ML20236S559
| ML20236S559 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 07/20/1998 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20236S561 | List: |
| References | |
| NUDOCS 9807270029 | |
| Download: ML20236S559 (25) | |
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CHARLES H. CRtJEE Baltimore Gas and Electric Company Vice President Calvert Cliffs Nuclear Power Plant Nuclear Ecergy 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 410 495-4455 July 20,1998 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos. I and 2; Docket Nos. 50-317 and 50-318 License Amendment Request; One-Time Technical Specification Change to Suonort the 1999 Refueling Outage Pursuant to 10 CFR 50.90, the Baltimore Gas and Electric Company hereby requests an Amendment to Operating License No.DPR-69 by incorporating the changes described below into the Technkal Specifications for Calvert Cliffs Unit 2.
Currently, Calvert Cliffs has four emergency diesel generators (EDGs), two per Unit, to provide the onsite emergency power supply for both Units. The Unit 2 EDGs rely on the Service Water (SRW)
System to provide their cooling water. During the Unit 21999 Refueling Outage, Baltimore Gas and Electric Company will replace the SRW heat exchangers on Unit 2.
During the period of the replacement, no SRW cooling will be available for Unit 2. Therefore, both Unit 2 EDGs would be inoperable during the replacement work. Unit I will continue at fall power operation during the refueling outage.
The loss of both EDGs on Unit 2 presents several challenges. First, a number of outage activities require
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an EDG be operable. We propose providing an alternate cooling water supply to maintain the EDGs operable to fulfill the Technical Specification requirements. One EDG will be provided with cooling f
water from the Unit i SRW System. The other EDG will be provided with cooling water from an independent external cooling system. Second, Unit 1 is scheduled to be in Mode 1 operation during this time. The No.12 Control Room Emergency Ventilation System, No.12 Control Room Emergency
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Temperature System, and a flydrogen Analyzer are affected by this work because they obtain their U
emergency power from a Unit 2 EDG. These components support Unit I continued operation.
Therefore, the loss of both Unit 2 EDGs would impact operations on both units.
There are several issues associated with this change that create an Unreviewed Safety Question as defined by 10 CFR 50.59. There is an increase in the probability of a malfunction due to the use of an independent cooling system that is non-safety related and unprotected from seismic or tornado events.
9807270029 980720 PDR ADOCK 05000317 p
.. e s 7 Docum:nt Control Desk July 20,1998 j
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The reliance of a Unit 2 EDG on Unit 1 SRW results in the increase of the probability of a malfunction, l
also. Additionally, these SRW lineups affect the probability of a malfunction for other equipment that l_
relies on SRW during an outage.' We are requesting approval of these Unreviewed Safety Questions, l
which will permit a Technical Specification Bases change to the description of an operable EDG while Unit 2 is in Modes 5 and 6. Attachment (1) describes the change in greater detail.
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- We believe that' approval of these Unreviewed Safety Questions does not create an undue risk to the public health and safety. The likelihood of a loss of offsite power (when the EDG would be needed) will l_
be reduced by the additional actions that will be taken to provide assurance that the offsite power supply will not be lost. The non-safety-related Station Blackout EDG is also available and capable of powering.
all shutdown loads on either Unit 2 safety bus, and as a power supply for No.12 Control Room Emergency Ventilation System, No.12 Control Room Emergency Temperature System, and the-Hydrogen Analyrer. Attachment (1) provides a complete discussion of the risks and mitigating actions.
l We have evaluated the significant hazards considerations associated with this change as required by 10 CFR 50.92, and determined that there are none (see Attachment 2 for a complete discussion). We have also determined that operation with the proposed amendment would not result in any significant change in the types or significant increases in the amounts of any effluents that may be released offsite, and in no significant increase in individual or cumulative occupational radiation exposure. Therefore, the proposed amendment is eligible for categorical exclusion as set forth in 10 CFR Sl.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment is needed in connection with the approval of the proposed amendment. The Plant Operations and Safety Review Committee and Offsite Safety Review Committee have reviewed the proposed change and concurred that operation with the proposed change will not result in an undue risk to the health and safety of the public.
The work' on the SRW System is scheduled to begin within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after we enter Mode 5 on Unit 2 (currently scheduled for March 14, 1999). To facilitate procurement of equipment, installation of the temporary modifications, and planning, we request that this change be approved well in advance of the
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. Unit 2 outage (by December 15,1998). As discussed above and in Attachment (1), delaying issuance of I
l this amendment will impact continued Unit 1 operation and the scheduled restart of Unit 2.
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' July 20,1948 l-Page 3
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l Should you have questions regarding this matter, we would be pleased to discuss them with you Very truly yours, -
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M STATE OF MARYLAND
- TO WIT:
COUNTY OF CALVERT 1, Ch' rles H. Cruse, being duly sworn, state that I am Vice President, Nuclear Energy Division, a
Baltimore Gas and Electric Company (BGE), and that I am duly authorized to execute and file' this License Amendment Request on behalf of BGE. To the best of my knowledge and belief, the statements contained in this document are true and correct. To the extent that these statements are not based on'my personal knowledge, they are based upon information provided by other BGE employees and/or consultants. Such information has been reviewed in accordance with company practice an believe it to
' be reliable, w
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St3 segibed and sworn before me, a Notary Public in and for the State of Maryland and County of bf El E/AIJ
.this A0 day of Of;ft/.1998.
WITNESS my Hand and Notarial Seal:
fA1]AiJ ItLLbb Notary Public My Commission Expires:
k 2Ob Date -
CHC/ PSF /bjd Attachments: (1)
Description and Licensing Basis Evaluation j
(2)
Determination of Significant Hazards (3)
Technical Specification Bases Proposed Addition l-cc:
R. S. Fleishman, Esquire H. J. Miller, NRC J. E. Silberg, Esquire Resident Inspector, NRC S. S. Bajwa, NRC R.1. McLean, DNR A. W. Dromerick, NRC J. H. Walter, PSC l
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ATTACHMENT (1) 1 i
DESCRIPTION AND LICENSING BASIS EVALUATION i
l Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant July 20,1998
v ATTACIIMENT (1)
DESCRIPTION AND LICENSING BASIS EVALUATION i
DESCRIPTION OF PLANT CONDITION Currently, Calvert Cliffs has four emergency diesel generators (EDGs) to provide the onsite emergency power supply for both Units. Two EDGs are dedicated to each Unit. During the Unit 21999 Refueling Outage, Baltimore Gas and Electric Company (BGE) will replace the heat exchangers in the Service Water (SRW) System. This system provides cooling water to both EDGs that provide emergency power to Unit 2. In order to minimize the impact on operable / operating plant equipment from SRW equipment removal and replacement activities, as well as to minimize testing and plant system configuration evolutions, both subsystems of the SRW must be removed from service at once. Therefore, during the heat exchanger replacement, alternate cooling water must be made available to the Unit 2 EDGs. This i
work is necessary to improve SRW System reliability by increasing the heat rejection capability of the SRW System and improving system performance.
