ML20235L205

Forwards Response to Generic Ltr 87-12 Re Loss of RHR While RCS Partially Filled

ML20235L205
Person / Time
Site:	Yankee Rowe
Issue date:	09/25/1987
From:	Heider L YANKEE ATOMIC ELECTRIC CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
FYR-87-103, GL-87-12, NUDOCS 8710050388
Download: ML20235L205 (20)

Text

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l Telephone (617) 872-8100 TWX 71(h3BO-7619 l

YANKEE ATOMIC ELECTRIC COMPANY 1671 WDicester Road, Framingham, Massachusetts 01701

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September 25, 1987 FYR 87-103 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

References:

(a) License No. DPR-3 (Docket No. 50-29)

(b) Letter, USNRC to YAEC, NYR 87-134, " Loss of Residual Heat Removal (RHR) While the Reactor Coolant System (RCS) is Partially Filled (Generic Letter 87-12)," dated July 9, 1987 Subj ect:

Response to Generic Letter 87-12

Dear Sir:

Reference (b) requested information on the operation of the plant When the Reactor Coolant System (RCS) water level is below the top of the reactor vessel. The attachment to this letter contains our retiponse to this generic letter.

We trust this information is satisfactory; however, if you have any questions please contact us.

Respectfully, YAN 'EE ATOMIC ELECTRIC COMPANY L. H. Heider Vice President and Manager of Operations GP/22.227 Attachment cc: USNRC Region I USNRC Resident inspector, YNPS 0

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ATTACHMENT RESPONSE TO GENERIC LETTER 87-12 QUESTION NO. 1 A detailed' description of the circumstances and conditions under which your plant would be entered into and brought through a drain-down process and operated with the RCS partially filled, including any interlocks that could cause a disturbance to the system. Examples of the type of information required are the time between full-power operation and reaching a partially

' filled condition (used to determine decay heat loads); requirements for minimum Steam Generator (SG) levels; changes in the status of equipment for maintenance and testing and coordination of such operations while the RCS is partially filled; restrictions regarding testing, operations, and maintenance that could perturb the Nuclear Steam Supply System (NSSS); ability of thc RCS to withstand pressurization if the reactor vessel head and steam generator manway are in place; require:aents pertaining to isolation of containment; the time required to replace the equipment hatch should replacement be necessary; and requirements pertinent to re-establishing the integrity of the RCS J

pressure boundary.

RESPONSE

The Yankee Nuclear Power Station (YNPS) is equipped with loop isolation valves which make it unnecessary to drain down the Main Coolant System (MCS) for the more frequent types of refueling activities.

The capability exists to 1:solate and drain a main coolant loop for steam generator and main coolant 1

. pump inspections, maintenance, and repairs without performing a partial drain l

down of the reactor vessel. The Shutdown Coolant System (SDCS) connections at I

YNPS are located on the reactor side of the loop isolation valves. The only normal refueling activity that requires a partial drain-down is reactor head removal and replacemcat. However, this only requires draining down below the level of the reactor vessel flange, leaving 2.5 feet of water above the top of the loop connections. -

5831R/23.49 l

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Partial drain-down to the level of the main coolant loop connections, both hot and cold legsr is only required at YNPS for maintenance on unisolable MCS components. This has only been required several times in the 27 years of operation at YNPS, and these have only required draining down to the top of the loop r:onnections.

Because of the infrequent nature of this mode of operation, a special procedure (OP-2119) has been prepared for partial drain-downs. Also, since the initial preparation requirements can vary depending upon the specific maintenance being planned, the procedure incorporates provisions for adding additional precautions and prerequisites, as well as special valving and tagging lists. The procedure must be reviewed by the Plant Operation Review Committee before it can be implemented, and receive Shift Supervisor approval before the procedure can be performed.

1 With regard to the specific information requested:

1.

