OECD/BIP

If OECD/BIP project starts we will participate that project. The information from that project is useful to compare our own experimental iodine test results, especially the modelling part could be helpful to understand the phenomena.

2. Shutdown conditions (Lindholm, Sevon, Kekki)

2.1 Severe accident progression during shutdown conditions (Funding: VYR, VTT)

First literature survey of this area will be done. The goal is to perform scoping analyses on severe accident starting at shutdown conditions in a case of Finnish BWR. The air ingression and release and spreading of fission products in the containment and release to the environment will be estimated. A rough estimate of the possibility and consequences of a hydrogen burn in air-filled containment will be performed using MELCOR code.

Deliverables

Task Deliverable

1.1 Facility design and test analysis report (Zilliacus)

1.2 Distribution of released OECD/BIP project reports (Kekki) 2.1 Report on MELCOR calculations (Lindholm)

Applications

Understanding the release of radioactive materials from a degrading core into the cooling circuits and the containment area will enable optimisation of mitigation measures and better prediction of the source terms.

The scoping study of SA phenomena during shutdown conditions will support the PSA level 2 efforts. The importance of different phenomena will be examined to discover the possible issues needing more detailed analyses or analyses involving e.g. structural analyses.

Education of experts

The goal of RADECO is to introduce one new expert to severe accident area.

Liite 2a SAFIR2010 22.1.2007 RESEARCH PLAN for 2007

Primary circuit chemistry of fission products (CHEMPC) Fissiotuotteiden primääripiirin kemia

Duration 2007 – 2010

Project manager Ari Auvinen,

Volume and funding 2007 2.8 person-years 312,368 k€

Funding sources (k€) 2007 VYR 95,868 k€, NKS 16,5 k€, VTT 120 k€, IRSN 80 k€

Objectives

The project is divided into four subtasks. In the first subtask is a joint project with IRSN Caradache research centre (2006-2010) for the determination of iodine chemistry in the primary circuit. The objective of the study at VTT is to determine iodine compounds released due to the reactions on the surface of primary circuit piping. At the same time IRSN will focus in the gas phase chemistry of iodine in similar experimental conditions. A further objective for 2007-2010 is to develop together with IRSN an online measurement system for fission product aerosols, which is capable to differentiate gaseous and vapour phase species from particles at a temperature of 700- 1000°C. Such a measurement system would provide information on high temperature chemistry unlike any facility before.

VTT will continue to follow up Phebus FP and International Source Term Programmes (ISTP) and participate in the interpretation of the results. VTT will also participate in an international experts group on the potential future uses of the Phebus facility in nuclear safety research.

The ruthenium transport experiments conducted at VTT will be modelled using Fluent CFD software. The objective of the study is to quantify the transportation phenomena observed in the experiments. The aim of the work is to apply the data obtained with the small scale experimental facility into a full scale primary circuit.

In ARTIST experimental program fission product retention in the structures of a steam generator is studied in tube rupture scenarios. The objective of the program is to provide a unique database to support safety assessments and analytical models. VTT conducts aerosol measurements and characterisation in ARTIST integral experiments at PSI. VTT also participates in the program by conducting aerosol deposition and resuspension experiments in order to develop a database for fine particle resuspension. Data will be applied in the validation of a resuspension model developed at VTT. In the frame of ARTIST program, data from VTT experiments is also applied in the modelling studies conducted at the University of Newcastle and at IRSN.

Background

Phebus FP program has been the largest nuclear safety program in the world focused on the issue of severe accidents. Between December 1993 and November 2004 five integral experiments were conducted, in which reactor accident phenomena were studied in a realistic environment. Phebus FP program has provided a lot of new experimental data especially on core damage, on fission product release and transport in the primary circuit and on iodine chemistry in the containment.

Phebus FP program also revealed that despite a very significant research effort the extent of the core damage could not be predicted at the time of the first experiment. Since the program was initiated it has greatly contributed to all code development done in the field of sever accidents.

