Systems Exam 2 - Pressurizer Pressure & Level Control Flashcards
(48 cards)
Pressurizer Pressure and Level Control systems are designed to accommodate what transients without a reactor trip?
→Loading or unloading at a rate of 5% per minute with automatic rod control
→Instantaneous load changes of 10% with automatic rod control
→Step-load reductions of 50% with automatic rod control and steam dumps
What is the 0% power Program PZR Level and T-ave?
What is the 100% power Program PZR Level and T-ave?
0%
→25% level,
→557°F no load T-ave
100%
→60% level
→585.4°F (589.2°F)
(Level controlled by average T-ave, not power)
What is the function of PZR handswitch PS-455G?
Selects what pressure channel feeds the PZR chart recorder on CB-05.
PZR Handswitch PS-455F top channel feeds what?
PZR Handswitch PS-455F bottom channel feeds what?
→Top: PORV PCV-455A
→Bottom: PORV PCV-456
What is the function of PZR Handswitch PS-455F?
3 position selector switch used to select which 2 channels will be used for pressure control.
PZR Pressure Hi Alarm setpoint
2310 psig
(also spray full open)
PK-455A feeds what?
→PCV-455A
→Pressurizer pressure Deviation High alarm
→Pressurizer pressure low, backup heaters on
→Backup heater control
→Variable heater control
→PK-455B (loop 1 spray)
→PK-455C (loop 4 spray)
‘Pressurizer Pressure Deviation High’ alarm comes in at what pressure?
> 75 psig above set point
(2310 psig)
Pressurizer pressure low alarm and turning on backup heaters actuate at what pressure?
> 25 psig below setpoint
(2210 psig)
What does PK-455B feed?
What does PK-455C feed?
→PK-455B: PZR Spray valve PCV-455B, loop 1
→PK-455C: PZR Spray valve PCV-455C, loop 4
At what pressure do PORVs open?
At what pressure do PORVs close?
Open: 2335 psig
Close: 2315 psig
(blocked from opening below 2185 psig)
How are the PORV accumulators sized?
Designed to allow cycling 100 times in a 10 minute period
If a conflict occurs between Level Control and Pressure Control which takes priority?
Level control is dominant
PORV rated flow
210,000 lbm/hr
When do pressurizer heaters energize?
→Decreasing pressure (PK-455A output at ~42%)
→Pressurizer Level 5% above program
How is LT-462 calibrated, and when should it be used?
→Cold calibrated: Low temperature conditions (70°F).
→Whenever RCS temperature is < 450°F.
→Note: cold cal always indicates lower than hot cal.
What does LK-459 provide control for?
→PDP speed
→FCV-121 position
What is the PZR lower program level limit and what is it designed to prevent?
→Lower program level limit of 25%
→Prevents emptying PZR on Rx trip and from uncovering heaters on normal transient.
What is the PZR upper program level limit and what is it designed to prevent?
→Upper program level limit of 60%
→Leave enough room for surges
→Prevents Rx trip on high level for transient
→Prevents water going out the safeties on a load reduction of 100%
What occurs if a PZR bottom level control channel fails low, with no operator action?
→LCV-460 Closes
→Orifice isolation valves close
→All heaters de-energize
→PDP Speed decreases or FCV-121 throttles closed as actual level increases
→Actual level will increase (very very slowly) until Rx Trip occurs on hi level.
What occurs if a PZR top level control channel fails high, with no operator action?
→All heaters energize (insurge of > 5% above program)
→PDP Speed goes to min or -FCV-121 throttles closed
→Actual level decreases until 17% is reached which causes letdown to isolate and heaters to de-energize
→Actual level will increase (very very slowly) until Rx Trip occurs on hi level.
What occurs if a PZR top level control channel fails low, with no operator action?
→LCV-459 Closes
→Orifice isolation valves close
→All heaters de-energize
→PDP Speed goes to Max or FCV-121 goes full open
→Actual level increase until Rx Trip occurs
What occurs at 17% PZR level with a decreasing level?
→17% on the Primary Control Channel causes LCV-459 to close (letdown isolation)
→17% on the Secondary Control -Channel causes LCV-460 to close (letdown isolation)
→Orifice isolation valves close (either control channel)
→PZR Heaters de-energize (either channel)
→Low Level Alarm
High Failure of PZR top pressure Channel 455 or 457
→Spray Valves go FULL OPEN
→Heaters go to FULL OFF
→PORV PCV-455A sees an actuation signal and lifts since actual plant pressure, as sensed by channel 458, is above the interlock setpoint of 2185 psig.
→Plant pressure lowers rapidly
→At 2185 psig, the interlock signal from channel 458 is removed to allow PCV-455A to close.
→Pressure continues to lower due to the open spray valves.
→An OT N-16 turbine runback occurs (could also provide Rx trip)
→The reactor trips on lead-lag compensated low pressure because channels 456, 457, and 458 are still available to provide the necessary 2 of 4 logic at 1880 psig for the reactor trip.
→Plant pressure continues to drop after the plant trip. At 1820 psig an SI occurs.
