ML20118B939
| ML20118B939 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 09/30/1992 |
| From: | Feigenbaum T NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO) |
| To: | |
| Shared Package | |
| ML20118B936 | List: |
| References | |
| NUDOCS 9210080143 | |
| Download: ML20118B939 (8) | |
Text
-
t
\\
North SEABROOK STATION UNIT 1 "O htiantIC Energy Service Corporation Facility Operating License NPF-86 Docket No. 50-443 License Amendment Request No. 92-13 Manual Operation of Cooling Tower Fans and Sprays This License Amendment Request is submitted by Noith Atlantic Energy Service Corporation pursuant to 10CFR50.90. The following information is enclosed in support of this License Amendment Request:
Introduction and Description of Proposed Changes
.Section I Markup of Proposed Changes
. Section 11 Retype of Proposed Changes
. Section til Safety Evaluation of Proposed Changes
.Section V Determination of Slgnificant Hazards for Proposed Changes
.Section VI Proposed Schedule for License Amendment issuance and Effectiveness Environmental Impact Assessment
. Section Vil
. Section Vill Additional Information Sworn and Subscribed to before me this
- @' day of qb.3 n,
1992
~
py _qu3 o '
'El Nf Y8/6 M
~
Ted[ Feigenbaum Notary Public
)
Senior Vice President and Chief Nuclear Officer 921006o143 920930 l
DR ADOCK OSoO 3
E
.s s
1.
Introduction and Description of Proposed Channes A.
Introduction
-The purpose of the proposed Technical Specification change is to revise Technical Specification 3/4.7.5 " Ultimate Heat Sink" to:
1.
Revise the Limiting Condition for Operation by adding a note stating that a cooling tower fan may be considered OPERABLE if it is capable of being manually started from the main control board. This change will allow cooling tower spray and fan operation to be manually initiated by the operator as opposed to automatically occurring during a cooling tower actuation. As described below this is necessary to prevent we build up on cooling tower components during cooling tower operation when ambient air temperature is below freezing.
2.
Delete the requirement to verify that the cooling tower fans automatically start on a Tower Actuation (TA) signal and add a requirement to verify that automatic valves actuate to their correct positions on a T.:
' znal.
3.
Increase the maximum allowed cooling tower basin temperature from the cerrent 67.3'F to 70.0*F. This change will minimize the potential for requiring cooling tower operation, with spray, to reduce basin temperature during the summer months.
The original cooling tower design allowed for autamatic initiation of sprays and fans upon receipt of a TA signal. In certain environmental conditions, however, this could result in icing of the tower fill tile. Ice has the potential to prevent cooling by impeding the flow of water through the fill tile.
In order to address this concern, a design change was implemented to install spray bypass valves 1 SW-V-139, and 1-SW-V-140, such that upon receipt of a TA signal, hot service water bypasses the spray header and is recirculated back to the tower basin, These valves were included in the Inservice Test program and are periodically survelhed pursuant to Technical Specification SurveClance Requirement 4.0.5.
In addition, the fan control switches were placed in the " pull to-lock" position since operation with ice buildup on the fan blades is not recommended by the fan manufacturer. Automatic initiation of both the sprays and fans was replaced by proceduralized manual initiation.
Upon receipt of a TA signal, the operator would manually initiate spray and fan opers ion based on the combination of primary component cooling water heat exchanger outlet temperature and ambient wet bulb temperature (sce Figure 2 of Section VIII), - Manual operation ensures adequate cooling of the service water and also ensures tile icing will not occur. Manual initiation of cooling tower sprays and fans is addressed in Seabrook Station -
abnormal operating procedure OS1216.01, " Degraded Ultimate Heat Sink" and emergency operat_ing procedure E-0, " Reactor Trip or Safety Injection". Control of the bypass valves and fans is performed from _ the main control board. The aforementioned operation of the cooling tower is documented in the Seabrook Station Updated Final Safety Analysis Report (UFS A R), section 9.2.5.2.
This section states, in part, that cooling tower spray and fan operation is manually initiated followirg a TA signal.
