than a unity reproduction ratio is required, as when the reproduction ratio is exactly unity no rise in neutron density will ocur. Under such conditions-the device will not develop high neutron densities or power in the form of heat. By loading additional channels, i. e., making the active portion greater than critical size, however, the reproduction ratio within the Vreactor can be ,brought above unity in order'that a rise in density can occur. Then this excess neutron reproduction can be absorbed by neutron absorbing materials deliberately inserted into the reactor in order to hold the reproduction ratio at an average value of unity after a desired power output has been obtained, as a result of the initial rise in density.

Consequently, in accordance Vwith the amount of excess reproduction ratio desired, from 450 to 600 channels may be loaded with uranium slugs. Most of the channels not loaded with uranium may be closed by inserting plugs, preferably of graphite, in suchV channels in order to conserve air; Some of the channels, however, in the peripheral portions of the cube may be left open for cooling of the graphite in those portions.

VEach uranium metal slug is 1.1 inches in diameter and 4 inches long covered with an'aluminum jacket approxi- `mately mils thick in good heat conductive relation to the uranium. The slugs weigh about 21/2 pounds each.

`The reactor is controlled by a conventional control rod. such as is shown in the aforementioned patent application.

A stable temperature is obtained in the device of the present invention by passing atmospheric air through the reactor, and in the specific example shown and described, the air is passed through the graphite channels andl directly in contact with the aluminum jackets of the slugs.

`Under these circumstances the reactor `can be operated Vcontinued operation of the pile.

continuously at 250 kilowatts electrical equivalent of heat by -passing 32,000 cubicfeet per minute through the reactor with a maximum temperature rise of the slugs to about 100 C., and at 500 kilowatts continuously with about 50,000 cubic feet per minute of air with a maximum metal temperature of 200 C. The output of the reactor can be stabilized at still higher powers by the use of larger fans if desired.

The means for loading the reactor is indicated generally by the reference character 45. For a complete description thereof reference is made to the aforementioned patent applicationfSerial No. 552,730, now Patent No. 2,774,730.

ln the course of a reloading operation any number of faulty operations may occur that may be detrimental to For example, large pieces of graphite might become loose from outlet face 1S and clog up the outlet pipe 91. Or perhaps jamming of `the slugs may occur in one of the channels 12. Or perhaps 'by accident one or more of the centrally disposed channels 12 lWill-not contain uranium slugs or a sutiicient number vof uranium slugs for Veicient operation. Another Vpossibility is that of an observable rupturing of one or more aluminum jackets surrounding the uranium slugs 36, which if not replaced, may cause abnormal radioactivity of the air used as a coolant resulting in pollution ofthe air in the territory surrounding the neutronic reactor even though a stack is used. Biologically this would be a menace to the health of the people in such territory.

All of the above named faults and many others may be readily detected by a plurality of viewing tubes, T1, T2, T3, T4, etc., constructed in accordance with the teachings of my invention and so positioned through the shields of the neutronic reactor as to make it possible to observe any particular internal portion of the reactor desired. For example, referring to Fig. l, viewing tube T1 with its associated lamp L1, may be used to observe the condition of outlet pipe 91, possible clogging of thev interior of the pipe, and to observe the wear and tear of pad plate whereas viewing tubes T2, T 3, T4, etc. may be used to observe different sections of outlet face 15 to determine possible jamming during unloading or for locating punctures or bad leaks in the aluminum jackets surrounding the uranium slugs, or to observe whether sutlicient slugs are contained in channels 12. Similarly, other interior portions of the reactor having parts that may become faulty after continued operation may be similarly observed with properly installed viewers. f

kReferring to Figs. 3 and 4 numeral 111 denotes an optical viewing tube previously generally referred to as T2,

.made of steel or other suitable material that is surrounded .tube 111 and -that extend through the depth of concrete shield 30. Tube 111 is lled with a transparent liquid V113 that absorbs penetrating radiations, such as gamma rays and particularly neutrons, that may be emitted by the radioactive objects viewed. Such liquid 113 may be introduced through an inlet port 114 and drained from tube 111 through an outlet port 115, as desired. Liquid 113 may comprise water or other liquid solution having a slightly higher index of refraction than water, such as, for example, a lead nitrate solution, which will give a larger angle of view and at the same time will allow the use of a shorter tube 111. Another outstanding advantage of using a lead nitrate solution or other solution having a relatively high density, more specifically, Vcontaining ions of an element having a relatively high atomic number, is that such liquids have a greater absorption for gamma rays than ordinary water and therefore offer better shielding from such radiations. The hydrogen content of the water effectively absorbs neutrons entering the tube. i

In order to minimize the possibility of coloration of liquid 113 as the result of continued exposure to penetrating radiations, the interior surface of tube 111 is preferably coated with a material to protect it against corrosion. For example, if tube 111 is made of steel it may be coated interiorly with pure block tin to prevent oxidation of the steel by the oxygen contained in water, and the tin, in turn, may be waxed to make the steel even more resistant to chemical change. Furthermore, an inhibitor, such as, for example, copper sulphate, may be :added to liquid 113 to increase its resistance to coloration.

