ML20217A476
| ML20217A476 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 09/12/1997 |
| From: | Dennis Morey SOUTHERN NUCLEAR OPERATING CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9709190187 | |
| Download: ML20217A476 (6) | |
Text
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Dave lAor:y Southern Nuclear VK e heirJent Op:*attg C::pany Iarley hc9ect PO 0x1295 Barninghrn. Alataama 35201 tel 205 932.5131 4
September 12. 1997 SOUTHERN COMPANY Energy to Serre )* ur World' o
Docket Nos.
50 348 50 364 U. S. Nuclear Regulatory Commission ATTN.: Document Control Desk Washington, DC 20555 Joseph h1 Farley Nuclear Plant Response to Request for information Related to Current Design and Licensing 11ases for Penetration Room Fihtation System Ladies and Gentlemen:
On August 14,1997, Southern Nuclear Operating Company (SNC) received a request for information related to the Farley design and licensing basis for the Penetration Room Filtration System. This request for information resulted from an enforcement conference on April 18,1997, where an issue was raised concerning apparent discrepancies in the licensing basis and design basis of this system as described in the Parley FSAR. SNC's response to the inforntation requested is provided in the Attachment.
If you have any questions, please advise.
Respectfully submitted,
[t 2/1ry Dave htorey JGS/ mar t'RFRAILT IXX' Attachment ec:
htr. L. A. Reyes, Region 11 Administrator hir. J.1. Zimmerman, NRR Project hianager hir. T. ht. Ross, Plant Sr. Resident inspector g
9709190187 970912 PDR ADOCK 05000348 P
PDR ll l ll
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A'lTACllMENT l
SNC Respense To NRC Request For information Related To Current Design And Licensing Basis for Penetration Room Filtration System Joseph M. Farley Nuclear Plant, Units 1 & 2 l
1
SNC Response to NRC Request for Information Related to Penetration Roorn Filtration System i
NBC Outstion No.1 Proside the original design basis for the PRF as described in the FSAR at the time oflicensing.
SNC Response No.1 OriginalDesign Basis The original design function of the penetration room filtration (PRF) system was to minimize activity levels in the fuel handling building following a fuel handling accident (Fila), to minimize activity levels resulting from all sources of containment leakage following a LOCA, and to collect and process potential containment leakage. He PRF system has always been credited in mitigating dose following a Fila in the spent fuel pool area. No credit in accident analyses is taken for filtration of containment airborne leakage. Credit for filtration of post LOCA ECCS leakage was not originally credited in dose analysis. Two safety related redundant 100 percent capacity fan and filter trains were provided to meet single failure criteria and the PRF system is classified as Seismic Category 1. no PRF system was designed to operate following a fuel handling accident in the spent fuel pool and following a design basis accident resulting in a containment isolation actuation signal (CIAS) phase "B". Following a fuel handling accident in the spent fuel pool, the PRF system is designed to operate in the exhaust mode only. A phase "B" signal is actuated by containment high high high pressure which occurs as the result of a LOCA.
Following a CIAS phase "B" the PRF operates in an exhaust mode and when a vacuum is established in the PRF boundary, the system operates in a split flow mode with partial exhaust and l
partial recirculation. The recirculation mode was included to provide for multi pass filtration of I
long-term containment leakage and to provide for dilution and mixing of the penetration room airborne activity. Ilowever, due to the PRF system design (fail open air operated exhaust valves) no credit has been taken for recirculation in evaluating the dose consequences of any accidents.
Subsequent to the enforcement conference held in April, SNC implemented a design modification to Unit I to delete the Containment Spray Addition Tank and replace it with baskets containing trisodium phosphate. %is was approved by the NRC as Amendment 123 to NPF 2. Dose calculations supporting this modification take credit for PRF filtration of ECCS pump room post LOCA recirculation leakage prior to release.
Current System Operation During normal plant operation, the penetration room filtration system is marmally aligned to automatically start and process the exhaust air from the spent fuel pool area on receipt of a high spent fuel area radiation signal or low flow in the spent fuel pool normal llVAC cxhaust.
