ML23299A261

Generic Ashfall Response Procedure

ML23299A261
Person / Time
Site:	Columbia
Issue date:	10/26/2023
From:	Energy Northwest
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
Download: ML23299A261 (1)

Text

The following material is an excerpt from Columbia Generating Stations ABN-ASH plant procedure, revision 029. This material has been trimmed for length (the original procedure contains several supporting attachments and is 97 pages long) and modified to make the steps generic, in order to serve as a guide in developing a volcanic tephra fallout operations procedure that could be used by any nuclear facility in any Member State.

Please note:

The steps taken in ABN-ASH were developed based on Columbia Generating Stations safety analysis derived volcanic tephra fallout conditions that could be experienced at this specific site in Washington State, USA, and Columbia Generating Stations safety functions, design and safety margins, and associated limits.

Other facilities may wish to consider developing similar procedures, but the steps within them should be based on their unique design and safety margin, safety analysis and evaluated tephra fallout conditions specific to their sites. The following material simply serves as a model to assist sites in developing such procedures.

1.0 ENTRY CONDITIONS NOTE: There are two websites which have been identified to provide information:

www.ssd.noaa.gov/VAAC/program.html provides information on the volcanic ash advisory page.

http://vulcan.wr.usgs.gov provides general information on volcanoes.

• Notification of a major Explosive Volcanic eruption in the Pacific Northwest.

• Volcanic ash advisory issued from the Washington DC Volcanic Ash Advisory Center.

• Notification of a pending volcanic event from USGS.

2.0 AUTOMATIC ACTIONS None 3.0 IMMEDIATE OPERATOR ACTIONS None 4.0 SUBSEQUENT OPERATOR ACTIONS NOTE:

The Plant is required to be shut down when the following limits are exceeded:

• A total un-compacted ash depth of (insert facility specific limit) inches OR

• An ash fall rate exceeding (insert facility specific rate) cm/hr.

4.1 IF at any time ash Plant Shutdown levels are reached, THEN PERFORM the following:

4.1.1 CLASSIFY the emergency per site procedure.

4.1.2 REDUCE reactor power with recirculation flow per site procedure.

4.1.3 SCRAM the Reactor per site procedure.

4.1.4 SHUTDOWN to Cold Shutdown per site procedure.

NOTE:

The following steps may be performed concurrently, as determined by the Control Room Supervisor (CRS).

4.2 BEFORE ash fall begins, PERFORM the following:

WARNING Inhaling volcanic dust may cause breathing problems and/or lung damage.

4.2.1 NOTIFY those individuals who are going to be outside to obtain particulate respirator N95 and safety goggles, from (designated location would be listed here), for protection from the volcanic dust.

4.2.2 OBTAIN the portable ash depth gage from the (designated location),

AND PLACE the portable ash depth gage on a flat section of open ground that is not in the shadow of a building or structure.

CAUTION To prevent ash from entering Diesel Generator (DG) intakes, DG Filters must be replaced prior to the postulated loss of offsite power at the 18* hour point of the 20*

hour ash fall event. (insert reference to action record or safety analysis document)

• (times above are specific to CGS event and may differ for other facilities)

NOTE: The RECOMMENDED priority for filter changeout is:

1 - Diesel Generator Building then DG Intake 2 - Service Water Pumphouse 3 - Reactor Building 4 - Radwaste Building 5 - Turbine and Auxiliary Buildings NOTE:

Keys required to access (filter designated location), and key lockers:

(Insert Building, Room, and Key tag numbers) 4.2.3 OBTAIN personnel support to changeout filters and assist in event response by performing ONE of the following as determined appropriate:

Signoff lines at right indicate step is completed.

ACTIVATE the Outage Control Center and Enter PPM 1.3.16 (a condition listed in issue management procedure).

UTILIZE the Management Automated Notification System (MANS).

ACTIVATE the Emergency Centers.

NOTE:

The following personnel are required to implement this procedure expeditiously, do not wait, commence filter changeouts with available personnel:

2 I&C Technicians*

2 Electricians*

14 Mechanics and/or Laborers*

• 2 Scaffolders*

• (staffing and skill mix above are specific to CGS event and may differ for other facilities) 4.2.4 CHANGE OUT diesel generator intake filters, and service water pump house HVAC filters as follows:

a) IF Extended Station Blackout/Extended Loss of AC Power occurs, THEN INITIATE actions to install ash filters and protect beyond design basis emergency response components in accordance with Attachments.

b) IF Extended Station Blackout/Extended Loss of AC Power occurs, THEN INITIATE actions to replace OEM filters to protect FLEX components in accordance with Attachments.

