ML20058G900
| ML20058G900 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 11/30/1993 |
| From: | Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20058G902 | List: |
| References | |
| NUDOCS 9312100172 | |
| Download: ML20058G900 (16) | |
Text
-
PHILADELPlHA ELECTRIC COMPANY NUCLEAR GROUP HEADQUARTERS 955-65 CHESTERBROOK BLVD.
WAYNE, PA 19087-5691 i (215) M04000 STATION SUPPORT DEPARTMENT November 30, 1993 Docket Nos. 50-352 ,
50-353-1.1 cense Nos, NPF-39 NPF-85 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk '
Washington, DC 20555
SUBJECT:
Limerick Generating Station, Units 1 and 2 Technical Specifications Change Request Gentlemen: ;
Philadelphia Electric Company (PECO) is submitting Technical i Specif#nt 9ns (TS) Change Request No. 93-07-0, in accordance with 10CFR50.90, reque m o change to the TS (i.e., Appendix A) of Operating License Nos.
Ni'F4 5 FPF-85 for Limerick Generating Station (LGS), Units 1 and 2.
"t 1 iS Change Request involves a change to extend the surveillance interve,
- the primary containment drywell-to-suppression chamber bypass leak test from the current 18 month interval as required by TS Surveillance Requirement 4.6.2.1.d to a 40 +/- 10 month interval. This change would allow the drywell-to-suppression chamber bypass test to coincide with the 10CFR50, Appendix J, Type A test (i.e., Containment Integrated Leakage Rate Test ,
(CILRT)) interval. Currently, TS would require performing the Unit I drywell-to-suppression chamber bypass leak test during the fifth Unit I refueling outage scheduled to begin January 29, 1993.
The NRC has previously approved a similar request for the Pennsylvania Power and Light Company, Susquehanna Steam Electric Station, Units 1 and 2, by letter dated August 11, 1993. The Susquehanna Steam Electric Station i containment design is essentially the same as that for LGS, Unit I and Unit 2.
Accordingly, this Change Request is considered a Cost Beneficini licensing Action.
('1700 J~ /
r n\ ,
fV I
vm _100172 931130 -
PLi; ADOCK 05000352 ,
i p PDR m -
d!S.NUCLEARREGULATORYCOMMISSION NOVEMBER 30, 1993 DOCUMENT CONTROL DESK. PAGE 2 ;
i Information supporting this TS Change Request is contained in Attachment !
I to this letter, and the proposed replacement pages for the LGS, Unit 1 and Unit 2 TS are contained in Attachment 2.
We request that, if approved, this TS Change Request for LGS, Units 1 and 2, be effective by February 14, 1994.
If you heve any questions, please do not hesitate to contact us.
Very truly yours, '
.h.b $AA, G. A. Hunge6 Jr.I,%.
Director Licensing Section !
Attachments cc: T. T. Martin, Administrator, Region I, USNRC (w/ attachments)
N. S. Perry, USNRC Senior Resident Inspector, LGS (w/ attachments) ;
W. P. Dornsife, Director, PA Bureau of Radiological Protection :
(w/ attachments) l t
l l
l
1 COMMONWEALTH OF PENNSY. ANIA :
- ss. ;
COUNTY OF CHESTER : !
?
D. R. Helwig, being first duly sworn, deposes and says:
That he is Vice President of Philadelphia Electric Company; the Applicant herein; that he has read the enclosed Technical Specifications Change Request No. !
93 ' " Extend the Drywell-to-Suppression Chamber Bypass Leak Test Surveillance j Interval," for Limerick Generating Station, Unit I and Unit 2) Facility Operating ;
License Nos. NPF-39 and NPF-85, and knows the contents thereof; and that the ,
, statements and matters set forth therein are true and correct to the best of his knowledge, information and belief.
I O ~
UI TN]4e- ' ;
Vice President ' i t
i Subscribed and sworn to before me this # day of' 7 L .1993.
/t
& h , ;nkh'&
/
i > , ,
c .
