Atom Indonesia
Preliminary Neutronic Design of High Burnup OTTO
Cycle Pebble Bed Reactor
Topan Setiadipura1*,Dwi Irwanto2, Zuhair1
1Center
forNuclear Reactor Technology and Safety, National Nuclear Energy Agency(BATAN), Puspiptek Area, Serpong, 15310,
Indonesia
2Nuclear Physics and BiophysicsResearch Group,Pyshics Dept.,Institut Teknologi Bandung ,JlGanesha 10, Bandung, 40132 ,
Indonesia
ARTICLE
INFO
AIJ use only:
Received date
Revised date
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Keywords:
High temperature gas-cooled reactor;
Pebble bed reactor;
Once-through-then-out cycle;
High burnup;
ABSTRACT
Pebble bed type High Temperature Gas-cooled Reactor (HTGR) is
among the interesting nuclear reactor design in term of safety and
flexibility for co-generation application. In addition, strong inherent
safety characteristic of the pebble bed reactor (PBR) which based on
natural mechanisms improve the simplicity of the PBR design, in
particular the Once-Through-Then-Out (OTTO) cycle PBR design.
One of the important challenge of the OTTO cycle PBR design, and
nuclear reactor design in general, is to improve the nuclear fuel
utilization which shown by higher burnup value. This study
performed apreliminary neutronic design study of a 200MWt
OTTO cycle PBR with high burnup while keeping the safety criteria
of the PBR design.Safety criteria of the design was represented by
the maximum power generation per pebble fuel of 4.5 kW/pebble.
The maximum burnup value also limited by the tested maximum
burnup value which maintain the integrity of the pebble fuel.The
optimized parameters in this study were the fuel enrichment, heavy
metal (HM) loading per pebble, and average axial speed of the
fuel. An optimum design with burnup value of 131.1 MWd/Kg-HM
was achieved in this study which is much higher compare to the
burnup of the reference design HTR-Module. This optimum design
use a 17% U-235 enrichment with 4g HM-loading per pebble fuel.
© 2014 Atom Indonesia. All rights reserved
INTRODUCTION
Pebble bed type high temperature gas-cooled
reactor (HTGR) is among the interesting nuclear
reactor design in term of safety and flexibility for
co-generation application. In addition, strong
inherent safety characteristic of the pebble bed
reactor (PBR) which based on natural mechanisms
improve the simplicity of the PBR core design.
Further simplification of the PBR design is offered
by the once-through-then-out (OTTO) cycle PBR
concept. Different with the conventional multipass
cycle PBR, in OTTO cycle PBR, the pebbles only
pass the core oncemaking the burnup measurement
and fuel reloading devices unnecessary. This design

Corresponding author.
E-mail address:[email protected]
also offers a better potential of high temperature
heat production for co-generation [1,2]. A peu-a-peu
(PAP) cycle PBR offer a more simple reactor
design[3], however this simplification sacrificesan
important feature of PBR, the ability to have a
continual online refueling capability of the PBR as
in the multipass and OTTO cycle PBR.
PBR design is very attractive to fulfill the
electricity and heat demands in Indonesia, a country
with very large population and natural resources.
In addition, a small PBR design is highly
appropriate with the small and distributed energy
(electricity and/ heat) demand in Indonesia. Studies
on the PBR designsand its applications in Indonesia
including the development of tools for the design
analysis of PBR have been performed in Indonesia
[4-7].Recent calculations on the OTTO cycle PBR
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design show a reviving interest of PBR application
in Indonesia, in particular the OTTO cycle PBR for
its simplicity and better high temperature potential.
The core power of 200MWt was considered to be
suitable for the Indonesian demands [8,9].
Main purpose of this research was to perform
a preliminary neutronic design study of a200MWt
OTTO cycle PBR with high burnup.This study can
contribute to current initiative on the PBR design in
Indonesia, particularly on the equilibrium core
neutronic design and its optimization. Generally,
increasing the burnup performance of the OTTO
cycle PBR while maintaining the safety
characteristic is one of important challenge for this
design [10].
DESIGN PRINCIPLES
Basically, current design study used the
HTR-Module [11] as the reference design. However,
different with the HTR-Module design which
applied the multipass cycle, current study use the
OTTO cycle design.Reactor design parameters are
given in Table. 1. Including the parameters which
was optimized in this study.
