1.
Additional Benchmark Evaluation of
the NRAD Reactor LEU Core
Conversion
John D. Bess
Margaret A. Marshall
Idaho National Laboratory
2012 ANS Annual Meeting
Chicago, Illinois
June 24-28, 2012
This paper was prepared at Idaho National Laboratory for the U.S.
Department of Energy under Contract Number (DE-AC07-05ID14517)

2.
Neutron Radiography (NRAD) Reactor
 250 kW TRIGA Mark II Linear channel
Safety channel 2
 Conversion-type North
beam
tube
 Located at INL G
North beam
aperture
N
 Former PRNC 2-MW reactor I H
Empty grid
J
 60 U(30/20)ErZrH rods location
Graphite
 Formerly HEU FLIP fuel A reflector
assembly
 12 graphite reflectors
B
C East
 3 control rods D
beam
tube
 2 neutron radiography E
East beam
beam lines F
aperture
 Empty positions for in- L
1 2 3 4 5 6
core experimentation K N
 Part of Hot Fuels M Safety channel 1
Log channel
Examination Facility (HFEF)
NW NE
Control rod
SW SE
Fuel cluster assembly
Neutron source (AmBe)
Standard fuel element
Irradiation positions
10-GA50002-04-3
2

3.
TRIGA Fuel Conversion
HEU LEU
Nominal
(FLIP) (30/20)
Design Data Core Configuration Operational
Fuel Fuel Number of Fuel Elements 60
Number of Fuel Rods 60 60 Total Mass (g) 2506.5 ± 3.4
Uranium Mass (g) 749.9 ± 2.7
Fuel Type UErZrH UErZrH
235U Mass (g) 148.0 ± 0.6
Uranium Enrichment % 70 19.75 235U Enrichment (%) 19.74 ± 0.02
Uranium Density wt-% 8.42 30 U Mass Content (wt.%) 29.92 ± 0.09
Erbium wt-% 1.48 0.90 H/Zr Ratio 1.58 ± 0.01
Zirconium Rod OD, mm 5.715 5.715 Er Content (wt.%) 0.90 ± 0.02
C Content (wt.%) 0.30 ± 0.02
Fuel Meat OD, mm 34.823 34.823
Fuel Element Length (mm) 380.2 ± 0.4
Fuel Meat L, mm 381 381 Fuel Element Diameter (mm) 34.805 ± 0.003
Clad Thickness, mm 0.508 0.508 Cladding Inner Diameter (mm) 34.894 ± 0.005
Clad Material 304 SS 304 SS Fuel-Clad Difference (mm) 0.089 ± 0.005
3

4.
Current Benchmark: NRAD-FUND-RESR-001
 60-fuel-rod critical
configuration
completed
 Available in March
2011 edition of
IRPhEP Handbook
 http://irphep.inl.gov/
 irphep@inl.gov
 Also available in
Sept. 2011 edition of
ICSBEP Handbook
 Useful for storage,
handling, and
transportation of UZrH
4

5.
International Handbook of Evaluated Reactor
Physics Benchmark Experiments
March 2012 Edition
 16 Contributing
Countries
 Data from 56
Experimental Series
performed at 32
Reactor Facilities
 Data from 52 out of the
56 series are
published as approved
benchmarks
 Data from 4 out of the
56 series are
published in DRAFT
form
5

6.
Summary of the Benchmark Process
6

7.
NRAD LEU TRIGA Start-Up Tests
 March 9 – June 7, 2010  Calorimetric power
calibrations
 Fuel loading approach  100, 200, 250 kW
to critical
 Full power operation
 Initial critical  ER
 56 fuel rods
 Graphite reflector
 Rod worths, ER, SDM movements
 Operational core  Dry tube worth
 60 fuel rods  Radiography beam
 Critical, rod worths, ER, characterization
SDM performed after start-
up tests were
completed
7

