ML20235E933
| ML20235E933 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 09/21/1987 |
| From: | George Thomas PUBLIC SERVICE CO. OF NEW HAMPSHIRE |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| GL-87-12, NYN-87114, NUDOCS 8709280333 | |
| Download: ML20235E933 (19) | |
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PENHI J Ntw Hampshire Yankee Division NYN- 87114 E a
September 21, 1987 h&
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United States Nuclear Regulatory Commission c Washington, DC 20555 "
i Attention: Document Control Desk
References:
(a) Facility Operating License NPF-56 and Construction Permit CPPR-136, Docket Nos. 50-443 and 50-444 (b) USNRC Generic Letter 87-12, " Loss of Residual Heat Removal (RHR) While the Reactor Coolant System (RCS) is Partially Filled", dated July 9, 1987
Subject:
Response to Generic Letter 87-12 Gentlemen:
Generic Letter 87-12 requested information pursuant to 10 CFR 50.54(f).
Enclosed are the results of the New Hampshire Yankee (NHY) evaluation of the '
concerns raised by this Generic Letter.
As indicated in the responses, the NHY evaluation of these concerns is still in progress. Several items require further review of the Seabrook Station Operating and Abnormal Procedures. This review will be completed prior to exceeding 5% power and a supplemental response will be submitted.
Additionally, the Westinghouse Owners Group (WOG) is developing a program to ;
assist WOG members in responding to these concerns. NHY will participate in the Owners Group effort and will review the results of this program for applicability to Seabrook Station.
0709280333 870921 ,
$o6 P.O. Box 300 . Seabrook, NH 03874 . Telephone (603) 474-9574 i (l i
United, States Nuclear Regulatory; Commission' September 21, 1987 Attention: Document' Control Desk 'Page 2-If you have any questions regarding this. matter, please contact-Mr. Richard R.~Belanger:st.(603) 474-9574, extension 4048.
Very truly yours,
, d{fke#d S. Thomas Enclosure-cc: Mr. William T.' Russell
. Regional-Administrator U.S. Nuclear Regulatory Commission Region I-631 Park Avenue King of' Prussia, PA 19406 Mr. A. C.'Cerne NRC Senior Resident Inspector Seabrook Station Seabrook, NH' 03874 STATE OF NEW HAMPSHIRE Rockingham, ss. September 21, 1987 Then personally appeared before me, the above-named George S. Thomas who, being duly sworn, did state that he is Vice President - Nuclear Production of Public Service Company of New Hampshire, that he is duly authorized to execute and file the foregoing information in the name and on behalf of Public Service Company of New Hampshire, and that the statements therein are true to the best L of his knowledge and belief.
I' & S Y sant Public
- i. Beverly My Est$111oway, Commission Expires: Notarj(h Marc ,, 6 1990
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l ENCLOSURE TO NYN-87114 l
RESPONSE TO GENERIC LETTER 87-12 ;
l NRC Generic Letter 87-12 requests information to assess safe operation when j the Reactor Coolant System (RCS) water level is below the top of the reactor ,
vessel. The letter indicates concern as to whether unanalyzed events may have l an impact on safety. New Hampshire Yankee (NHY) has been performing a ,
detailed safety assessment of such events over the past several months. This effort was initiated as a result of NRC questions about the risk of shutdown events. NHY recognized that a logical, systematic assessment of procedures, systems, and human actions could provide the framework to identify potential improvements and their benefits. This study is expected to be completed by November, 1987, and will be used as an input to any decisions regarding improvements.
Additionally, the Westinghouse Owners Group (WOG) is developing an initiative to assist the WOG member utilities in responding to Generic Letter 87-12. NHY will participate in this effort and apply the results, as appropriate, at Seabrook Station.
The NHY response to each item of Generic Letter 87-12 follows.
(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 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 to Item No. 1 A review of the plant operating, maintenance, and inspection procedures indicates that it is necessary to drain the RCS to the loop midplane for steam generator (SG) maintenance and inspections. Reactor Coolant Pump (RCP) seal repair or removal may be performed with the RCS loops drained to the midplane but does not require draindown.
