Andy M. Olson
200 Exelon Way, KSA2-N
Kennett Square, PA 19348
Incorporation of full three-dimensional (3D) models of the reactor core
into system transient codes allows for a “best-estimate”
of interactions between the core behavior and plant dynamics. Recent
in the computer technology has made development of coupled system
(T-H) and neutron kinetics code systems feasible. Considerable efforts
have been made in various countries and organizations in this
To verify the capability of the coupled codes to analyze complex
with coupled core-plant interactions and to fully test
coupling, appropriate Light Water Reactor (LWR) transient benchmarks
to be developed on a higher “best-estimate” level. The previous sets of
transient benchmark problems addressed separately system transients
mainly for thermal-hydraulic (T-H) system codes with point kinetics
and core transients (designed for T-H core boundary conditions models
with a three-dimensional (3-D) neutron kinetics models). The Nuclear
Agency (NEA) of the Organization for Economic Cooperation and
(OECD) has recently completed under the US Nuclear Regulatory
(NRC) sponsorship a PWR Main Steam Line (MSLB) Benchmark against
T-H and neuron kinetics codes. Small benchmark team from the
State University (PSU) has been responsible for developing the
specification, assisting the participants and coordinating the
activities. The benchmark was very well internationally accepted. It
felt among the participants that there should be a similar benchmark
the codes for a BWR plant transient. The Turbine Trip (TT) transients
a BWR are pressurization events in which the coupling between core
and system dynamics plays an important role. In addition the available
real plant experimental data makes the proposed benchmark problem very
valuable. NEA, OECD and US NRC have approved it for the purpose of
advanced system best-estimate analysis codes.
As a result a this benchmark project is established to
coupled system T-H/neutron kinetics codes against a Peach-Bottom-2 (a
GE-designed BWR/4) turbine trip transient with a sudden closure of the
turbine stop valve. Three-turbine trip (TT) transients at different
levels were performed at the Peach Bottom (PB)-2 BWR/4 Nuclear Power
(NPP) prior to shutdown for refueling at the end of Cycle 2 in April
The second test is selected for the benchmark problem to investigate
effect of the pressurization transient, (following the sudden closure
the turbine stop valve) on the neutron flux in the reactor core. In a
manner the test conditions approached the design basis conditions as
as possible. The actual data were collected, including a compilation of
reactor design and operating data for Cycles 1 and 2 of PB and the plant
transient experimental data. The transient was selected for
because it is a dynamically complex event for which neutron kinetics in
the core was coupled with thermal-hydraulics in the reactor primary
The reference problem chosen for simulation in a BWR is a Turbine Trip
transient, which begins with a sudden Turbine Stop Valve (TSV) closure.
The pressure oscillation generated in the main steam piping propagates
with relatively little attenuation into the reactor core. The induced
pressure oscillation results in dramatic changes of the core void
and fluid flow. The magnitude of the neutron flux transient taking
in the BWR core is strongly affected by the initial rate of pressure
caused by pressure oscillation and has a strong spatial variation. The
correct simulation of the power response to the pressure pulse and
void collapse requires a 3-D core modeling supplemented by 1-D
of the remainder of the reactor coolant system.
The purpose of this proposal is to establish a BWR TT
based on a well defined problem with complete set of input
and reference experimental data, for qualification of the coupled
neutron kinetics/thermal-hydraulic system transient codes. Since
kind of transient is a dynamically complex event with reactor variables
changing very rapidly, it constitutes a good benchmark problem to test
the coupled codes on both levels: neutronics/thermal-hydraulic coupling
and core/plant system coupling. Subsequently, the objectives of the
benchmark are: comprehensive feedback testing and examination of the
of coupled codes to analyze complex transients with coupled core/plant
interactions by comparison with actual experimental data.
Definition of the Benchmark Exercises
The benchmark consists of three separate exercises:
Exercise 1 - Power vs. Time Plant System Simulation with
Power Profile Table (Obtained from Experimental Data)
The purpose of the first exercise is to test the thermal-hydraulic
response and to initialize the participants' system models. Core power
response is fixed to reproduce the actual test results utilizing either
power or reactivity vs. time data.
Exercise 2 - Coupled 3-D Kinetics/Core
Thermal-Hydraulic BC Model
and/or 1-D Kinetics Plant System Simulation
The second exercise consists of two options. Option 1 of the second
is to perform a coupled 3-D kinetics/thermal-hydraulic calculation for
the reactor core using the PSU-provided boundary conditions at core
and exit. The core boundary conditions will be provided utilizing a
of the calculated PSU results and test data. Option 2 of the second
is to perform coupled 1-D neutron kinetics/thermal-hydraulics core
condition model calculation for the core using the same boundary
provided for option 1. 1-D cross-sections are collapsed from the
libraries generated for 3-D simulation. The participants can
in either or both options.
Exercise 3 - Best-Estimate Coupled 3-D
The third exercise consists also of 2 options. In Option 1 the
perform a coupled 3-D core/thermal-hydraulic calculation for the core
1-D thermal-hydraulics modeling for the balance of the plant. In option
2 the participants perform the calculation using a 1-D kinetics core
and 1-D thermal-hydraulics for the reactor primary system. This
combines elements of the first two exercises of this benchmark and is
analysis of the transient in its entirety.
Boiling Water Reactor Turbine Trip (TT) Benchmark - Volume
Specification (25 June 2001) by J. Solis, K.
Ivanov, B. Sarikaya, A. Olson and K.W. Hunt (final printed version),
Boiling Water Reactor Turbine Trip (TT) Benchmark - Volume III: Summary
Results of Exercise 2, by Bedirhan Akdeniz, Kostadin N.
Ivanov and Andy M. Olson, OECD 2006,
NEA/NSC/DOC(2006)23, ISBN 92-64-02331-3.
The discussion among participants in the benchmark is
archived in the BWRTT
of the fourth
BWR-TT Workshop, held in connection with the Physor-2002
conference at Seoul, Republic of Korea, 6 October 2002, followed
by a Physor-2002 Special Invited Session on "Numerical and
Issues of Coupled 3-D Kinetics/thermal-hydraulic System Simulations -
BWR TT Benchmark" in which benchmark participants present their models,
results and sensitivity studies.
of the fifth and
final BWR-TT Workshop,hosted by the Technical University of
(UPC) from 21-22 January 2003 in conjunction with the CRISSUE-S
(Revisiting Critical Issues In Nuclear Reactor Design/Safety by Using
(3-D) Neutronics/Thermal-hydraulics Models: State-of-the-Art) meeting
for 23-24 January 2003.
The Listserver of the benchmark is now closed. However the archive of exchanged e-mails sorted according
to date, subject, author and thread is accessible for those who wish to
find out more about the discussion that has taken place.
For more information on WPRS, please contact .
For more information on activities managed/supported by the NSC, please contact .