Approximately 32 hours3.703704e-4 days <br />0.00889 hours <br />5.291005e-5 weeks <br />1.2176e-5 months <br /> is needed to go from full-power operation to Mode 5 operation in which drain-down would be possible. This includes ten hours to reduce load from 100 percent to zero percent under normal ramp rates and 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br /> to cooldown to Mode 5 (cold shutdown conditions). During coastdown operation, the load reduction phase is somewhat shorter. The earliest drain-down has occurred from power operating conditions is approximately 69 hours7.986111e-4 days <br />0.0192 hours <br />1.140873e-4 weeks <br />2.62545e-5 months <br /> after shutdown.

1 2.

At least two main coolant loops must be operable with steam l

generator water level above the top of the tubes, or two Shutdown i

Cooling (SDC) loops must be operable. Normally, the two SDC loops are utilized during drain down. Althouf neither a procedural nor j

a Technical Specification requirement, it is common practice to maintain the steam generator secondary sides full in order to limit the radiation dose rates in the loop work areas.

In case of boiling due to loss of shutdown cooling during partially drained operation, the steam generators could, therefore, be available for reflux heat transfer, depending on the main coolant loop lineup, the location of any MCS openings, and the water level in the MCS. 5831R/23.49 j

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3.

There are no Technical Specificuticn requirements regarding containment integrity wnile in the drained-down condition.

Technical Specifications require that refueling integrity be set during core alterations or movement of irradiated fuel within the containment; however, the drained-down condition precludes such activities. Plant procedures do not require that containment integrity oe set either. A prerequisite was added to OP-2119 in I

1986 and 1987 to require that containment refueling integrity be set prior to and during the establishment of partially-drained I.,

operation; however, in 1987 a coincident procedural precaution allowed integrity to be broken as necessory to transport equipment to and from containment. This included removal of the equipment hatch, although time during which integrity was broken was to be minimized per the precaution. Replacement of the equipment hatch to establish integrity takes less than two hours.

See the response to Question No. 5 for additional precautions and prerequisites iciposed during partial drain-down operation.

QUESTION NO. 2 A detailed description of the instrumentation and alarms provided to the operators for controlling thermal oud hydraulic aspects of the NSSS during operation with the RCS partially filled. You should describe temporary connections, piping, and instrumentation used for this RCS condition and the quality control process to ensure proper functioning of such connections, piping, and instrumentation, including assurance that they do not contribute to loss of RCS inventory or otherwise lead to perturbation of the NSSS while the RCS is partially filled. You should also provide a description of your ability to monitor RCS pressure, temperature, and level after the RHR function may be lost.

RESPONSE

Level indication is provided both locally and remotely in the Control Room.

Local indication is via clear plastic hose connected to a MCS instrumentation tap.

Remote level indication in the Control Room is provided 5831R/23.49

l by a pressure transmitter connected to the same instrumentation tap as the local hose indication. The pressure transmitter and hose are both vented to containment atmosphere. The instrumentation tap for these level indicators is a 3/4-inch pressure tap set at 45 from vertical in the top of Loop 1 hot leg and, thus, they are accurate to approximately 2" below the top of the hot leg. For drain-down to near the top of the hot legs, additional local indication is provided by connection to the Main Coolant Drain System with

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clear plastic hose which is vented to containment atmosphere. This provides reactor level indication down to the bottom of the main coolant legs.

A core exit thermocouple is connected to the same cabinet in the Centrol Room which provides the remote level indication described above. This portable cabinet is referred to as the " refueling cabinet," and is installed during refueling periods as well as other times when the MCS is vented and level and temperature indication are needed.

It provides level, temperature, and heatup/cooldown rate indication to the operators. Level, and heatup rate alarms driven by the refueling cabinet are provided on the main control board.

The SDC control panel on the south wall of the Control Room provides indication of SDC flow and temperature. Temperature indication is from a point downstream of the SDC heat exchanger and is indicative of reactor vessel inlet conditions when SDC is in operation. Additional local indication of SDC temperature upstream of the heat exchanger is available in the Primary Auxiliary Building.

Instrumentation connections to the refueling cabinet are installed and calibrated by qualified I&C Department personnel in accordance with applicable procedures (0P-1600, OP-1601, DP-6727).

