2CAN098707, Responds to Generic Ltr 87-12, Loss of RHR While RCS Partially Filled. RCS Partially Filled Hot Leg Conditions Normally Result of Preparation to Accomplish Reactor Coolant Pump Removal
| ML20235J772 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 09/18/1987 |
| From: | Enos J ARKANSAS POWER & LIGHT CO. |
| To: | Miraglia F NRC, NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 2CAN098707, 2CAN98707, GL-87-12, NUDOCS 8710020088 | |
| Download: ML20235J772 (9) | |
Text
- h J ARKANSAS POWER & LIGHT COMPANY FOST OfflCE BOX 551 UTTLE ROCK, ARKANSAS 72203 (501)371-4000 September 18, 1987 2CAN098707 1
i U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 I
ATTN:
Mr. Frank J. Miraglia, Jr.
i Associate Director for Projects i
i
SUBJECT:
Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF 6 Loss of Residual Heat Removal (RHR)
While the Reactor Coolant' System (RCS) is Partially Filled (Generic Letter 87-12)
Dear Mr. Miraglia:
In response to Generic Letter 87-12 (0CNA078710) the following is submitted as specified in 10CFR50.54(f).
Question:
)
1.
A detailed description of the circumstances and conditions under which your plant would be entered into and brought through a draindown l
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 (uded to determine l
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.
EA*RB88RBWihE
))OSf P
MEMBER MCOLE SOUTM t. t luTiES SYSTEM
//
l September 18, 1987
Response
RCS partially filled hot leg conditions are normally a result of preparation to accomplish reactor coolant pump (RCP) removal, RCP seal removal, steam generator tube plugging / inspection or nitrogen purging.
Based on recent experience, the minimum time from full power operation to reaching a partially filled hot leg condition is 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />.
No minimum steam generator levels are required under the condition of a partially filled hot leg._ However, unless steam generator tube i
plugging operations are underway, the steam generators would normally be in wet layup with secondary levels.quite high, under partially filled hot leg conditions.
I Maintenance, testing and operations that have a potential impact on
)
the ability to remove decay heat are controlled by procedure as discussed later in response to Question 5.
This includes activities related to either LPSI motor, breaker or pump; any service water motor breaker or pump; either service water loop; either shutdown cooling i
heat exchanger; either diesel generator engine, generator or relay; any i
shutdown cooling or LPSI valve; recirculation actuation system (RAS);
i and 2A3 or 2A4 bus or relays.
The procedure requires the availability of redundant or diverse methods of decay heat removal, describes the options available for meeting that requirement and provides thirteen decision diagrams to logically and methodically decide whether that requirement has been met.
The low temperature overpressure protection (LTOP) system is required to be in service below 250 F and will protect the integrity of an intact reacto co'iant system pressure boundary.
In addition, the three inch l
ECCS ve.
and other smaller vents are opened during the draining operation and left open.
The procedure for loss of shutdown cooling flow with RCS open to the atmosphere requires that containment purge be secured.
If core alterations or movement of irradiated fuel is underway, technical specification 3.9.4 requires that connections to outside atmosphere from containment be secured except containment purge and that containment purge be operable.
The equipment hatch can be reinstalled within 30 minutes.
Openings in the reactor coolant system can provide a flow path for backup cooling methods.
Therefore, there are no requirements pertinent to reestablishing the integrity of the RCS pressure boundary on loss of shutdown cooling flow.
The only interlock that could disrupt the shutdown cooling flow is the closure of the shutdown cooling suction valves on high (300 psi) RCS pressure.
The breakers for these valves are required to be opened during any activities involving these valves or the interlock, thereby precluding spurious closure.
. -September 18, 1987 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 bay be lost.
Response
During partially filled hot leg conditions, several instruments and alarms are orovided to the operators for controlling thermal and hydraulic aspects of the NSSS.
If the RV head is installed core exit thermocouple are available.
The reactor vessel level monitoring system is also available with the RV head installed.
Shutdown cooling system flow and suction and discharge temperature are provided as well as several channels of RCS pressure indication.
RCS temperature is indicated by shutdown cooling system suction temperature unless flow is i
lost in which case the core exit thermocouple are still available if I
the head is installed.
If the head is not installed, RCS temperature can be monitored by use of RTDs on the lower part of each hot leg.
These RTDs, one on each hotleg, are located below the lowest water level permitted during partially filled hot leg conditions.
Level is also monitored, even without the RV head installed by use of a tygon tube connected to a hot leg that is routed outside the secondary shield wall.
