ML13330B254

Forwards Response to Items 1-9 of Generic Ltr 87-12, Loss of RHR While RCS Is Partially Filled. Info Includes Commitments Which Have Not Yet Been Implemented But Will Be Prior to Next mid-loop Operations

ML13330B254
Person / Time
Site:	San Onofre
Issue date:	09/24/1987
From:	Nandy F SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
GL-87-12, NUDOCS 8709300083
Download: ML13330B254 (29)

Text

Southern California Edison Company P. 0.

BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 September 24, 1987 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:

Subject:

Docket No. 50-206 Loss of Residual Heat Removal (RHR) While the Reactor Coolant System (RCS) is Partially Filled (Generic Letter 87-12)

San Onofre Nuclear Generating Station Unit 1 The enclosed information is in response to items 1 through 9 of Generic Letter 87-12, dated July 9, 1987, regarding loss of residual heat removal while the reactor coolant system is partially filled at Unit 1 of the San Onofre Nuclear Generating Station. It should be noted that some of this information includes commitments which have not been implemented yet but will be implemented prior to the next mid-loop operations.

If you have any questions, please let me know.

Subscribed on this zL/9 day of 4

4v, 1987.

Respectfully submitted, SOUTHERN CALIFORNIA EDI COMPANY 8709300083 870924 O By:

PDPDR Supervising Enginee Nuclear Rate Regul ion Subscribed and sworn o efore me this

,?fe day of,

/__.

OFFICIAL SEAL AGNES CRABTREE Not Pub ic in and for the County of Notarv Public-California Los Angeles, State of California o

uxp.

S 14,199 My Commission Expires: 14A 4>*/2'/79 Enclosure cc: J. 0. Bradfute, NRR Project Manager, San Onofre Unit 1 J. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3

Enclosure SAN ONOFRE UNIT 1 RESPONSES TO GENERIC LETTER 87-12 QUESTIONS QUESTION 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 would cause a disturbance to the system. Examples of the type of information required are the time between full-power operation and reaching a partially filled condition( used to determine decay heat loads); requirements for minimum steam generator (SG) levels; changes in the status of equipment for maintenance and testing and coordination of such operations while the RCS is partially filled; restrictions regarding testing, operations, and maintenance that could perturb the nuclear steam supply system (NSSS); ability of 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 plant would be entered into and brought through a drain down process and operated with the RCS partially filled in order to conduct work which can only occur with the reactor coolant system depressurized and open to containment.

Such work may include (1) the support of fuel shuffle during a refueling outage (drain down to below the reactor vessel flange in order to remove the vessel head), (2) the repair/maintenance of reactor coolant pump (RCP) seals, (3) the inspection/plugging of SG tubes, or (4) the repair/maintenance of RCS pressure boundary isolation valves or connected piping and instrumentation, each of which may require drain down, for at least some period of time, below the top of the reactor vessel inlet (cold leg) and/or outlet (hot leg) piping.

Since a typical refueling outage includes plans for RCS maintenance as noted in (2), (3) and (4) above, two separate drain down evolutions are normally planned. The first consists of a drain down to a level below the reactor vessel flange, but approximately 67 inches above the top of the RCS loops, in order to remove the reactor vessel head. During this evolution, the RCS piping remains filled. After the head is removed and preparations for core alterations are completed, refilling and flooding of the refueling cavity to support core alterations is accomplished. Subsequent to completion of fuel movement, a second drain down to mid-loop (partially filled condition of the hot and cold legs) is normally performed for SG/RCP maintenance. If the drain down is being accomplished solely for the purpose of performing RCS maintenance, (i.e., no RV head removal or fuel movement) the RCS will be drained in one controlled evolution to the level necessary to support the maintenance activity.

-2 The following is a detailed description of a drain down process during a otage. The alignments and activities conducted during the drpaindw rueing aoprtn with the RCS partially filled, are described in, and controlled by, the following operating instructions:

S01-3-5: Plant Shutdown from Hot Standby to Cold Shutdown S01-4-9: Residual Heat Removal (RHR) System Operation S01-4-2: Draining the Reactor Coolant System (RCS)

SOl-3-7: Plant Operation During Reactor Refueling SOl-3-: Plant Startup from Cold Shutdown to Hot Standby SOl-4-1: Filling and Venting the Reactor Coolant System (RCS) initially, the controlling procedure is S01-3-5. After entering Mode 4, and depressurizing the RCS to between 350 and 400 psig, the procedure contains directions which establish residual heat removal systpraton RH i mn accordance with S01-4-9. This procedure places both traine of RHRn eqipe in service and establishes the required conditions to he RHR oop solation motor operated valves (MOV's) are interlocked with RCS pressure to prevent them from opening with RCS pressure above 400 p i thane there is no auto-close circuit or auto-close interlock. At this point shutdown sequence, the RCS loops remain filled and, in accordance with Technical Specification Limiting Conditions for Operation (LCOs), two of the five available decay heat removal loops, as a minimum, are maintained operable. The five decay heat removal loops consist of the three RCS Loops (including the associated Reactor Coolant Pumps (RCP) and Steam Generators (SG)) and the two RHR Pumps and their associated heat exchangers and flow paths. Usually all five loops are available and operable during the entire shut down sequence.

After placingthe RHR system into operations the pressurizer bubble is then collapsed.

When the RCS temperature is less than or equal to 2000F, the Technical Specifications (and operating procedures) require one train of RHR to be operable and in operation and an additional RHR train to be operable or two SG's to be filled to greater than or equal to 256 inches of narrow range on cold calibrated scale. Both RHR trains are usually in operation at this point in the shutdown sequence and allI three SG's are usually at a level greater than 256 inches at all times. After the RCS is cooled down to approximately 140F, the RCP(s) still remaining in operation are stopped, and continued heat removal is accomplished primarily by the RHR system.

Typically, draining of the RCS is not initiated until at least 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> have elapsed since the reactor shutdown. If draining is to proceed prior to this nominal 120 hour0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> period, specific, written authorization by the plant superintendent is required.