_- ,/ -
4 ;
Notary Public f
tttauf SwJ Enca A.Sstort teray PJ4:
T%fhalle,Chrsted Cost /
i t/y Cemw.nEgmMy 10.1995 t
m, -
I l
i ATTACHMENT 1 l
LIMERICK GENERATING STATION i
UNITS 1 AND 2 DOCKET NOS. 50-352 i 50-353 j LICENSE NOS. NPF-39 NPF-85 l l
TECHNICAL SPECIFICATIONS CHANGE REQUEST NO. 93-07-0 l
" Revise Technical Specifications to Extend l the Drywell-to-Suppression Chamber Bypass l Leak Test Surveillance Interval"
\
Supporting Information for Changes - 12 pages. l l
l
~ '
PAGE 1 Philadelphia Electric Company (PEco), Licensee under Facility Operating License Nos. NPF-39 and NPF-85 for Limerick Generating Station (LGS), Units 1 and 2, requests that the Technical Specifications (TS) contained in appendix A to the Operating Licenses be amended as proposed herein, to extend the surveillance interval of the primary containment drywell-to-suppression chamber bypass leak test from the current 18 month interval to a 40 +/- 10 month interval. These changes would allow the drywell-to-suppression chamber bypass test to coincide with the 10CFR50, Appendix J, Type A test interval. i In addition, the proposed changes add an additional surveillance requirement to measure the leakage of the drywell-to-suppression chamber vacuum breakers during those unit outages when the drywell-to-suppression chamber bypass leak test is not required to be performed.
These proposed TS changes involve revising the current TS Surveillance Requirement (SR) 4.6.2.1.d which states in part that the suppression chamber shall be demonstrated operable, "At least once per 18 months by conducting a drywell-to-suppression chamber bypass leak test et an initial differential pressure of 4 psi and verifying that the A/(k calculated from the measured leakage is within the specified limit. If any drywell-to-suppression chamber bypass leak test fails to meet the specified limit, se test schedule for subsequent tests shall be reviewed and approved by the Commission. If two consecutive tests fail to meet the specified limit, a test shall be performed ,
at least every 9 months until two consecutive tests meet the specified limit, at which time the 18 month test schedule may be resumed."
These proposed TS changes also involve adding a new surveillance requirement to SR 4.6.2.1 and associated changes to TS Bases, "Depressurization Systems," which describe the above proposed changes.
The proposed changes to the TS pages are indicated by a vertical bar in the margin of the affected TS pages. The TS pages showing the proposed changes are contained in Attachment 2. ,
We request that, if approved, the amendment to the LGS, Un d I and '
Unit 2 TS be effective by February 14, 1994.
This submittal provides a discussion and description of the proposed TS changes, a Safety Assessment of the proposed TS changes, Information Supporting a Finding of No Significant Hazards Consideration, and Information Supporting an Environmental Assessment.
Discussion and Description of the Proposed Chanaes These proposed Technical Specifications (TS) changes involve revising .
the current Limerick Generating Station (LGS), TS Surveillance Requirement I (SR) 4.6.2.1.d which states in part that the suppression chamber shall be demonstrated operable, "At least once per 18 months by conducting a drywell-to-suppression chamber bypass leak test at an initial differential pressure of 4 psi and verifying that the A/(k calculated from the measured leakage is within the specified limit. If any drywell-to-suppression chamber bypass leak test fails to meet the specified limit, the test schedule for subsequent tests shall be reviewed and approved by the Commission. If two consecutive tests i fail to meet the specified limit, a test shall be performed at least every 9 I months until two consecutive tests meet the specified limit, at which time the l
' ~
PAGE 2 18 month test schedule may be resumed." These proposed TS changes also involve adding a new provision to SR 4.6.2.1 that requires the measurement of the leakage of the drywell-to-suppression chamber vacuum breakers during those unit outages when the drywell-to-suppression chamber bypass leak test is not ,
required to be performed, and associated changas to the TS Bases, "Depressurization Systems," describing the above proposed changes.
