24
ÚJV Řež, a. s. In Vessel Melt Retention The XII International Forum J. Zdarek Kiev, September 2014
ÚJV Řež, a. s.
In Vessel Melt Retention
The XII International Forum
J. Zdarek
Kiev, September 2014
Project Proposal HORIZON 2020
2
In-Vessel Retention Severe Accident Management Strategy for Existing and Future NPPs (IVMR)
List of ParticipantsParticipant No * Participant organization name Country
1 (Coordinator) IRSN France
2 UJV Czech Republic
3 JRC (IET / ITU) EC
4 CEA France
5 KHT Sweden
6 KIT Germany
7 AREVA France
8 EDF France
9 GRS Germany
10 HZDR Germany
11 FORTUM Finland
12 VTT Finland
13 MTA-EK Hungary
14 NUBIKI Hungary
15 IVS Slovakia
16 ENEA Italy
17 LEI Lithuania
18 GDF-SUEZ (Tractebel) Belgium
19 Imperial College UK
20 NRG Netherlands
21 INRNE Bulgaria
22 CVR Czech Republic
23 NCBJ Poland
IVMR Project Objectives
3
One of the new Severe Accident Management strategies which is attracting more and more interest form all EU main players (Utilities, TSOs, NPP vendors, Research Institutes…) is the In Vessel Melt Retention (IVMR) strategy for Light Water Reactors (PWR, BWR, VVER). Ensuring that the corium could stay in the RPV (like it happened during the TMI-2 accident) during a Severe Accident will reduce significantly the loads on the last barrier (the containment) and therefore reduce the risk of release of Fission Products to the environment for most of the Severe Accident Scenarios.
This type of Severe Accident Management strategy has already been incorporated recently in the SAMGs of several operating small size Light Water Reactors (reactor below 500 MWe (like VVER440)) and is part of the SAMG strategies for some Gen III + PWRs like the AP1000.
IVMR Project Benefit
4
• The concept is very attractive for several reasons:
o It ensures that corium is maintained in the vessel, avoiding the presence of large masses of radioactive materials in the containment and the risks of failure of the containment.
o In principle, external cooling of the vessel to be able to extract enough power in the most of the situations (following different accident scenarios) and is suitable for long term stabilization of corium
oThe practical design, under its simplest form, appears less expensive than an external core-catcher
IVMR Project Expected Impacts
5
• The project will contribute to reinforce research cooperation on reactor safety at EU level by bringing together research organizations, TSOs, utilities and designers from 14 different countries who all have an interest at investigating the benefits of IVMR, either for backfitting of existing reactors or for safety studies on future reactor designs. Korean organizations (who have worked extensively on the IVMR topic for the design of the APR-1400) have also mentioned their interest in the project and might also be associated to it later on, if the project is selected. The details of their involvement remain to be discussed.
• The project aims at providing recommendations and guidance for severe accident management in cases where IVMR is implemented.
• The project will provide a harmonized methodology for IVMR demonstration which will constitute a synthesis of existing knowledge gained during the project. This knowledge base will be used to develop models that will be implemented in various simulation tools to be used by the participants for severe accident studies.
IVMR WP 2: Methodology-Modelling-Reactor Calculations-Evaluations of Safety Margins
6
The WP2 covers all modeling activities necessary to better understand the behavior of molten corium when it is relocated in the Reactor Pressure Vessel Lower Plenum (RPV LP) (mixing of different corium materials, stratification material, turbulence, heat transfer, oxidation, etc…), to model more accurately the mechanical response of the RPV LP and to assess if external RPV LP cooling by water could be sufficient to extract the heat generated and avoid the vessel from failing. The work in this WP will be performed in close collaboration with the experimental and engineering activities to be done within WP3, WP4, and WP5 to support continuous improvement during the project of the modelling activities and improve the accuracy of the assessments performed for the different types of EU NPPs regarding the In Vessel Melt Retention (IVMR) as a Severe Accident Management strategy.
