ML20137G126
| ML20137G126 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 03/26/1997 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M98093, NUDOCS 9704010330 | |
| Download: ML20137G126 (20) | |
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h, Cur 0s Es 11. CuesE Baltimore Gas and Electric Company
' Vice President Calven Cliffs Nuclear Power Plant Nuclear Energy 1650 Calven Cliffs Parkway Lusby, Maryland 20657 410 495-4455 March 26,1997 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No. 2; Docket No. 50-318 Request for Additional Information --
License Amendment Request:
Modification to the Service Water liead Tanks, Unreviewed Safety Question (TAC No. M98093)
REFERENCES:
(a) Letter from C. H. Cruse (BGE) to Document Control Desk (NRC), dated March 6,1997, License Amendment Request: Modification to the Service Waterliead Tanks (b) Letter From A. W. Dromerick (NRC) to Mr C. II. Cruse (BGE), dated March 13,1997, Request for Additional Information - Proposed Amendment Regarding Modification to the Service Water liead Tanks (TAC No. M98093)
In Reference (a), Baltimore Gas and Electric Company submitted a license amendment request to the Nuclear Regulatory Commission (NRC) to support a modification to the Calvert Cliffs Unit 2 Service Water System. In Reference (b) the NRC requested additional information regarding the license amendment request. Attachment (1) provides Baltimore Gas and Electric Company's response to the questions posed in Reference (b) and additional questions by the NRC staff. Attachment (2) provides a drawing associated with the response to the questions.
I 9704010330 970326 PDR ADOCK 05000318 P
PDR 3100.15 l WMEPPppPM i
, '4 D. Document Control Desk March 26,1997 i
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l The attached information does not change the Significant liazards Determination presented in Reference (a). Should you have any further questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours,
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STATE OF MARYLAND . :
- TO WIT:
COUNTY OF CALVERT :
I, Charles II. Cruse, being duly sworn, state that I am Vice President, Nuclear Energy Division, 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 and I believe it to i be reliable. j l
l : # Amr ;
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l Subscribed and sworn before me, a Notary Public in and for the State of Maryland and County of fa/verP .this 24 day of /Th ec h .1997.
WITNESS mylland and Notarial Seal: #/
Notary Public My Commission Expires: /W N jDate CilC/EMT/bjd Attachments: (1) Response to NRC Questions (2) Simplified Drawing cc: D. A. Brune, Esquire 11. J. Miller, NRC J. E. Silberg, Esquire Resident Inspector, NRC Director, Project Directorate I-1, NRC R. I. McLean, DNR A. W. Dromerick, NRC J.11. Walter, PSC l
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i RESPONSE TO NRC QUESTIONS i
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Calvert Cliffs Nuclear Power Plant Unit 2 !
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D. ATTACIIMENT (1) l RESPONSE TO NRC QUESTIONS l la. Describe the operation of the Service Water (SRW) System during normal and accident conditions, including alignment andsequencing ofvalves and components.
REscolssE Service Water Synts The Service Water (SRW) System is a closed cooling water system designed to remove heat from various safety-related and non-safety-related plant components. The system removes heat from turbine building components, blowdown recovery heat exchangers, containment air cooling units, spent fuel pool cooling heat exchangers, and emergency diesel generator (EDG) heat exchangers. The SRW system functions as one system for non-safety-related heat loads in the Turbine Building and has two -
subsystems for the safety-related heat loads in the Auxiliary Building and Containment. The system is divided into two subsystems by manually operated valves. Each subsystem is provided with a head tank designed to accommodate surges and provide the net positive suction head to its associated SRW pump.
Each head tank has a normally open vent valve to the Auxiliary Building atmosphere, which can be ;
isolated with a manual isolation valve. Currently, a 6-inch overflow line connects the gas space of head I tanks 21 and 22. There are three SRW pumps in all. One pump remains in standby, while the other two i are aligned to the separate subsystems.
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, During normal operation, both subsystems are required and are independent to the degree necessary to l assure the safe operation and shutdown of the plant assuming a single active failure pre-recirculation l
actuation signal (RAS) and post-RAS and a single passive failure post-RAS. During shutdown, operation of the SRW system is the same as normal operation, except that the heat loads are reduced.
l The turbine plant heat loads are:
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+ Generator bus duct coolers;
- Exciter coolers;
- + Generator hydrogen coolers; d
+ Circulating water system priming pump seat water coolers;
- Condenser vacuum pump seal water coolers;
- Feed pump turbine lube oil coolers;
- Condensate booster pump coolers;
+ Instrument and plant air compressors and aflercoolers;
+ Turbine lube oil coolers;
+ Electro-hydraulic control coolers;
+ Turbine Building sample cooling system;
+ Seal oil system coolers; and
+ Auxiliary feed pump room air cooler On a safety injection actuation signal (SIAS), the SRW Turbine Building isolation valves automatically close. This allows the SRW system to be directed to the safety-related heat loads. The isolatit n valves j are located in the Auxiliary Building (Seismic Category I structure). During loss-of-coolant accident !
