Smidt, D.

Sommer, W.

English

KITopen

Oktober 1965Forschungszentrum KartsNhe GmbHIn der Helmholtz-GernelnschaftHauptabteilung Bibliothek und MedienInstitut für ReaktorentwicklungApplication of the Vented Fuel Concept to aSodium Cooled Power Breeder with 1000 MWeD. Smidt, W. SommerKFK 399KERNFORSCHUNGSZENTRUM KARLSRUHEOctober 1965Institut für ReaktorentwicklungApplication of the Vented Fuel Concept to aSodium Cooled Power Breeder with 1000 MWebyD.Smidt and W.SommerKFK 399This paper has been prepared within the framework of the associationEURATOM Gesellschaft für Kernforschung mbH. in the field of fastbreeder development.Gesellschaft für Kernforschung mbH,KarlsruheConference on Safety, Fuels and Core Designin Large Fast Power ReactorsArgonne. IllinoisOctober 11-14. 1965Application of the Vented Fuel Concept to aSodium Cooled Power Breeder with 1000 MWebyD.Smidt and W.SommerInstitute far Reactor DevelopmentKernforschungszentrum Karlsruhe +)+) This paper has been prepared within the framework of the associationEURATOM - Gesellschaft für Kernforschung mbH. in the field of fastbreeder development.- 1 -The principle of venting the fission gas of a fast ceramic reactor toits coolant is wellknown for some years [1J ' [2] • There is an impres-sive number of advantages:1. No stress of the fuel cladding by fission gas pressure. This resultsin:a. Improved safety against canning ruptureb. Smaller wall thickness of cladding+)c. Less structural material in the core, i.e. higher breeding ratiod. No need for the use of exotic canning materials.2. More compact subassembly, since no fission gas plenum is necessary.This results in:a. Smaller pressure drop of coolant, smaller pumping power, smallerwall thickness of subassembly-boxesb. Smaller height of reactor vessel, shielding, refueling equipmentand air locks.3. No storage of high pressure radioactive gas. This results in:a. No sudden uncontrollable gas eruption during reactor operationin case of canning rupture or melt down. This is of special im-portance in connection with the positive void coefficient.b. No sudden uncontrollable gas eruption during the fuel handlingand fuel reprocessing.+) This might not be true for fast excursions with sudden fuelmelting and subsequent fission gas release from the oxide.-2-- 2 -On the other side we need some special equipment which adds to thecapital costs of the station.The following additional equipment 1s necessary:1. Special plugs for the fuel rods2. The gas purification plant with all equipment (blowers, coolingaggregates, heat exchangers etc.)3. Additional filtering equipment with high retention ability for halogenes4. Excessive control system for radioactivity5. Special flanges and gaskets for high leak tightness.The most important item is the purification plant for the cover gas.But it should be kept in mind that we by this also save some costs forfission gas treatment at the reprocessing plant.It 1s the purpose of this paper to give some answers to the followingquestions:1. fVI1at are the pr1ncipal design specifications for the gas purificationplant with respect to operation and safety of the reactor?2. What are the numerical results for a reference reactor?3. What 1s the economical balance of the cited advantages and disadvant-ages of the "vented-to-coolant" concept?We are aware of the fact that many groups are working on this subjectand probably have arrived at similar results. But very few of thesehave appeared in the literature so far. So this contribution particu-larly is meant to stimulate the discussion on this very interestingmatter.-3-- 3 -1. Specifications for the Gas-purification PlantFig. 