IVMR WP 3: Experimental study of heat and mass transfer in stratified molten pool within RPV lower head
7
The main objectives of corium and simulant molten pool experiments are:
To improve understanding of physicochemical and thermohydraulic phenomena which influence melt pool configuration, composition and masses/thickness of molten layers and interfacial crusts, relative positions of the layers, heat and mass transfer between the layers and heat fluxes into the pool boundaries.
To generate corresponding experimental data necessary for model development and validation as well as to assess material properties data quality.
To determine, in particular, conditions in the molten pool which are critical for the system behavior, such as layer inversion, mixing and heat focusing, and coolability of a debris bed surrounding a molten pool.
To address possibilities for in-vessel molten pool and debris coolability improvement, e.g. top flooding, control rod guide tube cooling for BWRs, etc.
IVMR WP 4: Experimental and analytical assessment of RPV external cooling and long term operation
8
Key approach to justify efficiency of the external cooling is to provide
meaningful experimental facility. As it necessary to study external cooling
with deflector and also including the effect of status of the external surface
of the RPV, which was not studied in previous studies, it is efficient to
perform first series af small scale experiments with different conditions and
after that to perform large scale experiments with already optimized
conditions.
UJV Initiatives with respect to the IVMR project
1. IAEA Workshop on IVR with Lessons Learned output - 2013
2. Contract with KI Moscow to perform first SOCRAT calculation – 2013
3. JRC Benchmark calculation for VVER 1000/320 input data prepared by KI Moscow -2013-2014
4. NUGENIA Proposal on IVR, now finished as IVMR proposal to HORIZON 2020
5. Contract with PSU/USA on Phase I development “cold spray”
6. Small scale experimental matrix
7. Large scale experiments for VVER 1000/320 configuration
9
1. IAEA Workshop on IVR with Lessons Learned output - 2012
10
Summary of discussion
The consultants’ Meeting on the In-Vessel Retention (IVR) strategy for VVER-1000/320 reactors was held 24 – 26 July 2013 at the IAEA in Vienna. The selected consultants were invited by the IAEA based on their experience and capability to contribute to the assessment of applicability of the IVR strategy for existing reactors of VVER-1000/320 type. Scientific Secretary was Mr. K.S. Kang and Mr. Jiri Zdarek was selected as a chairman on the meeting.
Presentations and discussions were very open confirming that the IVR strategy have been studied in different countries and that existing knowledge allows assessing the applicability of the strategy for VVER-1000/320 reactors and to identify the main remaining issues. Copies of all presentations were distributed to the participants in electronic format. From each consultant’s presentation key points were identified and discussed. The key points are presented in the attachment.
1. IAEA Workshop on IVR with Lessons Learned output - 2013
11
In the near term it is considered important to focus on the following activities:
1. Continuation in the analytical works aimed at further identification and verification of conditions for successful IVR application. Existing preliminary results by SOCRAT predicting margins to the critical heat flux should be expanded by additional calculations, also using other codes, such as MELCOR or ASTEC.
2. Additional experimental support of the feasibility of the strategy and optimization of design specific solutions. Large scale experimental facility should preferably be used, possibly as a joint project of utilities in interested counties (Bulgaria, Czech Republic, Russian Federation, Ukraine, but also other PWR operators).
Since proposed activities reflect the findings and recommendations of the European stress tests, other sources of support can be also considered, such as future FP 7 or Horizon 2020 projects or NUGENIS joint project.
2. Contract with KI Moscow to perform first SOCRAT calculation – 2013
12
This paper provides a preliminary analysis of corium in-vessel feasibility for VVER-1000/V-320 reactors in case of a severe core-meltdown accident. Respective computer simulation was performed using SOCRAT code (both the complete set of code models and its individual key modules).
Two key aspects of this issue were analyzed:
- Implementation of measures intended to increase the critical heat flux density of external RPV cooling due to an optimized deflector installed in the reactor pit around the lower head of the vessel in order to streamline the water flow;
- Implementation of measures intended to slow down the formation of the corium pool on the RPV floor due to additional coolant supplied from dedicated tanks situated beyond the reactor containment.
Respective calculations based on realistic assessment of the decay (residual) heat rate show that the above measures (external PRV cooling improved by the deflector and water supply into the vessel) implemented together would make it possible to prevent the DNB occurrence on the outside surface of the RPV.
