DETAILED ANALYSIS OF PEBBLE-BED HTR PROTEUS EXPERIMENTS WITH THE

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					2nd International Topical Meeting on HIGH TEMPERATURE REACTOR TECHNOLOGY
Beijing, CHINA, September 22-24, 2004                                                      #Paper C12



 DETAILED ANALYSIS OF PEBBLE-BED HTR PROTEUS EXPERIMENTS WITH
                                        THE MONTE CARLO CODE TRIPOLI4


                                              O. Köberl 1, R. Seiler 2
1 CEA-Cadarache, 13108 Saint-Paul-Lez-Durance Cedex, France
2 Paul Scherrer Institute, 5232 Villigen, Switzerland


ABSTRACT: Within the framework of an IAEA co-ordinated research programme (CRP), high
temperature reactor experiments with low-enriched uranium fuel were carried out at the PROTEUS
facility of the Paul Scherrer Institute (PSI), Switzerland.. High quality and well-documented
experimental data were obtained from 13 pebble-bed arrangements, 9 of them were deterministic
loaded core configurations.
In this paper a calculation-to-experiment (C/E) comparison of keff values, control rod worths and
reaction rates, e.g. conversion ratios, is presented for 2 deterministic HTR-PROTEUS cores. The
calculations were performed with the Monte Carlo code TRIPOLI4 in conjunction with the nuclear
data libraries JEF2.2 and JEFF3.
The agreement between experimental and calculated keff values, reactions rate distribution and the
conversion ratios is good, however, the calculations slightly underestimates the worths of the
shutdown rods.
KEY WORDS: HTR-PROTEUS, Validation, TRIPOLI4, criticality, rod worth, reaction rates.


0. INTRODUCTION
High temperature gas-cooled reactors are considered as a very promising reactor concept for the next
generation of reactors. The outstanding features of the high temperature reactor (HTR) are the high
degree of safety through reliance on passive safety features and the production of heat at very high
temperatures. The latter feature makes the HTR an attractive candidate for the economical production
of Hydrogen. Moreover it has a high flexibility to adopt various fuel cycles, e.g. Uranium, Thorium
etc.
There are a number of projects, such as the Pebble Bed Reactor (PBR) being developed by ESKOM
[1], the VHTR project in the framework of the GEN-IV projects [2] and the GT-MHR concepts [3] to
burn weapon-grade Plutonium or the entire radioactive long-lived waste in a couple of HTRs (DEEP
BURN Concept).
Various critical experiments with high-enriched Uranium and Thorium were carried out in the 60s, 70s
and 80s; however, there was a lack of experimental data for the low-enriched Uranium fuel cycle,
particularly for small, under-moderated cores of current interest. In the framework of an IAEA co-
ordinated research programme (CRP), high temperature reactor experiments with low-enriched
Uranium fuel were carried out at the PROTEUS facility of the Paul Scherrer Institute (PSI) in
Switzerland. Between 1992-1996, 13 critical pebble-bed configurations with different moderation
ratios and pebble packing geometries were conducted to determine criticality, absorber rod worth and
reaction rate ratios and distributions. A detailed summary of the experimental data and the results
obtained by the benchmark participants is given in an IAEA technical documentation [4]. It is worth
mentioning that the numerical results were obtained with an effective absorption cross section of the
graphite reflector of 4.09 mbarn, which is an essential parameter for the interpretation of the
experiments. Recent publications [5], [6] have shown that the calculated keff values agree better with
the experimental ones, if the effective absorption cross section is increased to 4.47 mbarn [7].




