DEH Control System Flashcards
What is the purpose of DEH?
- Provides motive force for turbine valve actuators which allow operators to control turbine speed and load. Holds open the turbine valves.
- Provides a Reactor Trip on Turbine Trip to mitigate the challenge to the RCS pressure boundary integrity which results from the rapid decrease in the RCS heat removal rate.
Describe the DEH flowpath.
- DEH Pumps take suction on the reservoir, discharge through the Unloader Valves, accumulators maintain discharge header pressure in operating band, turbine valves, emergency fluid trip headers, orifice line routes a small amount of DEH fluid back to the reservoir through a polishing filter assembly.
- The hydraulic fluid is returned to the reservoir via drain return header via the cooler and filters.
Describe the DEH Reservoir.
- 200 gallons
- Hi Alarm -22”,
- Low Alarm - 17.25”
Describe the DEH Reservoir LO-LO Level Lockout.
Occurs @ 7 5/8”
Blocks AUTO START of both DEH pumps
Manual start remains functional
Uses 125 VDC - Loss of DC actuates lockout
Blue indicating light behind RTGB 101 [201] = normally on, flashes when locked out.
Lockout must be manually reset behind RTGB.
Air blanket maintains a positive pressure on tank to keep moisture out
Fyrquel Fluid added via a portable pump from a 55 gallon drum
Describe the DEH Pumps.
- 1[2] A – Powered from MCC 1[2] A1
- 1[2] B - Powered from MCC 1[2] B1
- One continuously running, one in AUTO
Four position spring return switch on RTGB 101 [201] - START / AUTO / STOP / PTL
* AUTO - Standby starts if DEH supply pressure is <1550 psig. Continues to run until manually stopped.
* STOP - Stops running pump. Since switch is spring return to Auto, Pump can restart on low pressure
* PULL TO LOCK - Defeats Auto Start
What does the DEH Pump Test Pushbutton do?
Starts standby DEH pump
Describe the DEH filters.
Remove particulates, lowers conductivity
Four fluid filters
1) DEH Pump Discharge Filter
2) DEH Heat Exchanger Inlet Filter
3) TV/GV Internal Filter and IV/RV Inlet Filters
4) MOOG Valve Filter
Fluid is supplied to the polishing filter via a line off the DEH pump discharge header. From the filter, the fluid returns to the DEH reservoir
Remove particulate impurities and also lowers conductivity and removes water which can adversely affect MOOG valve operation.
Unit 1
Three stages
a) Coalescing-particulate filter Removes 99% of water
b) Fuller Earth filter
c) Particulate-contaminate filter
Unit 2
Two stages
a) Fuller Earth filter
b) Corrugated cellulose filter.
c) Serve same purpose as Unit 1 filters
Describe the DEH Heat Exchangers.
Cooled by TCW, on return line to reservoir
Two redundant shell and straight tube heat exchangers.
TCW flows through the tubes, DEH fluid on the shell side.
TCW flow through the two coolers is normally full open (since EPU).
Describe the DEH HP Accumulators.
- Piston operated, nitrogen charged, store HP fluid for operation
- Pre-charged with Nitrogen to 1250 psig.
- Floating piston separates Nitrogen from DEH fluid
- Act as a surge volume & maintain pressure which minimizes RV chatter
Describe the DEH Drain Return Accumulators.
Bladder operated, nitrogen charged, surge chamber for load dump
Serve as a shock absorber or surge chamber for displaced fluid in the drain system during load dump
Installed in the pressurized drain return line to the fluid reservoir
Describe DEH Fluid.
Fyrqual - Carcinogenic
110-130°F, Lower limit 70°F – Run two pumps to raise temp
Alarm at 135F
Describe DEH Fluid.
Fyrqual - Carcinogenic
110-130°F, Lower limit 70°F – Run two pumps to raise temp
Alarm at 135F
Describe the Fluid operated Air Pilot Valves (Non-Return Valves).
Senses that the turbine is on-line as detected by:
a) {ETS Header pressure switch on Unit 1}
b) [All electronic on Unit 2]
When open, supplies air to non-return valves (NRVs).
When closed, air is removed from NRVs which allows them to close.
Feedwater Heaters 3/4/5
Describe the HP Turbine Throttle Valves.
(4) Double Plug Type
* Provides rapid isolation of steam on turbine trip signal
* Throttle Valve position provides turbine speed up to 1750 RPM
* Double plug construction (valve within a valve). Internal valve is referred to as throttle valve pilot valve.
* Spring tension and steam pressure apply force in close direction.
* DEH pressure used to overcome closing forces.
* Fully back seated during normal operations
Describe the Five Major Parts of the HP Turbine Throttle Valves.
1) Hydraulic cylinder and piston
* Motive force for Throttle Valve
2) Servo valve (Moog valve)
* Electric operated
* Fails as is
* Provides interface for controls
* Adds or drains DEH fluid from cylinder to move piston
3) Dump valve
* Normally held closed by Emergency Trip Header Oil Pressure.
* When closed, drain path from hydraulic cylinder is blocked, allowing pressure to build under piston.
* When Emergency Trip Header Oil Pressure drops, the dump valve opens path to return header which relieves pressure from under the piston
4) Linear variable differential transformer (LDVT)
* Electro-mechanical transducer that produces an electrical output proportional to actuator position
* Used as input to control circuit for servo valve
5) Limit Switch
* Provides open/close contact inputs
Describe the HP Turbine Governor Valves.
Governor Valve position provides turbine speed control when turbine speed is >1750 RPM
Control’s turbine load when generator output breaker is closed.
Close on:
– Turbine trip
– OPC (103% of rated speed)
– Load Drop Anticipator (LDA)
– Turbine Acceleration
Single seat plug valve.
Actuator operating principles are the same as the Throttle Valves (EO-16b)
Operate in ‘Single Valve” control. ALL valves operate together as if one large valve
Uses 2 LVDTs
Describe the LP Turbine Reheat Stop Valves.
Stop steam flow from MSR to LP Turbine
Close on:
1) Turbine trip signal
2) OPC – 103% of rated speed
3) LDA – Load Drop Anticipator
4) Turbine Acceleration
What are the DEH power Supplies?
Normal DEH Cabinet Power - Vital AC SUPS
TDM-1 & 2: 24 VDC
TDM-3: 125VDC
