Systems Exam 4 - Main Steam Flashcards
(33 cards)
How is pH controlled in the Main Steam System?
During power operation morpholine is used for pH control.
What is shrink, and how does it affect SG level?
Shrink:
→caused by events that suddenly decrease steam flow (rapid load decrease, RCP trip, control valve closure)
→feedwater flow > steam flow
→SG riser level decreases due to decreasing void fraction
→downcomer flow temporarily decreases to equalize downcomer/riser pressures
→less moisture is being returned to downcomer due to reduced steam flow
→SG level goes down
→will continue until conditions stabilize and steam/feed flow are balanced
What is swell, and how does it affect SG level?
Swell:
→caused by events that suddenly increase steam flow (steam break, rapid load increase)
→steam flow > feedwater flow
→SG riser level increases due to increased void fraction
→more moisture is entrained in the steam exiting the tube bundle
→downcomer flow temporarily decreases to equalize downcomer/riser pressures
→more moisture is returned to the downcomer due to increased moisture entrainment
→SG level goes up
→will continue until conditions stabilize and steam/feed flow are balanced
How does recirculation ratio follow power level?
→higher recirculation ratio at low power
→lower recirculation ratio at high power
(recirculation flow / feedwater flow)
What are the design differential pressures for the SG tubes and tubesheet?
→primary to secondary ΔP = 1600 psig
→secondary to primary ΔP = 670 psig
What are the Primary and Secondary SG pressure boundary designs?
→Primary: 2485 psig and 650°F in RCS
→Secondary: 1285 psig and 600°F
Steam Generator Flow Restrictor
→7 Venturi nozzles at SG outlet
→little flow restriction during normal operation (low ΔP, 2-3 psid)
→flow measurement for SGWLC
→limits steam flow in the event of a steam break; limits size of break to 1.388 sq ft
→protects against DNB/fuel integrity from cooldown rate/positive reactivity addition
→protects containment integrity by limiting rise of containment pressure and temperature for IRC steam break
→reduces thrust forces on main steam line
→limits stresses on SG internal components like tubesheet (RCS boundary)
TDAFWP Steam Supplies
→tap off main steam lines 1 & 4 before MSIVs
→Fail open AOV’s
→upstream check valve prevents backflow from feeding steamline break
→u-HV-2452-1 Train A from SG 4 (uED1-1)
→u-HV-2452-2 Train B from SG 1 (uED2-1)
→valves have accumulators that allow for maintaining valve closed for 7 hrs, plus 30 mins to allow for closing manual isolation
Open on ‘BLA’:
→Blackout (OL)
→Lo-Lo SG Level on 2/4 SGs (2/4 detectors per SG)
→AMSAC
MSIV Auto Close Signals?
(a.k.a. Main Steam Isolation signals)
MSIV’s Auto Close on:
→CNTMT Hi-2 (2/3) at 6.2 psig
→Lo Main Steam Line Pressure of 605 psig (rate compensated, blockable when < P-11)
→Main Steam Line Negative Rate - 100 psig per sec with 50 sec Time Constant (enabled when Lo MSL Pressure blocked)
→Manual 1/2 handswitches
→Control transfer of MSIV from MCB to RSP
Note: MSL Isolation also closes the before MSIV drip pot isolation AOVs, and a manual closure of an MSIV will close its associated upstream drip pot valve
ARV Accumulators
→provide minimum capacity to modulate an ARV 15 times over 4 hours
→1 full stroke and 14 modulations each equal to 10% of the valve full open capacity
Atmospheric Relief Valves
→not credited for overpressure protection; used for cooldown purposes (during SGTR)
→prevent safeties from lifting
→valve normally set to open @ 1125 psig but may be varied depending upon plant conditions (sat pressure/130 = pot setting)
→takes about 15%-20% output on controller to open valve initially due to pilot plug, but once open can be throttled below this point
→two required for adequate cooling capacity for U1; one required for U2
→considered operable if they can be manually cycled from the CR
How do adjust the lift setpoint for the ARVs?
saturation pressure/130 = number of turns
Where can ARVs be operated from?
→can be operated from MCB or RSP
→control must be transferred to RSP via junction boxes and Amphenol connectors; junction boxes located in ARV Accumulator room
How can ARV’s be opened from Control Room? Is that a unit difference?
