ML20212N873
| ML20212N873 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 08/07/1986 |
| From: | Tucker H DUKE POWER CO. |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| NUDOCS 8609020017 | |
| Download: ML20212N873 (4) | |
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i Dr. J. Nelson Grace, Regional Administrator U. S. Nuclear Reguistory Conunissiod Region II t
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101 Marietta Street, Nif, Suite 2900 Atlanta, Georgit 30323 L
Re: Catawba Vuelear Station,' Unit 2 Docket NU'.'50-414
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Dear Dr. Grace:
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Pursuant :fo Technical Specifications 4.8.M 1.3 and 6.9.2, please find attached a Special Report concerning the valid failure of Diesel Generator 2A which occurred on July 8, 1986. Since this is the 8th falldre of a Unit 2 diesel within thi last 100 vaUd -teits, additional information as required by Regulatory Guide
.12108, Section C.3.b'is included, d.
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Ral:B. Tucker
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Attachment cc: Director Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission M
Washington, D. C.
20555 NRC Resident Inspector Catawba Nuclear Station s
8609020017 860807 P LF' ADOCK 05000414 S
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r-d GENERAL The purpose of this report is to satisfy the requirements of Section C.3.b of Regulatory Guide 1.108, Revision 1 (Periodic Testing of Diesel Generator Units Used as Onsite Electrical Power Systems at Nuclear Power Plants). This section requires a special evaluation of the reliability of Diesel, Generator Units if the number of failures -in the last 100 tests is seven or more. On July 8, 1986 at 2054 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.81547e-4 months <br />, Diesel Generator (D/G) 2A experienced a valid failure. The valid failure on D/G 2A was the eighth failure within the last 86 valid tests for the Unit 2 D/G's.
It should be noted that as of July 8, 1986, D/G's 2A and 2B had only completed 86 valid tests (this includes the eight failures).
DESCRIPTION OF EIGHTH FAILURE OF UNIT 2 D/G's In an attempt to start D/G 2A for procedure PT/2/A/4350/02C (Available Power Source Operability Test), on July 8,1986 at 2054 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.81547e-4 months <br />, D/G 2A obtained rated speed in 19.01 seconds instead of less than or equal to 11 seconds as required by Technical Specifications. However, on the next successive start attempt at 2139 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.138895e-4 months <br /> for j
troubleshooting the cause of D/G 2A slow start, D/G 2A started in 6.73 seconds, and the D/G was declared operable. Upon review of the incident by management the next morning and in comparing the incident with previous intermittent failures of D/G 2A, it was suspected that fuel rack binding caused D/G 2A not to obtain rated speed in less than or equal to 11 seconds.
On July 9, 1986 at 0956 hours0.0111 days <br />0.266 hours <br />0.00158 weeks <br />3.63758e-4 months <br />, D/G 2A was removed from service to inspect the fuel l
racks. After the extensible rod assembly was disconnected from the governor, some difficulty was encountered when attempting to manually open the fuel racks. After operating the racks manually several times, a test to measure the force necessary to open the fuel racks revealed a reading of approximately 45#. After testing the I
fuel racks, the left and right fuel rack assembly was disconnected from the cross shaft to determine the exact location of the binding. It was found that the left bank fuel rack assembly required a significant amount of force to move-(20f as
. compared to 3# for the right bank). Causing the binding in the left bank fuel rack was misalignment of the fuel rack assembly bracket closest to the front of the engine (misalignment of this same bracket was determined to have caused previous l
D/G 2A failures). To achieve alignment on the bracket, it was necessary to raise l
the 3 racket higher with a shim. This could not be achieved, however, because the I
bracket was lodged against a flange on the left bank starting air header. To l
remedy the problem, the top of the bracket was ground down enough so that it could i
be raised to' achieve alignment but not come into contact with the starting air header flange.
Force necessary to open the left bank fuel rack was approximately 6f after lubricating the entire rack assembly and alignment of the bracket was completed. After connecting both left and right bank fuel racks to the cross shaft and then taking the force necessary to move the entire group, it was found to be approximately 40f. After completing a successful operability periodic test on D/G 2A, the D/G was returned to service on July'9, 1986 at 2330 hours0.027 days <br />0.647 hours <br />0.00385 weeks <br />8.86565e-4 months <br />.
i After reviewing the maintenance work on D/G 2A, it was determined that while the I
40f force to open the fuel racks was acceptable, it was still higher than desirable considering the work that had been performed. Therefore, it was decided to remove D/G 2A from service again to focus on other items that could possibly cause binding. After removing D/G 2A from service on July 15, 1986 at 0525 hours0.00608 days <br />0.146 hours <br />8.680556e-4 weeks <br />1.997625e-4 months <br />, maintenance found that the jpints that connect the left and right bank fuel racks j
to the cross shaft (Hein joints) were seized, thus preventing free movement of the racks. After replacement of those joints, force necessary to open the fuel racks was found to be 30f. The D/G was returned to service on July 16, 1986 at 0210
e-hours. Since vendor manuals did not specify a normal force to open the fuel racks, a similar test was performed on D/G IB, D/G 2B, and D/G 1A to use for comparative data. D/G 1B's reading was 35#, D/G 2B's reading was 50f, and D/G 1A's reading was 30f. The reading on D/G 2B seemed excessive compared to the other D/G's.