8.
Simplified Benchmark Model – 60 Rods
23.095 Fully
56 Rods
inserted
control rod Water
North
beam
tube
(void)
1.905
13.97
Fully
withdrawn
control rod
S2
East beam
38.1 16.51 tube (void)
Fuel 13.97
C
L
midplane
Graphite
108.73751 65.72251 Fuel Beam
reflector
rod filter tube S1
block
R
D
90
0.123825
5.08 Water
Fuel rod
S1 Shim 1 control rod
19.92
S2 Shim 2 control rod
R Regulating control rod
Dimensions in cm
Graphite reflector block 10-GA50002-145-6
Dimensions in cm
10-GA50002-145-9
8

9.
Update to Current Benchmark Model
 Fuel batch data  Zr data from Y-12,
from CERCA CERCA, and EAG
Updated 234U, 236U, measurements
and EBC in fuel Significant
Negligible reduction in Hf
computational bias content in model
50% Reduction in o +0.1 %Δkeff
associated 100% reduction in
uncertainties Hf uncertainty
9

10.
Highlights of Benchmark Evaluation
 Water Saturation of  Computational Bias of
Graphite Blocks ~1%
 Other TRIGAs with same
Largest Single problem
Uncertainty o Musashi Mark II (100 kW)
– MCNP+ENDF/B-V
±0.0025 Dk (56 rods) o Slovenia Mark II (250 kW)
– MCNP+ENDF/B-VII
±0.0021 Dk (60 rods)  Bias variation
o Quantity of fuel
o Cross Section Data
 Total Experimental o Monte Carlo Code
– KENO vs MCNP
Uncertainty
 Bias increases with
±0.0028 Dk (56 rods) core size
±0.0024 Dk (60 rods)  ~5¢ per fuel rod
10

11.
Effect of Graphite Water Saturation
60-Fuel-Element Core
11

12.
Criticality Results – 56 Rods
Experiment keff + Simplification Bias = Benchmark keff
1.0000 + 0.0014 = 1.0014 ± 0.0029 (±$0.39)
Analysis Calculated Bias
Neutron Library
Code keff ± σ Worth ($)
ENDF/B-VII.0 1.00906 ± 0.00007 0.76 1.02
JEFF-3.1 1.00712 ± 0.00007 0.57 0.76
MCNP5
JENDL-3.3 1.00616 ± 0.00007 0.48 0.63
ENDF/B-VI.8 1.00437 ± 0.00007 0.30 0.40
ENDF/B-VII.0
1.00901 ± 0.00007 0.76 1.01
(238-group)
KENO-VI
ENDF/B-VII.0*
1.00898 ± 0.00008 0.76 1.01
(continuous energy)
SERPENT ENDF/B-VII.0 1.00912 ± 0.00008 0.77 1.03
12

13.
Criticality Results – 60 Rods
Experiment keff + Simplification Bias = Benchmark keff
1.0000 + 0.0010 = 1.0010 ± 0.0025 (±$0.34)
Analysis Calculated Bias
Neutron Library
Code keff ± σ Worth ($)
ENDF/B-VII.0 1.01029 ± 0.00007 0.93 1.24
JEFF-3.1 1.00822 ± 0.00007 0.72 0.96
MCNP5
JENDL-3.3 1.00731 ± 0.00007 0.63 0.84
ENDF/B-VI.8 1.00558 ± 0.00007 0.46 0.61
ENDF/B-VII.0
1.01041 ± 0.00007 0.94 1.25
(238-group)
KENO-VI
ENDF/B-VII.0*
1.00933 ± 0.00008 0.83 1.11
(continuous energy)
SERPENT ENDF/B-VII.0 1.01032 ± 0.00008 0.93 1.24
13

14.
Reactivity Effects Measurements
 Rod measurements  Shim rods
 Uncertainty ~10%  Rod drop
o Technique (6%)  Reg rod
o Shadowing (8%)  Rod drop and
positive period
o Statistical Error (0.2%)
 SDM
 βeff  Rod drop sum
 NRAD = 0.0071  ER
 GA = 0.0078  Positive period
 Range = 0.007-0.008  Graphite blocks
 Benchmark =  Compare recalibrated
ER difference
0.0075 ± 5% (1σ)
 Dry tube
 Compare ER difference
14