→U1 ARVs provided with OPEN/OFF keyed switch, used to fully open ARV using separate solenoid powered from opposite train
→switches required per analysis for D-76 generators to prevent overfill of generator during a tube rupture in conjunction with a loss of a single train of power
→analysis requires 2 SGs for max cooldown. (U1 D-76 SGs have smaller steam space volume therefore would fill up faster during the tube rupture)
→U2 ARV only has single solenoid supplied from 1 train
Main Steam Line Rad Monitors:
→What type detectors and what are their ranges?
→EXPECTED Response for N-16 rad monitor with power changes?
Geiger-Mueller Tube:
→outside of pipe, upstream of safeties
→can detect 2.5 gpm primary to secondary tube leak
→leak detection based upon 1% fuel failure
→also labeled as “Main Steam Line Monitors” (u-RE-2325 thru 2328)
N-16 Scintillation Detector:
→just upstream of MSIVs (downstream of safeties)
→can 1.0 gpd with a range of 1.0 to 150 gpd
→Red Alarm at 15 gpd
→N-16s aren’t accurate below ≈40% power
→also labeled as “Steam Generator Leak Rate Monitors” (u-RE-2325A thru 2328A)
SG Safeties Setpoints
Setpoints:
→1185 psig
→1195 psig
→1205 psig
→1215 psig
→1235 psig
Other Info:
→ASME code overpressure protection for SGs
→for any one safety valve, the relieving capacity may not exceed a maximum design flow rate of 970,000 lbm/hr (≈25% SG rated steam flow)
→prevent steam line pressure from exceeding 110% of its design pressure of 1185
What action must be taken if SG Safety acoustic sensor control logic loses power?
Each safety is provided with an acoustic sensor that sends a signal to the plant computer. If the control logic experiences a loss of power, computer interface must be reset via interface in CSR.
What is the minimum N2 pressure required to close the MSIV within the required stroke time?
minimum N2 pressure ≈ 1839 psig
How are MSIVs locally operated?
→2 local manual overrides provided per MSIV
→may be operated in the clockwise direction to relieve hydraulic oil pressure back to the reservoir and allow N2 to close the MSIV
→wrenches for operation located outside MSIV room in safe shutdown cabinet
What are the mode restrictions and DP constraints for opening MSIVs and their bypasses?
Mode 1:
→all 4 bypasses locked closed
Modes 2, 3, or 4:
→only 1 MSIV bypass valve can be opened at a time to satisfy CNTMT Isolation requirements
→other three bypass valves locked closed and associated MSIVs are closed
→bypass valve is opened 1/4 turn at a time
→once DP is ≤15 psid, MSIV can be opened
→How does an MSIV work?
→What is its failure mode?
→air driven hydraulic pump to open
→N2 to close
→designed to stop flow within 5 sec
→on trip signal, hydraulic solenoids energized to open and dump fluid, and N2 closes valve
→loss of power to air solenoid for hydraulic pump fails open, causing the MSIV to open if hydraulic bleed solenoid valves have failed closed
→ensuring uD2 is aligned to battery charger prevents MSIVs from opening (operators are dispatched on an SI to align BCuD24 so that air solenoid remains closed)
Note: MSIVs designed to close w/in 5 sec to…
→prevent uncontrolled blowdown of more than one SG
→minimize RCS cooldown
→maintain CNTMT temp and pressure w/in limits following an MSL break inside CNTMT
Operation of Upstream (before) MSIV Drip Pot Isolation Valves
→fail closed AOVs
→close when MSIV given closed signal
→can be manually opened
In the case of a steam generator tube rupture, how are conditions in the penetration rooms improved?
Eductor action on exhaust piping removes steam from penetration room when steam is flowing through pipe.
How should MSR’s be removed from service?
→main turbine operation time without MSRs in service should be minimized - limited to 300 hrs/yr
→without MSRs, increased erosion of the LP turbine blades will occur
→if MSRs to be shut down, BOTH right and left MSRs should be shut down simultaneously to maintain a balanced steam flow
→MSRs may be taken out of service if steam flow is adjusted so that the max generator output is 1130 MWE (97%)
→single MSR operation NOT allowed