(LOCA) operation both subsystems have similar heat loads and flow requirements. Each subsystem will cool a maximum of two containment air coolers (CACs) and one EDG. The steam generator blowdown heat exchanger and spent fuel pool coolers are isolated on initiation of the containment spray actuation signal.
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RESPONSE TO NRC QUESTIONS j i
Subsystem 21 supplies flow through the SRW heat exchangers to CACs 21 and 22 and the 2A EDG.
Subsystem 22 supplies flow through the SRW heat exchangers to CACs 23 and 24 and the 2B EDG.
110 wever, any CAC can be supplied from any subsystem by positioning local manually-operated valves. l Service Water Head Tanks The two 2350 gallon SRW bead tanks provide surge capacity to accommodate system volume changes.
- Each tank supplies its respective subsystem. 11ead tank level is automatically maintained between 78 and 81 inches. A level switch (LS-1579 or LS-1565) signals the level control valve to open and close ,
i to add water to the tank. The head tank level may also be controlled by a manual bypass valve. l l Normally, make-up water to the head tanks can be supplied from either the demineralized water system 4
or condensate system. Emergency make-up can be provided by fire protection and salt water systems. i 4
liead tank level indication is provided at two locations. Each tank has local sightglass level indication
- and remote level indication (LT-1579 and LT-1565), connected to the Main Control Room and alarms at j 95 inches increasing (high level) and 75 inches decreasing (Iow level).
i Each head tank has a normally open manual vent valve located on top of the tank. A combined overflow line for the head tanks provides surge capacity between tanks and serves as overflow protection. The overflow line is directed to an Auxiliary Building floor drain located on the 69 foot elevation. !
i Cggininment Air Coolers
, Four, two-speed CACs are provided to remove ambient heat from Containment durint aormal plant operation. in the event of a LOCA or main steam line break (MSLB), the CACs, along with the containment spray system, limit the containment pressure to below the design value. During these accidents, the system also functions to reduce the leakage of airborne and gaseous radioactivity by ,
providing a means of cooling the containment atmosphere. The four CACs operate independently from '
. the Safety injection and Containment Spray Systems.
Service water is circulated through the CACs air cooling coils to remove heat from containment atmosphere. The top row of tubes in CACs 23 and 24 are at approximately the 77.2 foot elevation. The top row of tubes in CACs 21 and 22 are at approximately the 53.2 foot elevation. The difference in static head between the two sets of CACs is 24.0 feet (approximately 10 psi). The SRW supply line for each
- cooler has an air-operated control valve which is normally open (deenergized) and designed to fail open. !
4 The SRW return line from each cooler has two air-operated control valves in parallel. One control valve is used for normal cooling requirements; the other control valve opens automatically upon receipt of a SIAS and may be operated manually to supplement cooling during normal operation.
Three CACs are normally in operation. During normal conditions, the full flow (8") SRW outlet valves, which are used during a design basis accident, are closed, while the smaller (4") valves are open.
Occasionally, during extended periods of high outside temperature, all four coolers are used to limit the containment temperature below 120 F.
1 Upon receipt of a SIAS signal, the non-operating cooling unit (s) automatically start in low speed and, I simultaneously, the others are automatically switched from their normal high speed operation to low !
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RESPONSE TO NRC QUESTIONS speed operation. The full flow SRW outlet valve at each cooler ir opened and the SRW inlet valves move to a throttled position upon receipt of a SIAS. By throttling SRW flow to a pre-determined flow setting during SIAS, the CACs will remove enough heat to maintain the design pressure / temperature requirements of the containment structure while satisfying the SRW temperature criteria for the EDGs.
Emervency Diesel Generators The EDGs are designed to provide a dependable onsite power source capable of starting and supplying the essential loads necessary to safely shutdown the plant and maintain it in a safe shutdown condition.
Both EDG's heat exchangers are cooled by the SRW system. ,
ib. Identify worst-case scenarios and system response including re. <mt parameters and assumptions.
RESEONSE As it pertains to the modification, the following are two scenarios which are considered " worst-case" scenarios:
Low Service Water Head Tank Pressure The SRW head tanks are required to be operable to ensure that the associated SRW subsystem remains operable. The nitrogen pressure ensures that the water inside the CACs will not boil prior to the automatic restan of the SRW pumps during a loss-of-offsite power (LOOP)/LOCA or LOOP /MSLB.