NOTE:

If operation of the DGs is required, alternate between DG-1 and DG-2 to facilitate filter change outs and to extend filter functionality.

NOTE:

Filter replacement for one division of DG and SW HVAC systems will take approximately four man-hours. Filter installation assignments must consider ash fall projected start time and manpower assigned to achieve completion before ash fall.

NOTE:

Filter inventory does not include filters for DG-3. If use of DG-3 is required, filters for DG-3 should be obtained from stores or verify that inventory used for DG-3 does not compromise operation of DG-1 or DG-2.

NOTE:

Reference Attachments for approximate duration of filter replacements.

NOTE:

(Designated spare filter location) contains all the filters referenced in Attachments. (Primary designated spare filter location) has enough filters for the initial set of ash fall protection for each Diesel Generator. Additional filters are located in the (Alternate designated spare filter location).

c) MOVE ash filters from (designated spare filter location) storage to the equipment specified in Attachments.

d) INSTALL ash filters for DG-1 and DG-2 per attachments.

(locations listed on Attachments).

e) INSTALL ash filters for SW HVAC per attachments (locations listed on Attachments.

f) REQUEST Laborers bring up replacement filters for the filters removed from (secondary designated location) to (primary designated location), or the applicable rooms, as determined by the CRS/Shift Manager.

WARNING Opening the HVAC system to verify damper position will cause the respective Diesel Generator to be inoperable.

4.2.5 PERFORM the required DG-1 & DG-2 HVAC line up:

(insert steps for isolating one diesel generator at a time to change filters while the other diesel handles the load).

4.2.6 PERFORM the required DG-3 HVAC line up:

(For CGS, DG-3 is shut down during ash fall UNLESS there is a STATION BLACKOUT AND LOSS OF COOLING).

4.2.7 SHUT DOWN the following fans (List fans not required for SSC cooling):

4.2.8 ALIGN Control Room HVAC to the recirculation mode per (insert reference to procedure).

4.2.9 OPEN the following breakers (List breakers to shut off power to ventilation to be shut down in response to ash fallout).

4.2.10 ALIGN Technical Support Center HVAC to the recirculation mode per (insert reference to procedure).

NOTE:

The airwash controllers are set to maximize air wash operation during an ash fall event for the purpose of removing ash.

4.2.11 IF outside air temperature is expected to remain above (max set point for required cooling) for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, THEN PERFORM the following steps.

a) SET the following controllers: (This step involves setting thermostats in the reactor building, turbine building, and rad waste building to put HVAC in maximum recirculation mode to minimize outside air intake to extend filter life.) (list controllers here with respective set points for each) b) VERIFY one air wash pump is running (with controller settings as given in the Step above) with a normal basin level for each operating air wash in the following systems: (This step addresses evaporative cooling

systems intalled in the reactor building, turbine building, and rad waste buildings, listing SOPs for each system).

4.2.12 INSTALL ash filters for equipment locations listed in Attachment. (This step adds auxiliary ash filters on DG, SW pumphouse, reactor building, turbine building, rad waste building, and the cooling tower water pumphouse, per attached guidance.)

4.2.13 IF diesel fire pumps are required for system pressurization, AND diesel fire pumps are available, THEN PERFORM the following:

(This step involves swapping standby fire pumps to those located in buildings less impacted by ash and replacing combustion air filters when dirty.)

NOTE:

Ash Fall is defined as the following:

• Volcanic eruption in the Pacific Northwest AND

• Visible ash falling from the sky at Columbia Generating Station.

4.3 WHEN ash fall begins, OR as directed by the CRS/Shift Manager, THEN PERFORM the following:

4.3.1 CLASSIFY the emergency per (insert reference to emergency classification procedure).

4.3.2 VERIFY safe shutdown systems are operable.

4.3.3 START a once per hour temporary log of ash fall depth using the installed gauge near the Met Tower.

4.3.4 VERIFY dust-tight integrity for safe shutdown instrumentation (This step verifies instrument cabinets are closed and sealed, covers are mounted, seals or gaskets are in place, and inspection or calibration ports are covered and securely sealed to provide dust-tight integrity). If maintenance or surveillance testing is ongoing, restore the associated instruments.

