Text

Forwards Info Assessing Safe Operation of PWRs When RCS Water Level Below Top of Reactor Vessel,Per Generic Ltr 87-12
	ML20235J271
Person / Time
Site:	Byron, Braidwood, Zion, 05000000
Issue date:	09/25/1987
From:	Morgan W; COMMONWEALTH EDISON CO.
To:	Miraglia F; Office of Nuclear Reactor Regulation
References
	3626K, GL-87-12, NUDOCS 8710010375
	Download: ML20235J271 (40)
	v • d • e

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. [N CCommonwealth Edison'- q

[L ) One First National Plaza, Chicago, Illinois

'\ C ~J Kddress Reply to: Post Offics Box 767

~ \d Chicago, Illinois 60690 0767 September 25, 1987

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Mr. Frank J. Miraglia Associate Director For projects Office of Nuclear Reactor Regulation 7920 Norfolk Avenue Bethesda MD 20014 f3 l

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Subject:

Zion Station Units 1 and 2 l Byron Station Units 1 and 2 M~" %

-a Braidwood Station Units 1 and 2' NRC Docket Nos. 50-295/304, 50-454/455 and 50-456/457 "c$ $i :

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Reference:

Generic Letter 87-12 dated July 9, 1987.

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Dear Mr. Miraglia:

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The above referenced Generic Letter requested the licensee to submit j information to assess safe operation of pressurized-water reactors when the reactor coolant system water level is below the top of the reactor vessel.-

Commonwealth Edison has completed its review pursuant to the requests outlined in Generic Letter 87-12 for Zion, Byron and Braidwood Nuclear power )

Stations. This information is attached in enclosures 1 through 3 respectively, i To the best of my knowledge and belief, the statements contained above are true and correct. In some respect these statements are not based on my personel knowledge, but obtained information furnished by other.

Commonwealth Edison employees, contactor employees, and consultants. Such information has been reviewed in accordance with company practice, and I believe it to be reliable. _

Please direct any questions you may have regarding this letter to this office.

Respectfully, kA . 4M b G

W. E. iorgan Nuclear Licensing Administrator Attachments cc: A. B. Davis - RIII Resident Inspectors - Z/BY/BW SUBSCRIBED and S to l

befog me,thts - day of t >fNW4' , 1987

. 04f\

' Notary Public f \

3626K/bs

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ZION STATION 1

ATTACHMENT 1 ITEM 1 )

A detailed description of'the circumstances and conditions under which jour plant would be entered into and brought through a draindown process and I operated with the RCS partially filled, including any interlocks that could !

cause a disturbance to the system. -Exampics 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 j partially filled; restrictions regarding testing, operations, and <

maintenance that could perturb the nuclear steam supply system (NSSS);

ability of the RCS to withstand pressurization if the reactor vessel head f and steam generator manway are in place; requirements. pertaining to {

isolation of containment;.the time required to replace the equipment hatch j should replacement be necessary; and requirements pertinent to l reestablishing the integrity of the RCS pressure boundary, i

RESPONSE

The plant conditions which would require a partially drained down condition are maintenance, repair or inspection of steam generator primary side tubes, loop stop isolation valves, reactor coolant pump, loop bypass RTDs or leakage from RCS valves which could otherwise not be isolated.

Interlocks which could cause a disturbance to the RCS system prevent over pressurization of the RHR system. The interlocks will automatically close or prevent opening of the hot leg suction valves to the RHR system if RCS pressure is above RHR design pressure. When the refueling cavity is flooded the interlocks are bypassed by de-energizing ,

the valves in the open position to prevent inadvertent closure of the valves.

The worst case (shortest time) duration from full power operation to a drained down condition in the RCS which is to approximately the 591 ft I elevation (RX Vessel flange) is 6 days, 17 hours1.967593e-4 days 0.00472 hours 2.810847e-5 weeks 6.4685e-6 months .

For maintenance. Steam Generator tube draining, Steam Generator manway 1 cover removal, the minimal operating level of the RCS is 8 inches above the loop centerline. This level was based on calculations to preclude I vortexing.

There is no requirement on secondary side Steam Generator level at this time The draining of the RCS is controlled by procedures which outline the ;

methods for lowering and raising reactor coolant levels. Activities included are the actual drain down process, venting draining of the Steam Generator "U" tubes, Steam Generator manway cover removal.

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~2-Special maintenance activities such as Loop Isolation Valve and reactor Coolant Pump repair would require temporary change or special procedures generated in order to insure tight control over such activities.

i Any restrictions governing testing, operations, and maintenance that can l affect the RCS while in the drained down configuration would be imposed by the Station's Operating Engineers during the planning stage for that activity. During any Unit outage there are daily planning meetings that 1 are designated to cover those outage activities.

The Low Temperature /Over-Pressurization Protection System is required to .j be inservice when the RCS is in that configuration. The system is j required to be in' service when the RCS temperature is below 250* F. and l l the Rx Vessel head installed. Additionally the Pressurizer is always !

vented to the containment atmosphere when in this condition.

The only time that containment. integrity is required to be maintained l during cold shutdown and refueling modes is while core alterations are l taking place. The technical specifications allow the equipment hatch or j both doors on the personnel hatch open during this period as long as the ]

shutdown margin is maintained equal to or greater than 10% delta K/K and !

( RCS temperature is maintained less than 140' F. The containment f atmosphere is required to be negative during fuel moves. Any refueling mode accident would result in a minimal containment pressure increase.

Any gas release from fuel failure during this mode would be handled by the fuel building ventilation system.

The time to replace the equipment hatch is two to four hours. The replacement time assumes no interferences in the hatchway from equipment i or Reactor Coolant Pump Motor trackway, the maintenance crew is prepared l to start work, no hatch surveillance, and'the tie down bolts tightened but not torqued.

Actions required to reestablish the RCS pressure boundard are not proceduralized. Worst case scenerio would involve a loss of RHR event while the S/G manways were off during eddy current. The goal during this scenerio would be to reestablish cooling as soon as possible or inject water from other water source allowing water to fall to the 3 containment floor out of manways. j 1

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i A detailed description of the instrumentation and alarms provided to the !

operators for controlling thermal and hydraulic aspects of the NSSS during i operation with the RCS partially filled. You should describe temporary )

connections, piping, and instrumentation used for this RCS condition and the i quality control process to ensure proper functioning of such connections, l I 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.

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RESPONSE

Temporary level instrumentation such as tygon tube is no longer used.

Both units now employ as a permanent system, a stainless steel pipe /lexan sightglass which ties into the loop "D" drain header and is pressure compensated to the pressurizer. The system uses a permanently mounted 20ft. scale graduated in inches which has been benchmarked and physically verified to be accurate. q The RCS level is also monitored via a chart recorder in the centrol-room. The input to the chart recorder is from two transmitters located f in containment. The high pressure tap is located on the Reactor Coolant .J Loop B bypass flow line. The low pressure tap is vented directly to the l containment atmosphere. The transmitters, wide and narrow range, are j calibrated prior to service each refueling outage. l l

Additionally, a new system is going to be installed on botn units during j their next refueling outages replacing the existing level recorder i '

system. This system will employ a wide and narrow range transmitter which will be tied into an incore conduit and pressure compensated to the pressurizer. As to potentially affecting RCS inventory, both systems are (will be) constructed to seismic quality standards and are J (will be) tightly controlled procedurally. !

I Both level systems are controlled procedurally. The procedures instruct I operations when to valve in the level instrumentation, both the level transmitters and the sightglass. Valves critical to the operation of the sightglass are taken out of service to ensure indication is not affected by inadvertent valve manipulations. A comparison check between the two level systems assures agreement between the two. This j comparison is done shiftly when RCS level is below the Reactor Vessel I flange and currently a continuous sightglass watch is performed when the j level is below the top of the reactor coolant loop piping.

Reactor coolant System temperature is monitored via indication in the RHR system.

If the RHR function should be lost, the operators would rely on-direction provided in the procedure specifically for that condition.

They would be required to estimate time to RCS bulk boiling temperatures by using a curve provided in the procedure. The only actual temperature indication is via an operating RHR system. Since the RCS is always in a vented condition, any pressure increase would be negligible but could be monitored by the RHR System pressure indication. Level indication would still be available by the existing systems. .

I ITEM 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),

I and (c) an evaluation of items a and b (above) with respect to applicable TS requirements.

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RESPONSE

Pumps that are required for RCS water inventory control while in drained 1 down conditions are: ]

RHR pumps (2) Capacity each: 4500 GPM ;

1 Charging Pump Capacity 550 GPM

- used for normal make-up !

Other pumps that are administrative 1y out of service for low temperature /over-pressure protection but could be returned to service quickly if necessary are:

Charging Pumps (remaining two) Centrifugal,' capacity: 550 GPM Positive Displacement: 98 GPM Safety Injection Pumps (2) Capacity each: 650GPM

- These pumps are not required to be operable per Tech Specs during this mode of operation, therefore any of them could be out of service for i maintenance.

- Gravity feed from the RWST is also available.

C. See item B above.

ITEM 4 Provide a description of the containment closure condition you require for the conduct of operations while the RCS is partially filled. Areas of consideration should include the equipment hatch, personnel hatches, ;

containment purge valves, SG secondary-side condition upstream of the 1 isolation valves (including the valves) piping penetrations, and electrical penetrations.

RESPONSE

Technical Specifications do not require containment integrity during cold shutdown or refueling modes unless fuel moves are in progress or shutdown margin is equal to or greater than 10 % delta K/K and RCS temperature is less than 140' F.

The electrical and mechanical penetration pressurization systems are not required to be operable in cold shutdown and refueling modes as long as conditions above are maintained.

l The escape hatch is open during the outage to allow cable passage in order to perform maintenance activities such as Steam Generator tubeL l

I inspection, sludge lancing, sleeving, and plugging. The housing around the hatch is temporarily sealed with plastic and duct tape that restricts leakage to the outside atmosphere. In addition a shiftly surveillance is performed on the hatch temporary seal to ensure integrity is maintained. The containment and fuel building are at a negative pressure and leakage from the temporary seal would be into containment.

