Contents

1. ASTEC extension to other reactor types than Generation II PWRJ.P. Van Dorsselaere (IRSN), B.Schwinges (GRS), M.Buck (IKE), W.Ma (KTH), M.Constantin (INR), J.Jancovic (VUJE), G.Ratel (CEA)

2. Contents • ASTEC adaptation to Gen.II VVER • ASTEC adaptation to Gen.III PWR (incl. EPR) • ASTEC adaptation to BWR • ASTEC adaptation to CANDU • Conclusions

3. ASTEC requirements on NPP types • Initial IRSN-GRS requirements: to cover present and future PWR, VVER, BWR. • Priority was given to Gen.II PWR and VVER in the last years, • Under way: adaptation to BWR, • Next important stage: to cover new Gen.III+ designs, such as EPR in priority, then advanced NPP with capability of In-Vessel-Melt-Retention (IVMR). • At SARNET’s start, the objective to cover all European NPP was added, and reinforced in SARNET2  need of extension to CANDU reactors. • In ASTEC Topic, several partners worked with IRSN and GRS to investigate the modelling needs for BWR (IKE, KTH + PSI review) and CANDU (INR + AECL support)  ASTEC V2 plans and SARNET2 work.

4. ASTEC adaptation to Gen.II VVER (1/2) • Many benchmarks on VVER plant applications were performed by partners in SARNET, either on VVER-1000 or VVER-440, and for various SA scenarios (LOCA, SBO, LOFW…)  Shows ASTEC V1 applicability to VVER, up to iodine behaviour in containment. primary side secondary side VVER-440 case: assumptions to account for canisters  improv. in ASTEC V2 by BWR work Optimisation of horizontal SG CESAR nodalisation

5. ASTEC adaptation to Gen.II VVER (2/2) • Good results of VVER-specific validation: • CESAR on PACTEL scaled-down facility of Loviisa VVER-440/V213: natural circulation in primary system for single- and two- phase flow regimes, • Former CPA application to EREC T5 (LBLOCA) VVER-440 containment t/h exp., with bubble condenser towers. Containment pressure in EREC T5 Primary pressure on PACTEL-ISP33

6. ASTEC adaptation to EPR (1/2) • IRSN applied ASTEC stand-alone modules (MEDICIS, CPA) and analytical models in 2006 to EPR SA scenarios: • No model extension needed for RCS thermalhydraulics (CESAR) and core degradation (ICARE2), • No mod.extension for containment, esp. the two-room concept (CPA), • Only need: couple/“integrate” several existing models in ASTEC for core-catcher behaviour. • 1st integrated possible simulation with ASTEC V2.0 in March 09 (improvements will follow..).

7. ASTEC adaptation to EPR (2/2) • Modelling of core-catcher in 4 different parts: • MCCI in cavity: MEDICIS use with new model of radiative exchanges (absorbing atmosphere) between corium, vessel LH and cavity walls. Account for possible melt-through of concrete upper cavity walls. • Erosion of cavity substrate and corium pouring kinetics into the core-catcher: simple model (Bernoulli flow approach, MDB properties). • Corium spreading along spreading chamber: 2 levels of approaches, • At first: simplified analytical correlation (probably based on KTH one) for cases of fast and complete spreading, later a further correlation • Later on, more detailed model (such as LAVA GRS code) for cases of slow spreading. If incomplete spreading: flag for the user, out of ASTEC scope.Necessary also for existing PWR and BWR 69 • MCCI in spreading chamber with upward water cooling: MEDICIS use with boundary conditions for cooling circuit in the basemat (interface with 2D thermal codes for detailed analysis of these cooling structures).

8. Void fraction Twall hpipe Tpipe CESAR : closed loop ASTEC adaptation to IVMR (1/2) • CEA assessment of CESAR-DIVA capabilities: • CESAR calculation of external circuit as an independent channel. • Coupling CESAR-DIVA between vessel external surface and coolant. DIVA corium and LH

9. ASTEC adaptation to IVMR (2/2) • CEA validated CESAR (stand-alone mode) on SULTAN (CEA) and ULPU (Univ. Santa Barbara) experiments.  CESAR acceptable stability to simulate two-phase flow in natural convection but still numerical oscillations. • Further validation of CESAR-DIVA coupling on LIVE (FZK) and HERMES-HALF (KAERI) experiments. Example on SULTAN: Good results with correct reproduction of S-shape of pressure drop linked to the flow in a heating canal. CESAR simulation of SULTAN