The nitrogen pressure will be normally maintained at approximately 15 psig. The minimum allowable nitrogen pressure is 14 psig. If the SRW head tank, which is lined up to CACs 23 and 24, is less than 14 psig, CACs 23 and 24 would potentially be susceptible to a waterhammer during a LOOP /LOCA or LOOP /MSLB. For the same nitrogen pressure, the time required for the SRW to boil within CACs 21 and 22 is longer than in CACs 23 and 24, and therefore, if nitrogen pressure is maintained to prevent boiling within CACs 23 and 24, boiling will not occur in CACs 21 and 22. The functionality (i.e., the system meets Generic Letter 91-18 operability limits) of the SRW piping would be maintained if waterhammer(s) resulted from the above conditions. Therefore, the CACs remain operable, but are in a degraded condition, without nitrogen pressure in the SRW head tanks.
Normally, the SRW head tanks and their nitrogen supply system will be cross-tied in the gas space, and therefore, the pressures between the two head tanks should be equal. When cross-tied, the SRW head tank nitrogen supply system has redundant components so that if one component fails the system will continue to provide the needed pressure in both head tanks. Each nitrogen accumulator is sized to provide at least one volume of nitrogen at 16 psig to both head tanks. This capability is provided in case the non-safety-related nitrogen supply is not available for a period of time. As described, the nitrogen system is designed so that the failure of a component within the SRW head tank nitrogen supply system will not render the SRW system inoperable.
Larve Suree Volumes The occasional large surges into and out of the SRW head tanks have been accommodated within this modification. The current 6" cross-connect line will be enlarged to 8" piping. This will allow more 3
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RESPONSE TO NRC QUESTIONS water to pass from one head tank to another at a faster rate. The relief valves are sized and set to limit the volumes of gas and/or water relieved as a result of the water insurges.
Ic. Provide a simphfied diagram of the system showing all components that are relevant to the amendment request.
See Attachment (2).
- 2. Describe the specific design changes that are required to accommodate higher headpressure.
RESPDNSE The following is a list of design changes required to the existing system to accommodate the higher SRW system pressure:
+ Service water head tanks were re-rated to accommodate the higher pressure, resulting in a slight modification to the SRW head tanks. (see Question 3)
- The following were re-rated:
= Generator exciter coolers;
=> Generator hydrogen side seal oil cooler;
=> Generator air side seal oil cooler;
=> Instrument air and plant air compressor cylinder head intercooler;
=> Main turbine lube oil cooler; and
=> Diesel generator air, jacket water, and lube oil coolers.
+ The relief valve setpoints and pressure gauges on various components were changed. i
+ The SRW head tank overflow piping was increased in diameter.
- The demineralized water pumps are being evaluated for replacement.
- 3. Explain the basisfor increasing the head tank designpressurefrom 15 to 25 psig.
RESPDNSE
[ Note: The head tank design pressure has been increased to 30 psig, not 25 psig as stated in Reference (1).]
We have evaluated the impact of a nitrogen overpressure on the SRW head tanks and evaluated the enlargement of the overflow line nozzle from 6 inches to 8 inches.
The critical stresses of the SRW head tanks and associated nozzles were computed using applicable American Society of Mechanical Engineers (ASME) Section Vill rules, the methods outlined in Welding Research Council Bulletin 107, and general stress equations. These stresses were compared to ASME i
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RESPONSE TO NRC QUESTIONS Section VIII allowables and Calvert Cliffs Updated Final Safety Analysis Report (UFSAR) requirements.
The tanks were re-rated in accordance with the Baltimore Gas and Electric Company Section XI program. Since the tanks are within the ASME Class Ill boundary, all requirements of Section XI and the applicable construction codes were met.
In the calculation that re-rated the head tanks, the natural frequency, minimum shell thickness, reinforcement requirements and availability, minimum head thickness, and local stresses of nozzle / tank attachments were determined. The results of the calculation are that the SRW head tank will not be j negatively impacted by the addition of the nitrogen overpressure system or the enlargement of the '
- overfiow line nozzle. Where required, reinforcement will be added to the SRW head tank around the nozzles.
4a. Explain the specific head tank pressure and level requirementsfor system operability, including basis (i.e., worst case scenarios). Describe how level and pressure alarm setpoints were determined.
RESEQNSE The minimum SRW head tank pressure is 14 psig. The minimum pressure of 14 psig will allow time for l the SRW pumps to automatically start on the EDGs during a LOOP /LOCA, to preclude boiling the SRW in the CACs.