The equipment hatch is removed for.the duration of the outage allowing east access of equipment and personnel. The equipment hatch can be

. replaced in two to four hours.

There are no restrictions on the secondary-side equipment involving containment integrity when in the drained-down configuration.

ITEM 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 dre.indown 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 l RHR to core damage, level differences in the.RCS and the effect upon I 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 enalytic 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 l coordination of operations that could upset the condition of the NSSS; and I

(c) response to loss of RHR, including regaining control of RCS heat removal, operations involving the NSSS if RHR cannot be restored, control of effluent from the containment if containment was'not in an isolated condition 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).

l RESPONSE The procedures in the control room which outline the operations during a partially drained system are called maintenance instructions (MI). The MI contains specific instructions for draining thelRCS and specifies the different levels for which certain maintenance activities can be-performed. Such activities are venting, draining Steam Generator tubes, ;

Steam Generator manway removal, and placement of the Rx Vessel level systems in service. These procedures are very specific to ensure that all major evolutions occur in a very predictable manner.

The three MI's typically used during an outage are MI-1, MI-2 and MI-6.

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MI-1 is Zion Stations procedure for draining the reactor coolant system for refueling.. The RC system is initially solid and the pressure is approximately 100 psig. The system is prepared for drain down and the system pressure decreased to 50 psig by manipulating letdown flow. Once-drain down is commenced a 10 psig cover gas is maintained in the pressurizer and the pressurizer level is dropped to 20%. The reactos vessel level sightglass is placed in service and the next step lowers reactor vessel level to the 591 ft elevation (reactor flange). At the 591 ft elevation the steam generators are burped followed by purging the l

reactor head. The nitrogen cover gas is removed and system pressure is reduced to 0 psig. The redundant level indicator LT-22A and B is placed in service and the vessel level can be lowered to 584 ft 8 in level.

The 584 ft 8 in level corresponds to the lowest safe operating level which is 8 inches above the loop centerline. The steam generator manways are removed and drained down activities are performed. Upon completion of the maintenance activities the manways are replaced and the vessel level is raised to.589 ft in preparation for reactor head removal. When MI-l is completed the operator proceeds to MI-6.

MI-2 is Zion Stations procedure for reactor coolant system fill and vent. Upon completion of M1-6 the reactor coolant system is ready to fill and vent. Seal injection to the reactor coolant pumps is established. The letdown is adjusted to 0 flow and the reactor coolant level is raised to 20% pressurizer level. At 20% pressurizer level the level instrumentation is isolated and the reactor head is vented. The pressurizer is filled and vented. The reactor coolant system is increased to 100 psig at which time the reactor head and pressurizer are vented again. The pressurizer relief tank and the reactor coolant drain tank are aligned for normal operation. The reactor coolant system is pressurized between 375-400 psig in order to bump the reactor coolant pumps. The system pressure is decreased to 100 psig to vent the reactor head and pressurizer. After venting is completed the RC system is prepared to heatup.

l MI-6 is Zion Stations procedure for filling and draining the refueling cavity and fuel transfer canal. After MI-1 is complete MI-6 starts preparing the refueling cavity and the fuel transfer canal. The transfer canal is filled. The reactor head is removed simultaneously the refueling cavity level is raised. Once the cavity is full the refueling operations begin. After refueling the cavity is drained using specific drain paths outlined in the procedure and the reactor head is '

replaced. Reactor vessel level is maintained at the vessel flange and MI-6 is completed. The next step is to fill and vent the reactor vessel

, using MI-2.

1 The following variation of MI-1, MI-2 and MI-6 are used to. perform I specific activities.

1) MI-1A Draining a Reactor Coolant Loop with Steam Generator primary l Manways Installed, j

2) MI-1B Draining the Reactor Coolant System for Maintenance. '

3) MI-1C Draining the Reactor System for RCP Seal Repair.

4) 'MI-lD Draining and Filling a Single Reactor Coolant Loop.

5) -MI-1E Isolating and Draining the Reactor Coolant Loops.

6) MI-1F Draining RCS for Maintenance-After Refueling Outage.

7) MI-1G Draining the Reactor Coolant System to 20% pressurizer level, Uncouple RCP's, Raise Level to 80% for ILRT and Drain to 20%.

'8) MI-2A Reactor Coolant System Fill and vent after RCP Seal Repair.

9) MI-6E Unisolating and Filling A Reactor Coolant Loop (s).

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The MI contains all the necessary precautions and prerequisites placed in strategic locations throughout the procedures to ensure that the operator remains aware of the vulnerability of the Unit while in the drained-down configuration. Several examples are as follows:

1. Ensure redundant and diverse methods of decay heat removal are available to prevent the inability to remove decay heat.

2. purging and venting of the RCS is prohibited if the level indication is not acting in predictable manner.

3. Critical RCS levels are listed where it has been identified that there can be a potential of vortexing at the RHR suction t. the RCS.

4. RHR flow rate is reduced to the minimum necessary to maintain adequate RCS cooling thus further reducing the change of vortexing.

5. Requirements are placed on the operation of the level systems.

Shiftly comparisons between systems are required to ensure-consistency. When'the RCS is below the top of the RCS loop piping, a continuous sightglass watch is in effect with constant control room communication.

The treatment of level discrepancies between instruments is addressed in-the MI, whether the cause is from air entrainment or other sources.

l When the reactor vessel level is below the vessel flange a shiftly comparison between level instrumentation is required. If at any time there is a discrepancy between level indicators, all major evolutions must stop until the discrepancy is resolved. When the RCS level is below the top of the loop piping the sightglass is in continuous watch. :

The response to loss of RHR is contained in the Abnormal Operating procedures 6.3 titled " Loss of RHR Shutdoen Cooling". Time to RCS ,

sauration may be estimated from a graph that is contained in this !

procedure. The graph was generated from an energy balance equation based upon the following conservative assumptions: >

1) Three year core burnup

2) No heat losses.

3) Reactor Coolant level is at lop centerline.

4) Initial RC bulk temperature is at 100* f.

S. No RHR cooling.

The AOp addresses vortexing as well as other potential causes of loss of RHR; and it includes corrective actions to restore normal RHR operations 'l as well as alternative methods of decay heat removal.

The AOp addresses five possible causes for loss'of RHR and the actions required to restore normal RHR cooling. The causes and required actions are as follows:

1) If erratic RHR pump amps or flow indication or zero flow occurs, stop the running pump (s). If the system is solid maintain the pressure with the charging system. If vessel level is too low, l raise the level using charging or line up RHR suction to the Refueling Water Storage Tank (RWST). Vent the pump and verify ]

correct pump line-up and restart the RHR pump. ;

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2) IIf"the running RHR pump (s) trips and the system is solid adjust charging to maintain pressure. If the pump (s) trips to a low level

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restore. level by adjusting charging or line-up RHR suction to the j RWST. Start the other pump. .j

3) If the pump suction. valve closes, stop the pump and maintain 1 pressure with charging when solid. Find the cause for the valve '{

closure. Open the valve and restore RHR.

4) 'If the throttle valves close, check RCS temperature and open the :

1 other train's throttle valve.

5) If reactor vessel level is to low increase charging flow and/or !

line up RHR suction to the Rkv1. Once level is restored proceed to f normal RHR cooling. I procedures currently will not allow operations to lower the RCS level below 8 inches above the loop centerline. The only time the plant is in ;

this configuration is to drain the Steam Generator Tubes. This level )

was chosen for the following reasons:

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1) Past operational history dictates that whenever the RCS level is j l

below 6 inches above the loop centerline, at a RHR flow rate of l 3000 gpm, the pump will in many instances become airbound due to j vortexing. 1

2) When the system has operated at the purameters in item 1) above, the flow induced pipeline (cold leg injection) noise is high compared to tne operational parameters in use today.

3) Calculations based on an empirical formula obtained from a fluids I handbook shows that the current parameters in use are well above i the parameters where vortexing will occur. 1

4) During the past two refueling outages, there was no evidence of .

l vortexing when operating at the 8 inch above loop centerline level.

l l ITEM 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 partially filled. We are particularly interested in such areas as !

maintenance personnel training regarding avoidance of pertubing the NSSS and response to loss of decay heat removal while the RCS is partially filled.

RESPONSE

The following evolutions / transients pertaining to loss of shutdown cooling are included in Licensed Operating Retraining as a part of simulator i training during NPO 436 using IC-5 (Cold Shutdown / Partial Drain condition) i or IC-2 (Cold Shutdown):

1. RHR pump trip due to loss of suction (vessel level decreased below-minimum required).

2. RHR Pump fail to start.

3 .. Reactor Coolant System leak /small LOCA.

4. RH8701 and/or RH8702 (RHR Pump suction valves) fail closed.

5. RHR Heat Exchanger bypass valve failure.

6. RCp #1 Seal failure while starting Reactor Coolant Pumps.

7. FCV-121 (Charging Flow Control Valve) failed closed.'

8. Centrifugal Charging Pump trip,

9. Volume Control Tank leak.

10. pressurizer Power Operated Relief (PORV) failed open with isolation failed open.

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Annual retraining is provided on calibration of electronic instruments, (SOER85-4). Training is provided in recognition of loss of RHR during I&C simulator training.

l Although no training is conducted for the Mechanical Maintenance and Electrical Maintenance Departments that is specific to the issue of operation while the RCS is partially filled, it should be recognized that maintenance activities that these groups perform must be authorized by licensed shift supervisors and must be performed under the Ceco Out Of Service procedure.

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ITEM 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.

RESPONSE

Refer to the response to Request No. 6. At this time additional training is conducted with the operators prior to draining dcwn to the !

loops. Response to Request No. 9 discusses other resources in place and being developed.

