Steam Generators and FW Control Flashcards
(35 cards)
1
Q
What is the Steam Generator Design Basis?
A
Transfer RCS heat to the secondary
2
Q
Why is the S/G Secondary Side inventory mass limited?
A
- Prevent RCS overcooling during MSLB upstream of MSIV’s
- Prevent exceeding containment design pressure during MSLB.
- At 100%, contains {213,000} [218,045] pounds of water
3
Q
What are the S/G design transients?
A
Handle ramp load change of 5% per minute, 15 to 100%
Handle step load change of 10%, 15 to 100%
4
Q
List Important S/G numbers.
A
- S/G considered to be dry when level is <15% Wide Range
- ~22% WR required for natural circulation (1/3 tube height)
- ~33% NR at top of highest U-tube
- Top of Feed Ring at ~33% NR
- {Trcs & Tsg > 70F when Prcs or Psec >200 psig}, [Tsg > 100F when Psg > 200 psig]
5
Q
Describe S/G snubbers.
A
- Provide S/G support for a seismic event – Tech Spec related
- {Unit 1 only - Low snubber oil level alarms}
6
Q
Describe S/G blowdown.
A
- Assist chemistry control of secondary side of SG’s
- Allows sampling of secondary side of SG’s
- Supplies SG Temperature via DCS (used for TS SG temperature)
- 40 gpm per SG nominal – Chemistry Dept determines blowdown rate
- Changes to SGBD flow affect core reactivity
- Blowdown is monitored for activity and chemistry before discharges
7
Q
Describe S/G blowdown flowpath.
A
a) PCV’s – Maintain ~300 psig
b) FCV’s – Maintain ~40 gpm
c) TCV’s – isolate if >140F
8
Q
Describe S/G Blowdown Inside Containment Valves: (FCV-23-4 and FCV-23-6).
A
- Fail closed
- Auto close on low downstream pressure (<600 psig)
- 3 position CLOSE/AUTO/OPEN spring return to AUTO CS, on RTGB 106 [206]
a) IF held in “OPEN”, it defeats the auto low pressure close signal, and opens the valve
9
Q
Describe S/G Blowdown Outside Containment Isolation Valves: (FCV-23-3 and FCV-23-5).
A
- Fail closed
- Automatically close on:
a) Containment isolation (CIAS)
b) Hi S/G Blowdown radiation / monitor failure
c) Low downstream pressure (<600 psig) - 3 position CLOSE-OVRD / AUTO /OPEN spring return to AUTO CS, on RTGB 106 [206]
a) IF held in “OPEN”, it defeats the auto low pressure close signal, and opens the valve
b) IF taken to CLOSE-OVRD, then to OPEN, it defeats the CIAS & HI Rad signal, and opens the valve
10
Q
Describe S/G Blowdown Sample Valves: (FCV-23-7 and FCV-23-9).
A
- Fail closed.
- Automatically close on:
a) Containment isolation (CIAS)
b) Hi S/G Blowdown radiation / monitor failure - 3 position CLOSE/AUTO/OPEN spring return to AUTO CS, on RTGB 106 [206]
a) IF taken to CLOSE, then to OPEN, it defeats the CIAS & HI Rad signal, and opens the valve - When sample flow is restored during abnormal or emergency condition, the Unit 1 Rad Monitors are also restored, but the Unit 2 Rad Monitors remain isolated.
11
Q
Describe S/G Blowdown Flow Control Valves: (FCV-23-12 and FCV-23-14).
A
- Fail closed..
- Valves operated by flow controllers FIC-23-12 and FIC-23-14 located:
a) {on a cabinet behind RTGB 102}
b) [back of RTGB 202]. - Automatically close for their respective side if:
a) FCV-23-12: FCV-23-4 or FCV-23-3 close (‘A’ side)
b) FCV-23-14: FCV-23-6 or FCV-23-5 close (‘B’ side)
12
Q
Describe S/G Blowdown Flow Control Valves: (TCV-23-8).
A
- TCV-23-8 isolates resin beds at 140°F
13
Q
Describe S/G Blowdown Rad Monitors.
A
- {Unit 1: Rad Monitors on each sample line}
- [Unit 2: Rad Monitor on each blowdown process line]
- 1 additional Rad Monitor on SGBD discharge process line before canal release point
- On a Hi radiation Signal:
a) SGBD flow auto diverts to Demineralizer trains on Hi Rad - When sample flow is restored during abnormal or emergency condition, the Unit 1 Rad Monitors are also restored, but the Unit 2 Rad Monitors remain isolated.