Sensitivity and uncertainty analysis was performed to address the effect of input data uncertainties on calculated results. Successful IVR probability was estimated at about 85%.
Input data uncertainty reduction in the course of supplementary experimental and analytical studies might improve the reliability of IVR assessment for VVER-1000.
2. Contract with KI Moscow to perform first SOCRAT calculation – 2013
13
Results of calculations performed assuming realistic assessment of the decay heat rate show that a combination of measures such as external RPV cooling improved by the deflector baffle and water supply into the vessel would make it possible to prevent the DNB occurrence on the outsider surface of the RPV, with DNB margin of about 20%.
In addition, the analysis of sensitivity and uncertainties was performed respective to the critical phase of the accident (interaction between the corium pool and the reactor vessel wall). Thirteen variant calculations were performed using threshold values of uncertainly-known parameters. This sensitivity and uncertainty analysis showed that the key parameters having the strongest effect on corium in-vessel retention processes are:
• value and distribution of the CHF over the RPV wall;
• corium oxidation rate;
• temperature of down flowing melt;
• heat removed with FP release
3. JRC Benchmark calculation for VVER 1000/320 input data prepared by KI Moscow -2013-2014
14
EXPERT’s NAME EMPLOYER E-MAIL
ATKHEN Kresna EDF [email protected]
BAJARD Sophie CEA
BAKOUTA Nikolai EDF [email protected]
BATEK David UJV Rez, a. s. [email protected]
BUCK Michael IKE, Stuttgatr University [email protected]
DUSPIVA Jiri UJV Rez, a. s. [email protected]
EZZID Alexandre AREVA [email protected]
FICHOT Florian IRSN [email protected]
GRUDEV Pavlin INRNE-BAS [email protected]
IVANOV Ivan Sofia Technical Univarsity [email protected]
LE GUENNIC Clémentine EDF [email protected]
MATEJOVIC Peter IVS Trnava Ltd. [email protected]
MELNIKOV IVAN NRC KI [email protected]
MERKULOV Valery NRC KI [email protected]
NIEMINEN Anna VTT [email protected]
RASHKOV Krasen Kozloduj NPP [email protected]
ZDAREK Jiri UJV Rez, a. s. [email protected]
3. JRC Benchmark calculation for VVER 1000/320 input data prepared by KI Moscow -2013-2014
15
Meeting Objectives
G. Pascal presented the project objectives emphasizing that the main target is to drive to some conclusions and comparisons between the code results (especially ASTEC code, but also SOCRAT, MELCOR) regarding In Vessel Retention (IVR) for VVER1000. He recalled the past KoM, the definition of the Severe Accident scenario(s) to be calculated by each partners, and the exchange of data and VVER1000 computer code input deck to be used as starting point. He reminded everybody also that the work is purely based on „in kind“ contributions. This second workshop is focused in preliminary results of the calculations. The 3rd workshop will provide results comparison and presentation of final results. At the end of the project he asked to have final summaries of the calculations and mentioned that in the future peer review papers could be written among the participants. He mentioned that is was very important also to receive results and suggestions/recommendations from new participants.
J. Zdarek remembered that CZ Republic is actively investigating the VVER1000 IVR strategy but that the schedule is really tight. NUGENIA is still very active in this area; he mentioned very tight schedule related to the H2020 proposal for a project on IVMR (deadline September 2014). He would like to receive clear key findings of calculations (for example locations of most demanding HF to LP wall) in order to use them for that proposal, especially for designing IVR experiments needed to validate the code models. F. Fichot has already started to prepare a draft proposal for H2020. He proposed to have a review of a document prepared by F. Fichot at the end of this meeting. J. Zdarek emphasized that the work of this project is not paid by any institution and in kind contribution due to the interest in IVR studies.
4. NUGENIA Proposal on IVR, now finished as IVMR proposal to HORIZON 2020
16
NUGENIA Project Proposal : IVMR Strategy If approved by the NUGENIA ExCOM, project will be prepared for Horizon 2020, November
2014 call.