During this replacement, Unit 2 will be in either Mode 5, Mode 6, or defueled. The shut down unit is required to have one EDG operable in accordance with Technical Specification 3.8.2 in Modes 5 and 6 to perform refueling and fuel movement operations. Either Nos. 2A or 2B EDG can be used to meet this requirement. Although the Technical Specifications require only one EDG to be operable in Modes 5 and 6, it is desirable for defense-in-depth and for shutdown safety to keep both EDGs available.
Additionally, there are several common systems supporting Unit I continued operation that are affected by the loss of emergency power to one of the Unit 2 Engineered Safety Feature (ESF) buses (No.24).
The components described in the Technical Specifications are the No.12 Control Room Emergency Ventilation System (CREVS), the No.12 Control Room Emergency Temperature System (CRETS), and the No.6519 Hydrogen Analyzer. The No.12 CREVS and No.12 CRETS are one of two redundant trains of CREVS (and CRETS) for the common Control Room. As such, it is required to be operable whenever either unit is in Modes 1 through 4 (see Technical Specifications 3.7.8 and 3.7.9). The hydrogen analyzer is one of two redundant hydrogen analyzers and is part of the post-accident monitoring instrumentation that is required to be operable whenever either unit is in Modes 1 through 3 (see Technical Specification 3.3.10). The No.2B EDG supports the ESF bus that powers all of this equipment.
We are requesting approval to allow the Unit 2 EDGs to be declared conditionally operable for Modes 5 and 6 activities and to support the Unit 1 equipment described above using alternate cooling water supplies. Descriptions of the conditions necessary for an operable EDG are provided in Attachment (3).
This description will be incorporated in the Technical Specification Bases for the duration of this activity. This activity results in several Unreviewed Safety Questions (USQs). They are described beloW.
DESCRIPTION OF PLANT EOUI" MENT SRW System The SRW System is a closed system that uses plant demineralized water to remove heat from turbine plant components, blowdown recovery heat exchangers, containment air coolers, spent fuel pool cooling (SFPC) heat exchangers, and the EDG heat exchangers. For each unit (1 and 2), the SRW System is divided into two subsystems in the Auxiliary Building to meet single failure criteria. Each subsystem has a head tank to maintain the subsystem's pressure and to allow for thermal expansion. There are a total of three SRW pumps for each unit. Each of two pumps is powered from a different 4 kV ESF bus.
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ATTACHMENT (1) i DESCRIPTION AND LICENSING BASIS EVALUATION i
i The third pump is capaisle of being powered frot either 4 kV ESF bus. During the 1999 Refuelmg
- Outage, each Unit i SRW subsystem will have two parallel plate and frame type heat exchangers, and the Unit 2 SRW System will be modified to replace each existing shell and tube heat exchanger (one per subsystem) with two parallel plate and frame type heat exchangers. During Unit 2 shutdown (Modes 5, 6, and defueled), the SRW loads of concern are SFPC and cooling to EDGs (Nos. 2A and 2B).
i SFPC System The SFPC System is common to both units. The system is comprised of two half-capacity pumps and two half-capacity heat exchangers in parallel, a bypass filter that removes insoluble particulate, and a bypass demineralized that removes soluble ions. The SFPC heat exchangers are cooled by the SRW System. Connections are provided for tie-in to the Shutdown Cooling System to provide for additional heat removal in the event that 1830 fuel assemblies (including a new full core offload) are contained in the pool.
Emergency Diesel Generators The EDGs are designed to provide a dependable onsite power source capable of starting and supplying the essential loads necessary to safely shut down the plant and maintain it in a safe shutdown condition under all conditions. Two EDGs are provided for each unit, although only one EDG is required to supply the minimum power requirements for its ESF equipment.
Although only one EDG is required for a unit in shutdown, No.28 EDG provides power to shared systems and Unit 2 components credited in the Updated Final Safety Analysis Report for Unit i events.
Number 2B EDG provides emergency power to No.12 CREVS, No.12 CRETS, No. 6519 liydrogen Analyzer, No.12 SFPC pump, the Unit 2 motor-driven auxiliary feedwater pump, and the Nos. 21 and 24 Battery Chargers. It is noted that the CREVS, CRETS, hydrogen analyzer, and the SFPC System are systems shared between the units, and the Unit 2 mc.or-driven auxiliary feedwater pump is credited in the Technical Specifications as being available to mitigate a Unit I loss of feedwater event. Thus, operability of No.2B EDG is important to Unit 1 operations. Additionally, No.2A EDG provides emergency power to the Nos.22 and 23 Battery Chargers. Thus, operability of No.2A EDG is also important to Unit I operations.
Number OC Diesel Generator (Station Blackout Diesel Generator)
The Station Blackout (SBO) diesel generator was added as part of the plant's response to 10 CFR 50.63,
" Loss of All Alternating Current Power." The SBO diesel generator is a 4.16 kV, three-phase,60-cycle tandem engine diesel generator similar in design to No. lA EDG. The SBO diesel generator is electrically isolated from the ESF buses by two breakers in series and a Class 1E disconnect switch. The design of power connections from the SBO diesel generator allows for manual alignment to any one safety-related train in either unit via a Class IE ESF bus. Manual switching capability is provided through Class IE disconnect switches and Class IE breakers.