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DETAILED ANALYSIS OF PEBBLE-BED HTR PROTEUS EXPERIMENTS WITH THE MONTE CARLO CODE TRIPOLI4        #C12


The current paper is focused on the interpretation of keff values, control rod worths, reaction rate
distributions and reaction rate ratios for two deterministic PROTEUS configurations, namely Cores 5
and 9. Both cores have deterministic column hexagonal pebble bed loadings with a fuel-to-moderator
pebble ratio of 2:1 and 1:1, respectively. A brief description of the Monte Carlo models used for the
configurations is given. In order to compare these results with the former MCNP results [5] and [6],
keff-calculations were performed with a clean reflector. For the comparison of experimental absorber
rod worths and reaction rate ratios, a more detailed model of the radial reflector was used.
The calculations were performed with the Monte Carlo code TRIPOLI4 in conjunction with the
nuclear data libraries JEF2.2 and JEFF3. An attempt was made to quantify the neutron streaming
effect of the pebble-bed with various TRIPOLI4 models. These studies were also helpful to reduce the
deviation in the critical core-height calculations for the HTR-10 10 MW prototype pebble-bed reactor
in Beijing, where identical fuel pebbles were used (see publication at this conference [12]).


1. BRIEF DESCRIPTION OF THE EXPERIMENTAL CONFIGURATION
Fig. 1 gives a schematic view of the PROTEUS facility. The facility can be described as a graphite
cylinder of 3.26 m in diameter and 3.3 m in height with a central polygonal cavity of ~1.20 m in width
across flats. The 12-sided polygon cavity where the core was assembled has solid graphite reflectors in
all directions: 0.78 m thick in the lower and upper axial directions and 1.029 m (average) thick in the
radial direction. The radial reflector contained four boron-steel shutdown rods, located symmetrically
around the core at a radius of 0.684 m and four stainless-steel control rods, located at a radius of
0.906 m. The reactor was operated at room temperature at powers up to 1 kW, so that no active
cooling system was required.




                      Figure 1 : Schematic view of the HTR-PROTEUS reactor.


The cavity was partially filled with mixtures of moderator (pure graphite) and fuel (containing 16.7%
enriched UO2 particles of 0.5 mm diameter) pebbles, loaded either in deterministic or in random
arrangements to form the reactor core. Both pebble types had an outer radius of 3.0 cm and a fuel




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HTR2004                                                                                 Beijing, CHINA, 2004. 9.


region with a radius of 2.35 cm. The “Arbeitsgemeinschaft Versuchsreaktor” (AVR) in Germany
supplied the pebbles.1 Each fuel pebble contained about 1 g of 235U in ~ 9400 particles.
The presently reported results were calculated for the HTR-PROTEUS Core 5, which has a
rhombohedral pebble-lattice geometry with a fuel-to-moderator pebble (F/M) ratio of 2:1,
corresponding to a C-to-235U ratio of about 5670. This so-called column hexagonal point-on-point
(CHPOP) pebble-bed packing had a filling factor of 0.6046. In order to improve the homogeneity of
the core region, an ABCABC … loading scheme was adopted in which the layer pattern is repeated
every fourth layer. The packing frequency ABC was repeated up to layer 22. Each layer consists of
241 fuel pebbles and 120 moderator pebbles, however the position of the pebbles differed from layer
to layer. The arrangement of the 23rd layer (top layer) was changed because too few fuel pebbles
remained to form a complete 23rd layer. Therefore, the remaining 138 fuel pebbles were arranged in a
2:1 lattice in the centre of this layer, and the surrounding area was filled with moderator pebbles.
Table 1 summarises the main characteristics of Core 5 and 9.


The Core 9 configuration consists of a CHPOP arrangement with a F/M ratio of 1:1 corresponding to a
C-to-235U ratio of about 7540. In order to obtain a very homogeneous fuel and moderator pebble
arrangement, an ABCDEF, ABCDEF … loading scheme was adopted, in which the layer pattern is
repeated every 7th layer. With 27 loaded layers, the system was critical with all control rods fully
withdrawn. For the operational loading, an extra layer of moderator pebbles (28th layer) was added to
bring the critical control rod position into a convenient range.
For a more complete description, we refer the reader to [4] and [7]. These references contain very
detailed descriptions of the core of the HTR-PROTEUS facility and its components.