10. ASTEC adaptation to BWR (1/4) • KTH-IKE-GRS ranking concluded on: • Applicability of most ASTEC V1 models: few adaptations are necessary, • Main needs: • To adapt core degradation models, • New models for lower plenum (CRGTs..), formation of ex-vessel debris bed and coolability. • This was confirmed by ASTEC V1exploratory calculations: • DIVA application by IKE to the CORA-18 experiment on degradation of a BWR bundle, but application to real core • BWR benchmark by GRS on containment thermalhydraulics with COCOSYS code, • (under way) CESAR calculations by GRS of steady-state and transient (front end) with comparison to ATHLET code results.

11. ASTEC adaptation to BWR (2/4) CORA-18 bundle geometry Fuel temperatures at 750 mm Final ASTEC state of degraded bundle Hydrogen mass

12. ASTEC adaptation to BWR (3/4) • CPA application by GRS to a scenario “Loss of main heat sink plus loss of pressure limitation” in a German BWR (’72) containment • Global agreement between ASTEC and COCOSYS results, • but some differences (e.g. temperatures, mass flow rates through vent pipes), likely due to different heat transfer models. pressure temperature

13. ASTEC adaptation to BWR (4/4) • Conclusions on core degradation models: • Review of modelling in ASTEC and other SA codes indicates that BWR core components can be modelled based on available or only slightly modified ASTEC models, • But major effort required on t/h feedback with core degradation  need of a 2D CESAR in-core t/h (planned by IRSN in ASTEC V2). • Other main needs of model adaptations: • ICARE2 for complex geometry of lower plenum (CRGT…)  Should not create large difficulties… • Models for formation of debris beds at corium slump into a flooded cavity (plus its coolability). • Verification (or extension) of validity of containment iodine models up to 800K temperatures.

14. ASTEC adaptation to CANDU (1/4) • INR analysis of existing ASTEC models and of needs of adaptations: • Applicability of most ASTEC V1 models: very few adaptations are necessary, • Need to adapt core degradation models. • This was confirmed by INR exploratory plant applications in SARNET to CANDU: • Physically reliable results of coupled SOPHAEROS-CPA-IODE calculation on FP transport and behaviour  PHT plays a good filter role for FPs; similar results to literature ones. • CESAR simulation of PHT thermalhydraulics (benchmark with CATHENA code from AECL to be performed).  Consistent with BARC (India) conclusions, as presented in ERMSAR-2007.

15. ASTEC adaptation to CANDU (2/4) Example of CESAR and CPA INR nodalisations resp. for PHT and containment

16. ASTEC adaptation to CANDU (3/4) • Needs of ICARE2 model adaptations: • Heat transfers between fuel bundles, pressure tubes and moderator  adaptation of existing models, • Oxidation (internal and external) of pressure tubes, heat-up and deformation of fuel bundles  adaptation of existing models, • Good results of INR validation of fuel channels oxidation models on AECL experiments. • Ballooning and sagging (“disassembly”) of fuel channels  new specific models, • Formation of solid 3D debris beds on calandria, heat transfer between debris and water from the protection tank  use of the 2D ICARE/CATHARE debris models as basis for this investigation.

17. ASTEC adaptation to CANDU (4/4) • In SARNET2, INR will continue their investigations, with support of AECL knowledge: • Further validation of ASTEC models, • Benchmarks with AECL codes (CATHENA, MAAP4-CANDU). • All this work will take a great benefit of the strong bilateral collaboration on CANDU models between IRSN and BARC (India) that will still be reinforced from 2009.

18. Conclusions • ASTEC V1 is today fully applicable to Gen.II PWR and VVER (440 and 1000), and partly to CANDU reactors (BWR investigations are under way with promising results). • The 1st version V2.0 of the new series of ASTEC versions, to be released in March 09, will allow to simulate: • SA scenarios in EPR, • In-Vessel-Melt-Retention for some Gen.III designs. • The identification and ranking of needs of model adaptations to BWR and CANDU, done in SARNET, will lead to a further step in SARNET2, with model developments and assessment (validation and benchmarks). • Plans to get mid-2011 the 1st version applicable to the major part of SA sequences in BWR and CANDU.