ML20216J286

Special Rept:On 920712,determined That Valid Failure of Div 1 EDG Occurred.Caused by B-C Phase CV-2 Relay Telephone Coil Failing Due to Excessive Current.Design Change Mod Initiated.Also Reportable Per Part 21

ML20216J286
Person / Time
Site:	Clinton
Issue date:	08/08/1992
From:	Phares R ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9709170221
Download: ML20216J286 (11)

Text

_ _ _ _ _ _ - - _ _ - - -

libros Power Company

e a Ch ! ower Station Chnton. IL 61727 Tc1217 935 8881 P(wWER u-conu L47-94(08* 08)LP 8E.100c August 8, 1992 Docket No. 50-461 10CFR$0.36 Document Control Desk Nuclear Regulatoiy Commission Washington, D.C. 20555

Subject:

Special Report: Valid Test Failure of Division 1 Diesel Gantral.or at Clinton Power Station

Dear Sir:

Clinton Power Station (CPS) Technical Specification 4.8.1.1.3 requires all diesel generator failures, valid or non-valid to be reported to the NRC within 30 days pursuant to Specification 6.9.2, SPECIAL REPORTS. Due to a valid failure of the Division 1 diesel generator (DGI A) identified on July 12,1994, the attached Special Report is being submitted in accordance with the CPS Technical Specifications to provide the information required by Regulatory Guide 1.108, Revision 1, " Periodic Testing of Diesel Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants," Regulatory 4 Position C.3.b.

Additionally, as this event constitutes the eighth failure in the last 100 valid tests performed on DG1 A, and the second failure in the last 20 valid tests, additional information recommended in Regulatory Guide 1.108, Regulatory Position C.3.b is also provided in the attached Special Report as required by CPS Te chnical Specification 4.8.1.1.3.

Sincerely yours,

, ~? -

Richard F. Ph .es S

Nk ONN!61 Director, Licensmg POR AJP/csm Attachment lbfhfll$llfl0fllflfll

' O cc: NRC Clinton Licensing Project Manager NRC Resident Oflice, V-690

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Regional Administrator, Region III, USNRC q, j I '

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/ Illinois Department of Nuclear Safety I

i - ,

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Attachment to

-U-602323 Page1of11 i SPECIAL REPORT a .

Description'of Event . .

g dt 0110 hours0.00127 days <br />0.0306 hours <br />1.818783e-4 weeks <br />4.1855e-5 months <br /> on July 12,- 1994, IP determined that a valid failure of the Division 1-  !

. Lemergency diesel generator (DG1 A) had occurred._ During a routine tour of plant

- equipment at CPS, an operator observed relay targets showing in the DGI A A-B phase and B-C phase undervoltage relays (Westinghouse model CV-2), indicating a circuit

malfunction had occurred. The emergency diesel generator (EDG) was in its normal standby mode at the time the targets were observed. This event was considered a valid failure of the EDO since failure of either of these relays, which are part of the permissive-1to-close circuitry for the DGI A output breaker, could allow premature closure of the breaker upon receipt of an automatic start signal due to or coincident with a loss of offsite power.

- An investigation of this issue determined that the B-C phase CV-2 relay telephone coil had i failed (open-circuited) due to excessive current. This effectively tripped and sealed-in the logic involving both the A-B and B-C phase relays, thus causing the targets to drop for .

, both relays. The CV-2 relay (i.e., either relay) prevents EDG output breaker closure when the EDG output voltage is less than the EDG rated voltage. (The telephone coil associated with each relay is normally energized and becomes deenergized when the EDG reaches rated voltage.) In the event of a loss of offsite power (LOOP)_or a LOOP coincident with a loss of coolant accident (LOCA), a failed telephone coil would allow the EDG output breaker to close before the EDG reaches rated voltage. Premature closure of the breaker would likely cause the generator to start too slowly relative to the start time assumed in the accident enalyses. As a result, DGI A was declared inoperable in response to the identified failure of the telephone coil.  ;

The defect which resulted in the excessive current was found to be in the telephone coil current-limiting resistor which has a lower resistance value than the value implied in the

manufacturer's literature. The manufacturer's literature implies that the resistor is 2500 ohms, whereas a 1320-ohm resistor was installed in the telephone coil that failed at CPS.

