IR 05000244/1994001
| ML17311A017 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 03/04/1994 |
| From: | Linville J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Mecredy R ROCHESTER GAS & ELECTRIC CORP. |
| Shared Package | |
| ML17263A548 | List: |
| References | |
| NUDOCS 9403150007 | |
| Download: ML17311A017 (4) | |
Text
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I MAR
l9S4 Docket No. 50-244 Dr. Robert Vice President, Ginna Nuclear Production Rochester Gas and Electric Corporation 89 East Avenue Rochester, New York 14649
Dear Dr. Mecredy:
SUBJECT:
NRC INSPECTION 50-244/94-01 This letter transmits the January 1 to February 7, 1994 inspection findings of Messrs. T. Moslak and E. Knutson at the R. E. Ginna Nuclear Power Plant.
At the end of the inspection, the findings were discussed with Mr. J. Widay and other members of your staff.
The inspection was focused on areas relevant to public health and safety and examined the control of operations, maintenance, and plant support activities conducted during this period.
Within this scope, we found effective coordination between your operations, maintenance, and engineering staffs in responding to a reduction in screenhouse water level caused by water intake icing. Additionally, we noted the alertness ofa control room operator in identifying a subtle off-normal containment pressure indication that subsequently led to identifying a degraded condition in a portion of engineered safety feature actuating circuitry.
In accordance with 10 CFR 2.790 of the NRC's "Rules of Practice," a copy of this letter and its enclosure willbe placed in the NRC Public Document Room.
No response to this letter is required.
Your cooperation with us in this matter is appreciated.
Sincerely, prigin-.I Signod By'.
james G. Unvilte James C. Linville, Chief Projects Branch No. 3 Division of Reactor Projects Enclosure:
NRC Region I Inspection Report 50-244/94-01 OFPICiAJ. RECORD COPY
DETAILS 1.0 OPERATIONS (71707)
1.1 Operational Experiences During normal power operations on the early morning ofJanuary 20, 1994, a decreasing screen house water level was identified. This condition indicated that the flow through the intake canal was not sufficient to support the service and circulating water flowdemand.
Actions were taken to reduce this demand by reducing plant power and securing one of the two main condenser circulating water pumps.
Additionally, the intake structure heater bar voltage supply was increased from 240 to 480 volts to-reduce frazil ice formation on the intake grating.
Subsequently, normal screenhouse water level was restored.
During the early morning hours of the following day, the icing condition reappeared and actions were successfully taken to restore water level by reducing power and again temporarily securing a circulating water pump.
Power was then escalated and remained at 98 percent through the remainder of the inspection period.
1.2 Control of Operations Overall, the inspectors found the R. E. Ginna Nuclear Power plant to be operated safely.
Control room staffing was as required.
Operators exercised control over access to the control room.
Shift supervisors maintained authority over activities and provided detailed turnover briefings to relief crews.
Operators adhered to approved procedures and were knowledgeable of off-normal plant conditions.
The inspectors reviewed control room log books for activities and trends, observed recorder traces for abnormalities, assessed compliance with technical specifications, and verified equipment availability was consistent with the requirements for existing plant conditions.
During normal work hours and on backshifts, accessible areas of the plant were toured.
No operational inadequacies or concerns were identified.
1.3 Power Reductions Required Due To Lake Water Intake Structure Icing Lake Ontario is the normal source of cooling water for the Ginna plant.
Cooling for operation of the turbines that drive the main generator is provided by the circulating water system, while the reactor plant and auxiliary systems are cooled by the service water system.
Both of these cooling water systems draw suction from a common inlet bay in the screenhouse.
Lake water is supplied to the inlet bay through an underground pipe that opens to a shielded intake structure, located 3100 feet off shore.
On January 20, 1994, at 2:35 a.m., operators were alerted to slowly lowering water level in the screenhouse lake water inlet bay when level instrument channel LI-3007 alarmed on low level (240 inches, or 20 feet; normal screenhouse level is about 28 feet). The traveling screens (four sets of vertically mounted, segmented screen tracks that provide coarse filtration between the inlet bay and the pump suctions) were inspected and found to be clean and free of ice.
Power to the four groups of intake structure heaters was checked and found to be normal (approximately 40 amps per group). In light of the existing record low temperatures, operators suspected that ice was forming on the lake intake structure bars and thus restricting flow.
At 4: 14 a.m., in response to main control board alarm I-l, "Screen House Lo Level 17 Feet,"
operators commenced a plant power reduction in accordance with site contingency procedure (SC)-4.1, "Low Screenhouse Water Level."
In parallel with the power reduction, plant management authorized alteration of the intake heater power supplies to increase the supply voltage from 240 volts to 480 volts; this action would increase the amperage of these heaters by a factor of four.
