Safety analysis of supercritical-pressure light-water cooled reactor with water rods Yoshiaki Oka April 2003, GIF SCWR Mtg. at Madison

SCLWR-H plant system

Flow rate low Level 1 Reactor scram Level 2 AFS Level 3 MSIV/ADS/LPCI system Pressure low Level 1 Reactor scram Level 2 MSIV/ADS/LPCI system Pressure high Level 1 Reactor scram Level 2 SRV AFS: auxiliary feedwater system MSIV: main steam isolation valve ADS: automatic depressurization system LPCI: low pressure core injection system

Capacity: RCIC(AFS) TD 1 unit: 4%/unit AFS TD 2 units: 4%/unit ADS 8 units: 20%/unit at 25MPa LPCI MD 3 units: 150kg/s/unit at 1.0MPa Configuration: TD- RCIC LPCI/RHR TD-AFS LPCI/RHR RCIC: reactor core isolation cooling system RHR: residual heat removal system

Accidents 1Total loss of feedwater 2Reactor coolant pump seizure 3Control rod ejection at normal operation 4Control rod ejection at hot standby 5Control rod ejection at cold standby Transients 6Loss of feedwater heating 7Inadvertent startup of AFS 8Partial loss of feedwater 9Loss of offsite power 10Loss of load with turbine bypass 11Loss of load without turbine bypass 12Control rod withdrawal at normal operation 13Control rod withdrawal at hot standby 14Feedwater control system failure 15Pressure control system failure

Total loss of feedwater accident

Coast-down time [s]12345 PCT [ ℃ ] AFS capacity [%/unit]12346 PCT [ ℃ ] AFS delay [s]31030 PCT [ ℃ ] PCT: peak cladding temperature Total loss of feedwater accident

Loss of load without turbine bypass transient

Ratio of coolant density coefficient Maximum pressure [MPa] Maximum power [%] Peak cladding temperature [ ℃ ] SRV setpoint [MPa] Maximum pressure [MPa] Maximum power [%] Peak cladding temperature [ ℃ ] PCT: peak cladding temperature Loss of load without turbine bypass transient

Transients PCT [ ℃ ]Over 670 ℃ Over 700 ℃ Loss of feedwater heating s- Partial loss of flow s1.0 s Loss of load (no-bypass) s0.3 s PCT: Peak Cladding Temperature Durations of high cladding temperature

Result – 100% hot leg break (blowdown)

Result – 100% Cold leg break (blowdown)

LPCI 容量 (kg/s/unit) 被覆温度 ( ℃ )

T = 0 sec : Scram, T = 1 sec : ADS Core power does not exceed 100%. Cladding temperature does not exceed that of normal operation. Depressurization cools the core effectively

T = 0 sec : ADS, T = 0.55 sec : Scram Core power increases to 160% before scram. But cladding temperature does not exceed that of normal operation because core flow rate is higher.

Summary of the results Total loss of flow accident: maximum cladding temperature stays low, 833C (margins to the limit 1260C) Overpressurization transient without turbine bypass shows 50% power rise and Tc reaches 727C, (margins to the limit 800C ) Duration of high cladding temperature is short less than 5 sec. Potential for improvement of fuel integrity criteria at transients. Hot leg break LOCA gives rise to reactivity insertion. But Tc reaches only 550C. Core flow is induced by depressurization due to the once-through coolant cycle. Cold leg break LOCA, Tc reaches 930C, (margins to the limit 1260C) Depressurization cools the core effectively