ML20212H835
| ML20212H835 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 02/27/1987 |
| From: | Whittier G Maine Yankee |
| To: | Thadani A Office of Nuclear Reactor Regulation |
| References | |
| 8307L-GDW, GDW-87-13, MN-87-08, MN-87-8, NUDOCS 8703060232 | |
| Download: ML20212H835 (6) | |
Text
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MAIRE HARHEE MGMIOPOWER00MPARSe auavg,,K,?n"e o",le g
(207) 623-3521 e
February 27, 1987 MN-87-08 GDH-87-13 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington, D. C.
20555 Attention:
Mr. Ashok C. Thadani, Director PHR Project Directorate #8 Division of Licensing
References:
(a)
License No. DPR-36 (Docket No. 50-309)
Subject:
Maine Yankee Safety Improvements Gentlemen:
This letter provides a summary of some of the Maine Yankee activities conducted auring 1986 to improve plant safety.
Included are those associated with the resolution of NRC regulatory issues and those independently undertaken by Maine Yankee. Modifications planned for the 1987 refueling cutage have been included since they were initiated during 1986. A summary of major efforts to improve plant safety which were completed during 1984 and 1985 is provided as Attachment A.
Seismic - Maine Yankee agreed to participate in a seismic margins research program, to identify seismic margin inherent in the Maine Yankee design. This effort identified several areas where the seismic margin of l
the plant could be improved.
Several improvements, including replacement of two safety class station batteries, are scheduled for the upcoming refueling outage.
This study together with the resultant seismic improvements should resolve staff concerns regarding to adequacy of Maine Yankee Seismic Design.
Inadequate Core Cooling Instrumentation - In response to NRC staff concerns about the adequacy of Maine Yankee's Inadequate Core Cooling Instrumentation (ICCI), a redesign of the system has been proposed which should resolve staff concerns.
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MalNC YANKEE ATOMIC POWER COMPANY
' United States Nuc1 car Regulator Commission Page Two Attn: Mr. Ashok C. Thadani, Director MN-87-08 Renctor Coolant Pump Shaft Integrity - In response to NRC staff concerns about similarities between the Crystal River and Maine Yankee Reactor Coolant Pump Shaft designs, we performed an evaluation of the Maine Yankee shaft design and the effects of a postulated shaft failure.
He also developed a program for RCP shaft refurbishment.
The staff has accepted our response as adequate resolution of the issue.
Demineralized Hater Storage Tank Instrumentation - As a result of NRC staff concerns about the reliability of demineralized water storage tank level alarms, Maine Yankee agreed to install an additional alarm resolving the issue.
Pressurized Thermal Shock - Maine Yankee submitted a report in January of 1986 which demonstrated that NRC screening criteria would not be exceeded until approximately the year 2050.
The staff has accepted our report setting aside this concern for the licensed life of the plant.
4 Probabilistic Risk Assessment - Maine Yankee has began the development of a Probabilistic Risk Assessment (PRA). When completed, th_e PRA should enable us to better identify contributors to risk and to assess the safety contribution of proposed plant design changes.
Control Rods - He developed a program for the replacement of control rods to ensure their continued reliability. The program will begin with the replacement of fifteen control rods during 1987.
Fuel Rods - In order to improve the reliability of nuclear fuel, Maine Yankee, in conjunction with Yankee Nuclear Services Division and the fuel supplier, performed a review of the fuel design and the fuel manufacturing process. Several process improvements were made.
Steam Generator Tube Integrity - Industry studies have shown that copper ions in the steam generator enhance the corrosion of steam generator tubes. As a result, during the last several outages we have reduced the amount of copper tubing on.the secondary side by eighty percent. Another eight percent is scheduled for removal during the 1987 outage and the remainder before 1990.
In addition, the steam generators will be chemically cleaned during the 1987 refueling cutage to reduce the level of contaminants that could lead to tube degradation.
Improvements are also being made to the blowdown demineralizer and water treatment plant systems to improve the quality of steam generator makeup water.
Steam Drying Changes - The amount of moisture in steam is a primary contribution to piping and component erosion and failures.
During the 1987 refueling outage the steam generator moisture dryers will be replaced with larger, more efficient units and the moisture trapping system in the turbine exhaust installed in '.984 will be upgraded.
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MAINE YANKEE ATOMIC POWER COMPQNY United States Nuclear Regulator Commission Page Three Attn: Mr. Ashok C. Thadani, Director MN-87-08 Service Hater System Reliability - Two service water heat exchangers, which serve as the emergency core cooling system heat sinks, are being replaced with larger capacity titanium units to improve system capability and reliability.
. Steam Driven feed Pump Reliability - Several improvements were made to the-control systems for the. steam driven feed pump to improve the pump's reliability and reduce challenges to plant safety systems.
Feedwater Pipe Integrity - Following the feedwater pipe rupture incident at Surry, a program to inspect Maine Yankee's Feedwater Piping was developed and implemented.
Feedwater Check Valves - During the 1987 refueling outage, additional check valves will be _ installed in feedwater lines to reduce the likelihood of a damaging water hammer event.
Radiological Control Access to Primary Side - The Radiological
-Control l Checkpoint area has been expanded and refurbished. Approximately 3000 ftz of additional space for expanded and improved radiological controls, chemistry and personnel facilities were included in the area modification.
Chemistry Lab - The primary side chemistry laboratory has undergone general refurbishment to provide for additional workspace, improved equipment, and additional storage cabinets, facilitating more efficient operation.
This letter has summarized the major efforts to improve plant safety completed in 1986, or currently underway. Major design changes to improve plant safety completed during 1984 and 1985 are summarized in Attachment A.