In the event of a LOCA that raises containment pressure to a nominal 27 psig, the penetration filtration system automatically operates on receipt of a CIAS phase "B" On a CIAS Phase "B" signal, the recirculation fans (QE15C002A, B) and exhaust fans (QE15C001 A, B) start and valves
llV 3356A,11;ilV 3357A,11; and ht0V 3362A and D open. Initially, the recirculation and exliaust fans operate in the full exhaust mode with a total flow rate of approximately 5000 scfm per train. When the differential pressure between the penetration room boundary and auxiliary building reaches approximately 2.0 in, w.g. from 2 out of 3 differential pressure instruments (PDSL-3360AA, AB, AC, IIA, BB, IlC) the recirculation valves h10V 3361 A and 11 begin to open to initiate the recirculation phase. These valves do not have a scal in feature; therefore, these valves will begin to open at a nominal setpoint of 2.0 in, w g. and stop opening at the nominal reset limit of 1 A8 in. w.g. from 2 out of 3 differential pressure instruments to allow partial recirculation with flow still being exhausted to the vent stack and to also maintain a negative pressure within the PRF boundary. To assist in achieving maximum recirculation cleanup, exhaust valves llV 3356A and D, at the discharge of the recirculation fans, may be manually closed by the operator Note that following a CIAS phase "II" start of both trains, one filter train may be placed in standby and may be manually re-started if the operating system should fail, in the event of control air failure, valve ilV 3356A and D, ilV 3357A and B, and llV 3538A and H fail open, resulting in the recirculation and exhaust fans operating post LOCA to exhaust both the PRF boundary and spent fuel area. The PRF boundary suction valves are normally closed h10Vs, so the Fila alignment would be unaffected by control air failure. Original design (prior to 1976) had valves llV 3538A and B as fail closed type. A change by Change Notice Bht 1228 (D-175022, revision 3, dated 6/8/76) resulted in valves llV-3538A and H failing open in support of the Fila system alignment.
To maintain a filter efliciency of at least 95.0 percent, the original design basis required electric heaters in the PRF units to maintain the entering air below 70 percent relative humidity, Lisming Basis
'Ihe original licensing basis has not changed. SNC does agree that there are some conflicting descriptions of the PRF system in the FSAR and revisions to the FSAR as appropriate to correct the inconsistencies and inaccurate statements have been identified. SNC agrees that the guidance for analyzing the radiological consequences of a LOCA does not differentiate between large and snull break LOCAs. The original licensing basis was that the PRF system would automatically start for a Fila in the spent fuel pool area and for LOCA Condition IV events where it was required. The Condition IV start is accomplished by using the containment high high high pressure signal (nominal 27 psig). Containment pressure is also used to initiate an Si signal which occurs at a lower pressure. 'Ihis may explain the confusion found in the original FSAR and the NRC SER related to this matter. The system is not required to automatically start for small break LOCA events, and large break LOC A cvents are bounding with respect to offsite dose at FNP No credit has ever been taken in dose analysis for filtration of containment leakage. To ensure that the FSAR reflected the actual licensing basis from the original SER, Revision il of the updated FSAR dated June 1993 incorporated SER credit for filtration of ECCS pump room leakage due primarily to a RilR pump seal failure.
In the original FSAR, which the NRC SER was written from, paragraph 15.4.1.3.5 stated "Upon initiation of the SIS signal the penetration room ventilation systems will be switched to accident mode with the flow... In that same FSAR, in paragraph 6.2.3.5.2 it stated "When aligned in the normal operating mode, both trains of the penetration room filtration system are automatically started upon receipt of a containment isolation actuation signal, "P" signal." Also, in that same FSAR, logic diagrams for the starting and stopping of the PRF exhaust fan and the recirculation
fan were shown in Figures 7.2-41 & 42. Both of these figures had 'Contmt isol Signal (P) Phase
- B" K626' as input signals to automatically start cach fan. The statement in paragraph 15.4.1.3.5 used the tenn SIS signal. This can be taken as a generic term for all safety injection signals i
including both Phase A and Phase B. It is SNC's belief that the original FSAR presented the automatic start of the PRF fans as a Phase B signal and that the SER statement was based on the reading of only the information contained in Chapter 15. Resision 0 of the updated FSAR removed the statement regarding starting upon receipt of an SIS signal in paragraph 15.4.1.3.5.