In order to proceed to the partially filled condition, RCS drain down is initiated in accordance with SO1-4-2. This procedure contains alignments to depressurize and drain the RCS. As a prerequisite to lnitiating draindown, the RCS must be at less than 140*F, and typically at least 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> must have elapsed since the reactor was shut down. When the pressurizer level s

reduced to less than or equal to 58%, which corresponds to the top of the SG

-3 U-tubes, the RCS loops are no longer considered to be filled. At this point in the shutdown sequence, the Technical Specifications (and operating procedures) require that both trains of RHR be operable and at least one train be in operation. Drain down continues until pressurizer level is decreased to 10%. At this level and prior to continuing the drain down, the installed Loop A wide range refueling level indications, which consist of a local sight glass and remote control room indication via level transmitters, are placed in service. In addition, a temporary local wide range level indication on Loop B (tygon tube) and a temporary narrow range remote level indication (with alarm) in the control room (level transmitter) on Loop C, are verified to be properly installed. A more detailed description of these level indicating devices is included as part of the response to Question #2.

From this point on in the drain down process to mid-loop operation, which is considered to be 50% to 90% on the narrow range indication on Loop C, SO-4-2 provides acceptance criteria for agreement among these level indicating devices to ensure proper RCS level indication. If the criteria are not met, drain down is stopped and will not re-commence until the problem is identified and corrected.

Drain down is continued until pressurizer level instrumentation indicates 3*k_

level.

Draining is halted while all wide range refueling water level indicators are checked for proper agreement and then continued to a level of 47% as indicated by the Loop A wide range remote indication in the control room. This level corresponds to 67 inches above the top of the RCS loops. If refueling, or core alterations, are to be accomplished, the reactor head is removed and the refueling cavity is flooded to an elevation of 40 feet 3 inches, which corresponds to 63% pressurizer level.

After fuel shuffle is completed and the refueling cavity is again drained to 47% on the Loop A remote refueling level indicator, the reactor head is placed on the flange and the Unit enters Mode 5 as the head studs are tensioned.

The same procedure (SO1-4-2) is utilized to continue draining the RCS from 47%

to mid-loop if it is desired to inspect or repair SG tubes, RCP seals, or to perform other maintenance. RCS level is decreased to 40% Loop A remote wide range at which point draining is stopped and the various refueling water level indicators are again checked for proper agreement. RCS draining is then continued until level is within the RCS loops. At 11% Loop A remote wide range, the drain down is stopped and once again the various refueling level indicators are checked for proper agreement.

At this point the Loop C narrow range indicator and low level alarm, which annunciates in the control room at 40% indicated level, is placed in service.

The RCS level is then decreased to 6.25% Loop A remote wide range, which is 50% on the Loop C narrow range indication. Once again, the narrow and the wide range level indicators are checked for proper agreement. At this point, RCS level is at mid-loop, which is considered to be 50% to 90% on the Loop C narrow range indication. When the SG tube sheet draining is complete and stable mid-loop operation of the RHR system is established, work authorizations are issued to begin mid-loop maintenance.

-.4 Following the completion of all required mid-loop maintenance, the shutdown operations procedure is exited and SO-3-1, "Plant Startup from Cold Shutdown to Hot Standby," is entered. This procedure refers to S01-4-1, "Filling and Venting the RCS," which contains the steps necessary to refill the RCS loops.

With the loops filled, the Technical Specification LCO and operating procedure requiring operability of two RHR trains is exited. All three SG's are, at this time, filled and maintained above 256 inches narrow range and only one train of RHR is, therefore, required to be operable and in operation.

With the RCS filled and pressurized to between 350 and 400 psig, RCPs are returned to service to commence RCS heatup. Upon Mode 4 entry, the RHR trains are isolated.

At San Onofre, the Maintenance Planning/Equipment Control process is managed through a computer based information management system. For a safety related maintenance activity, it requires independent, mandatory review by Maintenance, Operations, QA/QC, and a mandatory review by the Technical Division if the activity is related to any of the following:

(1) Unprecedented or unusual failures, (2) Design changes or ASME code component (repairs/replacement) which are performed for the first time without engineering direction or vendor supplied manuals, and (3) Temporary Facility Modifications.

Maintenance work activities scheduled during all phases of the drain down, refueling, and refill sequence are no exception to this review/planning process.

For these activities, the equipment control review process evaluates each tag out requirement with particular emphasis to ensure that 1) RCS inventory or the ability to control RCS inventory will not be affected,

2) adequate alternate means for performing the safety function is available,

3) the requirements of the Technical Specifications are satisfied, 4) the administrative requirements of the applicable procedures are satisfied, and

5) the RCS pressure boundary integrity is maintained.

In addition, prior to the drain down, all previously authorized work activities are re-evaluated against the above criteria. Prior to issuing the work authorization to the work groups, on-shift Operations will once again verify all the prerequisite plant conditions identified in the Maintenance Planning/Equipment Control process are met. Prior to, during, and subsequent to the work activities when post-maintenance and functional tests are required, tailboard meetings are frequently and regularly conducted among Maintenance, Operations, Technical, QA/QC, and other appropriate personnel to resolve any problems that may arise.

Work activities involving breaching the RCS boundary integrity are scheduled for the shortest time possible. However, in the event that RCS boundary integrity is breached for activities such as RCP seal repair, SG tube inspection/plugging, and repacking of RCS boundary isolation valves, strict

-5 post maintenance and/or operational functional tests are performed to ensure that the RCS boundary integrity is re-established. For instance, in the case of repacking an RCS boundary isolation valve, post maintenance testing involves a visual inspection and operational functional test which involves actual cycling of the valve to ensure no leakage.

For a discussion of the ability to withstand RCS pressurization if the reactor vessel head and SG manways are in place, see the response to Question #5.

If a loss of RHR cooling should occur during a reduced RCS inventory period, abnormal operating instruction S01-2.1-9, "Loss of Residual Heat Removal System," will ensure the following:

1. Declaration of an appropriate emergency classification,

2. Make-up to the RCS,

3. Closure of the containment,

4. Restoration of the RCS pressure boundary,

5. Maximizing containment cooling,

6. Restoration of RHR system, and

7. NRC notification.

For a discussion of requirements pertaining to isolation of containment, and the time required to replace the equipment hatch should replacement be necessary, see the response to Question #4.

