radiation for industrial applications

8/4/2019 Radiation for Industrial Applications

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Th is is No .3 in the series: W hat Can Radioisotopes Do for Man?The Applicationof Radiation Technologyin Industrial ProcessesCurrent and Future Perspectivesby Joseph Silverman, Laboratory for Radiation and Polymer Science, University of Mary land, U SA.*The mention of specific companies or of their products or brand-names does not imply anyendorsement or recommendation on behalf of the International Atomic Energy Agency.

The developme nt of nuclear power h as been responsible for man y by-products, amo ng themradioactive fission products. In the late 1940's and early 1950's considerable efforts weremade to develop industrial processes that could make use of the fission products in largequantities. Although some fission products are uti lized today, the scale does not approachthe quantit ies that will be produced in a nuclear economy. The efforts have not been afailure, however, and the research to develop industrial processes has created markets, notfor the fission products a s one had hoped, but for the radioisotope Cobalt-60 prod ucedby neutron capture in a nuclear reactor, and for accelerators mach ines that produ ceradiation in a controlled manner. Success in finding uses for the major fission productsmay yet come, as research continues in the radiation chem istry a nd radiation biologyfields.Radiation processing is now a vigorously exp anding area because of sharp increases in thereliabil ity of electron beam generators, sharp drops in the unit cost of both electron beampower and electron beam energy, significant advances in radiation chemistry leading tolower dose requirements a nd increased engineering knowledge and practical exp erience.The principal reasons for its bright future promise arise from expectations of furthersharp decreases in the unit cos t of electron b eam energy and from the recent successfuladoption of radiation on a large scale for cross linking of telephone wire insulation in theUnited States.CURRENT STATUSAt this tim e there are more than a hundred electron beam generators and abou t th irt yCob alt-60 systems in routine industrial use. The m arket value of products treated orproduced by ionizing rad iation m ethods is well above $ 200 00 0 000 per annum . Let usgo dow n the l ist b r ief ly:

* Th is article is taken fro m an address delivered to the No rdic Society for Rad iation Research andRadiation Technology in Helsinki, Finland.15


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RADIATION STERILIZATION OF DISPOSABLE BIOLOGICAL AND MEDICALSUPPLIES - This is the oldest indu strial app licatio n. It was first successfully applied in1956 when machines cost $ 25 000 per kW and the cost of electron beam energy ran as highas $ 50 per kWh. A good deal of the high unit energy cost resulted fro m the low reliab ilityof the 3 MeW van de Graaff and the 4 MeV linear accelerator first used in industrial practice.Despite the very high cost of radiation energy, however, the products provided enoughadvantages in packaging and customer convenience to permit them to capture 80% of themarket wi th a high priced produc t. Eth icon , the first comm erical organization in this fieldin the U.S., and its parent company Johnson & Johnson, soon shifted to gamma sources inorder to em ploy a simpler, more reliable radiation technology. Since then, the develop-ments in linac radia tion ster ilization methods by Ris


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An other material of some interest is prevulcanized natural rubber latex. French scientistshave been wo rkin g on this process over the past ten years, and have developed a p rod uc tcalled Precurtex. It is produced by irra dia tion o f the latex wi th a small dose of gammasor electrons. The final forms can be manu factured in existing equipm ent by e vaporation ofthe serum at 70C. The con ven tional process requires higher temperatures and the ad ditio nof vulcanizing and accelerating agents.

DU RA BL E PRESS FABRICS - Beginning production in 1966 with co tton fabrics, Deering-Milliken in the United States is now processing over 50 000 000 meters per year of VISA, apolyester-cotton fabric by a radiation-induce d grafting me thod . The produ ct is a durablepress fab ric w ith exce llent soil release prop erties. It is sold prin cipally t o man ufacturers ofun iform s, overalls, etc. whose customers use comme rcial laundry services (hotels, garages,etc.). The produc t is made by padding the fabric w ith a viny l m onomer c ontaining ame thylo l group , and subjecting the wetted fab ric to electron irradiatio n. It is then paddedwith the soil release agent which is probably a prepolymer composed of acrylic and meth-acrylic acid. There are sufficient numbers of active grafting sites remaining from the irrad-iation so tha t the prepolym er is chemically "ta ck e d" onto the fabric . The fabric is sent to themanufacturer who forms it in to a garment. The finished garment receives its permanentpress characteristics after it is pressed at 165C|for tw elve m inutes. The condensationreaction between the me thylo l group and the fiber produces the necessary crosslinks. Anadd itional bene fit is tha t the waste effluents fr om the p lant have been reduced since nozinc chloride catalyzed treatmen t is required as in the co nventional durable pressprocesses.