15.
Location of Dry Tube and Graphite Blocks
North
beam
A5
tube
(void)
C1 13.97
S2
East beam
tube (void)
13.97
S1
R
D1 Dry tube
(void)
D
90
Water
Fuel element
S1 Shim 1 control rod
S2 Shim 2 control rod
R Regulating control rod
Dimensions in cm
Graphite reflector block
F4 11-GA50002-31-6
15

16.
Reactivity Effects Results – 56 Rods
Worth Measurement Benchmark ($) MCNP5 ($) C/E
Excess Reactivity 0.37 ± 0.02 0.43 ± 0.02 1.16 ± 0.10
Shutdown Margin -7.54 ± 0.49 -7.83 ± 0.23 1.04 ± 0.07
Shim Rod 1 -2.76 ± 0.31 -3.04 ± 0.15 1.10 ± 0.14
Shim Rod 2 -2.72 ± 0.30 -2.60 ± 0.13 0.96 ± 0.12
Reg Rod -2.43 ± 0.23 -2.62 ± 0.11 1.08 ± 0.10
16

17.
Reactivity Effects Results – 60 Rods
Worth Measurement Benchmark ($) MCNP5 ($) C/E
Graphite Block A5 -0.17 ± 0.06 -0.13 ± 0.06 0.79 ± 0.45
Graphite Block C1 -0.41 ± 0.06 -0.39 ± 0.04 0.96 ± 0.18
Graphite Block D1 -0.43 ± 0.06 -0.41 ± 0.04 0.95 ± 0.17
Graphite Block F4 -0.45 ± 0.06 -0.44 ± 0.04 0.98 ± 0.17
Excess Reactivity 1.12 ± 0.05 1.17 ± 0.04 1.05 ± 0.06
Shutdown Margin -6.73 ± 0.47 -6.66 ± 0.23 0.99 ± 0.08
Shim Rod 1 -2.68 ± 0.30 -2.79 ± 0.14 1.04 ± 0.13
Shim Rod 2 -2.75 ± 0.33 -2.63 ± 0.13 0.95 ± 0.12
Reg Rod -2.42 ± 0.16 -2.42 ± 0.08 1.00 ± 0.07
Dry Tube -0.06 ± 0.01 -0.04 ± 0.01 0.69 ± 0.25
17

18.
Future Work
 NRAD Upgrade
4 additional fuel North
beam
tube
rods (void)
13.97
4 graphite rods D
90
Repeat start-up
tests at 62 and 64 S2
East beam
rod loadings
tube (void)
13.97
Weigh graphite
S1
R
blocks
Flux measurements
Void effects
Water
Graphite element
Characterize beams
Fuel element
S1 Shim 1 control rod
S2 Shim 2 control rod
R Regulating control rod
Dimensions in cm
Graphite reflector block 11-GA50002-31-3
18

19.
Conclusion
 Completed
benchmark evaluation
of cold start-up
measurements
 Large uncertainty in
water saturation of
graphite blocks
 ~1% high
computational bias in
criticality
 Very good agreement
for worth
measurements
 Path forward for
additional benchmark
experiment data
19

20.
¿Questions?
20

21.
Extra Slides
21

22.
Experiment Evaluation – Biases
 Simplifications were  Noticeable biases
needed Simplification of
 Understand worth fuel rod end fittings
and sensitivity of Removal of steel
various components impurities
 Develop easier to use Use of average fuel
benchmark model composition
 Speed up calculation Replace control rod
time guide tubes with
H2O
 Most simplifications
caused minor Replace beam line
structure with void
changes in keff
22