To prepare for operation at the loop midplane, the plant would be brought through a normal cooldown which is limited to a maximum of 100*F per ,
hour. The RCS draindown procedure requires that the'RCS be maintained l between 100*F and 140*F prior to initiation of draindown. Based on I existing cooldown calculations, the RCS temperature can be reduced to j 140*F in slightly greater than 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> af ter reactor shutdown. Per Technical Specification requirements, while the plant is in Mode 5 with ]
the loops filled the secondary side of two steam generators must be i maintained at a minimum level of 17% full or the second Residual Heat Removal (RHR) train must be operable. However, no requirements exist for l minimum SG level once the loops have been partially drained. The draindown procedure precautions contain warnings regarding the .
inaccuracies of level indication while the SG U-tubes evacuate and also !
contain a warning that the control room reactor vessel (RV) level indication will not be accurate until the RCS pressure is equalized with the containment pressure. One of the prerequisites for beginning draindown is to have the RCS degassed, depressurized, and vented.
The procedure for draindown is prefaced by a note which indicates that
" DRAINING THE RCS VIA RHR LETDOWN IS THE PREFERRED METHOD OF DRAINING THE RCS...". The procedure also gives steps for draindown by using the loop drains. Either method assures a relatively slow draining of the loops; .
however, the letdown path assures a more easily controlled draining l process. Both procedures require opening of the pressurizer vent valve prior to beginning to drain the RCS. Both procedures also require a comparison of the pressurizer level instrumentation against the reactor vessel shutdown level indicator (temporary tygon tubing installed per operating procedure). Once the level reaches the 8' elevation (RV head vent at elevation 8' 1-7/8") the head vent is opened. The procedure '
requires that prior to draindown below the top of the hot leg nozzle, both RHR pump flow rates must be reduced to approximately 1000 gpm to prevent vortexing of their suctions. )
In addition, the procedures for the startup and operation of the RHR trains for operation at low RCS water l level are referenced once the level drops below the top of the hot leg j nozzles. The referenced procedure instructs the operators to frequently '
monitor RHR pump current, flow and discharge pressure for signs of cavitation. In addition, it instructs the operators on how to restore {
1evel in the vessel should cavitation occur. The procedure calls for the I draindown to be stopped at the (-) 7' elevation (loop midplane) as read 1 f rom the reactor vessel shutdown level indicator.
Seabrook Station has two RHR drop lines, one to each RHR pump. Thus, when the pump flow is reduced to 1000 gpm the RHR drop line flow is reduced to 1000 gpm.
During the draindown process, the equipment hatch will normally remain in (
place. The only need for opening the equipment hatch at Seabrook Station j occurs when the RV o-rings are brought into containment. However, if the !
hatch was open and its replacement was necessary, it could be replaced in approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> under ideal conditions. The personnel hatch / air lock could be shut immediately. Limitations on removal of the equipment hatch during draindown and operation at the loop midplane are being ,
considated as a result of the ongoing effort to identify potential impre aments.
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1 Changing of equipment statua, maintenance, testing or other activities, which could affect the status of the plant, the containment or RCS boundary, is governed by the Work Ccatrol Program, which requires that any work within the plant be cleared through the Unit Shift Supervisor prior to commencement. If the plant is in operation at the loop i midplane, the Unit Shift Supervisor will be aware of the condition.
Abnormal Procedure OS1213.01, " Loss of RHR During Shutdown Cooling",
requires that the RCS be immediately filled and vented in the event that shutdown cooling cannot be restored.
NHY is conducting an extensive review of the Station procedures pertaining to RCS draindown and operation of the RHR System with the RCS partially filled in light of the concerns raised in Generic Letter 87-12 and the accompanying NUREG-1269, Loss of Residual Heat Removal System.
The initial review will be completed prior to exceeding 5% power.
Additionally, the WOG is developing an initiative to assist the WOG members in responding to Generic Letter 87-12. NHY intends to participate in the WOG effort and to apply the results, as appropriate, to improve operations at.Seabrook.
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(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 I 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 f" 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 af ter the RHR function may be lost.
Response to Itam No. 2 !
1 The following instrumentation and alarms are available to the operators for. controlling RCS parameters during partially filled conditions.
a) Temperature i
- 1. Well type RTDs are installed on the inlet and outlet of each RHR heat exchanger. The heat exchanger temperatures can be read on the main control board (MCB) on both meters and recorders und all 4 of the temperatures are available on the main' plant computer (MPC) in analog form. {
- 2. Core exit thermocouple (TCs) are bottom entry TCs that share instrument thimbles with the incore power detectors. The TCs are divided between two trains and the data is processed by the Reactor Vessel Level Instrumentation System (RVLIS) process computers. The temperatures are displayed on the RVLIS PLASMA DISPLAYS in both graphic and tabular form. A train average is j available on a MCB meter and all temperatures are available on the MPC in analog form.
b) Level
- 1. A narrow range vessel level instrument is placed into service when the RCS is vented to provide indication of level utilizing the vessel flange as a reference. This instrument senses RCS Loop 1 intermediate leg pressure and provides MCB indication and input to the MPC in analog form.
