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Calculational Support for the QUENCH-10 and QUENCH-11 Experiments

Calculational Support for the QUENCH-10 and QUENCH-11 Experiments. J Birchley, T Haste, B Jaeckel. Introduction. Calculational support has continued at PSI for the QUENCH test series post-test calculations for QUENCH-10 pre-test calculations for QUENCH-11

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Calculational Support for the QUENCH-10 and QUENCH-11 Experiments

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  1. Calculational Support for the QUENCH-10 and QUENCH-11 Experiments J Birchley, T Haste, B Jaeckel

  2. Introduction • Calculational support has continued at PSI for the QUENCH test series • post-test calculations for QUENCH-10 • pre-test calculations for QUENCH-11 • This support has been provided using the two main calculational routes used at PSI for core degradation analysis • MELCOR1.8.5, integrated engineering-level approach, used extensively for plant studies • SCDAP-based codes (SCDAP/RELAP5/MOD3.2, SCDAPSIM/MOD3.4), for more detailed analysis of specific points • General aims are to help with test definition, and to improve understanding of the results

  3. Post-test calculations for QUENCH-10 • Pre-test and post-test calculations were reported at the 10th QUENCH Workshop • MELCOR1.8.5 RD • SCDAP/RELAP5/MOD3.2(hx) with improvements by FZK/IRS including modifications to the heater rod model • SCDAPSIM/MOD3.4 is being increasingly used at PSI for supporting plant sequence calculations • Faster and more stable performance in many circumstances • Post-test calculations have been repeated with SCDAPSIM to compare its performance with that of SCDAP/RELAP5 • Preparatory step to developing an air ingress model • A pre-requisite to calculating the air-oxidation is to replicate the initial thermal and oxidised state of the bundle; the current work benchmarks the models against the pre-oxidation phase

  4. QW-10 results with SCDAP/RELAP5/MOD3.2 PSI version – centre rod • Temporary modifications were made to S/R5 to model the air oxidation

  5. QW-10 results with SCDAP/RELAP5/MOD3.2 PSI version – shroud • Air oxidation modelling to be added later to SCDAPSIM

  6. QUENCH-10 input model using SCDAPSIM • Same basic model as used for SCDAP/RELAP5 • Derived from one supplied by FZK • Noding and components • Central unheated rod, inner heated rods, outer heated rods, corner rods, shroud, Ar and water cooling systems • 16 axial nodes to represent the test section • 10 x 0.1 m nodes for the tungsten heated section • Comparative calculations performed amongst SCDAPSIM, S/R5 PSI version and S/R5 IRS versions with the same input as far as possible • Some changes needed to take into account the different models and options available • External resistance of the heater rods used as a tuning parameter, aiming to match the total H2 production of 47.3g in the steam pre-oxidation period

  7. Differences between SCDAPSIM and S/R5/3.2hx (irs/psi) models

  8. Differences between SCDAPSIM and S/R5/3.2hx (irs/psi) input data • Shroud model • Constant composition with S/R5, but can treat different cooling jackets • Varying composition with SSim to treat absence of insulator above W heated section • Heater rod boundary condition • S/R5, constant temperature at each end, 300K • SSim, constant temperature of 400K at bottom (300K leads to condensation), tied to top RELAP volume gas temperature at the top via a control function • Shroud physical properties • Emissivity and thermal expansion of shroud materials not input for SSim, tried some mild tuning of the conductivity but this is not sufficient to improve the results • New option ’39’ for taking bigger timesteps in SSim tried, but no advantage in this case (but there is in some plant transients) • Cu tried for end nodes in SSim rather than Mo, more realistic but after retuning the external resistance there is no strong difference in the results

  9. Centre rod temperature histories for SCDAPSIM

  10. Comparison of hydrogen production in the pre-oxidation phase

  11. Axial temperature profile in bundle at end of high temperature oxidation phase

  12. Axial temperature profile in shroud at end of high temperature oxidation phase

  13. Conclusions from QUENCH-10 calculations • SCDAP/RELAP5/MOD3.2hx (irs/psi) gives temperature histories peaking at the same axial location as observed • Adequate for starting air phase calculation • However poorer agreement in the shroud above the heated section • SCDAPSIM gives peak one node (10cm) too low, with temperatures up to 200K too high in the mid region • Not adequate to start an air phase calculation, possibility of excursion starting in the wrong place • However improved agreement in the shroud region above the heated section, better shroud model • Need to modify SCDAPSIM with features of SCDAP/RELAP5/MOD3.2hx (irs/psi) to improve calculation of QUENCH facility • Heater rod model including boundary conditions, additional user-defined material properties, there may be others to be considered • Axially-dependent shroud properties and improved numerical performance are advantages for SCDAPSIM • GUI interface for SCDAPSIM improves the usability (control of run, inspection of results on-line) • Investigation into improving SCDAPSIM in this way in progress • No direct improvement for plant studies, but will aid assessment against QUENCH data, and is needed for validation of a prospective air ingress model against QUENCH-10

  14. Preliminary calculations for QUENCH-11 • SCDAPSIM/MOD3.4/bi5 • input based on deck used by ISS for ISP-45 submission • modifications for initial filling, additional heating and water supply • bundle and additional power history, injection rates as used in FZK planning calculations • MELCOR 1.8.5 RD • input based on deck used by PSI for analysis of QUENCH-10 • modifications analogous to SCDAPSIM • Final definition of QUENCH-11 protocol is pending outcome of vorversuch • Models set up to accommodate follow-on QUENCH-11 • demonstrated in conceptual calculations (not presented at QWS 11)

  15. Vorversuch prediction SCDAPSIM: Heat balance

  16. Vorversuch prediction MELCOR: Heat balance

  17. Vorversuch prediction SCDAPSIM and MELCOR: Liquid level

  18. Vorversuch prediction MELCOR: Maximum cladding temperature

  19. Vorversuch prediction SCDAPSIM: Cladding temperatures

  20. Vorversuch prediction MELCOR: Cladding temperatures

  21. Vorversuch prediction SCDAPSIM and MELCOR: Hydrogen mass

  22. Vorversuch prediction MELCOR: Oxide thickness

  23. Summary of QUENCH-11 support: Status and plans • Prediction of vorversuch demonstrated with SCDAPSIM and MELCOR • Definitive calculation of vorversuch to be performed as precursor to QUENCH-11 • adjustment of input to reproduce observed transient • Plan to perform pre-test (?) and post-test calculation of QUENCH-11 • SCDAPSIM appears better suited than MELCOR to boildown simulation • Non-negligible cladding oxidation during vorversuch

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