ML101160376
| ML101160376 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 04/23/2010 |
| From: | Price J Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML101160376 (13) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 April 23, 2010
- u. S. Nuclear Regulatory Commission Serial No.: 10-114 Attention: Document Control Desk NAPS/MES Washington, DC 20555-0001 Docket Nos.: 50-338 50-339 License Nos.: NPF-4 NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 10 CFR 50 APPENDIX B EXEMPTION REQUEST REACTOR COOLANT PUMP (RCP) OIL COLLECTION SYSTEMS In accordance with 10 GFR 50.12, Virginia Electric and Power Company (Dominion) requests an exemption from the requirements of 10 CFR 50, Appendix R, Section 111.0, for Operating Licenses NPF-4 and NPF-7 for North Anna Units 1 and 2. Section 111.0 requires that the Reactor Coolant Pumps (RCP) be equipped with an oil collection system if the containment is not inerted. In addition, Section 111.0 requires that collection systems shall be capable of collecting lube oil from all potential pressurized and unpressurized leakage sites in the RCP lube oil system.
The purpose of this exemption request is to address expected, minor RCP oil misting.
North Anna's existing F~CP motor Oil Collection Systems (OCS) was designed and Installed to collect potential oil leakage. However, minor oil misting may not be totally captured in that the surfaces on which the misting may condense as a sheen may not be an OCS surface. This phenomenon has been evaluated and determined to not present a significant fim hazard. This conclusion is based upon the quantity of oil expected to be lost due to misting outside the OCS, the physical properties of the oil, and the lack of available ignition sources within the RCP cubicle.
The North Anna RCP OCS functionally meets the safety intent of Section 111.0 to ensure that failure of the lube oil system will not lead to fire during normal or design basis accident conditions. However, minor oil misting may not be collected by the OCS.
Therefore, Dominion is requesting an exemption from the requirement to capture all potential leakage. Justification for this exemption request is included in Attachment 1.
This exemption request has been reviewed and approved by the Facility Safety Review Committee. In accordance with 10 CFR 50.12, this exemption is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security.
Dominion requests approval of this exemption by April 14, 2011.
Serial NO.1 0-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Page 2 of 2 If you have any questions or require additional information, please contact Mr. Tom Shaub at (804) 273-2763.
Sincerely, Ail ::I n'l-' rice sident - Nuclear Engineering itments contained in this letter: None Attachments:
1 10 CFR 50 Appendix R Exemption Request, Reactor Coolant Pump (RCP) Oil Collection Systems 2 Flow Path of Oil from Lower Pot through the Motor Stator Cooler cc: U.S. Nuclear Regulatory Commission - Region II 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257 Mr. J. E. Reasor, Jr.
Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.
Suite 300 Glen Allen, Virginia 23060 NRC Senior Resident Inspector North Anna Power Station Dr. V. Sreenivas NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 8 G9A 11555 Rockville Pike Rockville, MD 20852-2738 Ms. K. R. Cotton NRC Project Manager U. S. Nuclear Requlatory Commission One White Flint North Mail Stop 8 G9A 11555 Rockville Pike Rockville, Maryland 20852-2738
Serial No.10-114 Docket Nos. 50-338/339 Attachment 1 10 CFR 50 APPENDIX R EXEMPTION REQUEST REACTOR COOLANT PUMP (RCP) OIL COLLECTION SYSTEMS
'Virginia Electric and Power Company (Dominion)
North Anna Power Station Units 1 and 2
Serial No.1 0-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Attachment 1 North Anna Power Station Units 1 & 2 RCP Oil Misting Outside of Oil Collection System 1.0 PURPOSE The purpose of this exemption request is to address expected, minor oil misting.
