05000440/LER-1988-001, :on 880103,reactor Scram Occurred Due to Upscale Trip on intermediate-range Neutron Monitors.Caused by Excessive Feedwater Injection Into Reactor Vessel While Adjusting Potentiometer.Low Speed Stop Lowered

:on 880103,reactor Scram Occurred Due to Upscale Trip on intermediate-range Neutron Monitors.Caused by Excessive Feedwater Injection Into Reactor Vessel While Adjusting Potentiometer.Low Speed Stop Lowered

ML20235W477
Person / Time
Site:	Perry
Issue date:	03/03/1989
From:	Dunn G CLEVELAND ELECTRIC ILLUMINATING CO.
To:
Shared Package
ML20235W445	List: 05000440/LER-1988-001, :on 880103,reactor Scram Occurred Due to Upscale Trip on intermediate-range Neutron Monitors.Caused by Excessive Feedwater Injection Into Reactor Vessel While Adjusting Potentiometer.Low Speed Stop Lowered PY-CEI-NRR-0980, Forwards LERs 89-004-00 & 88-001-01
References
LER-88-001, LER-88-1, NUDOCS 8903130054
Download: ML20235W477 (4)

LER-1988-001, on 880103,reactor Scram Occurred Due to Upscale Trip on intermediate-range Neutron Monitors.Caused by Excessive Feedwater Injection Into Reactor Vessel While Adjusting Potentiometer.Low Speed Stop Lowered

Event date:
Report date:
4401988001R00 - NRC Website

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Perry Nuclear Power Plant, Unit 1 015 l 01010 l41410 1 lOFl014 Reactor Scram Results From Intermediate Range Neutron Monitors Upscale Trip Due To Excessive Feedwater Flow Uith Manual Control Of A Turbine Driven Feedwater Pump EVENT DATE 15)

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On January 3, 1988 at 0630, a reactor scram occurred due to an upscale trip on the Intermediate Range Neutron Monitors (IRM). The scram was a result of excessive feedwater injection into the reactor vessel while plant operators were adjusting the manual speed control potentiometer for the B Turbine Driven Feedwater Pump (TDFP) turbine.

The causes of the event were instruction inadequacy and design deficiency.

Integrated Operating Instruction (101)-4 " Shutdown" did not provide adequate guidancc and a proper sequence for feedwater control during a plant shutdown with a TDFP. The TDFP minimum flow valves are undersized making manual control j

l of the TDFP necessary during low flow conditions. The Low Flow Controller provides very little overlap with the Startup Level Controller and therefore, was not being used during this event.

In order to prevent recurrence 101-4 has been revised to include specific guidance for feedwater control during shutdown when the Motor Driven Feedwater Pump is unavailable. The total flow capacity through the Low Flow Control

.I Valve will be increased in order to provide greater overlap with the Startup Level Controller. The low speed stop for the TDFPs when on the Startup Level Controller will be lowered. Additionally, the TDFP manual speed controllers will be changed to reduce the sensitivity and provide better control.

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swimm maw.v, mumma. macr amuun on January 3, 1988 at 0630, a reactor scram occurred due to an upscale trip on the Intermediate Range Neutron Monitors (IRM) [IG).

Prior to the event,.the plant was in Operational Condition 2 (Startup), conducting a reactor shutdown for a planned maintenance outage. Reactor thermal power was less than 1.0 percent of rated with reactor vessel [RPV] pressure approximately 800 psig.

At approximately 0100 a plant shutdown was commenced for a planned maintenance outage. The Motor Driven Feedwater Pump (MFP) [SJ) and the B Turbine Driven P

Feedwater Pump (TDFP) were in operation at the time, the A TDFP was out of service for repairs. At 0259 the MFP was secured when reactor power was decreased to approximately 40 percent. At 0414 the B TDFP was placed on the Startup Level Controller in automatic.

Operational Condition 2 was entered at 0550 and reactor vessel pressure was decreasing at a rate of approximately 7 psi per minute. As the feed demand.

signal decreased the Startup Level Controller reached its minimum output and the B TDFP discharge pressure remained steady at approximately 865 psig. At approximately 0625 reactor vessel level began to increase as reactor pressure decreased below the B TDFP discharge pressure. The operator at the controls placed the Startup Level Controller in manual and attempted to reduce the B TDFP turbine speed. When this was unsuccessful, the B TDFP control was transferred to the manual potentiometer and turbine speed reduced, subsequently causing reactor vessel level to decrease. Preparations for starting the MFP were commenced. However, the MFP was not immediately available due to the lube oil temperature having decreased below the minimum required for pump start.

y At 0629 a second operator was directed to increase the B TDFP turbine speed to compensate for decreasing reactor vessel level. A first adjustment was not large enough to overcome reactor pressure and start feedwater flow. A second increase on the manual potentiometer was made and flow to the reactor vessel commenced. The injection of cold eater caused a power surge and the IRMs began N

to increase. The operator at the controls attempted to range-up the IRMs to

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avoid the upscale trip but was unable to range-up all of the IRMs rapidly J

enough and at 0630 IRM channels B and C reached the upscale trip causing a reactor scram.