ITEM 8 Compare the requirements implemented while the RCS is partially filled and the requirements used in other Mode 5 operations. Some requirements and procedures followed while the RCS is partially filled may not appear in the other Modes. An example of such differences is operation with reduced RHR flow rate to minimize the likelihood of vortexing and air ingestion.

RESPONSE

Requirements specifically for a partially filled system are as follows:

1) Reduced RHR flow and operation of one RHR pump when drained down below the top of the loop piping. l

2) The drain down procedures outline the drain paths to be used, thus f eliminating itiadvertent draining from an uncontrolled drain path. I

3) Minimum operating levels to prevent loss of RHR due to a low RCS I level.

4) A comparison between level indicators increases in frequency when j the RCS is lowered towards its minimum operating level. )

5) Redundant methods of decay heat removal are available when ;

partially drained.

6) Reactor coolant temperature must be between 100*F and 120*F when filling and venting reactor coolant system. Also the RC j temperature must be approximately 90*F when the refueling cavity level is being maintained, filled or drained.- The temperatures are in comparison to cold shutdown temperature of less than 140*F.

JTEM 9 As a result of consideration of these issues, changes to current programs may have resulted. If such changes have strengthened the ability to operate safely during a partially filled situation, describe the changes and tell when they were made or are scheduled to be made, c

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.. 3 RESPONSE j The current requirements were developed prior to receipt of Generic -

Letter 87-12 in response to previous loss of RHR events due to a low reactor coolant level. The changes which have enhanced the operation of the RHR system have taken place in procedure development, operator training and hardware modification.

The following is a brief summary of the changes that have been made or are currently in progress.

There have been changes to several operating and abnornial operating procedures. There have also been changes to maintenance procedures.

The revised procedures control major evolutions,-instrumentation, operational RCS levels, and RHR pump flow rates. These changes help to insure that the systems will perform in a predictable manner.

Among the changes to the operating procedures are the addition of a- i minimum operating level and reduced RHR flow rate requirements. These changes provide guidance to prevent vortexing.

There have been changes to the training procedures. 'The simulator has been reprogrammed to simulate a loss of RHR flow event similar to past Zion events. Currently there is an interim training requirement to provide a brief refresher on mid-loop operations prior to draining down to the mid-loop elevation. This requirement will be in effect until completion of all current modifications to the level monitoring systems.

Currently level monitoring instrumentation consists of an electronic system with indication in the control room and a rigid sightglass system for local indication in the containment, There are many precautions that have been added to procedures in order to ensure reliability of these systems.

The following are a few of the requirements for these systems. The level transmitters for the electronic level monitoring system are calibrated prior to use. Valves for both the sightglass and the electronic system are taken out of service to prevent inadvertent isolation of the valves when the RCS is at a critical level. Frequent cross-comparison between the electronic system and the sight-glass system is required. Any discrepancies (in excess of the calculated allowable) must be resolved prior to draining to critical levels and at any time during their operation. Eliminating the discrepancies enhances .)

level control and it increases operator confidence.

Several changes to instrumentation has taken place and future changes are planned which will enhance the ability to operate with a partially filled RCS. !

The sightglass has been converted from Tygon hose to a rigid plastic !

t (Lexan) system eliminating the problems associated with a temporary system, such as a floating scale, loop seals, and hose kinks. In addition, most of the Tygon that tied into the pressurizer has been !

replaced with stainless steel pipe and tube. The remaining Tygon will be replaced as a part of the modification to the electronic system.

That work will be done during the next refueling outages'in 1988.

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. l The new electronic level indication system will be installed during the l next two unit refueling outages. This new system significantly improves .]

accuracy and reli-bility. The transmitters will tie into one of the incore conduits. This increases the system monitoring range and it eliminates problems that may be caused.by dynamic effects. Additionally the reference leg will compensate the transmitters to the pressurizer.

The control room indication will be provided via a new chart recorder which has LED indicator and CRT display. Level alarms with set points for high, low and low-low levels will be added to the control' room 1 l

panels, Another modification which has been designed and will be installed soon will provide control room alarm of low RHR pump suction pressure. The I alarm will~ alert operators in the control room of a condition.which could result in the loss of RHR function.

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BYRON STATION ATTACHMENT 2 ITEM 1 A detailed description of the circumstances and conditions under which your plant would be entered into and brought through a draindown 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 3 maintenance and testing and coordination of such operations while the RCS is l' partially filled; restrictions regarding testing, operations, and l maintenance that could perturb the nuclear steam supply system (NSSS);

ability of the RCS to withstand pressurization if the reactor vessel head I and steam-generator manway are in place; requirements pertaining to.

l isolation of containment; the time required to replace the equipment hatch .

should replacement be necessary; and requirements pertinent to j reestablishing the integrity of the RCS pressure boundary.

RESPONSE

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Plant conditions that would require a drain down of the RCS to mid loop I levels can be separated into two groups. The first group being planned I maints1ance outage, the second being a forced outage for maintenance. I 1

i planned maintenance items that require drain down are; loop stop l

isolation valve maintenance, steam generator primary side testing and I inspections, reactor vessel head work (any head penetration work) and l loop bypass RTD work. j l Unplanned maintenance or forced outage work consists of the following:

reactor coolant pump seal repair / replacement, excessive RCS leakage such as that through RCS boundary valves and Emergency Core Cooling System check valves, and steam generator tube leakage. j

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Interlocks that could cause loss of RH cooling are the failure of RCS l pressure transmitters that prevent opening of hot leg suction valves or !

cause automatic closure of hot leg suction valves.

l The minimum time required from one hundred percent power operation to ;

mid loop operation, all four loops drained, is a nominal value of fifty !

hours. This is a minimum time assuming Mode 5 final conditions with a 1 minimum of chemistry and radiological related actions necessary to allow maintenance on an RCp seal. However, based on Zion Station Operating experience, a routine draindown for refueling activities could take up to six days. By Technical Specifications, with one RH train operable in i I

cold shutdown, a minimum of two steam generators with a secondary level of greater than forty one (41) percent are necessary. With all four steam generators drained two RH trains must be operable. Otherwise, no '

restrictions on steam generator level are maintained, i

Technical Specifications require a Cold Overpressure protection System i to be operable in Modes 4, 5, and 6 with the Reactor Vessel Head on.

The system shall consist of one of the following; 1) 2 power Operated

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Relief Valves with lift setpoints that vary with RCS temperature, 2) 2 ,

RH suction reliefs each with a setpoint of 450 psig i 1% or, 3) The RCS- K depressurized with an RCS vent of grecter than or equal to 2 square inches. This system should provide edaquate protection in the event of~ ,

a loss of RH Cooling and the resultant 3radual heatup and pressurization ;

of the RCS. )

The shift engineer (SRO), shift control. room engineer (SRO), unit operating engineer (SRO), and unit Reactor Operator limit work activities and have primary responsibility for all work and testing performed in any mode or power. level. The work planning department interfaces with Maintenance, Technical Staff and Operations to coordinate activities associated with specific plant conditions.

Licensed individuals within the work planning department add another l level of credibility and assurance that Technical Specifications are adhered to and minimum perturbance of the NSSS occurs during a partially filled condition of the RCS. No additional administrative restrictions are deemed necessary, i

No administrative restrictions on containment integrity during draindown operations currently exist or are anticipated. See response #4 for more detail.

The RCS pressure boundary is administratively controlled either by Out of Service Action, Nuclear Work Request (NWR), special test procedure, or temporary alteration procedures.

Mode change check lists and associated " checklist" sheets verify system lineup and containment integrity. Although no single specific procedure exists, the above listed administrative controls and procedures are used to achieve desired plant status. Outage computer schedules and Total Job Management NWR tracking are also used to assure proper plant restoration and safe plant operation.

The time required to replace the hatch, in an emergency situation, would be approximately six to eight hours.

ITEM 2 A detailed description of the instrumentation and alarms provided to the operators for controlling thermal and 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 j the RCS is partially filled. You should also provide a description of your j ability to monitor RCS pressure, temperature, and level after the RHR j function may be lost.

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1

RESPONSE

i Description of the Instrumentation and Alarms provided to the operators for controlling the thermal and hydraulic aspects of the NSSS during operation with the RCS partially filled.

_ _ _ - - 1

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1 Three methods of Reactor-Vessel Level Indication are available during Mode 5 operation when RCS level is at or near the mid-plane level of the 3 l RCS Loops. All three methods are either unaffected by changes in RCS 1 pressure or have a compensation feature to account for RCS pressure l changes. The three methods are as follows (please refer to Figure 1 for a relationship between the various level indicators available):

Reactor Vessel Level Indication System (RVLIS) i Two independent trains of indication consisting of two vertical stacks of Heated Junction Thermocouple (HJTC's) are mounted in the Upper Head i and Plenum of the Reactor Vessel. They require no pressure compensation to differentiate between collapsed water level and air / steam. Three of the sensors per train are specifically placed at the bottom of the RCS loop, mid plane of the loop and top of the loop. This placement allows j indication of water level either between bottom and mid plane of the l loop (27%) or between mid plane.and top of the loop (37%). An indication of 55% or greater would indicate an RCS level above the top of the loops. Two remote level indicators, one for each train, are i located on Main Control Room' panel 1/2PM05J. They provide continuous; indication of either Reactor Head or Plenum Level Indication. This system is permanently installed on both units and should normally be ,

available as redundant indication of RCS level in the Reactor Vessel ]

during Mode 5. However, it would likely not be'available in Mode 6 I because it would be disconnected as part of the Reactor Vessel Head !

removal. j i

ILI-RYO46 RCS Drained Level Indicator i

A differential pressure (d/p) level transmitter, ILT-RYO46 is placed in !

service at 5% level on Pressurizer Cold Calibrated Level Indicator l ILI-462*. This is accomplished by opening a manual valve placing the i reactor vessel water level static head from one side of the transmitter !

in service. The manual valve leads to a tee in Incore Tube N-8 through )

which RCS water level is sensed. The pressure compensating leg of the l transmitter is unisolated by a manual valve from the reference leg I 1LT-460. ILT-460 is one of 3 Pressurizer Hot Calibrated Level transmitters. The compensating leg of the level transmitter allows the level indication to remain accurate even after RCS pressurization. The instrument is designed for full RCS operating pressure although it is normally isolated prior to RCS pressurization. ILI-RYO46 is indicated on the main control board IPM06J and indicates in feet elevation. Its range is 392' to 402.5' with 393' representing the centerline of an RCS Loop. A low level annunciator associated'with ILT-RYO46 is located on Main Control panel IPM06J. It will alert the operator when a decreasing ,

level of 393' is reached. About 5 feet of elevation difference exists between 0% level on ILT-460 and 402.5' on ILI-RYO46. Tygon tube is used ,

to make this transition. ILI-RYO46 is another permanently installed indicator on Unit 1. It is expected that a similar modification will be installed on Unit 2 during its first refueling outage.

