ML19323E334
| ML19323E334 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 05/19/1980 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Rubenstein L Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8005230405 | |
| Download: ML19323E334 (19) | |
Text
,
s 400 Chestnut Street Tower II May 19, 1980 Director of Nuclear Reactor Regulation Attention:
Mr. L. S. Rubenstein, Acting Chief Light Water Reactors Branch No. 4 l
Division of Project Management U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Mr. Rubenstein:
In the Matter of the Application of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328
References:
1.
Letter from L. S. Rubenstein to H. G. Parris dated January 17, 1980 2.
Letter from L-M. Mills to L. S. Rubenstein dated February 7, 1980 In your letter dated January 17, 1980, you transmitted 14 questions to TVA regarding the diesel generator system at the Sequoyah Nuclear Plant.
Enclosed for your review are 10 copies of TVA's responses to these questions.
J Very truly yours, TENNESSEE VALLEY AUTHORITY n.
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L. M. Mills, Manager Nuclear Regulation and Safety i
Enclosure (10)
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i 105 80052SkB uut
8.35 Question:
Provide a discussion of the measures that have been taken in the design of the standby diesel generator air starting system to preclude the fouling of the air start valve or filter with moisture and contaminants such as oil carryover and rust.
(SPR 9.5.6, Part III, item 1).
Response
The starting air system at Sequoyah is arranged so that the compressor discharges air directly into an air receiver.
The moisture in the air may condense on the receiver wall and collect at the lowest point.
A " blow down" valve which is located at the low point is periodically cracked open to blow the collected moisture out of the receiver.
In addition, there is a line receiver to catch coarse rust particles., ion from the strainer at each engine air pipe connect This strainer is cleaned periodically.
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Q8.35-1
8.36 Question:
Experience at some operating plants has shown that diesel engines have failed to start due to accumulation of dust and other deleterious material on electrical equipment associated with starting of the diesel genera tors (e.g., auxiliary relay contacts, control switches - etc.).
Describe the provisions that have been made in your diesel generator building design, electrical starting system, and combustion air and ventilation air intake design (s) to preclude this condition to assure availability of the diesel generator on demand.
Also descrit, under normal plant operation what procedure (s) will be used to minimize accumulation of dust in the diesel generator room; specifically address concrete dust control.
In your response also consider the condition when Unit 1 is in operation and Unit 2 is under construction (abnormal generation of dust).
F.esconse:
Combustion air and ventilation air intakes are 18 feet above ground level.
Also, the combustion air system includes an oil-bath-type filter.
These features should restrict the introduction of dust into the diesel generator building.
In addition, provisions are made in the control relaying and switches to protect these items from accumulation of dust or other deleterious material by means of dust covers or enclosures.
Thus, dust will not have a deleterious effect on the availability and operability of the diesel generators.
Q8.36-1
a.37 Question:
The diesel generators are required to start automatically on loss of all offsite power and in the event of a LOCA.
The diesel generator sets should be capable of operation at less than full load for extended periods without degradation of performance or reliability.
Should a LOCA occur with availability of offsite power, discuss the design provisions and other parameters that have been considered in the selection of the diesel generators to enable them to run unloaded (on standby) for extended periods without degradation of engine performance or reliability.
Expand your PSAR/FSAR to include and explicitly define the capability of your design with regard to this requirement.
(SRP 9. 5. 5, Part III, Item 7).
Response
To our knowledge, there are no major diesel manufacturers that recommend no-or light-load operation.
The complications that can arise from extended no-load operation have been discussed at length with the diesel vendors.
In an effort to prevent the culmination of these complications, our operation of engines at no loaa has been minimized.
During the monthly diesel operability demonstration, the generators are loaded 100 percent to burn out the accumulated residue from no-load operation.
The emergency operating instructions are being revised to incorporate the procedure recommended by the vendor for burning out the residue accumulated at no-load operation during a loss of coolant accident (LOCA) with available offsite power.
Q8.37-1
8.38 Cuestion:
Section 9.5.4.1 emergency diesel engine fuel oil storage and transfer system (EDEFSS) does not specifically reference ANSI Standard N195 " Fuel Oil Systems for Standby Diesel Generators".
