— r—' Technische Mitteilung TM-HL-261 Abteilung: HL Bearbeiter: Prof., M, Taube Visum: o Betrift: Very high breeding ratio in the molten Datum: 28,7,75 chloride fast power reactor with external 58 e cooling. ~ Seiten Zeichnungen Introduction In the recent time the discussion about the breeding efficiency of fast breeders is dealing with the difficulties of obtaining a reaso- nable doubling time for nuclear power. In this paper the search for a significant improvement of both of these parameters, and therefore of the doubling time, is aimed to a design of a molten chloride fast breeder reactor, with as good as possible doubling time characteristics. This can be achieved by rather trivial improvements. But here it must be stressed that most of these improvements can be realised only in a fast reactor with liquid fuel and especially in molten plutonium chlorides. 1) The breeding gain 1s very sensitive to the hardness of the neutron spectrum in the core. Because in the molten fuel reactor it is possible to use fissile material also with elimination of fertile haterial, the spectrum can be rather hard. Abteilung | Name Expl. | Abteilung | Name Expl. GL Direktion. . 5 PH S. Padiyathn 1 Dr. W. Seifritz 1 J. Stepanek 1 HL [Dr. J. Peter 1l | ST |Dr. G. Sarlos 1 alle Gruppenleiter je 1 D. Haschke 1 Dr. M. Furrer 1 S. Kypreos 1 IN E.HMo;er 1 DO Bibliothek 3 .H. Bucher 1 Reserve 15 ME |G. Ullrich 1 PH |Dr. J. Brunner 1 J. Ligou 1 E. Ottewitte 1 - Dieses Dokument ist Eigentum des Eidg. Institutes flr Reaktorforschung - TM-HL=-261 page 2 The impact of elimination of tne fertile nuclide from the core e.g. on the Doppler-effect will be discussed later. 2. Because of hard spectrum the bonus of fast fission in fertile nuclides is high, wnich improves the breeding gain. 3. The elimination of structural material from the core in case of out-of-core cooling improves the neutron balance, L, Decrease of the fission products concentration because of continous reprocessing, improves the neutron balance, 5. Doubling time, more than breeding gain characterises the effi=- ciency of breeding process or for linear increasing power system the conservation coefficient which equals . . P S Gain x (Specific Power) The specific power in a liquid fuel reactor can be achieved on a level lower than 1 kg Pu tot/MWther, for the whole system: core + external heat exchanger + reprocessing plant. This preliminary report gives some selected datas about such a type of power reactor. This datas are calculated on the following basis: - ANISN reactor code - 23 neutron groups taken from GGC-3 condensed from ENDF/B III - 7 zones with 110 intervals - fourth order of quadrature, Sq - anisotropy by first order Legendre expansion, P1 - 1instead of F.,P, cross sections, here the datas for Cs-133, have been used. The reference reactor: TM=-HL-261 page 3 core The reference reactor is characterised on (see fig., 1) fig. 2. Short description of his properties: Total thermal power: Central zone: Wall: Fuel 2zone: Wall: External zone: Reflector: (see table 1) 6000 MWth Molten chlorides of uranium-238 diluted by sodium chloride as internal breeding zone. Also some amounts of Pu-239 from the breeding process are here present. Small amounts of fission products are present Radius of this zone 110 cm Material: iron with layer of molybdenum Width: 3 cm Molten chlorides of plutonium Pu-composition: 0,7 Pu-239, 0,2 Pu-240 0,1 Pu-241 diluted by sodium chloride. Significant amounts of uranium-238 (as chlori- des) are present for achieving an internal. breeding ratio of 0.22 Width of zone 18 cm Specific power ~1 KW/cm3 Flux total nal°1016h cmnzs-l Material: iron/molybdenum Width 3 cm The same as central breeding zone Width in all cases 100 cm Material: diron only Width in all cases 40 cm TM=-HL=-261 275,9 page U Table 1 CORE 200/C Thermal power 6 GWth Breeding ratio 1,75 Specific power in fuel 1,1 KW/cm3 Radius Width | Composition Flux Specific cm of Zone o4 3 thermal power zone atoms/10° cm total KW/cm3 Breeding temperature cm ratio 0 I U-238 6,4.107° Pu-239 6,0-107° 1,05-101% T 700%¢C Central g -5 2 . inlet 110,0 breeding F.P,. 