1 shows the principal plant. Room I is the covergas inside thereactor vessel, room II the inside of the safety containment.A flow rate g of fission gas enters room I. vA and vEare the flowrates to and from the purification plant respectively, a leakage. .flow rate L goes from room I to room II, and flow rates VA and VEare to and from the outer atmosphere.With the respective activity concentrations cg ' cE' cA' cL' CE' CA(all in Curie/cm3 ) we get the following balance:(1 )(2)In general is cE o •VA cA + L cLFor L cL « g c the result isgg c(3) vAgLVA CAthe input of the purification plant.VA is normally given by the air exchange rate of the containment volume.CA is either given by the allowed activity level inside the building orby the allowed activity output at the stack.The leakage L, therefore. is the most important parameter for the sizeof the purification plant. There are several flanges for refuellingpurposes and control rod drives on the top of our proposed sodium cooledreactor.-4-- 4 -The problem is the definition of a feasible leak-tightness on atechnical item.The cover-gas is helium. The most extensive tests on this have beenmade in connection with the Dragon-project [3,4,5]. These resultshave been converted to the cover gas pressure of 1,2 ata of our reac-tor according to the Knudsen equation, where the leakage is proport-ional to the pressure difference.The result is1,5 • 10-12 atm. cm3sec cmor with U = 12 500 cm sealing length we getL =for the total reactor top.8 -8I, 7 · 10 atm cm3secAfter determination of g and cg the purification plant can be speci-fied.We feel it important to underline that these specifications are basedon operational safety and not on the analysis of any major accident.The results of an accident of the vented-to-coolant and the vented-to-reservoir plant are the same, since in this case the destructions ofa number of fuel cans in the latter is probable.2. Fission Gas Production and Numerical ResultsThe 1000 MWe reference reactor [6 Jproduces 0,775 cm3/sec of thegaseous fission products Bromium, Iodine, Xenon and Krypton or appro-ximately 1 cm3 per fuel rod and day. We assume that these stay insidethe fuel for a time t c = 5 days at the ambient pressure of 2 ata.If it is possible to maintain higher gas pressures inside the rodthe retention time would rise proportionally, but it is extremely'. -5-- 5 -diffieult to build up any overpressure at sueh a low flow rate.During a time tBthe gases pass the axial blanket. tBis a funct10nof pressure. temperature and the free cross seetion.Taking into aeeount the produetion rate [7J of the different isotopesprodueed directly by fission and radioaetive deeay of their parents.in the eore zone and using the results of Burris and Dillon [8] theaetivity (Curie/em3 ) leaving the fuel rods can be calculated.For the burnup of 100 000 MWd/t release fraetions of 100 % foroXenon and Krypton and 50 /0 for the halogenes are assumed.The exit activity has been ealculated for 2 eases :a) the fission gas moves through the blanket as a rigid column.b) the gas entering the blanket zone always is completely mixedwith the gas already there.Tables 1 and 2 show the results for no mixing and complete mixingin the blanket respectively.land Br will be chemically bound in Sodium. We assume in accordancewith GE [9] that 0.02 0;'0 of the Iodine arriving at the coolant willbe contained in the cover gas. The activity of I in Na is small com-pared with the activity of the Na itself. The activity of Br in theNa and the cover gas can be neglected.Taking this into account c and g can be evaluated and with eq.(3)gthe input vA of the purification plant can be calculated. Fig. 2shows the results as a function of the fuel element pressure fordifferent assumptions for the process in blanket and plenum.It was assumed that== -11 310 IiC/cm-6-- 6 -(1/10 of maximum permissible concentration of unidentified mixture,however without a-emitters and without the ß-emitters Pb210 , Ac227,Ra228 and pu241 )3. Cost EvaluationA purification plant for 260 N m3/h Helium has been planned inconnection with Linde AG., Muenchen and evaluated for a fuel insidepressure of 2 ata, no plenum and eomplete mixing. Xenon and Kryptonare removed from the cover gas by low temperature adsorption.The plant will be relatively expensive by the need for continuousoperation and the large amount of decay heat. It needs 180 kWpumping power, 75 m3/h coolant water, and 35 l/h liquid nitrogen.Table 