4.3.5 CONTINUE the filter change out steps commenced in step 4.2 in order of the priority specified.

4.3.6 BEFORE (see Attachments for list) filter p limits are reached, THEN PRIORITIZE change out of filters for equipment listed.

4.3.7 CONSIDER Plant Shutdown per (procedure), based on the following criteria:

Total accumulation of ash buildup approaching shutdown limit Rate of change of ash buildup approaching shutdown limit Ability to maintain ventilation system filters clean Ability to maintain safe shutdown systems operable

Ability to maintain operating equipment free of ash NOTE:

Reactor building filters are equipped with p indicators for both roll and ash filters. In other systems, one p indicator is installed across both filters.

4.3.8 MONITOR ash build-up on the following roll filters, AND ADVANCE the following roll filters as needed to lower p by depressing the Manual Run pushbutton (locally in the filter):

(List tag numbers and location of roll filters in the reactor building, turbine building, radwaste building, and service building).

4.3.9 CHANGE the Division 1 Critical Switchgear HVAC mode of operation as follows:

(This step stops exhaust fan (rad waste exhaust), opens certain doors to promote natural convection for rooms with critical equipment, adjusts all fans and starts emergency room coolers (fan coil units supplied with pond cooling water).

(List equipment tag numbers, settings, and actions).

4.3.10 DISCONNECT the power source at the damper motors to place the following dampers at the TMU pump house in the recirculation position: (This step addresses the cooling tower makeup water building, putting ventilation in recirculating mode to protect pump motors from ash infiltration.)

(List equipment tag numbers, settings, and actions).

4.3.11 IF ash buildup occurs on the low-voltage bushings and insulators of transformers, THEN REMOVE the transformers from service on an alternating basis (plant shutdown is required),

AND CLEAN bushings and insulators.

(This step addresses cleaning of electrical insulators and bushings on the startup and backup transformers to prevent arcing.)

(List equipment tag numbers, settings, and actions).

4.3.12 IF either diesel fire pump starts or is operating, THEN MONITOR air cleaner filter cleanliness, AND REPLACE the air cleaner filters when visibly dirty.

4.3.13 MONITOR service water spray pond temperatures and levels locally at least once every four hours, AND COMPARE local service water spray pond temperatures and levels with control room indicators on boards (list designated set points and instrument locations).

4.3.14 IF SW pump discharge pressure readings are NOT normal (list normal setpoint) on control room indicators, THEN BLOW DOWN the sensing lines for (list tag number and location).

4.3.15 MONITOR the following Control Air Compressor Inlet filter P:

(List equipment tag numbers and locations).

4.3.16 IF Control Air Compressor Inlet filter P (list tag numbers) is greater than (list safety limit),

THEN START another compressor per (list procedure),

AND STOP the compressor with high inlet air filter P per (list procedure).

CAUTION Do not remove the screens covering the air vents.

4.3.17 MONITOR ash buildup around the spent fuel cask air ducts at least every four hours.

4.3.18 IF ash buildup increases to greater than (insert maximum acceptable depth), or one or more cask air duct(s) is blocked by ash, THEN REMOVE ash from around the affected cask(s).

NOTE:

If the normal temperature indication is not available or not accessible, then use an infrared thermometer from (insert building and location).

4.3.19 MONITOR Spent Fuel Pool level and temperature, at a frequency determined by the CRS/Shift Manager.

4.3.20 IF DG-1 starts, THEN ADJUST temperature controller to (insert setpoint and tag number). (This step involves setting DG room temperature back to normal setpoint to allow for heat load from running diesel).

4.3.21 IF DG-2 starts, THEN ADJUST temperature controller to (insert setpoint and tag number). (This step involves setting DG room temperature back to normal setpoint to allow for heat load from running diesel).

4.3.22 PERFORM the following HVAC operations:

Reactor Building HVAC

1. START standby gas train blower to maintain Reactor Building differential pressure negative per (insert procedure). (This step helps maintain reactor building negative and monitor and treat exhaust.)

