EOP Terms Flashcards
Large Oscillation Threshold
The peak-to-peak neutron flux oscillation amplitude which is equal to or less than 25%
Utilized to establish the condition beyond which boron injection must be initiated to provide reasonable assurance that rapidly growing oscillations are mitigated in a timely manner
Boron Injection Initiation Temperature
(Graph 5)
(BIIT)
The Boron Injection Initiation Temperature is defined to be the greater of either:
a. The highest Torus temperature at which initiation of boron injection will result in injection of the Hot Shutdown Boron Weight before Torus temperature exceeds the Heat Capacity Temperature Limit or,
b. The Torus temperature at which a Reactor scram is required by plant Technical Specifications.
Defines the point BEFORE which boron injected should be started, so that the Reactor will be shutdown prior to reaching the Heat Capacity Temperature Limit.
Upper left: For power less than decay heat (up to 2.21%) Torus heatup during Boron injection is independent of reactor power
Sloping: Torus heatup during boron injection is proportional to reactor power.
Bottom right: Torus Temperature of 110 F is when scram is required by Tech Specs.
Maximum Subcritical Banked Withdrawal Position
MSBWP
The Maximum Subcritical Banked Withdrawal Position is defined to be the greatest banked rod position at which the Reactor will remain shut down under all conditions.
The Maximum Subcritical Banked Withdrawal Position for Hatch is: Position 02.
Hot Shutdown Boron Weight
HSBW
Defined to be the least weight of soluble boron which, if injected into the RPV and mixed uniformly, will maintain the Reactor shutdown under hot standby conditions.
This weight is utilized to assure the Reactor will be shut down irrespective of control rod position when RPV water level is raised to uniformly mix the injected boron.
Hot Shutdown Boron Weight for Hatch 2 is: 573 lbm or 44% SBLC Tank Level.
Cold Shutdown Boron Weight
CSBW
Defined to be the least weight of soluble boron which, if injected into the RPV and mixed uniformly, will maintain the Reactor shutdown under all conditions.
The weight is utilized to assure the Reactor will remain shut down irrespective of control rod position or RPV water temperature
The Cold Shutdown Boron Weight for Hatch 2 is: 1008 lbm or 30% SBLC Tank Level.
Heat Capacity Temperature Limit
(Graph 2)
(HCTL)
- The Heat Capacity Temperature Limit (HCTL) is the highest Torus temperature from which emergency RPV depressurization will not raise:
a. Torus temperature above the maximum temperature capability of the Torus and equipment within the Torus which may be required to operate when the RPV is pressurized, or
b. Torus pressure above Primary Containment Pressure Limit,
while the rate of energy transfer from the RPV to the containment is greater than the capacity of the containment vent.
Depressurizing the RPV when Torus temperature and RPV pressure cannot be maintained below the HCTL thus avoids failure of the containment and the equipment necessary for safe shutdown of the plant
98 inches: elevation of the bottom of the downcomer.
Pressure lines: Above these lines is unsafe. Torus cannot handle the head addition of the Reactor during a DB LOCA without exceeding PCPL.
193 inches: Elevation of the bottom of the ring header.
Primary Containment Pressure Limit
PCPL
- The Primary Containment Pressure Limit is defined by the EPG to be the lesser of either:
a. The pressure capability of the containment, or
b. The maximum containment pressure at which Vent Valves can be opened and closed to reject all decay heat from the containment, or
c. The maximum containment pressure at which SRVs can be opened and will remain opened, or
d. The maximum containment pressure at which valves can be opened and closed to vent the RPV.
The pressure capability of the containment is limiting at Hatch
Upper left hand slope: Slope caused by torus pressure instrument tap coverage at this torus level
Right hand vertical: Drywell level (103.5 ft) in which the highest containment vent (18 inch vents) capable of rejecting decay heat becomes covered.
Maximum Pressure Suppression Primary Containment Water Level
MPSPCW
The highest primary containment water level at which the pressure suppression capability of the containment can be maintained.
Irrespective of the suppression chamber airspace volume, the pressure suppression feature of the primary containment can function as designed only when primary containment water level is below a certain limiting elevation. This elevation is a function of the containment type and is defined as is the primary containment water level corresponding to the bottom of the ring header.
For Plant Hatch - 193 inches for both Units.