QUESTION 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 the RCS is partially filled. You should also provide a description of your ability to monitor RCS pressure, temperature, and level after the RHR function may be lost."

RESPONSE

The following different types of instrumentation, alarms and other features associated with the RCS/RHR systems are available to the operators for controlling thermal and hydraulic aspects of the NSSS.

A. Instrumentation and Alarms

1.

RCS Level Instrumentation The NSSS at Unit 1 is a three loop Westinghouse Pressurized Water Reactor. The Reactor Vessel Level Indicating System (RVLIS) consists of independent local and remote wide and narrow range level indications.

Wide range indication is provided by a local sight glass and a remote wide range indicator (LI-445) connected to RCS Loop A. These wide range level indicators are supplemented by a temporary tygon tube connected to RCS Loop B. Elevations on the sight glass and the tygon tube are read directly from an elevation scale calibrated to both critical plant elevations and to the percentage scale on the wide range indicator.

Narrow range indication is provided by a narrow range transmitter/indicator attached to RCS Loop C. This is the same loop that provides suction to the RHR system. Experience at Unit 1 has shown that over the full range of RHR flow rates, very close agreement in level readings among the three loops is normal.

The differences in level readings are typically less than one inch.

An illustration of the Unit 1 RVLIS is provided in Figure I, "Unit-1 Refueling Water Level Detector."

Figure II shows the key plant elevations and the range of coverage of each level instrument.

2. Local Level Instrumentation Sight Glass A detailed description of the piping and connections for the two part sight glass LG-445 A and B is provided below. The dry reference leg for the sight glass is obtained through a locked open Power Operated Relief Valve CV-545 or CV-546. The PORVs are connected to Pressurizer Vent

Valve PZR-012, which is connected to a 3/4 inch "U" shaped stainless steel spool piece. This spool is flange connected between PZR-012 and a temporary T-connection. One branch of the T-connection is connected by a double pipe clamp to a tygon tube which runs down approximately 20 feet to the top of the Sight Glass Vent Valve RCS-061.

This valve connects directly to the top of the sight glass. The wet leg of the sight glass is connected to the Loop A hot leg via a stainless steel tubing connection and a run of tubing which connects to an isolation valve RCS-017. The isolation valve is connected to a tap on Flow Transmitter FT-400. The flow transmitter is connected to the bottom of the hot leg via isolation valve RCS-013. The upper sight glass provides water level indications from the top of the Reactor Vessel Flange to a point 24 inches below the top of the flange. The lower sight glass provides water level indications from just above the top of the hot leg to 6 1/2 inches below mid-loop.

Tygon Tube Since the sight glass actually consists of two vertical 24 inch long sight glasses connected in series with a 43 inch blind spot between them, a tygon tube is temporarily routed parallel to the sight glass to cover, this blind spot and to provide positive wide range indication from the top of the pressurizer to the bottom of the hot leg.

The dry reference leg of the tygon tube is obtained from the remaining branch of the T-connection used for the sight glass dry reference leg. The wet leg of the tygon tube is obtained from RCS Loop B via a calibration port on Flow Transmitter FT-410 and the isolation valve RCS-024.

Elevation Scale An elevation scale is installed adjacent to the tygon tube and the sight glass. This enables the operator to directly convert water levels observed in the tygon tube or sight glass to specific elevations in the plant. Key elevations in the RCS are indicated on the scale. The scale is marked in wide range percentage readings on one side and inches on the other side. The zero reference point is 12 1/2 inches below mid loop.

The zero reference point and the percentage scale are the same as that used in Wide Range Level Indicator LI-445. This provides a convenient means of cross checking the accuracy of the tygon tube and the sight glass with the wide range indicator.

3. Remote Level Instrumentation Narrow Range Indicator The dry reference leg for the Narrow Range Indicator is obtained through the Loop C flow transmitter upper vent valve RCS-034. The wet leg is connected to the bottom of the loop through flow transmitter FT-420 and its isolation valve RCS-032. The purpose of the Narrow Range Indicator is to provide accurate narrow range water level information to the Control Room for use during mid loop operations.

-8 The indicator is calibrated with Oto 100% corresponding to the bottom and the top of the loop. A control room low level alarm is set to annunciate at 40%.

Wide Range Indicator The Wide Range Indicator is connected in parallel with the sight glass discussed above. The purpose of the Wide Range Indicator is to provide water water level indication from near the bottom of the hot leg (approximately 13 foot elevation) to approximately the 30 foot elevation.

4. Temperature Instrumentation RCS Remote Temperature Instrumentation RCS Cold Leg and Hot Leg Temperature Instruments The RCS cold leg and hot leg temperature instruments are not normally used during RHR operations since they are not directly in the RHR flow path. However, these instruments are available and they read from 100 jo 700OF and are located on the Auxiliary Feedwater Panel.

Core Exit Thermocouple The RCS temperature can be obtained by initiating a computer generated Core Exit Thermocouple Map or individual thermocouple digital readout directly from the Control Room. Core Exit Thermocouple readings are not available from the time the reactor vessel head is removed until the head is replaced and required thermocouple inspections, repairs, testing, and surveillances are performed.

RHR Remote Temperature Indication RHR Pump discharge temperature (inlet to the Heat Exchanger) is available from Temperature Recorder TR-600. TI-601A and TI-601B indicate RHR Heat Exchanger outlet temperatures.

-RHR Local Temperature Indication TI-602 provides local indication of RHR Heat Exchanger Outlet Temperature.

5. Pressure Instrumentation Remote RCS Pressurizer Pressure Wide Range Pressure Indication can be obtained directly from Pressure Recorder PR-425. The transmitter associated with this recorder is PT 445 and is located near the top of the pressurizer.

-9 Remote RHR Pressure Indication The Letdown Backpressure Control System measures RCS pressure via PT-1105 which is located near the discharge of the RHR pumps.

PI-1105 is located in the Control Room and is the primary means of obtaining primary system pressure during RHR operations.

Local RHR Pressure Indication PI-600A and PI-600B provide local indication of the discharge pressure of the RHR Pumps G-14A and G-14B, respectively.

