Specific Goals in 2007
Liite 2a SAFIR2010 23.1.2007 RESEARCH PLAN for 2007/version 2
Condensation experiments with PPOOLEX facility (CONDEX) Lauhdutuskokeet PPOOLEX laitteistolla
Duration 2007 – 2010
Project manager Markku Puustinen, Lappeenranta University of Technology Volume and funding 2007 2.1 person-years 233,039 k€
Funding sources (k€) 2007 VYR 213,039 k€, NKS 20 k€
Objectives
The main goal of the project is to increase the understanding of the phenomena in the dry well and condensation pool of boiling water reactor (BWR) containment during steam discharge.
These phenomena could be connected, for example, to bubble dynamics, direct-contact condensation (DCC), heat transfer, pool swell and pressure oscillations. To achieve this understanding these phenomena has to be measured with sophisticated, high frequency instrumentation and/or captured on video with high-speed cameras or corresponding equipment.
For example, to estimate the loads on the pool structures by condensation pressure oscillations the frequency and the amplitude of the oscillations has to be known. Strains of the pool wall at exactly defined locations have to be measured for the verification of the structural analysis (NUMPOOL project proposal). The final result of the project will be an experimental database on condensation dynamics and heat transfer, which can be used as such or for testing and developing computational methods used for nuclear safety analysis. Furthermore, mechanistic models for load analysis could be coupled with reactor containment codes.
Background
The common feature of the current BWRs is the use of large suppression pools with a venting system for the mitigation of the immediate consequences of possible Large Break Loss-of-Coolant Accidents (LBLOCAs), such as a main steam line break. Also, in certain light water reactor concepts, during emergency cooling conditions, mixtures of steam and non-condensable gas are blown into a pool of water via an open pipe. In both cases, steam/gas bubbles form at the pipe exit and condense or break up. A pressure pulse generated by the collapse of steam bubbles due to rapid condensation may cause considerable loads or even damage when it impacts upon a structure.
The phenomena, which take place in the condensation pool after an internal pipe rupture in the containment, have been investigated at Lappeenranta University of Technology (LUT) and VTT within the national Finnish research programmes on nuclear power plant safety (FINNUS and SAFIR). In the FINNUS/TOKE project, the behaviour of non-condensable gas bubbles in the suppression pool and their effect on the performance of the ECCS strainer and pump has been studied in 2001-2002. In 2003-2006, the SAFIR/POOLEX project has concentrated on the tests with steam injection to the condensation pool in atmospheric pressure.
Pre- and post-test analysis of the loads on the pool structures and the structural analysis of the pool are necessary for the experiments. The experiments of the FINNUS and SAFIR programmes at LUT have been modelled with computational fluid dynamics (CFD) and structural analyses tools at VTT and LUT as part of the SAFIR/INTELI and ECE/NURESIM projects. In the VTT’s analyses, the loads calculated with CFD analysis have been transferred to structural analysis and the stresses and strains in the pool structures have been evaluated as a function of time. At first, the work concentrated on the analyses of blowdown of air to the pool. In 2003, studies of blowdown
of steam were started. The results of the detailed steam tests are utilized in the modelling of fluid- structure interactions and pool stratification tests in developing the models for APROS code.
A new pressurized test facility including an adequate model of the upper dry well compartment and withstanding prototypical system pressure (0.5 MPa) is being constructed at LUT. It will further increase the applicability of the experiment results of the project. Condensation in the dry well and DCC in the wet well can be examined and scenarios in terms of condensation modes threatening the integrity of pool structures can be identified and assessed. In order to model the experiments, new numerical models have to be developed in the existing CFD codes. Computer codes that can be evaluated with the help of the new test facility include, for example, GOTHIC, MAAP, FLUENT, ANSYS CFX, DYNA3D, GREEN, SPIEGEL, COPTA and NEPTUNE.