                 Table 1 : Main characteristics of the pebble bed configurations Core 5 and 9.
      Core         Packing     Number of       Number of          F/M                 Comments
                              Fuel Pebbles     Moderator
                                                Pebbles
                                   (F)
                                                   (M)
             A
5 (State 3 )       CHPOP          5433            2870         2.000378      Layer 1 to 22 with a F/M = 2


9 (State 2 B)      CHPOP          4870            5238           1.074       Layer 1 to 27 with a F/M = 1

A
    An extra layer (23rd) with 138 fuel and 223 moderator pebbles was loaded.
B
    An extra layer (28th) of moderator pebbles was loaded to slightly increase the reactivity.


Four safety rods, of similar construction as the shutdown rods, were located interstitially between them.
With an appropriate height of the pebble-bed core, criticality was achieved with the four shutdown
rods fully withdrawn and the four control rods partly inserted (see Figure 2). As indicated in Figure 2,
the width across flats of the central cavity was altering between 120.6 cm and 120.3 cm




1
    AVR was a 15 MW(e) pebble-bed type research reactor, which operated successfully for 21 years.



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DETAILED ANALYSIS OF PEBBLE-BED HTR PROTEUS EXPERIMENTS WITH THE MONTE CARLO CODE TRIPOLI4             #C12




  Figure 2 : A mid-plane view of the PROTEUS reactor showing a deterministic fuel and moderator
  pebble arrangement and the position of the shutdown, safety and control rods located in the radial
  reflector. No. 1 to 4 are the shutdown rods and No. 5-8 are the safety rods. No. 1 to 4 (underlined
                                     numbers) are the control rods.


2. REVIEW OF CRITICAL BALANCES FOR CORE 5 AND CORE 9
In the IAEA technical documentation [4] a description of all HTR cores is given including for each
core, an estimate of the reactivity for components which are normally not modelled. As mentioned
before, there are three reference states for Core 5 with slightly different keff values. In our analysis, we
refer to Core 5 State 3 and Core 9 State 2.
In Table 2 the reactivity corrections for the various components, control rod insertion, control rod
channels etc. are given. The table contains the keff values for 2 cases. The first one corresponds to a
core with a ‘clean reflector’. For Case 2 the keff value is corrected for control rod insertion, control,
safety and shutdown rod channels. It is the experimental reference value for the investigation of the
absorber rod worths. The number in parenthesis, in each case, indicates the 1σ uncertainty in the last
significant digits.




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HTR2004                                                                                  Beijing, CHINA, 2004. 9.


    Table 2: Reactivity corrections for critical loadings in Core 5 and 9. The βeff for these configurations
                                  is 720 pcm. The data are taken from [4].
                                                               Core 5                         Core 9
                                                     Reference State #3              Reference State #2
Reactivity       Corrections     for   Critical
Loadings                                          Reactivity       Reactivity      Reactivity          Reactivity
                                                    (cent)              (pcm)        (cent)              (pcm)
Control Rod Insertion                               -84.2               -606         -70.4                -507
Control Rod Channels                                 -2.2                -16          -2.5                -18
Safety + Shutdown Rod Channels                       -28                -202          -32                 -230
Others                                              38.7                 279          53.7                387
total                                              -154.2               -1102        -158.6              -1142
keff (Case 1, clean reflector)                               1.0110(5)                       1.0114(7)
keff (Case 2A)                                               1.0028(5)                      1.0039(7)
A
  The keff of the Case 2 is the keff of Case 1 corrected for the reactivity effects for the control rod
insertion, control, safety and shutdown rod channels (bold numbers)


For Core 5 and 9 the critical balances were reviewed. The reactivity correction for the reference State
2 of Core 9 was found to be 1.586$, which is slightly lower than the former reported value (1.59$). A
more significant difference of 280 pcm was observed between the value reviewed in this work and the
one given in [4]. It is believed that this is due to a typing error. All TRIPOLI4 results of Core 5 and 9
are compared with the corrected keff values in Table 2.