- Discussions with the manufacturer indicated that the resistor design had intentionally been changed to the smaller size, however, IP_was not made aware of the change. Use of a larger resistance was subsequently discussed with the vendor.

On June 7,1994, a similar failure occurred with the other Division 1 EDG CV-2 (i.e.,' A-B phase) relay. That failure was documented in a special report (IP letter U-602308) submitted July 7,1994. "As' a result of that failure, DGI A was being tested on a weekly Ms at the time the July 12 failure was identified.~ ' IP has determined that the previous

" tailure as well as the failure described above were the result of the incorrectly sized L telephone coil current-limiting resistor. IP has also determined this condition to be' potentially reportable under the provisions of 10CFR21J (See IP's part 21 notification, IP-

. letter U-602305 dated Ju e 27,~ 1994.) -

i k n ,.V- aq. &~n, - nn_ . _ , _______________________s __,

, y -

Attachment to c

- U-602323 ,

Page 2 ofil

" As the discovered failure of the telephone coil is a valid failure of DGI Al this event-- _ -

. constitutes the eighth valid failure in the last 100 valid tests and the second valid failure in

. the last 20 valid tests for DG1 A.? In accordance with CPS Technical Specification Table

. 4.8.1.1.2-1, DGl A is now required to be tested on a weekly basis until seven consecutive

failure-firee demands have been performed and the number of failures is less than or equal .

to one in the last 20 valid tests. (See note on page 3 of 11 of this Attachment / report).

Corrective Actions

~ In response to the June 7,1994 CV-2 relay failure, IP initiated development of a design change to modify the Division I and 2 EDG CV-2 relays. The design change would = <

correct the excessive current condition in the CV-2 relays by replacing the 1320-ohm resistor with a resistor properly sized for the relay application. Replacement parts (i.e.,

telephone coils and resistors) for implementing the design change had been ordered and l receipt of the parts was pending at the time the July 12 failure occurred. Following the

- CV-2 relay failure on July 12 and'afler receipt of the replacement parts on July 13, IP promptly implemented the design change on both Division 1 and Division 2. IP first replaced both CV-2 relays in DGl A with modified relays. For each relay, the telephone coil was replaced with a new coil and the 1320-ohm resistor was replacal with a 4000-ohm resistor. The Division 1 EDG was subsequently declared operable on July 13,1994.

The two comparable relays associated with the Division 2 diesel generator were then also replaced with relays that had been modified in the same manner as Division 1. The Division 2 relays were replaced and the diesel generator was returned to service on ,luly 14,1994.

i1

' Prior to declaring the Division I and 2 EDGs operable following the relay modification, e design-basis testing was performed to verify correct operation of the modified relays. The

= first test required application of the minimum DC voltage expected at the CV-2 relay to

- confirm the telephone coil would energize (pick-up). This was confirmed for both the g

Division 1 and division 2 modified relays. In addition, it was also confirmed that the telephone coil would de-energize (drop-out) at a voltage less than the pick-up voltage - ,

The final test performed required the application of the maximum DC voltage expected at the CV-2 relay to measure the corresponding current through the telephone coil. It was verified that the current through the Division 1 and Division 2 telephone coils was less than the maximum continuous current carrying capability of the coil to preclude coil burnout.

'_On' August 3,1993, a DGl_A CV-2 relay failure occurred which at the time was n .

~ determined to be age related but IP now suspects was also the result of an incorre ctly sized telephone current-limiting resistor. As part of the action plan developed following the August 3 failure it was verified that these relays are not used in the Division 3 diesel

- generator. ' (Therefore, the design change described above was not required to be

.. implemented for the Division 3 diesel generator.) In addition, the remaining safety-related 4

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6 4 Attachmert: to U 602323:

• Page 3 of 11 relays that utilize telephone coils in similar configurations at CPS are normally de _ .

s

-- energized and :herefore, similar features are not expected for these coils since they are not -

subject to age-related degradation from being continuously energized. It should be noted that operability of the re'ays is also being periodically verified as the CV-2 relays are checked at least once per shift as part of the routine tours of plant equipment by the plant operators.

Test Intervals 4

_ As noted in the cover letter for this report, this event constitutes the eighth valid failure in the last 100 valid tests and the second valid failure in the last 20 valid tests for the DGI A.

