ERMSAR 2012, Cologne March 21 – 23, OECD Benchmark: Objectives Starting from the previous ATMI Benchmark the objective is to examine three different severe accident sequences in the frame of a code-to-code benchmark The impact on hydrogen production, core coolability, corium relocation into the lower plenum and vessel failure will be addressed Conclusions will be drawn on the level of confidence achieved by current severe accident codes to predict in-vessel core melt progression The sensitivity to key code model parameters which are subject to major uncertainties will be addressed
ERMSAR 2012, Cologne March 21 23, 2012 OECD Benchmark Exercise
on the TMI-2 Plant: Analysis of an Alternative Severe Accident
Scenario G. Bandini (ENEA), S. Weber, H. Austregesilo (GRS), M.
Buck (IKE), P. Dray (IRSN), M. Barnack, P. Matejovic (IVS), J. H.
Park (KAERI), H. Muscher, F. Kretzschmar (KIT), L. Sallus, J. Bulle
(Tractebel), J. Duspiva (NRI), L. L. Humphries (SNL), M. Hoffmann
(RUB), H. G. Lele (BARC), K. Dolganov, A. Kapustin, D. Tomashchik
(IBRAE RAS), A. Amri (OECD/NEA), P. Groudev, A. Stefanova (INRNE)
ERMSAR 2012, Cologne March 21 23, Outline Objectives and Scope of
OECD Benchmark First Transient Calculation Participants and Codes
Code Modeling Features Code Result Comparison Conclusions ERMSAR
2012, Cologne March 21 23, OECD Benchmark: Objectives Starting from
the previous ATMI Benchmark the objective is to examine three
different severe accident sequences in the frame of a code-to-code
benchmark The impact on hydrogen production, core coolability,
corium relocation into the lower plenum and vessel failure will be
addressed Conclusions will be drawn on the level of confidence
achieved by current severe accident codes to predict in-vessel core
melt progression The sensitivity to key code model parameters which
are subject to major uncertainties will be addressed ERMSAR 2012,
Cologne March 21 23, OECD Benchmark: Scope The exercise will be a
code to code comparison and transposition to reactor scale of
results of experiments and previous benchmarks will help to judge
the consistency of code results The proposed directions for future
work are the following: To simulate three representative severe
accident sequences with well defined boundary conditions up to
different degree of in-vessel core melt progression: Two of the
sequences will address core reflooding issue starting from
different degree of core degradation One sequence will extend to
molten core slumping into the lower plenum ERMSAR 2012, Cologne
March 21 23, OECD Benchmark: Scope (cont.) To perform some
sensitivity studies on more important and uncertain key parameters
in order to evaluate their impact on core degradation, core
coolability and hydrogen production To extend the number of
participants in order to involve more countries, more users and
young engineers The project is linked with the WP5.4 Corium and
Debris Coolability Bringing Research into Reactor Applications of
EU/SARNET-2 network of excellence The activity will be carried out
by a Group of Participants including members from WGAMA Task Group
of OECD/CSNI and SARNET-2 ERMSAR 2012, Cologne March 21 23,
OrganizationCountryCode GRSGermanyATHLET-CD ENEAItalyASTEC
IKEGermanyATHLET-CD IRSNFranceICARE/CATHARE IVSSlovakiaASTEC
NRICzech Rep.MELCOR KAERIKoreaMELCOR KITGermanyASTEC & MELCOR
SANDIAUSAMELCOR TRACTEBELBelgiumMELCOR RUB GermanyATHLET-CD BARC
IndiaASTEC IBRAE RAS RussiaSOCRAT INRNE BulgariaASTEC OECD
Benchmark Participants 14Organizations 11Countries 5Codes
15Calculations: MELCOR (5) ASTEC (5) ATHLET-CD (3) ICARE/CATHARE
(1) SOCRAT (1) ERMSAR 2012, Cologne March 21 23, ACCIDENT SCENARIO:
Small break of 20 cm 2 in the hot leg of Loop A, with contemporary
loss of SG main feed water Reactor scram on high pressure signal
Auxiliary feed water startup after 100 s Primary pump coastdown
when primary mass inventory < 85 tons No HPI or LPI system
actuation Free evolution of the transient until vessel failure
SIMPLIFIED BOUNDARY CONDITIONS: Constant pressure (70 bar) and
water level (1 m) on the secondary side of steam generators
Constant make-up flow rate (3 kg/s) and letdown flow rate = 0 First
Transient Calculation ERMSAR 2012, Cologne March 21 23,
Calculations: ASTEC (4) ATHLET-CD (3) ICARE/CATHARE (1) MELCOR (1)
SOCRAT (1) Participants and Codes ERMSAR 2012, Cologne March 21 23,
Code Modelling Features Core degradation parameters The value of
the different parameters has been selected according to code best
practice guidelines and user experience Sensitivity studies are in
progress to investigate the influence of different parameters on
core melt progression and hydrogen generation ERMSAR 2012, Cologne
March 21 23, Main Steady-State Plant Parameters ERMSAR 2012,
Cologne March 21 23, Chronology of Main Events ERMSAR 2012, Cologne
March 21 23, Code Result Comparison (1) Break mass flow rate ERMSAR
2012, Cologne March 21 23, Total primary coolant mass Code Result
Comparison (2) ERMSAR 2012, Cologne March 21 23, Pressurizer
pressure Code Result Comparison (3) ERMSAR 2012, Cologne March 21
23, Core collapsed level Code Result Comparison (4) ERMSAR 2012,
Cologne March 21 23, Fuel rod clad temperature at core top Code
Result Comparison (5) ERMSAR 2012, Cologne March 21 23, Total mass
of degraded core material Code Result Comparison (6) ERMSAR 2012,
Cologne March 21 23, Total mass relocated into the lower plenum
Code Result Comparison (7) ERMSAR 2012, Cologne March 21 23,
Cumulated hydrogen production Code Result Comparison (8) ERMSAR
2012, Cologne March 21 23, The calculations confirm the robustness
of the codes all the codes where able to calculate the accident
sequence up to the more severe degradation conditions Also thanks
to the initial steady-state and boundary conditions harmonization
the uncertainties related to the prediction of thermal- hydraulic
behavior of the plant in the first phase of the transient until the
onset of core uncovery and heat-up have been minimized rather small
deviations observed in the calculations of the break flow rate and
then total primary mass which lead to an almost contemporary stop
of primary pumps in all calculations The more signifiacant
deviations in code results are registered after the initiation of
in-core melt progression and material relocation phenomena
Conclusions ERMSAR 2012, Cologne March 21 23, The use of different
core degradation parameters and late phase degradation modelling
might tend to increase the differences in code results sensitivity
studies are ongoing in order to investigate the importance of
various parameters In-vessel convective movements like in
ICARE/CATHARE calculation could affect the core heat-up rate and
then the timing of core melting Molten core material behaviour in
the lower head is strongly influenced by the assumptions taken on
molten jet break-up during slumping strong thermal interaction in
the water-filled lower plenum might lead to more or less coolable
debris bed and molten pool configuration which may significantly
delay or even exclude the vessel failure occurrence Conclusions
(cont.)
