Steam Generators and FW Control

Question 1

What is the Steam Generator Design Basis?

Answer 1

Transfer RCS heat to the secondary

Question 2

Why is the S/G Secondary Side inventory mass limited?

Answer 2

• 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

Question 3

What are the S/G design transients?

Answer 3

Handle ramp load change of 5% per minute, 15 to 100%
Handle step load change of 10%, 15 to 100%

Question 4

List Important S/G numbers.

Answer 4

• 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]

Question 5

Describe S/G snubbers.

Answer 5

• Provide S/G support for a seismic event – Tech Spec related
• {Unit 1 only - Low snubber oil level alarms}

Question 6

Describe S/G blowdown.

Answer 6

• 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

Question 7

Describe S/G blowdown flowpath.

Answer 7

a) PCV’s – Maintain ~300 psig
b) FCV’s – Maintain ~40 gpm
c) TCV’s – isolate if >140F

Question 8

Describe S/G Blowdown Inside Containment Valves: (FCV-23-4 and FCV-23-6).

Answer 8

• 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

Question 9

Describe S/G Blowdown Outside Containment Isolation Valves: (FCV-23-3 and FCV-23-5).

Answer 9

• 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

Question 10

Describe S/G Blowdown Sample Valves: (FCV-23-7 and FCV-23-9).

Answer 10

• 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.

Question 11

Describe S/G Blowdown Flow Control Valves: (FCV-23-12 and FCV-23-14).

Answer 11

• 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)

Question 12

Describe S/G Blowdown Flow Control Valves: (TCV-23-8).

Answer 12

• TCV-23-8 isolates resin beds at 140°F

Question 13

Describe S/G Blowdown Rad Monitors.

Answer 13

• {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.

Question 14

Describe the S/G feed ring.

Answer 14

• 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

Question 15

Describe SG Moisture Removal – Moisture Separators and Steam Dryers.

Answer 15

• 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

Question 16

Describe S/G level Shrink.

Answer 16

• 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

Question 17

Describe S/G level Swell.

Answer 17

• 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

Question 18

Describe LEFM.

Answer 18

• 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.

Question 19

What is the function of the Feedwater Control System?

Answer 19

• Automatically maintains SG Narrow Range level at 65% by controlling the Main FRV & 15% Bypass valve

Question 20

Describe S/G Level Control Low Power Mode: (<20% FW FLOW).

Answer 20

• 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

Question 21

Describe S/G Level Control High Power Mode: (>20% FW FLOW).

Answer 21

• 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

Question 22

Describe S/G Level Control T-800 Manual / Auto Stations.

Answer 22

• Actual SG Level / SG Level Setpoint
• Actual Valve Position / Valve Position Demand
• Auto / Manual
• Remote / Local

Question 23

Describe S/G Level Control Power Supplies.

Answer 23

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

Question 24

Describe Safety grade PT-8013A, B, C, D (‘A’ S/G) and PT-8023A, B, C, D (‘B’ S/G).

Answer 24

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

Question 25

Describe S/G WR Level Safety Channels (9012, 9014, 9022, 9024).

Answer 25

• 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

Question 26

Describe S/G NR Level Safety Channels (9013A-D, 9023A-D).

Answer 26

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%

Question 27

Describe S/G NR Level Control Channels (2 per S/G).

Answer 27

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)

Question 28

Describe High Level Override (HLO).

Answer 28

• 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].

Question 29

Describe Hi Level Override Cancel Pushbutton.

Answer 29

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

Question 30

Describe High S/G Level Trip.

Answer 30

• 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

Question 31

Describe FWCS Response to A Turbine Trip Signal.

Answer 31

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

Question 32

Describe the Manual Response to a Hi or Low S/G Level.

Answer 32

• 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%

Question 33

Describe SG Level WR / NR Overlap.

Answer 33

• 65% NR = 60% WR @ 100% Pwr
• 0% NR = 45% WR @ 100% Pwr

Question 34

Describe 1[2] EOP-6, “Total Loss of Feedwater” & 1[2] EOP-15, “Functional Recovery” cautions.

Answer 34

• 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.

Question 35

Describe S/G Level Milestones

Answer 35

• 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