ML19347C823
| ML19347C823 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 09/18/1973 |
| From: | Ross D JERSEY CENTRAL POWER & LIGHT CO. |
| To: | Giambusso A US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8103040963 | |
| Download: ML19347C823 (5) | |
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y Jersey Central P'o,Q68 & Light Company M ADISoN AVENUE AT PUNCH OoWL Ro Ao e MoRRISToWN, N.J. 07960 e 539-6111 g-, September 18, 1973 ,/'
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h: Mr. A. Giambusso -- % "6, - Deputy Director for Reactor Projects _-j ,f . g 9 , 7 . ., Directorate of Licensing United States Atomic Energy Commission M 4 tg7 ~ y:t b
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Dear Mr. Giambusso:
. Subj ect: Oyster Creek Station Docket No. 50-219 Power Failure The purpose of this letter is to report a violation of the Technical Specifications, paragraph 3.7.A.2., in that although both startup transformers were energized to carry power to the station 4160V AC buses, neither transformer could be considered operable due to an improper setting on the C phase differ-ential monitoring relays. Further, during the event, neither diesel generator was able to restart after having once been initiated in the " fast start" mode and been secured when power was again lost to the 4160V AC buses.
These situations are considered to be abnormal occurrences as defined in the Technical Specifications, paragraph 1.15.D. (failure of one or more compo-nents or an engineered safety feature that causes the feature to be incapable of performing its intended function) and 1.15.G. (observed inadequacies in the imple-mentation of procedural controls such that the inadequacy causes the existence or development of an unsafe condition in connection with the operation of the plant). Notification of this event, as required by the Technical Specifications, paragraph 6.6.2.a. , was made to AEC Region I, Directorate of Regulatory Operations, by telephone on September 8,1973, and further elaborated upon personally with Mr. B. Greenman from AEC Region I, Directorate of Regulatory Operations on Septem-ber 11, 1973 during his visit to the site. Further, the problem with the start-up transformers was telecopied to AEC Region I on September 10, 1973, and the difficulty experienced with the diesel generators was telecopied on September 13, 1973. . A plant shutdown had progressed to the point where, with electrical
- output at approximately 90 MWe, a transfer of station loads from the auxiliary transformer to the startup transformers was attempted. When a closing signal was applied to the SIA breaker, a loss of power occurred on the 1A 4160V AC bus which, among other things, caused two circulating water pumps, three reactor recirculation pumps, and the operating condensate and feedwater pumps to trip. Diesel generator 8/O3040 % 3
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1 1 Mr. Giambusso Septeder 18, 1973 1 No. I was initiated in the " fast start" mode, reenergizing the IC 4160V AC bus, restoring power to the requisite safeguard systems should they have been re-quired. An attempt was made to start the B and C condensate pumps, but before either pump could be started, the reactor scrammed due to low water level. In reconstructing the subsequent events, the following seems pertinent:
- 1. Following the scram, the IB 4160V AC bus was energized properly from the SB transformer.
- 2. The " lockout" relay, 86SA, was reset manually, the SIA breaker was closed, diesel generator No. I was synchronized with " system",
and the IC breaker was closed.
- 3. Diesel generator No. I was secured. At this time, the " trouble" alarm was annunciated in the control room and an electrician was dispatched to determine the cause.
- 4. An attempt was made to start the A condensate pump, but the in-rush current apparently tripped S1A breaker. Diesel generator No. I was not initiated in the " fast start" mode due to the engine
" lockout" relay whi< h has previously been actuated (the cause from the " trouble" alarm) .
- 5. An attempt was made to start the B or C condensate pumps, but the in-rush current apparently tripped the S1B breaker. Diesel generator No. 2 was initiated in the " fast start" mode reenergizing the ID 4160V AC bus. For the period of time taken for diesel generator No. 2 to come up to speed, buildup voltage and reenergize the bus (less than 15 seconds), the station was without AC power.
- 6. Both the SA and SB transformer " lockout" relays were reset manually and both SIA and SIB breakers were closed.
- 7. Diesel generator No. I was initiated in the " fast start" mode when the electrician reset the engine " lockout" relay.