<Table 1>
Current design employed standard pebble
fuel design based on Tristructural-Isotopic (TRISO)
coated particles as illustrated in Figure 1.This fuel
design assure a sound fission product retention
capability of the design resulting in low release of
radioactive material to the environment in any
condition of the core including the most severe
postulated accident. Graphite reflector which also
act as the core structure, in addition to the
significant content of graphite in the fuel, improve
the thermal characteristic of the core due to high
heat conductivity and capacity of the graphite.
Neutronically,
significant
graphite
material
compositionin the reactor improve the thermal
neutron spectrum of the core due to its effective
neutron thermalization capability. An inert He gas
coolant avoidany chemical or physical reaction that
might disrupt the neutron economy of the core.
<Figure 1>
A small diameter core conceptwas applied
in this design. The diameter of the core is 3 m to
allow the control rod only in the radial reflector
without penetrating the core, also to keep the
thermal capability to transfer the heat from the core
only by natural mechanisms giving the inherent
safety of the core.
Height of the core is 4.8 m to fulfill the
criteria given by Teuchert et.al [12] that the OTTO
cycle PBR core should be less than 5m in height.
This condition will avoid the Xenon (Xe) oscillation
by allowing sufficient transfer of neutrons from the
top part of the core which contain fresh fuel pebbles
to the bottom part containing older fuel pebbles.
The design also employed very low power
density,as low as 5.8 W/cm3.Although this power
density is higher compare to the 3 W/cm3 of HTRModule design, but this is about 1/20 of the light
water reactor’s power density.This means that the
amount of energy and heat produced inside the
reactor is volumetrically low so thatin an extreme
accident condition with no forced colling system
available, natural mechanisms such as conductive
and radiative heat trasnfer is enough to remove the
remaining heat so that no fuel damage and melt will
occurs.This is supported by tests and analyses
performed in Germany, Japan, China, South Africa
and the USA[13].
In a moving core PBR (multipass dan
OTTO cycle PBR), the lifetime of the core can be
divided into several phases. Initially,with certain
condition the core will achieve its first criticality.By
adding more pebble fuel the core will have the
initial core with full power, then as the fuel loading
continue the core will have a start-up or running-in
phase in which the neutron flux, power density
profile, and the effective multiplication factor (keff)
are still changing. Finally, the core will achieve the
equilibrium condition that will last along the
lifetime of the core. The phases prior to the
equilibrium phase are sometime jointly called as
pre-equilibrium phase. The core performance of the
PBR design is usually represented by the
performance of the core at the equilibrium, hence
equilibrium calculation is important and practically
the first phase in designing the PBR core[14].
A parametric survey of the uranium
enrichment, heavy-metal (HM) loading per pebble,
and axial fuel speed were perform in this study to
achieve a higher burnup compare to the HTRModule design which have an average burnup of 80
GWd/t-HM.The pebble fuel able to withstand a
burnup up to 150 MWd/Kg-HM [1], therefore it is
desirable to design a PBR with more effective fuel
utilization which shown by much higher burnup
value. A nuclear reactor design with effective fuel
utilization is important to support the sustainability
of nuclear reactor application in term of cost and
fuel supply. HTR-Module design use 7.8% U-235
enrichment and 7 g HM-loading, while in current
study the parametric survey of uranium enrichment
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exploited the limit of 20%defined by Internatioanl
Atomic Energy Agency (IAEA) for Low Enriched
Uranium (LEU) [15].Analysis to quantify the
effect of using higher enrichment, e.g. to the overall
cost of the design, is beyond this optimization study.
Integrity of the pebble fuel is the main
safety criteria of the PBR design to keep its sound
inherent safety characteristic. Therefore, the safety
criteria used in current study was the maximum
energy generation per pebble fuel ball which will
keep the integrity of the pebble fuel. Teuchert et.al
reportedthat 5.7 kW/pebbleis the technical limit of
the pebble fuel to keep its integrity [16]. However,
for HTR-Module design in particular, Teuchert
et.algive a lower limit of 4.5 kW/pebble [17]. In
current design study the 4.5 kW/pebble was used as
the safety criteria. This value of power generating
limit per pebble fuel also used as the safety criteria
in other PBR design studies [18,19]. A detail design
of control rod and dynamic parameter of the core to
assure the shutdown capability of the core are
beyond the scope of current study. However, adding
to the previous design criteria, it was desirable that
the equilibrium keff to be as low as possible.
Improving the burnup value under the limit
of certainmaximum power density while keeping the
desired core power of 200 MWt and reducing the
core height following OTTO cycle criteria was a
challenge to be solved in this study.
