Lgs Ilt - Cac And N2 Purge

Front 1

State the purpose of the Containment Atmosphere Control System.

Back 1

- The Containment Atmosphere Control System is designed to:
- Establish and maintain an inert Primary Containment atmosphere during normal plant operation to prevent the formation of an explosive mixture between oxygen and the hydrogen released during a design basis LOCA.
- Provide a means to continuously monitor drywell and suppression chamber hydrogen and oxygen concentrations.
- Provide a means to control the quantity of oxygen postulated to be generated in the primary containment after a LOCA.
- Provide a means to supply fresh air to the drywell during periods of maintenance.

Front 2

purpose of the following systems components:
a.      Nitrogen Storage Tanks

Back 2

- Two tanks are located at elevation 217, outside the South end of the Radwaste enclosure.
- Each tank has a capacity of 5800 gallons, with a maximum working pressure of 250 psig.
- Each tank has an inner and outer vessel, with the space between them insulated and maintained at a high vacuum to minimize heat absorption.
- Overpressure protection for the annulus is provided by a rupture disc, which blows at approximately 10 psig.

Front 3

purpose of the following systems components:
b.      Nitrogen Vaporizers

Back 3

- Two AMBIENT VAPORIZERS are installed to convert liquid nitrogen to the gaseous state for low flow (10-100 SCFM) conditions.
- The vaporizers are arranged with timer controlled solenoid operated switching valves, so that when one of the ambient vaporizers is defrosting, the other can convert liquid nitrogen to gas. Three-position control switches control the operation of the solenoid-operated valves.
- The ambient vaporizers are rated for 6000 SCFH, and a maximum working pressure of 300 psig.
- WATER BATH VAPORIZER (high flow)
- Converts liquid nitrogen to gas for high flow (100-3200 SCFM) pipeline delivery and tank pressure building. The water bath vaporizer consists of a pipeline supply coil and a pressure building coil immersed in a steam-heated water bath, and has a capacity of 200,000 SCFH at 300 psig. The steam is supplied to the water bath vaporizer from the auxiliary steam system

Front 4

purpose of the following systems components:
c.      Hydrogen and Oxygen Analyzers

Back 4

- The function of the H2 and O2 analyzers is to monitor drywell and suppression pool hydrogen and oxygen concentrations, and to provide indications and alarms associated with H2 and O2 concentrations.

Front 5

purpose of the following systems components:
d.      Reagent Gas

Back 5

- The reagent gas is supplied continuously to the analyzer cells for catalytic recombination. The reagent gas for the H2 analyzer is 100% oxygen. The reagent gas for the O2 analyzer is 100% hydrogen.
Q. How would the loss of reagent gas affect the operation of the analyzer?
A: Without reagent gas, the analyzer would not see a difference in thermal conductivity and it should indicate “zero” for whichever gas it is sampling.

Front 6

purpose of the following systems components:
e.      Span Gas

Back 6

- The span gas is used to calibrate the analyzers. The span gas for the H2 analyzer is 7% hydrogen. The span gas for the O2 analyzer is 7% oxygen.

Front 7

purpose of the following systems components:
f.        Hydrogen Recombiners

Back 7

- The containment hydrogen recombiners function to recombine hydrogen and oxygen to form water vapor, to prevent the accumulation of flammable concentrations H2 or O2 inside the containment following a LOCA.

Front 8

CAC System support
a. Auxiliary Steam System

Back 8

- Supplies heating steam to the Nitrogen inerting water bath vaporizer. A loss of the aux. steam system, which supplies PHS, removes high flow mode inerting capability.

- A regulator valve in the steam supply line controls the water bath temperature. The water bath is initially supplied with demin water via a hose from the Radwaste Enclosure or from the Diesel Generator Building. Once normal level is established, make-up to the tank is provided from the condensate from the aux. steam supplied to the heating coil.

Front 9

CAC System support
b. Standby Gas Treatment System

Back 9

- Receives, filters, and exhausts the gases discharged from the containment during inerting, de-inerting, venting, or high flow purging. A loss of the SBGT System removes this capability.