14
Q
Describe the S/G feed ring.
A
- Distributes FW evenly into downcomer annulus
- J-tubes: Prevents feed ring from immediate draining on loss of FW; and subsequent steam from filling the feed ring, and water hammer likelihood, when cold AFW restored
- Top of Feed Ring at ~33% NR
15
Q
Describe SG Moisture Removal – Moisture Separators and Steam Dryers.
A
- Steam leaving the separators and dryers has <0.1% moisture. This improves efficiency and increases component life
- Recirculation Ratio is normally at least 3.3 to 1 [2.5 to 1]
- High ratio is needed to prevent sludge buildup on tube sheet (corrosion), improve SG stability (lower void fraction) and preheat incoming FW
16
Q
Describe S/G level Shrink.
A
- Reduction in SG level following a reduction in steam flow or increase in the FW flow
- As steam flow is decreased, less energy is removed from the SG by the turbine causing SG pressure to increase, thus lessening the amount of boiling taking place and causing the steam bubbles to become smaller resulting in an increase in density Mass of the water in the SG is initially constant so this increase in density is seen as a decrease in SG level
17
Q
Describe S/G level Swell.
A
- Increase in SG level following an increase in steam flow due to more energy removed from the SG by the turbine causing SG pressure to decrease, causing the number and size of the steam bubbles to increase resulting in a decrease in water density Mass of the water in the SG is initially constant so this decrease in density is seen as an increase in SG level
18
Q
Describe LEFM.
A
- Green is good!
- Cannot have ‘B’ S/G Low Power 15% Valve open – will affect LEFM indication
- With One Feedwater Header S/G LEFM Indication Cyan and One Green:
a) REDUCE power to less than or equal to 99.8% within 48 hours - With Both Feedwater Header Indications Cyan or any White:
a) CHANGE CALORIMETRIC DATA SOURCES to DP FLOW/TEMP per 2-NOP-09.28, Changing DCS Calorimetric Data Source Between LEFM and DP FLOW/TEMP.
b) IF power is changed by greater than 10%, THEN MAINTAIN power less than or equal to 98.3%.
c) REDUCE power to less than or equal to 98.3% within 48 hrs.
19
Q
What is the function of the Feedwater Control System?
A
- Automatically maintains SG Narrow Range level at 65% by controlling the Main FRV & 15% Bypass valve
20
Q
Describe S/G Level Control Low Power Mode: (<20% FW FLOW).
A
- SG levels are controlled using single element level control using two level inputs
- NR level - signal is produced by comparing actual level to a setpoint of 65% in order to determine a level ‘error’ signal
- WR level - signal acts to both establish a baseline flow requirement signal and as an anticipatory signal because it responds quickly, linearly and consistently
21
Q
Describe S/G Level Control High Power Mode: (>20% FW FLOW).
A
- SG level control automatically swaps to a 3-Element control system with Steam Flow and Feedwater Flow signals being used in conjunction with a SG NR level error signal to control SG level
- Steam and feed flow rates can be accurately measured by their flow detection devices and their inclusion in the FWCS algorithm enhances level control
- Steam Flow/Feed flow error signal is determined and then combined with the SG level error signal for a total error signal that determines whether feedwater raised or lowered
- Being a “level” control system, the level error signal is always the dominant signal regardless of Mode
22
Q
Describe S/G Level Control T-800 Manual / Auto Stations.
A
- Actual SG Level / SG Level Setpoint
- Actual Valve Position / Valve Position Demand
- Auto / Manual
- Remote / Local
23
Q
Describe S/G Level Control Power Supplies.
A
Unit 1
Normal:
Both Trains: Vital SUPS #1
Backup:
A Train: A 125vdc
B Train: B 125vdc
Unit 2
Normal:
A Train: Vital SUPS 2A
B Train: Vital SUPS 2B
Backup:
A Train: A 125vdc
B Train: B 125vdc
24
Q
Describe Safety grade PT-8013A, B, C, D (‘A’ S/G) and PT-8023A, B, C, D (‘B’ S/G).
A
Tap off of the S/G water level transmitter reference leg root lines provide S/G pressure input to:
a) RPS Trip protection circuitry – < 600 psia [626 psig]
b) ASGT – 135 psid [120 psid]
c) MSIS – 600 psia
d) AFAS Hi SG DP isolation – 275 psid
25
Describe S/G WR Level Safety Channels (9012, 9014, 9022, 9024).