Technical Specification Table 4.8.1.1.2 1 requires the testing frequency for a diesel gencrator to be increased from at least once per 31 days to at least once per seven days

1. -  ! when the number of failures is greater than or equal to five in the last 100 valid tests or two in the last twenty valid tests. Therefore, DGl A is, and will continue to be, tested on a weekly basis until seven consecutive failure-free demands have been performed and the number of failures is less than or equal to one in the last 20 valid tests.

L Note l- By letter dated August 5,1994 (IP letter U-602316) IP submitted a request for

- enforcement discretion and an application for amendment of the CPS Operating License to waive the requirement for increased (weekly) testing of DG1 A in response to the recent CV-2 relay failures. IP's request is based on the position that the routine testing required by the Technical Specifications (to be increased from monthly to weekly) does not challenge the CV-2 relay since a relay failure can only be identified by automatic operation of the diesel generator output L breaker under loss-of-offsite-power conditions. Further, IP has taken appropriate j-corrective action in response to the CV-2 relay failures such that extended weekly testing is not necessary to assure acceptable reliability of the Division 1 diesel

- generator. Upon obtaining NRC approval ofIP's request for enforcement discretion and/or application for license amendment, monthly testing of DGI A will

- be resumed notwithstanding the requirements for performing seven consecutive failure-free tests and reducing the number of failures to less then or equal to one in the last 20 valid tests.

l With respect to the reporting of diesel generator failures, Technical Specification 4.8.1.1.3 also requires if the number of failures in the last 100 valid tests is seven or more, the additional information recommended in Regulatory Guide 1.108 Regulatory Position C.3.b be provided. This information is provided in the following section.

~ Additional Information Reauired per Renulatory Guide 1.108. Regulatory Position C.3.b

~

As describedibove, since this event caused the number of valid failures in the last 100 -

1 valid tests to be greater than or equal to seven (on a per-diesel generator basis), the f 4 .

u w- y 3 r--a* g- w- y - y - e.-' -

. . _ _ ___ ~ _ _ ___ _ . _ _ _ _ . . . _ _ _ . - _ _ _ , . . _ _

c ,

Attachment to --

U-602323  !

O ~- -

Page 4 of11 I additional information racommended in Regulatory Guide 1,108, Regulatory Position .

(C.3.b is provided belowJ  ;

~

Corrective Measures to Increase Diesel Generator Reliability j The eight valid failures of DGI A which have occurred in the last 100 valid tests occurred -  ;

on July 17,1992 and August 7,- 1992 (reference IP Special Repon dated August 20, 1992); September 21,1992 (reference IP Special Repon dated October 20,1992); June 23,1993 (rt,ference IP Special Report dated July 23,1993); July 21,1993 and August 3, t 1993 (reference IP Special Report dated August 20,1993); June 7,1994 (reference IP-Special Report dated July 7,1994); and July 12,1994 (reference this Special Report).

l The DGI A failures on July 17,1992 and August 7,1992 were the result of the output

- br eaker failing to close. A comprehensive action plan was developed and troubleshooting Ewas performed to identify the cause of the breaker failure. The root cause of the DGI A

- output breaker failure to close was determined to be a failure of the truck-operated contacts (TOC) switch Hl. The purpose of this switch is to signal the output breaker closing circuitry that the breaker is racked in. (Closure of the breaker is prevented ifit is not fully racked in.) IP determined that the 1-2 contact pair of the HI TOC switch lost electrical continuity due to (1) slight breaker movement and/or (2) buildup of

__ oxidation / pitting on the contact surfaces.

Corrective actions for the July 17 and August 7,1992 failures included replacing the H1 and H2 TOC switches in the DG1 A output breaker. The TOC switches in the Division 2

= output breaker cubicle were also replaced, and subsequent inspection of the removed TOC switches indicated no abnormal wear. I_n addition, the switches which perform a similar functi_on in the Division 3 output breaker cubicle were subsequently inspected and no -

abnormalities were identified - IP inspected a represeruative sample of TOC switches in sin'ilar breaker cubicles in safety-related applications during the fourth refueling outage.

The result of these inspections indicated that further corrective actions were unnecessary.