6. Pressure Alarm RHR pump high discharge pressure is alarmed at 480 psig by PC-600.

7. RHR Flow Instrumentation RHR flow can be read by the operator in the Control Room on Flow Indicator FI-602.

8. RHR Flow Alarm A Control Room Annunciator alarms whenever FC-602X senses that RHR flow has dropped to 400 gpm or less.

9. Instrumentation Available During Loss of RHR All of the instrumentation described above would be available in the event RHR were lost. The ability to directly observe level exists down to the bottom of the hot leg. However, for RCS temperature, the operator would be procedurally directed to use computer generated Core Exit Thermocouple Maps for temperature readings since the lack of flow would render the hot leg thermocouple ineffective. As previously discussed, such thermocouple outputs are not available when the reactor vessel head has been removed. During mid-loop operationl, S n-2.-9, "Loss of Residual Heat Removal System," provides detailed instructions on problem identification and corrective actions in responding to abnormal conditions (RCS low level alarm on Loop C narrow range, RHR low flow or high temperatures, etc.) associated with the RHR systems. In the event that the RHR systems are lost and cannot be restored, this procedure provides detailed guidance on eight alternate methods to remove decay heat and implements the emergency plan if necessary.

B. Additional Features The following additional features have been provided in the elevation drawings and the mid-loop operating procedure to verify operability of key level instruments.

-10 The critical elevations on the RCSwere determined by a combination of plant measurements, calculations and examination of engineering drawings. The above information was transferred to elevation drawings and to the elevation scale. The mid loop point on the elevation scale was determined by use of an electric transit surveying instrument. The required agreement between each level instrument was calculated and incorporated into the mid loop operating procedure as a means of verifying operability of the instruments at key points in the draindown.

C. Installation of the Temporary Level Indicators The following installation precautions are taken:

The routing of the tygon tubing is conducted in such a manner as to avoid kinks or loop seals. The routing path for the tygon tubing is specifically identified by the Cognizant Station Engineer. The Cognizant Station Engineer personally monitors the installation of the tygon tubing in order to assure correct installation.

The tygon tube is secured at specified intervals in order to hold it in place. Where necessary, supports are installed across open areas.

Installation and calibration of the narrow range level transmitter on Loop C is performed by an I&C technician under the supervision and approval of the Cognizant Station Engineer. Engineering and Operations walkdowns of the system are conducted after installation and again after filling the system.

The calibration and installation of these level instruments are treated as safety related activities and their use is controlled by established operating procedures. All physical equipment connections are detailed in Maintenance Work Plans reviewed and approved by Maintenance and Operations Supervision,Engineering, and Quality Assurance.

D. Piping and Connections The lines used in the RVLIS system are either stainless steel tubing or tygon tubing. The connections are flanges, Chicago fittings or hose clamps.

The hose clamps are only used on tygon tube to steel tube connections. All components are qualified at temperatures and pressures well above the temperatures and pressures that the RVLIS is expected to encounter in Modes 5 and 6.

E. Operational Controls Level instrument correlation checks are conducted at preestablished levels to verify the accuracies of key level instruments during the draindown of the RCS.

The criteria for agreement between various instruments are established by the Engineering Department and incorporated into the draindown procedure. In case of any apparent discrepancies between level instruments, the draindown is stopped until

the discrepancies can be resolved. No openings in the cold legs are allowed until the water elevel is stable and both flow and level alarms are in place. A special mid-loop valve alignment is established to control all potential drain points.

Because of the importance of the PORVs to wide range indicators, the hand switches on the PORVn are tagged to prevent their closure while the RCS is drained down.

During mid-loop operation, S01-2.1-9, "Loss of Residual Heat Removal System" provides detailed instructions on problem identification and corrective actions in responding to abnormal conditions (RCS low level alarm on Loop C narrow range, RHR low flow or high temperatures, etc.) associated with the RHR systems. In the event that the RHR systems are lost and cannot be restored, this procedure provides detailed guidance on eight alternate methods to remove decay heat and implements the emergency plan if necessary.

-.12 OUESTION 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

A. The following pumps can be used to control NSSS inventory either separately or in combinations.

PEma Delivered Flow Rate

1.

Test Pump 21 gpm

2. North or South Charging Pump 345 gpm (RWST suction) each

3. North or South Charging Pump 50 gpm (make-up suction) each

4. North or South Refueling 1000 gpm each Water Pump B.

Technical Specifications require that with fuel in the reactor, either one charging pump or the test pump be maintained operable for reactivity control.

This requirement can be waived only when borated water is in the refueling cavity provided, in addition, that an alternate source of borated water is available to establish at least one flow path to the core for boric acid injection which can be initiated from the control room. The minimum capability for boric acid addition shall be equivalent to that supplied by a charging pump from the refueling water storage tank. Maintenance can be performed on pumps that are not being relied upon to meet the minimum requirements. All pumps that are functional, whether technically operable or not, are maintained in standby and can be utilized if required.

C. Procedurally, a charging pump or a refueling water pump, with or without the test pump, with a minimum make-up capability of 50 gallons per minute, is maintained operable during mid-loop operation.

0

-13 QUESION o

ou require for the "A description of the containment closure co n ion tds amplee of area conduct of Operations while the RCS is partially fle. Eape faeso considerationathe equipment hatch, personnel hatches, containment purge valves, SG secondary-side condition upstream Of the isoainvle (including the valves), piping penetrations, and electrical penetrations."

RESPONSE

e closure capability within four hours i required by the procedures Containment clsr aaiiyw~ednfuroec (houes, cables, etc) are anytime the RCS is partially filled. Interferences (oecbeec r

anotmed to be routed through the personnel hatches, and points of not~~ ~

~

~ alwdqi nhac.Pp n

a on d

on disconnect are required adjacent to the equipmt hcaatl ch.ur)

Piping and electrical penetrations are maintained int (capable ofRclosre). yS i eS make up supply is required during periods when t pdartl filed cntainment closure within four hours will provide added assranitat thle health and safety of the public is not endangered if the emeurgency mhakeu/ce cooin water supply were to subsequently fail.