Phebus program has also provided meeting ground for experts studying severe accidents, where they can present their work and agree on future co-operation. Despite the experimental phase of

Phebus FP program has come to an end, interpretation and reporting of the experiments will continue until at least at the end of year 2008.

Phebus FP experiments raised a number of issues that needed to be studied further especially on core damage mechanisms, on primary circuit chemistry and on iodine behaviour in the containment. These topics are currently studied in separate effect experiments conducted in the frame of International Source Term Programme (ISTP).

As a particularly disturbing observation in the last Phebus FP experiment (FPT-3) was that approximately 80% of iodine released from the Phebus circuit was in a gaseous form. The reason why the proportion of gaseous iodine was so high is not fully understood. However, it is assumed that changing the control rod material from AIC to B4C may have contributed to iodine speciation. According to recent iodine status report by OECD NEA the greatest uncertainty related to iodine is its primary circuit chemistry. As a part of ISTP program, the gas phase chemistry of iodine in primary circuit conditions will be studied in CHIP project (Chemistry of Iodine in Primary Circuit). During 2005 VTT designed a hot leg sampling system for the CHIP- facility.

The transport of ruthenium in the primary circuit during an air ingress accident has been successfully studied at VTT in the SAFIR program. The ruthenium experiments are expected to be completed at the end of year 2006 as planned. The results from the experiments have been so far published in one scientific paper and presented in a number of international conferences.

Ruthenium experiments were also a part of Ulrika Backman’s doctoral thesis. In the frame of European SARNET network data VTT has obtained data from ruthenium release experiments conducted by EDF in VERCORS facility, ruthenium oxidation experiments conducted by AEKI and ruthenium containment chemistry experiments conducted by IRSN. Ruthenium studies have also been a part of Nordic NKS-R program. In that program Chalmers University is currently initiating experiments on ruthenium containment chemistry in co-operation with VTT.

Sequences such as a steam generator tube rupture (SGTR) with stuck-open safety relief valve represent a significant public risk by virtue of the open path for release of radioactivity. The release may be lessened by deposition of fission product containing aerosol on the steam generator (SG) tubes and other structures or by scrubbing of these particles in the secondary coolant. The absence of empirical data, the complexity of the geometry and controlling processes, however, make quantifying the retention very difficult. Therefore credit for FP retention is not taken in risk assessments. In ARTIST experimental program conducted at Paul Scherrer Institute (2003-2007), Switzerland, the retention of aerosol-borne fission products in the SG secondary is studied. It provides a unique database to support safety assessments and analytical models. Partners in the ARTIST program include NRC, JNES, AVN, IRSN, CSN, HSK, Beznau NPP Ringhals and HSE. VTT has expertise in conducting experiments on and modelling aerosol resuspension, which is considered to be a key uncertainty in SGTR sequences. In year 2005 a scientific paper on SGTR sequences was published in NED and results from resuspension experiments and modelling have been presented in a number of international conferences. VTT also has prepared a chapter on aerosol resuspension in CSNI State-of-the-Art report on aerosols in nuclear safety. Since VTT joined ARTIST program in the beginning of 2006, VTT has participated in aerosol measurements and characterisation in two ARTIST integral experiments. In addition, undergraduate student Tapani Raunio has conducted resuspension measurements in PSAERO facility at VTT.

Specific Goals in 2007

1 Primary circuit chemistry of iodine (Funding: VTT, VYR, IRSN)

1.1 A hot and a low temperature sampling and dilution systems for the CHIP facility will be manufactured and tested. M.Sc.Tech Teemu Kärkelä will assemble the sampling systems at IRSN Cadarache research centre and participate in the commissioning tests of the facility.