The work was performed as emergency maintenance, as provided for by administrative procedure (A)-1603, "Work Order Initiation." Three of the four intake heaters were converted-to 480 volts; the "C" intake heater was left connected to the 240 volt source because resistance readings were found to be lower than the other heaters, indicating that operation at higher voltage may'result in premature failure.
During the power reduction, a problem was noted with the screenhouse water level indications.
Two independent instruments provide indication of screenhouse water level; LI-3006 provides indication and annunciators on the main control board (MCB), and LI-3007 provides indication via the primary plant computer system (PPCS).
Operators noted that the levels indicated by these two instruments were diverging as screenhouse water level was lowering.
To provide reliable data, operations management directed that screenhouse water level be determined by direct measurement, using a weighted tape measure.
When power had been reduced to 50 percent, one of the two main circulating water pumps was secured.
The resultant reduction in flow out of the water inlet bay had the prompt effect of increasing level by approximately five feet. The increased voltage to the intake structure heaters was also proving effective, with ice and zebra mussels being observed collecting in the traveling scieens.-- By 8:40 a.m., normal screenhouse water level had been restored.
To resolve discrepancies between PPCS and MCB level indications, calibration checks were performed, and both instruments were found to be within acceptable tolerances.
The instrument sensing lines were blown down with air to eliminate any possible sources of blockage.
Following this action, the level instruments indicated in close agreement.
The Plant Operations Review Committee (PORC) subsequently reviewed the divergent level indications with respect to the requirements of emergency plan implementing procedure (EPIP)
1-0, "Ginna Station Event Evaluation and Classification."
EPIP 1-0 stipulates that a site area emergency be declared if, "Screenhouse Intake Water Level is less than or equal to the 15'o Level Alarm (1-9)." The lowest screenhouse water level reached prior to securing the circulating water pump was approximately 15.5 feet; the fact that MCB annunciator I-9, "Screen House Lo-Lo Level 15 Feet," never alarmed indicates that the LI-3006 level never fell below 15 feet.
PORC concluded that EPIP 1-0 was overly conservative in declaring a site area emergency based solely on low screenhouse water level. This conclusion was based on recent industry guidance on emergency action level (EAL) determinations, as well as on technical evaluation of the minimum water level required for service water pump operability.
As written, the technical basis for declaring a site area emergency at a screenhouse water level of 15 feet was the potential for loss of heat sink due to lowering lake level.
Preceding EAL determinations (unusual event and alert) in EPIP 1-0 were based on progressively lower lake levels; however, the criteria changed from lake level to screenhouse level for determination of a site area
emergency.
Consequently, the procedure did not accurately account for low screenhouse water level, when it was not the result of correspondingly low lake level (as in the case of intake structure icing).
At 12:02 p.m. on January 20, 1994, the plant commenced power escalation, and by 6:10 p.m.,
had returned to fullpower operation.
However, at 10:51 p.m., operators noted that screenhouse water level was again slowly trending downward.
Plant power was again reduced to just below 50 percent and, at 9:27 a.m. on January 21, 1994, a main circulating water pump was secured.
This action was successful in restoring and stabilizing screenhouse water level. Again, quantities of ice and zebra mussels were'noted in the traveling screens following the pump shutdown.
Later that day, full power operation was again restored, with no subsequent difficulties in maintaining screenhouse level.
From these observations, the inspector concluded that the cause of these two instances of low screenhouse water level was frazil ice formation on the intake structure bars. This ice formation was the result of extreme winter conditions, alo'ng with reduced heater bar efficiency due to zebra mussel infestation.
Higher intake structure temperature due to operation of the heaters at 480 volts appeared to reduce the zebra mussel infestation; this, along with more moderate weather, restored the capability of the intake structure heater bars to retard ice formation.
The inspector assessed the licensee's overall response to this event to have been good.
Strong
- management involvement, site and corporate engineering support, quality assurance oversight, and trade support were evident throughout the event.
The inspector considered that control of emergency maintenance, particularly requirements for PORC review, could be better delineated in the governing procedure.
Additionally, the inspector considered that the licensee should have recognized and expeditiously resolved the apparent disparity in EPIP 1-0 (that is, entry into a site area emergency without having transitioned through an unusual event and alert), given the relatively slow development of the event.
Throughout this event, the operations staff demonstrated strong attention-to-detail and strict adherence to procedures, from the initial indications of decreasing screenhouse water level, through responding to challenging operational concerns of electrical grid stability, condensate depression, elevated circulating water discharge temperatures, and plant power reductions/
escalations.
The operators demonstrated an excellent understanding of their procedures and further enhanced these procedures by capturing information gained through experiences during this infrequent occurrence of water intake structure icing.
To gain additional insight on icing events, the RG&E engineering staff has invited a representative from the James A. Fitzpatrick Plant to discuss the lessons learned from the three icing incidents that occurred there in 1993.