Further assurance is provided by: 1) the redundant level monitorinlg equipment which will help to ensure an early response to a change in.RCS inventory;

2) training and procedural guidance to ensure rapid and proper identification of abnormal plant conditions during partially filled RCS operations, and to ensure appropriate actions are taken to correct the abnormal conditions as necessary; 3) administrative controls to ensure the RCS inventory and inventory control system are not challenged by maintenance and testing activities.

-14 OUESTION 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 draindown to the condition where the RCS is partially filled, treatment of minor variations from expected behavior such as caused by air entrainment and de-entrainment, treatment of boiling in the core with and without RCS pressure boundary integrity, calculations of approximate time from loss of RHR to core damage, level differences in the RCS and the effect upon instrumentation indications, treatment of air in the RCS/RHR system, including the impact of air upon NSSS and instrumentation response, and treatment of vortexing at the connection of the RHR suction line(s) to the RCS.

Explain how your analytic basis supports the following as pertaining to your facility: (a) procedural guidance pertinent to timing of operations, required instrumentation, cautions, and critical parameters; (b) operations control and communications requirements regarding operations that may perturb the NSSS, including restrictions upon testing, maintenance, and coordination 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)."

RESPONSE

A summary description of procedures which describe activities conducted during RCS draindown modes and operation with the RCS partially filled is contained in response to Question (1).

The-analytical basis for procedures where applicable is described below.

Abnormal operating instruction S01-2.1-9 "Loss of Residual Heat Removal System" identifies operator actions in the event of a total loss of RCS heat removal capability while the RCS is in the mid-loop (partially filled) condition. If loss of RHR is due to pump cavitation, the RCS is refilled above mid-loop using a charging pump and the standby RHR pump is started. The procedure specifies that depending on RCS temperature and decay heat generation rate, a time interval of 15 minutes or more is available before an alternate core cooling method becomes necessary. If RHR cannot be restored within this time interval, then alternate core cooling is initiated.

Alternate core cooling consists of using a charging pump to maintain constant level (below SG manways) to make up for boiloff and allow installation of a SG cold leg manway. Cold leg injection is through any of the three loops until a manway is installed. Then cold leg injection is established to the loop with cold leg manway installed and heat removal is accomplished via feed and bleed to the containment. The response to Question (3) describes additional plant capabilities to control RCS inventory.

-15 C rre nt procedural guto initiate alternate core cooling is basedrO e b daerodledur of cdhre h function of time after reactor shutdown qalutatively assese

.u rth Cs close (RS preresbundar ofntact) and time to start bulk boiling following loss of4 Rminhereu tftesefo calculations indicate that bulk boiling would occur within 15 shutdown times of interest (5-50 days).

Calculations of time to core uncoVerY and makeup rate to maintain inventory have also been performed.

Results indicate time to core uncovery of 1.2 to 3.2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and makeup rates of 11-32 gpm for shutdown times of interest.

These results indicate that sufficient time exists to initiate alternate core cooling and that a charging pump has adequate make up capacity to makeup for core boiloff.

Current procedural guidance and analytical basis apply to the RCS when it is in a mid-loop onfiguration and is "open" to the containment atmosphere. As the result of GL 87-12 and evaluation of mid-loop operations, other possible mid-loop plant cnfigurations have been identified and RCS response has been qualitatively assessed. cThese include:

(1) Mid-loop operation with RCS closed (RCS pressure boundary intact) with and without SGs available, (2) Mid-loop operation in configuration (1) above with the addition of an opening in the RCS cold leg (e.g., for RCP seal replacement or other RCP maintenance).

The RCS response to loss of RHR for the above plant snfigurations is described below.

in the event the RCS is drained down to mid-loop and closed to the atmosphere (i.e., RV head on, SG manways closed, pressurizer and RV head vent's open), the RCS espnsedepndson the SG availability. If the SGs are available (i.e., there is water in the SG secondary side), the RCS will pressurizl ni the air in the system is compressed into the SG tubes sufficiently that heat transfer area is exposed (approximately one foot) to condense the steam produced by decay heat. A plant specific quasi-steady state calculation indicates this would require an RCS pressure of approximately 10 psig (assuming RCS temperature of 240*F and SG temperature of 212 0F). An independent computer calculation in Reference 1 using simplified Combustion Engineering System 80 plant data indicates an initial RCS pressurization of 5.4 psig (SG at 120.F) increasing to an RCS pressure of 32.1 psig (SG at 212 0F).

This calculation assumed a homogeneous air-steam mixture in the SG tubes with degraded heat transfer coefficient compared to pure steam condensation but with the full SG heat transfer area available.

This result would be applicable to San Onofre Unit 1 based on comparable power to SG heat.

transfer area ratio. The results indicate RCS pressurization is low (00s of psig) as the SGs are effective in removing decay heat by reflux condensing.

Current procedural guidance is appropriate in this case which is to (i) use a charging pump to maintain RCS level to make up for boiloff and provide makeup for small RCS inventory losses through vents, and (ii) provide auxiliary feedwater to the secondary side of the intact SG's.

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-16 In the event the RCS is at mid-loop, cl'osed to the atmosphere (i.e.,.RV head on, SG manways closed, pressurizer and RV head vents open) and the SGs are not available (SG water level less than 10% wide range level), the loss of RHR flow will cause the RCS to begin to pressurize. When the RCS is between 10%

pressurizer level and mid-loop, at least one PORV and its associated block valve is required to be open in order to vent the pressurizer to the pressurizer relief tank (PRT) for operation of the wide range refueling water level detectors. With the RCS vented by one PORV in addition to RV head vent and pressurizer head vent, it is estimated that the RCS will pressurize to approximately 500 psig based on decay heat level at approximately 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> (start of mid-loop operations) after shutdown. Pressurization above 500 psig may result in opening of the RHR relief valve (500 psig setpoint).

If one PORV is capable of removing decay heat (steam relief rate approximately equal to boiloff rate at 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> post shutdown), then RCS pressure will stabilize at some pressure below 500 psig such that relief rate matches boiloff rate with a charging pump providing for RCS makeup.