1.2 A facility to study high temperature chemistry of iodine will be built at VTT. The sampling system in the facility will be identical to that of the CHIP facility. Study at VTT will focus on the iodine compounds released due to reactions on primary circuit surfaces, whereas IRSN studies primarily the gas phase chemistry of iodine. We believe that the exceptionally high gaseous iodine fraction observed in Phebus FPT-3 experiment resulted from reactions of iodine compounds deposited in the hot leg of the Phebus circuit.

1.3 During 2007 retention of gaseous iodine into the facility, in sampling lines and in the filters will be studied by feeding radiolabelled gaseous iodine into the system in five experiments.

Temperature, total flow rate and sampling flow rate will be varied in the experiments. Further experiments in 2008-2010 will include using radiolabelled CsI sample as the source of iodine as well as addition of boron-, molybdenum-, tellurium- and uranium compounds into the samples.

2 Phebus FP and ISTP follow up (Funding: VTT, VYR)

2.1 VTT will review Phebus FPT-2 final report chapters related to fission product transport in the primary circuit and mass balance in the experiment. First draft of the report, reviewed in 2006, already revealed completely new information on the timing and mode of FP release as well as very significant retention of FPs in the circuit.

2.2 VTT will participate in Phebus FP and ISTP interpretation circle meetings as well as in the meetings of international experts group to study potential future uses of the Phebus facility in nuclear safety research.

3 Modelling of ruthenium transport (Funding: VTT, NKS, VYR)

3.1 The ruthenium transport experiments conducted at VTT during the SAFIR program will be modelled with Fluent CFD software. In order to set the boundary conditions and to validate the calculations, extensive set of temperature measurements will be conducted at the facility.

3.2 VTT will participate in the planning of ruthenium containment chemistry experiments at Chalmers University. Especially the measurement techniques to be applied will be reviewed.

4 ARTIST resuspension experiments (Funding: VTT, VYR)

4.1 VTT will conduct experiments with aerosol deposition and resuspension in internal tube flow.

In the experiments resuspension of particles will be measured online using technique based on light transmission. Based on the obtained data a model developed at VTT for particle resuspension in turbulent flow will be validated.

4.2 VTT will participate in the aerosol measurements during ARTIST integral experiment as well as in the interpretation of the data. VTT will also determine the shape factor of the aerosol, which is considered by NRC to be a major uncertainty in modelling ARTIST experiments.

Deliverables Task Deliverable

1.1 Technical Report on the sampling system, December 2007

1.2 Technical Report on the facility for iodine chemistry studies, September 2007 1.3 Progress Report on iodine chemistry in primary circuit, December 2007 2.1 Phebus FPT-2 final report, June 2007

2.2 Travel account on Phebus FP and ISTP meetings, May 2007 2.3 Travel account on Phebus FP and ISTP meetings, November 2007 3.1 Final report on modelling ruthenium experiments, September 2007 3.2 Scientific publication on ruthenium transport experiments, October 2007

3.3 Scientific publication on ruthenium studies in Europe and in Canada, October 2007 3.4 Scientific publication on modelling ruthenium transport, December 2007

3.5 Refereed abstract on ruthenium transport experiments (ICAPP 2007)

3.6 Refereed abstract on ruthenium studies in Europe and in Canada (ERMSAR 2007) 4.1 M.Sc Thesis on fine particle resuspension, June 2007

4.2 Refereed abstract on ARTIST experiments (ICAPP 2007) 4.3 Scientific publication on modelling resuspension, October 2007 4.4 Report on ARTIST integral experiments, December 2007 Applications

Primary circuit chemistry studies of iodine compounds can be applied in the estimation of nature and timing of the release as well as in the determination of the mechanism of gaseous iodine production. Such information is currently not available for PSA studies. The online aerosol measurement technique to be developed in this study would be far superior to any aerosol sampling techniques applied thus far in the field of nuclear safety. Such technique would be extremely valuable in large scale experiments planned to be started after 2010.