- 8. Diesel generator No. 2 was synchronized with " system", the ID breaker closed, and the diesel generator was secured. Upon securing the unit, the " trouble" alarm was annunciated (apparently due to the engine " lockout" relay being activated) . The electrician was advised of the situation.
- 9. Again, an attempt was made to start the B or C condensate pumps with the same results as befbre. Ilowever, diesel generator No. 2 failed to start.
i 10. The electrician reset the engine " lockout" relay for diesel generator No. 2 and the unit was initiated in the " fast start" mode.
j , O' L, Mr. Giambusso September 18, 1973
- 11. With two CRD pumps running, the control rod drive system hydraulic control station bypass valve was . opened to assist in the recovery of reactor water level. The minimum level reached, as recorded by the feedwater control system level recorder, was 9' above the core, l' 10" above the actuation point for initiating the core spray system and isolating the reactor.
- 12. The MSIV's were closed by the operator and the isolation condensers were manually initiated to eliminate the water inventory loss from the vessel and to provide for decay heat removal.
The problem experienced with the startup transformer breakers SIA and SIB was traced to an incorrect setting of the current transformer ratio matching taps for the C phase differential relay on both units. In attempting to either carry a sizeable load and/or start a large load, a differential fault current based upon the improper tap setting was sensed, tripping the bus supply breakers. ! Relay nomenclature is as follows: Manufacturer: General Electric Model No.: 12BDD15&11A 5 amps, 60 cycles, 125-250 DC Control Volts i-The problem experienced with the diesel generators was identified to be as a result of relay contact actuation which is inherent in the design of the circuit (see Figure 1). When the unit is initiated in the " fast start" mode, power to the engine fault circuit ia cut off. With the unit at speed, the OAD relay is energized closing contacts in the engine " lockout" circuit. Under normal conditions, i the bearing oil pressure switch would be closed, enabling the MBR relay to be i energized, opening a contact in the engine " lockout" circuit. However, that relay could not be energized due to the opened " fast start" relay contacts and consequently the bearing oil pressure contacts remained closed. When the unit was secured, j the " fast start" relay was deenergized, closing the " fast start" relay contacts. Before the MBR relay could be energized and its respective contacts opened in the engine " lockout" circuit, the " lockout" relay was actuated which prevented a
; subsequent start. The engines would remain locked out until the relays could be manually reset locally, as was the case.
P The current transformer ratio matching taps were set up properly and station loads were returned to normal. This action was completed by 8:30 a.m. The ' company Relay Department was contacted and load checks were conducted on each !
' of the transformer phase differential relays. All checks were satisfactory. As regards to the diesel generator problem, during the loss of power conditions, the
" lockout" relays were reset allowing the units to restart. A " fast start" test -
of diesel generator No. I was subsequently conducted while monitoring the engine : fault relay circuitry, turning up the problem as previously discussed. General Motors.has been contacted with regards to a modification which could be made to the circuit to circumvent the problem. . The designed redundancy for the station vital power supplies (i.e. , off-site power and diesel generators) was not present and, in fact, had not been , present since July 30, 1973, when a test of the startup transformer phase differ- i 2 i 4 l
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i l Mr. Giambusso September 18, 1973 ential relays had been conducted. Under a bona-fide loss of power condition, both diesel generators would have performed their intended function and, in fact, did since both units t Ltuated to energize their respective buses upon initially sensing undervoltage. Ilowever, had a problem arisen, which required a subsequent " fast start" immediately after the units had been secured from a " fast start", such as occurred here, no AC power would have been available to power any necessary safe-guards equipment until the engine " lockout" relays could be reset. To prevent a reoccurrence of this tyTe event, the following actions are being taken:
- 1. Prepare procedures, in conjunction with the Relay Department, for all Relay Department work in the Oyster Creek plant. All work in the future will be coordinated with the shift foreman.
- 2. Prepare a design change to the diesel generator logic circuits to prevent lockout following shutdown of the diesel. General Motors will be contacted for recommendations.
- 3. Review and revise Procedure No. 511 " Loss of Feedwater System" as required.
We are enclosing forty copics of this report. Very truly yours, 7 Donald A. Ross l Manager, Nuclear Generating Stations es Enclosures cc: Mr. J. P. O'Reilly, Director Directorate of Regulatory Operations, Region I
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