On August 7,1992, in response 17 an NRC concern, it was identified-that placing the cooling tower fan control switches in the " pull-to-lock" position - precluded demonstration of ~
operability of the cooling tower in accordance with Technical Specification Surveillance Requirement 4.7.5.d.1), This surveillance requirement requires that operability of the cooling 1
tower be demonstrated every-18 months by testing automatic actuation of each cooling tower fan on a TA test signal. This surveillance was. performed by taking the fan control switches out of the ' pull to-lock" position.
Since the fans were not terted in their normal configuration (i.e., pull-to. lock), this aspect of the Technical Specifications was not satisfied.
Therefore, the cooling tower was not verified to be OPERAI3LE pursuant to Surveillance Requirement 4.7.5.d.1).
This condition is documented in Seabrook Station Licensee Event Report (LER) 9211, entitled " Inoperable Cooling Tower Fans", which was transmitted to the NRC on September 4,1992, via NYN-92121.
LER 92-11 also identified that the design change that installed the spray bypass valves also circumvented the intent of Surveillance Requirement 4.7.5.d.1). Specifically, this surveillance requirement was designed to test automatic actuation cf the cooling towar in response to a TA signal. Since this design change prevents automatic actedion of the tower spiays, it -
also does not meet the intent of Technical Specification Surveillance Requirement 4.7.5.d.1).
To correct the situation pending the NRC review of the proposed Technical Specification change, the cooling tower fan control switches _have been placed in the automatic position j
and the spray bypass valves have been closed whenever the cooling tower is required to be 1
O P ER AllLE per Technical Specifications.
This action will allow the fans to start automatically and the cooling tower return water to be directed to the spray header following the receipt of a TA signal, This action satisfies the requirements of Surveillance Requirement 4.7.5.d.1), and is acceptable prior to the onset of winter conditions.
Technical Descriotion of Service Water System and Coolina Towers The function of the Service Water (SW) system is to transfer thu heat loads from various sources in both the primary and secondary portions of the plant to the ultimate heat sink.
The SW system has two sources of cooling water: the service water pumphouse (normal) and the service water cooling. tower (alternative)(See Figare 1 in Section Vill).
The SW system normally uses the Atlantic Ocean as the ultimate heat sink to dissipate primary and secondary heat loads. In this mode, seawater is drawn through.the Circulating Water system intake tunnel, to the service water pumphouse and distributed to the primary and secondary heat exchangers. The service water return flow is from the heat exchangers, through the discharge tunnel, to the Atlantic Ocean, in the unlikely event that seawater flow to the service water pumphouse_ is restricted (greater than 95% blockage) due to seismically induced darnage to the intake and discharge tunnels, a seismically qualified mechariical draf t evaporative cooling tower is provided to dissipate shutdown and accident heat loads.
The cooling tower is divided into three separate bays; two outboard bays, one serving Unit I train A distribution loop and one serving the Unit 11 train A-distribution loop, and-the f
center (common) bay, utilized by Units I and 1111 train loop. The spray area of the cooling tower bays are filled with ceramic materiai which provides a tortuous path for the water cascading down to the - cooling tower basin. This provides even water _ distribution and-an increased surface area, which enhances the evaporative cooling process. Fans are installed over the cooling tower bays to provide additional cooling. The cooling tower is constructed over.a common storage basin that contains approximately four million gallons of fresh water.
If the cooling tower b in use, the atmosphere is the ultimate heat sink and the service water-system operates as essentially a closed loop. The service water pumphouse is isolated from 2
the distribution system and redundant cooling tower pumps route water from the cooling
- tower storage basin through the SW system.
Heated water from the heat exchangers 'is --
_ returned to the cooling tower.
- The cooling tower itself has two modes of operation. The spray header bypass mode is used when wet bulb temperature is low or when the water returning to the cooling tower does not require cooling. In this mode the water returning to the. cooling tower bypasses the spray-header and returns directly to. the basin.'
The spray mode is used when ambient air temperature is above freezing or the water returning to the cooling tower requires cooling.
In this mode the water returning to the cooling tower is directed to the spray header. It then flows _ downward over the ceramic fill in the cooling tower. If additional cooling is-required large fans in the top of the cooling tower are started and the upward air flow provided by the fans provides the added cooling.
As the heated service water passes downward tiirough the fill, an induced flow of cooling air passes upward. The upward air flow increases the evaporative cooling process.
The cooled cervice water-falls into the storage basin and is ready to begin the cycle again.