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A'ITACHMENT m DESCRIPTION AND LICENSING BASIS EVALUATION CREVS and CRETS The safety function of the CREVS and CRETS is to maintain the Control Room habitable for operators and to maintain the environment needed for continued equipment operation. The CREVS consists of two trains, including redundant air intake ducts and redundant emergency recirculation filter trains that recirculate and filter the Control Room air. Each CREVS emergency recirculation filter train consists of a prriliter, a high efficiency particulate air filter, an activated charcoal adsorber section for removal of gaseous activity (principally iodine), and a fan. The CREVS is an emergency system, parts of which may also operate during normal unit operations. Actuation of the CREVS places the system into the emergency recirculation mode of operation, closes the unfiltered outside air intake and unfiltered exhaust to atmosphere valves, and aligns the system for emergency recirculation of Control Room air through the redundant trains of high efficiency particulate air and charcoal filters. One train of CREVS is powered from a Unit 1 EDG (I A) and the other train of CREVS is powered from a Unit 2 EDG (2B).
The CRETS provides temperature control for the Control Room following isolation of the Control Room.
The CRETS is a shared system that is supported by the CREVS, since the CREVS must be operating in its emergency recirculation mode for CRETS to perform its safety function. The CRETS consists of two redundant, independent trains that provide cooling of recirculated air. Each train consists of a refrigeration cycle, which includes cooling coils, instrumentation, and controls to pro::ide for Control Room temperature control. The CRETS is an emergency system, parts of which may also operate during normal unit operation. A single train will provide the required temperature control to maintain the Control Room below 104*F. One train of CRETS is powered from a Unit 1 EDG (l A) and the other train of CRETS is powered from a Unit 2 EDG (2B).
Hydrogen Analyzers The Containment hydrogen analyzers are a post accident sampling system, which are provided to detect high hydrogen concentration conditions that represent a potential for containment breach. Containment hydrogen analyzers can use samples from six locations inside the Containment. Two groups of three sample lines from each Containment provide samples to the two cabinets in the sampling room. The cabinets contain the hydrogen analyzers and related equipment. The sampling system is fully operational from a remote station. Each of the hydrogen analyzers is powered from an ESF bus, one Unit I bus and one Unit 2 bus, which are powered from their associated EDG.
REOUESTED ACTION Four USQs have been identified after evaluating EDG alternate cooling configurations under the criteria in 10 CFR 50.59. All of the USQs are related to an increase in the probability of a malfunction of equipment important to safety. This occurs because the equipment proposed for this temporary configuration is typically non-safety-related or is an alternate configuration of safety-related equipment.
i The specific USQs are described below. We are requesting approval of this temporary configuration as a i
license amendment under 10 CFR 50.90.
l This proposed amendment would add a description to the Bases to describe the conditions for operability
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of the EDGs during the outage. Any time these conditions are not met, the appropriate action statements will be entered. We believe that modifying the definition of operability for the Unit 2 EDGs is the least disruptive way to implement this temporary modification. The EDGs will continue to operate as they j
have in the past. Multiple action statements for other equipment will not have to be entered for this 1
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DESCRIPTION AND LICENSING BASIS EVALUATION d
condition, which allows the operators to focus on equipment problems if they should occur. Most of the modifications will be transparent to the operators, i.e., the EDGs will function as they normally do during an outage. These alternate cooling water supplies will provide reasonable assurance of operability for the EDGs. The added description will be removed from the Bases at the end of the 1999 Refueling Outage.
SCHEDUI Fn ACTIVITIES Rese temporary modifications will be installed during the Unit 2 outage. Outage activities have been planned to support the licensing basis and risk evaluation done for these temporary conditions. The outage schedule is subject to change as engineering and activities are funher refined. These changes will continue to support the risk evaluation done for these temporary conditions. Currently, the outage activities of concern are scheduled as follows.
Within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of entering Mode 5, the SRW System is taken out-of-service to begin the replacement of the heat exchangers. Prior to removing each associated train of the SRW System from service, each EDG (Nos. 2A and 2B) will have been removed from service, modified, tested, and returned to operable status in Mode 5, as described in the Technical Specification Bases (Attachment 3). Shortly after taking the SRW System out-of-service, the unit enters a period of reduced inventory (Iow water level) lasting 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> to perform outage-related preparation work. During this time, the No.2A EDG will remain operable. The No. 2B EDG will be removed from service, about nine days after entry into Mode 5, to perform a scheduled inspection lasting about six days. During the period that No. 2B EDG is removed from service, Unit I will be in a Technical Specification Condition because its support EDG has been I
removed from service. About 11 days after entry into Mode 5, we will begin moving fuel out of the reactor vessel and into the spent fuel pool (SFP). It takes a little less than four days to move all of the fuel into the SFP, During this period and while the fuel remains in the SFP, both trains of SFPC will be operating. For about one-third of the outage, the reactor remains defueled. During the defueled period, the No. 2A EDG is taken out-of-service for a scheduled inspection lasting about 6 days. About 25 days afler our initial entry into Mode 5, fuel is again moved back into the reactor vessel. Again the move takes less than four days. Following the fuel move, the unit again enters a period of reduced inventory j
(low water level) lasting about 1.5 days. ' The No. 2A EDG will remain operable during this period.
Testing of the SRW System is completed on each EDG prior to declaring each EDG operable for Mode 4.
UNREVIEWED SAFETV OUESTIONS l
In order to maintain two EDGs operable for the duration of the SRW beat exchanger replacement, temporary alterations must be performed to provide cooling water to the EDGs. The configuration l
chosen was one in which No. 2A EDG is cooled by Unit 1 No.12 SRW Subsystem and No. 2B EDG is I
l cooled by an independent, temporary cooling system (see Figure 1). This permits at least one train of all j
essential Unit I and Unit 2 systems to remain operable, following a failure of any EDG or SRW subsystem. This configuration maintains a defense-in-depth against single failure events challenging operation. A table is provided that identifies the systems and/or components affected by various initial system and component failures, when the temporary alterations are in place (see Table 1). This activity does not affect the design or operation of the No. l A EDG or No. 0C Diesel Generator, which are both cooled independently of the SRW System and are electrically separated and isolated from Nos. IB,2A, and 2B EDGs. Both temporary alterations are described below.
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+.8 ATTACHMENT (1)
DESCRIPTION AND LICENSING BASIS EVALUATION Number 2A EDG Cooled by No.12 SRW Subsystem To provide alternate cooling water to the No. 2A EDG, connections will be made to allow SRW from the No.12 SRW Subsystem to also provide cooling to the No.2A EDG. These connections will be made using existing piping with the addition of spool pieces. These spool pieces will meet or exceed the requirements for temperature and pressure of the SRW piping and will be installed Seismic Category 1.