2.0 BACKGROUND
Pursuant to 10 CFR 50, Appendix R, Section 111.0, North Anna's existing Reactor Coolant Pump (RCP) Oil Collection Systems (OCS) was designed and installed to collect potential oll leakaqe. In March 1979, North Anna received an NRC letter entitled, "Notice of Issuance of A.mendment 8 to License NPF-4," which stated, "As a result of our review of the licensee's fire hazards analysis for the areas inside containment, we find that, with the additional protection to be provided for the reactor coolant pumps ... the fire protection provisions meet the guidelines of Appendix A to Branch Technical Position APCSB 9.5-1 and are, therefore, acceptable."
However, expected, minor oil misting is not totally captured at North Anna. The misting in question is common in most large RCP motor designs. Further, although present in the original design of these RCP motors, oil misting was not specifically addressed in any review or SER performed for this component.
This phenomenon has been evaluated and determined to not present a significant fire hazard. This conclusion is based upon the quantity of oil expected to be lost due to misting outside the OCS during a fuel cycle, the physical properties of the oil and the lack of available ignition sources within the RCP cubicle.
Some of this oil mist has been found to accumulate on the RCP motor stator air coolers.
These components do 110t contain oil, but it is believed the oil mist migrates to this location from the motor's lower oil pot. The OCS is to be modified during the upcoming refueling outages to provide a means to collect any oil mist which might accumulate on the motor stator cooler and, if sufficient oil should accumulate, to provide a pathway to drain it into the existing OCS. This modification is being implemented to prevent lube oil from pooling on the motor stator cooler and then dripping onto the RCP flange below.
Although the total pooling (or collection of mist) on the motor stator coolers results in an aggregate volume of oil that is conservatively estimated to be less than 1.5 gallons per pump per cycle, the modification is being made for verbatim compliance with 10 CFR 50, Appendix R, Section 111.0.
Following the pending OCS modifications, a small sheen of oil mist may still remain uncollected by the OCS. This is expected, as oil misting is common for large motors of this age and design. At the time of discovery, Dominion performed a Reasonable Assurance of Safety evaluation and determined that the current level of oil misting will neither affect plant operation nor threaten the safe shutdown of the plant. Thus, the North Anna RCP oes meets the functional intent of Section 111.0 in assuring failure of the lube oil system will not lead to fire during normal or design basis accident conditions. However, the collection of all minor oil misting is impractical and was the Page 1 of 8
Serial No.1 0-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Attachment 1 subject of a NEI industry position paper that was submitted to the NRC in 2007
[Accession Number ML071590298]. As such, North Anna is requesting an exemption from 10 CFR 50, Appendix R, Section 111.0 for cases of minor oil misting from the RCPs which is uncollectable by the OCS.
Area Description Fire Areas 1-1 and 1-2 are the primary containments for North Anna Power Station (NAPS), Units 1 and 2, respectively. Each area is a multi-level structure with floor elevations of 216' 11",231' 6", 241' 0", 262' 10", and 291' 10". Of concern in this exemption request are the RCP motor cubicles and loop rooms, which occupy the 262' 10" and 241' levels of containment, respectively. The boundaries of Fire Areas 1-1 and 1-2 are made of reinforced concrete with an inherent fire rating in excess of three hours.
The RCPs are located in cubicles with the steam generators (SGs) and the Reactor Coolant System (RCS) piping. As water exits a SG, it travels through "intermediate leg" piping, into the RCP, out into the "cold leg" piping, and finally to the reactor vessel inlet.
Intermediate leg temperature is nominally 54rF during normal operation at 100%
power. Cold leg temperature is nominally 549°F, due to a slight heat-up from the RCPs.
The RCP motor cubicle walls are constructed of reinforced concrete, and extend up to the 291' 10" elevation. The cubicles contain access doors on elevations 262'-10" and 241'. Although the cubicles do not fully enclose the equipment, they do provide a large degree of physical separation.