Level indications for the tubing are clearly marked on the side of the secondary shield wall and the level indication of the tubing is l
verified with pressurizer level indication during draindown.
To prevent potential RCS pressurization from causing erroneous level indication in the tygon tube, the top of the tubing is tied into the top of the pressurizer.
This means that pressure at each end of the i
tube will differ by no more than the static head of the water level.
l Tube integrity is verified each time it is put in service.
Tubing i
level indication is monitored continuously during level changes.
In addition to all the above indications the following alarms are provided to alert the operator to abnormal conditions affecting decay heat removal.
1 1.
LPSI Pump A/B Overload 2.
LPSI Pump A/B Breaker Trip I
3.
SW Pump A/B/C Overload 4.
SW Pump A/B/C Breaker Trip 5.
SW Pump A/B/C Disch. Press. High 6.
SW Header Loop 1/2 Press. Low 7.
SW through SDC Hx Flow High Low 8.
Loss of SDC Suction - LPSI pump running and SDC suction valves not fully open
1 l September 18, 1987 i
Question:
l I'
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 j
in item a (above); and (c) an evaluation of items a and b (above) with I
respect to applicable TS requirements.
i l
l
Response
J During partially filled hot leg conditions, both LPSI pumps and either a charging pump or an HPSI pump are required to be operable by technical specifications.
One HPSI pump is required to be operable by procedure whether or not a charging pump is operable.
The containment spray pumps can also be used to control RCS inventory but are not required to be operable.
In addition, RCS inventory can be replenished I
by draining any of four safety injection tanks or the refueling water tank without the use of pumps.
Question:
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 i
electrical penetrations.
Response
l By procedure, if shutdown cooling flow is lost, containment purge must be secured.
Question:
5.
Reference to and a summary description of procedures in the control room of your plant which describe operation while the RCS is partially l
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 l
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 4
of the RHR suction line(s) to the RCS.
l l
I i
-S-September 18,' 1987 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, includiny restrictions j
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 in'_'"ing the NSSS if RHR canrat be restored, control of efflud containment if containment was not in an isolated cc#nt from che iditic, at the time j
of loss of RHR, and operations to provide containment isolation if containment was not isolated at the time of loss of RHR (guidance 1
pertinent to timing of operations, cautions and warnings, critical parameters, and notifications is to be clearly described).
Response
Applicable procedures include the following and are summarized below.
1015.08 Shutdown Cooling System maintenance This procedure lists components upon which maintenance (which includes testing) has a potential impact on the ability to remove decay heat and j
requires redundant or diverse methods of decay heat removal during any such maintenance.
Such redundant and diverse methods are described and 13 decision diagrams are provided to assure the diversity or redundancy is met.
2103.11 Draining the RCS i
This procedure describes in detail the evolutions used to drain the RCS.
Included are instructions and precautions for installation and use of the tygon tubing and level control and monitoring.
Steps.used j
to purge the RCS with nitrogen including precautions are also included.
Among other things, the procedure prohibits draining during purging operations, requires verification of tygon tubing level indication with pressurizer le.al during draindown, requires an integrity check of the tygon tubing prior to valving it in, specifies RCS level for various maintenance activities, specifies a minimum RCS level to prevent i
vortexing, requires continuous level monitoring during any evolution which changes RCS inventory, requires suspension of draining on any j
erratic level indication in the tygon tubing, describes expected and potential observations during draining and requires vessel head venting at all levels 15 feet or less above the bottom of the hog leg.
i 2203.29 Loss of Shutdown Cooling (SDC)
Section II of this procedure ac1resses loss of SDC with the RCS open to atmosphere.
Symptoms of a loss of SDC are described and immediate and follow up actions are given.
Among other things this procedure requires immediately securing SDC pump, correcting potential causes of the loss of SDC, securing containment purge, evacuation of containment, i
1 I
. September. 18, 1987 i
suspension of core alternations (if any); and describes alternatives-for removing decay heat including use of containment spray pumps, j
feeding and steaming or feeding and blowing down the steam generators I
and feed and bleed cooling through existing RCS openings or, if i
necessary by opening the ECCS vent valves on the pressurizer.
l 2104.04 Shutdown Cooling System l
l This procedure provides instructions for operation of the shutdown cooling system.
Included within the procedure of relevance here is l
instructions for transferring from SDC pumps to containment spray pumps for use in shutdown cooling and instructions for returning to SDC pump operation.
