1. 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

2. ERMSAR 2012, Cologne March 21 – 23, 2012 2 OUTLINE Context H2 sequence: description and results H3 sequence: description and results Conclusions

3. ERMSAR 2012, Cologne March 21 – 23, 2012 3 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 4.0.7 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

4. ERMSAR 2012, Cologne March 21 – 23, 2012 4 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

5. ERMSAR 2012, Cologne March 21 – 23, 2012 5 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

6. ERMSAR 2012, Cologne March 21 – 23, 2012 6 H2 SEQUENCE: RESULTS (2) Primary system pressure In-vessel hydrogen production

7. ERMSAR 2012, Cologne March 21 – 23, 2012 7 H2 SEQUENCE: RESULTS (3) Mass of corium discharged  into reactor pit  into lower head

8. ERMSAR 2012, Cologne March 21 – 23, 2012 8 VESSEL FAILURE MODES ASTEC V2.0: one step MAAP4: two steps Local failure: hole Global failure: circumferential

9. ERMSAR 2012, Cologne March 21 – 23, 2012 9 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

10. ERMSAR 2012, Cologne March 21 – 23, 2012 10 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

11. ERMSAR 2012, Cologne March 21 – 23, 2012 11 H3 SEQUENCE: RESULTS (2) Primary system pressure In-vessel hydrogen production

12. ERMSAR 2012, Cologne March 21 – 23, 2012 12 H3 SEQUENCE: RESULTS (3) Mass of corium discharged  into lower head  into reactor pit

13. ERMSAR 2012, Cologne March 21 – 23, 2012 13 VESSEL FAILURE MODES ASTEC V2.0: one step MAAP4: two steps Local failure: hole Global failure: circumferential

14. ERMSAR 2012, Cologne March 21 – 23, 2012 14 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.