The RCP motor stator coolers are located on the 262' 10" level. Two are attached to each RCP motor. The motor stator is cooled using forced circulation. Air is drawn in through motor ventilation ports at the top and bottom of the motor frame by two sets of fins located on the RCP rotor. The air is forced through the motor stator and discharges at the center of the motor frame where the RCP stator coolers are located. This pathway is torturous, which leads to some accumulation of oil on the coolers; this accumulation is to be collected by the planned OCS modifications.
The RCP stator coolers use Component Cooling Water to cool the air discharged from the motor stator to control the ambient temperature in the RCP motor cubicle. Note: the RCP motor stator coolers are not associated with the RCP motor lube oil system. See the "Source of Oil Leakage" section below for a description of how the oil is accumulating at this location. The motor stator coolers are oriented so as to discharge into the void space above both the intermediate leg and the cold leg piping of the RCS.
As shown in the figure below, the trajectory of the minor oil mist is not directly above the RCS piping, but some mist could reach these areas. Note, this drawing is not to scale; however, the trajectory of the oil misting relative to the RCS piping is correct.
Page 2 of 8
Serial No.10-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Attachment 1 Figure: Simplified layout of a Reactor Coolant System (RCS) loop, as viewed from above
..-rIfIII .... - .... --~""'-
r - ... -- Direction of Minor'" ......
Motor _.--:; Oil Misting ........
- ~or .....
Coolers <, ~ Rep Intermediate le ""
l I
)-/1 /
Direction of Min~r I I' Oil Misting I I I Hot leg .,
-/\
I Reactor Vessel RCPCubkal Wall Oil Collection System The OCS was installed on Unit 1 in March 1981 and on Unit 2 in November 1980.
Compliance with 10 CFR 50, Appendix R, Section 111.0, "Oil Collection System for Reactor Coolant Pumps," was reviewed by the NRC in Inspection Report 50-338/85-24 and 50-339/85-24. The inspection report specifies which lube oil components were pro-vided oil collection enclosures and determined that the system appeared to meet the requirements of Section 111.0.
Compliance was again reviewed by the NRC in Inspection Reports 05000338/2009004, 05000339/2009004, 05000338/2009501, and 05000339/2009501. These inspections questioned the system's ability to collect oil leakage from the Rep motor stator cooler; the oil which accumulates at this location is the result of oil misting, rather than direct oil leakage. As a corrective action, North Anna has initiated the previously discussed modifications to ensure the oil mist accumulating on the motor stator cooler would be collected, although the total amount of oil misting is conservatively estimated to be less than 1.5 gallons.
Source of Oil Leakage Engineering inspections and evaluation have determined the primary source of misting is the lower oil reservoir, which contains approximately 25 gallons of lubricating oil.
Small amounts of oil migrate through the labyrinth seal separating the oil reservoir from the stator ventilation airway. This labyrinth seal is located approximately 2 inches above the oil level. Due to the slightly negative pressure in the airway, small amounts of oil that migrate past the seal enter the ventilation airway and condense 1 accumulate Page 3 of 8
Serial NO.1 0-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Attachment 1 at the stator air cooler. This flow path is shown in Attachment 2 of this exemption request.
Additional misting or weeping may occur from the upper reservoir. Inspections have revealed some minor indications of oil on the upper portions of the motor, above the stator cooler. The source is believed to be the joint where the flywheel cover is attached to the motor. This joint is located above the oil level of the upper reservoir; however, it may be subjected to some contact with oil due to the turbulence created by the flywheel. Corrective actions are currently in progress to evaluate enhancements for sealing the flywheel cover joint. The flywheel housing is equipped with vents that have been verified dry (i.e., not sources of oil misting) during several recent inspections. As stated, the oil indications attributed to the upper reservoir are minor, and are limited to the upper portions of the motor, where temperatures are far less than that required for ignition.
This conclusion is based on the construction of the upper and lower oil reservoir pots and maintenance experience with these motors at the motor refurbishment facility. This conclusion was also verified with the Pump and Motor Specialist from the vendor who originally supplied the pump.