2203.22 Loss of Service Water Section II of this procedure addresses loss of service water during shutdown cooling system operation.
Symptoms of a loss of service water 1
are described and immediate and follow up action are given.
Among other things, this procedure requires maintaining SDC flow and, l
I if service water cannot be restored, suspension of any fuel movement.
2203.12 Series-Annunciator Corrective Actions For the alarms listed in item 2 above, this procedure series provides l
l the cause of the alarm, the action required and how to clear the alarm.
Instructions for switching to redundant equipment are included as are I
references (as applicable) to other procedures such as 2203.29 above l
and to technical specification operability requirements.
In general numerical analyses are not applicable as bases for these types of procedures.
These procedures are based on tests, experience and common sense coupled with a thorough knowledge of system l
configuration.
However, we have conservatively estimated the shortest possible time to uncovery of the top of the fuel following loss of shutdown cooling flow from a drained down condition assuming no action i
is taken to make use of the variety of options available to provide cooling and/or coolant inventory.
There is the potential for partial vessel level suppression (with the vessel head installed) after the onset of boiling due to the steaming rate exceeding the venting rate and the presence of a full cold leg loop seal with a disassembled Reactor Coolant Pump.
Recognizing such potential, this estimate assumed an instantaneous level drop in the inventory above the core at the onset of boiling to a level equal to that of the top of the cold leg loop seal.
Initial decay heat was taken at 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> post trip (ignoring time required to disassemble the pump), initial coolant temperature was assumed to be 200 F and initial coolant level was assumed to be 9" below the lowest level called for to perform work on I
the system (based on the level at which vortexing is expected).
The l
estimated half hour before uncovery of the top of the active fuel is l
adequate time to perform the actions described in SAR l
-7.
September 18, 1987 Section 9.3.6.3 to maintain continued core cooling with or without the vessel head removed or to make use of other options available to restore cooling and/or inventory, given a total unavailability.of the shutdown cooling system.
That section of the SAR also points out that similar shutdown cooling pumps at another facility have been known to operate without suction for about an hour with only non-catastrophic damage to the pump seals and no significant loss of function.
Question:
6.
A brief-discussion of training provided to operators and other affected personnel that is specific to the issue of operation while the RCS is partially filled.
We are particularly interested in such areas as maintenance personnel training regarding avoidance of perturbing the NSSS and response to loss of decay heat removal while the RCS is partially filled.
Response
The subject of loss of shutdown cooling is covered in operator training on the simulator, in the classroom and in required reading.
Industry j
experience in this area i.s also reviewed.
Operators receive this training in both initial training and requalification training.
Increased emphasis is provided during training held immediately prior to scheduled outages.
Since the August 1984 loss of shutdown cooling event at ANO-2, training attention in this area has more than tripled and continues to receive great emphasis.
All maintenance activities that could effect the availability of shutdown cooling are under the control of the operations staff on shift and are controlled by procedure.
Question:
i 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
The training, instructions and understanding provided to operators adequately preclude the need for greater than normal provisions for support during partially filled hot leg conditions.
Question:
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 HR flow rate to minimize the likelihood of vortexing and air ingesticn.
1
. September 18, 1987 f
Response
There are no mode 5 requirements implemented that are unique to partially filled hot leg conditions.
Procedural limits and precautions are provided for draining the RCS and to protect aga' inst loss of shutdown cooling flow as described above in respo'nse to Question 5.
Question:
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
No changes to our current program are anticipated to result from our j
review of Generic Letter 87-12.
Appropriate program enhancements have 1
already been implemented following the August 1984 loss of SDC event at l
ANO-2, and the issue continues to receive high visibility at Arkansas-Nuclear One.
l Very truly yours,
. Ted Enos, Manager l
Nuclear Engineering and Licensing j
JTE/DHW/sd I
i l
, September 18, 1987 STATE OF ARKANSAS
)
)
SS COUNTY OF PULASKI
)
I, J. Ted Enos, being duly sworn, subscribe to and say that I am Manager, Nuclear Engineering and Licensing for Arkansas Power & Light Company; that I have full authority to execute this oath; that I have read the document numbered 2CAN098707 and know the contents thereof; and that to the best of my knowledge, information and belief the statements in it are true.
1 l
J. Ted Enos l
I l
l 1
i SUBSCRIBED AND SWORN T0 before me, a Notary ublic in and for the I
W County and State above named, this day of i
1987.
0
/
k Notary blic My Commission Expires:
l Cw 1
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