ML082670292

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Post Exam E-Mail from Mike Wasem Re Q-54 Supplement
ML082670292
Person / Time
Site: Calvert Cliffs  Constellation icon.png
Issue date: 09/22/2008
From: David Silk
Division of Reactor Safety I
To: Cyndy Bixler
Operations Branch I
References
Download: ML082670292 (2)
v • d • e


Text

From:

David Silk Sent:

Monday, September 22, 2008 1:10 PM To:

Cyndy Bixler

Subject:

FW:

Attachments:

Q 54 supplement.doc This is the addendum to the licensee's post exam comments. I could not find this in ADAMS.

We need this put in ADAMS so I can put the ML number in the report. Thanks. (I found the final written exam in ADAMS.)

From: Wasem, Mike [1]

Sent: Friday, August 22, 2008 2:21 PM To: David Silk

Subject:

<>

Hope this helps Mike Wasem CCNPP Supervisor-ITU (410) 495-3638

>>> This e-mail and any attachments are confidential, may contain legal, professional or other privileged information, and are intended solely for the addressee. If you are not the intended recipient, do not use the information in this e-mail in any way, delete this e-mail and notify the sender. CEG-IP1 E-mail Properties Mail Envelope Properties (2856BC46F6A308418F033D973BB0EE72841ECBF49D)

Subject:

FW:

Sent Date: 09/22/2008 1:10:22 PM Received Date: 09/22/2008 1:10:22 PM From: David Silk Created By: David.Silk@nrc.gov Recipients:

Cyndy.Bixler@nrc.gov (Cyndy Bixler)

Tracking Status: None Post Office:

R1CLSTR01.nrc.gov

Files Size Date & Time MESSAGE 2124024 09/22/2008 Q 54 supplement.doc 2114866 Options Expiration Date:

Priority: olImportanceNormal ReplyRequested: False Return Notification: False Sensitivity: olNormal Recipients received:

RO Written Examination Question #54 (ID: Q50364)

Unit -1 is operating at 100% power when Instrument Air System pressure decreases to 96 psig.

Which of the following is correct?

A. Loss of Power to an IA dryer has occurred.

B. Standby Air Compressor has picked up C. Plant Air to I/A X-Conn, 1-IA-2061-CV has opened D. Both dryers are in service due to low IA pressure Original answer accepted was A Answer Explanation A. Correct per Alarm Manual for Window K-26 B. Incorrect, STBY compressor starts @ 93 PSIG per AOP7D section III.C notes C. Incorrect, This CV opens @ 88 psig per AOP 7B section III C. notes D. Incorrect, Pressure is 96 not 93 psig Original References Alarm Manual 1C13 pages 48-50 Compressed Air Lesson Plan - LOI-019-1-2 slides 62, 63 Justification for deleting question The question does not state that the INSTR AIR SYS MALFUNCTION alarm has annunciated or that the Air Dryer malfunction light on 1C13 is brightly lit. Without either of these indications listed, there is no correct answer. The Instrument Air Compressors normally cycle in the range of 97(+/- 1.86 psig) to 104 (+/- 1.86 psig).

Reference Alarm Manual pages 48 through 50 (attached)

Per the alarm response manual, any of three things will cause this alarm to annunciate:

1. 1-PS 2079 senses low instrument air pressure (setpoint 89.2 to 90.8 PSIG)
2. 1CR11/11 Dryer Malfunction
3. 2CR/12 Dryer Malfunction Under AUTOMATIC ACTIONS, the description of what happens at 93 PSIG is also what happens on a loss of power to the dryer. See RESPONSE in the alarm manual for K-26, page
50. Note that the action for loss of power or lower air pressure is the same--when the cause has been corrected, reset the IA dryer.

Air pressure below 93 PSIG or loss of power have the same effectboth towers are placed in service and regeneration purge is secured. If there is no other problem, instrument air pressure will return to normal. See attached portions of the Compressed Air System description for a full explanation of how the Air Dryers operate in all modes.

Regrade Request Question #54 should be deleted due to no correct answer. It is normal for instrument air system pressure to cycle between 95 psig and 106 psig. The question did not state that any alarms were present or that the dryer malfunction light is brightly lit.. Instrument Air Dryer failure cannot be properly diagnosed when the only indication given is that system pressure is 96 psig and no alarm exists.