3. MONTE CARLO MODELS FOR TRIPOLI4
The Monte Carlo code TRIPOLI4 version 4.3 [9] was employed along with the continuous energy
group cross-sections of the nuclear data libraries JEF2.2 and JEFF3. All calculations were performed
with a uniform temperature of 300°K.
For Core 5 and 9 a very detailed TRIPOLI4 model was developed with particles, pebbles, the 12-sided
polygon, absorber rod channels and the top reflector modelled in detail (as shown in Figure 1 and 2).
The corresponding nuclide densities of these regions were taken from [5]. In order to compare the
former results with those obtained by CRP participants, the criticality and absorber rod worths were
calculated with the lower absorption cross section of 4.09 mbarn instead of 4.47 mbarn.
3.1. Pebble
The complex form of the fuel pebble, the graphite shell and the grain structure of the fuel matrix is
explicitly modelled. The fuel matrix has a radius of 2.35 cm and is surrounded by a 0.65 cm thick
graphite shell. Each fuel pebble contained about 9400 particles. Although in reality the particles are
stochastically distributed, for the model purpose the particles are placed in a cubic lattice. The side
length of the cubic cell is 1.7954 mm. In order to estimate the effect of the particle arrangement, a
hexagonal lattice arrangement with a distance across flats of 0.221534 cm and a height of 0.13625 was
also used. The dimensions of the hexagonal lattice are chosen in such a way that the total volume of
the fuel kernels per pebble is kept constant, and the volume of a cube and a hexagon are almost
identical. The volumes are 0.005787 cm3 and 0.005791 cm3, respectively




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DETAILED ANALYSIS OF PEBBLE-BED HTR PROTEUS EXPERIMENTS WITH THE MONTE CARLO CODE TRIPOLI4                 #C12




        Figure 3: Sectional view of a fuel pebble with coated particles, in a cubic lattice (left) and a
                        hexagonal lattice (right), and with the outer graphite shell.


3.2. Reactor Core Configuration
The 12-sided polygon of the cavity was modelled in detail. The distance across flats of the 12-sided
polygon was slightly different (see Figure 2). Fig. 4 shows the vertical pebble loading of Core 5 and 9
produced by TRIPOLI4. The axial measurement channel is displayed for the upper axial reflector, the
cavity above the core and in the lower axial reflector.




    Figure 4: Cross sectional view (x-z) of Core 5 (left) and 9 (right). Two-dimensional cuts were
produced by TRIPOLI4. Radial positions of absorber rod and control rod channels are also indicated.


4. COMPARISON WITH CALCULATIONS
4.1. System Reactivity
In order to facilitate the discussion, the differences between the TRIPOLI4 models are summarised:
    •     Case 1: In this model no details of the radial reflector were modelled, and the calculated
          values of Core 5 and 9 are compared with the experimental values of 1.0110 and 1.0113,
          respectively.



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HTR2004                                                                                   Beijing, CHINA, 2004. 9.


    •     Case 2: The channels of the absorber rods with the inserted control rods were modelled. The
          experimental keff values for Core 5 and 9 are reduced to 1.0028 and 1.0038.
    •     Case 3: Same model as in Case 1, but the absorption cross-section of the graphite reflector is
          4.09 mbarn instead of 4.47 mbarn.
Table 3 is a summary of experimental and calculational results for Case 1. It contains the results of
this study and the recently published results obtained with the Monte Carlo code MCNP. It is seen that
the TRIPOLI4 results of Core 5 and 9 agree with the experiments within 140 pcm and 250 pcm. Table
4 gives the comparison of experimental and calculated keff values for Case 2. The calculated keff values
are in excellent agreement with the experimental data.