Front 10

CAC System support
c. AC Electrical System

Back 10

- The nitrogen inerting electric trim heater is powered from 480 VAC and control power is provided from 120 VAC.
- The H2 and O2 analyzer cabinets are powered from 120 VAC.
- The Containment Hydrogen Recombiners are powered from 480 VAC.
- All motor operated valves, solenoid valves, and the solenoids controlling air-operated valves are powered from 480/120 VAC power.

Front 11

CAC System support
d. RHR System

Back 11

- Supplies water to the containment hydrogen recombiner water-spray cooler. A loss of RHR flow will cause recombiner trip on high gas return temperature.

Front 12

CAC System support
e. NSSSS

Back 12

- Provides Containment Isolation signals in three groups, VIA, VIB, and VIC.
- Group VIA Isolations cause the containment purge supply and exhaust valves to isolate for both units.
- Group VIB Isolations cause the primary containment vents to REECE and N2 Makeup Block Valves to isolate for both units, on the same signals as for Group VIA, with the exception of the North Stack High Radiation signal.
- Group VIC Isolations cause the Primary Containment Sampling and Recombiner Lines to isolate for the affected unit only.

Front 13

CAC System support
f. Nitrogen Purge

Back 13

- The nitrogen inerting system functions to inert the containment atmosphere with nitrogen to reduce oxygen levels to less than 4% by volume.

Front 14

State the normal values for containment hydrogen and oxygen concentrations and discuss conditions that would cause those normal values to change.

Back 14

- H2 and O2 Analyzers
- H2 Range 0-30%
- O2 Range 0-10%, 0-25%
- Admin Limit of 3% O2
- Tech Spec Limit 4% O2
- Normal H2 value - less than 1%
- Normal O2 value - less than 3%
- Oxygen concentration is typically between 1% and 3% for Drywell and Suppression Pool. An admin limit is set at 3%. This value is affected by plant evolutions such as RCIC runs since RCIC vacuum condenser discharges to the Suppression Pool.

Front 15

List the containment isolation signals, their setpoints and which CAC system flowpaths isolate upon receipt of each signal.
- Group VIA; Containment Purge Supply and Exhaust

Back 15

Group isolates on any of the following signals:
(1) Reactor low level at -38 inches
(2) High drywell pressure at 1.68 psig
(3) Reactor enclosure ventilation exhaust duct high radiation at 1.35 mr/hr
(4) Refuel Floor ventilation exhaust duct high radiation at 2.0 mR/hr.
(5) Low reactor enclosure ΔP at -0.1 inches H2O with a 50 minute TD
(6) Low Refuel Enclosure ΔP at -0.1 inches H2O with a 100 sec TD
(7) SBGT system from Reactor HVAC crosstie damper fails open
(8) SBGT system from Refuel HVAC crosstie damper fails open
(9) North stack effluent radiation high at 2.1 micro Ci/cc maximum

- The following valves close on the isolations:
(1) Nitrogen Supply (Both Units)
(2) Purge Supply (Both Units)
(3) Drywell Purge Exhaust (Both Units)
(4) Suppression Pool Purge Exhaust (Both Units)

- Group VIA has no manual bypass for an isolation signal

Front 16

List the containment isolation signals, their setpoints and which CAC system flowpaths isolate upon receipt of each signal.
- Group VIB; Primary Containment Exhaust to Equipment Compartment

Back 16

- Group VIB isolates on any of the following signals:
(1) Reactor low level at -38 inches
(2) High drywell pressure at 1.68 psig
(3) Reactor enclosure ventilation exhaust duct at 1.35 mr/hr
(4) Refuel ventilation exhaust duct high radiation at 2.0 mR/hr
(5) Low reactor enclosure ΔP at -0.1 inches H2O with a 50 minute TD
(6) Low refuel enclosure ΔP at -0.1 inches H2O with a 100 sec TD
(7) Reactor HVAC to SBGT cross tie damper fails open
(8) Refuel HVAC to SBGT cross tie damper fails open

- The following valves close on the isolation:
(1) Drywell exhaust to Equip. Compt. Exh. (Both Units)
(2) Suppression Pool exhaust to Equip. Compt. Exh. (Both Units)
(3) Nitrogen supply valves (Both Units)

- Group VIB can be manually bypassed if a Reactor Enclosure Isolation signal is present by placing HSS-57-*91A and HSS-57-*91B on panel *0C601 in BYPASS. This permits venting and nitrogen supply during transients if required.