3 shows the heat production for different eonditions.Compared with the refercnce reactor with "venting to reservoir"the core height with venting to eoolant is reduced by 80 em. Themost important changes are:Reference reactor Vented to coolant[6]Pressure dropCladding thicknessCladding fraction of fuel elementBreeding ratio4,25 at0,35 mm0,251,423,20 at0,15 mm0,0961,59Table 4 shows the resulting capital costs.The main contribution comes from the smaller fabrication cost ofthe shorter fuel elements with $ 205 000 per core. For replacing1/3 of the core per year this is equivalent to $ 1,59 • 106 capi-tal costs for 15 years lifetime. The second largest contributionis the capitalized gain breeding ratio (capitalized for a loadfactor of 0,8).The radial blanket is also considerably shorter. For 4 blanketsduring the reactor lifetime this amount to 1,05 • 106 $.-7-- 7 -Smaller savings are gained by the reduction of pumping power.The gas purification and storage at the reprocessing plant is notneeded any more. The costs are evaluated according to [10].Finally, the reduced height of the core allows for some savingsfor the core vessel and its internals like supporting cylinders,insulation walls, reloading equipment and thermal shielding. However,this contribution is small.The right colurnn of table 4 shows the additional costs.6 0The net saving amounts to $ 2,19 • 10 or 2,1 /0 of the totalplant cost.4. Preliminary TestsThe important point is the development of a suitable plug. Thediving bell design of GE is wellknown [1] . It promises a veryreliable operation, but it must be of considerable length and,therefore. adds in pressure drop and capital costs. We, therefore.thought it useful to study the behaviour of a very simple porousplug of sintered metal.Two problems are of importance:a) The ability to retain sodium from the fuel. In the case of areactor shutdown and lowering of the fuel temperature theoutside overpressure of the sodium arnounts to 1 - 2 atmeb) The ability to stay porous for the fission gases.In a simple apparatus the following plug materials have been tested:Ni, CrNi 18/8. Fe. CrNi 18/10with pore sizes between 1 and 5 ~. Sodium leakage started at apressure difference of about 1.5 at for sodium temperatures ofo 6 0500 C. at about 0.5 at for 00 C.-8-- 8 -First plugging experiments by artificial evaporation of iodine didnot lead to apressure buildup of the gases. More tests are necessaryfor the evaluation of the sintered porous plug.5. ConclusionsFrom this study the following conclusions can be drawn:a) The venting of fission gases to the sodium coolant allows forsavings in the order of 2 % of the total plant cost J if com-pared to the reference reactor. In cornparison to a more optirnizedreactor the savings are much smaller.b) The main savings are from lower costs for core and radial blanketresulting from the dism1ssal of the fission gas plenum and thereduction of cladding thickness which causes a substantial risein breeding ratio.c) A low temperature adsorption process seems to be the most suit-able for the purification of the cover gas. The rnain problem 1sthe decay heat of several hundred kW J mainly from Xenon.d) The input specification of the purification plant comes fromoperational criteria. The unavoidable leakage into the contain-ment building is the determining factor.e) As the most important advantage we consider the gain in safety.Sudden bursts of gas into the coolant and the consequences witha positive void coefficient are avoided. The transient behaviourneeds further studies.