The low level alarm is set at 75 inches to allow sufficient time for operator action to align emergency make-up water to the system based on the maximum allowed leakage of the system. However, this level does not represent an operability limit, instead it is an action limit (i.e., operator response is required).
4b. Discuss minimum time to boilin the SRWsystem andavailable margin.
2 RESPONSE Nuclear Regulatory Commission Generic Letter 96-06 identifies a waterhammer concern in CACs due to the potential heat transferred to the stagnant SRW in the CACs following a postulated design basis accident. The concern is that if a LOOP occurs during a LOCA or a MSLB inside Containment, power would be temporarily interrupted to both the CAC fans and the SRW pumps, which supply water to the CACs. The steam voids would form, as described in Generic Letter 96-06, when the system 4
depressurizes below the local saturation pressure as a result of stopping of the SRW pumps. Upon restart of the SRW pumps, (after loading on the EDGs), the steam voids would collapse causing a waterhammer.
This modification provides a means to prevent formation of steam voids in SRW within the CACs until the SRW pumps automatically restart during the above scenarios. This is accomplished by adding a
, nitrogen blanket that would maintain a pressure of approximately 15 psig in the SRW head tanks. This will delay boiling in the CACs by maintaining SRW pressure above the fluid saturation pressure for the time required for the SRW pumps to automatically restart when loaded on the EDGs. This modification (the additional head pressure) was incorporated into the CACs thermal hydraulic analysis for a LOCA 5
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RESPONSE TO NRC QUESTIONS i
coincideia with a LOOP. The time for the SRW to start boiling within the CACs after a postulated LOCA/ LOO? or MSLB/ LOOP event is given below.
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f HEAD TANK PRESSURE TIME TO BOIL CACs 23/24 CACs 21/22 10 psig 20 sec 79.8 sec 14 psig 30.3 sec 131.8 sec 15 psig 34.4 sec 147.4 sec 17 psig 55.6 see ---
I Following the LOOP /LOCA or LOOP / MSLB event, the SRW pumps are loaded on the EDGs within l 30 seconds. Assuming a SRW head tank nitrogen pressure of 15 psig, the SRW pumps will start a i minimum of four seconds prior to the start of boiling. The four second margin in boiling is co- Mered adequate and, therefore,15 psig nitrogen pressure in the head tanks is being established as the dhgn basis for the modification. A pressure setpoint of 16 +\-1 psig was selected to allow for the variance in pressure control valve's (PCVs) (2PCV1566 and 2PCV1580) ability to control pressure. The minimum nitrogen pressure required in the SRW head tanks to prevent boiling prior to restart of the SRW pumps during the above scenario is approximately 14 psig.
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Sa. Discuss system leakage andpressure decay restrictions to maintain system operability. I RESPONSE I There is a maximum allowable leakage from the SRW system, which is measured by a periodic test. The I overall system leakage will have a tendency to increase due to the increased pressure in the system, but is l not expected to approach the allowable rate.
The pressure decay in the SRW head tanks will be limited. The modification is designed to control the SRW head tanks pressure at 16 +/- 1 psig. The alarm in the Control Room will be set at 14.2 +/-0.2 psig.
This alarm setpoint was selected because the minimum required pressure in the SRW head tanks is 14 psig and to limit the possibility of a nuisance alarm in the Control Room. The nitrogen accumulator low pressure setpoint is 130 +/-3 psig. The normal operating pressure for the accumulator is 140 to 250 psig. The SRW head tank pressure regulators are capable of maintaining 16 +/- 1 psig with an inlet range of 130 psig to 300 psig. The operator will have to take immediate action to restore nitrogen pressure if the low pressure alarm is received in the Control Room.
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RESPONSE TO NRC QUESTIONS 5b. Describe post-modification, periodic testing, and surveillances that will be performed to assure
.,ystem operability.
RESPONSE
After the modification, the following additional tests /surveillances will be performed to ensure system j operability:
+ The new check valves will be included in the Check Valve Reliability Program, as appropriate.
Initial testing will be performed on the newly installed check valves in accordance with the Check Valve Program
- A periodic test will be developed to ensure that the PCVs are operating properly, since a single failure of a PCV may go unnoticed until both PCVs fail.
- An initial service leak test will be performed for all SRW components. This will be done with flow through the entire system and with the system pressurized. However, since the SRW-cooled components in the Turbine Building may be isolated, every attempt will be made to have those components unisolated for at least a short period of time during the test.
- Hydrostatic testing will be performed in accordance with the applicable ASME Code.