Nonnal alignment of the PRF system per the licensing basis is to have the system aligned to take f action on the spent fuel pool area for a fuel handling accident. During a LOCA, the two pneumatically operated spent fuel pool suction valves are manually shut by the operator prior to post LOCA rreirculation to isolate the fuel handling area from the penetration room filtration system.
He FNP FSAR describes the large break LOCA (LBLOCA) analysis as a bounding condition for LOCA events and Control Rod Ejection events %c LBLOCA event is categorized as a Condition IV " limiting fault" and applies to breaks greater than or equal to 1 SQFT. The large break analysis is based on conservative worst case conditions including signi6 cant core damage and fuel melting.
The PRF system is needed for this accident to ensure that ECCS pump room leakage into the penetration room boundary during post LOCA recirculation is filtered prior to release. This ensures that 10 CFR Part 100 and GDC 19 limits will be met. During the LDLOCA event containment pressure is expected to reach a nominal 27 PSIO, which is the setpoint to automatically start the PRF system.
%c FNP FSA R considers breaks less than i SQFT to be small break LOCA (SBLOCA) conditions and classific.$ them as Condition ill " infrequent events". By defmition Condition ill events result in source terms that are small fractions of those from Condition IV cvents. Automatic starting of the PRF system will not always occur for SELOCA events. Recent dose calculations considering SBLOCA conservative source terms havr. been performed. ney assume no credit for PRF filtered release of both containment and ECCS system leakage and indicate that 10 CFR Part 100 and GDC 19 limits would not be exceeded even considering ECCS leakage. This is because the radioactive source tenns are considerably smaller than those assumed based on the limiting large break LOCA described in the FSAR. Manual starting of the PRF system is not necessary in this case to meet 10 CFR Part 100 and GDC 19 limits. This conclusion is also consistent with the automatic start design features of the system which would start the system automatically when it is needed.
The original Farley Technical Speci6 cations Bases section 3/4.7.8 states that the " operability of the penetration room filtration system ensures that radioactive materials leaking from the mechanical equipment in the pump rooms following a LOCA are filtered and adsorbed prior to reaching the emironment,"
In sununary 10 CFR Part 100 and GDC 19 limits are met with the current design and procedural operation of the system. Starting the PRF system for SBLOCA events is not required and LBLOCA events will result in automatic starting of the system. Based on ALARA considerations and overall dose reduction etTorts, procedures have been revised to require starting of the PRF system prior to establishing ECCS recirculation Cow for any LOCA event.
o De licensing basis of the penetration room filtration system is to filter releases from a Fila in the spent fuel pool area and to operate during the post LOCA recirculation phase of an accident to ensure that ECCS pump room leakage passes through the filter system prior to release to the environment. The alignment of the penetration room filtration system to the ECCS pump rooms is performed manually prior to the start of any post LOCA recirculation.
NRC Ouestion No. 2 If the original design basis has changed, please providejustification for the change. Please include any 10 CFR $0.59 evaluation that may have been donc and/or any other analyses that may have been made to support the current design and operating philosophy.
SNC Resnonse No.2
%cre have been no changes to the PRF system design basis except the changes as the result of the containment spray addition tank deletion on Unit 1. De automatic starting logic and design operation are the same as originally designed. %c FS AR did contain conflicting statements, but the automatic starting logic as presented in the FSAR has always been on a phase B signal (old Westinghouse P signal), %c conflicting statements in the FSAR have been identified and are being corrected using 10 CFR 50.59 cvaluations to correct the text to the design basis. Also, a Technical Specification amendment has been submitted for approval on the PRF system and other filtration systems and there are several changes to the FSAR associated with that amendment.
Copics of these evaluations and the associated changes are available for your review if you desire.
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