CALCULATIONAL METHOD
As a moving core reactor, the burnup analysis
of PBR should also consider the axial movement of
the pebble ball. The burnup equation to be solved in
this reactor is given in Eq.1 [20]
∂Nk
∂t
+
∂Nk
∂z
q
υ = ϕ ∑m
i=1 Ni σfi yik + ϕ ∑s=r Ns σas γsk +
∑pj=n Nj λj αjk − λk Nk − ϕNj αjk
Nk
υ
Φ
σfi
σas
λj
yik
=
=
=
=
=
=
=
γsk
=
αjk
=
(1)
atomic concentration of isotope k
axial fuel speed
flux of the core region
fission cross section of isotope i
absorption cross section of isotope i
decay constant of isotope i
yield of isotope k due to fission in isotope
i
probability that neutron absorption in
isotope s produces isotope k
probability that decay of isotope j produce
isotope k
The strategy to perform the burnup analysis
of PBR used in this research was by coupling a
neutron transport analysis including burnup analysis
and additional simulation to move the fuel following
the OTTO cycle fuel movement. The neutron
transport and burnup analysis was performed by a
continous energy Monte Carlo code called MVPBURN[21]. The statistical geometry model in the
MVP-BURN code is apropriate to model the double
heterogeneity of PBR core and fuel design correctly
in a simple way. Its monte carlo method also
preferable to have a more accurate neutronic
calculation compare to the standard diffusion
approximation. Several studies on the PBR design
also used MVP-BURN as the main calculational
tools [3,10].
Calculational and coupling method used in
this study is same with the method applied in
MCPBR code [22]. The heavy metal burnup chain
used in this calculation, as shown in Figure 2,
comprise of 28 heavy metal from Th-232 up to Cm246 [21]. This burnup chain able to accommodate
the uranium and thorium fuel cycle, although the
current study was limited to uranium cycle. JENDL4.0 [23], the latest nuclear data library from
Japanese Atomic Energy Agency (JAEA), was used
in this study.
<Figure 2>
Geometrically, the cone-shape at the bottom
of the PBR core was omitted in the current
calculational model. The core was model as
cyclindrical r-z geometry as shown in Figure 3. The
geometrical model is divided in to 20 region in axial
direction, and radially 5 region. This region mesh
dimension considering the neededcalculation
accuracy and also computational time [22]. This
model is acceptable, in particular for preliminary
design study, due to low neutron flux in the bottom
of the core as also performed in other PBR core
analysis [3,22,24].
<Figure 3>
The method applied in this calculation able to
simulate the the whole lifetime phases of PBR core
including the pre-equilibrium and equilibrium phase.
Hence, the method can be applied to perform the
optimization of the equilibrium condition and also
the pre-equilibrium condition. In this research, the
calculation start with the core fully loaded with
specific reactor design (fuel composition and
average axial fuel speed). This method was chosen
due to its robustness in which the pre-burnup
calculation to have pebble fuels with different
burnup values to fill the initial core is not needed.
Then as the fresh fuel continue loaded from the top
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core and the lowest fuel dischargefrom the core
following the OTTO cycle procedure, the core will
enter the running-in period shown by the changing
of keff and other parameters, and finally reach the
equilibrium condition.
RESULTS AND DISCUSSION
Transition of keff from the initial core up to
the equilibrium core in the equilibrium analysis for
different U-235 enrichment, HM-loading, and
average axial fuel speed are given in Figures 4 – 7.
In those each figures, as expected, for all the design
with same parameter except the average axial fuel
speed initial keffare the same. Value of the initial keff
given in those figures are too high for a practical
design of PBR core. These results was due to the
computational method used in this study, in which
initial core was simply loaded with fresh fuel.
Practically, the initial core can be loaded with many
different loading strategy involvingdummy graphite
pebbles which will give a different initial and
running-in phase condition. The tools and method
used in this study are capable to perform an analysis
of any initial core loading, however the current
study was focused on the performance of the
equilibrium condition.
<Figure 4>
<Figure 5>
<Figure 6>
<Figure 7>
For the equilibrium condition, different
average axial fuel speed affect the equilibrium keff.
As can be seen from each of those figures, higher
axial fuel speed will increase the equilibrium
keff.This is due to the lower fuel residence time in
higher axial fuel speed core making the core having,
generally, a more fissile nuclides and finally
resulted in higher equilibrium keff. This lower fuel
residence time also will decrease the discharge
burnup of the fuel. Figure 7 show that for 4 g HMloading with 17% U-235 enrichment, an axial fuel
speed of 0.8 cm/day did not give a critical
equilibrium core.