23.
Calculated Spectral Data – 56 rods (MCNP5)
Model Detailed Simple
Cross Section Library ENDF/B-VII.0 ENDF/B-VII.0
keff 1.00765 1.00906
±σk 0.00007 0.00007
Neutron Leakage (%) 0.03 2.28
Thermal
(<0.625 eV) 80.58 80.75
Fission Fraction, Intermediate 16.42 16.27
by Energy (%) Fast
(>100 keV) 2.99 2.98
234U 0.01 0.01
235U 98.74 98.74
Fission Fraction,
236U 0.01 0.01
by Isotope (%)
238U 1.24 1.23
Average Number of
Neutrons Produced 2.444 2.444
per Fission
Energy of Average
Neutron Lethargy 0.26679 0.26275
Causing Fission (eV)
23

24.
Calculated Spectral Data – 60 rods (MCNP5)
Model Detailed Simple
Cross Section Library ENDF/B-VII.0 ENDF/B-VII.0
keff 1.00934 1.01029
±σk 0.00007 0.00007
Neutron Leakage (%) 0.04 2.39
Thermal
(<0.625 eV) 80.38 80.54
Fission Fraction, Intermediate 16.60 16.46
by Energy (%) Fast
(>100 keV) 3.02 3.00
234U 0.01 0.01
235U 98.73 98.73
Fission Fraction,
236U 0.01 0.01
by Isotope (%)
238U 1.25 1.24
Average Number of
Neutrons Produced 2.444 2.444
per Fission
Energy of Average
Neutron Lethargy 0.27191 0.26810
Causing Fission (eV)
24

25.
Discussion of Cross Section Data
 Cause of Bias?  Er
 Cross section and/or code  KENO and MCNP keff
related values agree when Er is
 Fuel rods significant removed
 235U and 238U  Low-lying resonance
approximations in free-
 Small difference between gas scattering kernels ?
JENDL-3.3 and ENDF/B-
VII.0 data  Currently being
o JENDL thought to be “more investigated
correct” o KUCA
 91Zr and ZrH S(a,b)  Graphite (Cnat)
 Bias identified  (n,g) larger in JENDL-3.3
o Slovenia TRIGA Mark II than ENDF/B-VII.0
o Fuel contains no Er  (n,g) increased further
o ICNC 2011 (Sept.) in JENDL-4.0 base on
 ZrH S(a,b) calculated HTGR research
differently in JEFF-3.1 and
ENDF/B-VII.0
25

26.
Future Work – II
 Computational  Additional “To-Do”
Methods Benchmarks
Continue to SNAP 10A/2 water
immersion
investigate Er experiments
o KUCA experiments
Expand NRAD
Investigate thermal benchmark library
scattering S(α,β) Invite other
cross sections members of TRIGA
o Collaborative effort community to
benchmark their
reactors
26

27.
References
 Bess, J. D., Maddock, T. L., Marshall, M. A., “Fresh Core Reload of the
Neutron Radiography (NRAD) Reactor with Uranium(20)-Erbium-
Zirconium-Hydride Fuel,” INL/EXT-10-19486, Idaho National
Laboratory (2010).
 International Handbook of Evaluated Reactor Physics Benchmark
Experiments, NEA/NSC/DOC(2006)1, OECD-NEA, Paris, France (2011).
 Matsumoto, T., Hayakawa, N., “Benchmark Analysis of TRIGA Mark II
Reactivity Experiment Using a Continuous Energy Monte Carlo Code
MCNP,” J. Nucl. Sci. Tech., 37(12), 1082-1087 (2000).
 Snoj, L., Žerovnik, G., Trkov, A., “Analysis of Cross Section Libraries
on Zirconium Benchmarks,” Proc. ICNC 2011, Edinburgh, Scotland,
September 19-22 (2011).
 Jeraj, R., Ravnik, M., “TRIGA Mark II Reactor: U(20)-Zirconium Hydride
Fuel Rods in Water with Graphite Reflector,” IEU-COMP-THERM-003,
International Handbook of Evaluated Criticality Safety Benchmark
Experiments, NEA/NSC/DOC(95)03, OECD-NEA, Paris, France (2010).
 Shimakawa, S., Goto, M., Nakagawa, S., Tachibana, Y., “Impact of
Capture Cross-Section of Carbon on Nuclear Design for HTGRs,”
Proc. HTR 2010, Prague, Czech Republic, October 18-20 (2010).
27

