ML18101B214
| ML18101B214 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 02/08/1996 |
| From: | Eric Simpson Public Service Enterprise Group |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LR-N96024, NUDOCS 9602130061 | |
| Download: ML18101B214 (13) | |
Text
Public Service Electric and Gas Company E. C. Simpson Public Service Electric and Gas Company P.O. Box 236, Hancocks Bridge, NJ 08038 609-339-1700 Senior Vice President - Nuclear Engineering f EB 0 8 1996 LR-N96024 United States Nuclear Regulatory Commission Document control Desk Washington, DC 20555 Gentlemen:
PROPOSED MODIFICATION TO REMOVE THE EMERGENCY DIESEL GENERATOR AIR START SYSTEM AIR DRYERS SALEM GENERATING STATION UNIT NOS. 1 & 2 FACILITY OPERATING LICENSE NOS. DPR-70 & DPR-75 DOCKET NOS. 50-272 & 50-311 Public Service Electric & Gas Company (PSE&G) proposes to modify the existing Emergency Diesel Generator (EDG) Air Start System.
The modification consists of removal of the desiccant air dryers, provisions for moisture contr61, and replacement of carbon steel components with stainless steel components and other corrosion resistant material.
The most significant problem with the air dryers resulting in poor performance has been the water retention and desiccant carry over in the system components.
PSE&G has determined that the proposed design change to delete the air dryers for Salem Units 1 and 2 and provide measures for moisture removal is an acceptable alternative for addressing the starting air moisture issue previously reviewed and approved by the Nuclear Regulatory Commission (NRC) in Safety Evaluation Report Supplement 5 (NUREG-0517).
However, because of the nature of the proposed design change, PSE&G requests NRC review and concurrence that the proposed alternative is acceptable.
The detailed description of the proposed design change and the justification for considering the proposed change as an acceptable alternative to the recommendations contained in NRC standard Review Plan (SRP) Section 9.5.6 and NUREG/CR-0660 for moisture removal in the EDG Air Start System is provided in.
PSE&G plans to complete the proposed design changes to the EDG air start system during the current outages for Salem Units 1 and
- 2.
The current outage schedule requires implementation of the proposed design changes to begin by March 13, 1996 for the first 1:1>.. Printed on
~
Recycled Paper sJ ~ n 69
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9602130061 960208 PDR ADOCK 05000272 P
Document Control Desk LR-N96024 2
FEB 0 8 1996 EDG.
In support of this schedule for implementation, NRC review and concurrence for the proposed change is requested by March 6, 1996.
Should you have any questions on this submittal, please contact us.
Sincerely, Attachment c
Mr. T. T. Martin, Administrator - Region 1
- u. s. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Mr. L. N. Olshan, Licensing Project Manager -
Salem U. s. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 14E21 Rockville, MD 20852 Mr. c. s. Marschall {X24)
USNRC Senior Resident Inspector Mr. Kent Tosch, Manager, IV Bureau of Nuclear Engineering 33 Arctic Parkway CN 415 Trenton, NJ 08625
LR-N96024 ATTACHMENT 1 PROPOSED MODIFICATION TO REMOVE THE EMERGENCY DIESEL GENERATOR AIR START SYSTEM AIR DRYERS SALEM GENERATING STATION UNIT NOS. 1 & 2 FACILITY OPERATING LICENSE NOS. DPR-70 & DPR-75 DOCKET NOS. 50-272 & 50-311 I.
INTRODUCTION Public Service Electric & Gas Company (PSE&G) proposes to remove the existing Emergency Diesel Generator (EDG) Air Start System air dryers under Design Change Packages (DCP) 1EC3401 and 2EC3349.
The air dryers have a history of poor performance that has resulted in extensive maintenance, moisture retention and desiccant carry over in the system.
The compressors and air dryers only operate intermittently for 10 to 15 minutes and the air dryers may not have sufficient cycle time to ensure desiccant is properly regenerated.
The air dryers may have been saturated due to improper moisture removal by the moisture separator and trap.
Because of the ineffectiveness of the air dryers to perform their design function, moisture still exists in the carbon steel system and is causing rust.
The proposed design change will replace the carbon steel components with stainless steel components and other corrosion resistant material, with the exception of the existing air receivers that are carbon steel and will not be replaced.
