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Review VVER-1000 LBLOCA Report

Review VVER-1000 LBLOCA Report. Vietnam trainees. Sequence of events and operation of systems. Assumption: Location of break: reactor inlet (850 mm diameter pipe) Break type: double-ended guillotine break Loss of the primary coolant is maximal

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Review VVER-1000 LBLOCA Report

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  1. Review VVER-1000 LBLOCA Report Vietnam trainees

  2. Sequence of events and operation of systems • Assumption: • Location of break: reactor inlet (850 mm diameter pipe) • Break type: double-ended guillotine break • Loss of the primary coolant is maximal • Comment: ( OK the mots conservative case with maximal loss of coolant ) • Purpose of analysis: • Trace the change of some main parameters of RCS • Check of meeting the acceptance criteria • Comment: ( OK )

  3. Sequence of events and operation of systems • Phenomena: • Large of coolant inventory discharge through the break • Sharp decrease in the primary pressure occurs • Core may be uncovered and reduction in heat removal from the core • Sharp increase in temperature of fuel rod claddings • Sequence Events • LB LOCA occurs • Trip reactor when pressure decrease to 14.7 Mpa (1.5 s delay) • Pumps trip and coast down • Termination of steam bleeding from SG to the turbine • ECCS inject water into RX • Steam pressure in SG increases (Why?) • Comment: ( Assumption power at 100% of nominal?)

  4. Sequence of events and operation of systems • Additional condition together with the accidents: • LOOP (loss of offsite power) • Comment: (OK more conservative study ) • ECCS injection: • High-pressure safety injection system (JND) inject at high pressure • The ECCS passive part (JNG2) inject when pressure reach the set point • The low-pressure safety injection system (JNG1) inject when pressure decrease to 2.5 MPa • Delay for starting pump for JND and JND1 around 40 s • After around 120 s EFWP feed the SG level • Comment: ECCS passive part (acc) will inject first then HPSI and LPSI working later due to delay for DG start.

  5. Safety assessment criteria • Acceptance Criteria: • PCT less than 1200 oC • Oxidation depth not exceed 18% • Total amount of oxidized zirconium does not exceed 1% • Comment: (Oxidation depth need to be less than 17%) • Single failure assumption: • Filure of one diesel-generator then failure of one JND pump and one JNG1 pump • Failure of one accumulator • The most effective control rod remains in upper position upon the scram signal • Comment (OK)

  6. Calculation results • Blow down phase (Pressure decrease and Flow rate at break):

  7. Calculation results • Refill and reflood phases:

  8. Calculation results • Long term cooling phase:

  9. Calculation results • PCT:

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