3.1.5 Instrument Air Dryers The IA DRYERS remove moisture from the instrument air before the air is distributed to the system loads. The IA dryers receive air from the IA prefilters, dries the air, and sends it to the IA afterfilters (see Figures 19-1, 19-17, 19-18). By removing moisture from the instrument air, the IA dryers prevent corrosion and condensation in downstream piping and system loads. The dewpoint is lowered to approximately -40 degrees F pressure dewpoint to eliminate outside freezing concerns. The IA dryers are located next to the IA receivers on the Turbine Building 12-foot level. A bypass line and normally shut bypass valve 1-IA-148 (2-IA-134) are provided around the IA dryers. The bypass line allows continued operation of the IA System if the IA dryers are out of service due to a casualty or for maintenance.

11, 12, 21, and 22 Instrument Air Dryers are automatic, heater-less type dryers with dual desiccant filled chambers. The DHA dryer desiccant absorbs a large quantity of moisture per unit volume and readily releases it during the regeneration mode controlled by an electronic AMLOC system. The 11 (21) and 12 (22)

Instrument Air Dryers are different size and models. 11 (21) IA Dryer is a model 900 DHA capable of drying 900 CFM of air at 100 psig and 100°F, and the 12 (22)

IA Dryer is a model T650 DHA capable of drying 650 CFM of air at 100 psig and 100°F. The dryers are sized differently because 11 (21) dryers were more recently replaced (in 1996) and sized in anticipation of replacing Instrument Air Compressors with ones of larger capacity. Although the model number varies, all dryers are from the DHA family and operate on the same principle.

Each dryer consists of the following:

  • two drying towers
  • a flow orifice
  • a flow adjusting valve
  • five air-operated valves
  • AMLOC dryer control system
  • purge exhaust muffler
  • purge exhaust isolation valve
  • associated valves, instrumentation, and control devices Moisture-laden Instrument Air enters the dryer from the prefilters and flows downward through one of the desiccant chambers, the entrained moisture is attracted to and adsorbed on the surface of the desiccant. This adsorption is an exothermic (heat releasing) process which later contributes to the regeneration.

The desiccant material consists of beads of activated alumina. This substance has two characteristics that make it useful as an air-drying agent:

  • it is capable of adsorbing a large quantity of moisture per unit volume, and
  • it readily gives up adsorbed moisture, allowing the desiccant to be reused.

The dry air then exits the dryer and proceeds downstream through the afterfilters and on to the Instrument Air header (see Figures 19-1, 19-17, 19-18). A filter screen is provided on the outlet of each dryer tower to prevent any desiccant beads from escaping the tower.

While one desiccant chamber is in the Drying Cycle, the opposite, off-stream chamber can be pressurized in the Standby condition or in the Regeneration cycle.

Either the AMLOC or the fixed cycle control determines the condition of the chamber. Normally the dryer will be in the AMLOC mode, which will place a chamber in the Regeneration cycle only if the moisture detector determines it to be necessary. The fixed mode dryer operation is provided as backup control and will automatically place a chamber in the regeneration cycle on a timed basis regardless of chamber moisture.

The AMLOC control system mode of operation will automatically shift to a Fixed Mode to provide a backup means of operation should a CHAMBER PERFORMANCE DEGRADING ALARM occur. A self-check feature will return the dryer to the AMLOC Cycle mode when the fault has cleared.

The AMLOC Cycle

Upon pressurization with operating power secured, the inlet switching valves V1 and V2, and the repressurization valve V5 are opened (see Figure 19-17) by direct pressure exerted by the incoming wet air. Purge Exhaust Switching Valves V3 and V4 are instantaneously closed by pilot pressure supplied through the deenergized Dryer Control system. Instrument Air leaves the dryer via Outlet Check Valves V9 and V10. Initially the manual outlet valve is closed.

When the dryer is energized Inlet Switching Valve V2 to the right chamber will close. The left chamber will now be lined up to dry Instrument Air and the manual outlet isolation can be opened. Upon being energized the control circuit will begin a "self check sequence" on the moisture probes (labeled for the right chamber as 12 in Figure 19-18) and will immediately shift to the Fixed Cycle Mode of operation if a fault is found.

With no fault found, the right chamber is evaluated by moisture probe to determine if regeneration is necessary. The probe is a capacitance type AMLOC probe which produces an output proportional to the moisture in the chamber. The frequency of the signal is compared to a fixed setpoint to determine if the Regeneration Cycle is required. If this signal is above the setpoint a Regeneration Cycle is required prior to placing the right (off stream) chamber into service. If regeneration of the off service chamber is not required it simply remains pressurized and isolated until being placed in service by the control circuit.