 Table 3: Comparison of Calculated and Measured keff values for the Critical Core 5 and 9 (Case 1).
            Core              Experiment           TRIPOLI4, JEF2.2                  MCNP [6]
              5                1.0110(5)                1.0124(5)                     1.0120(6)
              9                1.0114(7)                1.0089(5)                           -


 Table 4: Comparison of Calculated and Measured keff values for the Critical Core 5 and 9 (Case 2).
            Core              Experiment           TRIPOLI4, JEF2.2               TRIPOLI4, JEF3
              5                1.0028(5)                1.0044(5)                     1.0058(5)
              9                1.0039(7)                1.0033(5)                           -


Table 5 shows the impact of the change of the effective absorption cross-section and the effect of the
homogenisation of the graphite in the core.
For Core 5, the keff increases by about 800 pcm when the absorption of the graphite reflector is
reduced from 4.47 mbarn to 4.09 mbarn. This effect is with 900 pcm similar in Core 9.
An appropriate treatment of the neutron streaming in the deterministic core configuration was
important for the interpretation of the experiments. As shown in [4] the calculations generally
overestimate the criticality of Core 5 and 9, if no streaming correction was applied. A better agreement
was obtained with a streaming correction, but this correction varied between 700 pcm and 1500 pcm
for Core 5 and between 1100 pcm and 1800 pcm for Core 9.
In order to calculate the neutron streaming effect, the graphite of the moderator pebble and the
graphite shell of the fuel pebble were homogenised with the inter-pebble void. With this approach the
‘pure’ streaming correction for Core 5 and 9 is about 500 pcm and 1500 pcm, respectively.


  Table 5: Sensitivity of keff to the effective absorption cross section of the graphite reflector and the
                       homogenisation of the graphite in the pebble core (Case 3).
  Core        Exp.          TRIPOLI4                                   Remarks
    5       1.0110(5)       1.0124(5)                            σabs,refl = 4.47 mbarn
                            1.0204(5)                            σabs,refl = 4.09 mbarn
                            1.0254(5)          σabs,refl = 4.09 mbarn + Homogenisation of the graphite
    9       1.0114(7)       1.0089(5)                            σabs,refl = 4.47 mbarn
                            1.0179(5)                            σabs,refl = 4.09 mbarn
                            1.0329(5)          σabs,refl = 4.09 mbarn + Homogenisation of the graphite



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DETAILED ANALYSIS OF PEBBLE-BED HTR PROTEUS EXPERIMENTS WITH THE MONTE CARLO CODE TRIPOLI4                                                                          #C12




The sensitivity of the particle models on keff was investigated for Core 5. The keff-value obtained with
the cubic lattice differed only by 50 pcm from the one obtained with the hexagonal lattice. The effect
is therefore negligible.
4.2. Reaction Rate Distributions and Ratios
Small fission chambers and activation foils were used to measure the fission rate in 235U (F5) and in
238
    U (F8) across the reactor. The capture rate in 238U (C8) was experimentally determined with particle
foils in special pebbles or whole pebbles [10].
The comparison of measured and calculated reaction rate distributions F5 and F8 in Core 5 is shown in
Figures 5 and 6. The fast reaction rate distribution F8 displays asymmetry in the core region caused by
the lower axial reflector and the cavity above the core. For the thermal traverse F5 the asymmetry is
more pronounced. The thermal flux in the adjacent lower reflector is significantly higher than at the
core centre. It is nearly constant in the cavity and peaks slightly in the upper reflector. The shape of
the axial traverse C8 is rather similar to the fast fission traverse F8.
The calculated reaction rate traverses agree quite well with the experimentally determined reaction
rates.