Even though start failures have not been a problem on D/G 2B, maintenance will'be f
performed on D/G 2B's fuel racks in an attempt to lower the reading to the 30#
range. Also, since D/G 2A's left bank fuel rack bracket was lodged against the starting air header, other D/G's were checked for the same problem. For each of the other D/G's, some clearance (although small) existed between the end bracket and the starting air header.
D/G 2A was verified operable by performing D/G 2A Operability Test. The total time D/G 2A was out of service to perform the nece<1ary corrective action on the fuel racks was 35 hours4.050926e-4 days <br />0.00972 hours <br />5.787037e-5 weeks <br />1.33175e-5 months <br /> and 4 minutes. The surveillance testing interval on Unit 2 j
D/G's will remain at 3 days which is in accordance with'Section C/2/d/4 of Regulatory Guide 1.108, Revision 1.
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PREVIOUS FAILURES (D/G 2B) 1 The first two failures on U it 2 D/G's occurred on D/G 2B.
One failure was caused n
by D/G 2B obtaining rated speed in 12.27 seconds during Solid State Protection System testing, greater than the required 11 seconds during Solid State Protection System testing, greater than the required 11 seconds maximum.
No problems of this type have been encountered on D/G 2B since.
The second failure on D/G 2B was caused by an overspeed condition which originated from a faulty fuel injector pump l
on cylinder 7R.
The pump was subsequently replaced. No failures have occurred on l
D/G 2B since the second failure occurred on February 10, 1986.
PREVIOUS FAILURES (D/G 2A)
Unit 2 failures number three through eight occurred on D/G 2A (failure number eight was described previously). Each failure was caused by the fuel racks binding while attempting to start D/G 2A.
Corrective action for t'ailures three through six was based on the suspected potential causes of the failures. Since D/G 2A would fail to start intermittently during this period, the actual cause of the start problems could not be observed. Corrective actions following each failure were based on suspected potential causes of the faiiares. After each corrective action was performed, D/G 2A would start properly and meet all surveillance test requirements.
While performing functional' verification of the corrective action for failure number seven, the root cause of all D/G 2A start failures was observed.
It was observed that the governor lever actuated to pull the fuel racks open. However, l
the fuel racks did not open, but the extensible rod assembly connected between the l
governor lever and the fuel rack cross shaft assembly became fully extended. After disassembling the racks, it was discovered that the left bank fuel rack assembly bracket closest to the front of the engine was misaligned, thus causing the binding. Alignment was achieved by placing a shim of proper thickness under the bracket. Also, the entire fuel rack assembly and linkage was cleaned and lubricated. The racks were verified to be free moving by manually opening and closing the racks and noting the minimal amount of force exerted to accomplish movement. However, from the information given previously, alignment on this bracket must have changed af ter failure seven since it was found to be misaligned i
again after failure number eight. All 35 starts between those two failures were satisfactory, and no problems were detected.
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..o e D/G 2B RELIABILITY ANALYSIS The following table outlines all tests on D/G 2B from completion of D/G 2B preoperational testing until July 8, 1986 in accordance with Regulatory Guide 1.108, Position C.2.a:
-Completed preoperational testing 1-31-86
-66 invalid tests
-40 valid tests (includes valid successes and failures)
-2 failures (occurred prior to Unit licensing)
-98% reliable (106 total starts with 2 failures)
D/G~2A RELIABILITY ANALYSIS The following table outlines all tests on D/G 2A form completion of D/G 2A
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preoperational testing until July 8, 1986 in accordance with Regulatory Guide 1.108, position C.2.a:
-Completed preoperational testing 1-13-86
-145 invalid tests
-46 valid tests (includes valid successes and failures)
-6 failures Since all failures have been start related, the most appropriate reliability analysis will compare start attempts vs. start failures rather than just considering valid tests as defined per Regulatory Guide 1.108:
-Completed 338 start attempts since records were first kept until July 8, 1986
-12 start failures (6 during troubleshooting with the engine inoperable) l
-Greater than 96% start reliability
-35 successful start attempts between lith and 12th start failure CONCLUSION From the information provided in this report, it has been shown that start failures since licensing are unique to D/G 2A and not generic. Also, since records were first kept on D/G 2A, D/G 2A has demonstrated an overall start reliability in excess of 96%. However, it is realized that alignment on the end bracket on the left bank fu(1 rack may have changed between failures seven and eight. D/G 2A did start when failure eight occurred, but was eight seconds slow. Readings of force to open fuel racks and subsequent testing showed D/G 2A capable of performing its intended function at all other times.
Additional maintenance on the fuel racks after the gfghth failure occurred was necessary to improve start reliability. To ensure that corrective actions taken for failure eight are adequate, fuel rack movement readings will be taken for D/G 2A on a weekly basis for two months to make certain that the binding problem has been corrected and changes in alignment of the bracke t are not occurring. Also, clearance between the starting air header and the fuel rack bracket will be monitored for changes.
Furthermore, fuel rack movement will be traced on D/G 2A startup via the visicorder to detect the early development of any problems. After two months, the need to continue these practices will be re-evaluated.
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