If the RHR relief valve opens, water relief will initially occur until the RCS water level reaches the bottom of the hot legs. Water relief via the RHR relief valve is not sufficient by itself to remove decay heat and depressurize the RCS. Charging flow is sufficient to remove decay heat but may not preve't RCS level from dropping to the bottom of the hot legs, as RHR relief valve liquid flow (350 gpm) exceeds charging flow (50 gpm or 345 gpm). When the RHR relief valve location becomes uncovered and steam relief occurs, the RCS will depressurize and the valve will close. Charging flow is sufficient to match the steam production rate, so that RCS pressure will subsequently cycle around the RHR relief valve setpoint to remove decay heat and charging will provide RCS makeup in a feed and bleed mode of core cooling. Having a SG available or 2 PORVs open would prevent RHR relief valve actuation and provide a preferable mode of alternate core cooling. Procedure modifications or other means to ensure a viable mode of decay heat removal will be evaluated and implemented prior to the next mid-loop operations.

A final category of plant configurations at mid-loop occurs when there is an opening in the discharge leg due to RCP seal replacement or RCP maintenance requiring partial RCP disassembly. If the RCS is otherwise closed (i.e., RV head on, SG manways closed, pressurizer and RV head vents open) on loss of RHR flow, the RCS will heatup and pressurize to approximately 10-30 psig or 500 psig (RHR relief valve setpoint), depending on whether the SGs are available.

The RCS pressure would act on the RV water level and crossover leg (loop seal) water level and force water out of the RCP opening. A larger opening and a higher pressure (SG not available) would relieve more water than a smaller opening or a lower pressure (SG available). Water would continue to be discharged through the opening until the loop seal vented or cleared, allowing a steam vent path to the opening which would depressurize the RCS. The potential for partial core uncovery exists during the loop seal clearing process, particularly if the loop seal elevation is lower than the top of the core elevation. Charging flow may mitigate the situation by providing flow which exceeds that being discharged through the opening.

-17 No plant specific evaluation of this scenario has been performed. However in Reference (1) discharge leg flow path sizes were calculated with discharge rates for water and steam which matched HPSI flow at RCS pressures of 50 psig and 400 psig (600 gpm and 450 gpm HPSI flow, respectively). The flow path sizes calculated were 2.74 in2 (liquid) and 114 in2 (steam) with SG available (50 psig), and.616 in2 (liquid) and 8.1 in2 (steam) with SG not available (400 psig).

The results indicate that with SG available RCP disassembly beyond seal removal (several square inches) is acceptable, but that major RCP disassemblies (i.e., > 114 in2) may not be acceptable as steam flow through the path exceeds HPSI injection at 50 psig. With SG not available, RCP disassembly beyond seal removal (i.e., > 8.1 in2) may not be acceptable as steam flow through the path exceeds HPSI injection at 400 psig.

These conclusions are generally applicable to San Onofre Unit 1 although the smaller capacity charging pump (345 gpm) would decrease these areas somewhat.

Hence, RCP seal replacement appears to be acceptable in this plant configuration with or without SG available, so long as 1 charging pump is available. For RCP openings of a few square inches, charging flow exceeds steam flow through the RCP flow path but is less than liquid flow so that flow path coverage (top of cold leg) would alternate between liquid and steam and the loop seal must vent to allow steam to the flow path. For San Onofre Unit 1 the loop seal elevation is lower than the top of the core, so that loop seal venting could partially uncover the core. For much larger RCP openings associated with major RCP disassembly, it has not been demonstrated in a dynamic sense that charging injection can keep up with steam flow through the RCP opening. Procedure modifications (e.g., SG availability, hot leg injection, hot leg vent) to minimize the potential for core uncovery and to ensure a viable mode of decay heat removal will be evaluated and implemented prior to the next mid-loop operations.

AOI S01-2.1-9 "Loss of Residual Heat Removal System" also provides for actions related to containment integrity. If RHR is not restored within 15 minutes, the procedure requires that containment be evacuated of non-essential personnel, containment purge be stopped and containment integrity be established (close all openings to outside atmosphere and isolate all lines which penetrate containment and are open to the atmosphere).

Containment integrity is required within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

A preliminary assessment of the onsite and offsite radiological consequences of a loss of RHR event was made assuming no core damage. The onsite assessment assumed an expected 1-131 concentration in the RCS and a boiloff rate corresponding to 5 days after shutdown which results in release of approximately 0.3 pCi/sec to containment atmosphere. Assuming no purge or other release from the containment building the 1-131 concentration in containment after 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> would be 0.3 x 10-1 pCi/cc or 3 MPCs. Personnel working within the containment would accumulate approximately 6 MPC-hours at the end of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> which is about 1% of the quarterly exposure allowed by regulations. Appendix I of 10 CFR 50 limits the total annual release of 1-131 in gaseous effluents to one curie. If all 1-131 discharged into containment were released to the environment, the cumulative release in 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> would be

.002 curie or 0.2% of the annual limit. The offsite dose assessment in Reference (1) assumed RCS specific activities using System 80 data based on

-18 ANSI N237 (no credit for degassing), a boiloff rate corresponding to 1 day after shutdown, site meteorology per Reg Guide 1.4, and no credit for containment integrity. The dose results were 31 mrem (thyroid) and 15 mrem (whole body) 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> dose at the site boundary. Use of actual RCS concentrations would reduce these dose results by roughly two orders of magnitude. Scaling for San Onofre Unit 1 power level would reduce doses further by a factor of three. Hence, onsite and offsite dose consequences are small as long as the loss of RHR event does not produce fuel damage.

The potential for core damage was also assessed. Core damage would not occur for some time after the onset of core uncovery. For the plant configuration where the RCS is "open" to the atmosphere, time to core uncovery following loss of RHR was estimated at 1.2 to 3.2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> (5 to 50 days after shutdown).

The preferred recovery method is to restore RHR. However, the availability of one charging pump is sufficient to make up for boiloff and other alternate methods of removing decay heat are also available. In Reference (1), the analysis indicated that substantial core damage via boiloff scenarios will not occur until the time the level drops below the core midpoint, as clad temperature remains below 1200OF due to steam heat transfer. This would provide an additional 45 minutes to 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> before core damage.