The September 21,1992 DGI A test failure resulted from the failure of the associated output breaker to close. It was subsequently determined that the root cause of this failure

= was a bent protective cover over the associated anti-pump relay (located within the

- breaker cubicle). The bent cover partially depressed the anti-pump relay plunger so that -

the contacts operated by the plunger were lightly touching. This resulted in erratic -

operation of the relay. Also, the bent cover may have cocked the plunger to the side, thus

' interfering with its operation.

TAs _a result of this failure, a corrective action plan was implemented. The DGl A output breaker was replaced with a spare breaker as part of the troubleshooting performed. All of the other Class IE 4160-volt Westinghouse breakers were inspected for damage to itheir protective covers, arid no similar conditions were found. Additional inspections of the failed breaker by the manufacturer did not change the root cause determination. In -

S

, u ,,,.% #--. 2 - ___--

' Attachment to U-602323 Page 5 of11 addition, a ten-week monitoring program was initiated to monitor the closing circuit of the installed output breaker during surveillance tests of DGI A. No additional failures were observed.

The DGI A failure on June 23,1993, was the result of the diesel generator failing to successfully synchronize with its associated safety bus due to an out-of-calibration reverse power relay. The relay was replaced (with a new model) and an analysis of the removed relay was performed, including examination of the relay for physical or electrical defects which could have affected its operability, and performance of a routine electrical test of the relay to determine its operability. It was concluded that since the relay was found to be out of calibration, and the analysis revealed the relay had no defects, the root cause of the failure was miscalibration of the reverse power relay. Factors contributing to the miscalibration were (1) the test equipment that had been used to calibrate the relay was less than state-of-the-art and (2) physical construction of the previous model GGP53B relay made calibration adjustments difficult compared to the new replacement GGP53C relay.

Corrective actions for the June 23,1993 failure included improving the test equipment used to calibrate the reverse power relay and revising the associated test procedures. In addition, each GGPS3B reverse power relay was upgraded (replaced) to the GGP53C relay to allow for easier calibration due to the physical construction of the relay. This relay is used for each of the emergency diesel generators and two are also used for the main generator. All five relays were thus replaced.

The July 21,1993 DGI A test failure resulted from the failure of the DGI A output breaker to close when the operator attempted to synchronize the gererator with offsite power.

The manual breaker control switch was replaced, subsequer tly tested, and inspected to determine the cause of the failure. It was determined that ween the switch was moved to the closed position, the normally closed contacts associated wnh the pull-to-lock position on the switch would intermittently open thereby preventing the breaker from closing.

Upon disassembly of the manual breaker control switch, it was noted that these contacts were severely pitted thus confirming that the contacts had opened intermittently. IP has determined that the failure of these contacts to remain closed was the root cause of this event.

Corrective actions for this event included monitoring of the manual breaker control switch using recording instmmentation temporarily connected to the diesel control circuitry. This monitoring was continued for 10 consecutive valid stans and confirmed that no other deficiencies existed in the control circuitry for DGI A. Additionally, the manual breaker control switches for all three divisions were replaced. In each case, the original switches were inspected and tested to confirm that the failure of the Division 1 manual breaker control switch experienced was not generic. A generic problem was not identified and no additional failures were observed.

. 3~

Attachment to

' ' U 602323-

+

Page 6 of11 The August 3,1993 failure of DGI A was the result of a condition discovered during .

- operational rounds by an area operator. The DGI A B-C phase and A B phar,e

'undervoltage relays (Westinghouse model CV-2) were found with dropped targets that -

were unable to be resetJ Failure of either of these relays, which are pan of the permissive-

- to-close circuitry for the DG1 A output breaker, could cause premature closure of the

_ breaker upon receipt of an automatic start signal coincident with a loss of offsite power.

Troubleshooting determined that the root cause of the undervoltage relay trip condition T was due to the failure of the normally energized telephone coil in the B C phase undervoltage relay. The failure was later determined to be the result of an incorrectly sized telephone coil current-limiting resistor.

The corrective action plan for the above included replacing the Division 1 B-C phase CV-2 relay.- Both Division 2 CV-2 relays were replaced during the first scheduled Division 2 outage.: Since the Division 1 A B phase CV-2 relay had been replaced less than 12 months earlier, it was determined that it was not necessary to replace this relay as part of the corrective action plan associated with this failure. It was also confirmed that these relays are not used in a similar function for the Division 3 diesel generator. The remaining safety-related relays that utilize telephone coils in similar configurations at CPS are

normally de-energized, and similar failures are not expected for these coils. A preventive

. maintenance task was initiated to replace the Division 1 and 2 A-B and B-C phase CV-2 relays at seven-year intervals.