- 6. Discuss the effect ofincreasedSRW systeinpressure onpipe break scenarios.
RtStosst At Calvert Cliffs Nuclea- Power Plant, there are existing flooding calculations for rooms that contain safety-related equipment. The rooms that contain SRW piping / components were reviewed and revised for the higher SRW pressure. All revised calculations demonstrated that the added SRW head tank pressure will not adversely afTect the flooding in the affected room (s). Therefore, there is no adverse effect of the increased SRW system pressure on pipe break scenarios.
- 7. Identify relief valve setpoint and bases. Discuss post-modification testing, periodic testing, and surveillances that will be performed to assure operability. t
_REstONSE The following discussion contains the relief valve setpoint and bases for the SRW head tank nitrogen supply system.
Each nitrogen accumulator will be protected by a gas relief valve (2RV1566A and 2RV1580A). These valves will discharge to the plant vent for personnel safety purposes. The valves will lift at 290 +/-9 psig, to protect the accumulators from overpressurization (300 psig).
Each head tank will be protected by a full flow water relief valve, located on the 8" cross-connect piping, set at 30 +/- 2 psig. This valve is an ASME Section Vill valve set at the head tank design pressure and 7
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will only relieve pressure if the tank should become water solid or if the SRW head tank pressure l increases. The relief valve will discharge to an existing floor drain similar to the existing overflow line. l l
There is a relief valve (2RV1566B and 2RV1580B) set at 23 +/- 2 psig downstream of each PCV (2PCV1566 and 2PCV1580). These valves will prevent the water re, lief valve from lifting if a nitrogen pressure regulator should fail open and will prevent possible overpressurization downstream of the PCV.
A common nitrogen relief valve will be provided for the SRW head tanks. This relief valve (2RV1573) is set at 20 +/-2 psig. The basis for the setpoint is to prevent overpressurization of the SRW head tanks and the nitrogen piping to the SRW head tanks. The supply PCVs are set at 16+/-l psig, with the maximum normal pressure at 17 psig. The minimum pressure of the common nitrogen relief valve is 18 psig, which isjust above the maximum normal pressure of the line. This relief valve is set lower than t the water relief valves (2RV1565 and 2RV1579) to prevent the water relief valves from lifting unnecessarily during anticipated system transients.
Testing and surveillances for the SRW and nitrogen systems are being developed, as described in Question 5b.
- 8. Performfailure modes and effects analysis and aiscuss the results.
RESPD2iSE The SRW head tanks, and the SRW head tank nitrogen supply system, are required to be operable for the following events and accidents: UFSAR Sections 14.2, 14.3, 14.4, 14.5, 14.6, 14.7, 14.9, 14.10, 14.12, l 14.13,14.14,14.15,14.16,14.17,14.18, and 14.20.
The portions of the SRW system that are required for the above events and accidents are safety-related, Seismic Category I components. They are mounted and/or supported as Seismic Category I components.
This modification will not adversely affect the SRW system's ability to mitigate the efTects of any of the above accidents or events. The added pressure is a static head and will have no impact on system cooling capacity or flow, or pump performance. Therefore, the SRW system will continue to operate as designed. On a SIAS, the non-safety-related compnnents will be isolated from the safety-related components as originally designed and with no challenges to the valves caused by the increased pressure.
This modification will not adversely affect the SRW system's ability to accommodate a postulated failure ofits original design or the SRW head tank nitrogen supply system.
For the components installed for this modification, Table 1 (attached) lists the new active components in the SRW head tank nitrogen supply system and the types of failures of those components and their effects. To summarize the table, no single activt failure of the nitrogen system will depressurize both SRW head tanks and challenge the operability of the system. l I
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RESPONSE TO NRC QUESTIONS
- 9. Discuss the design requirements and standards associated with indication, control, and Control Room annunciation for head tank level and pressure instruments and circuits, number of channelsfor each head tank, andpower supply requirements. Discuss post modification testing, periodic testing, andsurveillance that will be performed to assure operability.
RIR ONSE The electrical design and the instrument and control design includes the installation of four pressure switches and four pressure indicators at a local instrument mount, near the SRW head tanks. The new pressure indicators and pressure switches will monitor the nitrogen pressure in SRW Head Tanks 21 and 22 and the nitrogen accumulator tanks. This modification also includes the installation of cabling and conduit to provide Control Room annunciation wi n one alarm window on Panel 2Cl3 in the event that a low pressure signal is received from the pressure switches. Annunciation will be actuated by a normally closed contact of either of the pressure switches, indicating low pressure at any of the SRW head tanks or nitrogen accumulators. The new pressure instrumentation is classified as a safety-related pressure boundary, liowever, the function of the instrumentation installed by this modification is non-safety-related. Also, this modification will replace some existing local pressure indicators and will recalibrate related instrumentation throughout the SRW system.
