VVER-1000 Coolant Transient Benchmark - OECD Nuclear Energy ...

Chapter 1: Introduction
INTRODUCTION
Recently developed best-estimate computer code systems for modelling of 3-D coupled neutronics/
thermal-hydraulic transients and for the coupling of core and system dynamics need to be validated
against experimental results and compared against each other. International benchmark studies have
been set up for this purpose.
Coupled code benchmarks such as the OECD PWR MSLB problem (NEA, 1999) identified the
coolant mixing as an unresolved issue in the analysis of complex plant transients with reactivity
insertion. Phase 2 of the VVER-1000 Coolant Transient Benchmarks (V1000CT-2) (NEA, 2010a, 2010b;
Topalov, 2004; Bieder, 2004) was thus defined aiming at providing a framework for:
• assessment of single-phase vessel mixing models;
• assessment of coupled codes in MSLB simulations using validated mixing models.
The benchmark includes a complete set of input data and consists of three exercises as
summarised below.
1.1 Exercise 1 – Computation of a vessel mixing experiment
The vessel mixing problem is based on VVER-1000 plant experiments. The objective is to test the
capability of reactor vessel thermal-hydraulic models to represent single-phase flow mixing. The
specific objectives are:
• understanding the main physics;
• qualification of the available data;
• understanding the hard point of modelling;
• understanding the actual limits of CFD and coarse-mesh simulation.
The reference problem is a coolant transient initiated by steam generator isolation at low power,
considered as a pure thermal-hydraulic problem. The available plant data permit code validation on
different scales:
• separate effects;
• component level (reactor pressure vessel);
• system level.
Regarding CFD codes the task is to assess the ability of CFD to reproduce the experimentally
observed angular turn of the loop flow centres (swirl) and the core inlet temperature distribution,
given the vessel boundary conditions and the pressure above the core. The calculation of the vessel
outlet parameters (loop-to-loop mixing) is an option.
Regarding system codes, the task is to assess the ability of multi-1-D vessel models with
cross-flow and coarse 3-D models to reproduce the swirl and the core inlet temperature distribution,
as well as the vessel outlet temperatures. Given vessel boundary conditions or full plant simulation
can be used.
V1000CT-2: SUMMARY RESULTS OF EXERCISE 1 ON VESSEL MIXING SIMULATION – © OECD/NEA 2010 13