The LGS U..it I and Unit 2 containments are of the Mark II design, each having the drywell located over the suppression chamber. The drywell and suppression chamber are separated by a diaphragm slab. The suppression chamber contains a pool of water with a depth that varies between 22' and
- 24'3" during normal operation. Eighty-seven downcomers and 14 Main Steam Safety / Relief Valve (SRV) discharge lines penetrate the diaphragm slab and terminate at a pre-designed submergence within the pool. During a loss of Coolant Accident (LOCA) inside containment, the containment design directs steam from the drywell to the suppression pool by means of the downcomers through the pool of water to limit the maximum containment pressure response to less than the design value of 55.0 psig. The effectiveness of the LGS Unit I and Unit 2 containment design requires that the leak path from the drywell to the suppression chamber airspace be minimized. Steam that enters the suppression pool airspace through leak paths will bypass the suppression pool and can result in a rapid post-LOCA increase in containment pressure depending on the size of the bypass flow area. TS SR 4.6.2.1.d currently requires that this bypass leakage be measured every 18 months to ensure that it remains t within analyzed values.
The proposed TS changes revise TS SR 4.6.2.1.d to state the following.
"Drywell-to-suppression chamber bypass leak tests shall be conducted at 40 +/- 10 month intervals to coincide with the ILRT at an initial differential pressure of 4 psi and verifying that the A//k calculated from the measured leakage is within the specified limit. If any drywell-to-suppression chamber bypass leak test fails to meet the specified limit, the test schedule for subsequent tests shall be ,
reviewed and approved by the Commission. If two consecutive tests fail to meet the specified limit, a test shall be performed at least every 24
! months until two consecutive tests meet tM specified limit, at which time the test schedule may be resumed."
The proposed TS changes will include the following additional TS SR 4.6.2.1.e, for those unit uutages where the drywell-to-suppression chamber bypass leak test is not required to be performed.
"By conducting a leakage test on the drywell-to-suppression chamber vacuum breakers at a differential pressure of at least 4.0 psi and verifying that the total leakage area A/(k contributed by all vacuum breakers is less than or equal to 24% of the specified limit and the leakage area for an individual set of vacuum breakers is less than or l
equal to 12% of the specified limit. The vacuum breaker leakage test I shall be conducted during each refueling outage for which the drywell-to-suppression chamber bypass leak test in Specification 4.6.2.1.d is not conducted."
PAGE 3
^
The proposed TS changes revise TS Bases 4.6.2 to add two additional j paragraphs to clarify the purpose of the bypass and vacuum breaker leakage i tests. l "During a LOCA, potential leak paths between the drywell and suppression !
chamber airspace could result in excessive containment pressures, since i the steam flow into the airspace would bypass the heat sink capabilities- !
of the chamber airspace. Potential sources of bypass leakage are the !
suppre:,sion chamber-to-drywell vacuum breakers (VBs), penetrations in the diaphragm floor, and cracks in the diaphragm floor andhr liner ,
plate and downcomers located in the suppression chamber a' ' ace. The {
. containment pressure response to the postulated bypass 1. H.ge can be !
An ;
mitigated by manually analysis was performdactuating the suppression for a design chamber bypass leakage area spray of A/ k(s.equal to ;
0.0500 ft" to verify that the operator has sufficient time to initiate r the sprays prior to exceeding the containment design pressure of 55
~
psig. The limit of 10% of the design value of 0.0500 ft' ensures that i the design basis for steam bypass analysis is met. !
The drywell-to-suppression chamber bypass leak test at a differential ,
pressure of at least 4.0 psi verifies over&11 bypass leakage area for !
simulated LOCA conditions is less than the specified limit. For those
~
outages where the drywell-to-suppression chamber bypass leakage test is not conducted, the vacuum breakers leakage test verifies that the vacuum i breakers leakage area is less than the bypass limit, with a 76% margin j to the bypass limit to accommodate the remaining potential-' leakage area !
through the passive structural components. Previous drywell-to- 4 suppression chamber bypass leak test data indicates that the bypass :
leakage through the passive structural components will be much less than i the 76% margin. The vacuum breakers leakage limit, combined with the -
negligible passive structural leakage area, ensures that the drywell-to- i suppression chamber bypass leakage limit is met for those outages for 4 which the drywell-to-suppression chamber bypass leak test is not
~
scheduled."