For the plant configuration where the RCS is "closed" to the atmosphere, if RHR cannot be restored, then SG availability or primary feed and bleed using PORVs/charging are alternate methods of core cooling which will keep the core covered.

For the mid-loop plant configuration where the RCS is closed except for an opening in the cold leg (e.g., RCP seal replacement), a charging pump can makeup for liquid inventory losses through the opening. Heat removal is via SG or feed and bleed (charging/PORVs and/or RCP opening depending on RCS pressure).

For a larger opening in the cold leg (e.g., major RCP disassembly) the loop seal will vent steam to the opening. For San Onofre Unit 1 the top of the loop seal is below the top of the core, so that partial core uncovery may occur during the venting process.

Subsequently, charging flow will makeup for steam boiloff to remove decay heat.

Based on the above, the probability of core damage following a loss of RHR event is extremely low given the time available to restore RHR and the alternate methods of heat removal available. Procedure modifications to minimize the potential for core uncovery and to ensure a viable mode of decay heat removal will be evaluated and implemented prior to the next mid-loop operations.

Air entrainment in the RHR system could potentially cause transient RCS level differences between the hot leg and cold leg, as was observed at San Onofre Units 2 and 3. Air entrainment causes the apparent RCS level to rise in the cold leg as the air displaces the water. Levels eventually equalize as the air leaks out of the cold leg through the gaps between the hot leg and the downcomer and the core barrel alignment keys. The transient level difference does not affect RCS level indication which is correctly measured in the hot leg.

Historically, vortexing and air entrainment at the connection of the RHR suction line and the RCS which could lead to RHR pump cavitation has not been

-19 observed at San Onofre Unit 1. The potential for vortexing is minimized by (i) avoiding plant evolutions below mid-loop (i.e., nozzle dams are typically not used), (ii) by the relatively low RHR flow rate and (iii) by plant design. As an explanation of this last factor, the San Onofre Unit 1 RHR System utilizes two RHR pumps dedicated to the specific function of decay heat removal.

This is unlike other plants which use their LPSI pumps for decay heat removal.

These two RHR pumps are located inside containment, below and in close proximity to the RCS loops. In addition, the RHR pumps are designed to run under water in a post-LOCA environment if required. To ensure integrity, hot leg level is closely monitored during mid-loop operation by redundant channels of level indication which have been satisfactorily correlated.

Reference 1:

CE Owners Group, "Loss of RHR Scenarios --

Detailed Qualitative Assessment," dated September 1, 1987

-20 QUESION 6ted "A brief description of training provided to operators nd other aec personnel that is specific to the issue of operation h

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

RESPONSE

A) Operator Training Formal training for partially filled RCS operations and the associated potential loss of RHR systems is conducted in the form of theory review, systems training requalification/si mu lator training, and on-the job training. This frmal training, coordinated and conducted through the Training Division, has received INPO accreditation.

Theory Review, Science and Engineering Fundamentals Lesson Plan

DFD203, "Fluid Mechanics in Pumps," covers specifically the computation of net positive suction head (NP 'SH) and the various methods by which an operator can change NPSH. This training is intended to provide the necessary background knowledge for operations personnel in identifying and understanding the circumstances which could lead to a loss of NPSH on any pump. This becomes important in providing the proper level of understanding to allow the operator to deal with conditions which could lead to a loss of RHR pumps.

Systems Training, Plant Systems Lesson Plan 1XA202, "Reactor Coolant and RCS Instrumentation," contains an objective that covers the monitoring of instrumentation while in mid-loop.

System Description SDuS01-280, "Reactor Coolant System," contains reference to and discusses S01-4-2, "Draining The Reactor Coolant System."

Initial licensed Operator training Lesson Plan 1XB203,a Residual Heat Removal," contains references to NRC, INPO, and internal documents discussing the loss of RHR events.

System Description SD-SO1-3 20, "Residual Heat Removal System," contains references to.the loss of RHR procedure.

Initial Licensed Operator Training Lesson Plan oA1710, "Loss of RHR,"

covers in detail the loss of RHR both during normal and mid-loop conditions. This training with lesson plans and system descriptions as handouts provides the operator with knowledge of specific operational circumstances associated with loss of RHR. The lessons include review of actual station procedures which identify indications available and the procedural actions required of the operator if RHR is lost during mid-loop operations.

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-21 Requalification/Simulator Training.

The 1987 requalification training program contains a Lesson Plan 1RP724, "RHR System and Operation," which covers objectives dealing with the loss of RHR in all modes. Additionally, the lesson plan contains a review of significant loss of RHR events throughout the industry, including the Diablo Canyon incident, which is referred to in Generic Letter 87-12.

A portion of the 1987 simulator training Lesson Module 1RS721, is devoted specifically to operator actions during a loss of RHR. The operation of the RHR system has been, and will continue to be, one of the most important systems to receive on-going emphasis during requalification/simulator training.

The theory review, systems training, and requalification/simulator portion of the formal training program pertaining to shutdown cooling and partially filled RCS operations consists of approximately 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> of classroom time per year.

On-The-Job Training As part of the qualification for a particular watch-station, an operator must complete a qualification checkoff which requires the operator to verbally communicate knowledge of specific system operation and details.

This checkoff includes requirements for demonstrating knowledge of the RHR system and the associated operating procedures, including recovery of the RHR system during mid-loop operations. The response given by the qualifying operator is evaluated for correctness and completeness by a qualified operator before the qualified operator will validate the qualification checkoff.

Pre-shift Briefing In addition to the formal training described above, which provides the operator with an in-depth as well as a well rounded understanding of partially filled RCS operation and loss of shutdown cooling, a pre-shift briefing, which is formally conducted between the offgoing Operation Shift Superintendent and the oncoming shift operation crew, is another key component to facilitate partially filled RCS operation. This briefing ensures that important plant status and conditions are clearly and orderly transmitted from one operating crew to the next operating crew; it serves as a crucial forum to ensure that the latest key changes to procedural and administrative requirements affecting plant operations are transmitted in a real time manner.