NRC Standard Review Plan (SRP) (NUREG-0800), Section 9.5.6 recommends that measures be taken in the design of the EDG Starting Air System to preclude fouling of the air start valve or filter with moisture and contaminants such as oil and rust carryover.
The SRP states that an air dryer(s) should be installed upstream of the air receivers for the removal of entrained moisture.
The SRPs (NUREG-0800) are intended to provide guidance to licensees, and alternatives may be proposed that provide an acceptable method of complying with the recommendations of the SRPs.
The proposed design change to replace existing carbon steel material (with the exception of the air receivers) with non-corrosive material and upgrade components, along with measures for moisture removal for Salem Units 1 and 2, is considered an acceptable alternative to the installation of air dryers in the EDG starting air system previously reviewed and approved by the NRC in Safety Evaluation Report Supplement 5 (NUREG-0517), and the recommendations of NUREG/CR-0660, "Enhancement of On-Site Emergency Diesel Generator Reliability," and NRC Standard Review Plan (SRP) (NUREG-0800), Section 9.5.6.
However, because of the nature of the proposed design change, PSE&G requests NRC review Page 1 of 10
LR-N96024 ATTACHMENT 1 and concurrence that the proposed alternative to the recommendations contained in NUREG/CR-0660 and SRP Section 9.5.6 are acceptable.
The current licensing basis for the installation of the present desiccant air dryers is described in Section II.
The detailed description of the proposed design changes to support removal of the existing desiccant air dryers for Salem Units 1 and 2 and install stainless steel and corrosion resistant material and components is provided in Section III.
The justification for considering the proposed change as an acceptable alternative to the recommendations contained in NRC SRP (NUREG-0800), Section 9.5.6 and NUREG/CR-0660 for EDG Starting systems is provided in Section IV.
II.
CURRENT LICENSING BASIS FOR AIR DRYERS The proposed design change of using non-corrosive materials and upgraded components along with measures for moisture removal in place of the existing air dryers for Salem Units 1 and 2 is considered an acceptable alternative for addressing the moisture issue in the EDG starting air system as previously reviewed and approved by the NRC.
NUREG/CR-0660 provided specific recommendations on increasing the reliability of EDG's.
PSE&G was requested to address the following recommendations for Salem Unit 2 regarding the starting air system in response to a NRC Request for Additional Information (RAI) dated December 14, 1979:
Measures should be taken to preclude the fouling of the air start valve or filter with moisture and contaminants such as oil carryover and rust.
Condensation of entrained moisture in the air lines leading to the starting air SOVs and air start motors and condensation of moisture on the working surfaces of these components could cause rust, scale or water itself to buildup and score and jam the internal working parts of these components and could result in engine starting failures.
(NRC RAI Questions 8.1 and 8.7)
Starting air should be dried to a dew point not more than 50°F when installed in a normally controlled 70°F environment, otherwise the starting air dew point should be controlled to at least 10°F less than the lowest expected ambient temperature.
(NRC RAI Question 8.7)
In response to the NRC RAI Questions 8.1 and 8.7 concerning implementation of the recommendations of NUREG/CR-0660 (Letter dated February 14, 1980), PSE&G indicated that the design of the EOG starting air system will include desiccant air dryers to dry Page 2 of 10
LR-N96024 ATTACHMENT 1 the starting air to an atmospheric dew point of -100°F.
The response further states that this provision meets or exceeds the requirements of NUREG/CR-0660.
This design is similar for Salem Unit 1.
Based on the NRC review of the PSE&G response to the RAI, the NRC concluded that PSE&G provided reasonable assurance of diesel generator reliability based on conformance with the recommendations of NUREG/CR-0660 (See Safety Evaluation Report (SER) Supplement 5, Section 8.3 (NUREG-0517)).
The current Acceptance Criteria of NRC SRP (NUREG-0800) Section 9.5.6 for EDG Starting Systems includes the recommendation that starting air should be dried to a dew point not more than 50°F when installed in a normally controlled 70°F environment, otherwise the starting air dew point should be controlled to at least 10°F less than the lowest expected ambient temperature.
This Acceptance Criterion is identical to the recommendation contained in NRC RAI Question 8.7.
(Note: Salem Units 1 and 2 are not committed to the current SRPs (NUREG-0800).)
III. DESCRIPTION OF PROPOSED DESIGN CHANGE Each EDG is supplied with a starting air system and turbo boost system used to start the EDGs and attain rated speed after receipt of a start signal.