2,0+10 3,7+10 zone . o Na 3.4 1,0“3 T ut1et 800 C C1 2,27+10 0,490 110,0 - II Fe 7.107° ,15010%° 0 o 7 ~8507C 5 Wall Mo 1-10 9+10 3,0 113,0 = III Pu-239 1,410 Pu-240 4,2-10'“ | 1,1,KW/cm3 17,9 Fuel Pu-241 2,1.10°1 1,02°10%% o, 750°¢C zone -3 7 inlet U-238 4,2°+10 6,610 “ -5 O F.P. 2,0 10__3 T utlet 1050°C Na 3,10 0,22 Cl 2,6°10°° 130,9 =~ IV Fe 7,0°107% 8,24-10%° 8500 =3 g ~950 ¢ 3,0 Wall Mo 1,0-10 2,5°10 135,59 v o) T. 700°C External the same as 3,9'101u AL EE 5 100,0 breeding central breeding 1,9'109 Toutlet 800°C zone zone I 1,040 233,9 VI -2 . I uo Reflec- Fe 8’0 10 5)2'10u tor 510 TM-HL=-261 page 5 Fig. 1 Peculiarity of the Reference Reactor Uesign "Classical" fast breeder reactor with external blanket only fuel zone (core) external blanket zone This reference reactor Blanket-Core-Blanket internal blanket zone fuel zone external blanket zone for impact of internal breeding zone (see also DUCAT, MIT, 1974) TM~HL=-261 page 6 Fig. ¢ Power Reactor ¢ GWth AN 777 f /R o \ ‘B FeMo | \ /Heafaxchh/ er 1 U T AN = 117 11 . ] / / 1 V1V internal ' external / / g Fm'@r#/blanket 1 V1V Reflectgr ? ? ? | / / , 11 1 il /e 1 Vb 4 I 7 I V4 / 1 W 0 1 U U d ¢/ 777 TM=-HL=261 page 7 Fig. 3 Neutron Flux in Reference Reactor Total neutron flux \ 1010-,,a,———”""’ ‘I N \ \ \ \ . ) \ \ 1047 \! . N Fast neupper” flux N : (~370 keV) | \ \ 104+ | \ Neutropns : \ (—= ) \ \ cm< sep : N I 1013- : : . . '\ \ \ \ \ \ : 1012 - | Internal Blanket E ; \ \ i | 101t \ N :' ue Zoney A A .. 10 ) ! 10%0_ E Ell \ :External Blanket | : : Reflectdgr § \ \ 9 \ \ " | \ L™ - Thermal neutrons s B \ N ~~ flux - . \ \ 10% _ \ : '\ \ ! ; N AN 10 T T T T | A~ 4 T T L} 1 L L] 0 20 40 60 80 10* 140 160 180 200 260 RADIUS / CM Fig, 3 internal breedin zone 1,2 0,9 — WA ISS £ ud Total Flux in the Fuel Zone Fuel mean TM-HL=-261 page 0O pl = 0/ — YIS o external breeding zone TM=-HL-261 page 9 The neutron flux in the reference reactor is shown in fig. 3, 3' and 4. The thermal flux in all three zones, external breeding zone, fuel and external breeding zone is only 10-8 of the total flux and only in external blanket zone arrives 10-6. The total flux is relatively smoth distributed and also in the fuel zone the maximum to the mean value of the flux achieves approx 1,13 (fig. 3'). The neutron_flux is rather hard and the median energy of neutrons (here estimated as that to the left and to the right of this value the number of fission is equal) is approximately ~370 KeV (see fig. 4). In a typical liquid metal fast breeder and in gas cooled fast breeder this value equals: 120 KeV and 176 KeV respectively. As a good illustration of the impact of the most important parameters on the value of breeding ratio a simplified calculation is given on the table 2., The discrepancy between this calculations and the computer output is of 8%. 10 10 10 10 - Spectrum in Fuel Zone | TM=HL=-261 page 10 Median Energy | 1 3 1 : T 10° 10° Neutron Energy / eV 10 TM-HL=-261 page Tabelle 2 Simplified calculation of breeding ratio and neutron balance Median energy (10/11 group) Pu-238 of (from computer output) ogc v a n-1 §: fertile/fissile fission ! Bonus (v -1)8 1+a Total positive Losses ¥p, Cl, Na, Mo, Fe Leakage (arbitr,) Losses + o 1+ Calculated BR Computed BR 370 KeV 1.83 barn 0.180 ~2:.95 0.0984 1.6857 0.37 0.539 2.225 0.160 0.10 0.3%2 1.890 1.752 2 TM=-HL=261 page 12 Impact of the plutonium contents in the fuel One of the most important problems in achieving a high breeding ratio seems to be the hardness of the neutron flux, this is strongly influenced by the composition of the fuel, In this case the fuel has been postulated to be a