Nuclear Energy Agency Online Bulletin

December 2000

Nuclear Science

OECD/NEA - US/NRC PWR Main Steam Line Break Benchmark

This benchmark incorporates full 3D modelling of the reactor core into system transient codes for "best-estimate" simulations of the interactions between reactor core behaviour and plant dynamics and their testing on a number of transients of importance for plant behaviour and safety analysis. This includes verifying the capability of codes to analyse complex transients with coupled core-plant interactions, to fully test the 3D-neutronics/thermal-hydraulics coupling, and to evaluate discrepancies between predictions of coupled codes in best-estimate transient simulations.

Description of the problem

The benchmark is based on a well-defined problem concerning a PWR Main Steam Line Break (MSLB), which may occur as a consequence of the rupture of one steam line upstream of the main steam isolation valves. This event is characterised by significant space-time effects in the core caused by asymmetric cooling and an assumed stuck-out control rod during reactor trip. It is based on reference design and data from the Three Mile Island Unit 1 Nuclear Power Plant (TMI-1). It includes a description of the event sequence with set points of all activated system functions and typical plant conditions during the transient.


The benchmark consists of three exercises:

The first two exercises have helped to fine-tune the models used in the different codes in order to ensure they all solve the same problem. Parametric studies and scenarios were developed to help understand the source of uncertainties. A series of statistical methods has been applied to analyse code-to-code comparisons involving different types of data single-values, 1-D and 2-D distributions, and time histories. The statistical methods have been modified to analyse correctly relative normalised parameters.


The exercise was co-organised by the OECD/NEA Nuclear Science Committee, the OECD/NEA Committee on the Safety of Nuclear Installations, and the US Nuclear Regulatory Commission. It involved about 70 experts from 15 countries representing 30 organisations. It brought together specialists in neutronics and thermal hydraulics from universities, research centres, utilities, engineering companies and vendors. It was co-ordinated by the Penn State University Nuclear Engineering Program Team.

Conclusions and recommendations

This exercise has shown:

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