The starting air and turbo boost air receivers ensure sufficient air is available to start the EDGs during accident conditions.
The existing starting air system has an aftercooler, moisture separator, trap and air dryer to remove moisture entrained in the compressed air prior to discharge to the starting air receivers.
The turbo boost compressors discharge directly to the turbo boost receivers with no moisture removal equipment.
The turbo boost system is a separate system from the starting air system and is not impacted by the changes proposed below.
The attached Figure 1 provides the proposed configuration of the EDG starting air system from the starting air compressors to the air start motors and the booster rack connection.
The current air start system configuration has shown evidence of rusting which is a primary cause of component degradation that could potentially cause fouling of the solenoid operated valves (SOV) and failure of the air start motors.
Also several components and/or parts are obsolete and enhancements are required to utilize replacements and upgrade to current industry practice.
Removal of the air dryer units from the starting air system (including pre-and after filters) will minimize maintenance and eliminate the potential for water retention in the dryer and Page 3 of 10
LR-N96024 ATTACHMENT 1 desiccant carryover to the starting air receivers.
In support of the removal of the air dryers, the following starting air system piping and components will be replaced with stainless steel and other corrosion resistant material (except the air compressors and receivers which are not being replaced) to minimize the rusting within the systems:
Component and piping replacement with stainless steel and removal of the air dryers to minimize rusting and reduce maintenance.
Replacement of isolation and check valves with stainless steel, soft seated ball valves and in-line check valves constructed for ease of maintenance and operation and to increase seat tightness.
Replacement of moisture separator and trap with high efficiency components constructed of stainless steel.
Replacement of the associated starting air pressure regulating valves for the air start motors (bronze) and booster air pistons (aluminum) that include a strainer, and the air start motor solenoid-operated valves (SOVs)
(aluminum) to enhance operation and maintenance.
Replacement of the starting air pulsation dampeners with larger stainless steel units.
Also, the new in-line check valves are better suited for pulsation service.
The following additional design changes will be implemented to improve moisture removal and prevent fouling of the air start motors, sovs and associated pressure regulators, and booster air pistons due to moisture and contaminants:
New in-line strainers (20 mesh) will be installed (in addition to those installed in the new regulating valves) in the air line to the air start motors to eliminate the potential for rust and particulate from the air receivers getting into the air start motors, booster air pi~tons and associated SOVs and pressure regulators.
The strainers will have a blowdown valve to periodically remove rust particles collected in the strainer.
Inspection and cleaning of the existing receivers will be performed to remove corrosion products and other particulates that could reach the regulating valves, SOVs, and air start motors.
Installation of stainless steel, soft-seated globe valves Page 4 of 10
LR-N96024 ATTACHMENT 1 designed to enhance blowdown of the receivers and ensure efficient water removal.
Each EDG upgraded starting air system will have a new stainless steel aftercooler, moisture separator with automatic trap, and coalescing afterfilter to minimize moisture and particulates getting into the carbon steel air receivers.
In addition, the piping layout will result in drainage away from the air receivers and towards the moisture separator.
In addition, the existing obsolete starting air motors will be replaced with new starting air motors which have higher torque and therefore, are more efficient in starting the diesel.
The tubing connection to each booster air piston is currently stainless steel and will not be replaced.
The existing SOVs to the booster air pistons and the booster air pistons are currently constructed with corrosion resistant material (bronze, brass and stainless steel) and also will not be replaced.
As indicated above, only the pressure regulator to the booster air piston will be replaced.
Experience with instrument air and starting air systems has shown that effective periodic blowdown has significantly reduced water accumulation in the system and components.
Recent inspection of the starting air system receivers did not indicate evidence of water accumulation inside the receivers.
Indication, however, of light surface rusting and flaking was observed.
The existing practice to periodically blowdown the receivers to remove water and debris will continue.
IV.
JUSTIFICATION FOR PROPOSED DESIGN CHANGE The proposed change will remove the existing air dryer (including pre-and after-filters) due to heavy maintenance and poor performance.
The most significant problem with the air dryer resulting in poor performance has been the water retention and desiccant carry over in the system components.
The dryer, which is not designed to eliminate liquids, is suspected to be flooding and overloading the desiccant capabilities resulting in moisture and rusting within the system.
NUREG/CR-0660 identified that water accumulation in the starting air systems has been one of the most frequent causes of diesel engine failure to start on demand.