Two other level indicators ILI-RYO47 (Unit 1) and ILI-449 (Unit 2) exist and are shown in figure 1 but do not apply to the discussion of drained RCS level with the Reactor Vessel Head installed.

1LI-462, Pressurizer Cold Calibrated Level indicator,.is located on Main Control Panel-IPM05J. It indicates in percent pressurizer level and would be the first level indicator used in the draindown process.

Tygon Tube As previously mentioned, this indicator of RCS level is only needed on Unit 1 as a transition indicator between the Pressurizer Cold Calibrated Indicator and 1LI-RYO46 for near mid-plane operation on Unit.1. On Unit 2 however, it-is the only available indication, until.the ILI-RYO46 modification is completed, for Mode 6 operation with RVLIS disconnected. Using a Nuclear Work Request and by procedure the water level sensing side"of the tygon is attached to a temporarily disassembled process sampling line on RCS Loop 4. The process sampling line is outboard of the Loop Stop Isolation Valve,. relative to the Reactor Vessel, and is located in the crossover leg of the loop. It would therefore be indicating Cold Leg Loop 4 level. Although Cold Leg Level Indication is not entirely desirable, few penetrations' exist-l between the'RCS and the Loop Stop Isolation Valves or between the Hot i Leg Loop Stop Isolation Valve and the. Steam Generator.. An alternate I loop for installation'has been designated as Loop 1. The RCS pressure 1 compensating leg of the tygon is routed to another process sampling line which ties in at the top of the Pressurizer. ' Currently, the tygon is always installed as a part of the Operating RCS draining procedure BOP RC-4a/b.

Removal from service of both the Tygon and ILI-RYO46 will be performed j in procedures BOP RC-3a/b "RCS Fill and Vent" which are currently in Onsite Review. Quality of the temporary instrumentation is assured both by the use of a procedure for installation / removal and the Nuclear. Work Request system.

This is the only temporary level instrumentation used at this time.

Since the valving for this installation is proceduralized and the diameter of the permanent piping leading to it is 3/8 inch diameter any rupture with a resultant loss of inventory would be small and quickly isolated.

Ability to monitor RCS pressure and temperature before and after the RHR function is lost.

Pressure transmitters PT-403 and PT-405 provide redundant RCS pressure indication both before and after the RHR function is lost. The transmitters are located in the RCS to RH system suction pipes from RCS Loops 1 and 3 respectively. They cannot be isolated by any process pipe valving from the RCS and would remain operable even after' closure of either RH train's suction isolation valves. Both PT-403 and PT-405 are indicated on Main Control. Panel 1/2PM05J on pen pressure recorders. Pen Indicators for these pressure loops are also located on the Main Control l

Panels.

l l

Temperature indication may be provided by two'means. However, {

availability varies with plant conditions. If the RCS were drained and {

the plant were in Mode 5 the Core Exit Thermocouple (CETC's) would be 4 available for monitoring reactor vessel outlet temperature. If Mode 6' !

Were entered the CETC's would be uncoupled and unavailable as a result '

of Reactor Vessel Head remova1' preparations. The CETC's have two ,

indications on Main control Panel 1/2PM05J, and both would be available -

after a loss of RHR. The second means of temperature indication would be RH suction temperature and RH to RCS return temperature. There are .l temperature recorders for each train of RH. They would be available in either Mode 5 or Mode 6, but-are only indicative of RCS' temperature when :

the train of RH they are located in is operating. l' l

Note that RCS Wide Range Hot and Cold Leg temperature also exist,-but the location of the sensors is in the top half of the RCS Legs. They would therefore be non-indicative of temperature if RCS water levels I were at or below mid-plane of the RCS Loops.

RH flow indication for either. train of RH is available on Main Control panel 1pM06J. The pen indicators are fairly accurate in the 1000 to 3000 gpm range of normal operation.

ITEM 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 TS requirements.

RESPONSE

Pumps that can be used to control NSSS inventory:

A. During Mode 5 k

As required to be operable by Technical Specifications: {

)

1. 1 Residual Heat Removal (RHR) Pump with operable RWST suction.

With Reactor Coolant Loops not filled 2 RHR Pumps are required.

2. 1 Centrifugal Charging Pump 1

Pumps capable of operation if they are not temporarily disabled for testing and maintenance:

j 4

1. I additional Residual Heat Removal Pump.

i

2. I additional Centrifugal Charging Pump (CCP) or Positive l Displacement Charging Pumps (PDP).

1

3. 2 safety injection (SI) pumps.

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; Please note that the remaining CCP and PDP'as well:as both of the SI pumps,'are required by Technical Specifications to be removed from-service M enever the temperature;of one or more of the RCS cold legs.is less than or equal to @ 0*F., This li'nitation provides assurance that ai

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emass "4dition. pressure fransient can be relieved by the operation of a single'PORV.

B. .During Mode 6

~

As required to be operable by Technical Specifications s p

1. *2 Residual Heat Removal Pumps whenever Reactor Cavity level'is.less than c

23 feet above the reactor vessel flange.

1

2. 1 Centrifugal Charging Pump.

Pumps capable of. operation if they are not' temporarily disabled for testing and maintenance:

- l." 'I additional Centrifugal Charging Pump or Positive Displacement Charging Pump. y

- 2. 2 Safety Injection Pumps .

"3 Refueling Watering Purification Pump (This can only be used once 8

y water is'both in.the Reactor Cavity and Refueling Canal and probably would be ineffective due to low flow rate and flowpath l which would bypass the Re.c;or Vessel.)

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- The same conditiond.epply as mentioned above in Mode 5 with the exception that the remaining CCP and PDP and.both SI pumps are able to be placed in service provided the Reactor Vessel Head is off[

ITEM 4 s.

AdescriptionofthecontNinmentclosureconditionyourequirefor'the conduct of operations while the'RCS is partially filled. Examples of. areas ofconsiderationaretheequipmenthatch,personnelhatches, containment purge valves (including the valves), piping' penetrations, and electrica) ' .

penetration.,

RESPONQR S Technical Specifications require Containment'-Integrity be maint'ained in Modes 1-4. Centninment Integrity is not required in Mode 5. During Mode 6 only partial containment Integrity requirements exist and those are conditionally required during core alterations or movement of. ..

irkadiated fuel within the containm W , The equipment hatch could be removed throughout Mode 5 and 6', 'Ho w er, Technical Specifications require the Fuel Handling building to be maintained at a negative pressure of 1/4 inch water gauge relative to the outside atmosphere with

.the equipment hatch removed and core alterations in progress. . In addition, two independent'Puel Handling Buildling Exhaust filter. plenums are required to be operable whenever irradiated. fuelis present inlthe storage pool. 'These exhaust plenums contain High Efficiency Pat'riculate ,

i Absorbers HEPA's and Charcoal filter banks designed to remove )?

I radioactive mater 4al.Isleased from ruptured irrarliated %uel assemblies prior to _ discharge to the atmosphere. - Therefore,' witk the equipment 1

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hatch removed, a buffer zone exists in the Fuel Handling Buildling from which radioactive materials may be removed prior to release. The emergency personnel hatch, providing a direct path to the atmosphere, has been in the past maintained with a minimum of one door closed during outages. During Mode 6, past policy has dictated an administrative out of service be maintained in the name of the Shift Engineer to isolate those flowpaths which include: 1) containment purge valves, 2)

Feedwater Isolation Velves and Main Steam Isolation Valves (anytime Secondary manways or handhole covers are removed) to eliminate any

' direct paths from containment to outside atmosphere. piping and j electrical penetrations not under an out of Service do not vent to the outside atmosphere. These penetrations will vent to either the buxiliary Building or Fuel Handling Building. The areas to which piping penetrations are vented can also be serviced by HEpA/ Charcoal units of the Auxiliary Building Non-Accessible Filter plenums. Area radiation i monitors located throughout the Containment, Fuel Handling and Auxiliary Buildings could indicate switchover was necessary by providing alarm indication in the control room. i ITEM 5 1 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 J response should include the analytir basis you used for procedures )

development. We are particularly interested in your treatment of draindown {

to the condition where the RCS is partially filled, treatment of minor variations from expected behavior such as caused by air entrainment and )

i de-entrainment, trehtment of boiling in the core with and without RCS pressure boundary integrity, calculations of approximate time from loss of l j

RHR to core damage, level differences in the RCS and the effect upon i instrumentation indications, treatment of air in the RCS/RHR system, including the impact of air upon NSSS and instrumentation response, and ]

j treatment of vortexing at the connection of the RHR suction line(s) to the i RCS. 1 l 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 of operations that could upset the condition of the NSSS; and (c)_ response to loss of RHR, including regaining control of RCS heat removal, operations involving the NSSS if RHR cannot be restored, control of ,

effluent from the containment if containment was not in an isolated I condition 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).

I RESPONSE Below is a summary description of procedures used in the control room which describe plant operation while tne RCS is partially filled.