Switching the system supply from the normal (service water pumphouse) to the alternate (cooling tower) supply source is accomplished manually or, automatically upon failure of the service water pumphouse to supply sufficient service water pressure. Manual switching is accomplished by control switches on the main control board (MCB). Automatic transfer is I
accomplished by a TA signal generated manually from MCB controls or automatically upon I
a low service water header pressure.
The cooling tower was originally designed to support the operation of two units at the Seabrook site. The design basis for the cooling tower included the post-Loss Of Coolant Accident (LOCA) heat loads from one unit and the cooldown loads from the second unit.
With the cancellation of Seabrook Station Unit II, the cooling tower now only serves one unit. Therefore, significant performance inargin exists in the design of the cooling tower with respect to its current duty requirements.
i Cooline Tower Manual Onerr.tio.n_
The design basis for the cooling tower assumes that the seismic event which disables the intake and discharge tunnels also initiates a LOCA and a-Loss of Offsite. Power (LOP).
Thus, the design basis heat load for the cooling tcwcr consists of the Residual Heat Removal (RHR) system heat rejection, Containment Building Spray (CBS) system heat rejection, Diesel-Generator Cooling system heat rejection, the cooling tower pumps, and other small heat loads imposed on the Primary Component Cooling Water (PCCW) system during the accident.
During the initial stage of the LOCA the Emergency Core Cooling System (ECCS) aperates -
in the injection phase. In this phase, the water supply for the ECCS pumps is the Refueling
-Water Storage Tank (RWST) and the' heat loads imposed on the cooling tower by the' ECCS
~
equipment is minimal. The majority of the heat Ioed on the cooling tower occurs following switchover from the ECCS injection -phase to the rscirculation phase.
During the-
. recirculation - phase, valves are aligned to draw water' from the containment recirculation -
sump to be re injected into'the reactor vessel and containment building. This water, which had previously been cool water from the RWST, now must be cooled in the RHR and CBS heat exchangers, prior to re-injection. This heat is ulticiately rejected to the cooling tower and when this occurs, a significant heat load is imposed on the cooling tower.
L 3
1
~. - -.. - -, - - -
c The bulk temperature of the cooling tower basin water is currently limited to an initial temperature of 67.3'F by Technical Specification 3.7.5. This limit was chosen to ensure that the cooling tower basin temperature would be limited during the design basis event to ensure that the design limitations of the primary component water cooling system are not exceeded.
An nnalysis has been performed by, North Atlantic Energy Service Corporation (North Atlantic), which demonstrates that the cooling tower basin average temperature could be allowed to increan to 80*F during e single train post-LOCA cooldown, or to 87'F during a two train cooldown, prior to initiating sprays and fans without exceeding equipment limitations. North Atlantic has proposed, on the basis of this analysis, that the cooling tower
- Technical Specification basin temperature limit be increased to 70'F.
The analysis which demonstrates this is available for NRC review at Seabrook Station. This proposed change will alleviate a significant operational burden by minimizing the potential for requiring cooling tower operation, with spray, to reduce basin temperature below the current Technical Specification value (67.3'F), during the summer months. _The proposed increase in basin temperature v411 maintain an adequate amount of time for operator action to initiate spray and fan operation and c ill not adversely alfect the ability to remove the LOCA heat load.
If the cooling tower is manually operated, assuming maximum ECCS flows and the minimum d*
allowable RWS'l volume (i.e. minimizing the time to recirculation), and with the increased initial basin temperature, a minimum of 74 minutes will be availabic for operator action to initiate cooling tower sprays and fans prior to reaching either basin limiting temperature (80*F or 87'F); the time available between switchover to recirculation and spray activation is at least 51 minutes. This 74 minutes exceeds the 20 minutes stated b NUREG 0800, Section 6.3 as the basis for requiring automatic rather than manual actus n.
Although the post-LOCA couldown is the design basis case for the cooling tower, a norraal eucidown has also been evaluated with respect to the increased basin initial temperature and manual cooling tower spray and fan operation. The normal cooldown differs from the post-LOCA cooidown in that the initial heat load to the cooling tower is higher in the normal-cooldown case. This higher load' results from normal plant hea; loads, which would be isolated in tbc post-LOCA cooldown case remaining in service and therefore requiring cooling.
initially in the normi cooldown, RCS decay beat is removed by the steam generators. The actual couldown he.a load is not provided to the cooling tower until the RHR system is placed into service after the Reactor Coolant System (RCS) temperature-has been reduced 4
to less than 350'F. The time from normal operating temperature.until the RHR system is placed into operation requires about four hours. Therefore, the cooling tower heat load is constant during this initial four hour period, increasing at that time due to the decay heat being removed, and then gradually decreasing.