NUREG/CR-0660 recommended the use of air dryers, particularly refrigerant type, in diesel starting air systems for moisture removal.
Corrosion resulting Page 5 of 10
LR-N96024 ATTACHMENT 1 from entrained moisture could result in fouling of the air start sovs, air start motors, booster air piston and associated SOVs and pressure regulators that could result in engine starting failures.
Also, condensation of entrained moisture in the air lines leading to the sovs, booster air piston and air start motors and condensation of moisture on the working surfaces of these components could cause rust, scale or water itself to buildup and score and jam the internal working parts of these components and could result in engine starting failures.
Use of Corrosion Resistant Material Replacement of material and components that provide starting air to the air start motors from carbon steel to stainless steel and other corrosion resistant material will be performed with the exception of the air receivers which will remain unchanged.
The piping connection to the booster air piston is currently stainless steel and will not be replaced.
The existing SOV to the booster air piston and the booster air piston are currently constructed with corrosion resistant material (bronze, brass and stainless steel) and also will not be replaced.
The pressure regulator to the booster air SOV and piston will be replaced as part of the proposed change.
Although the moisture in the system may increase slightly, the change to stainless steel piping and components (except the air receivers) and the use of other corrosion resistant materials minimizes the potential for generating rust and contaminants within the system that could cause fouling of the SOVs, filters, air start motors or booster pistons.
New in-line strainers in the air line to the starting air motors and the booster air pistons will minimize the potential for rust from the air receivers fouling the starting air motors and valves.
The new in-line strainers will be provided with a blowdown valve to periodically remove rust particles collected in the strainer.
The strainer will be blown down after each EOG start in accordance with Technical Specification surveillance test requirements to remove potential contaminants.
The pressure regulators will also be provided with internal filters to minimize the potential for rust and contaminants from fouling the regulating valves.
In addition, a coalescing afterfilter is installed upstream of the starting air receivers to remove particulates, oil, and water prior to reaching the receivers.
The afterfilter cartridge will be inspected and replaced every refueling outage.
The sudden carryover of deposits downstream of the air receiver Page 6 of 10
LR-N96024 ATTACHMENT 1 upon a start demand is precluded by the routing of the air line which exits from the top of the receivers and by the frequent blowdown of the receivers discussed below to remove moisture.
Moisture Control to Prevent Fouling The new system will have an upgraded stainless steel aftercooler, moisture separator with automatic trap, and coalescing afterfilter to minimize moisture, oil and particulate getting into the carbon steel air receivers.
The moisture separator will remove 99% of entrained liquid and solids which exceed 10 microns in size and the afterfilter will remove 93% of 0.1 micron oil, water, and particulate.
In addition, the piping layout will result in drainage away from the air receivers and towards the moisture separator.
Experience with instrument air and starting air systems has shown that effective periodic blowdown has significantly reduced water accumulation in air systems and components.
The receivers are blown down twice a day, and this practice will continue for the starting air system in accordance with current operating procedures.
Recent inspection of the starting air system receivers did not indicate evidence of water accumulation inside the receivers.
No specific air quality requirements have been identified for the starting air motors, however, the starting air should be free of condensation.
A prime consideration is that the starting air is lubricated using an appropriate lubricant.
The effect of moisture in the air is minimized by the presence of the lubricating oil, which provides corrosion protection.
While corrosion can occur within the starting air motor, the motors themselves are tolerant of moisture, providing the moisture present is not allowed to accumulate within the motor.
The vendor installation instructions provided for these motors recommends routing the starting air line from the top of the receiver and orienting the air start motor exhaust downwards so as to minimize collection of moisture (assumed present) in the incoming air.
This good design practice currently exists in both the pre-and post-mod configuration as supported by piping and component layout.
In addition, the starting air motor exhausts will remove any significant moisture introduced following diesel starting.
The long term effects on the starting air motors, assuming saturated air, is minimal based upon the short duration (less than 10 seconds) that the starting air motor is operated, and the periodic surveillance and inspections that are performed.
The air start motors, booster air pistons and associated sovs and regulating valves are tested as part of periodic surveillance Page 7 of 10
LR-N96024 ATTACHMENT 1 testing (starting) of the EDGs.
The starting air motors are currently replaced with new or refurbished motors every second refueling outage.
The starting air motor SOV and booster air piston sov are normally closed and are susceptible to moisture and particulates collecting at the valve.
