Week 4: ECCS Flashcards
What is the overall function of the Emergency Core Cooling System?
To provide core cooling and negative reactivity to ensure the reactor is shut down after any of the following:
LOCA
Rod Ejection
MSLB/MFLB
SGTR
What are the safety design bases for the ECCS?
Protected from natural phenomena
Will remain functional after a Safe Shutdown Earthquake
Will be able to perform its designed function with a single active failure coincident with a LOOP
Active components are capable of being tested during plant operations
Component isolation is provided to ensure ECCS capability is not degraded to below the minimum required
Will function under all postulated accident environments
Will satisfy 10CFR50.46 acceptance criteria
What are the 10CFR50.46 acceptance criteria?
Per 10CFR50.46, the ECCS shall be design such that its cooling performance following a LOCA results in the following:
Peak Cladding Temperature <2200F
Cladding oxidation <17% of total thickness
Hydrogen generation <1% of total possible Zr-Water reaction hydrogen generation
Core remains in a coolable geometry
Long term cooling capability will be maintained
What are the modes of ECCS operation?
Injection
Cold leg recirculation
Hot leg recirculation
What subsystems make up the ECCS?
High Head Injection
Intermediate Head Injection
Low Head Injection
RWST
Accumulators
Describe the Injection mode of ECCS operation.
Water is taken from the RWST and injected into the RCA cold legs. The High, Intermediate, and Low head injection systems are all taking suction from the RWST separately.
Describe the Cold Leg Recirculation mode of ECCS operation.
When RWST lo-lo-1 reached (36% level), the RHR suction is transferred to the Containment sumps, cooled by CCW in the RHR heat exchangers, and returned to the RCS cold legs. The High and Intermediate injection systems now take suction from the RHR system, downstream of the RHR heat exchanger.
Describe the Hot Leg Recirculation mode of ECCS operation.
Approximately 13 hours after initiation of ECCS safety injection, the discharge of the RHR and SI pumps is shifted to the RCS Hot Legs. This is done because the top of the core is potentially in a boiling condition, which may plate out boron onto the core. This could potentially restrict the flow of water to/from the core, so this mode of operation provides a system backflush.
Describe the initiation signals for the ECCS.
The ECCS automatically starts Cold Leg injection when a SIS is generated. A SIS actuated by the following:
1849 psig PZR pressure, 2/4
615 psig SL pressure, 2/3 on 1/4 SGs
3.5 psig CTMT pressure, 2/3
Manual actuation
Describe the High Head Injection System and flowpaths.
High Head Injection is comprised of the 2 CVCS charging pumps and associated BIT. On a SIS, the VCT is isolated and charging pumps take direct suction from the RWST, pumping through the BIT and to the RCS cold legs. During Cold or Hot Leg Recirculation modes, HH injection takes suction from the RHR system and discharges to the RCS cold legs.
Describe the Intermediate Head Injection System and flowpaths.
Intermediate Head Injection is comprised of 2 Safety Injection pumps. The SI pump suction is normally aligned to the RWST and the discharge is aligned to the RCS cold legs; on SIS, the only action required is for the pumps to start. Once Cold Leg Recirculation is initiated, the only change to the SI flowpath is to realign suction to the RHR system. During these two phases, the SI pumps are aligned to a common header that feeds all 4 RCS loops. Once Hot Leg Recirculation is initiated, the SI pumps will be realigned to the Hot legs. The SI pump lines are separated at this point; Train A feeds Loops 2&3, Train B feeds Loops 1&4.
Describe the Accumulator Injection System and flowpaths.
The Accumulator Injection system is comprised of 4 pressurized tanks (1 per RCS cold leg) containing highly borated water. When RCS pressure drops below 700 psig, the accumulators discharge their contents into the RCS.
What is the nominal water volume of the RWST?
400,000 gallons
What are the RWST level setpoints?
Lo-Lo-1: 36% level, auto transfer of RHR pump suctions to containment sump (and realign HH and IH pumps to RHR discharge)
Lo-Lo-2: 20% level, alerts the operator that CTMT spray suction should be realigned to CTMT sump
What are the ECCS pump shutoff heads?
HH: 2690 psig
IH: 1538 psig
LH: 195 psig