Please contact me if you should have any questions.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY hW G. D. Whittier, Manager Nuclear Engineering and Licensing GD6'/bj p Attachment cc: Mr. Richard H. Vollmer Mr. Pat Sears Mr. Cornelius F. Holden 8307L-GDH
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- MAINE YANKEE ATOMIC POWER COMPANY
' ATTACHMENT A RE' CENT DESIGN CHANGES T0 THE ~ MAINE YANKEE ATOMIC P0HER PLANT.
TO IMPROVE PLANT SAFETY AND RELIABILITY.
~ STEAM GENERATOR CORROSION CONTROL Maine. Yankee.has always been aggressive and proactive in preserving steam generator integrity. As a result, it has operated.14 years without a Ltube'-
s leak.(perhaps a~world record for.PHRs). ~Hithin the,last three1 years the
- following_ additional design' changes have been-implemented to better control-corrosion:
' Secondary Side Boration System e
. This system permits faster ard more accurate control of steam-generator boron concentration. Boron is used as a buffer to' retard
. corrosion.
In addition to helping _ control corrosion, the system:
-reduces'the time necessary to conduct startup pretreatment operations, so it improves plant availability.
_ Wet Lavuo Recirculation System This system permits faster and more efficient control of steam
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generator chemistry during' prolonged wet layup periods.
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. Automated Condenser Leakage Monitorina System
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This system was installed to automatically monitor each of the'four condenser tube. banks.for leakage rather;than the entire condenser.
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This permits faster and more accurate' identification of leakage reducing the amount-of ingress before protective actions are taken.
Steam Generator Blowdown Monitors This system continuously monitors blowdown pH, sodium concentration and cation conductivity.
It is a significant improvement over the earlier system of monitoring total conductivity supplemented by grab L
samples.
It permits earlier detection of off-rormal chemistry conditions aed, therefore, earlier and more accurate initiation of corrective meacires.
l Main Condenser Reolacaent
~
All four main condenser tube bundles were replaced with all titanium
' units..This change significantly reduces the frequency of condenser tube leakage minimizing the ingress of-aggressive cont (aminants.
Moisture Seoarator Reheaters
~
These four large heat exchangers were replaced with stainless steel units continuing our copper removal program.
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M AINE YANKEE ATOMIC POWER COMPANY 2-STEAM PLANT RELIABILITY Recognizing that steam plant problems are often precursors to more serious events, Maine Yankee has made many reliability improvements:
Feed Pumo Control System Changes These changes include modifications to reduce the probability of plant-trips due both to the inadvertent opening of the. feed pump recirculation valve, and those caused by spurious or transient low suction pressure signals.
Main Generator Stator Reolacement Stator failures have resulted not only in plant trips but in major fires in power stations. This change involved the replacement of the entire stator with a far more reliable unit.
Condenser Surce Tank Addition This change. involved the addition of a new tank and associated piping / controls to provide condenser hotwell surge and makeup.
This permitted the dedication of the Demineralized Water Storage Tank, previously used for this purpose, to emergency feed use.
The change resulted in improved reliability, quality and quantity of emergency feedwater.
Steam Dumo Control System Modification This system, which is used to mitigate a loss of load accident, has been improved by changes which permit its on-line testing for operability.
Modifications to Feedwater Preheat System This change reduces feedwater line thermal stress by automatically controlling preheater condensate level during hot standby condition.
Modifications to Excess Flow Check Valves This change involves the installation of improved valve operator components reducing the probability of spurious operation
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leading to plant trips.
New NNS Battery Bank The installation of a large additional battery bank permitted the removal of major non-vital electrical loads from the safety class batteries.
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M AINE YANKEE ATOMIC POWER C'OMPANY
- t Imorovement of Plant Cooldown Caoability A vacuum line was installed from the main condenser to the main steam non-return valves to allow use of the steam generators for reactor cooldown to a cold condition as an alternative to the normal residual heat removal system. _This decreases the time to
' achieve cold shutdown by twelve hours and reduces the thermal stresses imposed on the residual. heat removal system when placed in service.
-PRIMARY / SAFETY SYSTEM RELIABILITY IMPROVEMENTS Many improvements have been made to increase the reliability of safety system components. ~ Examples of these initiatives include:
RHST Level Transmitters Refueling Water Storage Tank (RHST) level switches were replaced with state-of-the-art transmitters which produce a more accurate and reliable signal for level indication and control functions.
Charaina Pumo Temoerature Monitorina System Resistance Temperature Directors (RTD) where added to the discharge line of each charging pump to provide computer-generated temperature indication and an alarm message on pump high discharge temperature. The conservative alarm setpoint will provide adequate warning to prevent damage from overheating to these pumps.
These pumps also function as High Pressure Safety Injection (HPSI) pumps.
Reactor Coolant Pumo Refurbishina Maine Yankee has initiated a program to refurbish the Reactor Coolant Pumps (RCP) motors. During the Cycle 8/9 refueling outage', one RCP motor was removed from service and replaced with a new motor. The old motor was refurbished and will be returned to service during the next refueling outage. This program will be continued until all three motors have been refurbished.
FACILITY CHANGES TO IMPROVE OUALITY OF OPERATION Several changes have been made to improve the efficiency and effectiveness of plant support activities. Perhaps the most significant of these changes was the addition of a plant specific simulator.
Maine Yankee was the first operating plant in New England to install a plant-specific simulator. The simulator, capable of simulating 27 plant systems plus simulation of the plant process computer, is used extensively for operator training. Other applications included NRC licensing examinations, Emergency Operator Procedure (EOP) set
. verification, and real-time response to emergency plan exercises and drills.
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