mixture of a PuCl, * b NaCl » ¢ UC1 5 3 a = 0,1 - 0,2 b =0,7 - 0,8 c = 0,1 - 0,2 Unfortunately not all datas for this system are available (fig. 5). The rough calculation of the changing concentration of PuCl3 in the melt with NaCl (fig. 6) shows a rather sharp decrease of breeding gain BG for decreasing plutonium concentration, especially when the plutonium molar ratio to the sodium is lower than 0,25. In spite of these uncertainties of the P‘uClB-NaCl—UCl3 system here has been calculated the impact of uranium-238 in the fuel., For a constant PuCl3 concentration, with simplified correction of NaCl concentration, the results are given on the fig. 7. For the increasing ratio of uranium to plutonium in fuel from 0 to 3 the total breeding gain increases from 0,65 to 0,95. It is a rather clear situation; and therefore the reference reactor includes uranium in fuel 1n a ratio of 2:1 to the plutonium. PuCl TM=-HL=-261 page 13 Fig, 5 The System PuClB-NaC1-UC13 800 800 50 NaCl 4o PuCl UcCl whts 3 .800/ Usl UCl TM-HL-261 Fig. 6 Plutonium Concentration page 14 800 = TEO = Tempe1 o (7C) 600 = 500 - 400 T T T T R T 0.3 0.,20.1 0.0 Mol ratio of plutonium \ . 006 - p-l.5 1.4 -103 05 o 142 gpeciric Breeding 1.1 bover gain T (KW/em”) 0.4 — -1.0 0.9 ~0,8 0.3 = 0.7 ~0.6 0.2 0.5 TM—HL—261 page 15 Fig., 7 Impact of U-238 Concentration in the Fuel Pu-Concentration: 0.0021-10214 atom/cm3 0.6 | . ; | | 1 O — o 3 U/Pu ratio _ p— =—— == = 3 0 ! 2 jT 4 ; oN 24 Atom U in fuel / (0.001.10%"/cmo) 0.9 0.7 0.6 0.5 with U TM=-HL=261 page 16 Impact of Uranium Concentration in the Fuel Uranium Concentration &6.3:10° 4,2410° Q o) - (¢4] no (] (@] ~ N = r3,15'1o3 ®2,1°107° without U Central Blanket 110 cm TM=-HL=-261 page 17 Problem of geometry: Central breeding zone versus central fuel zone The reference reactor 1is a rather nonconventional one because of three zones structure: - internal blanket zone - fuel zone - external blanket zone This type of reactor has been checked with the conventional type (table 2). For all other more or less constant parameters, inclusive total power, the obtained results for breeding gain are equal. But the difference is to see in the specific power changes more than one order of magnitude, being higher in the '"conventional" central fuel zone reactor. It is trivial that also the mean neutron flux increases from 1,2+10%% om %5~ 17 for nonconventional central blanket zone to approx 2+107'n cm_25-1 for the conventional central fuel zone. Because the specific power and intensity of neutron flux is doubtless a very serious problem from point of view of ingeneering design of the reactor (cooling, radiation damage of structural material and fuel) the both systems that is without internal blanket zone and with radius up to 110 cm have been calculated, The results are giVen on fig. 8 for fuel without uranium and with uranium in fuel for both extrem cases; no internal blanket zone and by internal blanket zone. Table 2 6 GWth "Chlorophil" TM-HL=-261 page 18 Fuel in central zone versus fuel in middle zone Core ]conventional nonconventional number of case) _____________ o-of180) oo f200) L Geometry Central Fuel Blanket 110 cm Middle ———- Fuel ~18 cm Quter Blanket >100 cm Blanket 100 em Pu/FP 2,1-107°/2.107° | 2,1-107%/2-107° Spec. power KW/cm~ | %17,7 1,41 Power in fuel % 190,9 % 76,2 % n . i . 17 . 16 Flux total 1left ) boundary §2‘OU 1017 1,2 1016 in fuel right) 11,15410 1,08+10 Flux in left ) '8,99.101° 9,7+10% ) | boundary @ _ outer ; t « gD | 14 blanket right) %2,16 10 2,510 Breeding gain ? 