Included is the basis or reason for the procedures' development.

i i

l 6._____._ _ _ _ _ _ _ _ _ _ _ _ . _ . _ -

a The procedures, both normal-and abnormal, were developed from previous Ceco Zion experience withiloss of RH and in some cases pre-existing Zion procedures. In addition, recent.INPO SOER's.and other industry " lessons learned" were incorporated into our procedures.

A. Operating procedures for normal plant operation while the RCS is partially filled.

Mode 5 Operation

'1/2 BGP 100-5, Byron General. Procedure for " PLANT SHUTDOWN AND COOLDOWN" describes the steps necessary and references other. procedures necessary to take the plant from Startup. Conditions'(Mode 2)ito cold Shutdown (Mode 5). When the'RCS temperature has been' reduced below 350*F and RCS pressure is stabilized at approximately 350 psig the RH system is placed on line.in the Shutdown Cooling Mode per Byron Operating Procedure BOP RH-6. Then 1/2 BGP 100-5 further reduces RCS temperature and pressure first to."less than 200*F'(Modo 5)" and finally "less than 140*F". .At' this point all RCPs are stopped and the RCS can be' completely.

depressurized. If it is desired, 1/2 BGP 100-5 then directs the !

operating department to use' BOP RC-4a/b to drain the entire RCS to a-predetermined level or use BOP RC-10 to drain a single.RCS. loop after it .

has been isolated per " isolating an RCS Loop", BOP.RC-7.

Mode 6 Operation. i 1/2 BGP 100-6, Pyron General Procedure for " REFUELING OUTAGE" describes- )

the steps necessary and references other procedures necesary to go from cold shutdown to Refueling and back into Cold shutdown. . This procedure assumes 1/2 BGP 100-5 has been completed so'that'the RCS has'been depressurized and cooled to less than 140*F. 'However, draining may not i have begun in Cold Shutdown prior to entry into' Refueling. 1/2 BGP i 100-6 begins by assuring conditions of the Refueling Technical i specifications are met, such as two trains of RH operable or:for example' .l l two Source Range Neutron Flux Monitors are. operable., Mechanical 1 i Maintenance is then notified to remove the containment Equipment Hatch. '

The RCS is then drained per BOP RC-4a/b to just below the Reactor Vessel Flange (several feet above the top of the RCS Loop)',;or to the RCS Loop Centerline. ' Serious consideration is being given to raising the minimum level for RH operation. As a parallel operation to the draining,

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electrical connections to the Reactor Head Package are disconnected.

The two train Reactor Vessel Level Indication System (RVLIS) and the i l 1

Core Exit Thermo couples (CETC) are disconnected inLthis operation. The- I two redundant methods of RCS level indication, installed during the i draining process.of BOP RC-4a/b, are 1) A tygon tube with vent-path'to .)

the pressurizer 2) ILT-RYO46, a differential pressure sensor providing'_

remote indication in the control room-(Unit 1 only).

The following is done af ter: the draining operation 'is completed. to just below the Reactor Vessel Flange:

Movable Incore Detector (MID) Tubes are withdrawn and their low pressure i seals installed at;the seal table. r' Reactor Cavity Boot is verified installed and. pressurized.

I i_ _ _ _ __ L _ _ _ _ _ _ ____ m ____o-._____ -1 -_ _ _-_1_---__ - - - - - - _ - - _ n -__ _-- = 1- - - -

The Reactor Vessel' Head is lifted and simultaneously the reactor vessel cavity-is flooded per BOP.RH-8 by transferring borated water from the ,

Refueling Water Storage Tank (RWST) to the RCS via the RH system. j l

After reaching the Technical Specification level.in the Reactor Cavity for refueling the Upper Internals are removed and Core Alterations are performed.

The core loading is verified and the upper internals reinstalled. !

Reactor Cavity Level is lowered just below the Reactor Vessel Flange per BOP RH-9 by transferring water back to the RWST'from the cavity via the RH system.

1 Restoration of the Reactor Vessel Head to the vessel and all head i attachments is then begun with Reactor Vessel Level being maintained (

just below the Reactor Vessel Flange.

t The MID thimble tubes are reinserted into the fuel and the high pressure seals restored.

The RCS is then filled and vented using BOP RC-3, " Reactor Coolant j System Fill and Vent". Charging, Seal Injection and Letdown via RH is I

, established during this procedure.

l RCP bumps and pressurization are performed to fill the RCS loops, restoring Steam Generators as a heat sink (assuming the secondary side I of the steam Generators are adequately filled),

i Additional Specifics of Operating procedures used for normal operation other 1 than BGP's. 3 i

BOP RH-6 " PLACING THE RH SYSTEM IN COOLING SHUTDOWN" Provides the valve lineup for recirculation of an RH loop and gradually placing the loop in service removing decay heat from the RCS.

Precautions and limitations and actions are provided to ensure compliance with Technical Specifications as in all operating procedures.

BOP RC-3 " Reactor Coolant System Fill and Vent" The procedure performs valve lineups to start Charging, Seal Injection and Letdown. It identifies high point vents to be used for removing non-condensible gases in various parts of the RCS. Steps are included to isolate the tygon and ILT-RYO46 when Pressurizer Cold Calibrated Level Loop 1LI-462 indicates greater than 0% level in the pressurizer.

RCS pressurization with RCP bumps sweep the Steam Generator tubes free of air. Venting of the Reactor Head and Pressurizer follow sweeps, after_RCS depressurization to approximately 50 psig. Sweeps and venting continue until a negligible amount of air remains in the RCS.

BOP RC-4a Reactor Coolant Unit 1 System Drain The "4a" procedure applies to Unit I while "4b" applies to Unit 2. Unit I has had a modification completed which installed new level transmitters ILT-RYO46 and ILT-RYO47 to be used for Cold Shutdown and Refueling RCS level indication. Whereas Unit 2 has not, and Reactor Cavity Level indicator 2LI-449 is the only indication otherithan tygon below the pressurizer.

The procedure assumes the RCS temperature is less than 160*F and RCS pressure is less than 50 psig with all RCPs off. Detailed steps are given for installing and placing in service Tygon tubing level indication between the process sample lines of RCS Loop 4 and the pressurizer. The pressurizer relief tank is then purged with N2 to remove H2 An observer is stationed at the tygon level indicator with communication to the control room while draining is in progress through j

RH to the Chemical and Volume Control System. At 5% level on l Pressurizer level indication ILI-462, draining of the RCS is halted.

The isolation valves for ILT-RYO46 and ILT-RYO47 are opened to i provide a redundant level indication on ILI-RYO46 to the tygon after level is reduced to approximately 9 feet above the top of the Reactor vessel legs. Draining of the RCS is re-established. It should be noted that if RVLIS is in service, which it normally would be in Mode 5, two additional indications of approximate RCS Water level are available.

The procedure then gives the user an option of either stopping the I draining just below the Reactor Vessel Flange or at the mid plane of the RCS Hot Leg. RH system flow is further reduced to 1000gpm if level is to be drained to the mid plane of the Hot Leg. When the draining is halted, by use-of the available instrumentation operating must conduct !

l hourly RCS level checks by use of the tygon and hourly checks of the l running RH Pump. Watching for abnormalities while.RCS level remains at '

or near the centerline of the loop.

l Numerous cautions relating to level indication vortexing, air

! entrainment and pump cavitation exist throughout the procedure.

Examples follow:

If while draining, any doubt as to actual level arises draining will be secured until actual level has been verified. I l'

RH flow shall be throttled to less than 1500 gpm through each RH loop prior to draining to loop centerline.

The draining must be stopped if RH Pump Amps / Flow fluctuate.

Level indication may become erratic once S/G Tubes begin to burp.

If the Reactor Coolant level decreases below the loop centerline or RH flowrate is greater than 1500 gpm, the' pumps could cavitate due to air l entrapment from vortexing. A close vigilance must be maintained when the reactor coolant level is at or near the loop centerline of 393'-0".

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BOP RC-4b Reactor Coolant Unit 2 System Drain This procedure essentially has the same steps and cautions as the Unit 1 procedure "4a" with the exception that 2LI-449 Reactor Cavity Level Indicator is referenced as available indication other than RVLIS, Tygon and the pressurizer Cold Calibrated Level Loop 2LI-462. Mid-Loop i operation level indication is dependent on either Tygon'or RVLIS on Unit

]

2 because 2LI-449 does not span below the top of the Hot Leg. l

)

DOP RC-10 Draining An Isolated Reactor' Coolant Loop This procedure performs valve lineups to drain an RCS loop after it has i been isolated by its respective Loop Stop Isolation Valves. Use of this procedure, if successful in isolating a loop and draining it, would ;

allow pressurizer level to be maintained while RCp or Steam Generator l work was undertaken.

]

B. Operating procedures for abnormal plant operation while the RCS is on RH and/or may be partially filled:

Mode 5 operations j l

1/2 BOA PRI-10, Loss of RH Cooling, Byron Abnormal procedure describes step by step the method of regaining RCS level by recognizing the reason' for loss of RH cooling and the subsequent steps for correction.

1/2 BOA PRI-10 provides alternate methods of RCS cooling, when the operable RH train cannot immediately be restored. Starting of the redundant train of RH is permitted if the same condition that caused loss of RH cooling does not exist for that train. When the. redundant train is not available the secondary heat sink steaming intact non-isolated steam generators may procedurally be used to cool the RCS; two other options are Bleed and Feed using Excess Letdown through loop drains and normal charging or Bleed and Feed the RCS using pressurizer PORV(s) with normal charging.

Mode 6 Operations 1/2 BOA Refuel 4, Byron Abnormal procedure " Loss of RH During Refueling" provides a step by step method of restoring RCS level as follows:

i Verification of electrical bus energization.

Verification RCS status such as level and pressure.

Verification of RH system status.

RH hot leg suction valves open, no system leakage and sufficient component cooling flow to RH heat exchangers.