This TS Change Request involves proposed changes to extend the surveillance interval of the drywell-to-suppression chamber bypass leak test [
from the current 18 month interval to a 40 +/- 10 month interval, and to ,
increase the test interval from nine to 24 months if two consecutive tests fail to meet the specified limit. These changes would allow the drywell-to- t suppression chamber bypass test to coincide with the 10CFR50, Appendix J, Type :
A test interval. This TS Change Request also proposes to add a new ,
surveillance requirement that measure the leakage of the drywell-to- 1~
suppression chamber vacuum breakers during those unit outages when the drywell-to-suppression chamber bypass leak test is not required to be .
performed. The LGS Updated Final Safety Analysis Report (UFSAR) Section 6.2.6 i describes the requirements for performing the drywell to suppression chamber bypass leak test. '
Safety Assessment The proposed Technical Specifications (TS) changes will extend the !
Limerick Generating Station (LGS) Unit I and Unit 2 TS surveillance interval :
for the drywell-to-suppression chamber bypass leak test from 18 months .to 40 l
+/- 10 months. This will allow this test to be performed during the same j interyc1 as the 10CFR50, Appendix J, Type A test (i.e., Containment Integrated !
J
- s. .
PAGE 4
, Leakage Rate Test (CILRT)). In addition, the proposed changes will add an I additional surveillance requirement to be performed on the drywell-to- I suppression chamber vacuum breaker assemblies during refueling outages when l the drywell-to-suppression chamber bypass leak test is not required to be :
performed. The proposed changes do not increase the consequences of an I accident as previously evaluated. This is based on the evaluation below which '
demonstrates that the overall impact, if any, on the plant primary containment integrity is negligible. Furthermore,- the performance history for the ,
previous LGS bypass leak test < do not indica' any time based failures. The ;
proposed TS changes also include a change to ' frequency of testing, if two consecutive bypass leak tests fail, from once every nine (9) months to once every 24 months. This change has no impact on the probability.of excess !
bypass leakage based on maintaining the original requirement to increase the !
frequency of testing if two consecutive bypass leak tests fail and maintaining l the TS requirement for the NRC to review the schedule for subsequent tests. l During a Loss of Coolant Accident (LOCA) inside containment, potential i leakage paths between the drywell and suppression chamber airspace could i result in excessive containment pressures, since the steam flow into the airspace would bypass the heat sink capabilities of the suppression pool. The
- containment pressure response to the postulated bypass leakage can be mitigated by manually actuating the suppression chamber sprays. Accordingly, since the sprays are manually actuated, an analysis was performed to show that ,
the operator has sufficient time to initiate the sprays prior to exceeding the containment design pressure. This analysis is described in Section 6.2.1.1.5 -
of the LGS Updated Final Safety Analysis Report (UFSAR). The analysis is based on a tmall break LOCA inside containment with a differential pressure l between the drywell and the suppression chamber equal to the static pressure due to the downcomer submergence. The analysis concludes that the containment design pressure of 55 psig will be reached in over 30 minutes from-the onset of the small break LOCA assuming a drywell-to-suppression chamber bypass flow 1 area (i.e., A//k) equal to 7.20 in' without operator intervention.
Since these proposed TS changes introduce the possibi?ity that the ,
drywell-to-suppression chamber bypass leakage would go und stected during the :
proposed extension, two potential bypass leakage path categories were i evaluated. q
- 1) Leakage pathways other than those associated with the drywell-to-suppression chamber vacuum breaker assemblies ;
such as diaphragm floor penetrations (i.e., downcomer and i Main Steam Safety / Relief Valve (SRV) discharge line :
penetrations), cracks in the diaphragm floor and / or liner ;
plate, and cracks in the downcomers and SRV discharge lines :
that pass through the suppression chamber airspace.