The refueling level transmitter is a pernenently installed component that is wired through to a jack inside the main control board in the Control Room to which the refueling cabinet is connected. Similarly, a thermocouple jack is permanently installed in the main control board to which a thermocouple extension lead from the refueling cabinet is connected. The thermocouple jack is connected to one of the permanently installed core exit thermocouple. Other than plugging the cabinet into a 115 V outlet, the only temporary connections needed to place the refueling cabinet level and temperature instrumentation into service are these plug-in-type connections made within the main control board. These 5831R/23.49

l connections are made in accordance with plant Procedure OP-1600, " Assembly of the Refueling Main Coolant Level and Temperature Channels RF-L-704 and RF-T-703."

Calibrations of_the refueling level and temperature instrumentation are performed in accordance with plant Procedures OP-1601,

" Refueling Main Coolant Level Channel (RF-L-704) Calibration" and DP-6727,

" Calibration of the Doric Series 410 Trendicator and Munro Heatup/Cooldown Indicator," respectively.

The connection, valving, and reading of the clear plastic hoses used for manometer-type indication of Main Coolant System level is performed by the Operations Department. A hose is connected to the same Main Coolant System instrumentation tap as the refueling level transmitter via its own isolation valve and sees the same differential pressure as the transmitter; i.e.,

the Main Coolant System (top of Loop 1 hot leg) to containment atmosphere differential pressure. Ordinarily, this manometer hose is only valved in when a reading is taken locally to verify the remote level indication observed in the Control Room. Level is gauged by comparing the hose level to permanent markings affixed to the shield wall in the loop compartment.

Because an operator is present to perform the valving and take the level readings when the manometer hose is unisolated, any leakage of Main Coolant System inventory due to hose connection error or degradation should be immediately detected and mitigated.

Loss of SDC would render the SDC temperature indication inaccurate as far as core temperature monitoring is concerned.

The refueling cabinet temperature indication would continue to provide accurate core exit temperature conditions independent of shutdown cooling flow. Accurate level indication would also be available provided the Main Coolant System remains vented to and at the same pressure as the containment atmosphere.

Should shutdown cooling be absent long enough, however, pressurization of the Main Coolant System (or portions of it) due to boiling would lead to erroneously high level indication; i.e.,

indicated level would be higher than the actual level. Under pressurized conditions, the refueling level channel wculd actually indicate main coolant pressure, in inches of water, up to its scale limit of 360 inches (about 13 psig). local hose manometer level indications would be similarly erroneous under pressurized conditions as these are vented in the same fashion as the level transmitter. 5831R/23.49

.9 During partiel drain-down operation to approximately one foot below the reactor head flange for head removal, it is necessary to disconnect all of the core exit thermocouple because their leads penetrate the head.

In this condition, a loss of shutdown cooling flow would result in no direct indication of main coolant temperature. Loss of shutdown cooling due to vortexing in this condition is not plausible because the main coolant legs remain in a filled condition with approximately 2.5 feet of water above the top of the loop connections to the reactor vessel. Upon loss of shutdown cooling in this condition, only reactor level indication would be available.

Level instrumentation would provide accurate level indication until saturation conditions are reached, at which time, reactor vessel pressurization would cause an erroneous, increasing trend in indicated level.

It has been plant practice to station dedicated operators to continuously monitor:

o Shutdown Cooling System flow indication in the Control Room, o

Shutdown cooling pump operation locally at the pump cubicle, o

Main Coolant System local hose level indication, and o

Main Coolant System opening (s),

i during partial drain-down operations.

QUESTION No. 3 Identification of all pumps that can be used to control NSSS inventory include:

(a) pumps you require be operable or capable of operation (include information about such pumps that may be temporarily removed from service for testing or maintenance); (b) other pumps not included in Item a (above); and (c) an evaluation of Items a and b (above) with respect to applicable Technical Specification requirements. 5831R/23.49 l

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RESPONSE

Partial drain-down of the MCS would occur in either Mode 5 or Mode 6 operation. The pumps required to be available per plant Technical Specifications depend upon the mode of operation. ' Mode 5 operation requires an average coolant temperature 1200 F and the reactor vessel head installed and bolted. Mode 6 operation requires an average coolant temperature 1140 F with the reactor vessel head unbolted or removed with fuel in the vessel.