The No.12 SRW Subsystem pump gets its emergency power from the No. IB EDG.
The additional heat load on the No.12 SRW Subsystem will not adversely impact its ability to provide cooling to the normally connected safety-related loads. To preserve the capability of the No.12 SRW Subsystem to support its normally connected loads under LOCA conditions of Unit 1, a limit will be placed on the ultimate heat sink temperature which would require the removal of the No. 2A EDG from No.12 SRW Subsystem if the limit is exceeded. With the exception of this temperature limit, the operation of the No.12 SRW Subsystem will not be affected by this alternate lineup. This alternate lineup does result in two USQs, one related to a postulated valve failure and one related to the reliance of No. 2A EDG operability on the operation of the No.1B EDG. They are described below.
The first USQ addresses the change in the probability of malfunction due to the reliance of the EDGs on an additional SRW control valve. Each EDG has its own SRW control valve and both must work properly to provide adequate SRW to each EDG. The SRW control valves to the EDGs are backed by the safety-related saltwater air compressors and are designed to fail in the full open position. It has been determined that a failure of either the Nos. IB or 2A EDG SRW control valve in the open position may result in insufficient SRW flow to or increased SRW temperatures, as the two EDGs share the same cooling water supply. Insufficient cooling to an EDG will result in its inoperability. Thus, this activity inert:ases the probability of a malfunction an EDG.
He second USQ comes about because the No.2A EDG will be dependent upon No. IB EDG for its cooling water. This is because the No. IB EDG provides the emergency power source for the SRW pump, which in turn provides the motive force for circulating the SRW System fluid and provides cooling to the No.2A EDG, However, there is no electrical interdependence and, thus, electrical separation is not affected. In the normal configuration, loss of an EDG results in the loss of the SRW subsystem that cools it, due to the absence of a power supply for the SRW pump. Alternately, a loss of an SRW subsystem results in a loss of the EDG associated with that SRW subsystem, due to a lack of cooling for the EDO. In the temporary configuration, the No.12 SRW Subsystem pump is only fed from No.1B EDG. Upon a loss of No.1B EDG, No. SRW Subsystem will be lost (due to loss of power to the associated SRW pump), which leads to a loss of cooling to No. 2A EDG, and failure of that diesel to function. Thus, while the type of malfunction is no different than is currently postulated (i.e., loss of SRW cooling, resulting in failure of an EDG), the probability of malfunction of No. 2A EDG will be increased because the reliability of SRW cooling to this diesel is now dependent on a separate l
diesel (No. IB EDG).
fannection of No. 2B EDG to Temocrarv Cooling System We propose providing a temporary cooling system for the No. 2B EDG to replace the cooling provided by SRW. The cooling system consists of a cooling tower and its associated pumps, piping, and controls.
He cooling tower is a skid-mounted, mechanical draft cooling tower rated for about 10-15 million 1
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v ATTACHMENT m DESCRIPTION AND LICENSING BASIS EVALUATION l
L BTU /hr. It is constructed of stain'ess and galvanized steel. It has three fans to provide the airflow l
through the cooling tower and two pumps (a primary and a backup) to pump the water through the EDG and into the cooling tower. Makeup water is provided from the pre-treated water tank and is gravity-fed i
into the cooling system. The pumps are powered from a diesel-backed bus. The piping from the cooling tower to the EDG is steel and has flexible joints. The piping from the pre-treated water tank to the cooling tower is run underground for pan of its length. The cooling system will be controlled by the EDG start circuit and, therefore, it will automatically stan when the EDG is started. The cooling system requires no additional operator action to perform its function when the EDG is started.
Number 2B EDG's normal supply of cooling water (Unit 2 SRW) is safety-related and is seismically designed. In addition, the SRW piping is enclosed in the Auxiliary Building, which is a seismic, tornado-proof structure. He temporary cooling system will not provide a safety-related pressure boundary, will not be seismically designed, and will not be tornado-missile protected. Installation of the cooling system will not affect the No.2B EDG's seismic or tornado protection. Operating conditions (temperature, ventilation) for the No.2B EDG will not be adversely affected by installation and operation of the cooling system. The cooling fluid circulated by the temporary cooling system will be demineralized water, in order to prevent degradation of the EDG by corrosion.
During operation of the cooling system, depending upon the heat load on the system and the environmental conditions, a fog plume may develop. His fog plume will consist of saturated air with water condensation droplets. This mist-like condition may result in wetting nearby structures and roadway. Considering the possible period of operation of the cooling tower and the chemistry of the cooling water, any fog plume or drift from the cooling tower will not result in adverse affects to the operation of the EDGs, to the diesel generator room ventilation system, or to the Auxiliary Building ventilation system. The conditions created by the fog plume are similar to those experienced during a rainstorm. The EDGs are designed to operate with up to 100% relative humidity combustion air.
Required makeup water to the cooling tower will be provided from a pre-treated water storage tank.
In order to ensure that the cooling system is available upon No. 2B EDG start, the cooling system loads (i.e., fans and pumps) will be energized at time t=0 seconds, when the generator breaker is closed. The diesel sequencer may be inoperable in Mode 5 or 6. However, the loads added at t=0 are energized independent of sequencer action, similar to other diesel generator auxiliary loads such as the diesel generator room exhaust fan. The additional loads on the motor control center or load center and EDG have been evaluated and found not to have an adverse impact on these components. In addition, the impact of these loads has been evaluated with respect to the ability of the EDG to maintain the frequency j
within 95% of normal and the voltage within 75% of normal during load sequencing. There will be no effect on these requirements.
The EDG protective devices (such as high jacket coolant temperature and low jacket coolant pressure trips) will remain enabled. This will provide the same protection to the EDG against damage, as the current trips. Bypasses of these trips, under an emergency start, will function as currently designed.
Failure of the temporary cooling system results in a loss of EDG cooling, as would a loss of a SRW subsystem. The EDG engine protective devices remain operable to protect the engine from a loss of cooling. Because the temporary cooling system will not be safety-related, seismie, or tornado-6
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ATTACHMENT (1)
DESCRIPTION AND LICENSING BASIS EVALUATION j.
missile protected, the probability of No.2B EDG to fall to function due to a loss of cooling water l
resulting from a seismic event or tornado damage is increased by this activity.
