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ABSTRACT
If any severe accident occurs, application of the Severe Accident Management Guidance (SAMG) is initiated by the Technical Support Center (TSC). In order to provide advisory information to the TSC, required safety injection flow rate for maintaining the coolability of the reactor core has been suggested in terms of the depressurization pressure. In this study, mechanistic development of the safety injection flow map was performed by post-processing the core exit temperature (CET) data from MELCOR simulation. In addition, effect of oxidation during the core degradation was incorporated by including simulation data of core water level decrease rate. Using the CET increase rate and core water level decrease rate, safety injection flow maps required for removing the decay and oxidation heat and finally for maintaining the coolability of the reactor core were developed. Three initiating events of small break loss of coolant accidents without safety injection, station black out, and total loss of feed water were considered. Reactor coolant system depressurization pressure targeting the suggested injection flow achievable with one or two high pressure safety injections was included in the map. This study contributes on improving the current SAMG by providing more practical and mechanistic information to manage the severe accidents.
Acknowledgements
This work was supported by the Nuclear Safety Research Program through the Korea Radiation Safety Foundation (KORSAFe); granted financial resource from the Nuclear Safety and Security Commission (NSSC), Republic of Korea [grant number 1403002]; National Research Foundation of Korea (NRF) grants funded by MISP [grant number NRF-2015M2A8A4021654].
Disclosure statement
No potential conflict of interest was reported by the authors.
| Nomenclature | ||
| Acronym description | = | |
| ADVs | = | atmospheric dump valves |
| BDBA | = | beyond data basis accident |
| BWR | = | boiling water reactor |
| CDVs | = | condenser dump valves |
| CEOG | = | Combustion Engineering Owners Group |
| CET | = | core exit temperature |
| CHG | = | charging pump |
| DBA | = | design basis accident |
| ECCS | = | emergency core cooling system |
| EPRI | = | electric power research institute |
| FCVS | = | filtered containment venting system |
| HPME | = | high pressure melt eject |
| HPSI | = | high pressure safety injection |
| IAEA | = | International Atomic Energy Agency |
| IFR | = | injection flow rate |
| IPE | = | Individual Plant Examination |
| LBLOCA | = | large break loss of coolant accident |
| LPSI | = | low pressure safety injection |
| MSIVs | = | main steam isolation valves |
| MSSVs | = | main steam safety valves |
| NRC | = | Nuclear Regulatory Committee |
| NSSS | = | Nuclear Steam Supply Systems |
| OPR1000 | = | Optimized Power Reactor 1000 |
| PSA | = | Probabilistic Safety Analysis |
| PSRV | = | pressurizer safety relief valve |
| PWR | = | pressurized water reactor |
| RCS | = | reactor coolant system |
| RPV | = | reactor pressure vessel |
| SAMG | = | Severe Accident Management Guidance |
| SBLOCA | = | small break loss of coolant accident |
| SBO | = | station black out |
| SDS | = | safety depressurization system |
| SITs | = | safety injection tanks |
| TLOFW | = | total loss of feed water |
| TSC | = | Technical Support Center |
Symbol subscript description unit
| A | = | cross sectional area of core (m2) |
| cp | = | specific heat (J/kg) |
| hfg | = | specific enthalpy of vaporization (J/kg) |
| hinj | = | specific enthalpy of injected coolant (J/kg) |
| hsat, g | = | specific enthalpy of saturated coolant (J/kg) |
| L | = | height of uncovered core (m) |
| = | decreasing rate of core water level (m/s) | |
| = | temporal vapor mass in the upper head and core (kg/s) | |
| = | minimum required flow rate (kg/s) | |
| = | required flow rate (kg/s) | |
| Mg | = | steam mass in core (kg) |
| = | molecular weight of water (kg/mol) | |
| PRCS | = | pressure of RCS (Pa) |
| = | total heat in the core (W) | |
| R | = | gas constant (J/Kmol) |
| trefill | = | refilling time (sec) |
| TCET | = | core exit temperature (K) |
| = | increasing rate of CET (K/s) | |
| ΔTCET | = | change of core exit temperature (K) |
| V0 | = | volume of upper head (m3) |
Greek symbol subscript description unit
| ρf | = | density of coolant (kgm3) |