As in the post-LOCA cooldown case, the cooling tower basin is assumed to be at it s maximum initial temperature and minimum volume. The tower basin temperature is again limiicd to a maximum temperature of 80*F prior to initiating cooling tower spray and f a operation. This 80'F limit 'is conservative for this case as it is based on the larger heat -
loads expericreed in the post-LOCA cooldown case. With the maximum normal cooldown heat load, and assuming a loss of offsite power which adds the heat rejection from both diesel generatms, greater than 106 mieutes is available for operator action to start the 4
6
=
4 cooling tower sprays and fans prior to reaching 3 cooling tower basin average temperature-of 80*F.
I'f the cooling tower. design basis scenario were to occur, oper3 tors would begin to monitor ultimate heat sink performance at step 10 of Seabrook Station emergency operating procedure.
E 0, " Reactor Trip or Safety injection". This step directs. operators to verify ultimate heat sink operation, if the cooling tower is the. ultimate heat sink operators are directed to initiate cooling tower spray and fan operation based on the combination of ambient wet bulb temperature and PCCW heat exchanger outlet temperature. If there is no need to initiate cooling tower spray and fan operation when step 10 of procedure E-0 is reached, operators will periodically tnonitor cooling tower operation to ascertain the need for spray and fan operation.
-In addition, there are PCCW high temperature alarms, !ocated in the main -
control room, which will alert operators to the need to i Ctiate cooling tower spray and fan operation.
If a Tower Actuation were to occur without an accompanying. entry into the emergency operating procedures, abnormal operating procedure OS1216A1, ' Degraded Ultimate lleat Sink" provides guidance on cooling tower fan and spray operation.
Operator training is conducted using abnormal and emergency simulator scenarios which emphasize monitoring ultimate heat sink performance. These training scenarios verify that 6
appropriue operator action is taken during a cooling tower actuation occurring both with and without entry into E-0, " Reactor Trip or Safety injection".
There is sufficient time available, even with the increased basin temperature, for manual operator action to initiate cooling tower spray and fan operation following the cooling tower design basis event. Therefore, operation of the cooling tower with the sprays and fans manually controlled does not require immediate operator ' action to mitigate the effects of an accident and therefore the proposed Technical Specification change is not detrimental to safe ooeration.
IL Descrip: ion of _ Proposed Changes Tne following changes are proposed to Technic;.1 Specification 3/4.7.5-and its-Bases:
1.
Limiting Conditica foi Operation 3.7.5.b is being revised to add " following the word OPER ABLE in two locations.
A. n',te is to he alded to the bottom of page 3/4 7-14 stating that a fan may be considercJ OPERABLE if it is capable of being manually started from the main control-board. These changes will pernit the cooling tower fans to be considered OPERABLE when their control switches are in the " pull to-lock position.
2.
Limiting Condition for Operation 3.7.5.b and _ Surveillance Requirement 4.7.5.b are being revised to increase the maximum allowable basin temperature from 67.3'F to 70'F.
Increasing the temperature will minimize the potential for requiring cooling
-tower operation with spray,.to reduce basin temperature, during summer months.
3.
Existing Surveillance Requitement 4.7.5 d.1); which verif'es that the cooling tower fans automatically start on a tower actuation test signal, is replaccci with a requirement t
to verify that each automatic valve in the flowpath actuates to its c'orrect position on b
5 i
q a tower actuation test signal.- This change will allow cooling tower spray andL fan s
operation io be manually initiated... The current-surveillance ~ requirement will be enhanced by reiuiting verification that automatic valves align to the correct position l
on a tower actuation test signal, 4,
The liases for Technical Specification 3/4.7.5 L are.- sevised by adding -a paragraph discussing' manual operation of the cooling tower sprays and fans.
~
?
h
=2 6
is
1
+: i Markui> of Prot >osed Chnners See attached markup' of proposed changes to Technical Specifications.
1 l
Y l
1
-i 7-i
,