The June 7,1994 failure of DGl A was the result of a condition discovered during operational rounds by an area operator. The DGI A A-B phase and B-C phase

- undervoltage relays (Westinghouse model CV-2) were found with dropped targets that were unable to be reset. Failure of either of these relays, which are part of the permissive-to-close circuitry for the DGI A output breaker, could cause premature closure of the breaker upon receipt of an automatic start signal coincident with a loss of offsite power.

Troubleshooting revealed that the cause of the undervoltage relay trip condition was due to the failure of the normally energized telephone coil in the A-B phase undervoltage relay. IP subsequently determined that the June 7,1994 failure as well as the July 12, 1994 (addressed in this Special Report) were the result of the incorrectly sized telephone L coil current-limiting resistor.

In response to the June 7,1994 CV-2 relay failure, IP initiated develwent of a design changito modify the Division I and 2 EDG CV-2 relays. The design change would correct the excessive current conoition in the CV-2 relays by replacing the 1320-ohm resistor with a resistor properly sized for the relay application. Replacement parts (i.e.,

telephone coils and resistors) for implementing the design change had been ordered and receipt of the parts was pending at the time the July 12 failure occurred.' Following the CV-2 relay failure on July 12 and after receipt of the replacement parts on July 13, IP promptly implemented the design change on both Division 1 and Division 2. IP first -

replaced both CV-2 relays in DG1 A with modified relays'. For each relay, the telephone coil was replaced with a new commercially dedicated coil and the 1320-ohm resistor was 4

+ ..

9

Attachment to U-602323 Page 7 of11 replaced with a commercially dedicated 4000-ohm resistor. The Division 1 EDG was subsequently declared operable on July 13,1994. The two comparable relays associated with the Division 2 diesel generator were then also replaced with relays that had been modified in the same manner as Division 1. The Division 2 relays were replaced and the diesel generator was returned to service on July 14,1994.

The root cause and corrective actions for the valid failure of DG1 A on July 12,1994 was previously discussed in this report.

Autumentpf the Existing Reliability of Electric Power to Engineered Safety Featurc Eguipment The IP electrical system provides a diversity of power supplies. The 138 kV offsite power system provides power to CPS via one transmission line from the Clinton Route 54 Substation which effectively connects CPS to the Illinois Power Company grid. Electrical power can be fed to this substation through a line from the v.,uth Bloomington substation

.or through a line from the north Decatur substation, or both. The line from the Clinton Route 54 substation terminates directly (through a circuit switcher) at the station Emergency Reserve Auxiliary Transformer, which transforms the electrical power to 4160 volt auxiliary bus voltage.

The 345kV offsite power system provides power to CPS via three separate transmission lines. These lines connect CPS to the Illinois Power Company grid at the Brokaw, Rising, and Latham Substations. All three lines terminate at the station switchyard ring bus which feeds the Reserve Auxiliary Transformer (through a circuit switcher), which in turn transforms the electrical power to 6900-volt and 4160-volt auxiliary bus voltages. Only one 138-kV line and one 345 kV line are required to be available by the CPS Technical Specifications There are three diesel generator units on site that automatically provide emergency power in the unlikely event that the offsite AC power sources described above become unavailable. Diesel generator 1 A (DGI A) supplies power to Division 1 electrical equipment, diesel generator IB (DGlB) supplies power to Division 2 electrical equipment, and diesel generator 1C (DGlC) supplies power to Division 3 electrical equipment (primarily the High Pressure Core Spray System). In supporting safe shutdown of the facility in the event of an emergency or accident, Division 1 is redundant to Division 2.

Based on plant operation to date, overall reliability of electric power for engineered-safety feature equipment has proved to be very high when both onsite and offsite sources are l

considered. Offsite source availability has historically been especially high. All events to i date which impacted offsite source availability are briefly summarized below, i

T I Attachment to

, ,, U-602323

-Page8ofil With respect to the offsite transmission lines, CPS has never experienced 's complete loss -

of offsite power. Since CPS began operation, the 138 kV line has been 100% available (except for planned maintenance). 345 kV power has also never been lost, though

__ outages of at least one (or two) of the three 345 kV lines have occurred. A very short-

. 1 term interruption (approximately 4 seconds) occurred in 1989 for one of the 345 kV lines.