In Mode 5 operation, plant Technical Specifications require that at least one charging pump be operable. Mode 6 operation requires that at least two charging pumps In operable. Mode 6 operation at a low water level also requires that both RHR loops be operable. This requires that both the SDC pump and its backup, the Low Pressure Surge Tank (LPST) cooling pump, are operable. One of these two SDC pumps would be in operation providing cooling to the core while in a drained down condition. The other pump would be available, but valved out.

This pump could be used to control NSSS inventory by aligning its suction to the LPST and its return to the MCS.

The pumps listed above are those required to be operable by plant Technical Specification. Plant Procedure OP-2162, Attachment E, " Operation of the Shutdown Cooling System During Periods of Low Main Coolant Level,"

requires the following pumps available:

1.

The SDC pump is operating normally.

2.

The LPST cooling pump is availtble as a backup.

3.

All three positive displacement charging pumps are available for makeup, if possible.

In addition, this procedure states that the method for increasing or decreasing MCS level should be defined.

In addition to the pumps that are required to be operable, the following pumps are capable of adding water to the MCS: 5831R/23.49

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'1.

Three-trains of safety injection pumps. Each train consists of a high and a low pressure pump in series. Any one pump can provide MCS makeup. This results in six pumps capable of providing~ makeup.

2.

Two motor-driven emergency feedwater: pumps (150 gpm each) and one steam-driven pump (80 gpm). Because-of the installation of a cross-connect line to the charging line, the capability exists to use any one of these three pumps to add water to the MCS.

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3.

The Safe Shutdown System primary makeup pump. This pump is part of a dedicated shutdown ysteu installed in response to Appendix R to 10CFR50. This pump can add 15 gpm to the MCS.

1 The availability of the pumps listed above would depend upon any needed maintenance. All of the pumps listed are used in emergency systems only, and have no normal operation requirement minimizing maintenance due to normal wear.

QUESTION NO. 4 A description of the containment closure condition you require for the conduct of operations while the RCS is partially filled. Examples of areas of consideration are the equipment hatch, personnel hatches, containment purge valves, SG secondary-side condition upstream of the isolation valves (including the valves), piping penetrations, and electrical penetrations.

RESPONSE

There are no Technical Specification or permanent procedural requirements regarding containment closure during partially filled operation.

Drain down to partially-filled operation is only performed in either Mode 5 or Mode 6.

There are no Technical Specification requirements for containment integrity during Mode 5 operation.

In Mode 6 Technical Specifications require that a form of containment integrity known as " refueling integrity" be set during core alterations or movement of irradiated fuel within the containment.

Refueling integrity is a state in which the equipment hatch is closed and secured by at least four bolts, at least one of the two personnel airlock doors is closed, and each penetration providing direct access from 5831R/23.49

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containment atmosphere to the outside atmosphere is either closed or capable l

i of being closed by an operable isolation valve.

Water level requirements for core alterations and irradiated fuel movement preclude drain-down to partially-filled operating conditions; and, therefore, the refueling integrity requirement does not apply.

In 1986, refueling integrity was required by procedure throughout the partially-filled operating condition.

In 1987, refueling integrity was required as a procedure prerequisite to achieving the partially-filled condition; however, a coincident procedural precaution allowed for breaking integrity, for limited periods, once a stable, partially-filled operating condition had been established.

Review of plant-logs during partially-drained operation prior to 1986 indicates that, although not required, refueling integrity was typically established, however, this cannot be shown definitively.

QUESTION NO. 5 Reference to and a summary description of procedures in the Control Room of your plant which describe operation while the RCS is partially filled. Your response should include the analytic' basis you used for procedures development. We are particularly interested in your treatment of drain-down to the condition where the RCS is partially filled; treatment of minor variations from expected behavior such as caused by air entrainment and de-entrainment; treatment of boiling in the core with and without RCS pressure boundary integrity; calculations of approximate time from loss of RHR to core damage; level differences in the RCS and the effect upon instrumentation indications; treatment of air in the RCS/RHR System, including the impact of air upon NSSS and instrumentation response; and treatment of vortexing at the connection of the RHR suction line(s) to the RCS.