RA DIA TIO N-C UR ED COA TINGS - Almost every dashboard made by Ford MotorCompany in the United States passes through an electrostatic spray coating machine and anelectron beam curing . Other autom obile parts also go through on a pro du ction basis andmore are expected to fo llo w . Despite the Fo rd success in producing an excellent and inex-pensive substitute for the corresponding metal parts, the Ford experience has not beensuccessfully followed by others.There has been a discernible change since 1973, however. A plant in Switzerland and a plantin the U nited States wi th a capacity o f almost 10 000 0 00 square meters per year forcoated woo d panels are being planned and two add itional plants in Europe to produceradiation-cured coatings were being discussed in 1973.The upsurge in interest seems to arise from pollution problems associated with heat-curedcoatings. Ultraviolet-cured coatings are proving to be a formida ble co mp etitor f or t h in ,clear coatings. But if the coating m ust be heavily pigmented or thic k, then electrons mayhave a decisive advantage.

WO OD-PLA STIC COMPOSITES - For all practical purposes, there is on ly one produce r,Arco C hemical in the U nited States, and on ly one prod uct, parquet floo ring . Tha t companyis producing some 300 000 square meters per y[ear and adding to its 6 0C o capac ity. ThusArco Chem ical is succeeding on a modest and expand ing scale in the o nly gamma process ofsignificance which is not biological in nature, but there is little evidence of other industrialinterest.17


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RA DIA TIO N DE GR AD AT ION - Ab out f ive years ago, Union Carbide Corporation decidedto m arket polye thylene o xide for a wide range of applications, whic h, in turn, required awide spectrum of m olecular weights. Rather than adjust processing con ditions to prov idethe molecular we ight requirements of each application , UCC decided to produce a highmolecular weight product under constant plant conditions and to submit the product to aninexpensive degradation to meet individua l customer needs. A gamma-induced chainreaction in the presence of oxygen was to serve as the degradation step. A special irrad iationfac ility was designed and con struction initiate d, but the plant had not gone into operationby 1973 , as the ma rket had not y et developed.Rad iation degradation is being turn ed to advantage by Co lumb ia Research Co rpo ratio n, avendor of electron beam services. They are degrading waste polytetrafluoroethylene (PTFE)molding powder by elec tron-irradiation in air. The produ ct is then used in spray lubricants.The ir business in this area is surprisingly good ; almost every producer of PTFE passes itsscrap thro ug h Colum bia's beam. Nevertheless this is still a low-volum e app licatio n.More imp ortan t is the p ossibil ity th at the UCC approach of manufacture and degradationmay be applied successfully to the technology of polypropylene, which has a large salesvolum e. I believe that the approach deserves detailed cons ideration wh ich i t has no t ye treceived.There is another radiation degradation project in progress which concerns the electronirrad iation of w oo d chips prior to storage and subsequent conversion to pu lp. It is well-kno wn that ionizing rad iation k il ls insects, fungi and bacteria, and also tha t ionizingradiation degrades woo d. Thus irradiation of wo od chips should delay their spoilage anddecrease the energy required to convert them into pu lp. When the cost of the energyrequired to obtain these added advantages falls below the financial gains to be derived fromthem, radiation becomes a profitab le and p ractical to ol at the p ulp mil l . RadiationDevelopm ent Co., L td . of Canada has installed tw o accelerator systems at the Georgia-PacificPlyw ood m ill near Alba ny , Oregon, and processed more than 10% of the plant's prod uctio n.For the present Georgia-Pacific has rejected the RDC L process as effects ob tained in thelaboratory have not been obtained in the field in a reproducible way. If this performancecan be improved about 2 000 pulp mills throughout the world become potential customersfor what could be the biggest radiation application by any standard of measurement(production volume, ki lowatts, and product value).CH EM ICA L SYN THES IS - This has been the source of considerable disappointm ent tothose who fol low developments in radiation processing. Aside fro m the prod uctio n of ab out1 000 tons per annum of e thyl bromide by Dow Chemical Company, none of the proposedrad iation -initiate d chemical syntheses have been practiced on an indus trial scale. One recentdevelopm ent suggests a favourable tu rn of events. A plan t is now under co ns truc tion inJapan to produce a prepolymer which will be a principal component of a paint formulation.(This is not to be confused with the electron beam curing of pain t). The paint com ponen tis produced by a reaction initiated by electron irradiation ; the paints based on it can becured by thermal, UV, or irradiation methods.