The operators performed the required actions of Off Normal Instruction (ONI)-C71 " Reactor Scram (Unit 1)" to place the plant in a stable condition.

At 0642 the MFP was started and placed on the Startup Level Controller to maintain reactor vessel level. The 3 TDFP was secured. The transient analysis was completed and approval to restart was granted by the Plant Manager on January 5.

The plant entered Operational Condition 2 on January 27 following; completion of the planned maintenance.

The causes of the event were instruction inadequacy and design deficiency.

Integrated Operating Instruction (101)-3 " Power Changes" and 101-4 "Shutdowr" did not provide adequate guidance to utilize the MFP, whenever available, for plant shutdown. 101-4 also failed to provide a proper sequence for feedwater control when the MFP is unavailable.

By making the decision to use the B TDFP and without other guidance, the operators were ultimately required to use manual potentiometer turbine speed adjustment for feedwater flow control. This

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.emmumace== mumm method of feedwater control is extremely sensitive and has no feedback to dampen changes.

The Startup Level Controller and the Low Flow controller do not provide adequate overlap for easy transition from one mode of Feedwater control to the other. Manual control of the TDFP is required when reactor pressure decreases below 850 psi due to the flow capacity of the TDFPs minimum flow valves. The maximum flow through the TDFPs minimum flow valves is less than the minimum flow for the Startup Level Controller in automatic. If the capacity of the minimum flow valves was greater, the IDFP controlled by the Startup Level Controller could be utilized to reduce feedwater flow to the reactor vessel to zero.

The Low Flow Controller is utilized to control feedwater flow to the reactor vessel by establishing 100 psi differential pressure across the Low Flow Centrol Valve and throttling the valve to provide the required flow. This method of feedwater control provides the ability to more easily change flow in small incremental steps. However, the maximum capacity of the Low Flow Control Valve is approximately 800 gpm due to the limited span on the Low Flow Controller which allows very little overlap with the Startup Level Controller and therefore, was not being used during this event.

Reactor power level was low during this event and the resulting thermal transient was small. Plant systems responded to the plant transient as designed to maintain the plant in a safe condition. For high power levels, FSAR section 15.1.1 analyzed the Loss of Feedwater Heating as the limiting transient which leads to the reactor vessel receiving cooler feedwater flow.

The high neutron flux scram is the mitigating system and is designed to be single failure proof. Therefore, this event is considered to have no safety significance.

l A previous similar event occurred November 26, 1986 when a reactor scram f

occurred due to an upscale trip on the IRMs (LER 86-086). The scram was a-result of excessive feedwater injection into the reactor vessel during a plant startup while operators were adjusting the Manual Flow Controller of the TDFP A in preparation to transfer feedwater supply over from the MFP. The operator at the controls failed to recognize the magnitude of increasing feedwater flow and the increase in reactor vessel level while adjusting the TDFP A Manual Flow Controller. In response to the event all on-shift licensed operators received training regarding the operation of the Feedwater Control system and the i

sequence of events involved in this reactor scram. A contributing cause to the error was a lack of necessary precautions in the Feedwater Control system operating instruction. This instruction has been revised to caution the operator to ensure sufficient stabilization time is provided while performing controller adjustments.

l In order to prevent recurrence, specific guidance has been provided in 101-3 and 101-4 to utilize the MFP, whenever available, during plant shutdown ar.d steps added to provide a sequence for feedwater control when the MFP is unavailable.

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.nonewance==asmewnn An engineering evaluation was conducted to consider various options available to provide greater overlap of feedwater flow control between the Startup Level Controller and the Low Flow Controller. Either the flow to the reactor vessel when using the Startup Level Controller must be reduced or the flow through the Low Flow Controller must be increased in. order to provide the overlap. The Low Flow Controller will be recalibrates to increase the span allowing up to 2000 gpm flow through the Low Flow Control Valve. The low speed stop for the TDFPs when on the Startup Level Controller will be lowered which will allow the Startup Level Controller to control feedwater flow at a lower rate to the reactor vessel. Additionally, the TDFP manual speed controllers will be changed to reduce the sensitivity by installing a potentiometer with a greater number of turns.

It has been determined that with the above changes, increasing the size of the TDFP minimum flow valves is not necessary to provide adequate overlap between the Startup Level Controller and the Low Flow Controller.

Energy Industry Identification System Codes are identified in the text as [XX].