Historically, it is common over the normal operating cycle to lose varying amounts of oil, depending on factors including motor age, oil type, and containment type. It is not known precisely how much oil passes through the ventilation path in this manner.
However, vendor information indicates that approximately 0.5 to 1.5 gallons of oil can be lost over an 18 month cycle. Oil mist found outside of the oes is removed during each refueling outage.
The modification to be installed will collect the oil that accumulates on the motor stator cooler. This modification, is expected to prevent any pooling of oil outside the oes (i.e., to reduce the amount of oil mist escaping the OCS to a sheen only).
A catastrophic failure of the lower reservoir is not considered credible due to the rugged design of the reservoir and seal. In addition, a drip pan is installed as part of the oes directly under this reservoir to collect any other leakage from the reservoir not described above.
3.0 TECHNICAL JUSTIFICATION OF ACCEPTABILITY Fire Protection Features Linear heat detection is provided for each RCP. The heat detection is located in the space between the pump insulation and the volute area of the pump. Annunciation is provided in the Main Control Room. Additional fire protection features provided for containment consist of three portable extinguishers staged at the entrance of the personnel hatch, a 100 lb. wheeled CO2 unit on each floor of containment, a dry standpipe system, fire detection (smoke and heat) within the cable penetration area (elevation 262'-10"), heat detection for the Residual Heat Removal Pump area, and smoke detection within the containment air recirculation system.
Page 4 of 8
Serial No.10-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Attachment 1 Safe Shutdown Features Indication of the RCS hot leg temperature is provided in the Control Room by means of three Resistance Temperature Detectors (RTDs). These RTDs are located in the RCS piping in the RCP loop rooms. Their safe shutdown function is to provide temperature indication during core cooldown. RTDs are also installed in the cold leg; however, only the hot leg RTDs are credited Appendix R equipment.
There is no credible means for minor oil misting to impact the safe shutdown function of the hot legs RTDs. Loss of the hot leg RTDs in one loop does not affect safe shutdown because redundant indication is provided by the other two loops, which are physically separated from one another. Further, the hot leg RTDs and associated instrument wiring are not in the vicinity of the previously-identified oil puddles. Thus, the potential for a fire caused by RCP oil misting that could impact the safe shutdown function of the hot leg RTDs is not deemed credible.
Fire Hazards Analysis Prior to the modification of the OCS, some pooling / dripping of oil was observed on the RCP flange. Using industry fire modeling tools, it can be shown that if ignited, these small pools would result in fires of low heat release rates and small duration. In addition, there are no significant fire targets (additional combustibles or safe shutdown components) in the proximity of observed pooling that could be ignited or damaged.
The RCP flange is located directly below the motor stator cooler. The OCS modifications to be implemented during the next two refueling outages will install troughs below the motor stator coolers to collect any accumulation of oil. Uncollected oil misting that may occur following the planned modification is expected to be of significantly less volume than that prior to the modification and of sufficiently low volume to result only in a sheen, rather than accumulating into a puddle.
Additional defense in depth is achieved through the physical properties of the oil itself combined with the limited amount of ignition sources within the area. The flashpoint of the oil currently used is 374°F, with an auto-ignition temperature of 608°F. Nominal temperatures of the RCP motor and pump flange are approximately 220°F and 550°F, respectively. These temperatures would not be sufficient to cause auto-ignition of the oil. However, given the flashpoint of the oil, it is conceivable that the oil could be ignited in the presence of an ignition source.
A review of equipment in the area has identified one potential ignition source. The RCP IS in close proximity to the cold leg Loop Stop Valve (LSV) Motor Operated Valve (MOV). Due to the size of the LSV MOV actuator motor, it could be considered an Ignition source. However, the supply breakers to the cold leg LSVs is opened prior to start-up and administratively verified open throughout the cycle.
All other aspects reviewed were found to have negligible risk as an ignition source.