The optical viewing tube 111 as a whole is a negative lens comprising liquid 113 and a curved interior window 116. Window 116 is preferably made of a transparent plastic'material, such as, for example, Lucite which is a solid polymer of methyl methacrylate, polished styrene, cyclohexyl methacrylate, or the like, as such materials are not as subject to coloration as glass is when subjected Vto continued exposure to penetrating radiations. Generally speaking curved window 116 is preferably made of a material that does not contain metallic elements, inasmuch as gamma radiation causes molecular structural changes, particularly in optical glasses resulting in absorption of visible light. Apparently, there is a looser bond of the electrons forming metallic molecules than those forming hydro-carbon molecules, and consequently, in the former, there is a greater likelihood of releasing electrons as the result of irradiation by penetrating rays. The electrons so released absorb visible light and cause coloration. On the other hand, plastic materials, particularly the transparent hydro-carbons, are generally free from metals that tend to induce coloration such as, for example, silicon and iron. While gamma rays may effect small changes in the molecular structure of plastics, causing release of electrons, there is apparently a much firmer bond tending to urge return of such released electrons to their original position in the molecular structure rather than to allow the electrons to remain free and absorb visible light and thus cause coloration. For this reason, plastics are particularly suitable since they are resistant to coloration even after a considerable time of exposure to penetrating rays. It should be noted that certain glasses, other than plastics, may also be suitable, such as, for example, Extra Dense Flint Glass EDFl having an index of refraction (Nd) of 1.649.

Curved window 116 is attached to the end of tube 111 by means of gaskets 117 that are clamped between a pair of clamps 11S. Likewise, a flat glass plate 119 is attached to the other end of tube 111 by means of gaskets 120 clamped between clamps 121 thus completing the negative lens. Glass plate 119 serves as a window adjacent which an observer positions his eye for viewing. If desired, a lens may be substituted for glass plate 119 to control the field of view as desired.

While the structure in Figs. 3 and 4 may be of any desired dimension, a typical set of dimensions will be given to more clearly illustrate my optical system. If tube 111 is 4 feet long, 18 inches in diameter, and iillled with water, and if curved window 116 has a radius of curvature of 20 inches, then the angle of view at the objective portion, that is, adjacent window 116, is approximately 70 degrees. By using lead nitrate or other liquids having a higher index ofrefraction, the angle of View will be slightly greater. In order to give substantially equal protection against gamma rays, the water tube should he about twice as long as the thickness of the concrete shield wall. However, by using liquid solutions of higher atomic weight than water, then the liquid containing tube may approach the same length as the thickness of the shield as shown in Fig. 3.

Inasmuch as the interior of the neutronic reactor is generally dark, it is advisable to provide a lamp therein Y 6 for illuminating at least that portion of the interior that is being viewed. Such lamps are preferably removable, as the lamp envelopes become colored as a result of radiation and therefore may require replacing.

Referring to Figs. 5 and 6, numeral 122 denotes a lamp such as, for example, an automobile headlight bulb having a reflector 123 preferably made of Stellite or other material that can be highly polished and that is highly resistant to corrosion so as to withstand corrosive gases, such as nitrous oxide or ozone that may be accidentally released within the reacter and which will not break down under continued radiation. A lead-in 124 of lead or other material that absorbs penetrating radiations is extended through a concrete Wall portion 30, and has a.

tortuous longitudinal path 125 extending therethrough for accommodating the electrical lead-in conductor 126 for energizing lamp 122. The reason for the tortuous path is to substantially prevent escape of gamma rays through the path 125, inasmuch as gamma rays primarily radiate along straight paths. The lamps 122 are then disposed in the shields to illuminate the elds of view of the viewers.

Thus it will be seen that I have provided an efficient optical system that is suitable for viewing irradiated objects, such as, for example, objects interiorly of a neutronic reactor, which optical system includes materials that absorb penetrating radiations otherwise harmful to the operator and that do not become appreciably colored as a result of extended exposure to penetrating radiations. Furthermore, I have provided in such an optical system a negative lens giving a wide angle of view.

While the theory set forth herein is based on the best presently known experimental evidence, I do not wish to be bound thereby, as additional experimental data later discovered may modify the theory disclosed. Any such modifi-cation of theory, however, will in no way affect the results to be obtained in the practice of the invention herein described and claimed.