An evaluation of the flooding that could possibly occur due to a failure of the non-safety-related, non-seismic temporary cooling water piping to No. 2B EDG was made to assess the impact of such flooding on the No 2B EDG Room, It was determined, assuming that the entire contents of the cooling system were introduced into the room, that the subsequent flood height is enveloped by other postulated flooding i
events and is not sufficient as to impact safety-related components within the room. However, because the temporary piping added in the No.2B EDG Room is non-safety-related and non-seismic (and thus subject to mechanistic failures such as those resulting from a seismic event), this activity will increase the probability of a flooding event in the No. 2B EDG Room due to pipe rupture.
LICENSING BASIS EVALUATION USQs All of the USQs identified above are related to an increase in the probability of a malfunction in a system important to safety. This results from the use of safety-related equipment in alternate configurations that do not maintain all safety-related aspects for the equipment, and from use of non-safety-related equipment to support safety-related equipment. In general, this proposal relies upon the use of safety-related equipment or the low probability that the equipment will be needed to establish the acceptability ofthese alternate configurations. Each is described below.
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- 1. The first identified USQ is due to the realignment of a Unit 1 SRW subsystem to also support a Unit 2 EDG (No.2A). This alignment will rely on two control valves (one to each EDG) to function properly in order to provide adequate SRW flow to both EDGs. If one of the valves should fail open, it may result in insufficient SRW flow or increased SRW temperatures, as the I
two EDGs share the same cooling water supply. This is an increase in the probability of a malfunction because the operability of a EDG relies on both control valves performing properly.
We believe that this is an acceptable condition because the control valves and their air supply are safety-related and will be performing their design function. The control valves are not being modified by the temporary configuration nor will any operator action be required. The control valves will continue to operate in the same manner. Therefore, we believe that the probability of malfunction has increased only slightly and is acceptable for the limited time requested.
- 2. The next USQ identifies a condition where a Unit 2 EDG is dependent on a Unit 1 EDG for cooling water. The Unit 1 EDG powers the pump for the cooling tvater system that will now provide cooling to both EDGs. Although the consequences of a loss of cooling water is the same (i.e., the EDG fails), the probability of a malfunction for the Unit 2 EDG has increased because it now depends on the Unit i EDG to maintain its operability. We believe that this is an acceptable condition because the Unit 1 EDG is safety-related and is proven reliable through testing.
Additionally, the EDG will not be operated in a manner different than it is currently. It is not being modified by the proposed change nor will any additional operator actions be required.
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'Iherefore, we believe that the probability of malfunction is not significantly increased.
Additionally, a failure analysis (Table 1) shows that failure of the No. IB EDG will not result in the total loss of any safety function for either unit.
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ATTACHMENT (1) l DESCRIPTION AND LICENSING BASIS EVALUATION
- 3. A USQ has been identified related to the use of a temporary cooling system to provide cooling to an EDG The cooling system that is proposed is not safety-related and is not protected from natural phenomenon. This leads to an increase in the probability of a malfunction because the cooling system is more likely to fail than a safety-related, protected system. We believe that this is an acceptable condition for the limited time we propose to use the cooling system. The events most likely to cause the cooling system to fail are seismic events and severe weather. As noted below, severe weather is not highly probable during this time of year. Significant seismic events are not probable on this pad of the east coast. The cooling tower has been used before at Calvert Cliffs to support, testing of the EDGs during outages. The cooling tower will have enhanced design features that will improve its reliability, such as two pumps. The piping provided to and from the cooling tower will be steel and will be provided with flexible joints making it rugged and flexible. Additionally, the cooling tower will be placed close to the Auxiliary Building and the makeup water piping will be run underground for pan ofits length. These measures help to protect the cooling tower and its piping from severe weather events. The EDG is not being altered by this temporary configuration. It will continue to operate as before. No additional operator action is required for the cooling tower to perform its function. Therefore, we believe that the probability of malfunction has increased only slightly and is acceptable.
- 4. This USQ exists because the piping from the cooling tower to the EDG is not safety-related and could break, causing a flood in the EDG room. This creates an increase in the probability of a malfunction because of the increased probability of flooding in the room. We believe that this increase is acceptable because the piping is constructed from rugged materials and is flexibly connected to the EDG. This reduces the chance that flooding will occur. The close proximity of the cooling tower to the EDG limits the inventory available for ficoding. If flooding were to occur and the contents of the cooling system were spilled into the room, it would not impact safety-related components in the room because the water would not be deep enough. Therefore, although the probability of a flood has increased slightly, the consequences of a flood are acceptable.
Heed for Emergency Power The only design basis event that could interrupt normal power to both units is a loss of offsite power.
The offsite power system consists of three 500 kV transmission lines that meet in a common switchyard, and a separate 69 kV transmission line that connects to our 13 kV buses. The three 500 kV lines are independent of each other and are mounted on weather-resistant towers along a single right-of-way. The 69 kV transmission line comes into a separate substation on the site along a different right-of-way l
(meeting General Design Criteria 17 requirements) and is buried for most ofits length on BGE property.
Two of the transmission lines (one 500 kV and the 69 kV line) are connected to non BGE power sources.
Two ways that offsite power could be inadvertently lost are through maintenance activities and weather-related events. To reduce the possibility that maintenance activities could contribute to a loss of offsite power, we will restrict maintenance activities on our portion of three of the four offsite transmission lines I
until the Unit 2 EDGs are returned to their normal configuration. This restriction provides additional l'
margin beyond the two transmission lines required by Technical Specification 3.8.1.
i The design and construction of the four transmission lines lessens their vulnerability to weather-related events. Tornados and hurricanes are weather-related threats to the transmission systera. We anticipate that all of the work on the SRW heat exchanger replacement will be completed before the time of year 8
l L_.__.__.____________._
v' i,
ATTACHMENT m DESCRIPTION AND LICENSING BASIS EVALUATION I
when tornados and hurricanes are at their highest frequency for the Calvert Clifts site. The probability of tornados and hurricanes striking Calvert Cliffs were previously evaluated for the SBO rule response.