These pieces of wood are processed by irradiation in the Centre d'Application des Ravonnementsionisants CAP RI in France. P hoto : Pierre Jahan18


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Composesboi$-pbstiques


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MIS CE LLA NE OU S - Most of the applications described involve relatively low-volume pro-duction. There are several other app lications wh ich are conducted at an even lower scale.These include battery separators produced by radiation-induced grafting, a laminate ofmetal foi l and a fi l m composed of p olyethylene and an acrylic a cid graft, radiation cross-linked fasterners which expand on heating, irradiated quartz and pearls for jewelry, and soon. These represent some success in ing enu ity and ma rketing, bu t none of them is likely toinfluence the f ie ld.WESTERN ELECTRIC Looking back at the list of products and processes, almost all ofthe applications in actual indus trial practice are relatively old and we llkno wn . Un til no w,one might have concluded th at new industrial applications wo uld develop rather slowly dueto the state of the art, the state of the economy, and the state of mind of industrial manage-men t. This conclusion n ow wo uld appear to be too pessimistic.The main reasons for this change can be found in the recent decisions and actions ofWestern Electric Co., the man ufacturing arm of the Am erican Telephone and Telegraph Co.In 1973 Western E lectric began the pro duc tion of telephone w ire wit h radiation-crosslinkedPVC insulation at the rate of 2.7 X 10

9meters per annum. Two additional productionlines have been ordered and will be installed to provide a production rate of 8 X 10 9 metersper year. The new p roduc t replaces an older one wh ich consisted of a copper w iresurrounded by PVC ins ulation, a fabric jack et, and a lacquer c oating. The new one has acopper wire surrounded by a PVC-TE GD MA * coating wh ich is crosslinked by electronirradiation. This gives it fine electric properties as well as high resistence to the heat of asoldering i ron, abrasion, solvents, and flames. The unirradiated form ula tion is extrude deasily and the omission o f the lacquer step reduces po llu tion problems . The produ ct isused in central telephone exchanges where a decrease of almost 70% in packed area isobtained. This saving alone wo uld jus tify the process. However, even wit ho ut it, theprocess is reported to have provided a savings of $ 4 000 000 in the firs t seven m onths

of its operation.The large-scale implementation of this radiation process by Western Electric demonstratesthat :1) there are electron beam generators which can operate with a level of reliabilitycomparable to tha t of plastics extruders;2) the radiation engineering practice associated with the routine use of the machine isfair ly well understood;3) the cost of electron beam energy is low;4) the radiation chemistry associated with the use of crosslinking agents provides majorreduc tions in the dose requirem ents. In ad dit ion , the crosslinking agent is responsiblefor some of the important mechanical properties of the product.The successful implementation of this process should encourage the management of otherindu strial com panies to treat radia tion processing as a reasonable alternative to com pe titivemethods when considerations o f cost are favourable. In the past, cost advantage based onthe assum ption that rad iation processing is a rou tine industrial opera tion has been anecessary but insufficient condition.

* Tetraethyleneglycol dimethacrylate20


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THE FUTUREIn add ition to the developments at Western Electric, there are two other phenomena w hichmay have a profou nd effect on the future of ra diation processing: the trend in costs andenvironmental problems. \The cost of electron beam generators is generally below $ 4 000 per kW and a futu re costof $ 2 00 0 is forseeable. One producer of machines claims electron energy can be produ cedat a cost of $ 0.25 per kW h; a second producer has estimated costs wi th curren t machinesas low as $ 0.20 per kW h. Bo th estimates were for high-powered machines with two -shiftope ration and a ten-year machine life. Cost estimates by suppliers of accelerators havealways been treated w ith suspicion. This conservative attitud e is usually jus tified bu timprovements in design and performance have been marching righ t behind the advancingclaims, and they may even be catching up .