In the numerical modelling of the experiments, close co-operation will be done with the proposed SAFIR2010/NUMPOOL project and the EU/NURESIM subproject at VTT, where model for DCC is being developed. In addition, an attempt is made to enhance Nordic co-operation within the Northnet Roadmap 3 project proposal on “Modelling and Experiments of direct-contact condensation in pool geometry”.
Specific Goals in 2007
1 PPOOLEX tests
Test program with the new test facility including a dry well and withstanding prototypical system pressure starts. Numerical simulation work continues in accordance with the experiments carried out in the new facility and with findings from the current project.
1.1 Characterizing tests (Funding: VYR 70 k€, NKS 8 k€)
Characterizing tests with cautious air and steam discharge will be carried out in the new facility.
The general behaviour of the facility will be observed and compared to that of the preceding POOLEX facility. Automation and control systems as well as instrumentation will be tested.
Particularly, correct control values for the system regulating the pressure difference between the dry well and wet well compartments will be found out. A report on the characterizing test series will be written. Possibilities for advanced instrumentation to be used in the experiments focusing on the whole sequence of a main steam line rupture (in 2008) will be studied and reported.
1.2 Pre-test CFD analysis of experiments on the early phase of a main steam line rupture (Funding:
VYR 36 k€, NKS 4 k€)
A CFD model of the new PPOOLEX test facility will be constructed and pre-test calculations on the discharge of non-condensable gas (air) to the dry well compartment and from there through one blowdown pipe into the condensation pool will be performed. Main focus will be on helping the planning of the experiments simulating the early phase of a main steam line rupture. A report on the pre-test calculation results will be written.
1.3 Experiments on the early phase of a main steam line rupture (Funding: VYR 95 k€, NKS 8 k€) Specific experiments on the discharge of non-condensable gas (air) to the dry well compartment and from there through one blowdown pipe into the condensation pool related to the very first seconds of a main steam line break inside the containment will be carried out. Effects of pressure feedback on the dynamics of gas bubbles will be studied and comparison to the existing POOLEX data on gas discharge will be made. Data from the beginning of the blowdown, i.e. when water is expelled from the blowdown pipe, will be delivered to VTT for the verification of CFD simulations related to the estimation of pressure loads. A report on the results of the experiments will be written.
2 Project management and international contacts
2.1 Project management and international contacts (Funding: VYR 19 k€)
Participation in the international bodies or working groups ensures the international connections needed for the research unit. Activities will be reported to Finland.
Deliverables
Task Deliverable
1.1 A report on the characterizing test series will be written. It will also include suggestions of more advanced instrumentation to be used in future tests.
1.2 A report on the pre-test CFD calculation results will be written.
1.3 A report of the experiments on the early phase of a main steam line rupture will be written.
Applications
Using the information gained from the experiments could directly solve certain open questions of suppression pool related safety systems in existing BWRs. Additional benefit of the project will be the use of the test results in developing and validating CFD codes for nuclear safety analysis. The connections of thermal hydraulics and structural loads will be studied in real conditions. This connection is planned to be built also in the computational environment and to be verified against the experimental data at VTT. The project outcome will allow the end users to reduce the safety risk of the pool structures threatened by the dynamic loading of direct-contact condensation. Better understanding of the suppression pool behaviour, which is gained from the experiments and from the validation of new tools (combined CFD and structural analysis code), can be directly utilized in the safety analysis of the plant.
The research strengthens Finnish knowledge and networking and the results are available for the power companies, nuclear safety authorities and research organizations.
Being a part of the SAFIR2010 research programme gives this project an excellent forum for the exchange of knowledge and experience also internationally. Through the programmes in SAFIR2010 and NORTHNET, the Finnish and Swedish BWR operators will be participating in the project. The use of test rigs at Lappeenranta University of Technology promotes the education of new nuclear experts by giving opportunities to take part in experimental research. Hence, the project fits well to the SAFIR2010 programme.
Education of experts
Interdisciplinary publications dealing with the phenomena observed in the experiments as well as with the simulation of the experiments with CFD codes will be written and included in three doctoral theses.