Steam Dumps Flashcards
On a turbine trip/load rejection what are the steam dump controls based on
- Auctioneered High Tavg
Which group(s) stagger open instead of opening all together? ***
- Group 1 only
Where are the arm/block solenoids powered from?
- VDCD (Train “A”)
- VDAB (Train “B”)
How do the arm/block solenoids fail?
- Fail to Vent (Blocks Steam Dumps)
What are CRID 1 steam dump loads?
- Turbine Trip Controller
- Load Rejection Controller
- MPC-253 (T-Ref)
- UPC-101 (bypass steam header)
What are CRID 2 steam dump loads?
- Steam Pressure Controller
- MPC-254
- Tref Computer
What are CRID 3 steam dump loads?
- No CRID 3 loads are associated with steam dumps
What are CRID 4 steam dump loads?
- Arm/Block Solenoid Relays
- Auctioneered High Tavg computer
What is Conditional C7A and is it an arming or blocking signal? **
- Arming signal (Load Rej)
- 10% Step Load Change or 5% / min on MPC-254.
Allows operation of Group 1 and 2 Valves
What is Conditional C7B and is it an arming or blocking signal? **
- Arming Signal (Load Rej)
- 30% Step Load Change on MPC-254.
Allows operation of Group 3 Valves
What is Conditional C8 and is it an arming or blocking signal? **
- Arming Signal (Turb Trip)
- 4/4 Main Turbine Stop Valves Closed
OR - 2/3 Oil Pressure switches below 800#
What is Conditional C9 and is it an arming or blocking signal? **
- Blocking Signal
- 1 Circulating Water pp breaker closed.
- CRID 2 energized.
- Pressure switches on 3/3 Condensers ≥ 20.6 inHg
What is Conditional P12 and is it an arming or blocking signal?
- Blocking Signal
- 2/4 Tave < 541°F - Status Light ON
(P-12 Active (Status Light ON) Steam Dumps are Blocked in All Modes until placed in “Bypass Interlock“)
(3/4 Tave > 541°F - Status Light OFF)
What does the bypass interlock for P12 allow?
- allows group I steam dumps to operate when P12 met
Bypass seals in until reset or P-12 block clears
Which ctrl switch will reset C7A and C7B conditionals and how are they reset?
- Mode Ctrl Switch and must be taken to off/reset
Which steam dump groups are allowed to operate when the turbine trip controller is activated?
- Groups I and II
Which steam dump groups are allowed to operate when the load rejection controller is activated?
- Groups I, II, and III
What is the design capacity of the steam dumps? **
- Plant design accepts a step load reduction of 50% from full power by using the 40% from Non-Safety Related Steam Dump system and 10% from Rods
What is the purpose of the steam dumps?
- Reduce RCS transients following substantial turbine load reductions by dumping steam to the condensers.
- Remove decay and sensible heat stored in the RCS following a reactor & turbine trip without actuating SG safety valves.
- Control RCS temperature when the turbine is at low load, or during startup, cooldown, and when maintaining mode 3.
What is high Auctioneered Tavg?
- The highest Tavg of all 4 rcs loops
What signals does the turbine trip ctrlr use to open steam dumps?
- Auctioneered High Tavg - Tno-load
What signals does the load rejection ctrlr use to open steam dumps?
- Auctioneered High Tavg - Tref
What signal gives you Tref?
- MPC-253 (First Stage Impulse #)
When will group I open with the Turbine Trip Ctrlr?
- 0°F to 10°F ΔT - Modulates open
- 0%-33% Demand
- If > 10°F ΔT -Trips Open
When will group II open with the Turbine Trip Ctrlr?
- 10°F to 20°F ΔT - Modulates Open
- 33%-67% Demand
- If > 20°F ΔT - Trips Open
When will group I open with the Load Reject Ctrlr?
- 5°F to 9°F ΔT - Modulates open
- 0%-33% Demand
- If > 9°F ΔT - Trips Open
When will group II open with the Load Reject Ctrlr?
- 9°F to 13°F ΔT - Modulates open
- 33%-67% Demand
- If > 13°F ΔT - Trips Open
When will group III open with the Load Reject Ctrlr?
- 13°F to 17°F ΔT - Modulates open
- 67%-100% Demand
- If > 17°F ΔT - Trips Open
Why do none of the steams dumps open in the first 5°F ΔT on a load rejection?
- Rods are good for a 10% load rejection
What are the two modes of the steam pressure controller?
- Auto (setpoint is 1005#)
- Manual
Which mode only allows modulating of steam dumps?
- Steam Pressure Mode
No trip functions
How much turbine load are the steam dumps designed to handle on a load rejection?
- 40% Load
How do the Trip Open Solenoids fail?
- Fail to Modulate
What is the Power Supply for the trip open solenoids?
- VDAB
*** A Unit 2 reactor trip occurred from 90% power. The following plant conditions exist:
- Reactor trip breakers: OPEN
- Main turbine stop valve (C): OPEN
- Condenser vacuum: 21.4 in. Hg.
- RCS Tavg: 561°F
- Auto Stop Oil Pressure: 400 psig
Assuming all other equipment operated as designed and no operator actions are taken, the Steam Dump system is:
A. armed and dumping steam to the condenser with group 1 trip open solenoid bistables energized and group 2 modulating.
B. armed and dumping steam to the condenser with groups 1 and 2 trip open solenoid bistables energized.
C. armed but not dumping steam to the condenser because of a blocking signal.
D. not armed and not dumping steam to the condenser.
A. armed and dumping steam to the condenser with group 1 trip open solenoid bistables energized and group 2 modulating.
If MPC-253 or MPC-254 Fail High in Tavg mode, what affect will it have on steam dumps?
- Will have no affect
If MPC-253 Fails low in Tavg mode, what affect will it have on steam dumps?
- Will have no affect because it has no arming signal
If MPC-254 Fails low in Tavg mode, what affect will it have on steam dumps?
- Will have no affect because it has no demand signal
If you take the ctrl selector switch to off/reset, what will it do?
- If you previously bypassed your P12 signal, it will re-enable P12
- De-energizes arm/block solenoids
What are the trip open signals for Turbine Trip bistables for steam dumps? ***
- 10°F Group I
- 20°F Group II
(Direct 20# air to the trip/open valves)
What are the trip open signals for Load Rejection bistables for steam dumps?
- 9°F Group I
- 13°F Group II
- 17°F Group III
(Direct 20# air to the trip/open valves)
If CRID 1, 2 and 4 are lost, can steam dumps still operate?
No, steam dumps remain closed
Whats the fastest cooldown rate allowed with steam dumps?
- 100°F per hour
If UPC-101 fails high while in steam pressure mode, what will happen to steam dumps?
- Groups I and II will go full open until P12 is met
If UPC-101 fails low while in steam pressure mode, what will happen to steam dumps?
- Any open steam dump valves will close
If Tavg fails high > 20°F ΔT with no turbine trip, what will happen to steam dumps?
- Nothing will happen, because the C7A and C7B arming signals are not in
If Tavg fails high > 20°F ΔT with a turbine trip, what will happen to steam dumps?
- Groups I and II will go full open and stay full open until P12 is met and then it will cycle at 541°F
Load Rejection control will maintain temperature within ___ between Auctioneered High Tavg and Tref with no rod motion. ***
- 5°F
While in Tavg mode if MPC-254 fails low, what will the happen to the steam dumps
- Since no actual temperature deviation is present, no air signal will be developed to open the steam dumps even though C7A and C7B are present
