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The use of Relap5 in the structural verification of a Swedish NPP

The use of Relap5 in the structural verification of a Swedish NPP. Thomas.Probert@OKG.Eon.Se. Relap5 can be used in different applications. LOCA and transient analysis Pipe break flows Flooding Pressure build-up in rooms Forces on piping Pressure and forces on RPV internals.

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The use of Relap5 in the structural verification of a Swedish NPP

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  1. The use of Relap5 in the structural verification of a Swedish NPP Thomas.Probert@OKG.Eon.Se Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  2. Relap5 can be used in different applications • LOCA and transient analysis • Pipe break flows • Flooding • Pressure build-up in rooms • Forces on piping • Pressure and forces on RPV internals Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  3. How has Relap5 been used in the structural verification? • Relap5 has been used in Sweden for calculating thermo-hydraulic forces in piping and for forces on the RPV and RPV internals since the middle of the nineties • Forces and pressures are then used in a structure model to determine strains, stresses and displacements • The stresses are then evaluated to prove the structural integrity Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  4. Type of load generating events analysed Water and steam hammers caused by • Pipe-breaks • Valve closing • Valve opening • Rupture disc opening • Pump trips • Steam collapse Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  5. Example: The hydraulic SCRAM system of Oskarshamn Unit 1 has been modelled i Relap5 Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  6. Example (cont’d): Forces are calculated … Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  7. Example (cont’d): … for all the piping in the SCRAM system Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  8. MSL-break for Oskarshamn Unit 3 (W. Baltyn’s Relap5-model) Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  9. Modelling considerations • Careful attention must be taken to ensure that the node length is sufficiently small enough to capture the thermo-hydraulic process (pressure event) and that the time step is smaller than the (sonic) Courant time step Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  10. Large model, long execution times and large result files • Small node length to capture the pressure event  Large model (many components) • Fulfilment of the (sonic) Courant condition (maximum time step smaller than the Courant time step)  Long execution times • Fast events (pipe-break, valve closure, valve opening, rupture disc opening, steam collapse, pump trip)  Rapid TH state changes  Small time step Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  11. Typical values • Node lengths are typically 0,1 m for water hammer problems and 0,3 m for steam hammer problems • Some consideration is taken to the piping geometry and the pressure rate change but node lengths are usually not smaller than 0,1 m • The maximum time step (10-5 s) is chosen to at least fulfil the sonic Courant limit but in some cases a smaller value is used (sensitivity analysis) Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  12. Some observations • Node lengths are chosen smaller than the pipe diameter (violation of recommendation given on page 13, section 2.2.2.2 of volume 5 (Relap5 Code Manual, User’s Guidelines)) • Relap5 used to determine forces in piping (not recommended on pages 4-7, section 2.1.2 of volume 5) • Forces are not calculated directly which means either a lot of pre-processing or post-processing Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  13. Checks • Sensitivity analyses with respect to the time step are always performed to check convergence of forces • Parameters important to the force amplitudes are reviewed • Uncertainties are analysed with respect to their affect on force amplitudes • All work is reviewed by an independent third party appointed by our Regulator SSM Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  14. Validation and verification • Pressure and mass flows have been validated against water hammer experiments • Even strains have been validated • Forces have been verified against other validated codes Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

  15. The future • We will still use Relap5 in structural analysis • We have tested Trace in the past but results were not very good • We are not in a hurry to change from Relap5 to Trace Thomas.Probert@OKG.Eon.Se CAMP Spring meeting, 11th of June 2010, AlbaNova building KTH, Stockholm, Sweden

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