Front 17

List the containment isolation signals, their setpoints and which CAC system flowpaths isolate upon receipt of each signal.
- Group VIC; Primary Containment Sampling and Recombiner Lines

Back 17

- Group isolates on any of the following signals:
(1) Reactor low level at -38 inches
(2) High drywell pressure at 1.68 psig
(3) Refuel floor ventilation exhaust duct high radiation at 2.0 mr/hr
(4) Reactor enclosure ventilation exhaust duct high radiation at 1.35 mr/hr

- The following valves close on the isolations:
(1) A Recombiner
(2) B Recombiner
(3) Containment Atmosphere Sampling
(4) Drywell Radiation Sample System
(5) Common N2 Purge Makeup Supply

- Isolation Bypasses -
- "A" Recombiner isolation is bypassed when HS in BYPASS
- "B" Recombiner isolation is bypassed when HS in BYPASS
- Containment Atmosphere Sampling System valves isolation can be bypassed with HSS-57-*91A, B, C and D in BYPASS to allow containment atmosphere monitoring following transients.

Front 18

List the flowpaths that are provided with isolation bypass capabilities.

Back 18

- Group VIB can be manually bypassed if a Reactor Enclosure Isolation signal is present by placing HSS-57-*91A and HSS-57-*91B on panel *0C601 in BYPASS. This permits venting and nitrogen supply during transients if required.
- "A" Recombiner isolation (valves HV-57-*61, HV-57-*62, and HV-57-*66) can be bypassed by placing HSS-57-*91C on panel *0C601 in BYPASS
- "B" Recombiner isolation (valves HV-57-*63, HV-57-*64, HV-57-*69, and HV-57-*16) can be bypassed by placing HSS-57-*91D on panel *0C601 in BYPASS.
- Containment Atmosphere Sampling System valves can be bypassed with a valid isolations present by placing HSS-57-*91A, B, C and D on panel *OC601 in BYPASS to allow containment atmosphere monitoring following transients.

Front 19

List the three major mechanisms for hydrogen production during post LOCA conditions and summarize each process.

Back 19

(1) The metal-water reaction of steam and zirconium cladding requires a relatively high clad temperature (>1600°F) to become self-sustaining. This reaction is always occurring but the rate increases with elevated temperatures. The formula for this reaction is:
Zr + 2H2O  ZrO2 + 2H2 + Energy in the form of heat
- The amount of H2 production depends on the cladding temperature, the time at this temperature, and the effectiveness of ECCS.
(2) Radiolysis is another source of H2 - Water decomposes in a radiation field by the following formula:
2H2O + Radiation  2H2 + O2
- Radiolysis is always occurring in the reactor and the amount of H2 produced depends on the intensity of radiation or power history, the energy of this radiation, and the amount of H2 and O2 in the coolant.
(3) Corrosion of containment metals can also produce significant H2. Zinc based paint, galvanizing, and aluminum surfaces can react with water to produce hydrogen.
- Zinc is the prime concern from galvanized steel and zinc based paint using the formula:
Zn + 2H2O  Zn(OH)2 + H2
- The amount of H2 produced depends on temperature, composition of the material, surface area, and the pH of the water solution.

Front 20

List the conditions that will trip post accident recombiners and state the setpoints for each.

Back 20

- Blower inlet high temperature - 250°F
- High reaction chamber temperature - 1422°F
- Heater wall high temperature - 1422°F
- High inlet pressure - 40 psia (25.3 psig)
- High return temperature - 250°F
- Heater will de-energize on low flow (40%)…