ENVIRONMENTAL PROBLEMSA recent proposal in the U.S. to build a plant for the irradiation of dilute sewage sludgewith a dose of 0.1 Mrad to provide E. coli control equivalent to that obtained withch lorina tion, claimed that an irradiation cost of $ 0.10 per kWh of absorbed beam energycou ld be achieved. This proposal leads int o the:use of rad iation processing in solvingenvironme ntal problems . Tw o types of applications in this category have already beenbrought to a ttentio n: substi tut ion of a non-pol lut ing radiat ion process for a po l lut ingnon-radiation alterna tive; use of ion izing radiatijon to d estroy po llutants. The first isexe mp lified by the electron curing of paints as a substitute for therm al cu ring; thetreatment of sewage and industrial wastes is an example of the second.The use of radiation to trea t human wastes has a long bu t inglorious h istory. Much of thereported work is poorly done and some of the more extravagantclaimsare difficult toaccept. Suffice it to say, radiation w ill k il l m icr.oflora and even (with some dif fic ul ty )viruses, bu t it is diffic ul t t o learn wha t m inim um dose level is needed to pe rform sufficien tdamage to microscopic life to m ake the necessary engineering calculations. A pi lo t scaleplant fo r the irradiation of dilute sludge is now [under way near Mun ich, F.R.G.; hop efullysome useful data w ill be made av aila ble / j

IIThe irrad iation of plant efflue nt has been suggested to treat effluents fro m te xtile plants todestroy the dissolved dyes. Irrad iation renders the dyes colourless under special cond itionsof p H and oxida nt co nce ntration. The same is true fo r plan t effluents bearing traces ofphenol or cyanides. One of the m ore interesting applications proposed in recent years isthe irradiation of waste gases from power stations to convert gaseous SO 2 to an aerosol orH 2SO 4mis t wh ich wo uld be trapped in the precipitator. Preliminary results have beenvery encouraging. The work, now going on at the Takasaki Laboratory of the Japan AtomicEnergy Institute and performed in collaboration wit h the Ebara Ind ustrial Co., is the subjectof widespread interest.

* An Interna tional Symposium on "T he Use of HighrLevel Radiation in Waste Treatmen t Statusand Prospects" is being held in Mu nich 17-21 March 1J375.I 2 1


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Environmental considerations may turn out to be the dom inant factor in determining therole to be assumed by ioniz ing radiation in our industrialized w or ld . The energy requiredto cure coatings wit h electrons is 7% of tha t required wi th heat. The energy required t osterilize fo od w it h electrons or gammas is far less than th at req uired w ith heat. As thecom pe tition for clean fuels increases, the cost of energy may prove to be the d om inant cost.A detailed analysis of t ota l energy expenditures is needed to determine whe ther it w illbenefit our society to place strong emphasis on energy conservation by widespread sub-st itu tio n of electr on beam processes fo r the rmal processes. It is w it h such a challengethat I f inish.The futu re looks bright and rewarding. The present isn't too bad, either. It's about tim e.

The Oklo Phenomenonby Roger Naudet*

Subject of an Internat ional IAEA-Sy mpo sium from 23 to 27 June 1975During 19 72 , research workers of the French Commissariat a I 'Energie Ato miq ue madean astonishing discovery: fission chain reactions had been triggered spontan eously in thevery remote past within a uranium deposit in Gabon and parts of the deposit had behavedlike a mo dern nuclear reactor for hundreds of thousands of years. Subsequen t investigationsshowed that the reaction sites had remained in a remarkable state of preservation, so thatdetailed study was possible.The IAEA felt that the Oklo phenomenon would be an excellent subject for internationalco-operation in fundamental research and agreed to the suggestion of the Gabon Govern-ment and the French Commissariat a I 'Energie Atom ique th at a jointly organizedsymposium be held. The sym posium wil l take place at F ranceville, Gab on , fro m 2 3 to27 June 1975.It is a fam iliar fac t that , of the two principal isotopes of uraniu m, which are naturallyradioactive, 2 3 5 U has a shorter h alf-life than 2 3 8 U (7.1 X 10 8 years as against 4.5 1 X 10 9years). Consequently, the conce ntration of 2 3 S U in natural uranium is decreasingconstantly with time; in the very remote past it was much higher than it is now (3.65%tw o thousand m illio n years ago as against 0.72% now ).A "FO SS ILIZE D" NUCLEAR REACTORIt was therefore suggested some time ago that fission chain reactions might have beentriggered spontaneously w ith in uranium deposits in the very remote past, given theexistence of certain conditio ns: high concentrations of uran ium ; the absence of stronglyneutron-a bsorbing elem ents; and the presence of wa ter. It did no t seem ou t of the qu estion

Mr. Roger Naudet in the head of the project "Fran cev ille". He works in the Department ofReactor Physics and Applied Mathematics, C.E.N., Saclay.22

radiation for industrial applications

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