Transient combustibles and hot work are non-existent within the RCP cubicle during power operations. Area heat trace electrical cabinets have been abandoned and de-energized. There are a number of solenoid operated valves, MOVs, trip valves, and Page 5 of 8
Serial No.1 0-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Attachment 1 hand control valves in these areas; however, they are low energy components and are not considered credible ignition sources. Cables within the motor cubicles and loop rooms are routed in conduit. No cable trays are routed through the areas. Therefore, no other credible ignition sources exist within these areas.
Industry events have shown the most credible ignition source for RCP oil is hot RCS piping. Ignition has typically occurred due to the oil soaking combustible insulation.
Combustible insulation is not used at North Anna; the intermediate leg and cold leg piping are insulated with reflective, non-combustible insulation.
At normal operating conditions, no credible fire hazard from the oil misting would exist in the motor cubicles or loop rooms due to the RCS operating temperature being below the auto-ignition point of the oil. This is also true during all design basis accidents (DBAs), with the exception of one scenario. During a main feedline rupture event inside containment, which is an ANS Condition IV event, the cold and intermediate legs reach a peak temperature of 639°F after approximately 126 minutes. Thereafter, RCS temperature will decrease slowly with auxiliary feedwater heat removal capacity exceeding core decay heat plus RCP heat.
Under these specific DBA conditions, the RCS piping would only present a fire hazard if the oil mist were to seep through the insulation and make contact with bare RCS piping.
As stated above, no oil accumulation was identified on this RCS piping during previous walkdowns and insulation would be expected to remain in place during this DBA. In addition, containment spray systems would be in operation, which would further reduce the potential of a fire. Finally, combustible materials within the RCP cubicles and loop rooms are negligible and not sufficient to promote fire propagation. In aggregate, Dominion concludes that any postulated fire would be insignificant and bounded by those previously discussed above.
In summary, the modifications to the OCS scheduled to be installed during the next refueling outages will eliminate the potential for oil pooling to occur outside the OCS.
The remaining oil sheen that may develop due to misting does not present a safety concern due to the small volume of oil, fire protection features such as automatic fire detection, manual suppression capability, the physical properties of the oil, and the limited presence of ignition sources within the area.
Industry Experience with Oil Misting Dominion has contacted several nuclear power stations and concluded the following:
- The phenomenon of minor oil misting from RCP motors is a common experience and not all misting can be collected,
- Some stations have performed specific evaluations in the past of the misting condition (similar to the Fire Hazards Analysis discussed above) and have found no impact on Safe Shutdown Capability, and
- Not all collection systems are the same; however, most have a catch pan at the bottom of the motor to collect any significant leakage down the shaft and no Page 6 of 8
Serial No.10-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Attachment 1 direct method of capturing oil misting (similar to NAPS).
Dominion's vendor for RCP motor refurbishment was also contacted. Their technical representative has experience with RCP motors from a number of nuclear power stations and has overseen the refurbishment of four North Anna motors. He confirmed that the misting issue is not uncommon and that he had personally observed it in his experience with the industry.
Previous Exemptions from 10 CFR 50, Appendix R. Section 111.0 Two previous permanent exemptions to 10 CFR 50, Appendix R, Section 111.0 are germane to this request. Both exemptions allowed at least 15 gallons of combustible liquid to be uncollected by the OCS on the basis that modifications to the OCS would not provide a significant increase in fire safety.
The first exemption was granted to the La Crosse Boiling Water Reactor (LACBWR)
[LS05-81-06-004]. They reduced the quantity of flammable liquid in their lube oil system from 90 gallons to 15 gallons by replacing existing inventory with a non-flammable fluid.
The NRC concluded LACBWR did not need to install an OCS because providing collection for the remaining 15 gallons of flammable lube oil "would not enhance fire protection safety."
The second exemption was granted to Big Rock Point [LS05-82-04-014]. This exemption was based on two conclusions from the NRC fire analysis. First, the entire lube oil inventory of a single pump was 31.75 gallons and complete combustion of this entire inventory did not present a significant hazard. Second, the potential for leakage of the entire quantity of oil was small and any credible fire would be of a limited magnitude.
