Week 4: Residual Heat Removal System Flashcards
What are the design bases for the Residual Heat Removal System?
To remove core decay heat and thus reduce the temperature of the RCS during a plant cooldown.
To maintain the core in a coolable geometry and provide core cooling following an accident.
To perform its designated function with a single active failure during the injection phase or with a single active/passive failure during the recirculation phase following a LOCA.
To start automatically after a LOCA and to ensure that adequate net positive suction head is available at the suction of the RHR pumps during all operating modes.
To ensure that the loss of one train will only extend the time required for plant cooldown and will not endanger the plant.
What is the definition of an Active Failure?
The failure of a powered component such as mechanical equipment, electrical supply, or I&C system to perform its design function on command.
What is the definition of a Passive Failure?
The structural failure of a static component which limits the effectiveness of carrying out its design function.
What are the potential suction sources for the RHR pumps?
RWST
RCS Hot Legs 1 and 4
Containment Sump
How is RHR flow through its heat exchanger controlled?
The RHR pump flow rate of 3800 gpm is maintained via the use of a bypass valve. The operator controls a Hx discharge valve to control the amount of flow through the Hx (thereby controlling the amount of fluid cooled); the bypass valve moves in concert with this discharge valve to ensure a constant return flowrate back to the RCS.
What is the purpose of the RHR pump miniflow line?
To ensure that the RHR pump does not overheat when the discharge line is closed or when RCS pressure exceeds the pump shutoff head during the ECCS injection phase.
Describe the role of the RHR system in a plant startup.
As the startup begins, the RHR will be running for heat removal, with a portion of its discharge directed to the CVCS for cleanup purposes. As PZR heatup commences, the RHR will be used to increase letdown flow until the PZR reaches its no-load level of 25%. From there, the RCPs will start, and the RHR pumps are isolated.
Describe the role of the RHR system in a plant cooldown.
The RCS is cooled to 350F/360psig via the steam dumps or SG ARVs. Once accomplished, CCW flow is established to the RHR Hx and the RHR pumps are started.
Describe the role of the RHR system during the Injection phase of ECCS operation.
Upon receipt of a SIS, all ECCS pumps, including RHR, start. The RHR pumps will deliver water from the RWST to the RCS cold legs when the RCS pressure drops below the pump shutoff head of 195 psig. The injection phase ends when the RWST reaches its lo-lo-1 setpoint of 36%; at this point, RHR suction will be realigned to the CTMT sump.
Describe the role of the RHR system during the Cold Leg Recirculation phase of ECCS operation.
When the RWST reaches its lo-lo-1 setpoint of 36%, the recirculation sump isolation valves (normally closed) open fully and the RWST suction valves close. The operators will need to manually align CCW to the RHR Hx and align the suction of the SI and CCP from the RWST to the discharge of the RHR Hx during this phase of operation.
Describe the role of the RHR system during the Hot Leg Recirculation phase of ECCS operation.
Due to boiling in the upper region of the core following a LOCA, boric acid precipitation can cause possible flow restrictions. To prevent this, the RHR pumps are realigned to discharge to RCS Hot Legs 2 and 3 after approximately 13 hours. The CTMT sump remains the suction source, and the CCP/SI pumps continue to take suction off of the RHR Hx discharge.
What are the RHR system valve interlocks?
RCS Hot Leg Suction Valves
RWST Suction Valves
Recirculation Suction Valves
What are the conditions of the RHR RCS Hot Leg Suction Valve Interlocks?
To Open:
Recirc sump suction, RWST suction, and discharge to SI and CCP closed.
RCS pressure less than 360 psig.
What are the conditions of the RHR RWST Suction Valve Interlocks?
To Open:
Recirc sump suction closed
Auto-Close:
SIS and Sump recirc valves full open
What are the conditions of the RHR Recirculation Suction Valve Interlocks?
To Open:
RWST suction closed
1 RCS HL suction valves closed
Auto-Open:
SIS
RWST lo-lo-1 (36%)