4 The probabilities reported were,7.7 x 10 per year for tornados, and 0.13 per year for hurricanes.
Winter ice storms are another potential threat to the transmission system. Although data on ice accumulation is not available, the temperatures are generally above freezing and snowfall and sleet are minimal during March and April. Southern Maryland Electric Cooperative has not had ice damage to their transmission lines in the last 40 years, although their lines are designed for one-half-inch coating of ice, liowever, the 500 kV lines are designed to remain functional with a one-and-one-half-inch coating ofice. Based on the design of the transmission system and the time of year that the work is scheduled, we believe that the vulnerability of the transmission system to a weather-related event is minimized and
{
is acceptable.
Alternate Power Sunolv During this temporary condition, the No. OC Diesel Generator will remain available for use on any of the safety-related buses on either unit. The No. 0C Diesel Generator is not affected by the SRW work on Unit 2. It can easily carry the loads of any of the Unit I or Unit 2 buses. If an EDG should fail when needed, the No. OC Diesel Generator could be used in its place. As part of the testing required for SBO use, it was demonstrated that the No. 0C Diesel Generator could be started and provide power to any bus within one hour. This is an acceptable period of time to provide power to any Unit 2 bus while Unit 2 is i
in Mode 5 or 6.
RISK HASIS EVALUATION This risk increase to Unit 1 (at-power unit) resulting from this temporary configuration is comparable to many typical on-line maintenance activities. The instantaneous risk increase is less than 1.3 times the 4
base risk. The cumulative risk is approximately 4x10. When compared to a " typical" six-day EDG j
inspection outage, the cumulative risk increase is approximately twice as high. Thus, the difference 4
between this alignment and a " typical" EDG outage is a 2x10 increase in annual core damage frequency (CDF). If the cooling tower was not installed on No.2B EDG, and it remained out-of-service for the entire 40 days, with No.12 SRW header supplying cooling to No. 2A EDG, the increase in risk would be 4
9x10. This is an increase in annual CDF for 1999 of 2.9%.
The current version of the Calvert Cliffs Probabilistic Risk Assessment is used for this at-power assessment, it includes both internal and external events (fire, seismic, and high winds). Although some aspects of this model are still being refined and documented, it is believed that the Calvert Cliffs Probabilistic Risk Assessment is fully capable of assessing this issue.
The shutdown risk to Unit 2 has been qualitatively evaluated. Based on the assumptions regarding EDG outage periods and reduced inventory operation, the risk increases for Unit 2 would be less then or equal to those seen for Unit 1.
Considering the magnitude of work being performed on the SRW System, the risk involved with the temporary alignment are acceptable. The addition of the cooling tower to No.2B EDG significantly reduces the risk increase associated with an extended outage of this EDG.
l 9
E_----______________--__
Y l ',
ATTACHMFNT. (1)
DESCRIPTION AND LICENSING BASIS EVALUATION
)
Assumptions:
The temporary cooling tower for No. 2B EDG will not be seismically rugged. It is assumed to j
fail for any seismic event that fails secondary piping.
The temporary cooling tower is assumed to fail ifimpacted by tornado or hurricane-force winds.
e Service Water IIcader No.12 can provide all required Unit I emergency cooling loads with both No.1 B and No. 2A EDGs running at full load.
During reduced inventory operations on Unit 2, there will be an EDG available for Unit 2 that is qualified to withstand scismic and high wind events. Thus, if the cooling tower is installed on No. 2B EDG, and Unit 2 is in reduced inventory, No. 2A EDG will be avai!able, Number 2B EDG cooling water will start automatically on diesel start.
The expected e
configuration will include approximately three cooling fans, a normal and backup cooling water pump, and automatic makeup water from a secure source. The cooling water pumps and fans will be supplied from a bus that is backed by No. 2B EDO.
Makeup water will be gravity-fed from a pre-treated water storage tank. The pre-treated water storage tank also supplies the Fire Protection System; thus, the cooling tower is assumed to fail on worst-case fire scenarios.
This evaluation does not consider any maintenance beyond the Unit 2 SRW work. Taking Unit 1 j
or relevant Unit 2 equipment out-of-service for routine maintenance or overhaul will be evaluated in the Unit I weekly quarterly system schedule evaluations. This includes No.0C Diesel i
Generator.
Results The proposed temporary change, including the cooling system and No.12 SRW lleader supplying 4
No.2A EDG, does cause a risk increase for the at-power unit. A 4x10 increase in annual CDF for
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temporary configuration for 1999 is noticeable, but acceptable. This is based on judgment as the present regulatory position on temprary changes to plant configurations is not clear. SECY 97-287 states that
" changes less then 1.0x10 per reactor year" are defined as "very small." This change does exceed the 4
1.0x10 threshold. However, this SECY appears to be discussing changes that will permanently increase the plant's CDF. This is only a temporary change, and will only cause the risk increase during the 40-day SRW outage. SECY 97-287 states that guidelines for temporary changes will be developed in the future. Thus, detailed guidance is not available.
It is clear that the installation of the independent cooling system has a significant risk advantage when compared to leaving No.2B EDG out-of-service for the entire SRW outage. Also, the risks involved with this alignment are not high when compared to the risk increases seen in typical on-line maintenance 4
evaluations. The threshold for a medium cumulative risk for on-line maintenance is a 1x10 increase over a one-week time period. This proposed change exceeds this threshold, but risk involved with this j
change is over a 40-day period. Maintenance alignments routinely cause cumulative medium risks over l
a weeks time. Thus, this risk is relatively small when compared to normal quarterly system schedule on-line maintenance.
I I
10 1
!v' i,
l ATTACHMENT (1)
DESCRIPTION AND LICENSING BASIS EVALUATION MITIGATING FEATURES To provide additional assurance that all reasonable steps have been taken to ensure the operability of the Unit 2 EDGs while in this temporary configuration, the following actions will be taken in addition to the installation of the tsmporary modifications as described above:
To prevent the loss of the normal power supply to the CREVS and CRETS, we will restrict maintenance activities on three of the four offsite transmission lines until the Unit 2 EDGs are returned to norma; configuration.
To monitor risk, Units I and 2 equipment taken out-of-service during this period will be evaluated in the Unit I weekly quarterly system schedule evaluations.