Results from Phebus FP program can be applied in studies related to severe accidents. New information is gained especially on the release and transport of fission products as well as on the degradation of the core. For example FPT-2 experiment has provided excellent set of data on the revaporisation of several fission product compounds from the surface of the circuit. A lot of information is already available also on iodine chemistry in the containment.

Experiments conducted in ISTP programme provide data on the oxidation of zircalloy as well as B4C control rods in specific conditions. Some facilities concentrate in fission product chemistry in the primary circuit, whereas others study especially iodine chemistry in the containment building.

These issues have been identified in Phebus FP experiments as important uncertainties, which need further data from separate effect experiments in order to be solved.

Studies on ruthenium increased the knowledge of the behaviour of ruthenium in accidents with air ingression. Such accident could take place during the plant shutdown, when the reactor pressure vessel is open to the containment atmosphere. Experiments at VTT provide data on ruthenium transport and speciation, whereas experiments performed at CEA, EDF and KFKI AEKI provide data on ruthenium release and oxidation. IRSN as well as Chalmers experiments provide

information on ruthenium chemistry in the containment building. The data is needed for PSA level 2 analysis of the existing nuclear power plants.

ARTIST experimental program aims to provide an estimate of aerosol retention into the structures of vertical team generator in case of a SGTR scenario. Currently, the absence of experimental data prevents taking credit of particle retention in risk assessments.

Education of experts

Young researcher M. Sc. Teemu Kärkelä participates in the project. He will be educated to conduct advanced aerosol measurements in the field of nuclear safety. The publications from the ruthenium project as well as those from the iodine experiments will be part of his Ph.D. thesis. During year 2007 Teemu Kärkelä will work 3 months as a visiting scientist at IRSN Cadarache research centre.

VTT will also advice in a Ph.D. thesis work conducted at IRSN Cadarache related to high temperature aerosol measurements.

Undergraduate student Tapani Raunio conducts fine particle resuspension experiments at VTT as a part of his M.Sc. degree. Publications from the resuspension modelling will be a part of Ari Auvinen’s Ph.D. thesis. The results from VTT resuspension experiments will also be applied in a Ph.D. thesis work related to resuspension modelling, which is conducted jointly by IRSN and University of Newcastle.

Nordic co-operation will be promoted by continuing collaboration with Chalmers technical university and taking part in the NKS -program. International co-operation will be continued by providing information on the ruthenium and resuspension experiments to SARNET network and by taking part in the ARTIST, Phebus FP and ISTP programs.

Liite 2a SAFIR2010 12.1.2007 RESEARCH PLAN for 2007/version 2

Core Melt Stabilization (COMESTA) Sydänsulan stabilointi

Duration 2007 – 2008

Project manager Tuomo Sevón

Volume and funding 2007 1.28 person-years 232,508 k€

Funding sources (k€) 2007 VYR 89,508 k€, VTT 128 k€, KTM 15 k€

1 person year = 10.5 person months.

Objectives

The objective of the project is to investigate the phenomena of molten core – concrete interactions and coolability of core melt and to develop competence for computational modeling of severe accidents. The behavior of the special sacrificial concrete in the EPR reactor pit under pouring of metallic melt from the reactor pressure vessel will be examined in the HECLA experiments. The international OECD/MCCI-2 project will generate new knowledge of the interactions between oxidic corium and concrete in 2-dimensional geometry and of the coolability of core melt. Via the CSARP agreement the latest versions of the severe accident simulation program MELCOR will be got into use. In addition, the competence to use the CORQUENCH code for calculating the coolability of core melt will be created.

Background

The target of severe accident management is to keep the containment intact and to prevent the release of radioactive materials to the environment. To reach this target, the core melt must be cooled down. The phenomena of core melt coolability and melt–concrete interactions are very complex, and simulating them requires experimental research and development of computational models. Because experiments with real reactor materials are very expensive, this kind of research is usually conducted as international cooperation. In Finland it is possible to make experiments that are related to the essential details of corium coolability especially at the Finnish power plants. In addition to research on the phenomena, it is essential to maintain and improve the competence to perform analyses with severe accident analysis programs that contain the state-of-the-art computational models.

