День атомної енергетики 2014. Доповідь: «In vessel melt retention for VVER 1000» «Стратегія управління важкими аваріями «Внутрішньокорпусне утримання розплаву активної зони РУ ВВЕР-1000». Їржи Ждярек, віце-президент з ділового розвитку інституту ядерних досліджень Ржеж (Чехія)

1. ÚJV Řež, a. s.
In Vessel Melt Retention
The XII International
Forum
J. Zdarek
Kiev, September 2014

2. Project Proposal HORIZON 2020
In-Vessel Retention Severe Accident Management Strategy for Existing and Future NPPs (IVMR)
List of Participants
Participant 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
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22 CVR Czech Republic
23 NCBJ Poland

3. IVMR Project Objectives
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.
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4. IVMR Project Benefit
• The concept is very attractive for several reasons:
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oIt 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.
oIn 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

5. IVMR Project Expected Impacts
• 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.
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6. IVMR WP 2: Methodology-Modelling-Reactor
Calculations-Evaluations of Safety Margins
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.
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7. IVMR WP 3: Experimental study of heat and
mass transfer in stratified molten pool within
RPV lower head
The main objectives of corium and simulant molten pool experiments are:
 To improve understanding of physicochemical and thermohydraulic
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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.

8. IVMR WP 4: Experimental and analytical
assessment of RPV external cooling and long
term operation
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.
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9. 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
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10. 1. IAEA Workshop on IVR with Lessons Learned
output - 2012
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.
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11. 1. IAEA Workshop on IVR with Lessons Learned
output - 2013
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
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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.

12. 2. Contract with KI Moscow to perform first
SOCRAT calculation – 2013
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.
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13. 2. Contract with KI Moscow to perform first
SOCRAT calculation – 2013
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:
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• value and distribution of the CHF over the RPV wall;
• corium oxidation rate;
• temperature of down flowing melt;
• heat removed with FP release

14. 3. JRC Benchmark calculation for VVER
1000/320 input data prepared by KI Moscow -
2013-2014
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EXPERT’s NAME EMPLOYER E-MAIL
ATKHEN Kresna EDF kresna.atkhen@edf.fr
BAJARD Sophie CEA
BAKOUTA Nikolai EDF nikolai.bakouta@edf.fr
BATEK David UJV Rez, a. s. bae@ujv.cz
BUCK Michael IKE, Stuttgatr University michael.buck@ike.uni-stuttgart.de
DUSPIVA Jiri UJV Rez, a. s. jiri.duspiva@ujv.cz
EZZID Alexandre AREVA alexandre.ezzidi@areva.com
FICHOT Florian IRSN florian.fichot@irsn.fr
GRUDEV Pavlin INRNE-BAS pavlinpg@inme.bas.bg
IVANOV Ivan Sofia Technical Univarsity ivec@tu-sofia.bg
LE GUENNIC Clémentine EDF clementine.le-guennic@edf.fr
MATEJOVIC Peter IVS Trnava Ltd. ivstt@nextra.sk
MELNIKOV IVAN NRC KI corpuskula@gmail.com
MERKULOV Valery NRC KI Merkulov_VV@nrcki.ru
NIEMINEN Anna VTT Anna.Niemienen@vtt.fi
RASHKOV Krasen Kozloduj NPP kprashkov@yahoo.com
ZDAREK Jiri UJV Rez, a. s. zda@ujv.cz

15. 3. JRC Benchmark calculation for VVER
1000/320 input data prepared by KI Moscow -
2013-2014
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.
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16. 4. NUGENIA Proposal on IVR, now finished as
IVMR proposal to HORIZON 2020
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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

17. 5. Contract with PSU/USA on Phase I
development “cold spray”
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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.

18. 5. Contract with PSU/USA on Phase I
development “cold spray”
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19. 6. Small scale experimental matrix
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20. 6. Small scale experimental matrix
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21. 6. Small scale experimental matrix
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
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22. 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.
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23. 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
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24. Many thanks
Thank you very much for your attention
Questions are more than welcome
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