The new instrumentation to be provided at the SRW head tank local instrument panel is classified as a safety-related pressure boundary. Safety-related pressure boundary components are not required to l function during a seismic event, but must maintain the system pressure boundary. l l
The new instrumentation and ajunction box for electrical connections will be mounted on a seismically-supported panel. The spare cable to be used is non-safety-related and will be routed in accordance with separation requirements for channel separation in accordance with voltage classification and function as delineated in the UFSAR. The routing will be through existing trays, existing conduits, and new conduits. The new conduit routing is not required to be Seismic Category II/I since it is less than one inch.
Existing instrumentation is being replaced since the new operating pressure is outside the desired band for indication. The new components will be procured to ensure that they meet the same current safety-related or non-safety-related function as comparable existing components. Based on the new increased 1 operating pressure of the SRW system, existing instrumentation throughout the system was reviewed to j ensure acceptable scaling and design ratings were present.
Local pressure indication will be provided for both the SRW head tanks and the nitrogen accumulators.
Four pressure switches, four pressure gauges, and a junction box will be installed on the local instrument l panel to provide local pressure indication and a Control Room annunciator upon a system pressure I degradation. l This annunciator will be triggered by any one of four pressure switches. Pressure switch 2PS1565 will l monitor SRW llead Tank 22 pressure and will initiate the annunciator when the pressure in the head tank falls below 14.2 psig. Pressure switch 2PS1579 will monitor the pressure in SRW Head Tank 21 and will initiate the annunciator when the prese N head tank falls below 14.2 psig. Pressure switches 2PS1566 and 2PS1580 will monitor the .sure in SRW Nitrogen Accumulators 22 and 21, 9
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RESPONSE TO NRC QUESTIONS respectively. The nitrogen accumulator pressure switches will initiate the annunciator on a decrease in pressure at a setpoint of130 psig.
The addition of the pressure switches was reviewed and, since they do not add a load to the 125 VDC system, were found to be acceptable.
The post modification testing of the annunciator circuit will include the initiating devices, which will require testing of each pressure switch, and with the testing, a verification of annunciator triggering will be performed.
- 10. Discuss the local temperature efect: on the head tanks during accident conditions.
RESPONSE
The SRW head tank nitrogen supply system (the new components and piping) will be located in the 69 foot elevation Main Plant Exhaust Equipment Room. The conditions in that room are considered mild with the following values assigned to that room:
Normal LOCA I Maximum Temperature 110 F 110 F l Maximum Pressure ATM ATM l Radiation Level (RADS) --- 1.54E2 l Maximum Relative liumidity 70 % 70 %
The environment in which this modification will be installed will not adversely affect the modification or the SRW system.
- 11. Discuss the basisfor continued operability ofthe SRW systemsfor both Units 1 and 2.
RESPONSE
Unit 2 SRW system is being modified to eliminate the water hammer concern put forward in Generic Letter 96-06. Upon completion of the modification, operability related to the generic letter will not be a concern.
The basis for continued operability of both units (pre-modification) was discussed in Reference (2). The SRW piping system for Unit 1 (Unit 2 was accepted by similarity) was analyzed using the force time history data generated using a fluid dynamics model. A forcing function which consists of force versus time was applied to each piping segment. For this analysis, a piping segment is the run of piping between bends, elbows or piping discontinuities such as tees or reducers. The pipe stress levels and restraint / anchor loads were reviewed against the operability limits identified in ASME Section III, Appendix F and the acceptance criteria of Nuclear Regulatory Commission Bulletins 79-02 and 79-14 as discussed in Calvert Cliffs UFSAR, Revision 19, Chapters 4 and SA, and Generic Letter 91-18. To provide a more realistic assessment of the overall magnitude of the postulated waterhammer, the presence of dissolved gasses was considered. Accounting for dissolved gasses resulted in an 10
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RESPONSE TO NRC QUESTIONS 1
approximately 50% reduction in the magnitude of the postulated waterhammer. The CACs were also '
evaluated. The coil assemblies were found to be sufficiently robust to withstand the postulated pressure loads. The results of these analyses indicated that although the CACs and the SRW system components l would exceed design basis limits during the postulated waterhammer, they would still perform their safety function. !
- 12. Describe any additionalpost-modification testing, periodic testing, and surveillances that will be performed to assure system operability (e.g., integratedsystem response testing). i i
RESPDNSE See responses to questions 5 and 9 for testing and surveillances.