As discussed above, the use of moisture removal equipment, periodic blowdown of the air receivers, and the in-line strainers will prevent moisture and particulates from reaching the SOVs.
In addition, the sovs are fabricated from material which is corrosion resistant.
The starting air pressure to the air start motors and booster air piston is reduced by the in-line pressure regulators as shown on Figure 1.
The capacity of air to hold moisture increases with decreasing pressure.
Air saturated at 250 psig will no longer be saturated when regulated to 150 psig or 100 psig to the starting air motors and booster air pistons, respectively.
The air to the starting air motors is vented directly to the atmosphere through the motor exhaust during the EDG start, and the air is isolated by the closure of the SOV after the EDG start (10 seconds).
The air to the booster air piston is admitted by opening a 3-way sov, and is vented back through the sov which vents to atmosphere after the EDG starts.
Therefore, condensation is not expected to occur in these components during engine starts.
The specific requirement to dry the air to a dewpoint at least 10°F below the lowest expected ambient temperature will no longer be met.
With the use of stainless steel virtually eliminating rusting in the piping system, the use of the moisture separator, coalescing afterfilter, and strainers to remove moisture, oil, and particulates, venting of the booster rack and starting air motors, and the continued effective practice of blowdown, the intent of the NUREG/CR-0660 requirements will be met.
Therefore, the reliability of the starting air system will not be adversely impacted by the removal of the air dryer.
The NRC has indicated during the operating license review of another plant that other alternatives to the use of air dryers would be the elimination of all ferrous materials (carbon steel) in contact with starting air in conjunction with some system for moisture reduction.
With the exception of the air receivers, the.
proposed design changes to be made in conjunction with removal of the air dryers and the planned maintenance activities discussed below will continue to ensure that fouling of the air start motors, booster air pistons, filters, pressure regulators or sovs due to moisture or contaminants such as rust that could result in engine starting failures will not occur.
Page 8 of 10
LR-N96024 ATTACHMENT 1 Planned Recurring Maintenance Activities The following maintenance activities are planned or will continue to provide further assurance that the starting air system motors, booster air pistons, and associated sovs and regulating valves will not be fouled due to condensation and particulates.
Blowdown receivers twice a day in accordance with current procedure. -This procedure will be revised to include the requirement to blowdown the moisture separator at this frequency to provide indication that the automatic trap is functioning properly.
Blowdown each in-line strainer after each EDG start performed in accordance with Technical Specification surveillance test requirements.
Replace afterfilter cartridge during each refueling outage.
Replace or rebuild the air start motors every second refueling outage in accordance with current plant procedure, or at an interval defined based on operating experience and condition of the new air start motors to be installed.
The sovs and pressure regulators are replaced or refurbished periodically as per the current Preventive Maintenance (PM)
Program.
The frequency for inspections and determination of maintenance requirements for the sovs, pressure regulators (strainers) and booster air piston will be determined based on operating experience.
Inspections will be completed during the next refueling outage to ensure moisture and particulate removal effectiveness, and will be used to establish and change the above PM requirements, as necessary.
V.
SUMMARY
The upgraded starting air system will provide equivalent protection by preventing condensed moisture or particulates from reaching the starting air motors, booster air pistons and associated sovs and pressure regulators.
The periodic blowdown of the starting air receivers will preclude the buildup of moisture and contaminants in the system and the change to corrosion-resistant piping and components will minimize the production of corrosion products.
The in-line strainer and the capability to blowdown this strainer following diesel starts Page 9 of 10
0 LR-N96024 ATTACHMENT 1 performed in accordance with Technical Specification surveillance test requirements will further prevent contaminants such as rust from fouling the air start motors, booster air pistons and associated SOVs and regulators.
Venting of the air start motors and booster racks will remove excessive moisture following a diesel start.
Planned maintenance activities will provide further assurance that these components will not become fouled due to moisture or particulates.
Based on the above, PSE&G has determined that the proposed design change to delete the air dryers for Salem Units 1 and 2 and provide measures for moisture removal is an acceptable alternative for addressing the starting air moisture issue previously reviewed and approved by the NRC in Safety Evaluation Report Supplement 5 (NUREG-0517), and the recommendations of NUREG/CR-0660 and Standard Review Plan (SRP) (NUREG-0800),
Section 9.5.6.
Page 10 of 10
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