                                                                                      Lower Axial            Core              Cavity           Upper Axial
                                                                          2.0
                                                                                       Reflector                                                 Reflector
                Relative Reaction Rate normalised to unity at 69 cm (-)




                                                                          1.8
                                                                                                                               F5 Experiment
                                                                          1.6                                                  F5 Calculation
                                                                                                                               F8 Experiment
                                                                          1.4
                                                                                                                               F8 Calculation
                                                                          1.2

                                                                          1.0

                                                                          0.8

                                                                          0.6

                                                                          0.4

                                                                          0.2

                                                                          0.0
                                                                                -80        -40      0   40     80        120   160      200         240       280
                                                                                                               Height (cm)

Figure 5: Experimental and calculated axial reaction rates F5 and F8 in Core 5. All distributions are
                            normalised to 1.0 at the middle of the core.




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HTR2004                                                                                                                                                       Beijing, CHINA, 2004. 9.


                                                                          1.2
                                                                                    Lower Axial             Core                Cavity         Upper Axial




                Relative Reaction Rate normalised to unity at 69 cm (-)
                                                                                     Reflector                                                  Reflector

                                                                          1.0                                                        C8 Experiment
                                                                                                                                     C8 Calculation

                                                                          0.8


                                                                          0.6


                                                                          0.4


                                                                          0.2


                                                                          0.0
                                                                             -120    -80     -40      0    40     80    120    160       200    240     280
                                                                                                            Height (cm)

    Figure 6: Experimental and calculated axial reaction rates C8 in Core 5. All distributions are
                            normalised to 1.0 at the middle of the core.


The reaction rate ratios C8/F5 and F8/F5 were measured in the centre of the core. Core-averaged
reaction rate ratios were deduced from these ratios and the reaction rates distributions across the core
[11]. The experimental uncertainty of C8/F5 and F8/F5 was 2% and 5%, respectively. Table 6 shows
the comparison of experimental and calculated core-averaged reaction rates of Core 5. It can be seen
that TRIPOLI4 calculates accurately the reaction rate ratio C8/F5, but underestimates significantly the
ratio F8/F5. It is noteworthy that the latter ratio plays no important role in terms of neutron balance
component; therefore, the underestimation of F8/F5 has no impact on the keff value.


Table 6: The calculated-to-experimental (C/E) core-averaged reaction rate ratios of HTR-PROTEUS
                                              Core 5.
                                                                                       Reaction Rate Ratio                      C/E
                                                                                                                              TRIPOLI4


                                                                                                   C8/F5                      0.991(2)
                                                                                                   F8/F5                      0.743(5)


4.3. Absorber Rod Worth
Table 7 shows the experimental reactivity worths of various combinations of shutdown rods and the
C/E comparison of TRIPOLI4 results and MCNP results. It can be seen that the TRIPOLI4 in general
underestimates the shutdown rod worth, whereas the MCNP results agree better with the experimental
values. Bearing in mind, that the keff-values are well predicted with TRIPOLI4 (see Chapter 5.1.), the
underestimation probably results from the cross section data of the absorber rod material. Further
investigation is required.




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DETAILED ANALYSIS OF PEBBLE-BED HTR PROTEUS EXPERIMENTS WITH THE MONTE CARLO CODE TRIPOLI4          #C12


       Table 7 : Comparison of calculated-to-experimental (C/E) results for shutdown rods in HTR-
                                        PROTEUS Core 5 and 9.
                                                                             C/E
              Core            Rods         Experiment (E)         TRIPOLI4            MCNP
                             Inserted              ($)                                  [6]
                   A
               5                6                -3.57(4)          0.92(2)               -
                               5+6              -7.50(10)          0.93(2)
                              5+6+7             -11.45(18)         0.94(2)
                            5+6+7+8             -15.13(17)         0.93(2)
                   B
               9                5               -3.68(6)           0.95(2)              0.99
                               5+6              -7.85(14)          0.94(2)              0.97
                              5+6+7             -11.61(16)         0.96(2)              1.00
                            5+6+7+8             -16.43(45)         0.95(2)              0.99
A
    The experimental data are taken from [4].
B
    The experimental data are taken from [5].


