ML20196J128
| ML20196J128 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 06/30/1988 |
| From: | Drawbridge B YANKEE ATOMIC ELECTRIC CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| FYR-88-93, NUDOCS 8807060328 | |
| Download: ML20196J128 (5) | |
Text
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k Telephone (617) 8N*0 #
y TWX 110*300*I '9
. YANKEE ATOMIC ELECTRIC COMPANY y
1671 Worcester Road, Framingham, Massachusetts 01701 e
June 30, 1988 FYR 88-93 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555
References:
(a) License No. DPR-3 (Docket No. 50-29)
(b) Letter, USNRC to YAEC, dated April 27, 1988 (c) Letter, YAEC to USNRC, dated April 26, 1988 (d) YAEC, LER 50-29/87-15 Revision 1, dated April 26, 1988 (e) Letter, YAEC to USNRC, dated May 25, 1988
Subject:
Additional Information for Inspection Report No. 50-29/88-02
Dear Sir:
Reference (b) documents a safety assessment team inspection conducted by Mr. N. Blumberg on January 10 through 15, 1988 at the Yankee Nuclear Power Station, Rowe, Massachusetts and the Yankee Atomic Electric Company, Framingham, Massachusetts. Reference (d) documents our response to portions of Reference (b).
This letter provides Yankee Atomic Electric Company's response to the additional items in the latter.
l Reference (b) requested that Yankee Atomic respond to an unresolved item I
concerning the main steam line pressure switches. Areas of NRC concern and our responses are as follows:
l 1.
Technical Specification Limits Based on the failure analysis results and vendor recommendations, a l
program has been instituted that has maintained the plant within the Technical Specification limits, As discussed in the LER, Reference. (d), the routine monthly surveillance cycle is being perft-med biweekly until further evaluations are completed. The prel' nnary failure analysis by ASCO indicates that extrusion of an organic diaphragm due to the constant pressure experienced by the switches may be causing the malfunctions. ASCO recommended more frequent cycling of the pressure switches as a possible solution; therefore, each pressure switch is being cycled a minimum of three times during each surveillance test.
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.Unitid States Nucisar Regulatory Commission Juna 30, 1988 Page 2 FYR 88-93
- In addition to the cycling, additional switches have been ordered, and' based on their availability, the remaining pressure switches tthat have not been replaced during this cycle will be replaced to minimize the service time.. Since the' malfunctions appear to be related to.their time in service, frequent change outs will. assure the operability of the-switches.
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12.~
Steam Line Pressure Switches Yankee has a multi-phased approach to ensure that'the pressure switches perform properly.
a.
As discusaed above, the short-term actions have been to perform a failure analysis by ASCO with Yankee Nuclear Service Division (YNSD) and plant personnel present, perform surveillance of the switches more frequently, cycle the switches during each surveillance, and finally to replace switches on a shorter time interval.
b.
We are pursuing a 100% switch replacement for the 1988
. refueling outage. Vendors are being contacted to provide replacements of a different switch design that does not have organic material in direct contact with the process fluid.
c.
A test Lis scheduled at the plant to determine if syphons and snubbers can be added to the sensing lines to alleviate any potential for over pressurization as a mechanism for switch malfunction.
d.
We are also working with ASCO, the switch vendor, to review the present switch materials and design.
3.
Timeliness There has been no lack of attention in pursuing corrective actions for the main steam line pressure switches.- The pressure switches were installed in 1981 to provide signals to allow automation of the main steam nonreturn valves. The original set of 12 pressure switches operated from 1981 until 1985 without requiring replacement.
In the early years of switch operation, the data from the pressure switches were trended to conficm that setpoint drif t met the h
conservative design allowance. The switches were set at a nominal 270 psig and are only required to operate at 200 psig for main steam i
.ine break purposes.
The setpoint value has been conservatively set. There has been no instances where more than one of the three L
pressure switches on a line was found to be below the accident analyses requirement.
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i Unitzd States Nuclear Rsgulatory Commission Juna 30, 1988 Page 3 FYR 88-93 During surveillance ter.ing in 1985, ac was determined that two switches were found to operate outside of their Technical Specification limits. A first switch was replaced on July 18, 1985. A second switch was replaced on August 16, 1985.
This switch was disassembled at the plant, and ASCO was contacted based on.the visual inspection. The swit,S was sent to ASCO for their evaluation. A third _ switch was repla,ed on September 12, 1985.
This switch met the Technical Specifications limits, but was outside the surveillance tolerance criteria.
Based on the failures in 1985, a decision was made to coase atively replace all of the remaining nine switches that were part o the original installation. A decision was also made to start a 10CFR Part 21, evaluation. As part of that evaluation, an independent E
testing laboratory was contracted to perform a failure analysis on four switches. Two of the switches came from the group of three switches that were replaced.
In addition, a new unused switch was sent plus a switch that had only seen one month of service.