The time each chamber is on line and drying is approximately 3 minutes.

Regeneration Cycle The regeneration cycle is begun by opening the PURGE EXHAUST SWITCHING VALVE (V3 for left chamber, V4 for the right chamber). This depressurizes the chamber being regenerated and closes V5 the REPRESSURIZATION VALVE. A regulated flow of dry Instrument Air enters the regenerating chamber from the outlet of the on-service chamber via the PURGE ADJUSTING VALVE - V8, the PURGE ORIFICE, and the PURGE CHECK VALVE (V6/V7). The dry air passing upwards through the chamber at atmospheric pressure causes the desiccant to release its moisture.

At the end of the regeneration cycle the PURGE EXHAUST VALVE (V3/V4) is closed and the REPRESSURIZATION VALVE (V5) is opened. This repressurizes the chamber and closes the PURGE CHECK VALVE (V6/V7).

The REPRESSURIZATION VALVE (V5) then closes and the off service chamber is now prepared to be placed on service.

Upon switching initiation the INLET SWITCHING VALVE (V1/V2) will open for the off service chamber. Immediately afterwards the INLET SWITCHING VALVE for the previously on service chamber will close. The need for regeneration is then determined by the moisture probe for the off service chamber.

Fixed Cycle Mode of Operation The following faults or conditions will cause IA Dryers to automatically shift from the AMLOC (moisture sensitive) mode of operation to the Fixed Mode of operation.

  • Damaged or faulty AMLOC (moisture) probe
  • Bad connection in or between the AMLOC probe and remote sensor assembly and its terminal block
  • Operation of dryer beyond its maximum flow rate - alarm would be caused by probe detecting excessive moisture causing CHAMBER PERFORMANCE DEGRADING ALARM
  • Operation of the dryer for extended periods with the dryer deenergized. Causing excessive moisture in chambers and giving a CHAMBER PERFORMANCE DEGRADING ALARM WHEN ENERGIZED An IA Dryer operates in the Fixed Mode fully automatically in the same manner as it does in the AMLOC mode with the following exception. When a chamber goes off service, it automatically enters the Regeneration Cycle regardless of moisture content. Once regenerated it cycles back into service on timer control just as it does in the AMLOC mode.

An IA Dryer will automatically perform a self check at the sequence on the AMLOC probes at the beginning of the drying cycle for the left chamber. If the malfunction has cleared the system will automatically return to the AMLOC (moisture sensitive) Mode of operation.

Valve Malfunction Alarm The IA Dryer alarm circuit uses a VALVE MALFUNCTION ALARM PRESSURE SENSOR ASSEMBLY. This checks the pressure of the chambers with pressure switches during each Repressurization or Regeneration cycle and ensures the correct pressure is in the chamber for the present cycle. If the pressure is inappropriate for that cycle the INLET and/or OUTLET VALVE MALFUNCTION will alarm. Upon receipt of this alarm the control circuit will attempt to correct the valve malfunction by

repeating the original signal sent to the valve. The controller will not move forward in the cycle until the malfunction is cleared.

Automatic Purge Exhaust Isolation and Controls As a result of 22 IA Dryer blowdown, the IA Dryers were modified to install an automatic purge isolation valve in the purge exhaust line on all four dryers. A lowering IA system header pressure will cause a 2 way poppet valve to close, thereby isolating the dryer exhaust purge path (see figures 19-17, 19-18). The on-service IA Dryer will also deenergize on lowering IA system pressure and the 1/2C13 Control Room Window Instr.Air Sys Malfunction alarm will actuate. The dryer will continue to pass air through both chambers of the dryer to the header until the dryer is either isolated or reset.

The following components were added by the Modification:

  • Purge Shutoff Poppett Valve; Normally Open, Air to Open, Fail Closed
  • Solenoid SOL F; Normally energized, Normally Closed, Fails to Vent
  • Pressure Switch 3PS; Normally Closed, Senses Dry Gas Outlet Pressure, Opens to Alarm.
  • Control Relay 2CR; Normally Energized, Deenergized to receive Instr Air Sys Malfunction Alarm, Deenergize to turn off power to IA Dryer Controller.
  • Push Button 1PB; Normally Open RESET Contact.