- 2) The four sets of drywell-to-suppression chamber vacuum breaker assemblies, i The conclusion of this evaluation determined that leakage from pathways
. other than drywell-to-suppression chamber vacuum breaker assemblies is ;
negligible based on the design features and fabrication specifications for i drywell-to-suppression chamber components. Previous LGS Unit I and Unit.2 drywell-to-suppression chamber test results, and applicable test data from l Pennsylvania Power and Light, Susquehanna Steam Electric Station (SSES), j further verify this-conclusion. The Mark 11 containment design employed for
1
Since the most likely source of potential drywell-to-suppression chamber bypass leakage are the four sets of drywell-to-suppression chamber containment vacuum breakers, this Change Request includes a proposed requirement to perform a leakage test on each set of drywell-to-suppression chamber vacuum breakers (i.e., there are four vacuum breaker sets per unit) during each refueling outage when the TS drywell-to-suppression chamber bypass leak test would not be required to be performed. If maintenance is performed on the vacuum breakers, this proposed test will be required to be performed to verify that the post-maintenance vacuum breaker leakage is acceptable. Appropriate controls associated with vacuum breaker post-maintenance testing will be established. This proposed test will be conducted at a drywell-to-suppression chamber differential pressure of 4.0 psi (i.e., the same differential pressure as required for the drywell-to-suppression chamber bypass leak test) by either pressurizing the drywell side of the vacuum breakers or inducing a vacuum on the suppression chamber side of the vacuum breakers.
In addition, a review of the potential bypass flow paths between the drywell and suppression chamber airspace by means of cross-connected piping systems external to the containment was performed. Based on the information below, we have concluded that the potential leakage from these lines has minimal affect on the drywell-to-suppression chamber bypass leakage area and ,
therefore supports the proposed TS changes. '
The systems with piping external to the containment that are a potential source of drywell-to-suppression chamber leakage are listed below.
- 1) Containment vent and purge lines (20" and 24" diameter lines with two flow paths from the drywell to the suppression chamber).
- 2) Drywell and suppression chamber spray lines (18" and 6" diameter lines with two flow paths from the drywell to the suppression chamber).
- 3) Containment Integrated Leak Rate Test data acquisition system line (3/4" diameter lines with one flow path from the drywell to the suppression chamber).
- 4) Containment atmosphere sampling lines (1" and 2" diameter lines with two flow paths from the drywell to the suppression chamber).
- 5) Containment instrument gas line (l" diameter lines with two flow paths from the drywell to the suppression chamber).
The potential bypass leakage from the above cross-connected piping systems flow paths is considered to be negligible compared to the TS allowable drywell-to-suppression chamber bypass leakage (i.e., 0.720 in') based on the following.
The cross-connected piping is isolated from containment by drywell and suppression chamber containment isolation valves. All flow paths have multiple, in-series containment isolation valves that are designed to meet
.l
- i l
PAGE 6 l stringent leakage criteria as specified in 10CFR50, Appendix J. TS require performance of a periodic Local Leak Rate Test (LLRT) to ensure that the valves comply with the 10CFR50, Appendix J, Type C test criteria. Therefore, :
leakage from the drywell to the suppression chamber airspace can only occur through multiple isolation valves.
A bounding analysis has been performed to determine the maximum potential bypass leakage area from the above sources. The leakage area was <
derived from the TS allowable leakage for the containment isolation valves located in the potential flow paths. The TS allowable leakage from the 10CfR50, Appendix J, Type B and Type C (i.e., LLRT) testing boundaries is 60% i (0.6) of the allowed leakage, La (i.e., 94,964 scc / min). A conservative estimate of the potential leakage can be determined by assuming that the total TS allowable leakage is bypassed to the suppression chamber airspace. The 0.6 La is a bounding leakage rate since it includes valves with the potential to '
bypass and includes all other valves and penetrations subject to Type B and Type C testing. The equivalent leakage area (i.e., A/(k) for a leakage rate of 94,964 scc / min at the safety analysis peak accident primary containment pressure of 44 psig is 0.00845 in' which is 1.17 % of the TS allowable bypcss leakage area of 0.720 in'. The average total LLRT results for the previous six LGS refueling outages is 56,222 scc / min. The equivalent leakage area (i.e., Alk) corresponding to this average leakage is 0.0050 in' or 0.7 % of the TS allowable bypass leakage area of 0.720 in'.
