VALIDATION OF IMPROVED 3D ATR MODEL Page: 2 of 3
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Validation of Improved 3D ATR Model
Soon S. Kim and Bruce G. Schnitzler
P. O. Box 1625, Idaho Falls, ID 83415-3458, Soon.Kim@inl.govINTRODUCTION
A full-core Monte Carlo based 3D model of the
Advanced Test Reactor (ATR) was previously developed.
[1] An improved 3D model has been developed by the
International Criticality Safety Benchmark Evaluation
Project (ICSBEP) to eliminate homogeneity of fuel plates
of the old model, incorporate core changes into the new
model, and to validate against a newer, more complicated
core configuration. This new 3D model adds capability
for fuel loading design and azimuthal power peaking
studies of the ATR fuel elements.
MCNP MODELING
The ATR, located at the Idaho National Laboratory is
a 250 MW (thermal) high flux test reactor designed 1) to
study irradiation effects on reactor/fuel materials, 2) to
generate radioisotopes for medical/research application,
and 3) to irradiate cobalt target capsules. The ATR
contains forty fuel elements arranged in a serpentine
fashion to form flux traps (see Fig. 1). The fuel element
consists of nineteen curved plates of different widths,
attached to side plates forming a 45 degree sector of a
circular annulus. The fuel meat contains highly enriched
(93%) uranium-aluminide fuel powder dispersed in
aluminum powder. The fuel elements are moderated by
light-water, and reflected by beryllium.
The full-core model was developed using MCNP [2].
In the new model, each of the forty fuel elements was
represented by 117 radial and 5 axial regions. The
borated fuel plates 1 - 4 and 16 - 19 as well as the non-
borated plates 5 - 15, were explicitly modeled. The
arcuate fuel meat, cladding, non-fuel regions next to the
meat, side plates, and water gap between fuel elements
were explicitly modeled. Various irradiation holes and
fillers in the core were explicitly modeled. New
irradiation facilities were added in the new model. The
new model was validated against a critical core
configuration achieved in 1994. This critical core
contains fresh fuel elements and cobalt target loadings in
the Northeast, Center, East, and South flux traps, and a
fresh beryllium reflector, which were explicitly modeled.
The outer shim control cylinders were set to 51.8 degrees,
and all of the safety rods were fully withdrawn. All of the
shims rods, except two regulating rods, were fully
inserted in the critical core configuration.N
Fig. 1. Plan View of the 3D ATR Model.
RESULTS
The MCNP calculated keff for the 1994 critical core
was 0.99875 + 0.00034, which is 0.1% subcritical. Fig. 2
compares normalized fuel element power for each of the
forty fuel elements. In general, good agreement was
observed between measurement data and MCNP
calculated data. The uncertainty in the fuel element
power measurements was + 1.5%. Calculated lobe
powers were within 4.3% of the measured data. The
MCNP element powers were compared with PDQ [3]
results. The results from the two codes agreed with each
other with a maximum difference of 6.7%. Extensive
sensitivity calculations were performed to determine
material effects and geometric uncertainties of various
core components on keff. The sum of the uncertainties is
calculated to be 0.24 %Akeff.
The detailed model developed and documented
through the ICSBEP project provides valuable data for
ATR programs. The full-core model can be used for
physics analysis of asymmetric experiment loading in the
core, and now for new fuel loading design and azimuthal
power peaking studies of the ATR fuel elements.
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Kim, Soon Sam & Schnitzler, Bruce G. VALIDATION OF IMPROVED 3D ATR MODEL, article, November 1, 2005; [Idaho Falls, Idaho]. (https://digital.library.unt.edu/ark:/67531/metadc887589/m1/2/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.