2. STOP the Reactor Building HVAC system per (insert procedure). (This step helps minimize deposited ash by shutting off supply fans to the reactor building.)

3. OPERATE emergency room coolers to control temperatures below (insert set point and procedure).

4. OPERATE Reactor Building HVAC system intermittently to maintain Reactor Building temperatures below (insert set points).

Turbine Building HVAC

5. ADJUST the turbine outside air differential pressure controllers for the running turbine outside air (supply) fans to (insert setpoint). (This step minimizes intake of outside air to the turbine building during ashfall).

6. MAINTAIN Turbine Building temperature below (insert setpoint and procedure).

7. REDUCE the number of Turbine Building HVAC operating fans to one exhaust fan and two supply fans (one operating supply fan at each end of the building) as heat removal requirements diminish.

Radwaste Building HVAC

8. REQUEST HP initiate monitoring for loss of Radwaste Building HVAC.

9. OPERATE Radwaste Building HVAC to maintain building temperature in compliance with (licensing document per procedure)

Circulating Water Pump House NOTE:

Operate exhaust fans located over running circulating water pumps if available.

10. IF a Circulating Water pump is in operation, THEN STOP exhaust fans to reduce vacuum that may draw in ash per (insert procedure),

AND MAINTAIN temperature below (max allowable temperature).

11. IF hypochlorite tank room temperature can be maintained less than (insert set point),

AND electrical room temperature can be maintained less than (insert setpoint),

THEN SHUTDOWN Circ Water Pump House HVAC per (insert procedure).

12. IF Circulating Water Pump House HVAC must be operated, THEN MONITOR and CLEAN air filters and cooling/condensing coils as required for continued operation.

Cooling Tower Electrical Buildings

13. STOP fans and compressors NOT required to maintain temperature below (insert setpoint and procedure).

14. SET cooling tower mix air recirculation/outside air damper control to (insert setpoint). (This step puts cooling towers in recirculating mode.)

15. IF HVAC units must be operated to maintain temperature less than (insert set point),

THEN CHANGE filters,

AND CLEAN (air or water wash) cooling coils to maintain temperature less than (insert set point).

TMU Pump House

16. OPERATE pump house fans alternately as required to maintain building temperature less than (insert set point and procedure). (This step turns off fans until needed to maintain less than maximum allowable temperature).

17. CHANGE filters (insert tag numbers for TMU pump house fans) at (insert maximum p for filter changeout).

Service Building

18. STOP machine shop fan (insert tag number and procedure). (This step stops unneeded fan to limit ash infiltration).

19. SHUTDOWN the Service Building HVAC system per (insert procedure).

20. MAINTAIN Service Bldg. temperature less than (maximum allowable temperature) as follows:

ADJUST the following temperature controller setpoints to full scale for maximum recirculation: (insert tag numbers)

OPERATE the Service Building chillers intermittently per (insert procedure).

Flocculator Building

21. SHUTDOWN the following Flocculator Building Fans per (insert procedure):

(insert tag numbers).

4.3.23 CONSIDER performing thermography inspections on Transformer Yard equipment to inspect for possible damage.

4.3.24 MONITOR ash deposition on the following structures:

CAUTION Ash should not be shoveled or swept onto other roof structures or into air intake systems (DGs, HVAC).

Reactor Building

1. IF (insert max dry depth) of dry or (insert max wetted depth) of wet ash accumulates, THEN CLEAN the structural steel parapet enclosing the existing sloping metal deck and roof framing system.

2. IF (insert max dry depth) of dry or (insert max wetted depth) of wet ash accumulates, THEN CLEAN banks of conduit with sheet metal hoods.

Turbine Building

3. IF (insert max dry depth) of dry or (insert max wetted depth) of wet ash accumulates, THEN CLEAN high roof structural steel framing supporting the sloping metal roof deck.

Radwaste Building

4. IF (insert max dry depth) of dry or (insert max wetted depth) of wet ash accumulates, THEN CLEAN high roof structural steel framing supporting the sloping metal roof deck.

5. IF (insert max dry depth) of dry or (insert max wetted depth) of wet ash accumulates, THEN CLEAN low roof, structural steel framing supporting the sloping metal roof deck.

Service Building

6. IF (insert max dry depth) of dry or (insert max wetted depth) of wet ash accumulates, THEN CLEAN the structural steel framing supporting the sloping metal roof deck.

