Off Gas Flashcards
What happens to the Off Gas system on a loss of Vital AC or Instrument Bus A?
Off Gas Stack Isolation Valve F057 (F527) will go closed
What is the purpose of purging Off Gas with air for 1 hour prior to starting up the system?
- Off Gas system is purged for 1 hour w/ air prior to use to dilute any H2 left from previous use
- Also provides flow thru recombiner while heating to 350°F to ensure that it is free of moisture
What is adsorption and what is its effects on gaseous atoms?
Big picture: Adsorption = electrostatic attraction
Adsorption is the process by which a material exhibits an electrostatic attraction between the material surface and particular molecules. The material surface will attract and hold this molecule until another molecule comes along that has a stronger electrostatic attraction. At this time the material will release the first molecule and adsorb the one that has the stronger attraction.
What are the isolation signals associated with the Off Gas system and what does it cause?
Signal:
- Inop, Downscale, or Hi-Hi-Hi
- Any Combination simultaneously in both trip channels of Posttreatment Monitors
Causes closure of the following:
- Main Stack Inlet Valve F057 (F527)
- Cooler Condenser and Moisture Separator, F030A/B
- Holdup volume F085(F086)
Loop Seal Drain valves close to prevent an inadvertent release
Closure of the main stack inlet valve will cause condenser vacuum to degrade
What happens if a single Posttreatment Hi signal is sensed in the Off Gas System with the off gas mode switch in Auto?
Bypass valve F043 to close
Charcoal bed inlet F042 to open
If switch is not in auto, nothing happens.
What is the normal lineup for the Off Gas system?
Normally in Series lineup through the charcoal adsorption beds.
What is the unit difference for preheating in the Off Gas system?
Unit 2 - uses nuclear steam from SJAE pressure regulator
Unit 1 - electric strip heaters
Catalytic reaction could be inhibited by moisture contained in mixture
What is the unit difference in cooling the off gas condenser?
Unit 2 - FW/condensate is the cooling medium (in the turbine building)
Unit 1 - Cooled by Recombiner Building closed cooling water system (in the recombine building)
Where do the pre-treatment monitors sample off gas, and what type of detectors are they? What are the limits associated with them?
Pretreatment Monitors sample Off Gas just prior to Holdup Volume (gamma compensated Ion Chambers) ≤ 240mCi/sec, ≤ 500 mr/yr whole body, ≤ 3000 mr/yr skin
Where do the post treatment monitors sample off gas and what type of detectors are they?
Sample the exhaust of the Off Gas System prior to the after-filters (Scintillation detectors)
Or from the discharge of the first carbon bed in each train
When will the standby glycol system auto start in the off gas system?
- Standby refrigeration machine will auto start at 36°F.
- Standby refrigeration machine compressor or Glycol pump will auto start if the running component fails.
Where is preheat inlet pressure normally maintained in the off gas system? What can happen if pressure gets too high? How are the drains operated during startup?
- Normally 2-3psig
- > 6 psig requires closing Loop Seal Isolation Valves - F085 (F086), F030A/B
- This valve closure prevents blowing the loop seals out which could result in an uncontrolled radioactive gas release
Closed initially during startup to fill them with water, maintaining the seal.
What is the T.S. associated with the off gas system? What is the basis for this?
3.7.6. Mode 1 and Mode 2 & 3 w/ any MSL not isol and SJAE in operation LCO Gross gamma activity (pre treat monitor) shall be ≤ 240 mCi/sec Conditions Activity not w/i limits - Restore in 72 hrs Not Met B.1 Isolate ALL MSL - 12 hrs OR B.2 Isolate SJAE - 12 hrs OR B.3 Mode 3 in 12 & Mode 4 in 36
Basis:
The analysis assumes a gross failure in the Main Condenser Offgas System that results in the rupture of the Main Condenser Offgas System pressure boundary.