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- 13. Does the addition ofnitrogen piping as depicted in thefigure attached to Reference (1) conflict with the UFSAR statement that the two subsystems of the SRW System are independent of each
. other?
RESPRNSE I
No. The two trains are currently connected in the gas space of the head tanks. This cross-connect (6-inch pipe) is above the normal water level in the head twks. It is provided to allow surges in one train to be directed into the other train. At normal water levels, the fluid part of the trains is not cross-connected through this pipe and thus the two subsystems are considered " independent to the degree necessary," as stated in UFSAR Section 9.5.2.2. This means that the effects of a single active failure must be considered pre- and post-RAS, and a single passive failure must be considered post-RAS. The cross-connect pipe will be modified to be 8 inches vice the current 6 inches. This modification does not change the UFSAR statement on independence. The nitrogen piping proposed to be added to the SRW head tanks is also above the normal water level and thus will not cross-connect the fluid portions of the two trains. Each side of the nitrogen system proposed to be attached to the head tanks can maintain i pressure on both head tanks. Should one pressure regulator fail open, its downstream relief valve will lift I without impacting the nitrogen supply to the head tanks from the redundant accumulator. Should a l pressure regulator fail shut, nitrogen supply from the redundant accumulator will still be available to pressurize both head tanks. No credible single active failure of the nitrogen supplies to the SRW head tanks during the pre-RAS phase of the design-basis accident will result in the loss of nitrogen pressure to both head tanks. The proposed nitrogen supply is not required during the post-RAS phase of the design basis accident. Thus, a passive failure of the proposed nitrogen supply during post-RAS operation is of no consequence.
14 List any other exceptions (ifany) that BGE will take to the Calvert Chfs UFSAR as result of this modification.
RESPDNSE The SRW system is described in UFSAR Section 9.5.2.2 and Table 9-17A. As stated above, the addition of the nitrogen system does not change the statement in the UFSAR that the SRW subsystems are
" independent to the degree necessary" to assure proper system operation. The addition of nitrogen 11
.. 1 !
ATTACIIMENT (1)
RESPONSE TO NRC QUESTIONS j pressure to the SRW head tanks will not cause a conflict with any other part of the current UFSAR description of the SRW System. Therefore, no exceptions are taken to the SRW System concepts presented in the UFSAR.
REFERENCES:
(1) Letter from C.11. Cruse (BGE) to Document Control Desk (NRC), dated March 6,1997, License Amendment Request: Modification to the Service Water liead Tanks )
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(2) Letter From Mr. C.11. Cruse (BGE) to Document Control Desk (NRC), dated ,
January 28,1997,120-Day Response to Generic Letter 96-06, " Assurance of )
Equipment Operability and Containment Integrity During Design-Basis Accident Conditions" I
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ATTACHMENT (1) )
RESPONSE TO NRC QUESTIONS TABLE 1 j l
FAH URE MODES AND EFFECTS FOR THE NEW COMPONENTS I INSTAI1FD FOR SRW HEAD TANK N2 SUPPLY SYSTEM l
- Safety-1 Component Component related Failure l Number Description Class Mode Failure efrect(s) l 2RV1580A SRW N2 PB Open The failure of this relief valve will
. Accumulator depressurize the associated accumulator. I i 21 Relief This will cause the accumulator outlet check Valve valve (2-N2-112) to close, isolating the I affected accumulator, and allowing the other accumulator to provide the needed nitrogen to the SRW head tanks.
2RV1566A SRW N2 PB Open The failure of this relief valve will !
Accumulator depressurize the associated accumulator.
- 22 Relief This will cause the accumulator outlet check i Valve valve (2-N2-122) to close, isolating the j affected accumulator, and allowing the other accumulator to provide the needed nitrogen to the SRW head tanks.
2PCV1580 SRW Head PB,IM Open A failure to the open position of this PCV Tank 21 N2 will allow full pressure of the nitrogen Inlet PCV accumulator to pass through the PCV. This will cause the associated relief valve j (2RV1580B) to open. Thus protecting the SRW head tanks from overpressurization. ,
When the relief valve lifts, the associated !
check valve will close which will isolate the affected PCV and allow the unaffected PCV to provide the needed nitrogen to the SRW head tanks.
2PCV1580 SRW Head PB,1M Closed A failure to the closed position of this PCV l Tank 21 N2 will isolate the accumulator and nitrogen l Inlet PCV supply to the SRW head tanks. The unaffected accumulator and PCV will provide the needed nitrogen to the SRW head tanks.
