ERMSAR 2012, Cologne March 21 – 23, 2012 ASTEC V2.0 rev 1 Reactor Applications French PWR 900 MWe Accident Sequences Comparison with MAAP4 V. Lombard, G. Azarian, E. Ducousso, P. Gandrille AREVA NP SAS, Paris La Défense

ERMSAR 2012, Cologne March 21 – 23, OUTLINE Context H2 sequence: description and results H3 sequence: description and results Conclusions

ERMSAR 2012, Cologne March 21 – 23, CONTEXT SARNET2 project – Work Package 4 Work presented in "Second Periodic Progress Report on ASTEC topic" D4.4 ASTEC V2.0 / MAAP 4 comparison – ASTEC V2.0 revision 1 patch 2 beta version (released in March 2011) – MAAP version Reactor application on a French PWR 900 MWe Two accident sequences: H2 and H3 Physical phenomena studied – In-vessel thermal-hydraulics phenomena – Core degradation – Corium behavior in the lower head

ERMSAR 2012, Cologne March 21 – 23, H2 SEQUENCE: DESCRIPTION t = 0 s: – Loss of Main FeedWater – Loss of Emergency FeedWater – Loss of Safety Injections t = 28 s: reactor scram  closure of Main Steam Isolation Valves ΔT sat < 10°C: coastdown of Reactor Coolant Pumps by the operator T COTMAX > 330°C: total opening of pressurizer SEBIM valves P primary < 40 bar: accumulator discharge P primary < 15 bar: accumulator isolation No containment spray activation

ERMSAR 2012, Cologne March 21 – 23, H2 SEQUENCE: RESULTS (1) Key event timings MAAP 4ASTEC V2.0 Loss of feedwater0 s (initiator) Reactor scram28 s T COTMAX > 330°C38 min42 min Accumulator injection onset57 min1 h 08 min Accumulator isolation2 h 30 min2 h 36 min Start of relocation to lower plenum3 h 54 min3 h 30 min First reactor vessel failure5 h 03 min5 h 11 min

ERMSAR 2012, Cologne March 21 – 23, H2 SEQUENCE: RESULTS (2) Primary system pressure In-vessel hydrogen production

ERMSAR 2012, Cologne March 21 – 23, H2 SEQUENCE: RESULTS (3) Mass of corium discharged  into reactor pit  into lower head

ERMSAR 2012, Cologne March 21 – 23, VESSEL FAILURE MODES ASTEC V2.0: one step MAAP4: two steps Local failure: hole Global failure: circumferential

ERMSAR 2012, Cologne March 21 – 23, H3 SEQUENCE: DESCRIPTION t = 0 s: reactor scram with – Loss of Main FeedWater – Closure of Main Steam Isolation Valves – Loss of Emergency FeedWater – Coastdown of Reactor Coolant Pumps – Loss of Safety Injection pumps – Loss of spray T COTMAX > 1100°C: total opening of pressurizer SEBIM valves P primary < 40 bar: accumulator discharge P primary < 15 bar: accumulator isolation

ERMSAR 2012, Cologne March 21 – 23, H3 SEQUENCE: RESULTS (1) Key event timings MAAP 4ASTEC V2.0 Reactor scram0 s T COTMAX > 1100°C2 h 40 min2 h 39 min Accumulator injection onset2 h 47 min2 h 45 min Accumulator isolation4 h 08 min3 h 54 min Start of relocation to lower plenum5 h 47 min4 h 58 min First reactor vessel failure6 h 57 min6 h 40 min

ERMSAR 2012, Cologne March 21 – 23, H3 SEQUENCE: RESULTS (2) Primary system pressure In-vessel hydrogen production

ERMSAR 2012, Cologne March 21 – 23, H3 SEQUENCE: RESULTS (3) Mass of corium discharged  into lower head  into reactor pit

ERMSAR 2012, Cologne March 21 – 23, VESSEL FAILURE MODES ASTEC V2.0: one step MAAP4: two steps Local failure: hole Global failure: circumferential

ERMSAR 2012, Cologne March 21 – 23, CONCLUSIONS Regarding global hydrogen production both codes are in good agreement. Main differences in hydrogen production modes and release rates: – ASTEC V2.0 predicts a larger fraction of hydrogen produced during corium relocation in the lower head, whereas some corium is still in the core. – In MAAP 4, no significant amount of hydrogen produced during relocation, – Hydrogen production rate lower in ASTEC V2.0 than in MAAP4. Masses of corium accumulated in lower head at vessel failure are of same order of magnitude – Impact of vessel failure modes. Next step for 2012: focus on fission products with last version ASTEC V2.0 rev2.