- 2. The reactor vessel shutdown level indicator is installed between the RCP suction leg and the pressurizer vent. The suction leg connection is made to the Loop 3 RCS flow transmitter. The
) pressurizer vent connection provides a reference pressure to minimize uncertainty in the level reading. f The tubing is suitable from 27 inches of vacuum to 50 psig with a 1 burst pressure of 150 psig. A level cross check is performed with the pressurizer level instrument prior to relying on the reactor vessel shutdown level indicator. During the actual i
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i draindown process, an operator observes the reactor vessel l
shutdown level indicator locally and has established ;
communication with the control room operators. 1 c) Flow I
RHR loop flow.is monitored and displayed on a MCB meter and is input i to the MPC in analog form. An RHR low flow alarm is provided at ;
2900 gpm.
l d) Pressure Two RCS wide range pressure instruments provide MCB meter indication, ,
RVLIS PLASMA DISPLAY indication'and input to the MPC in analog {
form. The instruments input to the LTOP System that opens the PORVs j and provides an alarm at 100 psig below actuation pressure of the. j PORVs. These instruments will automatically shut the RHR suction i valves at 660 psig.
RHR pump discharge pressure is indicated on the MCB and alarms on high RHR pump discharge pressure (560 psig).
e) Current Each RHR pump running current is indicated on the MCB.
All level indication listed above remains intact if RHR is lost during a draindown condition. Core exit TCs are available to monitor RCS temperature if RHR is lost.
All instrumentation and alarms used during a partially drained condition a,re being evaluated to determine if:
- 1. Additional alarms or indications are necessary.
- 2. The accuracy or utility of the instrumentation can be improved by modification.
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- 3. The procedures utilize all indication and alarms giving operators accurate temperature and level information.
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(3) Identification of all pumps that can be used to control NSSS inventory. l Include: (a) pumps you require be operable or capable of operation i (include information about'such pumps that may be temporarily removed j from service for ter Ling or maintenance); (b) other ptcaps not included in j item a (above); and (c) an evaluation of items a and b (ahove) with Ej respect to applicable Technical Specification requirements. j Response to Item No. 3 Pumps available for RCS inventory cuntrol, per Technical Specification requirements, in a partially drained condition include one centrifugal I charging pump (CCP) and two RHR pumps. f The CCP could be used in the normal charging mode taking suction from the volume control tank and charging through normal charging lines to Loop 1 or 4 cold legs. The CCP can also be used in the injection mode taking I suction from the Refueling Water Storage Tank (RWST) to all 4 cold legs.
The RHR system can be used to gravity drain the RWST to the RCS via RHR .
pump suction off the RWST through the RHR loop suctions. The RWST is at l the 25' elevation. N loop midplane is at the -7' elevation. The height difference allows gravity feeding the RCS when in the vented condition. The RHR pumps can also be used in the injection mode by taking suction from the RWST and pumping to all 4 cold legs via injection flow paths.
Additionalpumpswh.ibhareoutofservice,perTechnicalSpecification requirements include one positive displacement charging pump, one ,
centrifugal charging pump, and two Safety Injection (SI) pumps. These f pumps could be put into service, if available and needed, for inventory control.
Seabrook Station is evaluating existing abnormal procedures for restoring inventory during loss of RHR in a partially drained condition. The procedures will be modified or nen procedures will be developed, if necessary, utilizing the results of the evaluation. l 1
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(4) A' description of the containment closure condition you require for the conduct of operations while the RCS is partially filled. Examples of areas of consideration are the equipment hatch, personnel hatches, containment purge valves, SG secondary-side condition upstream of the isolation valves (including the valves), piping penetrations, and electrical penetrations.