Normal Conditions (IA Header Pressure > ~99 psig & Pushbutton 1PB depressed)

  • The momentary depressing of RESET Pushbutton energizes 2CR relay to close 2CR1. 3PS is already closed, and Solenoid F is energized. The applied 120 VAC coil power causes the valve to port high pressure pilot supply pressure to the Purge Shutoff Poppet valve, and the poppet valve is held open to allow normal muffler passage for purging.
  • The 2CR2 contacts are in their non-alarming state (contacts open)
  • The Dryer Controller remains energized via 2CR3 contact closed Lowering Header Pressure (IA Header Pressure < ~93 psig.)
  • The Backup Air Compressor starts and attempts to restore IA Header Pressure.
  • Switch 3PS opens and Solenoid F deenergizes. The solenoid valve vents the high pressure pilot supply pressure from the poppet valve, and the poppet valve closes. The muffler is now isolated, and purge is disabled. This may allow IA Header pressure to restore to normal.
  • The 2CR2 contacts close, and the Instr. Air Sys Malfunction alarm is received in the Control Room.
  • The Dryer deenergizes when 2CR3 contacts open. Inlet valves V1 and V2 fail open, and purge exhaust valves V3 and V4 fail closed. Instrument System Pressure is maintained through the Dryer.
  • All circuitry and valves return to normal state when the low pressure condition clears and RESET is pushed.

Loss of 120 VAC Power to Dryer

  • This results in the loss of 12 VDC power supply at the ADC Enclosure for the IA Dryer Controller.
  • Solenoid F deenergizes, and the poppet valve closes. Purge is disabled.
  • Relay 2CR deenergizes, and the 2CR2 contacts close, causing the Control Room Alarm to come in, since the annunciator circuit is powered from another power supply.

Dryer Inlet Valve Fails to Open

  • The lowering Dry Gas Outlet Pressure, and therefore High Pressure Pilot Supply Pressure, causes switch 3PS to open. Same failure effects as Lowering IA Header Pressure, above.
  • Instrument Air header pressure will restore to normal.

Solenoid Valve F Sticks Shut Following Auto Isolation

  • Poppet Valve remains shut. During the manual Dryer reset procedure, the Operator verifies that muffler flow exists during purge cycle, thus verifying that the solenoid valve F has opened.
  • The Solenoid Valve F remains open for all other Dryer operational modes or failures, therefore not a failure concern.

Aquadex Moisture Indicator Each IA Dryer is equipped with an Aquadex Moisture Indicator that receives Instrument Air from the outlet of the dryer. The granular indicator used inside is specially treated with "silica gel" which changes color from blue to pink when a wet gas sample is received. The air leaves the indicator through a porous disc at the back of the indicator then through an adjustable bleed valve.

Control Room "Dryer Malfunction Alarm" On 1C13 (2C13) there is a "Dryer Malfunction" alarm and light. This alarm is for both 11(21) and 12(22) Instrument Air Dryers. The following will give a dryer malfunction alarm:

  • Loss of Power
  • Depress Failure Alarm
  • Repress Failure Alarm
  • Online Pressure Alarm
  • High humidity Warning
  • AMLOC Failure Warning
  • Purge Isolation

From the Procedure Change description for the first dryer Modification on unit 1:

General Description of Change:

Installing a Mod to 11 IA Dryer to which will cause it to fail safe (fail safe = de-energize, place both towers in service and isolate purge exhaust) on lowering IA press (93 =/- 1 psig) or loss of power to the dryer, also when 11 dryer fails safe it will annunciate the INSTR AIR SYS MALFUNCTION alarm on 1C13 and brightly lite the 11 dryer malfunction light. The Mod consists of installing a Purge exhaust isolation CV in the purge exhaust line and a reset pushbutton. The IA Dryer will have to be reset to allow it to return to regular service.

OI-19 modified section 6.8, startup of 11 AI dryer, to incorporate new reset switch.

Added a new section 6.23, resetting an IA dryer, to allow operators to reset 22 IA Dryer when needed. Added new valves to valve lineup.

AOP-7D Added the automatic actions to the notes section of the AOP. Also added a note to steps V.B.3 and VI.A.4 to alert the operator to expect the malfunction alarms for 11 IA dryer when IA press reaches 93 psig.

1C13 added the automatic actions to window k-26, INSTR AIR SYS MALFUNCTION, and also added the new possible causes (loss of power to 11 dryer or lower air pressure (93 psig)).

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