3 i
To ensure that weather-related events cannot cause a loss of all emergency power on Unit 2 e
during periods of reduced inventory, the No.2A EDG will remain operable during reduced inventory periods.
1 To ensure that backup power is available to any of the safety-related buses, the No.OC Diesel e
Generator will not be taken out-of service for planned maintent.nce and will remain available to be connected to any of the safety-related buses.
1 ALTERNATE CONFIGURATIONS CONSIDERED A number of configurations have been evaluated in addressing the unavailability of both subsystems of Unit 2 SRW. Based upon maximizing equipment availability subsequent to a failure of an EDG, SRW subsystem, or temporary cooling system, it was determined that the option identified in this letter was the l
best option. Other alternatives are shown on Tables 2 and 3. As can be seen from these tables, these
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alternatives resulted in a single failure causing a total loss of a safety function. Not all plant equipment is listed on these tables; however, the equipment shared by both units or relied upon by the opposite unit is listed. The other equipment listed is equipment impacted by the loss of SRW. Additionally, the use of a portable diesel generator as a substitute for the No. 2B EDG was considered. We have used these types of diesel generators in the past. Ilowever, they have the same weather vulnerabilities that the proposed cooling system has. In fact, because the portable diesel generator needs an external fuel oil tank, it has more vulnerability than the cooling system to weather-related events. They are also not safety-related (similar to the cooling system) and the portable diesel generator requires local, manual action to start and load it. Therefore, it was not chosen as an option. The option selected (Table 1) was chosen because a single failure of an EDG (Unit I or 2) or a Unit i SRW subsystem cannot affect:
Both trains of SRW; i
Both trains of SFPC; e
Both facilities of EDGs (on either unit);
Both trains of CREVS or CRETS; 1
Battery chargers such that any station battery is affected; or Both the Unit I and Unit 2 motor-driven auxiliary feedwater pumps. (Note: During a loss of e
feedwater event on Unit 1, Emergency Operating Procedures direct use of the Unit 2 motor-driven auxiliary feedwater pump as a backup.)
11 L__
s*
i, j
ATTACHMENT (1) j DESCRIPTION AND LICENSING BASIS EVALUATION Thus, one trainhubsystem of the above equipment will be available following a failure for the selected option.
CONCLUSION i
We believe the proposed temporary cooling lineup for the EDGs on Unit 2 to be a safe, low-risk configuration for the duration of the SRW heat exchanger replacement. We have evaluated this configuration under the provisions cf 10 CFR 50.59 and have determined that it involves several USQs.
Therefore, we are submitting this proposed license amendment to the Nuclear Regulatory Commission for approval.
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ATTACHMENT (2) l l
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l DETERMINATION OF SIGNIFICANT HAZARDS I
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Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant j
July 20,1998 u____--_---------------_------
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ATTACHMENT (2)
DETERMINATION OF SIGNIFICANT HAZARDS t
Currently, Calvert Cliffs has four emergency diesel generators (EDGs), two per Unit, to provide the onsite emergency power supply for both Units. The Unit 2 EDGs rely on the Service Water (SRW) l System to provide their cooling water. During the Unit 21999 Refueling Outage, Baltimore Gas and Electric Company will replace the SRW heat exchangers on Unit 2.
During the period of the replacement, no SRW cooling will be available for Unit 2. Therefore, both Unit 2 EDGs would be inoperable during the replacement work. Unit I will continue at full power operation during the refueling outage.
l The loss of both EDGs on Unit 2 presents several challenges. First, a number of outage activities require an EDG be operable. We propose providing an alternate cooling water supply to maintain the EDGs operable to fulfill the Technical Specification requirements. One EDG will be provided with cooling water from the Unit 1 SRW System. The other EDG will be provided with cooling water from an independent external cooling system. Second, Unit 1 is scheduled to be in Mode 1 operation during this time. The No.12 Control Room Emergency Ventilation System, No.12 Control Room Emergency Temperature System, and a Hydrogen Analyzer are affected by this work because they obtain their emergency power from a Unit 2 EDG. These components support Unit I continued operation.
Therefore,the loss of both Unit 2 EDGs would impact operations on both units.
j There are several issues associated with this change that create an Unreviewed Safety Question (USQ) as l
defined by 10 CFR 50.59. There is an increase in the probability of a malfunction due to the use of an independent cooling system that is non-safety-related and unprotected from seismic or tornado events.
The reliance of a Unit 2 EDG on Unit 1 SRW results in the increase of the probability of a malfunction also. Additionally, these SRW lineups affect the probability of a malfunction for other equipment that rely on SRW during an outage. We are requesting approval of these USQ, which will permit a Technical
. Specification Bases change to the description of an operable EDG while Unit 2 is in Modes 5 and 6 and to support Unit I continued operation.
All of the USQs are related to an increase in the probability of a malfunction in a system important to safety. This results from the use of safety-related equipment in alternate configurations that do not maintain all safety-related aspects for the equipment, and from use of non-safety-related equipment to support safety-related equipment. In general, this proposal relies upon the use of safety-related equipment or the low probability that the equipment will be needed to establish the acceptability of these alternate configurations.
The proposed change has been evaluated against the standards in 10 CFR 50.92 and has been determined I
to not involve a significant hazards consideration, in that operation of the facility in accordance with the proposed amendment:
1.
Would not involve a sigm'ficant increase in the probability or consequences of an accident previously evaluated.
The EDGs are used to mitigate the consequences of an accident. They are designed to stait and load safety-related loads within a specified time period. There are two EDGs for Unit 2. Only one is required during the refueling outage, since a single failure criterion does not apply during this time. However, it is desirable for defense-in-depth and shutdown safety reasons to keep both EDGs operable. Additionally, one of the EDGs supports operable equipment on Unit I that I
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DETERMINATION OF SIGNIFICANT HAZARDS remains at power. We are proposing an amendment that would allow the EDGs to continue to be operable with an alternate cooling water supply. Other than the change in cooling water supply, we are not affecting or modifying the operation of the EDGs. The EDGs are not an accident initiator for any previously evaluated accident. Therefore, the proposed change does not involve an increase in the probability of an accident previously evaluated.