Explain how your analytic basis supports the following as pertaining to your facility:

(a) procedural guidance pertinent to timing of operations, required instrumentation, cautions, and critical parameters; (b) operations control and communications requirements regarding operations that may perturb the NSSS, including restrictions upon testing, maintenance, and coordination 5831R/23.49

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of operations that could upset the condition of the NSSS; (c) response to loss of RHR, including regaining control of RCS heat removal, operations involving l

the NSSS if RHR cannot be restored, control of effluent from the containment if containment was not isolated at the time of loss of RHR, and operations to provide containment isolation if containment was not isolated at the time of loss of RHR (guidance pertinent to timing of operations, cautions and warnings, critical parameters, and notifications is to be clearly described).

RESPONSE

Yankee would like to emphasize that the Yankee plant is equipped with hot and cold leg isolation valves on each main coolant loop. Maintenance of components on the steam generator side of the valves is accomplished by isolating and draining individual main coolant loops.

The only time that a reduction in level to the elevation of the loop piping would be required is for maintenance on either the loop isolation valves themselves, or on unisolable components on the reactor vessel side of the valves.

In this situation, the water level is maintained as high as is practicable to perform the maintenance. This usually results in a water level at or just above the top of the hot and cold leg piping. Due to the absence of air in the loop piping for most maintenance operations that require a reduced level, Yankee's susceptibility to air entrainment due to vortexing and a subsequent loss of decay heat removal is very low.

There are several procedures applicable to operation at reduced main coolant levels necessitated by the need for maintenance of unisolable primary components. Each is described briefly below, along with the precautions and prerequisites applicable to the vortexing phenomenon:

o OP-2162, Attachment E " Operation of the Shutdown Cooling System During Periods of Low Main Coolant Level" l

i This procedure provides the steps necessary to safely lower and maintain the desired main coolant level while ensuring adequate decay heat removal via the Shutdown Cooling System. The procedure contains a number of precautions and prerequisites to provide 5831R/23.49 l

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additional dedicated monitoring of the critical parameters during low level operation. These include:

Changes in the Charging or Purification System operation or-alignment which could affect the main coolant level are prohibited unless absolutely necessary.

Dedicated personnel are required to monitor main coolant level i

and ensure that the level instrumentation functions properly (i.e., no leaks, kinks, or bubbles which could result in false level indication).

Eedicated personnel are required to locally monitor the operating shutdown cooling pump for loss of suction pressure or flow.

Dedicated personnel are required to monitor any openings in the Main Coolant System for spillage.

All hoses and other level instrumentation must be verified responsive to expected level changes prior to decreasing level.

All involved personnel are instructed as to their duties and responsibilities in the event of a loss of level.

If possible, all charging pumps should be available for makeup to the Main Coolant System.

Communications between the Control Room and the various monitoring stations are required.

Shutdown cooling piping interconnections which could cause a level decrease must be checked closed.

Interconnections between the feed and bleed and drain headers must also be checked. 5831R/23.49

s. m-et 23

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o OP-2119. '" Preparation for ~ Maintenance and/or ' Inspection and Return to Service of Unisolable' Main Coolant System Components" This procedure.contains the. steps necessary'to safely. ready,

.unisolable primary components for maintenance or inspection. and to-

. return them to service. This includes a review of'all safety-related valve positions, positioning requirements, and administrative controls to ensure that valves are' maintained in positions -that wil1~ ensure proper operation of all engineered safety features. Reference is. repeatedly made to OP-2162, Attachment'E (discussed above), for main coolant level control.

The procedure contains a~ number of precautions and prerequisites which. ensure maintenance of an adequate main coolant level and-

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-decay heat removal via the Shutdown Cooling System. These include:

The operators are directed to-compare the remote level indication in the Control Room to the local hose indications several times per. shift.

A dedicated operator is required to locally monitor the operating shutdown cooling pump for a loss of suction.