Two more events which occurred recently are described below.

On June 8,1993, high winds downed a portion of one of the 345 kV transmission lines to the station switchyard (line 4571 to Latham substation). Approximately 17 miles of supporting structures colle.psed between the Latham substation and the double-circuit

tower east of Maroa. The remaining two 345 kV transmission lines to the CPS switchyard remained in service during the severe weather. (The 138 kV offsite circuit was also.

unaffected.) Repairs to this line were completed, and the line was restored to service at 1840 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />7.0012e-4 months <br /> on September 22,1993.

On August 4,1993, one of the remaining two 345 kV transmission lines in service to the -

CPS switchyard (line 4535 to Brokaw substation) experienced a momentary fault causing -

the plant to isolate to the remaining transmission line. During this event, a voltage 4

. transient occurred that resulted in main generator terminal voltage declining to approximately 70%.- The entire event lasted for a duration of about 7 seconds. This resulted in some plant equipment tripping but the equipment was quickly restored to

. service by plant operators, thus preventing the plant from tripping offline. (A similar fault occurred on August 19,1993 without a voltage transient occurring).

! One other event involving a switchyard component occurred during a plant outage that began on November 11,1988 due to a failure of the C-phase main power transformer. On November 14,1988 arcing was observed on a station switchyard circuit switcher (4538) associated with the reserve auxiliary transformer (RAT). Load was successfully shedded or transferred from the RAT, and the RAT was disconnected from the station switchyard ring bus to facilitate inspection of the circuit switcher Inspection of the circuit switcher revealed that the base disconnect hinge assembly on the B phase, lhic side, was damaged.

Following repairs, the RAT was re-energized approximately 14-1/2 hours after it was removed from service. This event did not result in any unplanned actuation of any engineered safety features. Periodic infrared thermography is now performed on the circuit switcher connections to identify degradation before it becomes severe or damage

. occurs.-

Basis For Continued Plant Operation

As' described previously, Illinois Power electrical system design provides a diversity of

'offsite sources for supplying power to the safety-related equipment needed to achieve and maintain _the plant in a safe shutdown condition. These power supplies consist of(1) the

- 138 kV.offsite transmission line from the Clinton Route 54 Substation which supplies the station Emergency _ Reserve Auxiliary Transformer (ERAT), and (2) the station switch '

[ Attachment to U-602323 Page 9 of 11 yard ring bus which supplies the Reserve Auxiliary Transformer (RAT). The Clinton Route 54 Substation can be fed by two separate lines from two separate substations. The ERAT is sized to carry all the safety-related loads of CPS. The station switchyard ring bus can be fed by three separate 345 kV lines which originate from three separate substations. The RAT is sized to carry all the stations loads (safety and non-safety related).

In the event of a complete loss of offsite power, each of three diesel generators supplies onsite emergency power to its respective division of safety-related equipment. As also noted previously, with respect to supporting safe shutdown of the facility in the event of an emergency or accident, Division 1 is redundant to Division 2, while Division 3 is primarily associated with the high pressure core spray system.

Test history for the Division 2 and Division 3 diesel generators indicates that these onsite emergency power sources are highly reliable. DGIC has never experienced a valid test faibre since CPS began operation. Only six valid test failures have been recorded for DGlB, and DGlB has only experienced four valid failures in the last 100 valid test performed.

Based on the high reliability of the offsite power supply system for CPS, the redundancy built into the CPS design to accommodate a single-failure, the proven reliability of the Division 2 and 3 diesel generators, and in light of the corrective action taken for the recent DGl A test failures, continued plant operation isjustified.

Summary of Testing of the Diesel Generators Dul A Of the last 100 valid tests performed for DGI A, eight have resulted in valid failures.

These valid failures were previously discussed in detail. Additionally,35 non-valid tests were conducted during this testing period in order to perform troubleshooting and post-maintenance testing. One of these non-valid tests resulted in a non-valid failure on January 9,1992. This non-valid failure was reported in IP letter /Special Report U-601931 (dated Febmary 5,1992) and was the result of a reverse power trip during diesel generator synchronization. This trip was caused by operator error during closure of the output breaker.