Both lower HM-loading and U-235
enrichment will decrease the equilibrium
keff.Change of HM-loading per pebble effect the
balance between fissile inventory and moderation
level. Lower HM-loading will decrease the fissile
inventory but improve the moderation level, vice
versa.In the 4 g and 5 g HM-loading design, the
effect of low fissile inventory is stronger compare to
the moderation level improvement, hence the
equilibrium keff is decreasing with lower HMloading. This effect is not always the case, effect of
the HM-loading to the equilibrium keff depend on
wether the design is over or less moderated [25].
The results show that the current design to achieve
high burnup using 4 g and 5 g HM loading are an
over moderated design.It can be understood that the
design options to find the desired equilibrium keffare
to decrease the axial fuel speed, HM-loading per
pebble, and fuel enrichment.
<Figure 8>
<Figure 9>
<Figure 10>
Calculation results of the power density
profile of the equilibrium cores are shown in Figures
8 – 10. Effect of different axial fuel speed to the
maximum power density is given in Figure 8. It
shows that higher axial fuel speed is preferebble for
the safety aspect due to its low maximum power
density. However, increasing the axial fuel speed is
also decrease the burnup of the core.Figure 9 shows
that decreasing the HM-loading per pebble which
preferable to increase the burnup of the core will
also increase the maximum power density which is
displeasing for the core design.Effect of different
enrichment to the maximum power density is shown
in Figure 10. Higher fuel enrichment will decrease
the maximum power density, however, as discussed
earlier it will also have a higher equilibrium keff.
These results show that the axial fuel speed, HMloading, and fuel enrichment need to be optimized
to have an optimum burnup while keeping the
maximum power density below the technical limit.
<Figure 11>
<Figure 12>
Results of the optimization study of the axial
fuel speed, HM-loading, and fuel enrichment to the
burnup value and maximum power density are given
in Figure 11, while Figure 12 shows the
optimization of these parameters to burnup and
equilibrium keff.Both figures show the characteristic
of OTTO cycle PBR optimization involving fuel
enrichment, HM-loading, and axial fuel speed
parameters. Based on the parametric survey results,
for the 5 g HM/pebble design with fuel enrichment
20% and axial fuel speed 0.8 cm/day fulfill the
maximum power density limit and have a burnup
value of 131.1 MWd/Kg-HM, the equilibrium keff
was 1.15. For this design, increasing the axial fuel
speed will further increase the equilibrium keff,
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while decreasing the axial fuel speed will increase
the max. power density beyond the technical limit.A
lower fuel enrichment of 17%decreased the
equilibrium keff to1.08, however the max. power
density was increased to 4.3 kW/pebble. For the
design with 4 g HM loading per peeble, in general,
the burnup is higher but the max. power density also
become increasing. A burnup of 145.7 MWd/KgHM can be achieved with 4 g HM/pebble and 20%
enrichment while maintaining the maximum power
density limit, however the equilibrium keffwas
1.12.Combining the desired criteria of optimum
burnup, the maximum power density constrain, and
the low equilibrium keff, the optimization study
show that the design with 4 g HM/pebble, 17% fuel
enrichment, and axial fuel speed of 1 cm/day was
the optimum design. It has a burnup value of 131.1
MWd/Kg-HM with maximum power density of 4.1
kW/cm3, and equilibrium keffof 1.07.Burnup of this
optimized design is much higher compare to the
burnup value of reference HTR-Module design and
also the 100MWt OTTO cycle PBR design by
Teuchert et.al [12]. Although the maximum power
density of this design is below the technical limit to
assure the integrity of the pebble, a thermofluid
analysis is needed in the next phase of this design
study. Basically, the thermal load effect to the
pebble due to this max. power density can be
reduced because this maximum power density
occurred at the top part of the core containing a
quite fresh pebble ball and low temperature He
coolant..
ACKNOWLEDGMENT
The authors thank to the Neutronic Group at
Center for Nuclear Reactor Technology and Safety
of BATAN for the discussion on the design
principles of PBR design.
REFERENCES
1.
A. Bredimas, K. Kugeler, and M.A. Futterer,
Nucl. Eng. Des. 271 (2014) 193.
2.
U. Hansen, R.Schulten, and E.Teuchert, Nucl.
Sci. Eng. 47 (1972) 132.
3.
4.
D. Irwanto and T. Obara, J. Nucl. Sci. Tech. 48
(2011) 1385.
P.H. Liem, Ann. Nucl. Energy 21 (1994) 281
5.
