Open/Closed Blowdown

Question 1

Discuss Blowdown.

Answer 1

• 40 gpm / SG
• Closed blowdown flow is cooled by the Open Blowdown system.
• Open Blowdown system cooled by ICW (prevents release)

Question 2

Discuss Open and Closed Blowdown Cooling Systems.

Answer 2

• Non Safety Related
• Loss of demin water results in loss of makeup water source to the closed blowdown system (Makeup water to surge tank / Chemical Feed Pot through auto LCV or manual valve)
• Blowdown AOV’s fail closed on loss of air (with exception of ICW to OBCS HX, fail OPEN)

Question 3

Discuss Closed Blowdown Cooling Pumps.

Answer 3

‘A’ Pump: MCC {1A2} [2A1]
‘B’ Pump: MCC {1B2} [2B1]
Local control only, Start-Stop pushbutton at PP & Control Switches in SGBTF

Question 4

Discuss Closed Blowdown Cooling Surge & Chemical Feed Tank.

Answer 4

• Located on the 62’ elevation of the Turbine deck. Provides NPSH for pumps
• Tank M/U from Demin Water. Auto LCV-34-1 controls level -2” to +4” of tank centerline
• Feed Pot located next to surge tank. Allows chemical addition for corrosion control
• Local level indication only

Question 5

Discuss Closed BD HX.

Answer 5

• Purpose: Reduces S/G blowdown water from a temperature of approximately 550ºF to 120ºF
• Three sets of two ® “A – B – C”. Normally two HX sets in operation with the third in standby
• The CBCS Hx are located on the RAB roof on the 43’ elevation (SNPO land).
• CBCS water makes a single pass through the shell side of each HX
• OBD cooling water flows through the tubes
  Designed to handle heat loads from S/G B/D between 25 – 125 gpm per SG (normal 40 GPM)
  Open blowdown flow enters at 100ºF, exits at 172ºF before returning to shell side of the OBCS Heat Exchangers
• If blowdown exceeds 140ºF downstream of the HX, blowdown isolates (TCV-23-8 will close to protect the SGBTF Demineralizer)
• NOTE: TCV-23-8 is common BD ISOL valve to SGBTF (1 valve / unit)
• PCV Maintains 300#
• Enters at 100ºF, exits at 172ºF before returning to shell side of the OBCS Heat Exchangers
• 700 gpm per heat exchanger

Question 6

Discuss Open BD HX.

Answer 6

• Provides the heat sink for the heat removed from the S/G blowdown.
• (2) single pass heat exchangers located on north side of the Turbine Building mezzanine level
• Lined up in parallel, both in service
• CBCS water flows through the shell side of the HX, cooled from 172°F to 100°F
• ICW flows through the tube side of the heat exchanger
• TCV-34-3A & 3B – located in the ICW piping on the outlet side of the OBCS HX’s
• Automatically vary the flow of ICW through the tube side of the OBCS HX’s in response to control air signals sent from TIC-34-3A & 3B
• Regulating setpoint of 90°F
• OBDHX TCV’s fail open (full cooling) on:
  a) Loss of instrument air
  b) Loss of electrical power.
• ICW supply valves to OBDHX’s (MV-21-2 and 21-3) fail “as is” on a loss of power

Question 7

Discuss normal blowdown operation.

Answer 7

• 2/3 CBHX’s are in service anytime a CBCS Pump is in operation
• When Isolating one CBHX, always place the spare heat exchanger in service first and allow for heat up time if possible
• Maximum combined (U1 + U2) blowdown flow is limited to 300 GPM to prevent channeling of resin beds in the SGBTF
• If Closed Blowdown Cooling flow lost to the CBHX, blowdown must be immediately isolated
• Loss of Instrument Air – All AOV’s fail closed with exception of the OBHX TCV’s fail open
• Unit 2 SNPO covers the Blowdown Building
• Monitor Storage Tank used for SGBD minimum level is 10 FT to preclude sucking air into the condenser, which could occur @ ~ 5 ft