Testing of DGI A has been accomplished at the frequency required by the CPS Technical Specifications. The required frequency of surveillance testing of the diesel generators at CPS is specified by Technical Specification Table 4.8.1.1.2-1. The frequency of testing for a given diesel generator is determined by the demonstrated reliability of that diesel generator. Technical Specification Table 4.8.1.1.2-1 states that the diesel generator testing frequency shall be at least once per 31 days if the number of failures in the last 20 valid tests performed is one or less and in the last 100 valid tests performed is four or less.

The surveillance frequency must be increased to at least once per seven days if the number of failures in the last 20 valid tests performed is two or more of if the number of failures in

I Attachment to U-602323 Page 10 of Il-the last 100 valid tests performed is fi_ve or move. Footnote """ of Technical Specification Table 4.8.1;1.2-1 further states that the seven-day surveillance interval must be maintained until seven consecutive failure-free demands have been performed ~and the

number of failures in the last 20 valid tests performed has been reduced to one or less.

The testing period for the last 100 valid tests of DG1 A began on June 3,1991. As of

. June 3,1991, DGI A had experienced one valid failures in the last 20 valid tests and six valid failures out of the previo.isly performed 100 valid tests. The required testing

_ - fre:luency as of June 3,1991, was monthly.

'The valid failure on July 17,1992 constituted the first valid failure in the last 20 valid tests

- and the seventh vtjid failure in the last 100 valid tests. As a result, the testing frequency i required by Technical _ Specification Table 4.8.1.1.2-1 for DGI A was increased to weekly.

The valid failure on August 7,1992 was the second valid failure in the last 20 valid tests and the eighth valid failure in the last 100 valid tests. As a result, the testing frequency

' required by Technical Specification Table 4.8.1.1.2-1 for DGI A remained at weekly.

' Another valid failure of DGI A was experienced on September 21,1992. DGI A had, at that time, experienced six valid failures in the last 100 valid tests performed, and three

valid failures in the last 20 valid tests performed. Weekly testing of DGI A was thus continued. -Monthly testing was resumed after completion of a successful test on

November 30,1992 when seven consecutive failure-free demands had been performed and the number of failures in the last 20 valid tests had been reduced to one.

The next valid test failure for DGI A did not occur until June 23,1993. DGl A had then experienced four valid failures in the last 100 valid tests performed. This test failure was initially regarded as a non-valid failure, and therefore, DGl A continued to be tested on a nionthly basis. However, as discussed in IP letter /Special Report U-602174 (dated

' August 20,1993) this failure was later reclassified as a valid failure. In the mean time, an additional failure occurred on July 21,1993 which did require the testing frequency for DGI A to be increwed.

- With the occurrence of the DG1 A test failure that occurred on July 21,1993, the Technical Specification criterion for increased testing had been met, and the DGl A testing b frequency was increased to weekly (as noted above). With the reclassification of the June -

23,1993 failure (from non-valid to valid), the July 21,1993 valid failure was the sixth

. valid failure in the last 100 valid tests for DGl A, and the second valid failure in the last 20 valid tests for DGI A.

r Another valid failure of DGI A occurred on August 3,1993. DGI A had at that time experienced three valid failures in the last 20 valid tests and seven valid failures in the last 100 valid tests.- Therefore, the testing frequency for DGI A remained at weekly in i accordance with CPS Technical Specification Table 4.8.1.1.2-1. The criterion for

~

. . resuming monthly testing was subsequently met on October 3,1993.

1. <.+ m...

Attachment to

• U 602323 Page1Iof11

-.The DGl A failure on June 7,1994 constituted the seventh valid failure in the last 100 valid tests and the first valid failure in the last 20 valid tests. This required the test frequency for DGI A to be increased to weekly. Weekly testing was still ongoing when

'the July 12,1994 failure of DGI A was identified.

As described previously, the DGl A failure on July 12,1994 constituted the eighth valid failure in the last 100 valid tests and the second valid N1ure in the last 20 valid tests. As of August 2,1994 weekly testing of DGI A continues, and 4 valid test have been completed for DGl A.

In summary, as can be seen from the above discussion, the surveillance testing for DGI A has been conducted in accordance with the frequencies required by CPS Technical Specification Table 4.8.1.1.2 1.

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