Start the redundant train of RH providing the cause of failure of RH is no longer present. If the redundant train is not available' attempt to restore the train previously in service. If neither train can be restored continue with RH train restoration. Note RCS temperatures and l determine whether RCS pressure transmitters have failed preventing l opening of RH Hot Leg suction valves.

e Pursue optional RCS cooling procedures such as bleed and feed using excess letdown through loop drains and normal charging; refueling water purification ~ pump suction on reactor cavity with discharge to the spent fuel pit, refueling tube gate valve open'and spent fuel pit service gate open. The Safety Injection system in the cold leg injection mode may be used provided sufficient cavity capacity and refueling water storage tank level exists to provide suction' head to the SI pumps. Vith'the reactor vessel head removed Safety Injection system accumulators can also be used if RCS temperatures are at 140*F and increasing.

Sufficient cavity capacity must be verified prior to dumping pressurized-accumulators.

1

' ITEM 6 j A brief description of training provided to operators and other affected personnel that is specific to the issue of operation while the RCS is ,

partially filled. We are particularly interested in such. areas as 1 maintenance personnel training regarding avoidance of perturbing the NSSS and response to loss of decay heat removal while the RCS is partially filled.

RESPONSE

i l

A separate lesson plan was written in October of 1986 covering operation 4 of the RH system while in refueling and the RCS partially drained. All l licensed individuals are trained and tested on the material. The lesson )

plan includes the following:

{

l Instrumentation available to the operators during refueling and partial )

drain for vessel level, cavity level, RH/RCS temperature, pressure, j flow, and RH pump motor current. !

RH suction valve interlocks.

RH mini-flow operation..

RH/RCS overpressure protection.

Cautions while operating RH.

The procedures used for normal cooldown, solid plant operations, partial drain, filling and draining the refueling cavity, and heatup.

Technical Specifications Cavitation and vortexing.

Significant Industry Events grouped as follows: Loss of RH mini-flow, RH overpressurization, RH suction valves closed, loss of vessel level, loss of running RH pump, cavity seal, failure.

Additionally, INPO SER 17-86, Loss of Shutdown Cooling Flow, is distributed through the required' reading program prior to drained loop operations.

I i L . i Maintenance personnel do not per se receive training on the avoidance of I perturbing tha NSSS or response to loss of decay heat removal while the RCS is partially filled. This is because all work that would have effect on the

, status of RCS level is planned in the Work planning group which includes an l SRO licensed individual. Prior to the actual performance of the work, an ]

j l SRO licensed supervisor on shift must authorize the beginning of the work, if it is Technical Specification or safety related.

ITEM 7 I i

I 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.

RESPONSE

edditional operators are furnished specifically.for mid-plane c,arations. During periods of heavy control room work loading an extra reactor operator is added. There is also a center desk operator that could be used as required to enable the reactor operator controlling specific evolutions to dedicate his full attention to that duty. The !

Shift Control Room Engineer coordinates and ihmits work activities with the reactor operators to assure adequate attention to detail is provided. All reactor operators and senior reactor operators have received the training described in response #6.

ITEM 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 RCS is partially filled may not appear in the other modes. An example of such differences is operation with a reduced RRR flow rate to minimize the likelihood of vortexing and air ingestion.

\

RESPONSE 1 k

Mode 5 or 6 operations at or near loop centerline are procedurally more j i

restrictive than other operations. procedures BOP RC-3 and bop RC-4a/b as described in the answer to Concern 5 contain the majority of cautions and procedural controls relating to mid-plane operation.

ITEM 9 l 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 situation, describe those changes and tell when they were made or are scheduled to be made.

RESPONSE

primary responsibility for the response to this question was assigned to pWR Engineering. However, the response to Concern's #2 and #5 partially address this concern.

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

RESPONSE

i As a result of industry wide concerns in the area of loss of shutdown cooling during mid-loop operation changes which have enhanced the operation of the RHR system have taken place in procedure development, operator training, and hardware modifications <

As described in response 5, both abnormal and normal procedures were developed from previous Ceco Zion experience with loss of RH and in some cases pre-existing Zion procedures. In addition, recent INPO SOER's and other industry " lessons learned" were incorporated in the procedures.

i Operator training, as discussed in response 6, now includes a lesson ',

plan which covers operation of the RH system while in refueling and the RCS partially filled. Additionally, INPO SOER 17-86, " Loss of Shutdown Cooling Flow", is distributed through the required reading program prior to drained loop operations.

Hardware changes were recently completed on Unit 1 during its first refueling outage. The same changes are scheduled to be_ completed on Unit 2 during its first refueling outage. The hardware changes included a new level indicating system which monitors reactor vessel level during shutdown. The new level indicating system required two new level instrumentation taps. The lower tap utilized one of the incore instrumentation tubes and the upper tap utilized an existing pressurizer level instrumentation sensing line. Sensing lines from these connections were routed to two new, locally mounted level transmitters.

One transmitter measures the reactor coolant system (RCS) level and the other measures a span of 12 to 25 feet above the reactor vessel flange, for refueling cavity level. Each transmitter provides input signals to a new indicator on the MCB. The transmitter used to monitor RCS level l provides input to a current relay which annunciated RHR pump low suction pressure on the Main Control Board, (MCB). The transmitter used to monitor the refueling cavity provides input to a current relay which annunciated loss of refueling cavity level on the MCB. The previous transmitter and MCB indicator were deleted and replaced with the above mentioned transmitters and indicators. This new level indicating system provides level indication in any refueling configuration. In addition, a handswitch was provided on the MCB for manual actuation of the containment evacuation alarm in the event of a loss of refueling cavity level.

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^BRAIDWOOD STATION ATTACHMENT 3 l ITEM 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 I maintenance and testing and coordination of such operations while the RCS is partially filled; restrictions regarding testing, operations, and maintenance i that could perturb the nuclear steam supply system (NSSS); ability of the RCS to withstand pressurization if the reactor vessel head and steam generator manway are in place; requirements pertaining to isolation of containment; the time required to replace the equipment hatch should replacement be necessary; and requirements pertinent to reestablishing the integrity of the RCS pressure boundary.

RESPONSE

The circumstances and/or reasons under which Braidwood would be brought through a draindown process and operated with the RCS partially filled include the following:

(a) Reactor coolant pump seal repair / replacement.

(b) Eddy current testing of the steam generators.

(c) Steam generator tube plugging and thermocouple i replacement / flow device work. j The prerequisites for entering the draindown process. include the following:

(a) The unit is in Mode 5.

(b) The RCS temperature is less than 160*F, the RCS pressure is I less than 50 psig and the pressurizer is water solid. '

s (c) All the reactor coolant pumps are secured.

1 (d) The RH system is operating in the shutdown cooling mode and i is supplying letdown flow. I (e) One centrifugal charging pump is in operation providing ;

charging flow.

l

(f) Technical Specification 3.4.1.4.1 requires that, in Mode 5 with loops filled, at least one residual heat removal loop shall be operable and in operation and at least one additional RH loop be operable or the secondary side narrow range water level of at least two steam ~ generators shall be greater than 41% for Unit 1 (18% for Unit 2).

Interlocks that could cause loss of RH cooling are the failure of RCS pressure transmitting that prevent opening of hot leg suction valves or cause automatic closure of hot leg suction valves.

The time required between full-power operation and reaching a partially filled condition is based on experience and not available at this time. However, Technical Specifications allow a maximum cooldown rate of 100'F in any one-hour period and General Operating procedure BwGp 100-5 " plant Shutdown and Cooldown" allows a maximum cooldown rate of 50'F in any one-hour period. At this rate the minimum time between full-power operation and the point at which draining may begin'is approximately 9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months .

However, information provided by other Commonwealth Edison pWR units with more operating experience indicate that a routine draindown for refueling activities could take up to six days.

l l Technical Specifications require a Cold overpressure protection System to be operable in Modes 4, 5, and 6 with the Reactor Vessel Head on.

The system shall consist of one of the following; 1) 2 power Operated Relief Valves with lift setpoints that vary with RCS temperature, 2) RH suction reliefs each with a setpoint of 450 psig i 1% or, 3) The RCS

, depressurized with an RCS vent of greater than or equal to 2 square l

inches. This system should provide adequate protection in the event of a loss of RH Cooling and the resultant gradual heatup and pressurization of the RCS.

During a partially filled condition in Mode 5 there are no requirements for secondary side water IcVels in the steam generators..There are not containment integrity requirements during a partially filled condition, refer to response 4. If equipment hatch replacement were required it I would take approximately 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

With respect to coordination of maintenance and testing activities, the j l Shift Engineer is responsible for overseeing these activities. l l Equipment status changes are made based on the concept of having one '

completely operable train of protection equipment. In addition, the Work planning Department interfaces with Maintenance, Technical Staff, and operations to coordinate activities associated with specific plant conditions. Licensed individuals within the Work planning Department-add another level of credibility and assurance that Technical specifications are adhered to and minimum perturbance of the NSSS ,

occurs during a partially filled condition of the RCS.

]l

ITEM 2 A detailed description of the instrumentation and alarms provided to the operators for controlling thermal and hydraulic aspects of the NSSS during operation with the RCS partially filled. You.should describe temporary connections, piping,andinstrumentationus)$ProrthisRCSconditionandthe 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.

1 RESPONSE 2 '

The draining of the RCS is done in accordance with Braidwood Operating Procedure BwOP RC-4a " Reactor Coole.nt Unit 1 System Drain". This 4 procedure requires that a tygon tube level indication system be -

installed between the process sampling lines of the RCS loop 4 and the pressurizer prior to draining. During the draining process an observer j will constantly monitor the RCS level indication with communication to the control room. In addition to this method, the control room operator has two displays in the control room which aid him in !

l controlling RCS level; the refueling cavity level indicator ILI-449 and the Reactor Vessel Level Indication System (RVLIS), Both displays are for level indication only and no alarm functions related to the loss of shutdown cooling are provided with either.

Installation of the tygon tubing will be performed under one or both of !

the following; (1) a maintenance work request which will have Quality i Control involvement or (2) a temporary alteration which will receive an independent verification.