Indicate if you intend to comply with this standard in your design of the EDEFSS; otherwise provide justification for noncompliance.
(SEP 9.5.4, Rev.
1, Part II, item 12).
Response
The fuel oil system from the day tank to the engine is the standard system which has been developed by the engine manufacturer.
The fuel oil day tanks comply with paragraph 6.1 of ANSI N 195.
The engine fuel system is designed to be redundant utilizing an engine-driven and a direct-current motor-driven pump to supply fuel to the engine from the day tank.
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8.39 Question:
i Assume an unlikely event has occurred requiring operation of a diesel generator for a prolonged period that would require replenishment of fuel oil without interrupting operation of the diesel generator.
What provision will be made in the design of the fuel oil storage fill system to minimize the creation of turbulence of the sediment in the bottom of the storage tank.
Stirring of this sediment during addition of new fuel has the pocential of causing the overall quality of the fuel to become unacceptable and could potentially lead to the degradation or failure of the diesel generator.
Resconse:
The fuel oil storage tanks have baffles on all the truck fill nozzles to prevent sediment from be'ing stirred during filling.
i Q8.39-1 m
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8.40 Question:
Discuss the precautionary measures that will be taken to assure the quality and reliability of the fuel oil supply for emergency diesel generator operation.
Include the type of fuel oil, impurity and quality limitations as well as diesel index number or its equivalent, cloud point, entrained moisture, sulfur, particulates and other deliterious insoluble substances; procedure for testing newly delivered fuel, periodic sampling and testing of on-site fuel oil (including interval between tests), interval of time between periodic removal of condensate from fuel tanks and periodic system inspection.
In your discussion include reference to industry (or other) standard which will be followed to assure a reliable fuel oil supply to the emergency generators.
(SRP 9.5.4, Part III, items 3 and
- 4).
1 a
Resoonse:
Each shipment of No. 2 diesel fuel is checked for condensate entrainment, flash point, and viscosity at the plant.
Samples from each shipment are sent to our central laboratories where they are tested in accordance with Federal Requirement VVF8008.
The 7-day tanks are checked after each 1-hour diesel run (monthly) for cond ensate.
The stored fuel oil is checked for viscosity, sediment, and entrained moisture in accordance with the technical specifications.
Q8.40-1 l
8.41 Question:
Operating experience has shown that accumulation of water in the starting air system has been one of the most frequent causes of diesel engine failure to start on demand.
Condensation of entrained moisture in compressed air lines leading to contrei and starting air valves, air start motors, and condensation of moisture on the working surfaces of these componeats has-caused rust, scale and water itself to build up and score and jam the internal working parts of these vital components thereby preventing starting of the diesel generators.
In the event of loss of offsite power the diesel generators must function since they are vital to the safe shutdown of the reactor (s).
Failure of the diesel engines to start from the effects of moisture condensation in air starting systems and from other causes have lowered their operational reliability to substantially less than the desired reli, ability of 0.99 as specified in Branch Technical Position ICSB (PSB) 2
" Diesel Generator Reliability Testing" and Regulatory Guide 1.108 " Periodic Testing of Diesel Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants."
In an ef fort toward improving diesel engine starting reliability NUREG-0660 indicates that compressed air starting system designs include air dryers for the removal of entrained moisture.
The two air dryers most commonly used are the dessicant and refrigerant types.
Of these two types, the refrigerant type is the one most suited for this application and therefore is preferred.
Starting air shoald be dried to a dew point of not more than 500F when installed in a normally controlled 700F environment, otherwise the starting air dewpoint should be controlled to at least 100F less than the lowest expected ambient temperature.
Describe your diesel engine air starting system and indicate how your system meets the recommendation stated in NUREG-0660.
If there are any differences between your design and the recommendations of NUREG-0660, provide justification for your design or plans for implementaticn.
Response
There are presently no means of removing moisture from the starting air system at Sequoyah.
TVA's Division of Nuclear Power is presently investigating the possible l
l Q8.41-1
enhancement of the air start system that a refrigerant-or desiccant-type air dryer might provide.