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.. *1; k ATTACHMENT (1)
RESPONSE TO NRC QUESTIONS TABLE 1 FAILURE MODES AND EFFECTS FOR THE NEW COMPONENTS '
- INSTA1 LFD FOR SRW HEAD TANK N2 SUPPLY SYSTEM
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Safety- 1
, Component Component related Failure Number Description Class Mode Failure effect(s) 2PCV1566 SRW Head PB,IM Open A failure to the open position of this PCV Tank 22 N2 will allow full pressure of the nitrogen Inlet PCV accumulator to pass through the PCV. This will cause the associated relief valve (2RV1566B) to open. Thus protecting the SRW head tanks from overpressurization. l
- When the relief valve lifts, the associated check valve will close which will isolate the i affected PCV and allow the unaffected PCV !
to provide the needed nitrogen to the SRW head tanks.
. 2PCV1566 SRW Head PB,IM Closed A failure to the closed position of this PCV Tank 22 N2 will isolate the accumulator and nitrogen Inlet PCV supply to the SRW head tanks. The unaffected accumulator and PCV will provide the needed nitrogen to the SRW head tanks.
2RV1580B SRW Head PB Open The failure of this relief valve will prevent the
- Tank 21 N2 associated accumulator from providing Inlet Relief nitrogen to the SRW head tanks. This will i
Valve cause the accumulator outlet check valve (2 N2-Il2) to close, isolating the affected relief valve, and allowing the other accumulator to provide the needed nitrogen to the SRW head tanks.
2RV1566B SRW Head PB Open The f ailure of this relief valve will prevent the Tank 22 N2 associated accumulator from providing Inlet Relief nitrogen to the SRW head tanks. This will Valve cause the accumulator outlet check valve (2-N2-122) to close, isolating the affected relief valve, and allowing the other
- accumulator to provide the needed nitrogen to
, the SRW head tanks.
2-N2-112 SRW N2 PB Closed The closure of check valve will isolate the Accumulator associated accumulator from the SRW head 21 Outlet tanks. The unaffected accumulator will Check Valve provide the needed nitrogen to the SRW head I tanks.
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ATTACHMENT (1)
, RESPONSE TO NRC QUESTIONS TABLE 1 FAH URE MODES AND EFFECTS FOR THE NEW COMPONENTS l INSTAL 1FD FOR SRW HEAD TANK N2 SUPPLY SYSTEM Safety- l Component Component related Failure j Number Description Class Mode Failure effect(s) l 2-N2-122 SRW N2 PB Closed The closure of check valve will isolate the ;
Accumulator associated accumulator from the SRW head l
22 Outlet tanks. The unaffected accumulator will ;
Check Valve provide the needed nitrogen to the SRW head ,
tanks. j The failure of this relief valve will 2RV1573 SRW N2 PB Open
^
Header Cross- depressurize the nitrogen in the SRW head Connect tanks. On receipt of the low pressure alarm, ,
ReliefValve the relief valve can be manually isolated, and I therefore, isolating the failure.
- 2RV1579 SRW Head PB Open The failure of this relief valve will Tank 21 depressurize the nitrogen in the SRW head ReliefValve tanks. On receipt of the low pressure alarm, the SRW head tanks can be isolated from each other allowing only one head tank to be affected by this failure. The other head tank
- will automatically repressurize. This relief valve is above the normal water level range, and therefore, water should not drain from the SRW system.
2RV1565 SRW llead PB Open The failure of this relief valve will Tank 22 depressurize the nitrogen in the SRW head ReliefValve tanks. On receipt of the low pressure alarm, the SRW head tanks can be isolated from each other allowing only one head tank to be affected by this failure. The other head tank will automatically repressurize. This relief ;
valve is above the normal water level range, j i and therefore, water should not drain from the l
SRW system.
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- ATTACHMENT (2) i<
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I i I i i j SIMPLIFIED DRAWING l a
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i Calvert Cliffs Nuclear Power Plant Unit 2 March 26,1997
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- VARIOUS AUXILIARY _e '
i TANKS SRW HEAT BLDG COMPONENTS 21 22 VARIOUS EXCIIANGER - -
- TURB BLDG 21 l __ CONTAINMENT i 7 LOADS l
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COOLERS l
- t l- - - VARIOUS AUXILIARY ,
SRW l SRW IIEAT i BLDG COMPONENTS . 'I PUMPS EXCIIANGER l l 22 L__ CONTAINMENT _ _l COOLERS l , ,
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CHEMICAL WATER RETURN '
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LINES e' l
l ADDITION ' /
TANK
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,- SERVICE WATER SYSTEM 1.____________________________F____ ______________________, / BLOCK DIAGRAM
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