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L OSS- O F- C OOLANT A CCIDENT IB-LOCA

L OSS- O F- C OOLANT A CCIDENT IB-LOCA. R. FREITAS IRSN/PSN-RES/SEMIA/BAST. CONTENTS. FUNDAMENTAL PRINCIPLES OF SAFETY General approaches of the safety Defense in-depth - Functions of safety LOSS OF COOLANT ACCIDENTS Position of the problem Consequences and systems of protection

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L OSS- O F- C OOLANT A CCIDENT IB-LOCA

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  1. LOSS-OF-COOLANTACCIDENT IB-LOCA R. FREITAS IRSN/PSN-RES/SEMIA/BAST

  2. CONTENTS • FUNDAMENTAL PRINCIPLES OF SAFETY • General approaches of the safety • Defense in-depth - Functions of safety • LOSS OF COOLANT ACCIDENTS • Position of the problem • Consequences and systems of protection • Automatic Protections • LOCA ACCIDENTS • Classification • Protection and safeguard system design • Intermediate LOCA transient • Large break LOCA transient Loss of Coolant Accident R. Freitas - IRSN

  3. FUNDAMENTAL PRINCIPES OF SAFETY Loss of Coolant Accident R. Freitas - IRSN

  4. GENERAL APPROACHES OF THE SAFETY Objective of the Nuclear Safety Limitation of the dispersal of radioactive products into the environment, under any circumstances. • NUCLEAR REACTORS • A large quantity of radioactive products • Risk for the man and the environment • REQUIREMENT: NUCLEAR SAFETY • Assure the normal exploitation by limiting the discharges of effluents, • Prevent the incidents or the accidents • Limit their possible consequences Loss of Coolant Accident R. Freitas - IRSN

  5. FONCTIONS OF SAFETY • FUNDAMENTAL PRINCIPLES OF THE SAFETY: Interposition of 3 sealed barriers between the radioactive products and the environment I – FUEL CLADDING 900 MWe PWR French reactors : 40 000 fuel rods Avoid that the products of fission ( PF) move into the fluid II – REACTOR COOLANT PRESSURE BOUNDARY Limitation of the dispersal of the fission products contained in the water Extension of the barrier: connection of the RHRS in shutdownstates III – REACTOR CONTAINEMENT BUILDING Avoid dispersion of PF into the environment Supported pressure: ~ 5 bar according to the landing Loss of Coolant Accident R. Freitas - IRSN

  6. FONCTIONS OF SAFETY • FUNDAMENTAL PRINCIPLES OF THE SAFETY: Safety relies on the guaranteed integrity of these 3 sealed barriers • SAFETY FUNCTIONS: I - Sub criticality • To maintain the reactor under sub critical conditions II - Residual power removal • Primary Coolant Pump – Safety Injection Systems III - Containment of radioactive products • Primary Circuit Loss of Coolant Accident R. Freitas - IRSN

  7. Acceptable consequences POSITION OF THE PROBLEM Pn = 100% PPZR = 155 bar TBC = 330 °C TBF = 290 °C PGV = 70 bar Postulated Accident … Residual Power Protection and Safety Systems Loss of Coolant Accident R. Freitas - IRSN

  8. POSITION OF THE PROBLEM Loss Of Coolant Accident LOCA = Break of the second barrier Loss of Coolant Accident R. Freitas - IRSN

  9. LOCA CONSEQUENCES LOCA Loss of reactor coolant inventory Degradation of core cooling Potential degradation First barrier • Fuel and • clad damage • Fusion Loss of Coolant Accident R. Freitas - IRSN

  10. SCRAM • Decay heat power Accu Safety systems • ECCS • Mass inventory HPSI, LPSI LOCA CONSEQUENCES To avoidpotentialdegradation of first barrier LOCA Loss of Coolant Accident R. Freitas - IRSN

  11. Containment pressure Accu Potential degradation third barrier HPSI, LPSI LOCA CONSEQUENCES LOCA Flashing primary water in the containment Loss of Coolant Accident R. Freitas - IRSN

  12. Accu Safety systems HPSI, LPSI LOCA CONSEQUENCES LOCA To avoid Degradation of third barrier (containment) • Containment pressure • CSS Loss of Coolant Accident R. Freitas - IRSN

  13. Reactor coolant system radioactive • Radioativity in the containment Accu Release of radiological products HPSI, LPSI LOCA CONSEQUENCES LOCA Loss of Coolant Accident R. Freitas - IRSN