The diesel generator vendor does not recommend the use of refrigerant type air dryers in applications where the ambient temperature is below 480-500 F.
Also, they run continuously to stay cold.
If air dryers are to be used, the vendor recommends that a Regenerative (Dual Tower) Desiccant type with a coalescing pre-filter and particulate after filter be used.
1 Q8.41-2
8.42 Ouestion:
Operating experience at certain nuclear power plants which have two cycle turbocharged diesel engines manufactured by the EJ ectromotive Division (E3D) of General Motors driving emergency generators have experienced a significant number of turbocharger mechanical gear drive failures.
The failures have occurred as the result of running the emergency diesel generators at no load or light load conditions for extended periods.
No load or light load operation could occur during periodic equipment testing or during accident conditions with availability of offsite power.
When this equipment is operated under no load conditions insufficient exhaust gas volume is generated to operate the turbocharger.
As a result the turbocharger is driven mechanically from a gear drive in order to supply enough combusion air to the engine to maintain rated speed.
The turbocharger and mechanical drive gear normally supplied with these engines are, not designed for standby service encountered in nuclear power plant application where the equipment may be called upon to operate at no load or light load condition and full rated speed for a prolonged period.
The E5D equipment was originally designed for locomotive service where no load speeds for the engine and generator are much lower i
than full load speeds.
The locomotive turbocharged l
diesel hardly ever runs at full speed except at full load.
The EMD has strongly recommended to users of this diesel engine design against operation at no load or light load conditions at full rated speed for extended periods because of the short life expectancy of the turbocharger mechanical gear drive unit normally furnished.
No load or light load operation also causes general deterioration in any diesel engine.
To cope with the severe service the equipment is normally subjected to and in the interest of reducing failures and increasing the availability of their equipment E5D has developed a heavy duty turbocharger drive gear unit that can replace existing equipment.
This is available as a replacement kit, or engines can be ordered with the heavy duty turbocharger drive gear assembly.
To assure optimum availability of emergency diesel generators on demand, applicant's who have on order or intend to order emergency generators driven by two cycle diesel engines manufactured by EKD should be provided with the heavy duty turbocharger mechanical drive gear assembly as recommended by EMD for the class of service encountered in nuclear power plants.
Confirm your l
compliance with this requirement.
Q8.42-1
Response
The diesel generators at Sequoyah were furnished with the normal turbocharger mechanical drive gear assembly which has a gear ratio of 18:1 and should be operated under the lindtations of Section 200.01 (see question
- 8. 3).
The heavy-duty drive gear assembly recommended by i
NUREG 0660 has a gear ratio of 16.8:1.
If installed, i
this would require reducing the rated engine output to 94 percent of that available with the 18: 1 gear ratio for the first 3 to 5 minutes of operation.
The heavy-j duty assembly will extend the accumulative time limits for the turbochargers to 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> at 0-20 percent load and 4000 hours0.0463 days <br />1.111 hours <br />0.00661 weeks <br />0.00152 months <br /> at 20-50 percent load.
The vendor has also informed us of another heavy-duty turbocharger drive gear assembly which will be available in the near future.
This assembly will have a gear ratio of 17.9:1 and will extend the accumulative time limits to that of the 16.821 assembly without reducing engine rating.
Before a decision to use the 16.8:1 assembly is made, a survey must be made to confirm that reducing the rated engine output to 94 percent of the present rating will not affect the capability of the diesel generators to perform their intended safety functions.
Q8.42-2
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8.43 Question:
Provide a detail discussion (or plan) of the level of training proposed for your operators, maintenance crew, quality assurance, and supervisor personnel responsible for the operation and maintenance of the emergency diesel generators.
Identify the number and type of personnel that will be dedicated to the operations and maintenance of the emergency diesel generators and the number and type that will be assigned from your general plant operations and maintenance groups to assist when needed.
In your discussion identify the amount and kind of training that will be received by each of the above categories and the type of ongoing training program planned to assure optimum availability of the emergency generators.