It should be noted that equivalent structures and materials within the scope of my invention may be readily suggested to others skilled in the art after having had the benefit of the teachings of the present specication. For example, while I have shown an optical system with relation to Ian aircooled neutronic reactor, such optical system may be used, instead, in a liquid cooled neutronic reactor of entirely different construction than that shown in Fig. l. In fact, my optical system is useful for viewing radioactive objects wherever it is desired to interpose a shield between the operator and such objects.

Also instead of making tube 111 of steel it may be made of or may be coated interiorly with a plastic material. Moreover instead of using a liquid 113 the entire negative lens 113-116 may be made of one large mass of plastic material inasmuch as plastic materials are also highly resistant to chemical change. In this case, the hydrogen content of the plastic constitutes the neutron absorber. If desired, additional lenses (not shown) which are not subject to coloration may be placed between window 116 and the interior of the reactor. Likewise, other liquids than those described may be used for absorbing penetrating radiations, and other lens materials having the properties set forth may be used. For this reason, the invention should not be restricted except insofar as set forth in the following claims.

I claim:

l. A radiation absorbing optical system for viewing radioactive objects comprising a viewing tube flanged at each end, a lens at one anged end of said tube, said lens being made of a polymerized organic material selected from the group consisting of methyl methacrylate, styrene, cyclohexyl methacrylate and mixtures thereof, means for maintaining said lens in liquid-tight contact with said flanged end of the tube, a radiation absorbent light transparent solid member at the opposite lianged end of said tube, meansfor maintaining said transparent member in liquid-tight contact with said opposite anged 7 end, oi the tube, a transparent aqueous liquid within said tube, @Shield Surrounding SaidV tube between Said flanges, saidshield having outside` dimensions at least equal to those of the anges andl comprising a gamma ray absorbing material.`

2. The `optical system of claim 1 wherein the transparent solid member comprises an organic plastic material.

3. The optical system of claim 1 wherein the polymerized organic material is a methyl methacrylate solid polymer. n

' 4. The optical system of claim 1 wherein the lens is a negative lens, the transparent solid member is an organic plastic material, and the transparent aqueous liquid is Water.

5. The optical system of claim 1 wherein the aqueous transparent liquid contains copper sulfate.

6. The optical system of claim 1 wherein the aqueous transparent liquid contains lead nitrate.

7. The `optical system of claim 1 wherein the aqueous transparent liquid contains lead nitrate and the transparent solid member comprises an organic plastic.

8. The optical system of claim 1 wherein said tube is coated interiorly withy a corrosion-resistant material.

9. The optical system of claim 1 wherein said lens isA a negative lens, and the franispare,ut aqueous lisuid. contains ions of an element having a relativelyl higu atomic number...

Referenees Cited in the tile of this patent UNITED STATES PATENTS Re. 13,849 Simpson Dec. 15, 1,914, 57,602 Warden Aug. 28, 1866 183,443 Alt T Oct. 17, 1876 1,269,422 Gordon, June l1, 19,18 1,469,973 Goettert Ian. 19, 1926 1,880,806 Ciofli V Oct. 4, 1932 2,193,742 ROhmGt'fll Maf 12., 1940 2,206,634 Fermil et al. I uly 2, 1940 2.297.240 Neumann Sept. 29. 19.42 2,312,542 Goodman 1- Mar. 2,1943 214051301 Grey r..1.r f 6J 19.46 2,423,492 Fairbank T V T- July 8, 19,47 r 2,708,656 Fermi et al. 4 v- May 17, 19,55 FOREIGN PATENTS 2,193 Great Britain of 185,9 6,194 Great Britain V- k of 1901 114,150 Australia May 2, 17940 233,011 Switzerland n Oct. 2, 1944

Claims (1)

1. A RADIATION ABSORBING OPTICAL SYSTEM FOR VIEWING RADIOACTIVE OBJECTS COMPRISING A VIEWING TUBE FLANGED AT EACH END, A LENS AT ONE FLANGED END OF SAID TUBE, SAID LENS BEING MADE OF A POLYMERIZED ORGANIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF METHYL METHACRYLATE, STYRENE, CYCLOHEXYL METHACRYLATE AND MIXTURES THEREOF, MEANS FOR MAINTAINING SAID LENS IN LIQUID-TIGHT CONTACT WITH SAID FLANGED END OF THE TUBE, A RADIATION ABSORBENT LIGHT TRANSPARENT SOLID MEMBER AT THE OPPOSITE FLANGED END OF SAID TUBE, MEANS FOR MAINTAINING SAID TRANSPARENT

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