Following the planned modifications, less than 1.5 gallons of oil are expected to mist out of the North Anna RCP during an operating cycle.
4.0 JUSTIFICATION OF EXEMPTION 10 CFR 50.12, "Specific Exemptions," states that the NRC may grant exemptions from the requirements of the regulations of this part of the Code of Federal Regulations provided three conditions are met. The three conditions are: 1) the exemption is authorized by law; 2) the exemption will not present an undue risk to the health and safety of the public; and 3) the exemption is consistent with the common defense and security.
The requested exemption to address expected minor oil misting which results in a fine sheen, not pooling, satisfies these criteria as described below.
- 1. This exemption is authorized by law.
As required by 10 CFR 50.12 (a)(I), this requested exemption is "authorized by law."
The safety intent of 10 CFR 50, Appendix R, Section 111.0 is to ensure that safe shutdown capabilities will not be compromised by a fire associated with oil leakage during either normal or design basis accidents. The NRC has in the past used their Page 7 of 8
Serial NO.1 0-114 Docket Nos. 50-338/339 10 CFR 50 Appendix R Exemption Request Attachment 1 authority under Section 50.12 to grant exemptions from the requirements of Section 111.0.
Exemptions have been granted for systems that meet the functional intent of this regulation, but do not meet verbatim compliance with it. In addition to those previously discussed, General Letter 86-10 addressed an exemption for systems that utilize splash guards in conjunction with a sump system instead of a leakage collection system with drain lines. Regulatory Guide 1.189 also allows an exemption to be taken for oil collection tanks whose capacity is only sufficient to hold the oil inventory of a single RCP motor, instead of the entire lube oil system inventory, provided the RCP motors themselves are seismically qualified.
By submitting this exemption request, Dominion does not seek an exemption from the safety intent of 10 CFR Part 50, Appendix R, Section 111.0. The intent of the request is solely to address the generic concern of minor, uncollected oil misting that results in a fine sheen of oil, for which there is a negligible fire hazard.
- 2. This exemption will not present an undue risk to public health and safety.
Section 3.0 of this exemption request addresses the potential consequences of a fire that could result from minor oil misting. As indicated in that section, any minor misting that may not be collected by the OCS would be bounded by the Fire Hazards Analysis contained in Section 3.0 of this exemption request. This analysis demonstrated such a postulated fire would neither adversely impact the safe operation nor the safe shutdown capability of the plant. Defense in depth is also provided by the limited availability of ignition sources outside the OCS. Thus, the granting of this exemption request will not pose an undue risk to public health and safety.
- 3. This exemption is consistent with common defense and security.
Minor oil misting from the RCP motor will not adversely affect safe shutdown of the plant and will not compromise common defense and security.
5.0 CONCLUSION
S Planned modifications to the RCP motor stator cooler will provide oil collection capability of the small amount of oil accumulation previously observed at this location. Following this modification, the North Anna OCS will meet the safety intent of 10 CFR 50, Appen-dix R, Section 111.0 to assure failure of the lube oil system will not lead to fire during normal or design basis accident conditions. However, minor oil misting is expected to continue and may not be collected by the OCS. Any uncollected oil would be bounded by existing fire hazards and would not adversely impact the safe operation of the plant.
Based upon the preceding evaluation and consistent with 10 CFR 50.12, an exemption from 10 CFR 50, Appendix R, Section 111.0 is requested for cases in which minor oil misting from the RCPs is uncollected.
Page 8 of 8
Serial No.10-114 Docket Nos. 50-338/339 Attachment 2 FLOW PATH OF OIL FROM THE LOWER POT THROUGH THE MOTOR STATOR COOLER Virginia Electric and Power Company (Dominion)
North Anna Power Station Units 1 and 2
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