As part of an in-house effort to augment operator knowledge, Unit 1 Operations has held training discussions on shutdown cooling-related industry events. Among the events discussed was the April 10, 1987 loss of RHR at Diablo Canyon Unit 2 as described in NUREG-1269.

-22 B) Maintenance Personnel Training Formal Classroom Lessons As discussed in the response to Question #1, the Maintenance Planning/Equipment Control review process plays a key role in ensuring that maintenance activities do not result in any adverse impact on partially filled RCS operations and shutdown cooling. Accordingly, all appropriate maintenance personnel are taught the following topics via the Training Division:

Equipment Control Work Authorizations Administrative Procedures (such as maintenance planning)

Procedure Compliance Plant and Industry Events These training topics also place emphasis on areas such as actions to be taken if an unexpected condition arises during the performance of a work evolution and the personnel to be notified if a parameter is found to be unsatisfactory during performance of a maintenance procedure. By reporting abnormal conditions in a timely manner to Operations based on the ongoing maintenance activities out in the field, maintenance personnel assist operators in recognizing potential loss of RHR conditions earlier than might otherwise be expected. This additional awareness also provides for a rapid response by maintenance personnel in responding to a loss of RHR.

Maintenance Crew Briefing Similar to the Operations pre-shift briefing, the maintenance crew briefing serves as a crucial forum to ensure that maintenance status is transmitted in a clear and orderly fashion from one crew to the next, and that the latest important changes affecting ongoing maintenance activities are communicated in a timely manner. During partially filled RCS operations with the Unit in an outage condition, a shift maintenance supervisor regularly attends the Operations pre-shift briefing. This maintenance supervisor also serves as a maintenance focal point to the Operation Shift Superintendent. In this way, abnormal maintenance conditions are effectively communicated to Operations, and likewise changes in plant conditions which can affect ongoing maintenance activities are effectively communicated to Maintenance.

While the maintenance training, formal or otherwise (maintenance crew briefings) are not as extensive as the Operations training in the area of partially filled RCS operations and loss of shutdown cooling, it is sufficient to complement and assist Operations in handling any problems that may arise during partially filled RCS operations.

-23 QUESTION 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

Based on our experience with loss of RHR, and industry experience, considerable resources are provided to aid the operators while the RCS is partially filled. Additional personnel have not been added to the normal shift complement, but the normal shift complement includes additional personnel not required by the Technical Specification minimum staffing requirement. Each shift is normally staffed with I&C technicians, maintenance personnel, and two levels of Operations supervision (the Control Room Supervisor and the Shift Superintendent) both of whom hold active SRO licenses. This staffing level ensures that an adequate level of expertise is available during periods when the RCS is partially filled.

The procedures for controlling plant status during partially filled periods contain notes, cautions, checks, and specific acceptance criteria, all writtan specifically to aid the operators during periods when the RCS is partially filled.

The guidance is clear and specific, not general and superficial.

Specialized training has been conducted and is conducted as part of the INPO accredited requalification training program to ensure operator understanding and familiarization with the effects of a loss of RHR on instrumentation (e.g., loss of direct temperature detection capability), on core heat removal, and on inventory control such that the proper priority perspective will be used to recover all safety functions. The following division personnel either are available to the operators around the clock on site, or can be called to the site on short notice:

TECHNICAL DIVISION Cognizant Engineers are assigned to provide required technical input and evaluations on an "on-call" basis.

OPERATIONS & MAINTENANCE SUPPORT DIVISION Additional personnel are assigned to provide up to the.minute status on SG tube inspection and plugging activities and Inservice Inspection activities.

REFUELING GROUP Additional personnel continuously monitor and provide up to the minute status on fuel movement and/or other core alterations.

MAINTENANCE DIVISION Additional personnel monitor and provide up to the minute status on key, partially filled RCS maintenance repair work such as RCP seals, and RCS boundary isolation valves.

-24 OUTAGE MANAGEMENT DIVISION Outage managers resolve scheduling conflicts when competing activities need to be performed in the same plant condition window. Containment coordinators are assigned specifically to monitor all activity inside containment throughout the outage. In reality, all these division personnel, and the operators, work as a team to ensure that partially filled RCS operations, repair and test activities are conducted smoothly.

At San Onofre, it is recognized that the Operations Shift Superintendent, in addition to having the responsibility to ensure the safe operation of the unit, is a key member in the overall management structure of the site. For this reason, he is authorized and encouraged by management to utilize any site resources or personnel to resolve his concerns. These include direct communication with the Station Manager or the Vice President and Site Manager, if necessary.

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-25 OUESTION 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

The requirements that differ from a Loops Filled status are contained both in the Technical Specifications and in applicable operating instructions. The Technical Specifications require two trains of RHR to be operable with one of those trains in operation when in a Loops Partially Filled status. Prior to draining down to a Loops Partially Filled status, and during the period of being in a partially filled status, the procedures require the following items that are not applicable while in a Loops Filled status. RHR flow rate should be less than 1000 gpm (typically 500 gpm) and RCS temperature must be less than 140*F. The Reactor Vessel Level Instrument System (RVLIS) is required to be operable before level is lowered below 10% in the pressurizer; a special daily RVLIS surveillance (channel check) is required thereafter. A makeup pump with 50 gpm capacity and associated support systems are required. All primary makeup water sources are tagged shut to prevent inadvertent dilution during refueling evolutions. The minimum hot leg level (40% of Loop C narrow range) and the maximum RHR flow (1000 gpm) are specified to prevent excessive air ingestion. Four hour containment closure capability is required. If a loss of RHR occurs during a Loops Partially Filled condition (loss of direct temperature indication event), the operators are required to use a table (heat up rate versus time after shutdown) to declare an Alert emergency event rather than rely on questionable temperature indicators. A specific valve alignment, including tagging, is required to ensure RCS integrity.

-26 QUESTION:

have made changes "As a result of your consideration of these issues, youm have maed 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.

The information discussed in the responses to the other questions forms the basis of the Unit 1 program for operation in a partially filled RCS condition.

The program has evolved over a period of years and many changes have been implemented that considerably strengthen our ability to operate safely in a partially filled RCS condition.

All of the commitments included in this response have either been implemented or will be implemented prior to the next mid-loop operations.

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