  14. Accu Safety systems HPSI, LPSI LOCA CONSEQUENCES LOCA Necessary to limit the radioactive product • Containment isolation Loss of Coolant Accident R. Freitas - IRSN

  15. Accu Safety systems HPSI, LPSI LOCA CONSEQUENCES LOCA Necessary to limit the radioactive product • Containment isolation Loss of Coolant Accident R. Freitas - IRSN

  16. Accu HPSI, LPSI AUTOMATIC PROTECTIONS Protection and safeguard systems actuation LOCA • SCRAM (Reactor Trip) • ECCS (Satety Injection) • CSS (Containment Spray) • Containment isolation Loss of Coolant Accident R. Freitas - IRSN

  17. Peak Clad Temperature < 1204 °C • Maximum cladding oxidation < 17% total cladding thickness • Maximum H2 generation < 1% of the maximum possible if all the cladding had reacted • The core geometry remains coolable • Long term cooling in the core SAFETY CRITERIA LOCA + ECCS design • Safety criteria Loss of Coolant Accident R. Freitas - IRSN

  18. LOCA - CLASSIFICATION Reactor state Pressure: 1 to 155 bar Temperature: 60 to 320 °C RCS: close or open ECCS: potentiality inhibited Break Size Break Size Loss of Coolant Accident R. Freitas - IRSN

  19. Hot leg SGTR Pressurizer Upper plenum Lower plenum Cold leg LOCA - CLASSIFICATION Reactor state Break location Break Size Loss of Coolant Accident R. Freitas - IRSN

  20. Very small break BREAK SPECTRUM ANALYSIS Small break Break Size Intermediate break Large break Loss of Coolant Accident R. Freitas - IRSN

  21. Very small break Very small break Very small break • < 3/8’’ < 9,5 mm Small break Intermediate break CVCS is efficient Regulation pressurizer level Large break BREAK SPECTRUM ANALYSIS • pressurizer level Break Size • charging flow rate Loss of Coolant Accident R. Freitas - IRSN

  22. Very small break • < 3/8’’ < 9,5 mm Small break Intermediate break Large break BREAK SPECTRUM ANALYSIS • CVCS is efficient • Safety injection: NO Break Size Loss of Coolant Accident R. Freitas - IRSN

  23. Very small break • < 3/8’’ < 9,5 mm Small break Intermediate break Large break BREAK SPECTRUM ANALYSIS • CVCS is efficient • Safety injection: NO • Safety injection: YES • Break flowrate compensated by ECCS without core uncovery 3/8’’ << 1’’ 9,5 mm << 25 mm Break Size Loss of Coolant Accident R. Freitas - IRSN

  24. Very small break • < 3/8’’ < 9,5 mm Small break Intermediate break Large break BREAK SPECTRUM ANALYSIS • CVCS is efficient • Safety injection: NO • Safety injection: YES • Break flowrate compensated by ECCS without core uncovery 3/8’’ << 1’’ 9,5 mm << 25 mm Break Size • Safety injection: YES • Core uncovery • Operator action required 1’’ << 14’’ 2,5 cm << 34,5 cm Loss of Coolant Accident R. Freitas - IRSN

  25. Very small break • < 3/8’’ < 9,5 mm Small break Intermediate break Large break BREAK SPECTRUM ANALYSIS • CVCS is efficient • Safety injection: NO • Safety injection: YES • Break flowrate compensated by ECCS without core uncovery 3/8’’ << 1’’ 9,5 mm << 25 mm Break Size • Safety injection: YES • Core uncovery • Operator action required 1’’ << 14’’ 2,5 cm << 34,5 cm • Fast kinetics (few minutes) • Without operator actions • > 34,5 cm Loss of Coolant Accident R. Freitas - IRSN

  26. CONTENTS • FUNDAMENTAL PRINCIPLES OF SAFETY • General approaches of the safety • Defense in-depth - Functions of safety • LOSS OF COOLANT ACCIDENTS • Position of the problem • Consequences and systems of protection • Automatic Protections • LOCA ACCIDENTS • Classification • Protection and safeguard system design • Intermediate LOCA transient • Large break LOCA transient Loss of Coolant Accident R. Freitas - IRSN