Drywell Spray Initiation Limit
(Graph 8)
(DSIL)
- The Drywell Spray Initiation Limit is defined to be the highest Drywell temperature at which initiation of Drywell sprays will not result in a rapid pressure drop to below either:
a. The Drywell below torus design differential pressure capability, or
b. The high Drywell pressure scram setpoint.
This temperature is a function of Drywell pressure, and the Limit is utilized to preclude containment failure or
de-inertion following initiation of Drywell sprays.
Left hand up slope: Prevents de-inerting the DW through the Torus/Reactor building vacuum breakers.
Middle down slope: Prevent drywell failure by preventing exceeding the Drywell negative design pressure.
Flat line: The total mass of gasses that can be put into the Drywell is limited; above 25 psig the limit is constant.
Minimum Drywell Spray Flow
MDSF
The Minimum Drywell Spray Flow (MDSF) is 5,000 gpm and is the lowest spray flow that assures uniform circumferential spray distribution within the drywell.
Utilized to provide direct cooling of core debris outside of the RPV and to delay or prevent containment failure once it has been determined that core debris has breached the RPV
Suppression Chamber Spray Initiation Pressure
SCSIP
The lowest suppression chamber pressure which can occur when 95% of the noncondensibles in the drywell have been transferred to the suppression chamber.
The SCSIP is utilized to preclude chugging which could cause failure of the downcomer vents.
- As steam collapses at the exit of the downcomers, the rush of water filling the void enters the downcomer pipe.
a. This “chugging” of water in the downcomer places severe cyclic stresses at the junction of the downcomer and the vent header, and could cause cracks.
b. Subsequently, any steam entering the vent header could leak freely into the suppression chamber airspace and pressurize the suppression chamber. - Chugging can be avoided if noncondensibles are mixed with the steam. The
Pressure Suppression Pressure
(Graph 7)
(PSP)
This pressure is a function of primary containment water level
Utilized to assure the pressure suppression function of the primary containment is maintained while the Reactor is at pressure or primary containment flooding is required.
Left vertical: Elevation of the bottom of the downcomer (98 inches)
Upward slope: Highest torus pressure that can occur without steam in the torus airspace. All the nitrogen is in the torus.
Right vertical: Elevation of the bottom of the ring header (193 inches)
SRV Tail Pipe Level Limit
(Graph 6)
(SRVTPLL)
The SRV Tail Pipe Level Limit is the lesser of:
a. The Maximum Pressure Suppression Primary Containment Water Level
b. The highest Torus water level at which opening an SRV will not result in damage to the SRV tail pipe, tail pipe supports, quencher, or quencher supports.
The SRVTPLL is a function of RPV pressure. SRV operation with Torus water level above the SRVTPLL could damage the SRV discharge lines. This, in turn, could lead to containment failure from direct pressurization and damage to equipment inside the containment (ECCS piping, RPV water level instrument runs, torus-to-dry well vacuum breakers, etc.) from pipe-whip and jet-impingement loads.
Upper horizontal: Elevation of the bottom of th ring header (193 inches)
Right hand downslope: The highest torus water level at which opening an SRV will not result in damage to the SRV tail pipe, tail pipe supports, quencher, or quencher supports. If there is a break, the SRVs would discharge directly to primary containment air space
Minimum RPV
Flooding Pressure
(MRPVFP)
The MRPVFP is defined to be the greater of:
a. The lowest differential pressure between the
RPV and the suppression chamber at which
steam flow through five SRVs is sufficient to
remove all decay heat from the core.
OR
b. The Minimum SRV Re-opening Pressure
Utilized to define the depressurized state of the RPV and to
assure sufficient liquid injection into the RPV to maintain
SRVs open and to flood the RPV to the elevation of the main
steam lines during the RPV flooding evolution when the
reactor is shutdown.
The Minimum SRV Re-opening Pressure is the greater value at
Hatch. Reactor pressure 50 psid above suppression chamber
pressure.
Minimum Steam
Cooling Pressure
(MSCP)
1. This pressure represents one of the two methods of steam cooling with or without injection a. It is used to assure adequate core cooling when a cold shutdown rod configuration cannot be assured and: 1) RPV Flooding is required, or 2) RWL cannot be maintained above -180 inches, or 3) Emergency depressurization is required. 2. MSCP is defined to be the lowest RPV pressure at which steam flow through open SRVs is sufficient to preclude any clad temperature from exceeding 1500°F even if the Reactor core is not completely covered
Number of open SRVs and Minimum Steam Cooling pressure-
7 or more – 120 psig
6 – 140 psig
5 – 170 psig
