Analysis and Comparison of Experimental Data of QUENCH-07 to QUENCH-09 Review and Progress

1. Analysis and Comparison of Experimental Data of QUENCH-07 to QUENCH-09Review and Progress Ch. Homann, W. Hering Forschungszentrum Karlsruhe P.O. Box 3640 D-76021 Karlsruhe, Germany 11th International QUENCH Workshop Forschungszentrum Karlsruhe 25-27 October 2005 QWS11, KA, 25.-27.10.2005

2. Introduction • QUENCH-07 – QUENCH-09 • devoted to B4C control rod behaviour • cover wide range of accident conditions (LOOP / LOCA) • Several aspects presented at previous QWSs • CR behaviour • General findings • Time for an state of the art overview • Totally based on experimental on-line data • Demonstrates their value as “stand alone” information • Further work possible and appreciated • Report FZKA 7101 in work QWS11, KA, 25.-27.10.2005

3. Main Results (QWS10) CR fails near upper end of heated zone near end of first transient in two steps Clad (Q-7/-9: Δt = 33 s) Guide tube (Δt = 196 s) Subsequent test conduct/ development different Steam starvation significant test parameter Sequence diagram established,necessary for model development CR degradation is embedded in general bundle damage and degradation B4C Contribution to Oxidation (1) Analysis based on MS data Analysis is globalassessment Basis B4C + 7 H2O  2 B2O3 + CO + 7 H2 – 760 B4C + 8 H2O  2 B2O3 + CO2 + 8 H2 – 792 B4C + 6 H2O  2 B2O3 + CH4 + 4 H2 – 987 Zr + 2 H2O  ZrO2 + 2 H2 – 595 Restrictions Analysis uncertain in late phase (further chem / phys phenomena) MS based on mass numbers  Deduction ofchemical compounds ambiguous B4C oxidation probably in smaller bundle region than Zr oxidation Control Rod Damage and Degradation QWS11, KA, 25.-27.10.2005

4. B4C Contribution to Oxidation (2) QWS11, KA, 25.-27.10.2005

5. Material Relocation Basis • MR normally detected in PTE • Guide tube failure Q-7/-9: 2136 / 2590 s(1896 / 2125 s into first transient) • Absorber melt at low temperature TCs may indicate MR Results • Wide axial & radial spreading • Effects confirmed by PTE • Number of detected events not representative for total number • Additional phenomena in later test phases  interpretation difficult • Similar results in QUENCH-09 in spite of different test conduct QWS11, KA, 25.-27.10.2005

6. First Transient (1) Experimental findings • Heat-up rates quite close together • But: CR degradation different Closer look at tests helpful? Differences between tests • Test conduct • Steam: 3.0, 3.15, 3.4 g/s • Initial bundle temperatures • Radial heat losses • Further differences • Geometry tolerances • Assembly tolerances • Other items QWS11, KA, 25.-27.10.2005

7. First Transient (2) Results • More than one reason for differences • Effects • may be localized • may compensate one another Consequences • Heat-up time within ±5 % • Margin measure for bandwidth(facility, test conduct) • Much more tests needed for proper statistics… QWS11, KA, 25.-27.10.2005

8. Second Transient in Q-07/-08 Experimental findings Differences in test conduct sum up with time, but • Bundle conditions similar at start of second transient (T2) • Test conducts of T2 similar Problem H2 production very different Solution See figure Consequences • Direct comparison of test results impossible • Pay special attention on duration of hot phase of T2, if good agreement of tests required QWS11, KA, 25.-27.10.2005

9. Cool-Down Phase Experimental findings in Q-07 • Shroud failure at 3486 s • TCI 15/0 always below Tsat • Fast final decrease of TSH/TCI • Pressure signals not helpful Results • Condensation in annulus • Steam mass flow rate decreases in upper part of bundle measured rate valid for bundle exit • Radial heat flux reversed during c/d • Large azimuthal asymmetry even in cooling jacket • Maximum temperature in c/j later at lower elevations • Similar results for QUENCH-09 • Premature end of data acquisition in QUENCH-08 QWS11, KA, 25.-27.10.2005

10. Problems Time synchronization of PCs diverged Condensation in steam feed pipe Solution difficult(MS sampling freq small) Common Recommendations Synchronization based on P 411 (rod pressure) Time shift MS 15 … 21 s Delay H2 rate 5 … 7 s Recommendations Distributed by E-mail Included in this presentation Delay of H2 Production in Cool-Down Phase of QUENCH-07 QWS11, KA, 25.-27.10.2005

11. MS Measurement Q-07 Problem • Consumed steam exceeds provided steam by up to ~50% • Even higher peak measured with PRISMA • Steam supply credible • Strong evaporation or entrainment of condensate in steam feed pipe unlikely • No physical explanation found  Transient MS tests in bundle necessary QWS11, KA, 25.-27.10.2005

12. CR behaviour Analysis of on-line data alone yields much insight Sequence of CR degradation understood CR failure in first transient Large scatter for guide tube failure CR contribution to oxidation assessed roughly Relocation of absorber melt identified from TC readings General outcome Understanding of tests widely extended Work gives basis to model CR degradation Bundle behaviour Heat-up to ~ 1700 K: Δt/t = ±5 %; several reasons compete Reason for different hydrogen release in T2 of Q-7/Q-8 understood Thermal-hydraulic consequences of shroud failure investigated Q-7 data synchronisation corrected Interpretation of MS signals in c/d phase needs further work General outcome Direct comparison of test results impossible due to differences in test conduct Only thorough and detailed work can give insight Summary & Conclusions QWS11, KA, 25.-27.10.2005