OECD Nuclear Energy Agency (NEA), Gesellschaft für Anlagen und Reaktorsicherheit(GRS) mbH,  Penn State University (PSU)



KALININ-3 Coolant Transient Benchmark – Switching-off of One of the Four Operating Main Circulation Pumps at Nominal Reactor Power


Introduction

During the last several years a considerable effort was devoted and progress has been made in various countries and organizations in incorporating full three-dimensional (3D) reactor core models into system transient codes. The coupled thermal-hydraulic (TH) and neutron kinetics (NK) code systems allow performing of a "best-estimate" calculation of interactions between the core behaviour and plant dynamics. Several benchmarks have been developed to verify and validate the capability of the coupled codes in order to analyze complex transients with coupled core-plant interactions for different types of reactors.

The Nuclear Energy Agency (NEA) of the Organization for Economic Cooperation and Development (OECD) has recently completed the VVER-1000 Coolant transient benchmark (V1000CT-1) and (V1000CT-2) for evaluating coupled TH system NK codes by simulating transients at the Bulgarian NPP Kozloduy Unit #6. The available real plant experimental data made these benchmark problems very valuable.

This benchmark is a continuation of the above activities and it defines a coupled code problem for further validation of thermal-hydraulics system codes for application to Russian-designed VVER-1000 reactors based on actual plant data from the Russian NPP Kalinin Unit #3 (Kalinin-3). The selected transient 'Switching-off of one Main Circulation Pump (MCP)' is performed at a nominal power and leads to asymmetric core conditions with broad ranges of the parameter changes. The experimental data is very well documented. Measurements were carried out with a quite high frequency and their uncertainties are known for almost all measured parameters. This fact allows applying the studied transient not only for validation purposes but also for uncertainty analysis as a part of the NEA/OECD LWR Uncertainty Analysis in Modelling (UAM) Benchmark.

This report provides the specifications for the international, coupled VVER-1000 Coolant Transient (KALININ-3) benchmark problem. The specification report has been prepared jointly by leading specialists of the All-Russian Research Institute Nuclear Power Plant Operation (VNIIAES), the Russian Research Centre "Kurchatov Institute"(KIAE), the Gesellschaft für Anlagen und Reaktorsicherheit mbH (GRS) and the Pennsylvania State University (PSU).

The specification covers the four exercises: point kinetics model inputs, transient core calculations, transient coupled calculations, and uncertainty analysis In addition, a CD-ROM is also made available with the detailed data for the transient boundary conditions, decay heat values as a function of time, and cross-section libraries.

In December 2008 the NEA Nuclear Science Committee (NSC) Bureau has expressed support for the coupled Kalinin-3 benchmark problem in general to become an international standard problem for validation of the best-estimate safety codes. The Working Party on Scientific Issues of Reactor Systems (WPRS) discussed in its February 2009 meeting the proposal and endorsed it as it is of particular importance for the last phase of the Uncertainty Analysis in Modelling (UAM) activities.

Background and Purpose of the Benchmark


Under the guidance of the NEA/OECD many benchmarks have been performed concerning the application of coupled 3D TH/NK codes. Some of them have utilized code-to-code comparisons, others have compared code predictions with real measured data.

Most transients in a VVER reactor can be properly analyzed with a system thermal-hydraulics code, with simplified neutron kinetics models (point kinetics). A few specific transients require more advanced modeling for neutron kinetics for a proper description. A coupled thermal-hydraulics 3D neutron kinetics code would be the right tool for such tasks.

The proposed benchmark problem has already been analyzed by the coupled system code ATHLET-BIPR-VVER. This allowed a better fixing of the Benchmark Specifications. However, within the present context the results of participants will be compared against the measurements. Interesting additional problems have to be solved in order to perform correctly the comparisons. This experience is incorporated in the text of the specification.

The reference problem chosen for simulation is the MCP #1 switching off at nominal power when the other three main coolant pumps are in operation, which is a real transient of an operating VVER-1000 power plant. This event is characterized by rapid rearrangement of the coolant flow through the reactor pressure vessel resulting in a coolant temperature change, which is spatially dependent. This leads to insertion of spatially distributed positive reactivity due to the modeled feedback mechanisms and a non-symmetric power distribution. Simulation of the transient requires evaluation of core response from a multi-dimensional perspective (coupled 3D neutronics/core thermal-hydraulics) supplemented by a one-dimensional (1D) simulation of the remainder of the reactor coolant system. The purpose of this benchmark is four-fold:

Exercises


The benchmark includes a set of input data for the NPP Kalinin-3 and consists of four exercises

Exercise 1 - Point kinetics plant simulation

The purpose of this exercise is to test the primary and secondary system model responses. Provided are compatible point kinetics model inputs, which preserve the axial, and radial power distribution, and CR #10 and #9 reactivity obtained using a 3D code neutronics model and a complete system description.

Exercise 2 - Coupled 3-D neutronics/core T-H response evaluation

The purpose of this exercise is to model the core and the vessel only. Inlet and outlet core transient boundary conditions are provided by the benchmark team on the basis of calculations performed with the ATHLET-BIPR-VVER coupled code system: alternatively the participants can apply the measured data. HFP state (Exercise #2a) of the core is required for comparison.

Exercise 3

This exercise combines elements of the first two exercises of this benchmark and represents an analysis of the transient in its entirety. For participants that have already taken part in the Kozloduy-6 NEA/OECD Benchmark [6], it is suggested to start directly with this exercise. As a preliminary step for these latter participants it is recommended to perform steady state core calculations at HZP state (Exercise #3a), HFP (Exercise #3b) and deliver the results for comparisons. Exercise #3a and Exercise #3b will ensure and check out the correct application of the cross section libraries, the core loading and the core design geometry.

Exercise 4 - Performing of uncertainty analysis for the purpose of Phase-III

(System Phase) of the OECD Benchmark for Uncertainty Analysis in Best -Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs.
The aim and the specification of this exercise will be described in a separate volume, which will depict the state of the art of the results and requirements identified after performing the UAM Phases I and II.

The specification document (Edition 1) that covers Exercises 1-3 of the OECD Kalinin-3 VVER-1000 Coupled Code Benchmark and the corresponding experimental database and report will be available to participants

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Last reviewed: 2 July 2012