Response to item No. 4 Currently, Technical Specifications require that containment building penetratioits be closed or capable of being closed by an operable automatic containment isolation valve in Mode 6 during core alterations or movement of irradiated fuel. An evaluation is being performed to determine if any additional restrictions are appropriate. If appropriate, guidelines will j be established to govern maintenance / operation during partially drained l conditions. l I
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I (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 ere 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 RRR 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 communication 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; (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 to Item No. 5 Procedures available to the operators in the control room for operation while the RCS is partially filled include the following:
OS1001.01, Rev. 4 - Reactor Coolant System Evacuation Fill and Vent OS1001.02, Rev. 1 - Draining The Reactor Coolant System OS1013.03, Rev. 5 - Residual Heat Removal Train A Startup and Operation 081013.04, Rev. 4 - Residual Heat Removal Train B Startup and Operation OS1213.01, Rev. 1 - Loss of RHR During Shutdown Cooling OS1246.01, Rev. 1 - Loss of Offsite Power - Plant Shutdown.
Procedure OS1001.01, " Reactor Coolant System Evacuation Fill and Vent",
provides methods for evacuating and filling the RCS with borated water, and venting of free and entrained gas from the system and the coolant.
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. I The procedure includes references to the applicable Technical Specifications, and precautions related to RCS, RHR System, reactor coolant pump operation, and RCS overpressure protection. The procedure j also identifies the reactor vessel shutdown level indicator as the means i for RCS level indication. The limits of using the reactor vessel level j instrument are identified. '
Among the prerequisites to initiating the procedure are that the pressurizer level indication be available and cold calibrated, that an operator be. stationed at the reactor vessel shutdown level indicator and communication be established.with the control room, and that reactor vessel level be monitored on the appropriate instrument. !
Suitable notes and caution statements are included in the procedure to alert the operator to critical functions. In the procedure, the RCS is filled using the charging pumps taking suction from the refueling water storage tank and delivering to the RCS via the normal charging line and the RCP seals. A caution is included in the procedure to monitor the running RHR pump (s) for possible cavitation.
Procedure OS1001.02, " Draining the Reactor Coolant System", provides a method for draining the RCS to the bot leg nozzle midplane by using either the letdown path from the RHR System to the Chemical and Volume Control System or by using the loop drain connections located in the RCP suction pipe.
) The procedure includes references to the applicable Technical j Specifications, and precautions for erratic level indication at the level for draining the steam generator tubes and proper alignment for operation of the RCS level instrument, The procedure also provides for reducing RHR pump flow to 1000 gpm prior to draining below the top of the hot leg nozzles, and includes the indicated level for the midplane of the hot leg nozzles, and level positions for the top, midplane and bottom of the hot leg nozzles.
Prerequisites for initiating the RCS draindown include: RCS in Mode 5 or 6; RCS degassed and depressurized; RCS temperature between 100*F and 140*F; accumulator injection is isolated and tagged out; safety injection pumps, positive displacement charging pump, and one centrifugal charging pump ace de-energized and tagged out; all reactor coolant pumps are de-energized and tagged out; and sufficient primary drain tank (PDT) capacity is available to receive the expected reactor coolant drainage.
RCS draindown is accomplished by increasing letdown relative to charging flow. The RCS drainage is then directed to the primary drain tank for storage and processing. The draindown flow rate is limited to 140 gpm and is controlled using the RHR to letdown control valve.
An alternate means of RCS draindown is by using a temporary connection i from the RCS loop drains aligned to the Reactor Coolant Drain Tank (RCDT) i pumps. The RCS drainage is directed to the PDT and the draindown rate is limited by the capacity of the RCDT pumps.
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During the RCS draindown. process the reactor vessel chutdown level 4 j
indicator is aligned for monitoring RCS level. As the pressurizer is I drained, the level reading in the reactor vessel level shutdown level j indicator is cross-calibrated with the pressurizer level instrument at (
5-10% pressurizer level. The procedure requires that.an operator must {
monitor the RCS reactor vessel shutdown level indicator during the )
draindown process. i This procedure contains suitable notes and caution statements to alert )
the operator to critical functions. One such note tells the operator j that if it is not necessary to drain the RCS to the hot leg nozzle mid- j plane, then drain the RCS to the desired level. The procedure includes an RCS elevation drawing showing the relative location of the steam generators, reactor coolant pumps, reactor vessel, pressur'ser and key elevations Procedures OS1013.03 and OS1013.04, " Residual Heat Removal Train A Startup.and Operation" and " Residual Heat Removal Train B Startup and Operation", respectively, provide a method for RHR System pressurization and boron concentration verification, RHR System warmup, RCS cooldown with RHR Train A or B, and RHR operation with low RCS water level.
