Systems Exam 3 - Emergency Core Cooling Flashcards
(37 cards)
ECCS Design Basis
CLOTH
→C - coolable core geometry shall be maintained, i.e. the core can be cooled
→L - long term cooling will be available to maintain core cooling after an ECCS operation and be able to remove decay heat for a extended time period (1 year w/o significant maintenance)
→O - oxidation of cladding (17%) shall not exceed 0.17 times the total cladding thickness before oxidation
→T - temperature of cladding shall not exceed 2200°F
→H - hydrogen generation shall not exceed 0.01 (1%) times the hypothetical amount that would be generated if all fuel cladding were to react with water or steam
Equipment Design Basis & Safe Shutdown Earthquake (SSE) Criteria
All ECCS equipment is designed to perform its function for at least one year without any significant periodic maintenance
The Emergency Core Cooling System is designed to remain functional after a Safe Shutdown Earthquake
SI Pumps & Recirc Valves
→Shutoff head is ~ 1558 psid
→Intermediate Head Injection at 1520 psig
→Recirculation Valves 8814A and B are both Train A power supplies
→Recirculation valve 8813 is powered from Train B
→Alarm occurs if SIP Suction valve (8806) not open above P-11, followed by another alarm 45 mins later if valve still not open
→auto starts on SI and SIS (no auto start on BO)
→trips on bus undervoltage, 86M lockout on motor breaker from overcurrent
RHR Pump Injection Flow & Pump Facts
→begins flow at ≈200 psig (approx shutoff head)
→≈4900 gpm at depressurized
→minimum flow required for seals = 500 gpm
→auto-starts on SI with SIS (NO auto-start on blackout)
→receives BOS auto-lockout for 109 sec
Accumulators Injection Pressure and Tech Spec Requirements
→623 - 644 psig, pressurize with N2
→boron concentration 2300-2600 ppm
→39% - 61% level per TDM (6119 gal to 6597 gal)
→Alarm occurs if outlet valves not open above P-11 (1960 psig), followed by another alarm 45 minutes later if valves still not open
→assumed that 3 accumulators will inject and fill reactor downcomer, lower plenum, and half the core while 1 accumulator will spill out onto the floor
Note: accumulator pressure can vary with changes in level or temperature. For this reason, level should always be adjusted before adjusting pressure.
RWST Tech Spec Requirements
Modes 1-4
→Temp: 40°F to 120°F, fix within 8 hrs
→Boron: 2400-2600 ppm, fix within 8 hrs
→Level: 473,731 ( >95% per TS Bases), fix within 1 hour
Note: If low temp alarm comes in (≈45°), recirc through containment spray pumps to warm it up.
Containment Sumps
→level indication on MCB from 808’ - 817.5’
→level probes are heated RTDs
→trash racks on 3 sides, removed on wall side to ensure debris level against the trash racks doesn’t stop flow to strainers
→strainers have 0.115” openings to ensure particles large enough to block flow through the reactor core or the Containment Spray nozzles are not allowed into the sump
Cold Leg Injection Flow Path & Suction Headers
→Flowpath from RWST thru all pumps to cold legs
→Separate 12” suction header for CCPs
→SIPs, RHR Pumps and CS Pumps tap off separate 24” suction header
Cold Leg Recirc
→Once RWST reaches 33% (2 of 4) and RHR Auto Swapover Permissive met (SI Signal generates this) then CNTM Sumps suction valves 8811A/B automatically open
→RHR Pump RWST suction valves 8812A/B are manually closed
→Without CCW available to RHR HX the effected train can only be used for injection phase, per bases in EOS-1.3 should not pump water >120°F without CCW
Hot Leg Recirc
→3 hours after initiating event swap to hot leg injection
→Done to minimize boron precipitation on top of fuel and minimize boiling at top of core
→A single RHR pump discharge valve is closed (8809A or B), not a concern since flow is still available thru CCPs and SIPs along with auto mini flow recirculation
→Swap between cold and hot leg recirculation every 24 hours or as directed
To manually open 8804A/B
SIP RWST recirc valves closed (8814A and B OR 8813)
AND
CCP RWST recirc valves closed (8511A or 8512B AND 8511B or 8512A)
AND
Hot leg Recirc Valves closed (8701A or 8702AAND 8701B or 8702B)
To manually open 8811A/B
→Hot leg Recirc Valves closed (8701A or 8702AAND 8701B or 8702B)
AND
→RSWT Suction Valves closed (8812A/B)
To manually open 8812A/B RWST to RHR Pump Suction Valves
CNTMT Sump Suction valve closed (8811A/B)
SI Accumulator outlet valves 8808A-D
→required to be open and de-energized when RCS >1,000 psig
→auto-open on SI signal or P-11 (1960 psig)
→inject from 650 psig down to 200 psig
→keyed switches however the key only prevents closing the valve, the valve can be opened at any time in manual
→Accumulator fill line valves (8964, 8888 and 8871 close on phase A)
To manually open CCP RWST Recirc Valves 8511A/B
→8804A and B must be closed (RHR to SIP and CCP suction)
AND
→LCV-112B or C must be closed (VCT outlet to CCP suction)
To manually open CCP RWST Recirc Valves 8512A/B
8804A and B must be closed (RHR to SIP and CCP suction)
To manually open SIP RWST Recirc Valves 8514A/B or 8513
8804A and B must be closed (RHR to SIP and CCP suction)
Accumulator outlet valves (8808A-D) automatically open on
→P-11 (1960#)
OR
→SI Signal
RHR Auto Switchover
→causes 8811 A/B to open - containment sumps to RHR suction
→occurs at RWST Level < 33% (2/4) if SI signal present
→relay is energize to actuate - auto-switchover would not occur if there’s a loss of power
Design Basis Accidents
→Rod Ejection Accident: leads to LOCA and reactivity event
→Large Break LOCA - Pipe breaks in the Reactor Coolant System which cause leakage greater than the capacity of the normal makeup system, up to and including the instantaneous double ended severance of the largest diameter pipe in the RCS
→Faulted S/G - shrinkage of the reactor coolant from the rapid cooldown due to a steam or feed line break, up to and including the instantaneous rupture of the largest pipe in the steam system (positive reactivity also added due to temperature reduction
→S/G Tube Rupture
Active & Passive Failure Definitions and 10CFR50 Failure Allowances
10CFR50:
→one active failure allowed during injection phase
→one active OR passive failure allowed during long-term recirculation, 24 hrs
→worst case single active failure is a loss of a Safeguards Bus
Definitions:
→active failure is a “malfunction, excluding passive failures, of a component that relies on mechanical movement to complete its intended function upon request.”
→passive failure is “a failure of a component to maintain its structural integrity or the blockage of a process flow path.”
(defined by ANS 58.9 “Single Failure Criteria for Light Water Reactor Safety Related Fluid Systems”)
How long does it take to drain the RWST to 33%?
Flow estimates on large break LOCA: ≈14-15 minutes to get to 33% with approximately 22,000 gpm flowing out
→CS Pumps: 3,000 gpm/pump for total of 12,000 gpm
→RHR Pumps: 4,000 gpm/pump for total of 8,000 gpm
→SI Pumps: 700 gpm/pump for total of 1,400 gpm
→CCPs: 300 gpm/pump for total of 600 gpm
ECCS Valve Interlocks
What causes a Safety Injection Signal?
→Low PZR pressure 1820 psig (2/4), can be manually blocked <P-11
→Low steam line pressure 605 psig (2/3), rate compensated, can be manually blocked <P-11
→Hi-1 Containment Pressure 3.2 psig (2/3)
→Manual, one of two handswitches