-9-- 9 -LiteratureF.J.Leitz: Sodium cooled reactor program GEAP 3888, firstquarterly report, October - December 1961G.L.O'Neill, J.H.Davies, M.C.Johnson: Demonstration of fissiongas venting from fast oxide reactor fuels, General Electric,June 1964N.Pollit: The leak-tightness of demountable flange assembliesusing soft iron gaskets, Dragon Project Report 28,April 1961D.Barnes, F.Wade: Leaktesting of the test vessel and experi-mental gaskets at Mannesmann, Hueckingen, Dragon ProjectReports 23, 44, 66; 1961[5)[ 8 J[10 ]D.Barnes, F.Wade: Leaktesting the Dragon reactor pressurevessel, Dragon Project Report 154, January 1963D.Smidt, A.MUller: Referenzstudie für den 1000 MWe natrium-gekühlten Schnellen Brutreaktor (Na I), KFK-299, December 1964S.Katcoff: Fission-product yields from U, T.h and Pu,Nucleonics, Vol.18, No.1l, November 1960L.Burris, l.G.Dillon: Estimation of fission product spectrain discharged fuel from fast reactors, ANL-5743, July 1957Personal communicationH.W.Alter: A fuel reprocessing plant for fast ceramic reactors,GEAP-4028, February 1962- 10 -Table 1Exit concentration of gaseous fission products [Curies!Ncm3gasproduced in core] as a furction of fuel inside pressure.(no plenum, no mixing in blanket)fuel inside pressure [ataJisotope half-life2 4 8 12 34Kr 83 m 1,3 h 0,004 - - - -v 85 m 4,4 h 1,2 0,035 0,001".r - -Kr 85 10,6 a 0,0047 0,0046 0,0045 0,0044 0,0044Kr 87 78,0 rn 0,0033 - - - -Kr 88 2,8 h 0,9 0,0046 - - -Kr 89 3,2 m - - - - -T 131 8,1 d 50,4 39,5 24,2 16,1 3,0ur 132 2,3 h 0,9 0,0017tJ - - -,} 133 21,0 h 105,5 28,9 '+,5 0,9 -J 134- 53,0 m - - - - -tT 135 6,7 h 29,6 2,3 0,025 - -Xe 133 5,3 d 197,0 127,9 72,2 41,9 5,1Xe 135 m 15,7 m - - - - -Xe 135 9,2 h 204,9 34,0 1,3 0,038 -Xe 138 17,0 - - - - -- 11 -Table 2Exit conce~tration of gaseous fission products [Curies/Ncm3gasproduced in coreJ as a function of fuel inside pressure.(no plenum, complete mixing in blanket)isotope half-life fuel inside pressure [ata]2 4 8 12 34Kr 83 m 1,3 h 0,4 0,2 - - -Kr 85 m 4,4 h 7,0 1 0, 0,) 0,2 0,024, ,Kr 85 10,6 a 0,0044 0,0046 0,0045 0,0044 0,0044Kr 87 78,0 m 5,4 1 ,2 0,3 0,2 0,024Kr 88 2,8 h 17,2 4,3 1 ,1 0,5 0,049y,... 89 3,2 m 0,4 0,2 - - -'-...J 131 8,1 d 52,2 42,2 27,6 19,7 5,4J 132 2,3 h 36,5 8,4 2,3 1 ,1 0,1J 133 21,0 h 144,3 55,5 19,0 8,7 1,2J 134 53,0 m 13,7 3,5 0,9 0,035 0,005lT 135 6,7 h 87,9 25,3 6,5 1,5 0,4Xe 133 5,3 d 193,8 132,0 83,4 54,3 12,9IXe 135 m 15,7 m 1,2 0,6 0,3 0,07 I -IXe 135 9,2 h 310,1 109,3 30,4I10,1 1,8Xe 138 17,0 m 7,9 -1 ,9 0,5 0,2 0,024- 12 -Table 3Decay heat to be removed from the adsorbers after 3000 hoperation time for different mechanism of fission gas re-lease. ( 2 ata fuel pressure)decay heat of isotopes decay heat[k'~ [k~JJrelease mechanismXe 133 Xe 135 Kr 85 totalno plenumno mixing 280,0 r:r-) 5 0,15 337,7./! ,no plenumcomplete mixing 276,2 94,0 0,15 370,4plenum (40 cm)complete mixing 200,0 11,7 0,15 211,9plenum (80 cm)complete mixing 139,0 6,9 0,15 146,1- 13 -Table 4Cost balance for application of a vented fuel conceptsavings 106 $ additional costs n06 $core fabrication 1,59 gas purfication plant 2,30breeding ratio 1,58 operational costs 0,77radial blanket 1,04circulation pumps 0,50gas treatment atreprocessing 0,34reactor vessel 0,215,26 3,07basic equations:- 14 -room Iroom 1/3.I.H.ILcontainmentcover oscorereactor vessel5 3 24-'.....70I\Jl9 8-7-'6-5 , 3-70 9 8 7 6 2970I 56f-'.:56789103I ,3I 322678970,56789702,J32 2,56789v7'567897033222-comp{lItllmixing,nop{lInum...----nom/xing,nop{enum........~1'.....~f'..t-.._.-comp{lItllmixing,p//lnum'Oem~-.,-comp{lItllmix/ng,p{/lnum80em~I'1'...i'............"'.....""-t-..r-.........•"............'"I....."f'............... f'......."...........~............I......................'"r"--.r...................................'"~. t--................71""'0..........r-............................................."'"I'-.:-.........r......,................................. i'o........."".................................I'-....................I'.....~"""..............r--'" ~r..............t'...~... ~1'.~I..........1.."-".1', r-.....",'".r--....r-,,,,,"'''''."'". .........2 25 ,7 9 6 730; :::. .....,co. .. :::. 111 111 .. .. Q. ... c: .. E ~ ..?r70"0r-9'--'8 7 6 5Fig.2input~Theoreticalinputintopurificationplant[~J

Application of the vented fuel concept to a sodium cooled power breeder with 1000 MWe

https://publikationen.bibliothek.kit.edu/270001354/3809633

Application of the vented fuel concept to a sodium cooled power breeder with 1000 MWe

Abstract

Similar works

Full text

Available Versions

KITopen