Also discuss the level of education and minimum experience requirements for the various ' categories of operations and maintenance personnel associated with the emergency diesel generators.
Response
TVA's Division of Nuclear Power is taking advantage of every available source of training to improve the level of understanding and expertise of our operating and maintenance employees.
The training is continuous in nature and encompasses all phases of proper operation and maintenance of our diesel generators.
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08.43-1
8.44 Question:
Several fires have occurred at some operating plants in the area of the diesel engine exhaust manifold and inside the turbocharger housing which have resulted in equipment unavailability.
The fires were started from lube oil leaking and accumulating on the engine exhaust 1
mainfold and accumulating and igniting inside the turbocharger housing.
Accumulation of lube oil in these areas, on some engines, is apparently caused from an excessively long prelube period, generally longer than j
five minutes, prior to manual starting of a diesel generator.
This condition does not occur on an i
emergency start since the prelube period is minimal.
When manually starting the diesel generators for any reason, to minimize the potential fire hazard and to j
improve equiment availability, NUREG-0660 recommends j
that the prelube period should be limited to a maximum j
of three to five minutes unless otherwis,e recommended by the diesel engine manufacturer.
l Provide the prelube time interval your diesel engine will be exposed to prior to manual start and if this 1
interval does not agree with the recommendations of NUREG-0660 provide justification why your interval time is acceptable.
Response
The lubricating oil system for the diesel generators at Sequoyah is designed to continuously supply oil to the engine moving parts while on standby.
Thus, a pre-lube period prior to manual starts is not performed.
Q8.44-1
8.45 Question:
An emergency diesel generator unit in a nuclear power plant is normally in the ready standby mode unless there is a loss of offsite power, an accident, or the diesel generator is under test.
Long periods of standby have a tendency to drain or nearly empty the engine lube oil piping system.
On an emergency start of the engine as much as 5 to 14 or more seconds may elapse from the start of cranking until full lube oil pressure is attained even though full engine speed ic generally reached in about five seconds.
With an essentially dry engine, the momentary lack of lubrication at the various moving parts may damage bearing sufaces producing incipient or actual component failure with resultant equipment unavailability.
The emergency condition of readiness requires this equipment to attain full rated speed and enable automatic sequencing of electric load within ten seconds.
For this reason, and to improv'e upon the availability of this equipment on demand, it is necessary to establish as quickly as possible an oil film in the wearing parts of the diesel engine.
Lubricating oil is normally delivered to the engine wearing parts by one or more engine driven pump (s).
During the starting cycle the pump (s) accelerates slowly with the engine and may not supply the required quantity of lubricating oil where needed fast enough.
To remedy this condition, as a minimum, an electrically driven lubricating oil pump, powered from a reliable DC power supply, should be installed in the lube oil system to operate in parallel with the engine driven main lube pump.
The electric driven prelube pump should operate only during the engine cranking cyle or until satisfactory lube oil pressure is established in the engine main lube distribution header.
The installation of this prelube pump should be coordinated with the respective engine manufacturer.
Some diesel engines include a lube oil circulating pump as an intregal part of the lube oil preheating system which is in use while the diesel engine is in the standby mode.
In this case an additional prelube oil pump may not be needed.
Indicate whether your design includes an electric prelube oil pump.
If your design does not include this pump, provide justification why it is not necessary.
Resoonse:
since the lubricating oil system for the diesel
{
generators at Sequoyah constantly supplies lubricating l
Q8.45-1 l
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9 oil to the engine while on standby, the system will a t drain the oil from the moving parts of the engine.
Thus, the problem of an emergency start with an essentially dry engine is not applicable to sequoyah.
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Q8.45-2
8.46 Question:
Periodic testing and test loading of an emergency diesel generator in a nuclear power plant is a necessary function to demonstrate the operability, capability and availability of the unit on demand.
Periodic testing coupled with good preventive maintenance practices will assure optimum equipment readiness and availability on demand.
This is the desired goal.
To achieve this optimum equipment readiness status, NUREG 0660 recommends the following:
1.
The equipment should be tested with a minimum loading of 25 percent of rated load.