Main coolant temperature is required to be maintained less than 180 F during the repair period.

To prevent inadvertent level changes, all electrically-operated equipment within the Main Coolant System or portion of the system to be worked on are required to be made electrically inoperative and tagged prior to releasing the system for maintenance.

All valves that can be closed that would admit liquids or gases to the system or portion of the system to be worked on are required to be closed and tagged prior to releasing the system for umintenance. 5831R/23.49

e' Dedicated' personnel are required to monitor any Main Coolant:

System opening for spillage.

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, - - The: operators.are cautionedJthat a loss of decay heat _ removal

- with reduced main coolant levels can be. serious. Redundant decay heat removal methods'are required to be available prior-

'to lowering level below the reactor vessel head flange..

-- - Hoses used for leve1' indication are required to be free of.

kinks, sharp bends, or air bubbles which'could interfere with accurate level indication.

Two level indications are required. The normal-refueling' level

. channel provides remote indication in the Control Room down to the top of the loop piping. A hose connected to the drain-header provides local indication down to the bottom of-thc loop piping.. In addition, the drain header isolation valve is required to be tagged closed, with a loop drain valve open to the drain header.

This procedure requires Plant Operational Review Committee and

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Shift Supervisor approval prior to implementation.

9 Maintenance is required to have the necessary equipment and' personnel staged and ready prior to reducing level to minimize the time spent at a reduced level condition.

In addition to the above requirements, which are a permanent part of the procedure, the following items have been included as additional precautions and prerequisites in this procedure:

Containment refueling integrity is required to prevent gross leakage to the atmosphere in the event of a loss of decay heat removal. Refueling integrity is allowed to be broken to bring necessary equipment into the containment. However, the time during which integrity is broken must be kept to a minimum.

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Core exit thermocouple indication is required ir. the Control Room to provide temperature indication in the event decay heat j

reloval is lost.

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The operator is cautioned that main coolant level must be 1

l restored prior to venting and restarting the shutdown cooling j

pump if suction is lost.

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All dedicated personnel are required to review the applicable procedures for loss of shutdown cooling, changeover from the shutdown cooling to the low pressure surge tank cooling pump, and a total loss of ac without Main Coolant System integrity.

o OP-3113, " Loss of Shutdown Cooling" This procedure contains the actions necessary in the event of a loss of decay hest removal due to low main coolant level. The operators are directed to restore main coolant level with charging or safety injection pumps prior to restoring shutdown cooling flow.

The procedure also lists alternate methods of decay heat removal if shutdown cooling flow cannot be restored.

Yankee has not specifically analyzed a loss of shutdown cooling under i

low main coolant level conditions. This analysis will be performed prior to any operation with fuel in the reactor vessel and level below the top of the main coolant legs.

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i As mentioned previously, Ya.ikee has operated on several occasions with q

level at the top of the main coolant legs. No instances of pump cavitation

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were experienced. Therefore, operation with water level at the top of the main coolant legs is possible without concern for vortexing and air ingestion i

l into the SDC pump suction.

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The analysis needed to support procedural modifications will be

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completed by the end of May 1988. The need to perform any additional analysis

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in this area will also be determined by this date.

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L QUESTION NO._6 A brief description of training provided to operators and other

-affected personnel that.is' specific to the issue of operation while the RCS is Lpartially filled. We are particul'arly interested in such areas as maintenance personnel training regarding avoidance ~of perturbing the NSSS and response to l

loss'of decay heat' removal while the RCS is p;rtially filled.

RESPONSE.

Training is provided to all operators'directly involved in partially idrained operation. Training typically-consists of' operating procedure review, emergency procedure review,-responsibility assignment, and. discussion of actions ~to be taken in response.to unexpected level changes or loss of shutdown cooling while in the partially drained condition. Operator licensing l

'andfrequalification training address the general topics of thermal hydraulics, heat transfer and pump operation. This training has recently been revised, as a result of industry experience with partially-drained operations, to include topics specifically associated with partially-drained operation especially vortexing phenomena.