These proced:tres include references to the applicable Technical Specifications, precautions for proper startup and alignment of the RHR pump, heat exchanger and system. A precaution, applicable to midplane operation, is to reduce the RHR pump flow to 1000 gpm to avoid drawing air into the RHR system and to frequently monitor RHR pump current, flow, and discharge pressure for signs of cavitation.
The section of these procedures that provides direction for operation with low RCS water levels includes a caution that RHR pump cavitation could occur and to maintain the RCS level at the proper midplane level indicated on the applicable level indicator. This section is, in general, a recovery procedure for possible RHR pump cavitation. To j recover, the RCS is filled to the top of the hot leg nozzle either by increasing charging flow or by manually opening a closed motor operated valve to align makeup flow f rom the RWST to the RHR pump suction. If the RHR pump continues to cavitate, the pump is stopped, vented, and restarted.
Procedure OS1213.01, " Loss of RHR During Shutdown Cooling", is a station Abnormal Procedure to enable the operator to re-establish RHR cooling to the RCS. The procedure is applicable in Mode 4, Mode 5 with loops filled, Mode 5 with loops drained or being drained, Mode 6 with the l cavity empty, and Mode 6 with m cavity full. In Mode 5 with the loops drained, if shutdown cooling annot be restored, the procedure calls for immediately filling the RCS ut,'w .ne ECCS pumps, pressurizing and venting the RCS and operating one RCS pump. If the plant is in Mode 6 and the reactor vessel head is off, the procedure calls for establishing containment integrity.
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Procedure OS1246.01, " Loss of Offsite Power - Plant Shutdown", is a station Abnormal Procedure that provides directions to maintain core cooling and restore power following e loss of offsite power when shutdown (Modes 5 or 6).
This procedure develops power restoration via the onsite diesel generators or via offsite power. If power cannot be restored and the RCS is partially drained, the procedure calls for gravity feed to the RCS from the refueling water storage tank via the RHR suction lines. If the plant is in Mode 6, the procedure calls for establishing containment integrity. . This procedure alerts the operator to notify the Shift Superintendent for Classification of Emergencies.
The following information was considered in the development of the Seabrook Station operating procedures relating to shutdown cooling while the RCS is partially drained:
- 1. Calculations were performed to verify that adequate NPSH is available to the RHR pumps while taking suction from the RCS at the design flow rate.
- 2. The NSSS vendor has provided a precaution to " carefully control the water level in the Reactor Coolant System during refueling / maintenance operations to ensure the RHR inlet lines are adequately covered with water to avoid drawing air in the system. Throttle the RHR flow to about 1000 gpm in each inlet line from the RCS before the water level is drained to the elevation of the hot legs centerline."
- 3. The reactor vessel shutdown level indicator was provided with a reference leg connection to the pressurizer steam space. This precludes level variations that may be experienced when the reactor vessel shutdown level indicator is referenced to atmosphere.
- 4. Seabrook Station Operating Procedures and Abnormal Procedures were developed to preclude boiling in the core due to loss of shutdown cooling capability. Procedures call for increasing the RCS level to the top of the RCS hot leg nozzle and re-establishing RHR cooling.
- 5. The control room reactor vessel level indication is only effective after the reactor vessel has been adequately vented. The procedures provide suitable cautions to the operator as a result of this consideration.
- 6. Technical Specifications provide the requirements for Reactivity Control Boration Systems, Reactor Coolant Loops and Coolant Circulation, RCS Overpressure Protection Systems, Energency Core Cooling System Accumulators and Subsystems, Containment Integrity, AC and DC Power and Refueling Operations relating to containment building penetrations, residual heat removal and coolant circulation, Containment Purge and Exhaust Isolation System, and reactor vessel water level.
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- 7. Seabrook Station procedures cover normal draindown functions, maintaining shutdown cooling capability with the RCS partially drained,.and provide Abnormal Procedures for loss of RHR during shutdown cooling and loss of offsite power during plant shutdown.
Abnormal Procedure OS1213.01, " Loss of RHR During Shutdown Cooling",
is a symptom-based procedure. Entry conditions for this procedure are:
- Increasing RHR heat exchanger outlet temperature.
- Decreased RHR flow.
- Loss of voltage on either emergency electric buses.