  27. LOCA INTERMEDIATE BREAK Typicaltransient Pressure T0: Open Break Primary pressure primaire Secondary pressure secondaire 155 Compensated by CVCS Very small break T1: SCRAM Small break T2: SI Compensated by SI Intermediate break T3: Boiling in upper plenum T7: Open discharge valve SG T4: Boiling in U tubes T8: Evacuation of the Presid by SI and break T5: Stopped production vapour T6: Stopped flow EFWS by high level SG 72 T9: Equilibrium betweenmass and energy Time 130 120 86 Equilibriumenergy - SG SI and break Loss of Coolant Accident R. Freitas - IRSN 12-05-2014

  28. LOCA INTERMEDIATE BREAK Typicaltransient - + Energy removal • Break EBa Break flow • Steam Generator valves (GCTa) • Esa (Tprim -Tsec) • a (Pprim – Psec) Energy sources • Stored energy • Residual power • Reactor Coolant Pump Energy balance: RCP • Energy removed by the break > energy sources • depressurisation Loss of Coolant Accident R. Freitas - IRSN

  29. LOCA INTERMEDIATE BREAK Typicaltransient • Liquidflowrate Enthalpy = 1350 KJ/kg • Steamflowrate Enthalpy= 2750 KJ/kg End of the stabilization pressure (at SG pressure) Loss of Coolant Accident R. Freitas - IRSN

  30. LOCA INTERMEDIATE BREAK Typicaltransient Boiling in upper plenum Boiling in U tubes Pressure 155 130 SCRAM ECCS 120 86 72 40 time Primary pressure Secondary pressure Loss of Coolant Accident R. Freitas - IRSN

  31. LOCA INTERMEDIATE BREAK Typicaltransient Mass balance Pressure Saturated steam ECCS Saturated liquid Subcooled liquid SG pressure Flowrate (kg/s) • Loss of mass Loss of Coolant Accident R. Freitas - IRSN

  32. LOCA INTERMEDIATE BREAK Typicaltransient Core uncovery Pressure Mass time time Loss of Coolant Accident R. Freitas - IRSN

  33. LOCA INTERMEDIATE BREAK Steam Generator depressurization MEANS Secondary pressure decrease (valve opening) to decrease primary pressure Case when time for reaching accumulators set point is too late • Primary pressure OBJECTIVE • Accumulators • Increased ECCS flowrate Loss of Coolant Accident R. Freitas - IRSN

  34. LOCA INTERMEDIATE BREAK Steam Generator depressurization Pressure SG valve opening Mass Time of accumulators discharge Loss of Coolant Accident R. Freitas - IRSN

  35. LOCA INTERMEDIATE BREAK Steam Generator depressurization Pressure Stabilization pressure is low if the size break is large Mass Loss of Coolant Accident R. Freitas - IRSN

  36. LOCA INTERMEDIATE BREAK Reactor Coolant Pump effect • RCP in operation • emulsion in the RCS • Two-phase flow in the break • Loss of mass inventory • +Core mixture level in the core • Efficient cooling Penalize the core inventory Loss of Coolant Accident R. Freitas - IRSN

  37. RCP shutdown Stratification • Liquid break flow then steam • Lower mass inventory loss • Faster depressurization (Accumulator and SI) • Collapsed level in the core • Uncovery in the upper part of the core LOCA INTERMEDIATE BREAK Reactor Coolant Pump effect Penalize the clad temperature Loss of Coolant Accident R. Freitas - IRSN

  38. RCP in operation RCP shutdown LOCA INTERMEDIATE BREAK Reactor Coolant Pump effect Penalise the mass Penalise the T° Loss of Coolant Accident R. Freitas - IRSN

  39. RCP shutdownatscram time Mass RCP in operation Pressure • Collapsedlevel • Swelledlevel LOCA INTERMEDIATE BREAK Reactor Coolant Pump effect • RCP shutdown penalising with regard to temperature Loss of Coolant Accident R. Freitas - IRSN

  40. RCP shutdownatscram time RCP in operation delay trip Masse Delay trip Pression • Collapsedlevel • Lower mass • Collapse LOCA INTERMEDIATE BREAK Reactor Coolant Pump effect • Delayed RCP shutdown more penalising Loss of Coolant Accident R. Freitas - IRSN

  41. CONTENTS • FUNDAMENTAL PRINCIPLES OF SAFETY • General approaches of the safety • Defense in-depth - Functions of safety • LOSS OF COOLANT ACCIDENTS • Position of the problem • Consequences and systems of protection • Automatic Protections • LOCA ACCIDENTS • Classification • Protection and safeguard system design • Intermediate LOCA transient • Large break LOCA transient Loss of Coolant Accident R. Freitas - IRSN

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