The sensing line for the re rveling cavity level transmitter ILT-449 taps from the RCS loop 4 precess sampling line and employs a ,

differential pressure cel} type arrangement which feeds level indicator l 1LI-449 (0-100%) in the control room. Zero percent corresponds to i 394'6" and one hundred percent corresponds to 411'2" while the loop center line is at 393'0". The RVLIS utilizes heated junction l 4

thermocouple as sensors to provide percent level indication in the upper plenum and reactor head region. The percent level is provided in !

discrete steps due to the limited number of sensors rather than a i continuous percent level reading. Provided in procedure BwOP RC-4a is {'

a level correlation between these level indicators. If, during draining, any discrepancies exist between the RCS level indicators I draining must stop until they are resolved.

If the RCS is drained to loop centerline and the RHR function is lost, ;

only the RCS pressure and level can be monitored from the control room. The following instruments will monitor RCS pressure. ;

i I

I 1

1

^

I, FUNCTION INSTRUMENT RANGE LOCATION j RC LOOP 1A. IPI-403 0-600 psig IPM05J i

'WR Pressure 1PI-403A 0-3000psig IPM06J IPI-RCO21 0-800 psig IPM05J RC Loop IC IPI-405 0-3000 psig 1PM06J WR Pressure 1PI-405A 0-600 psig IPM05J The following instruments will monitor RCS level:

(a) Reactor Vessel Level Indication System: may only be i used with reactor vessel head in place. f (b) Reactor Cavity Level Indication (c) Tygon Tubing Level Indication

.i ITEM 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 . j temporarily removed from service for testing or maintenance); (b) j other pumps not included in item a (above); and (c) an evaluation of

)

items a and b (above) with respect to applicable TS requirements.

{

RESPONSE

Pumps that can be used to control NSSS inventory:

(a) During Mode 5 i

As required to be operable by Technical l Specifications- 1

']

(1) One Residual Heat Removal (RHR) Pump with operable Refueling Water Storage Tank suction. !

With Reactor Coolant Loops not filled two RHR Pumps are required.

(2) One Centrifugal Charging Pump Pumps capable of operation if they are not temporarily disabled for testing and j maintenance:

(1) One additional Residual Heat Removal Pump

(2) One additional Centrifugal Charging Pump (CCP) j o_r Positive Displacement Charging Pumps (PDP).

(3) Two Safety Injection (SI) Pumps.

Please note that the remaining CCP and PDP'as well as both of the SI Pumps, are requird by Technical Specifications to be removed from service whenever the temperature of one or more of the RCS cold. legs is less than or equal to 330*F. .This limitation provides assurance that a mass addition pressure transient'can be relieved by the operation of a single PORV.

c (b~) During Mode 6 As required to be operable by Technical Specifications (1) Two Residual Heat Removal Pumps whenever Reactor

. Cavity level is less than twenty-three feet above the reactor vessel flange.

(2) One Centrifugal Charging Pump.

Pumps capable of operation if they are not temporarily disabled for testing and maintenance:

- (l) One additional Centrifugal Charging Pump or Positive Displacement Charging Pump.

- (2) Two Safety Injection Pumps (3) Refueling Watering Purification Pump (This can only be used once water is both in the Reactor Cavity'and Refueling Canal and'probably would be ineffective due i l to low flow rate and flowpath which would bypass the l Reactor Vessel.)

- This note is the same as the one mentioned'above in Mode 5 with the exception that the remaining CCP and PDP and both SI are able to be in placed service provided the Reactor Vessel Head is off..

l n

ITEM 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.

i RESPONSE 4 l 1

3 At Braidwood, there are no special containment closure 'I provisions required for the conduct of operations associated i with mid-loop operation. Containment integrity is not required I

i since this evolution is carried'out in Modes 5 or 6 with no fuel movement. i ITEM 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 . I development. We are particularly interested in your treatment of draindown I 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 3 l

1 i

. l o

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, 5 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 of operations that could upset.the condition of the NSSS; and {

(c) response to loss of RHR, including regaining control of RCS heat removal, operations involving the NSSS if RHR cannot be restored, control of effluent from the containment if containment was not in an isolated condition 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). 4 RESPONSE 5 f

.{

Braidwood Operating Procedure BwOP RC-4a " Reactor coolant Unit 1 System !

Drain" which covers approach to and operation of a partially filled RCS ]

as well as the other procedures mentioned below were developed through 1 experience and lessons learned from other Commonwealth Edison. operating i Nuclear Stations.

As previously discussed in response (2) a tygon tubing level indication system must be installed prior to draining the RCS. Any level q

indication discrepancies between either the tygon tube, the reactor l cavity level indication system or the RVLIS must be resolved prior to l further draining. Treatment of boiling in the core, vortexing and air in the RCS/RH system is covered by Braidwood Operating Abnormal )

l Procedure BwOA PRI-10 " Loss of RH Cooling Unit 1". Covered are actions I required to restore RH system cooling in the event it is lost during Modes 4 and 5.

A summary description of the procedures used in the control room which describe plant operation approaching and during a partially' filled condition follow:

IBwGP 100-5 " Plant Shutdown and Cooldown" The procedure describes the steps necessary and references other procedures necessary to take the plant from Startup Conditions (Mode 2) to Cold Shutdown (Mode 5). When the RCS temperature has been reduced below 350*F and RCS pressure is stabilized at approximately 360 psig the RH system is placed online in the Shutdown Cooling Mode per.

Braidwood Operating Procedure BwOP RH-6. Then 1BwGP 100-5 further reduces RCS temperature and pressure first to less than 200' F (Mode 5) and finally to less than 140'F. At this point all RCPs are stopped and the RCS can be completely depressurized. If it is desired, BwOP RC-4a/b may be used to drain the entire RCS to a predetermined level or BwOP RC-10 may be used to drain a single RCS loop.

e_

y o .

1BwGP 100-6 " Refueling Outage" The procedure describes the steps necessary and references other

. procedures necessary to go from Cold Shutdown to Refueling and back into Cold Shutdown. This procedure assumes 1BwGP 100-5 has been completed so that the RCS has been depressurized and cooled to less than 140*F. 1BwGP 100-6 begins by assuring conditions of the Refueling Technical Specifications are met, such as two trains of RH operable or for example two Source Range Neutron Flux Monitors are operable.

Mechanical Maintenance is then notified to remove the Containment Equipment Hatch. The RCS is then drained per BwOP RC-4a to just below-the Reactor Vessel Flange (several feet above the top of the RCS Loop),

or to the RCS Loop Centerline. As a parallel operation to the draining, electrical connections to the Reactor Head Package are disconnected. The two train Reactor Vessel Level Indication System (RVLIS) and the Core Exit Thermo Couples (CETC) are disconnected in ,

this operation, i The following is done after the draining operation is completed to just below the Reactor Vessel Flange:

Movable Incore Detector Tubes are withdrawn and their low pressure-seals installed at the seal table.

I Reactor Cavity Boot is verified installed and pressurized.

The Reactor Vessel Head is lifted and simultaneously the reactor vessel' cavity is flooded per BwOP RH-8 by transferring borated water from the Refueling Water Storage _ Tank (RWST) to the RCS via the RH system.

After reaching the Technical Specification level in the Reactor i l Cavity for refueling, the Upper Internals are removed and Core Alterations are performed.

The core loading is verified and the upper internals reinstalled.

l -

Reactor Cavity Level is lowered just below the Reactor. Vessel Flange per BwOP RH-9 by transferring water back to the RWST from the cavity via the RH system. q Restoration of the Reactor Vessel Head to the vessel and all head attachments is then begun with Reactor Vessel Level being ;

maintained just below the Reactor Vessel Flange. '

- q The Movable Incore Detector thimble tubes are reinserted into the '

fuel and the high pressure seals restored.

The RCS is then filled and vented using BwOP RC-3, " Reactor Coolant System Fill and Vent". Charging, Seal Injection and Letdown Flow via RH is established during.this procedure.

s

)

I RCP bumps and pressurization are performed to fill the RCS loops j restoring Steam Generators as a heat sink (assuming the secondary I side of.the Steam Generators are adequately filled).

BwOP RH-6 " Placing the RH System in Cooling Shutdown" Provides the valve lineup for recirculation of an RH loop and gradually 1 places the loop inservice removing decay heat from the RCS. :

Precautions and Limitations and Actions are provided to ensure j compliance with Technical Specifications. I Bw0p RC-3 " Reactor Coolant System Fill and Vent" The procedure performs valve lineups to start Charging Seal' Injection and Letdown. It identifies high point vents to be used for removing non-condensible gases in various parts of the RCS. Steps are included to isolate the tygon when the Pressurizer Cold Calibrated Level Loop indicator ILI-462 reads greater than 0% level in the pressurizer-.

.RCS pressurization with RCP bumps sweep the Steam Generator tubes free of air. Venting of the Reactor Head and Pressurizer follow sweeps, i after RCS depressurization to approximately 50 psig. Sweeps and venting continue until.a negligible amount of air remains.in the RCS.

BwOP RC-4a " Reactor Coolant Unit 1 System Drain" The procedure assumes the RCS temperature is less than.160*F and RCS pressure is less than 50 psig with all RCPs.off. Detailed steps are given for installing and placing in service Tygon tubing level indication between the process sample lines of RCS Loop 4 and the pren;urizer. The Pressurizer Relief Tank-(PRT) is then purged with

'2 to remove H 3 2 . An observer is stationed at the tygon level-indicator with communication to the control room while draining is in progress. It should be noted that if RVLIS is in service, which it normally would be in Mode 5, two additional indications of approximate RCS Water level are available. The procedure'then gives the user an

, option of either stopping the draining just below the Reactor Vessel Flange or at the mid-plane of the RCS Hot Leg. RH system flow is further reduced to 1000 gpm if level is to be drained to the mid plane l of the Hot Leg. When the draining is halted by use of the available

! instrumentation operating must conduct hourly RCS level checks by use l of the tygon and hourly checks of the running RH Pump.