28.
Detailed Model Development
28

29.
Fuel Clusters
Top
Assembly
7.7089
Fuel Rods
3.8862
3.8862
Top View
8.10006
Bottom Dimensions in cm
Assembly 10-GA50002-145-5
10-GA50002-74-2 Dimensions in cm
10-GA50002-145-4
29

30.
Top fuel fitting
Fuel Rods
Top end fitting (SS 304/304L)
OD 3.4894 cm Cladding 0.180 MIN.
1.27
Void gap 0.724535
Upper
Top axial reflector (graphite) 8.6868 fuel
reflector
OD 3.27914
Cladding (SS 304/304L)
ID 3.4894, OD 3.591
Zirconium rod
U-Er-Zr-H fuel
ID 0.635, OD 3.4805
23.125 (REF)
38.02 58.73751 + 0.000
25.875 - 0.031
Fuel pellets (3)
Zirconium rod
OD 0.5715
Molybdenum poison disc + 0.003
1.370 - 0.000 I.D.
(REF)
0.079375
Molybdenum poison disc Lower
fuel
OD 3.46964 reflector
Bottom axial reflector (graphite)
OD 3.27914
8.6868
Bottom end fitting (SS 304/304L)
OD 3.4894
1.27
Dimensions in cm Bottom fuel fitting
10-GA50002-145-1
1.414 DIA. Dimensions in inches
NOM. (REF) 10-GA50002-76
30

31.
Control Rods Detail of top fitting
2.5
1.25
0.5
Top end fitting (Al 6061) 5/8 flats 0.5 0.625
OD 3.03276
1.9685 0.40 D 1.194 D
1/2-13 UNC-2A 0.125
+ 0.000
0.060 - 0.004
0.1875
Void
Void 17.78
Cladding (Al 6061)
ID 3.03276 1-1/8" O.D. x 0.035" wall
OD 3.175 L 6.5
Al alloy tube
Spacer
1.187 +0.005 O. D.
-
0.000
0.5 D thru
L 0.5
59.436
24.00
REF 23.40
B4C absorber 23.25 1-1/4" O.D. x 0.028" wall
OD 3.01498 L 23.4
Al alloy tube
38.1
15.0
Boron carbide
D 1.187 +0.030
-
0.000
Detail of bottom fitting
D 1.194 0.75
Bottom end fitting (Al 6061) 0.625
OD 3.03276 0.1875 1/16 x 1/16 groove
1.5874
Dimensions in cm
10-GA50002-145-2
0.060 +0.000 0.125
1/16 DIA -0.004
THRU
Dimensions in inches
10-GA50002-90
31

32.
Guide Tube
32

33.
Graphite Reflectors
Handle
W0170-0089-DE (REF)
Screw, HEX SOC HD
5/8-11 UNC-2A x 2 LG
ALUM 2011-T3
2 REQD
Graphite element
reactor grade
0.9525 cm x 45° chamfer 25.875
± 0.125
65.72251
7.366
7.366
Top View
0.656 +0.002 DIA DRILL
-
0.005
x 0.875 ± 0.060 DP
2 places
5/8-11 UNC-2A THD
Dowel pin Both ends
0.645 DIA x 1-1/2 LG
Alum 2011-T3, 2 REQD
Tie rod + 0.000
D 1.968 - 0.030
5/8 x 7-7/8 LG
ALUM 2011-T3
Adapter
ALUM 2011-T3
Dimensions in cm
Adapter
10-GA50002-145-3
W0170-0090-DD (REF)
0.375 ± 0.030 x 45° ± 5°
Hex nut
Chamfer TYP
5/8-11 UNC-2B THD
ALUM 2011-T3
2.900 +0.100
-
0.000
square
Dimensions in inches 10-GA50002-05-1
33

34.
Photograph of NRAD Tank
34