P.H. Liem, Ann. Nucl. Energy 23 (1996) 207
6.
B.Arbie and Y.R. Akhmad, Is there a chance
for commercializing the HTGR in Indonesia,
High temperature gas cooled reactor
technology development, IAEA-TECDOC-988
(1996).
7.
A.N. Lasman and M.D. Isnaeni, The EOR
system in DURI: Comparison between
conventional and non-conventional systems,
High temperature gas cooled reactor
technology development, IAEA-TECDOC988(1996).
Suwoto and Zuhair, Effect of latest nuclear
cross section library on neutronic design
calculation of RGTT200K core, Proceeding of
18th National Seminar on Technology and
Safety of NPP and Nuclear Facilities,
Indonesia (2012) 502. (in Indonesian)
8.
CONCLUSION
Preliminary neutronic design of a 200MWt
OTTO Cycle PBR with high burnup of 131.1
MWd/Kg-HM was achieved with 17% U-235
enrichment and loading of 4 g-HM/pebble. The
burnup improvement of this design is quite
significant compare to the HTR-Module and
previously proposed OTTO cycle PBR. Maximum
power generation of the design was 4.1kW/pebble
which fulfill the criteria of lower than technical limit
4.5 kW/pebble. This optimized OTTO cycle PBR
design is an interesting nuclear reactor design to be
used for electricity and co-generation application in
developing country, such as Indonesia, particularly,
due to its efficient nuclear fuel utilization and
simplicity. Also,in general,due tostrong inherent
safety of PBR design. Further study which include
initial core optimization, and thermofluid aspect of
this PBR design are some of the important agenda to
be studied in the near future.
9.
Zuhair, Suwoto, and P.I. Yazid, Jurnal Sains
dan Teknologi Nuklir Indonesia 14 (2013) 65.
(in Indonesian)
10. H.N. Tran, Prog. Nucl. Energy 60 (2012) 47.
11. G.H. Lohnert, Technical design features and
essential safety-related properties of the HTRModule, Nucl. Eng. Des. 121 (1990) 256-275
12. E. Teuchert, H. Gerwin, and K.A. Haas,
Simplification of the Pebble Bed HighTemperature Reactor, Potential of Small
Nuclear Reactors for Future Clean and Safe
Energy Sources, Hiroshi Sekimoto (Ed.),
Elsevier Science Publishers B.V., Japan (1992).
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13. A.C. Kadak, Int. J. Critical Infrastructures 1
(2005) 330.
14. H. Sekimoto, T. Obara, S. Yukinori, E.
Suetomi, J. Nucl. Sci. Technol. 24 (1987) 756
15. International
Atomic
Energy
Agency.
Safeguards
Glossary.
2001
Edition.
International NuclearVerification Series, No.
3. Vienna, (2002).
16. E. Teuchert, K.A. Haas, H.Gerwin, Method for
loading operating, and unloading a ball-bed
nuclear reactor, US-Patent 4695423 (1987).
17. E. Teuchert, H.Ruetten, K.A. Hass,
Rechnerische
Darstellung
des
HTR-.
Modulreaktors, Jul 2618, Julich (1992).
18. P.H. Liem, Ann. Nucl. Energy 23 (1996) 207.
19. E.E. Bende, Plutonium burning in a PebbleBed type high temperature nuclear reactor,
Ph.D. Thesis, Delft University of Technology
(1999).
20. L. Massimo, Physics of High Temperature
Reactor, Pergamon Press (1976).
21. K. Okumura, Y. Nagaya, M. Takamasa, MVPBURN: Burnup Calculation Code Using a
Continuous Energy Monte Carlo Code MVP,
Japan Atomic Energy Agency (JAERI), Japan
(2006).
22. T. Setiadipura and T. Obara, Ann. of Nucl.
Energy 71 (2014) 313.
23. K. Shibata, O. Iwamoto, T. Nakagawa, N.
Iwamoto, A. Ichihara, S. Kunieda, K. Chiba, K.
Furutaka, N. Otuka, T. Ohasawa, T. Murata, H.
Matsunobu, A. Zukeran, S. Kamada, J.
Katakura, J. Nucl. Sci. Technol. 48 (2011) 1.
24. H.D. Gougar, F. Reitsma, and W. Joubert, A
comparison of pebble mixing and depletion
algorithms used in pebble-bed reactor
equilibrium cycle simulation, Idaho National
Laboratory, USA (2009).
25. T. Setiadipura, Study on optimization of startup of OTTO cycle pebble bed reactors, Ph.D
Thesis, Tokyo Institute of Technology (2014).