Numerous cautions relating to level indication, vortexing, air entrainment and pump cavitation exist.throughout the procedure. ,

Examples' follow:

If while draining, any doubt as to actual level arises draining )

will be secured until actual' level has been verified. .I RH flow shall be throttled to less than 1000 gpm through each RH loop prior to draining to loop centerline. '

The draining must be stopped if RH Pump amperage and/or flow >

fluctuate. I 1

i a

4 1

l

e. ,

Level indication may become erratic once S/G Tubes begin to burp.

If the Reactor Coolant level decreases below the loop centerline or RH flowrote is greater than 1000 gpm, the pumps could cavitate due to air entrapment from vortexing. A close vigilance must be maintained when the reactor coolant level.is at or near the loop centerline of 393'-0".

BwOp RC-4b " Reactor Coolant Unit 2 System Drain" This procedure essentially has the same steps and cautions as the Unit 1 procedure "4a".

Bw0p RC-10 " Draining An Isolated Reactor Coolant Loop" This procedure performs valve lineups to drain an RCS loop after it has been isolated by its respective Loop Stop Isolation Valves. Use of this procedure, if successful in isolating a loop and draining it, would allow pressurizer level to be maintained while RCp or Steam Generator work is being undertaken.

1BwOA PRI-10 " Loss of RH Cooling Unit 1"

( This procedure describes step by step the method of regaining RCS level

by recognizing the reason for loss of RH cooling and the subsequent steps for correction.

! 1BwOA PRI-10 provides alternate methods of RCS cooling when the l

operable RH train cannot be immediately restored. Starting of the redundant train of RH is permitted if the same condition that caused loss of RH cooling does not exist for that train. When the redundant train is not available the secondary heat sink steaming intact-non-isolated steam generator may procedurally be used to cool the RCS; two other options are bleed and feed using excess letdown through Loop Drains and normal charging or bleed and feed the RCS using pressurizer power Operated Relief Valves (pORV) with normal charging.

IBwOA REFUEL 4 " Loss of RH During Refueling Unit 1" This procedure describes step by step the method of regaining RCS level by recognizing the reason for loss of RH cooling and the subsequent steps for correction.

The procedure provides alternate methods of RCS cooling when the operable RH train cannot immediately be restored. Starting of the redundant train of RH is permitted if the same condition that caused loss of RH cooling does not exist for that train. When the redundant train is not available pursue optional cooling procedures such as bleed and feed using excess letdown through loop drains and normal charging or refueling purification pump suction on reactor cavity with discharge:

to the spent fuel pit with refueling tube gate valve open and spent fuel pit service gate open. Safety injection system in the cold leg recirculation mode may be used providing sufficient cavity level exists and the Refueling Water Storage Tank level is' sufficient to provide suction head to SI pumps. Safety injection system accumulators can also be used if RCS temperatures are at 140'F and increasing.- This

q e .-

f

' method of cooling may rearrange fuel-assemblies in the vicinity of the '(

injection path.

1 Sufficient cavity capacity.must also be verified prior to dumping pressurized accumulators. i ITEM 6 1 1

A brief description of training provided to operators.and other affected

-personnel that is specific to the issue of operation while the RCS is partially filled. We are particularly interested in such areas as ,

maintenance personnel training regarding avoidance of perturbing the NSSS

-and-response to loss of decay heat removal while the RCS is partially filled.

RESPONSE 6 At Braidwood the following training was provided to operators and other i affected personnel regarding operation while the RCS is partially j filled:

i (a) The initial Licensed operator: training lesson plans at Commonwealth Edison's Production Training Center (PTC) ,

covered loss'of RHR suction. l (b) Previous correspondence on this subject, related industry 1 events and recovery methods were covered in the third cycle

1987 Licensed operator Requalification.

1 (c) I.E. Information Notice 87-23 " Loss of Decay Heat Removal During Low' Reactor Coolant Level Operation"'has been included l in Licensed Operator Required Reading Package 87-08.

(d) During Maintenance Continuing Training on PWR systems, -j Generic Letter 87-12'was discussed with Mechanical,-

Electrical and Instrument Maintenance' personnel. The 1 following topics were discussed:

(1) Operations while partially drained for steam generator maintenance.

(2) Level control problems leading to vortexing and '

pump cavitation.

(3) Loss of RHR and heat up of the RCS to boiling without containment integrity.

(4) Maintenance actions that can inadvertently cause loss of RHR.

l (5) Interconnections with other systems that can create problems with the RHR system.

(6) Licensee Event Report 87-044 on Braidwood l Station's personnel error involving a valve l lineup during recirculation of the RHO "B" train. The focus was on RHR system loss during !

Modes 5 and 6. .

1

a o

It should also be noted that all work that would have an effect on the status of RCS level is planned in the Work planning Department which includes a licensed SRO. In addition, prior to the actual performance of work, a licensed SRO supervisor on shift must authorize the beginning of work if it is Technical Specification or safety related.

l ITEM 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.

RESPONSE 7 At Braidwood, during an RCS draining operation, an operator would be stationed in the containment in order to monitor the local tygon tubing indication in accordance with procedure BwOp RC-4a, Revision 51. The l operator will be in constant communication with the control room and I

any discrepancies between the RCS level indicators are to be resolved j prior to further draining. Once the draining process has been completed and the RCS level is stabilized, the same procedure requires the operators to perform hourly checks of the tygon tube level reading !

as well as hourly checks of the RH pump for signs of cavitation and I excessive vibration.

In general, no additional licensed operators are furnished specifically ;

for mid-plane operations. During periods of heavy control room work l loading an extra reactor operator specific evolutions to dedicate his full attention to that duty. The Shift control Room Engineer i

coordinates and limits work activities with the reactor operators to l assure adequate attention to detail is provided. All reactor operators and seniot reactor operators have received the training described in response #6.

ITEM 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 RCS 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 8 As previously discussed, Braidwood procedure BwOp RC-4a " Reactor Coolant Unit 1 System Drain" will be used when draining the RCS from a water solid to a partially filled condition in Mode 5. The following I requirements are implemented while the RCS is partially filled vs other I

Mode 5 operations:

) (a) Technical specification requirement.3.4.1.4.2 stating two residual heat removal (RHR) loops shall be operable and at least one RHR loop shall be in operation.

1

f

.o o

(b) RHR flow will be reduced to approximately 1000 gpm through each RH loop prior to draining to minimize the likelihood of vortexing and air ingestion in the RH pumps.

(c) A tygon tubing level indication system must be installed and constantly monitored during the draining process.

(d) After level stabilization hourly checks will be performed of the level indication and the RH pumps for signs of cavitation and excessive vibration.

ITEM 9 I 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 situation, describe those changes and tell when they were made or are !

scheduled to be made.

l RESPONSE 9 As a result of industry wide concerns in the area of loss of shutdown cooling during mid-loop operation the following actions have been and/or are being taken at Braidwood Station: ,

i (a) Procedure BwoP RC-4 " Reactor Coolant System Drain" was.

replaced with enhanced versions of the procedure for Units 1 and 2, Bv0P RC-4a Revision 51 and Bwop RC-4b, Revision 51.

The changes include reducea RH flow (1500 to 1000 gpm) during draining and mid-loop operation, hourly checks of tygon tube level indication and RH pump condition, and improved cautions i and notes. The'new procedures were approved on 9-8-87 and !

8-31-87 respectively. )

l l (b) Modification request number RY001 has been initiated to !

install a more accurate RCS and refueling cavity level indication system. The modification will be installed during ]

each unit's first refueling outage and consists of the 1 following parts:

(1) A low Residual Heat Removal (RHR) pump suction pressure }

alarm will be added to the Main control board (MCB) on ]

1pM06J to indicate low reactor vessel level. I l

(2) An alarm for loss of refueling cavity level will be f added to the MCB on IPM06J. l (3) A handswitch will be provided on IPM06J for manual 1 l

actuation of the Containment Evacuation Alarm in the event of a loss of retaeling cavity level.

i l

1

__-_-_ - -- ---- --- - 1

, lhi ; -

4 Xs ?K ' -

q

.(4) 'A new? level ihdicating" system!will be'provided toi,

-monitor' reactor vesse1 71evel during shutdown. !This new "

system will requireitwo'new level instrumentation taps?

The lower tap;in one of Lthe/incore, instrumentation tubes:

and .the upper;in one: of. the existing pressurizer: level.

-instrumentation sensing lines. Sensing linesjfrom these; .

P connections willibe' routed'to two new. locally mounted

.non-safety,related" level: transmitters located outsideJ the containment' shield wall. One1 transmitter, measures .

'RCS level'and the other transmitter:measuresia span of, 25 fee,t'above.the reactor vesselvflange,lfor . .

refueling l cavity' level. Leach transmitter provides. input- '

signals to a'new non-safety related indicator on the McB!

+ onilpM06J. 'The transmitter used to monitor-RCS11evel-provides input to a' current. relay which annunciated,RHR' pump low suction pressure on the MCBR1The transmitter .

used to monitor the' refueling cavityjlevel providesl o input to a; current relay,which annunciatesolossLof refueling: cavity'leve1 Eon-the'MCB. The! previous: '

transmitter (1LT-449) and MCB indicatorL(1LI-449) will' be deleted and replaced'with the'above mentioned transmitters and indicators.

(c) The Braidwood Station Training"RHR lesson plan was modified' to, include SOER 85-4 " Loss or Degradation'of Residual Heat Removal Capability in PWRs". . previous correspondenceion' loss

'of.RHR,'related. industry events and recovery methods were-covered in the-third cycle 1987 Licensed;0perator-Requalification.~ : Additionally, the Commonwealth Edison production Training Center is developing a simulator model for mid-loop RCS operation and' loss.of RHR~due tol air-binding.

l' 3626K k

4 I I wm

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