1.
Benchmark Evaluation of the
Start-Up Core Reactor
Physics Measurements of the
High Temperature
Engineering Test Reactor
John Darrell Bess
R&D Staff Engineer
Reactor Physics Analysis and Design
www.inl.gov
PHYSOR 2010
May 12, 2010
This paper was prepared at Idaho National Laboratory for the U.S.
Department of Energy under Contract Number (DE-AC07-05ID14517)

2.
Objective
• Perform a detailed benchmark analysis of the
start-up physics tests at the High Temperature
Engineering Test Reactor
– High priority benchmark
for the Next Generation
Nuclear Plant (NGNP)
Project and Very High
Temperature Reactor
(VHTR) Program
– Submit completed
work for inclusion in the
IRPhEP Handbook
2

3.
3

4.
Evaluation Process: ICSBEP & IRPhEP
4

5.
High Temperature Test Reactor
(HTTR)
• 30 MWt
• Graphite
Moderated/Reflected
• Core Diameter = 2.3 m
• Core Height = 2.9 m
• Helium Coolant
• 150 Fuel Assemblies
• 30 Fuel Columns
5

6.
HTTR Core
• Prismatic Pin-in-Block Fuel
• UO2 Fuel
– Enriched 3 to 10 wt.%
– ~6 wt.% average
• Reflector
Thickness ~1 m
• 16 Pairs of B4C
Control Rods
• Burnable Poison Pellets
– 2.0 and 2.5 wt.% Bnat
6

7.
Summary of Start-Up and Zero-Power Tests
• Six cold critical • Three axial reaction rate
configurations measurements
– One full core – Instrumentation columns
– Five annular cores • Full core
• Excess reactivity • 24-column core (2)
measurements • Isothermal temperature
– Fuel loading coefficients
• Shutdown margins – 340 to 740 K
– All rods at once • Two warm criticals
– Two-step by region – 400 and 420 K
• Full core subcritical • Differential rod worth (C)
– Insufficient data
7

8.
Challenges
• Limitation in available
public information
• Some data is unknown
• Availability of some
information only in
Japanese
• Conflicting reported
values for some
information
• Large biases in
eigenvalue calculations
8

9.
TRISO in Prismatic Fuel Blocks
09-GA50001-158-4
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10.
Fuel and Burnable Poison Loading
The top The bottom
number of number
each block represents the
represents boron content
the uranium in the burnable
enrichment. poison pellets.
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11.
Fully-Loaded Core Configuration
11

12.
Control Rods
12

13.
Annular Core Loadings
19 21
24 27
13

14.
MCNP5 : ENDF/B-VII.0
Criticality T = 300 K
MCNP5 : JENDL-3.3
results ~0.5% lower
Uncertainties in Graphite
Impurities and Cross
Section Data
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15.
Excess Reactivity Measurements
• Obtained by measuring and adding all fuel loading increments
15

16.
Shutdown Margin
1. Full insertion of reflector region
rods from critical
2. Full insertion of fuel region rods
from previous insertion
3. Full insertion of all control rods
from critical
Shadowing Effects
in the Core
16

17.
Isothermal Temperature Coefficients
• Two different 0.000
reports
-0.005
13σ
• IAEA-TECDOC-
Temperature Reactivty Coefficient (%∆k/k/K)
Good 3σ - 4σ
1382 data invalid -0.010
• CR positions -0.015
known exactly for
first two points -0.020
• CR positions -0.025
Bad
estimated with Measurement?
adjusted rod worth -0.030
data for others Experimental
-0.035
Calculated
• Significant
shadowing effect -0.040
300 350 400 450 500 550 600 650 700 750 800
Isothermal Temperature (K)
17

18.
Instrumentation holes
Axial Reaction Rates 10
108
360
D123
• Instrumentation columns in
24- and 30-fuel column cores
• Uncertainties Evaluated
– Measurement 4160
– Repeatability Total height
5220 mm
(522 segments)
– Graphite Composition
– Graphite Dimensions
– Control Rod Positions
– Digitization
– Renormalization
1060
Dimensions in mm 09-GA50001-103
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19.
Axial Neutron Reaction-Rate in the Instrumentation Axial Neutron Reaction-Rate in the Instrumentation
Columns of the Fully-Loaded HTTR Core Columns of the Annular 24(F23)-Fuel-Column HTTR
Core
500 500
400 400
Axial Distance (cm) from the Bottom of the Lowest Fuel Block
Axial Distance (cm) from the Bottom of the Lowest Fuel Block
Core Top Core Top
300 300
Fuel Top Fuel Top
200 200
100 100
0 0
Fuel Bottom Fuel Bottom
-100 -100
Core Bottom Core Bottom
-200 -200
0 0.2 0.4 0.6 0.8 1 1.2 0 0.2 0.4 0.6 0.8 1 1.2
Normalized Neutron Flux Normalized Neutron Flux
19
Instrumentation Columns Benchmark Values Core Boundaries Instrumentation Columns Benchmark Values Core Boundaries

20.
Additional Eigenvalue Measurements
• Full shutdown subcritical of fully loaded core
• Two warm criticals in support of temperature coefficients
• Warm critical in IAEA-TECDOC-1382 invalid
• Similar results to cold critical analyses
MCNP5 : ENDF/B-VII.0
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21.
Benchmark Status
• Evaluation of the start-up physics tests has been
completed
– Two approved benchmarks included in the 2010 edition
(in press) of the IRPhEP Handbook
• Evaluation of the zero-power, elevated-
temperature measurements has been performed
– Benchmark to be prepared and submitted for inclusion
in the 2011 edition of the IRPhEP Handbook
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22.
Conclusions
• Eigenvalue calculations ~2% higher than
benchmark values
– Comparable to results from Japanese evaluations
– Graphite composition and cross section uncertainties
• Generally good agreement for excess reactivity,
shutdown margin, axial reaction rate, and
isothermal temperature coefficient measurements
• All completed benchmark analysis to be publicly
available in the IRPhEP Handbook
22

23.
Acknowledgments
• Nozomu Fujimoto – JAEA
• Luka Snoj – Jožef Stefan Institute
• Atsushi Zukeran – Consultant
• Blair Briggs, Barbara Dolphin, Hikaru Hiruta,
Dave Nigg, Jim Sterbentz, and Chris White –
INL
23

24.
Questions