5. CONCLUSION
Two HTR-PROTEUS pebble-bed configurations were analysed with detailed models using the Monte
Carlo code TRIPOLI4. The agreement between experimental and calculated keff values and reactions
rate distribution is extremely good, if the new recommended effective absorption cross section of
4.47 mbarn is used. Higher keff values of about 800 pcm and 900 pcm were obtained for Core 5 and 9
using the former value - 4.09 mbarn reported in the IAEA technical documentation.
The calculated conversion ratio agreed quite well with the experimental one. The core-averaged fast to
thermal reaction rate fission in 238U to 235U is significantly underestimated. TRIPOLI4 slightly
underestimates the worths of the shutdown rods.


The neutron streaming effect was determined with Monte Carlo calculations, and the results indicate
that it is about 500 pcm and 1500 pcm for Core 5 and 9, respectively. No significant change in the
system reactivity occurred with the nuclear data library JEF2.2 and JEFF3.
These studies were also very helpful to reduce the deviation in the critical core-height calculations for
the HTR-10 prototype pebble-bed reactor in Beijing (see publication at this conference, [12]).


6. ACKNOWLEDGEMENTS
The authors would like to sincerely thank Y. Pénéliau for his advice and help with the Monte
Carlo calculations. We acknowledge Electricité de France and Framatome-ANP for their support to
conduct this work.




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HTR2004                                                                          Beijing, CHINA, 2004. 9.


REFERENCES

[1]    F. Reitsma, “The Pebble Bed Modular Reactor Layout and Neutronics Design of the
       Equilibrium Cycle”, Conf. PHYSOR 2004, Chicago April 25-29 (2004).
[2]    “ A Technology Roadmap for Generation IV Nuclear Energy Systems” U.S. DOE NERSAC
       and GIF December (2002).
[3]    “Gas Turbine Modular Helium Reactor Conceptual Design Report,” General Atomics, July
       (1996).
[4]    “Critical Experiments and Reactor Physics Calculations for Low-Enriched High Temperature
       Gas Cooled Reactors,” IAEA TECDOC 1249, IAEA Vienna (2001).
[5]    R. Chawla, O.P. Joneja, M. Rosselet, T. Williams, “Definition and Analysis of an Experimental
       Benchmark on Shutdown Rod Worth in LEU-HTR Configurations,” Nuclear Technology
       Volume 139, N° 1, p. 50-60 (July 2002).
[6]    F. C. Difilippo, “Monte Carlo Calculations of Pebble Bed Benchmark Configurations of the
       PROTEUS Facility,” Nucl. Sci. & Eng., 143, 240-253 (2003).
[7]    T. Williams, “LEU-HTR PROTEUS: Configuration Descriptions and Critical Balances for the
       Cores of the HTR-PROTEUS Experimental Programme,” PSI Technical Note TM-41-95-18,
       Paul Scherrer Institute (1996).
[8]    D. Mathews, “LEU-HTR PROTEUS: Revised Reflector Graphite Impurity Estimate,” Internal
       Memorandum, Paul Scherrer Institute (1999).
[9]    J.P. Both, Y. Pénéliau, “The Monte Carlo code TRIPOLI-4 and its first benchmark
       interpretations,” International Conference on the Physics of Reactors PHYSOR 1996, Mito,
       Ibaraki, Japan (September 1996).

[10]   O. Köberl, R. Seiler, R. Chawla, “Experimental Determination of the Ratio of 238U Capture to
       235
         U Fission Rates in LEU-HTR Configurations,” Nuclear Science & Engineering, Vol. 146, p.
       1-12 (2004).
[11]   O. Köberl, “Experimentelle Neutronenbilanzuntersuchungen zum Wassereinbruch in einen
       Hochtemperaturreaktor mit niedrig angereichertem Uranbrennstoff’,” Thesis N°1803, Swiss
       Federal Institute of Technology, Lausanne (1998).
[12]   H. Chang et al., “Treatment of Stochastic Geometry in Pebble Bed Reactors with Monte Carlo
       Code Tripoli-4.3,” this conference.




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