26. Y. Hirose, P.H. Liem, E. Suetomi, T. Obara,
H.Sekimoto, J. Nucl. Sci. Tech. 26 (1989)
1385.
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Table 1. Reactor design parameter.
Parameter
Core
Power
Diameter / Heigt
Height of void (above the active core)
Max. power generation per pebble
U-235 enrichment
HM-loading per pebble
Average of axial fuel speed
Average burnup
Fuel pebble
Diameter
Thickness of outside graphite shell
TRISO coated fuel particle
UO2 Kernel radius
Density of UO2 Kernel
Coating type (inside – out)
Thicknes of each coating
Density of each coating
Unit
MWt
cm
cm
kW/pebble
%
g
cm/day
MWd/Kg-HM
Value
200
300 / 480
40
4.5
optimized in this study
optimized in this study
optimized in this study
optimized in this study
cm
cm
6
0.5
cm
Kg/m3
cm
0.025
10.4
buffer/I-PyC/SiC/OPyC
0.009/0.004/0.0035/0.004
g/cm3
1.05/1.9/3.19/1.9
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Fig.1. Illustration of the pebble fuel elemen and TRISO fuel particle used in Pebble Bed Reactor design.
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Fig.2. Heavy Nuclide Chain used in the burnup calculation [21].
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Fig. 3. Cylindrical r-z geometry used in the calculation to model the PBR core. In the figure, dN/dS is the
change of the nuclide density along the fuel pebble path.
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1.5
Effective Multiplication Factor
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
1.05
1
0
500
1000
1500
2000
2500
Operation Time (days)
v=0.8cm/day;20wt%
v=0.9cm/day;20wt%
v=1cm/day;20wt%
Fig. 4. Effective multiplication factorstransition from initial core to equilibrium core for 20% U-235
enrichment and 5 g HM/pebble.
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1.5
Effective Multiplication Factor
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
1.05
1
0
500
1000
1500
2000
2500
Operation Time (days)
v=0.8cm/day;17wt%
v=0.9cm/day;17wt%
v=1cm/day;17wt%
Fig. 5. Effective multiplication factors transition from initial core to equilibrium core for 17% U-235
enrichment and 5 g HM/pebble.
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Effective Multiplication Factor
1.5
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
1.05
1
0
500
1000
1500
2000
2500
Operation Time (days)
v=0.8cm/day;20wt%
v=0.9cm/day;20wt%
v=1cm/day;20wt%
Fig. 6. Effective multiplication factors transition from initial core to equilibrium core for 20% U-235
enrichment and 4 g HM/pebble.
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1.5
Effective Multiplication Factor
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
1.05
1
0
500
1000
1500
2000
2500
Operation Time (days)
v=0.8cm/day;17wt%
v=0.9cm/day;17wt%
v=1cm/day;17wt%
Fig. 7. Effective multiplication factors transition from initial core to equilibrium core for for 17% U-235
enrichment and 4 g HM/pebble.
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Power Density [kW/pebble]
6.00
5.07
5.00
4.06
4.00
3.00 3.44
2.00
1.00
0.00
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
Axial Region (top to bottom)
v=0.8cm/day;20wt%
v=0.9cm/day;20wt%
v=1cm/day;20wt%
Fig. 8. Effect of different average axial speed to the maximum power density. (200 MWt, 20%,
4gHM/pebble)
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Power Density [kW/pebble]
6.00
5.07
5.00
4.00
3.77
3.00
2.00
1.00
0.00
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
Axial Region (top to bottom)
4gHM/pebble
5gHM/pebble
Fig. 9. Effect of different HM-loadings per pebble to the axial power density profiles for 20% U-235
enrichment, 4 g HM/pebble, at average axial fuel speed 0.8 cm/day.
Atom Indonesia
4.50
4.07
Power Density [kW/pebble]
4.00
3.50
3.44
3.00
2.50
2.00
1.50
1.00
0.50
0.00
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
Axial Region (top to bottom)
v=1cm/day;20wt%
v=1cm/day;17wt%
Fig. 10. Effect of different U-235 enrichments to the axial power density profiles for 4 g HM/pebble, at
average axial fuel speed 1 cm/day.
Atom Indonesia
Fig. 11. Parametric survey results of average axial velocity, HM-loading, and U-235 enrichment to the
maximum power density and burnup.
Atom Indonesia
Fig. 12. Parametric survey results of average axial velocity, HM-loading, and U-235 enrichment to the
equilibrium keff and burnup.