Specific Goals in 2007

1 HECLA Experiments

The subproject aims at investigating the accident scenario in which metallic melt flows from the reactor pressure vessel on to the concrete in the reactor pit. The target is to find out whether the spalling phenomenon, i.e. pieces cracking off from the concrete surface, may occur in the reactor accident. Another target is to examine the behavior of the special concrete type used in the EPR.

1.1 Experiments (Funding: VYR 34 k€, VTT 50.7 k€)

Experiments will be performed in which about 50 kg of melt will be poured into a cylindrical crucible that is made of the special sacrificial concrete type used in the EPR reactor pit. An existing facility at VTT has been modified and tested for the HECLA experiments in the SAFIR program in 2006. The erosion rate of the concrete will be measured with arrays of thermocouples embedded in the concrete floor and sidewalls. The temperature of the melt during the interaction will be measured. The target is to perform two experiments in 2007, the first one with molten steel and the second one with molten stainless steel. The experiments are performed in collaboration

between three VTT knowledge centers. The Nuclear energy center coordinates the project and is responsible for the general design of the experiments and the reporting and analysis. The Materials performance center provides the know-how on the measurement techniques. The experimental facility is owned and operated by the Production systems center.

1.2 Reporting and analyses (Funding: VYR 12 k€, VTT 16.7 k€)

Reports of the HECLA experiments will be written. The results of the experiments will be analyzed and compared with the predictions with MELCOR. Pre-test calculations will be performed as necessary.

2 OECD/MCCI-2

The subproject aims at following the international research program on melt coolability and concrete interaction.

2.1 Follow-on and information exchange (Funding: VYR 11 k€, VTT 6.5 k€, KTM 20 k€)

The program review group and the management board meetings (twice a year) will be attended.

Emphasis to the phenomena that are important to the Finnish nuclear power plants will be promoted in the planning of the experiments. The results of the experiments will be distributed to STUK, TVO and FNS. KTM pays the participation fee, 20 000 USD/year.

2.2 Experiment analysis and workshop (Funding: VYR 5 k€, VTT 19.2 k€)

Pre- and/or post-test calculations of the CCI experiments will be performed with e.g. MELCOR.

Possible benchmark calculation exercises will be participated. The workshop on the results of the finished MCCI program will be attended and a presentation on the WATING water ingression model, which was created at VTT in the SAFIR program, will be given.

3 CSARP (Funding: VYR 17 k€, VTT 16.7 k€)

Via CSARP (Cooperative Severe Accident Research Program) the latest versions of the integral severe accident analysis program MELCOR will be got into use for the Finnish nuclear energy organizations. Furthermore, the annual CSARP/MCAP (MELCOR Cooperative Assessment Program) meeting will be attended.

4 CORQUENCH (Funding: VYR 9 k€, VTT 14 k€)

CORQUENCH program is developed at Argonne National Laboratory. It includes the state-of-the- art models on MCCI, water ingression and melt eruption. The program will be distributed to the participants of OECD/MCCI-2 project during the first year of the project. Argonne develops the calculation models further on the basis of the results obtained from the MCCI-2 project. In the COMESTA project, the usage of the CORQUENCH program will be learned and its applicability for calculating the coolability of core melt in the Olkiluoto power plants will be assessed.

Deliverables

Task Deliverable

1.2 Reports of the performed HECLA experiments

2.1 Trip reports from program review group and management board meetings with brief technical descriptions of the results obtained in the research program

Distribution of the experiment reports to STUK, TVO and FNS 2.2 Report on pre- and/or post-test calculations of the CCI experiments

Workshop presentation on the WATING water ingression model

No documento Project Research Plans for 2007 (páginas 57-78)