OECD/NEA PBMR Coupled Neutronics/Thermal-hydraulics Transients Benchmark - The PBMR-400 Core Design 

Background and purpose

This international benchmark, concerns Pebble-Bed Modular Reactor (PBMR) coupled neutronics/thermal hydraulics transients based on the PBMR-400MW design. The deterministic neutronics, thermal-hydraulics and transient analysis tools and methods available to design and analyse PBMRs lag, in many cases, 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 given 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 design
• 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 two parts (phases), each part consisting of different exercises:s:

• Phase I: Steady State Benchmark Calculational Cases

• Phase II: Transient Benchmark

Reference

Material available to participants on CD-ROM

    Records of meetings

• Proceedings of the first workshop (PBMRT1)
• Summary of the First workshop, Paris, 16-17 June 2005 (PBMRT1)
• Proposed Agenda for Ad-hoc meeting, Avignon, 13 September 2005 (PBMRT1.5)
• Proposed Agenda for  Second workshop (PBMRT2) OECD/NEA Issy les Moulineaux, France, 26-27 January 2006
• Update concerning the Benchmark (20 October 2006)
• Proceedings of the second workshop (PBMRT2)
• Summary of Second workshop, Issy les Moulineaux, 26-27 January 2006
• Proposed Agenda for Third workshop (PBMRT3) OECD/NEA Issy les Moulineaux, France, 1-2 February 2007
• Summary of Third workshop (PBMRT3) OECD/NEA Issy les Moulineaux, France, 1-2 February 2007

    Benchmark Specification

• Updated Benchmark specifications document Draft V107 (dated 20 June 2007)
• The Simplified Cross Section Set: "OECD-PBMR400-Simplified.XS"
• Decay Heat Values (12 December 2006)
  
• The multi-dimensional interpolation routine "lint5d.for"
• Sample Excel spreadsheets to report results for steady-states (1, 2, 3)  and transient cases (1, 2, 3, 4a, 4b, 5a, 5b, 5c, 5d, 6) (20 June 2007), zipped Excel spreadsheets
• Questionnaire for submitting results for OECD PBMR-400 Benchmark (Word) (20 August 2007)
  

    Latest comparisons of results for Exercises 1, 2 and 3 of the PBMR-400 benchmark (update: 14  December 2006)

• PBMR-400 Exercise 1 comparison sheets
• PBMR-400 Exercise 2 comparison sheets
• PBMR-400 Exercise 3 and Transient Cases comparison templates

• Updated library description (Section 7 from the specification) (14 November 2006)

• Cross section library OECD-PBMR400.XS.zip or unzipped XS (20 June 2007) - Only change is in 1/v data of void areas - was zero - now a typical value is included

• RESULTS used in the COMPARISONS for the 3rd WORKSHOP (PBMRT3)  held on 1-2 Feb 2007 (6 June 2007).

• RESULTS used in the COMPARISONS for the 4th WORKSHOP (PBMRT4) held on 21-25 January 2008 NEW
  Steady state results
  Transient results
  

 Action List

• Update of actions and solutions on Task list / Outstanding issues - PBMRT3 meeting (20 June 2007)
  

    Archived information

• 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). (Superceded)
  
• Library “OECD-PBMR400-NoBuck.XS” that contains no buckling dependencies, only fuel and moderator temperature and xenon concentration dependencies (5 Mbytes). (Superceded)