In co-operation with PBMR Pty Ltd, Penn State University (PSU)
Background and purpose
This international benchmark, concerns Pebble Bed Modular
Reactor (PBMR) coupled neutronics/thermal-hydraulics transients based
on the PBMR-400MW design. In many cases the deterministic neutronics,
thermal-hydraulics and transient analysis tools and methods available
to design and analyse PBMRs lag behind the state of the art compared to
other reactor technologies. This has motivated the testing of existing
methods for HTGRs but also the development of more accurate and
efficient tools to analyse the neutronics and thermal-hydraulic
behaviour for the design and safety evaluations of the PBMR. In
addition to the development of new methods, this includes defining
appropriate benchmarks to verify and validate the new methods in
computer codes.
The scope of the benchmark is to establish well-defined problems, based
on a common set of cross-sections, to compare methods and tools in core
simulation and thermal-hydraulics analysis with a specific focus on
transient events through a set of multi-dimensional computational test
problems.
The benchmark exercise has the following objectives:
establish a standard benchmark for coupled codes
(neutronics/thermal-hydraulics) for PBMR designs;
code-to-code comparison using a common cross-section
library;
obtain a detailed understanding of the events and the
processes;
benefit from different approaches, understanding
limitations and approximations.
Major design and operating
characteristics of the PBMR
PBMR characteristic
Value
Installed thermal
capacity
400
MW(t)
Installed electric
capacity
165MW(e)
Load following
capability
100-40-100%
Availability
>
=
95%
Core configuration
Vertical
with fixed centre
graphite reflector
Fuel
TRISO
ceramic coated U-235 in graphite spheres
Primary coolant
Helium
Primary coolant
pressure
9MPa
Moderator
Graphite
Core outlet
temperature
900°C.
Core inlet
temperature
500°C
Cycle type
Direct
Number of circuits
1
Cycle efficiency
>=
41%
Emergency planning
zone
400
meters
The PBMR functions under a direct Brayton cycle with primary coolant
helium flowing downward through the core and exiting at 900°C. The
helium then enters the turbine relinquishing energy to drive the
electric generator and compressors. After leaving the turbine, the
helium then passes consecutively through the LP primary side of the
recuperator, then the pre-cooler, the low-pressure compressor,
intercooler, high-pressure compressor and then on to the HP secondary
side of the recuperator before re-entering the reactor vessel at
500°C. Power is adjusted by regulating the mass flow rate of gas
inside the primary circuit. This is achieved by a combination of
compressor bypass and system pressure changes. Increasing the pressure
results in an increase in mass flow rate, which results in an increase
in the power removed from the core. Power reduction is achieved by
removing gas from the circuit. A Helium Inventory Control System is
used to provide an increase or decrease in system pressure.
The PBMR-400 benchmark consists of phases, each consisting
of different exercises:
Phase I: Steady state benchmark calculational cases
Exercise 1: Neutronics solution
with fixed cross-sections;
Exercise 2: Thermal-hydraulic solution with given power/heat sources;
Exercise 3: Combined neutronics thermal-hydraulics calculation -
starting condition for the transients.
Phase II: Transient benchmark
Exercise 1: Depressurised loss of
forced cooling (DLOFC) without SCRAM;
Exercise 2 : Depressurised loss of forced cooling (DLOFC) with SCRAM;
Exercise 3: Pressurised loss of forced cooling (PLOFC) with SCRAM;
Exercise 4 : 100-40-100 load follow;
Exercise 5 : Fast reactivity insertion - control rod withdrawal (CRW)
and control rod ejection (CRE) scenarios at hot full power conditions;
Exercise 6 : Cold helium inlet.
Reference
Frederik Reitsma, Kostadin
Ivanov,Tom Downar, Han de Haas, Sonat
Sen, Gerhard Strydom, Ramatsemela Mphahlele, Bismark Tyobeka, Volkan Seker, Hans D Gougar: PBMR Coupled Neutronics/Thermal Hydraulics Transient Benchmark - The PBMR-400 Core Design, Benchmark Definition, Draft V03, published by the NEA in 2005.
Material available to
participants on CD-ROM
Proceedings
of the first workshop (PBMRT1);
Updated benchmark specifications document Draft V103, dated 1 September 2005;
The simplified cross-section set: "OECD-PBMR400-Simplified.XS";
The multi-dimensional interpolation routine "lint5d.for";
Sample Excel spreadsheets to report results for transient cases;
Sample Excel spreadsheets to report the steady state case results;
Library “OECD-PBMR400.XS” that contains cross-sections as a function of fuel and moderator temperatures; xenon concentrations, and fast and thermal buckling values (42 Mbytes);
Library “OECD-PBMR400-NoBuck.XS” that contains no buckling dependencies, only fuel and moderator temperature and xenon
concentration dependencies (5 Mbytes).
Contacts
For more information, please contact .
For more information on activities managed/supported by the NSC, please contact .