Maintenance personnel training does not specifically include the topics o'f avoiding NSSS perturbations and response to loss of decay heat removal while in the partially-drained condition. They are, however, trained to

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obtain the Shift Supervisor's approval prior to starting, as well as maintaining.him cognizant of the status of activities in the plant.'

In general, maintenance personnel are prohibited from operating any plant system equipment unless released to them by the Operations Department, with the permission of the Shift Supervisor.

QUESTION NO. 7 Identification of additional resources provided to the operators while the RCS is partially filled, such as assignment of additional personnel with specialized knowledge involving the phenomena and instrumentation. 5831R/23.49

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RESPONSE

During partial drain-down operation, personnel are stationed, on a dedicated basis, at various locations in the plant to continuously monitor conditions important to maintaining shutdown cooling. An operator is stationed at.the shutdown cooling pump to continuously monitor pump discharge pressure and flow as well as listen for audible indication of cavitation.

Another operator is located at the shutdown cooling control panel in the Control Room to continuously monitor shutdown cooling flow. Dedicated

. operators are also' assigned to continuously monitor local main coolant level indication and openings in the Main Coolant System (these functions have both been performed by one operator using video monitoring equipment). When assigned, these operators perform only these monitoring duties and serve to augment the normal shift staffing. They have direct communications with the Control Room to immediately report on abnormal or unexpected operating l

conditions while operating with the Main Coolant System partially filled.

QUESTION NO. 8 Comparison of the requirements implemented while the RCS is partially filled and requirements used in other Mode 5 operations.

Some requirements and procedures followed while the ECS is partially filled may not appear in the other modes. An example of such differences is operation with a reduced RHR flow rate to minimize the likelihood of vortexing and air ingestion.

RESPONSE

Other than the dedicated operator assignments and containment integrity requirements discussed in Items 4 and 7, there are no requirements implemented beyond those for normal Mode 5 or Mode 6 operations.

QUESTION NO. 9 As a result of your consideration of these issues, you may have made changes to your current program related to these issues.

If such changes have strengthened your ability to operate safely during a partially filled 5831R/23.49 m

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situation, ' describe;those changes and tell when they were made or are scheduled to be made.-

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RESPONSE

I In response.to the potential loss of decay heat removal due to..

operation at reduced main coolant water levels,' Yankee has implemented changes or is' evaluating.the need for. work in the following areas:

dperator Training

.Following our review of IE Information o.

' Notice 86-101, " Loss of Decay Heat Removal Due to Loss of Fluidi Levels in Reactor Coolant System," Yankee developed a lesson plan covering the vortexing phenomenon and its potential impact'on decay.

heat removal.' It was transmitted to the plant on' August 18, 1987, for incorporation into the Operator' Training Program. Training on the vortexing phenomenon is now given in conjunction with training on the Shutdown Cooling System.

o Analysis'of Plant Response - As indicated in'the response'to Question 5, Yankee will perform an analysis of a loss of shutdown '

cooling under low main coolant level conditions. Operation with fuel in the reactor vessel and level below the top of the main coolant legs (where they connect to the reactor. vessel) will be prohibited'until engineering analysis supporting procedural guidelines on allowabic level and flow conditions for mid-loop operation have been developed. This analysis will be completed by the end of May 1988. At the same time, it will be determined whether any additional analysis is required for this issue.

o Instrumentation - The current shutdown cooling' indications available in the Control Room include shutdown' cooling flow and heat exchanger outlet temperature. However, shutdown cooling inlet temperature is available locally.' Yankee is currently evaluating the'need for shutdown cooling inlet temperature and pump amperage i

indications in the Control Room, and improvements to level instrumentation to increase precision during low-level operation.

This evaluation will be completed by the end of February 1988. 5831R/23.49

o' Procedures - A' review of. procedures related to reduced level operation will be completed prior to the next drained-down operation. This' review will assure consistency between equipment and system status requirements and recommended recovery actions in the event'of loss of shutdown cooling function.

o Equipment - Temporary covers for the main coolant stop valves will be designed and manufactured prior to the next drained-down operation. This will permit re-establishment of normal operating levels during maintenance when the valve body is. removed.

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