The EDGs are designed to mitigate the consequences of an accident. They will continue to perform that function while being supplied with an alternate source of cooling water. The consequences of a design basis accident during the period when the alternate cooling water is being supplie.1 is not increased because the operation of the EDGs has not been adversely affected. Any additional electrical loads (such as cooling tower pumps and fans) or additional l
cooling loads (such as additional SRW flow to the No. 2A EDG) have been evaluated and found to be acceptable under conditions postulated to exist during the outage. Therefore, the proposed change does not significantly increase the consequences of an accident previously evaluated.
2.
Would not create the possibility of a new or di[ferent type of accident from any accident previously evaluated.
The EDGs are not being modified by this proposed change nor will any unusual operator actions be required. The EDGs will continue to operate in the same manner as before. However, the j
cooling water supplies have been altered and were evaluated under the provisions of 10 CFR 50.59 and determined to result in a USQ. These USQs are evaluated below.
The first identified USQ is due to the realignment of a Unit i SRW subsystem to also support a Unit 2 EDG (2A). This alignment will rely on two control valves (one to each EDG) to function properly in order to provide adequate SRW flow to both EDGs. If one of the valves should fail open, it may result in insufficient SRW flow or increased SRW temperatures, as the EDGs share the same cooling supply. This is an increase in the probability of a malfunction because the operability of a EDG relies on both control valves performing properly. We believe that this is an acceptable condition because the control valves and their air supply are safety-related and will be performing their design function. The control valves are not being modified by the temporary configuration nor will any operator action be required. The control valves will continue to operate in the same manner. Therefore, because the malfunction is the same as previously identified for i
l these valves and only the probability has increased, a new or different type of accident has not been created.
The next USQ identifies a condition where a Unit 2 EPG is dependent on a Unit 1 EDG for cooling water. The Unit i EDG powers the pump for the cooling water system that will now provide cooling to both EDGs. Although the consequences of a loss of cooling l
water is the same (i.e., the EDG failG, the probability of a malfunction for the Unit 2 l
EDG has increased because it now depends on the Unit i EDG to maintain its operability.
We believe that this is an acceptable condition because the Unit 1 EDG is safety-related and is proven reliable through testing. Additionally, the EDG will not be operated in a manner different than it is currently, it is not being modified by the proposed change nor will any additional operator actions be required. A failure analysis shows that failure of 2
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ATTACHMENT m DETERMINATION OF SIGNIFICANT IIAZARDS i
4 the No. IB EDG will not result in the total loss of any safety function for either unit.
Therefore, the possibility of a new or different type of accident has not been created.
A USQ has been identified related to the use of a temporary cooling system to provide l
cooling to an EDO. The cooling system that is proposed is not safety-related and is not protected from natural phenomenon. His leads to an increase in the probability of a malfunction because the cooling system is more likely to fail than a safety-related, protected system. We believe that this is an acceptable condition for the limited time we propose to use the cooling system. The consequences of a cooling system failure are no different than those of a failure of the SRW System. The events most likely to cause the cooling system to fail are seismic events and severe weather. Severe weather is not highly probable during this time of year. Significant seismic events are not probable on j
this part of the east coast. The cooling tower has been used before at Calvert Cliffs to
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support testing of the EDGs during outages. The cooling tower will have enhanced design features that will improve its reliability, such as two pumps. The piping provided to and from the cooling system will be steel and will be provided with flexible joints making it rugged and flexible. Additionally, the cooling tower will be placed close to the Auxiliary Building and the makeup water piping will be run underground for part of its length. These measures help to protect the cooling tower and its piping from severe weather events. The EDG is not being altered by this temporary configuration. It will continue to operate as before. No additional operator action is required for the cooling l
tower to perform its function. Therefore, the possibility of a new or different type of accident has not been created.
e.
This USQ exists because the piping from the cooling tower to the EDG is not safety-related and could break, causing a flood in the EDG room. His creates an increase in the probability of a malfunction because of the increased probability of flooding in the room.
We believe that this increase is acceptable because the piping is constructed from rugged materials and is flexibly connected to the EDO. This reduces the chance that flooding will occur. If flooding were to occur and the contents of the cooling system were spilled into the room it would not impact safety related components in the room because the water would not be deep enough. Therefore, the possibility of a new or different accident has not been created.
Therefore, the possibility of a new or different type of accident from any accident previously evaluated has not been created.
3.
Would not involve a significant reduction in a margin ofsafety.
The operability of the EDGs in Modes 5 and 6 ensures that emergency power is available to mitigate the consequences of a fuel handling accident and a boron dilution accident.
Additionally, it provides emergency power for shutdown cooling and spent fuel pool cooling.
One of the Unit 2 EDGs provides power to the shared Control Room Emergency Ventilation System, Control Room Emergency Temperature System, and the Hydrogen Analyzer needed to support Unit I power operation. The proposed change does not affect the function of the EDGs.
Because of the increased probability of a malfunction of equipment imponant to safety (SRW support for the EDGs), the margin of safety is reduced. However, the reduction is not l
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DETERMINATION OF SIGNIFICANT HAZARDS significant. As described above, each USQ has been evaluated and determined to not have a significant impact on safety.
To provide additional assurance that all reasonable steps have been taken to ensure the 1
operability of the Unit 2 EDGs while in this temporary configuration, the following actions will i
be taken in addition to the installation of the temporary modifications as described above:
To prevent the loss of the normal power supply to the Control Room Emergency i
Ventilation System and Control Room Emergency Temperature System, we will restrict maintenance activities on three of the four offsite transmission lines until the Unit 2 EDGs are returned to normal configuration.
l To monitor risk, Units I and 2 equipment taken out-of-service during this period will be evaluated in the Unit I weekly quarterly system schedule evaluations.
To ensure that weather-related events cannot cause a loss of all emergency power on Unit 2 during periods of reduced inventory, the No. 2A EDG will remain operable during reduced inventory periods.
To ensure that backup power is available to any of the safety-related buses, the No. 0C Diesel Generator will not be taken out-of-service for planned maintenance and I
will remain available to be connected to any of the safety-related buses.
We believe that the reduction in the margin of safety represented by this temporary license amendment is not significant based on our evaluation and management of plant risk, the reliability of the EDGs, the availability of redundant EDGs, the availability of the Station Blackout Diesel Generator ud the mitigating features described above. 'Iherefore, the proposed change does not involve a %5 Leant recation in the margin of safety.
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