Background
Project was originally prepared as Template No.1 „IVR strategy for VVER-1000“. Based on thorough discussion with IRSN and later with CEA, also with gradually obtained support from industry partners such as AREVA, EdF, CEZ, it was decided to extend this project to other reactors with goal to develop:
„The IVMR Strategy for VVER-1000 and Guidelines for Future Designs with IVMR Strategy“.
IVMR Project Tasks proposed Task 1: Analytical assessment of measures for reduction of heat fluxes into RPV wall
during the IVMR Task 2: Mechanical resistance of the ablated vessel wall Task 3: Technical engineering research and support work – Research on new designs and
systems for IVMR Task 4: IVMR assessment – Reactor Calculations – Evaluations of safety Margins
5. Contract with PSU/USA on Phase I development “cold spray”
17
Because of the many difficulties associated with traditional thermal spray methods, a new and extremely versatile method of coating deposition known as the High Velocity Particle Consolidation (HVPC) or Cold-Spray was conceived [9-12]. HVPC is a promising lower-temperature direct spray method that rapidly and efficiently creates or repairs coatings by exposing a substrate to a high-velocity jet of solid-phase particles. Since the particles are accelerated by a supersonic jet at temperatures well below the melting point, the problems common with traditional thermal spray methods such as the preclusion of porosity, oxidation, evaporation, melting, crystallization, residual stresses, deboning, gas release, etc., can be avoided. Moreover, the method allows the tailoring of the rating via thickness, composition including functional grading if needed, and/or porosity, as well as the ability to repeatedly repair a variety of surfaces including those with curvature. Additionally, HVPC can readily create intentionally textured coatings to increase available surface area for heat transfer, as well as also functionally graded properties, porosity, materials etc. as needed. Since the HVPC method does not require special chambers and can be readily scaled and automated, a system can be fabricated and used in existing reactors provided there is adequate space directly below. Hence, the safety margins of existing reactors can be potentially increased by using HVPC and tailored coatings.
5. Contract with PSU/USA on Phase I development “cold spray”
18
6. Small scale experimental matrix
19
6. Small scale experimental matrix
20
6. Small scale experimental matrix
21
We plan to perform over 150 small scale experiments with above show facility, which is already in operation.
Following key parameters will be studied:
Different surface of the RPV test sample: clean, oxidized, clean before HVPC and with HVPC
Angle position from 0 to 90 degrees
Cooling media: clear water, dirty water from the RPV cavity and combination with boric acid
Small scale test matrix is of crucial importance to perform final matrix of large scale experiments
Small scale experiments will be supported by analytical assessment also to confirm validity of performed calculations
7. Large scale experiments for VVER 1000/320 configuration
Large scale experiments were already performed to justify the IVR strategy for VVER 440, AP600 and AP 1000 on ULPU 2000 and ULPU 2400 experimental facility.
However all these experiments were performed with simulation of spherical lower head. For VVER 1000 we need to perform tests with semieliptical lower head.
At present extensive design work is started to properly design heating elements, baffle channel around the whole tested slice of tested sample.
Design of the experiment has to fully simulate the input of the cooling media and also steam release at the top.
Work is well under way also with identified lab to be carried out.
22
Conclusions
When our first proposal on IVR strategy for VVER 1000 started, we have no support
From our presentation you could see that at present , in the IVMR HORIZON 2020 project which we have initiated, the name is IVMR for Existing and Future design and not only for VVER 1000. Total number of participants within this project is 22
We have strong support from the EC to perform Bench Mark calculation again for VVER 1000 with input data prepared by Kurchatov Institute
Small scale experiments already started with very interesting and promising results
We believe that large scale experiments and prepared other WP within HORIZON IVMR project will justify the IVMR strategy in general
23
Many thanks
Thank you very much for your attention
Questions are more than welcome
24
![[Введите подзаголовок документа]chechelnik-rada.gov.ua/upload/files/Стратегія... · Web viewзабезпечення реалізації та](https://static.documents.pub/doc/80x56/5e541c99808d8a39ba433179/-fchechelnik-radagovuauploadfiles.jpg)