Circulating Water Pump House

7. IF (insert max dry depth) of dry or (insert max wetted depth) of wet ash accumulates, THEN CLEAN the structural steel parapet enclosing the existing sloping metal roof deck and structural steel roof framing.

Flocculator Building

8. IF (insert max dry depth) of dry or (insert max wetted depth) of wet ash accumulates, THEN CLEAN the sloping metal roof deck and structural steel roof framing.

4.4 Restoration (Directed by Recovery Manager) 4.4.1 (This step contains all the instructions to reset ventilation to pre-event conditions following the event, once return to normal operations can resume.)

AND REPLENISH the filters as required.

5.0 BASES This section, for each step in the procedure, provides the rationale and basis for the actions described at each step, and links the steps to the goal of reducing tephra impact on various SSCs relied upon for safety functions to address design basis events, and to perform functions deemed necessary for beyond design basis events.

The tephra fallout safety strategy of the Columbia Generating Station Boiling Water Reactor is based upon experience from Mount St. Helens 1980, as well as extensive analysis and preparation. Guided by this procedure, CGS can respond immediately to notification of volcanic unrest and notification of an eruption with preparatory measures allowing the facility to bring on necessary staffing, stage necessary components, and respond to the challenge to filtration, cooling, and structures on a prioritized basis, and informed by SSC design margin and safety limits, included in this procedure.

Consistent with the licensing basis requirements for Columbia Generating Station, a plant shutdown is required for a design basis ash fall event. The goal is to shutdown before design basis ash fall at the site, or as soon thereafter as possible. In all cases, time is available to reduce reactor power with recirculation flow prior to a scram.

One of the first steps taken in the procedure, a portable gage is placed to track the rate of tephra deposition and the total amount of tephra accumulation.

Key features of this procedure include:

Ventilation alignment and filter changeouts needed to ensure necessary cooling and limit tephra infiltration to key SSCs during an event, including to protect air cooled equipment and diesel combustion air.

Actions required in the event of an extended Station Black Out (SBO) or Loss of AC power.

A prioritized list of systems that must be protected from ash, giving the response team guidelines for how and when and how often to change filters, clean roofs, check temperatures, and what adverse conditions operators should monitor for.

Skilled technicians, including skill mix and quantity needed, and how they are activitated and transported to site.

Supplies, including filters, tools, auxiliary cooling equipment, and PPE, including estimate of quantities and types needed and storage location.

Maximum temperature setpoints, beyond which other cooling means must be implemented, and how and when to implement other means of cooling.

Ash depth limits (dry and wet) for each structure, governing when to clean roofs.

Steps to protect electrical transformers from flashover and to ensure instrument cabinets are sealed to prevent or mitigate ash contamination.

Locations of auxiliary components such as oil bath filters, and procedures for installation and operation.

Steps to protect spent fuel cask air ducts to preserve convective cooling, and monitor and protect spent fuel pool temperatures.

6.0 REFERENCES

The reference list includes procedures on protection of equipment, ash evaluations of equipment and structural impacts, licensing documents, design basis criteria.

7.0 ATTACHMENTS The attachments include the following materials to assist plant personnel during a tephra fallout event:

ASH FALL FILTER REQUIREMENTS (This section included a table which lists, by system, filter component ID numbers, spare filter staging areas, engineering drawing, supply catalog ID number, filter dimensions, filter differential pressure limits, predicted changeout frequency during a design basis ashfall event, filter change procedure number, differential pressure monitor component ID number, and estimated time for personnel to change filters. A table is included for two cases: offsite power available, and loss of offsite power.)

ASH FALL SHUTDOWN INSTRUMENTATION (This section included a table which lists all instruments required for safe shutdown, by panel, location, component ID number, and safety function.)

REPLACE ENGINE AIR INTAKE FILTERS (Procedure for changing diesel engine intake filters).

BEYOND DESIGN BASIS COMPONENT OIL BATH FILTER INSTALLATION (This section provides details on installation of oil bath filters for beyond design basis staged equipment such as diesel generators, emergency portable pumps, pumper trucks, and diesel generators.)

BEYOND DESIGN BASIS OEM FILTER REPLACEMENT (This section provides details on installation of OEM filter replacements for components that would be required in a Beyond-Design Basis ashfall event.)