EIR-TM-HL-261.txt

— 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:

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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

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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)
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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

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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

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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

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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"

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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)