The evaluation by the independent lab included:
1.
A detailed visual exam of all four switches.
2.
Fourier Transform Infared Spectroscopy - Attenuated Total Reflectance (PTIR-ATR) of three diaphragms.
3.
A Differential Scanning Calorimetry (DSC) test on four diaphragms.
4.
thermomechanical analysis on four diaphragms.
As a result of the laboratory analysis in June of 1986, the Part 21 evaluation concluded that the problem was aging of the urethane disk and was most likely related to our process conditions and therefore, not reportable. This same conclusion was reached by ASCO independently based on visual examination. The conservative action of 100% switch replacement in 1985 was in agreeaient with the evaluation recommendations. This was confirmed by no switch replacements in 1986.
In 1987, a design change was also started to eliminate any possibility of overpressurization of the switches as the cause of tue aalfunction through installation of syphons and snubbers in the sensing lines. The effect on the response time of the pressure switches due to the addition of the syphons and snubbers is going to be assessed by a test at the plant prior to their possible use.
On December 3, 1987, two additional switches were found to be malfunctioning. Based on the previous failure analysis, the nature of these switch malfunctions, the plans for replacing the switches, and the design change to eliminate possible overpressurization, it was decided to continue the program of frequent surveillance and
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p Unitsd States Nuclear Rsguletory Commission Juns 30, 1988 Page 4 FYR 88-93 replacement. An expedited purchase of eight additional switches was pursued to ensure that adequate spare switches were available. The plant also increased the surveillance frequency on the switches from monthly to twice a month.
During the period between March 10 and March 26, 1988, an additional four switches were replaced due to deadband widening and setpoint drift.
Based on these additional findings, four pressure switches were sent to ASCO for failure analysis. Both the lead I&C engineer from YNSD and the Yankee plant I&C Supervisor attended the testing, performed on Apri: 5, 1988.
The formal results of the second failure analysis have not been received; however, based on the informal results, recommendations have been made by ASCO to exercise the switches more frequently.
This recommendation has been incorporated into the surveillances performed on the switches.
As discussed in Item 4 below, a second 10CFR Part 21, evaluation concluded that the recent switch failures be reported as a Part 21.
The switch failures were reported as a Part 21 on April 26, 1988.
The switches do not represen* a safety risk to Yankee because of our monitoring and replacement program, but it was reported to alert other utilitiec of the malfunctions.
As can be seen by the above discussion, substantial corrective actions have been taken over sometime to alleviate the malfunctioning of the pressure switches. The action included two independent laboratory failure analyses, two 10CFR Part 21 evaluations, and modification of our surveillance procedures to er.sure operation of the pressure switches within Technical Specification limits. Trending of the available testing parameters was initiated when the switches were installed and the vendor was informed and active in our corrective action program from the initial malfunction. We believe that our actions were proper and sufficient to maintain the plant in a safe condition, and the reporting of the latest preliminary testing results as a Part 21 gave the industry proper notification of a potential problem.
4.
Reportability Part of the investigation into the failed pressure switches was conducted at ASCO's facility on April 5, 1988. Based on witnessing the inspection of four failed pressure switches by Yankee personnel, and the verbal recommendations of ASCO's engineering personnel, a Part 21 review of the f ailures and plant conditions was commenced.
This review was completed on April 25, 1988, and it was determined that this was reportable. A letter was sent to Region 1 of the USNRC on April 26, 1988 in accordance with 10CFR21.
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-United Sts:ss Nuciser R guistory Commission Juna 30, 1988 Page 5 FYR 88-93 s.
The inspection report, Keference (b), also noted the following weaknesses. Yankee's response to eacb is as follows:
o There. appeared to be a occasional lack of aggressiveness in resolving problems observed during plant operation and a lack of a questioning attitude.
~ Reference (b) notes that an occasional complacency can occur in a highly successful operation. The conccrn is for the consistency of applications rather than the basic skills of the plant staff.
Standards and expectations will be re-emphasized to the plant staff during the third quarter of 1988 and plant management will monitor and correct this human factor in the future.
o Maintenance Support Department (MSD) concentrates on modifications rather than the plant maintenance activities.
Yank.e management has recognized this as a concern and are currently engaged in efforts to put together a comprehensive long-term plan to effectively increase MSD's involvement in plant maintenance activities.
o Vendor manual control.
The Vendor Technical Manual Control Program will be revise.1 by the end of 1988 to include those balance of plant technical manuals important te the reliability of the plant as well as safety related manuals.
If you have any questions or desire additional information, please
. contact us.
Very truly you s,
/
Y TJE ATOMI ELECTRIC COMPANY Jhu B. L. Dr wbridge Vice President and Manager of Operations WGJ/25.675 cc: USNRC Region I USNRC Resident Inspector, YNPS L
William V. Johnston Acting Director, Division of Reactor Safety, USNRC Region I
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