0,63 0,70 Median energy (group) é9 1/2 10 TM=HL=261 page 19 Fig, 9 Impact of Internal Radius (No U in Fuel) 0,9 = Breediing gain|total 0.8 - Core ® 0.7 _ | 133 Core —0 Breeding Gain -1} Core 20C | i I ! I I ' | v L i 0 10 20 50 40 50 60 70 80 90 100 110 Internal Blanket cm TM=-HL=261 page 20 On the fig. 9 and 10 are given some results of different radii of the central breeding zone., Als breeding on From all o the simplified calculation of internal zone breeding ratio, table 3. increase of the internal breeding zone from zero up to 110 cm ratio in fuel and external zone breeding ratio is shown these datas the following conclusions can be obtained: increases the breeding gain for given type of fuel, wall and fertile material only unsignificant, less than 10% relative, the specific power increases dramatically and makes the solution of in the design very difficult. the increase of U/Pu ratio from 2 up to 3,6 does not influence the total breeding gain (see fig. 10). Table 3 (in arbitrary units) Internal zone Fuel OQuter zone - . « - -24 -z . Case Pu-239 UflS Ucap Pu 239f Pu-2 lf Pu 239f Ufls Ucap Total number Bree- oXV oXV OXV oXV OXV oXxV ding Ratio * ) 0,14 0,308 0,8 3,05 0,351 0,30 0,47 1,83 200 1,70 **) ) 3,63 0,367 0,04 o,46 2,50 180 1,63 *) **) nonconventional conventional TM=HL=261 page 21 i Fig, 10 Breeding Ratio Versus Radius of Internal Fertile Zone ing Neutron flux 1016n cm | \ Specific \\power i | 50 100 Radius of internal breeding zone, cm TM=-HL-261 page 22 Fig., 11 Impact of Fission Products Concentration in Fuel (very simplified, from different calculations) O 7 = Breefling gain - 4 0.6 specific BG power (KW/cmB) =3 0 o 5y - 0.4 _ spec. wower dwelling time of fuel in core (days) i o.’B‘J T~2 *~10 1*20 | T " 107 10" . 24, 3 Concentration of F.P, atoms « 10" /cm TM=-HL=261 page 23 Impact of reflector The impact of the 40 cm with reflector, when changing from iron to lead is rather unsignificant as is to see from table 4, Impact of F.P., concentration This parameter play a very important role. For given reactor design and given fuel and fertile composition the increase the concentration of F.P. (here simulated by Cs=133 only) from 2°10—5 to 2'10-u(in 102u/cm3)decrease the breeding gain from 0,65 up to 0,38, when specific power decreases less than twice, In steady state reactor a cbncentration of 2'10”5 lOeu/cm5 for a specific power of 2 KW/cm atoms F,P. for a fuel with 2,1"10'-3 atoms Pu~102u/cm3 is to achieve 5 after a time period of ye10~De1nt t = 2%0 19 10 e 1561°105 sec 2+107+3,1°107 "2 that is after 1,87 days. The higher value of F.P. concentration that 1is 2«10-4 corresponds to 18,7 days of mean dwelling time of fuel 1in reactor. page 24 Table N Central fuel (Core 18") e . F N . (wall 2,5 emy Pu = 2,1°10 at./'lo84 em”) Case A B C U in fuel no yes no 4,210 ° Reflector 40 cm Fe Fe Pb & 5 3 # ¢ 3 1 I'a) Volume fuel «107cm 2,95 2,40 2,97 A power in fuel % 90,6 92,1 90,8 spec. power in fuel KW/cm? 18,4 23,0 18,3 BR tot 1,64 1,94 1,66 Flux total right bound zone 3 1,18'1017 1,25-1017 1,187°1O17 TM~-HL=-261 page 25 Impact of chlor-37 separation a separated chlorine C1-37 which has much lower absorption cross section than Cl-35, The impact of each adsorber on the breeding ratio is given by: 15 A+D+L+a 1l+a AB = decrement'of breeding ratio A = absorption Qate in given absorber D = absorption fate in rest of absorbers L = leakage o = ogc/of Because in typical case for strong absorber in hard spectrum fast core A (D+L) %2 a = 0,15 The relativ impact on the rather high breeding ratio of B = 1,0 results in a case when the "profit" of the separation factor will be e.g. 0,9 A, than 0,90,15 1,15 AB 0,12 and in relation to breeding gain 0,12 26 = FEEE = 0,20 T, G | doubling time T = = 0,83 2 G+AG TM-HL=-261 page 26 Acknowledgment A1l the results have been achieved in close cooperation with J. Ligou. The best thanks for the help of k. Ottewitte (nuclear datas and ANISN-=code management) and S. Padiyath for computer technique help. Literature M. Taube, J., Ligou EIR-Report 215, June 1972 J. Ligou EIR-Report 229, November 1972 M. Taube, J. Ligou Ann. Hucl., Sci, Eng. 1, 227 (1974) G.,A., Ducat, M.J. Driscoll, N.E. Todreas MITNE-157 (1974)