- Loss of the primary component cooling water system.
- Autoclosure of the RHR suction valves due to high reactor coolant pressur(
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- An RHR low flow alarm.
Abnormal Procedure OS1246.01, " Loss of Offsite Power - Plant Shutdown" is a symptom-based procedure. Entry conditions for this procedure are:
- Visual Alarm System alarms:
Bus voltage low RAT incoming line voltage low RAT incoming line breakers trip & lockout UAT incoming line breakers trip & lockout Bus E-5 loss of power Bus E-6 loss of power Bus E-5 voltage low Bus E-6 voltage low Loss of all AC power i
- Loss of running equipment
- MCB volt meters indicate zero volts
- DG Emergency start f
- EPS Actuation
- 345 kV breakers open 3 NHY is performing calculations to verify adequate protection from vortexing at the RHR pump design flow rate and the reduced flow rate, to verify the RHR decay heat removal capability at reduced RHR pump flow ratea and to determine the time to heat the itCS water to the boiling
) point and the time to begin uncovery of the fuel assemblies.
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NHY is conducting an extensive review of the Station procedures l
pertaining to RCS draindown and operation of the RHR System with the RCS l partially filled in light of the concerns rs.ised in Generic Letter 87-12 ,
and the. accompanying NUREG-1269, Loss of Residual Heat Removal System. '
The WOG is developing an initiative to assist the WOG members in responding to Generic Letter 87-12. NHY intends to participate'in the WOG effort and-to apply the results, as appropriate, to improve operations at Seabrook Station.
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- 'Seabrook Station operating procedures do not provide information to the operators that identify the limited time available to heat the RCS water i to the boiling point and the time to begin uncovery of the. fuel assemblies. This information will be included in operating procedures, as appropriate.
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(6) A brief description of training provided to operators and other, effected 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 to Item No. 6 As a result of a review of training provided to operators, two areas have been identified which require further training to address the concerns raised by this Generic Letter. This training is currently under
' development and is scheduled to be implemented prior to the first L
refueling outage. Requirements for training of maintenance or other personnel are still being evaluated at this time.
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l (7) Identification.of additional resources provided to the operators while i the RCS is partially filled, such as assignment of additional personnel with specialized knowledge involving the phenomena and instrumentation.
Response to item No. 7 Currently there are no plans to provide additional personnel with specialized knowledge involving operation with a partially filled RCS.
The plant staff will be adequately trained to handle the potential problems for operation at the loop midplane. The technical support staff will continue to be available as needed.
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(8) Comparison of the requirements implemented while the RCS is partially filled and requirements used in other Mode 5 operations. Some requirements and procedares followed while the RCS is partially filled may not appear in the other modes. An example of such differences is i operation with a reduced RHR flow rate to minimize the likelihood of vortexing and air ingestion.
Response to Item No. 8 An additional requirement imposed by procedure OS1001.02, " Draining the Reactor Coolant System" is to reduce RRR flow to 1000 gpm when the pressurizer level is between 5-10%. This is done in preparation of draining to the loop midplane to prevent vortexing. The normal Mode 5 flow is 3000 gpm. The preferred method of draining the RCS is through the letdown system which limits the drain rate to 120 gpm. Procedure OS1001.01, " Reactor Coolant System Evacuation Fill and Vent", refers the operator to procedures OS1013.03 and OS1013.04, " Residual Heat Removal Train A Startup and Operation" and " Residual Heat Removal Train B Startup and Operation", for operation with low RCS water level for further guidance when in the partial drained condition.
A review of these operating precedures is being conducted to determine if any additional procedures or improvements are needed. Their interface with Abnormal Procedure OS1213.01 " Loss of RHR During Shutdown Cooling" will also be reviewed to determi.;e if any additional guidance is necessary.
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(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 to Item No. 9 1 The NHY detailed safety assessment of shutdown events has identified potential improvements that are currently being evaluated. These improvements address the same issues identified in Generic Letter 87-12, and include the following areas:
- 1. Level monitoring instrumentation
- 2. Audible alarms
- 3. Shutdown procedures 4.-Abnormal procedures (shutdown)
- 5. Training
- 6. Control of work activity NHY will evaluate these improvements utilizing input from the NHY Shutdown Cooling Safety Assessment, Generic Letter 87-12, and NUREG-1269, to develop, where applicable, final design changes, procedure changes, training, and implementation schedules.
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