The LGS LLRT program is procedurally controlled and requires that program goals be set to define a target LLRT leakage rate for each isolation valve. The target leakage rates are based on the prior leakage history for each valve, coupled with a LLRT program philosophy that emphasizes the need to ,
maintain LLRT leakage as low as practical. The program requires leakages that exceed the target values be investigated to determine if corrections must be :
made to LLRT totals. .
Information Supportina a Findina of No Sionificant Hazards Consideration. ,
i We have concluded that the proposed changes to the Limerick Generation Station (LGS), Units 1 and 2, Technical Specifications (TS) to extend the surveillance interval of the drywell-to-suppression chamber bypass leak test from the current 18 month interval to a 40 +/- 10 month interval that would ,
coincide with the 10CFR50, Appendix J, Type A test interval does not involve a Significant Hazards Consideration. In support of this determination, an ,
evaluation of each of the three (3) standards, set forth in 10CFR50.92 is provided below.
- 1. The proposed Technical Specifications (TSL chanaes do not involve a sianificant increase in the probability or consecuences of an accident previous 1v evaluated.
The failure effects that are potentially created by the proposed '
Technical Specifications (TS) changes have been considered. The accident which is potentially negatively impacted by the proposed TS -
changes are any Loss of Coolant Accident (LOCA) inside primary containment with or without off:ite power available.
l l
1 i
1 4
PAGE 7 !
'The proposed TS changes increase the surveillance interval of the ,
drywell-to-suppression chamber bypass leak test required by TS Section 4.6.2.1.d., and will require that an additional test be performed on the downcomer vacuum breakers assemblies. The primary containment structure and associated equipment are not considered to be accident initiators, they act to mitigate the consequences of an accident. There are no physical or operational changes being made as a result of these proposed changes. Therefore, the probability of occurrence of an accident previously evaluated is not increased.
There is a potential increased risk that an increase in the bypass leakage may go undetected for the duration of the proposed extension of the interval between the performance of the drywell-to-suppression chamber bypass leak test. However, as discussed below, the increased risk is considered to be negligible due to the design of the diaphragm structure and past test data. Therefore, we have concluded that the probability of bypass leakage exceeding the allowed value is not '
increased as a result of the proposed TS changes.
The proposed TS changes will extend the surveillance interval for the drywell-to-suppression chamber bypass leak test from 18 months to 40 +/- 10 months. These proposed changes would allow this test to be performed at the same interval as the 10CFR50, Appendix J, Type A test (i.e., Containment Integrated Leakap Rate Test (CILRT)). In addition, the proposed changer. will add an additional surveillance requirement to be performed on tic vacuum breaker assemblies during refueling outages when the drywell-to-suppression chamber bypass leak test is not required to be performed. The proposed TS changes do not increase the .
consequences of an accident previously evaluated. This is based on the i evaluation summarized below that demonstrates that the overall impact, if any, on the plant containment integrity is negligible. Furthermore, ,
the performance history for the previous LGS bypass leak tests does not -
indicate any time based failures. The proposed TS changes also include a change to the frequency of testing, if two consecutive tests fail, from once every nine (9) months to once every 24 months in order to '
coincide with the 24 month refueling cycle. This change is has no impact on the consequences of an accident based on maintaining the original requirement to increase the frequency of testing if two consecutive bypass leak tests fail, and maintaining a TS requirement for the NRC to review the schedule for subsequent tests.
During a LOCA inside contair. ment, potential leak paths between the drywell and suppression chamber airspace could result in excessive containment pressures, since the steam flow into the airspace would i bypass the heat sink capabilities of the suppression pool. The '
containment pressure response to the postulated bypass leakage can be mitigated by manually actuating the suppression chamber sprays.