No load or light load operation will cause incomplete combustion of fuel resulting in the formation of gum and varnish deposits on the cylinder walls, intake and exhaust valves, pistons and piston rings, etc., and accumulation of un, burned fuel in the turbocharger and exhaust system.
The consequences of no load or light load opera' tion are potential equipment failure due to the gum and varnish deposits and fire in the engine exhaust system.
2.
Periodic surveillance testing should be performed in accordance with the applicable NRC guidelines (R.G. 1.108), and with the recommendations of the engine manufacturer.
Conflicts between any such recommendations and the NRC guidelines, particularly with respect to test frequency, loading and duration, should be identified and justified.
3.
Preventive maintenance should go beyond the normal routine adjustments, servicing and repair of components when a malfunction occurs.
Preventive maintenance should encompass investigative testing of components which have a history of repeated malfunctioning and require constant attention and repair.
In such cases consideration should he given to replacement of those components with other products which have a record of demonstrated reliability, rather than repetitive repair and maintenance of the the existing components.
Testing of the unit after adjustments or repairs have been made only confirms that the equipment is operable and does not necessarily mean that the root cause of the problem has been eliminated or alleviated.
1 4.
Upon completion of repairs or maintenance and prior to an actual start, run, and load test a final l
Q8.46-1 I
equipment check should be made to assure that all electrical circuits are f unctional, i.e., fuses are in place, switches and circuit breakers are in their proper position, no loose wires, all test leads have been removed, and all valves are in the proper position to permit a manual start of the equipment.
After the unit has been satisfactorily started and load tasted, return the unit to ready automatic standby service and under the control of the control room operator.
Provide a discussion of whether the recommendations of NUREG-0660 have been implemented in the emergency diesel generator system design and how they will be considered when the plant is in commercial operation, i.e., by what means will the above requirements be enforced.
Response
1.
The diesel generator surveillance instructions and post maintenance instructions provide for the diesels to be loaded 100 percent during the monthly, quarterly, semiannual, and annual inspections and also af ter a major outage.
All feasible precautions have been taken to preclude accumulation of gum and varnish deposits in the exhaust manifolds.
2.
There are no discrepancies identified in this area.
3.
We are actively involved and dedicated to this recommended type of preventive maintenance program.
Common areas of component problems are transmitted between plaats for information.
Maintenance records and parts usage records are maintained for the purpose of identifying major problem areas.
4.
Upon completion of repairs or maintenance and prior to an actual start, run, or load test, the Sequoyah maintenance forces devised various job control forms to ensure a final equipment check, thus securing the operability of electric circuits.
Maintenance Instruction MI 10.1 covers the necessary steps to be taken to ensure this objective.
Surveillance Instruction SI.7 requires that various parts and components of a diesel generator system be visually inspected periodically to ensure that the system is mechanically and electrically operable.
Q8.46-2
The alignment of the four diesel generators for standby operaticn (checking of fuses, switches, circuit breakers, etc.) is verified by plant operation forces in accordance with System operating Instructions SOI.82.1, SOI.82.2, SOI.82.3, and SOI.82.4 In addition to the above instructions, all other emergency repairs or maintenance are controlled by plant maintenance request forms.
A post maintenance check, including removal of test signals and jumpers, is required as well as a post repair subsystem f unctional test prior to return to standby status.
This control is designed to verify that all wiring and related components disturbed during repair are returned to normal.
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08.46-3
8.47 Ouestion:
Experience at operating plants has shown that a diesel engine that is provided with an engine cooling water temperature control system employing a 3-way bypass-type thermostatically controlled valve have demonstrated consistent trouble free operation over engines provided with other methods of temperature control such as shutter controls on radiators.
Does your cystem employ a water thermostat of the 3-way or bypass-type which splits the water flow so only as much water passes through the cooler or radiator as needed to maintain the proper outlet temperature?
If your engine cooling water system does not use a 3-way valve, describe your installed system and justify its design as opposed to a design employing a 3-way valve.
Pesponse:
The cooling water system of the sequoyah diesel generators employs a three-way water temperature control valve.
Q8.47-1