* 4 level instruments (2 per S/G)
* 'A' S/G: LT 9012 & LT 9014
* 'B' S/G: LT 9022 & LT 9024
* Post Accident monitoring qualified
26
Describe S/G NR Level Safety Channels (9013A-D, 9023A-D).
a) RPS Low Level trip @ 35%
b) High S/G Level Turbine Trip & FW PP Trip – {90%} [81%]
c) FW High Level Override – { ≥ 82%} [ ≥ 77%]
d) AFAS (2/4 per SG) – 19%
27
Describe S/G NR Level Control Channels (2 per S/G).
a) Both SG Level Control Channels Input to the LPFWCS via a High Value Select
b) Indications on RTGB 103 [203] & RTGB Rear
c) Downcomer Level Alarm behind RTGB also provides S/G Hi/Low Level Annunciator
d) Only 1 SG Level Control Channel Inputs to the Main Feedwater Control System
e) LT 9011/9021 (LT 9005/9006 go to LPFWCS)
28
Describe High Level Override (HLO).
* If 2/4 Safety Channel LICs for one S/G are { ≥ 82%} [ ≥ 77%]:
a) Opens that side MFP Recirc Valve
b) Close signal to FRV. DCS clamps output signal to the FRV’s @ 0% open
c) {Unit 1:Closes 100% Bypass valve for 35 seconds}
* Reset at { ≤ 77%} [ ≤ 72% ] - FRV remains in manual & closes MFP Recirc Valve
* Key switches also blocks inputs to HLO
* HLO cancel pushbuttons at HLO channels restore MFRV control, located behind RTGB 102 [202].
29
Describe Hi Level Override Cancel Pushbutton.
a) No effect on the Turbine Trip Signal that closes the FRV and puts bypass to 5%,
b) Located on rear of RTGB 103/104 [203/204] – restores MFRV control
30
Describe High S/G Level Trip.
* If 2/4 S/G NR level instruments are { ≥ 90%} [ ≥ 81% ]:
a) Main Turbine trip
b) MFP’s trip
c) {Unit 1 only – The 100% Bypass valve gets a close signal for 35 seconds}
* Inputs can be blocked
31
Describe FWCS Response to A Turbine Trip Signal.
a) MFRV’s close
b) Feed Pump recirc valves open
c) 15% Bypass valve goes to 5% flow position
d) {Closes the Unit 1 100% bypass valve for 35 seconds}
e) Hi Power Valve Controller shifts to Manual
f) Low Power Valve Controller remains as is
32
Describe the Manual Response to a Hi or Low S/G Level.
* If auto control is malfunctioning, take manual control and stabilize S/G level between 60-70% NR
* If S/G NR level is < 40%, Trip the Reactor
* If NR level is { ≥ 80%} [ ≥ 75% ]
THEN:
1) Trip the Turbine if power is <15%
2) Trip the Reactor and Turbine if >15%
33
Describe SG Level WR / NR Overlap.
* 65% NR = 60% WR @ 100% Pwr
* 0% NR = 45% WR @ 100% Pwr
34
Describe 1[2] EOP-6, “Total Loss of Feedwater” & 1[2] EOP-15, “Functional Recovery” cautions.
* When restoring S/G level, feed rate should be maintained <150 gpm, until level increase is observed or continuous flow has been maintained for 5 minutes. (~Twice the volume of the Feed Ring).
* FW should not be restored to a dry S/G if another available.
* If both S/Gs dry, only restore FW to one. Top of Feed Ring at ~33% NR
* 1[2] EOP-6, “Total Loss of Feedwater” & 1[2] EOP-15, “Functional Recovery” cautions operator on S/G feed restoration. When restoring S/G level, feed rate should be maintained <150 gpm, until level increase is observed or continuous flow has been maintained for 5 minutes. (~Twice the volume of the Feed Ring).
* S/G considered to be dry when level is <15% Wide Range
FW should not be restored to a dry S/G if another available. If both S/Gs dry, only restore FW to one.
35
Describe S/G Level Milestones
* 90% [81%] Turbine Trip (Rx trip if >15%) Both MFP’s Trip
* 82% [77%] MFRV’s go closed, will automatically re-open when condition clears
{100% Bypass Valves Close – 35 second signal}
* 80% [75%] and rising Manual Turbine Trip Required on High S/G Level (Rx trip if > 15%)
* 70% High Level Alarm
* 65% Normal Level
* 60% Low Level Alarm
* 40% and lowering Manual Rx & Turbine Trip Required on Low S/G Level
* 35% Automatic Rx & Turbine Trip