Accordingly, since the sprays are manually actuated, an analysis was performed to show that the operator has sufficient time to initiate the sprays prior to exceeding the containment design pressure. This analysis is described in section 6.2.1.1.5 of the LGS Updated Final Safety Analysis Report (UFSAR). The analysis is based on a small break i LOCA inside containment with a differential pressure between the 1 drywell-to-suppression chamber equal to the static pressure due to :
downcomer submergence. The analysis concludes that the containment design pressure of 55 psig will be reached in over 30 minutes from the
- i. .
PAGE 8
' onset of a small break LOCA assuming a drywell-to-suppression chamber bypass flow area (i.e., A/(k) equal to 7.20 in' without operator intervention.
TS Limiting Condition for Operation 3.6.2.1.b conservatively specifies a #
maximum allowable bypass area of 10 % of the design value of 7.20 in'.
This TS limit provides an additional safety factor of 10 above the conservatism taken in the steam bypass analysis (i.e., 0.720 in') . The drywell-to-suppression chamber bypass leak test required by TS Surveillance Requirement 4.6.2.1.d verifies that the actual bypass flow area is less than or equal to the TS limit of 0.720 in'. The bypass leakage test ensures that degradation in the measured bypass area is '
identified and corrected to ensure containment integrity during LOCA events.
The potential bypass leakage paths can be divided into two categories as described below.
- 1) Letkage pathways other than those associated with the :
drywell-to-suppression chamber vacuum breaker assemblies such as diaphragm floor penetrations (i.e., downcomer and Safety / Relief Valve (SRV) discharge line penetrations),
cracks in the diaphragm floor and/or liner plate, and cracks in the downcomers and SRV discharge lines that pass through the suppression chamber airspace.
- 2) The four sets of drywell-to-suppression chamber. vacuum breaker assemblies. ;
All other potential bypass leakage pathways have at least two isolation I valves in the potential leakage path. These valves are high quality leak-tight containment isolation valves that are normally closed and receive an isolation signal to close. All Air Operated Valves (A0Vs) in these paths fail closed. J Several plant design features and the bypass leak test data measured to date confirm that the leakage from other than the vacuum breaker assemblies is negligible and indicates that this leakage will continue :
to be negligible for the proposed increased duration between tests. All l pressure boundary penetrations between the drywell and the suppression l chamber are welded except the vacuum breaker valves and the blind flanges closing 10 spare nozzles in the downcomers. All pressure boundary penetrations between the drywell-to-suppression chamber have ,
been fabricated, erected, and inspected in accordance with the American i Society of Mechanical Engineers (ASME) Code,Section III, Subsection NC, 1971 Edition, with the exception of the tees supporting the vacuum l breakers. !
l The downcomer and SRV discharoe lines penetrate through the diaphragm slab and terminate in the suppression pool. A steel ring plate is welded to the outside of the downcomers. The downcomer/ ring plate assemblies are embedded in the diaphragm slab with the top surface of
4 PAGE 9
'the ring plate flush with the drywell side of the diaphragm slab. All connections are welded to form a continuous steel membrane between the liner plate and downcomer penetrations. The SRV discharge lines are routed through welded flued heads at the diaphragm floor. The flued head design and construction are similar to the downcomer penetrations and also provide a continuous steel barrier. The downcomer and SRV discharge lines are designed and constructed to safety-related requirements. In addition, they are designed for all postulated loading conditions, includin-) seismic, hydrodynamic, pressure, and temperature loads. The conservative design requirements ensure that the SRV discharge and the downcomer lines will not contribute to bypass leakage.
The diaphragm floor is a reinforced concrete slab approximately 3.5 feet thick. The drywell side surface of the diaphragm slab is capped with a 1/4 inch thick carbon steel liner plate. The liner plate and diaphragm slab provide a barrier against the potential for bypass leakage through the diaphragm floor. The structural integrity of the diaphragm floor and penetrations was demonstrated during the pre-operational test program.
The drywell was pressurized to a drywell-to-suppression chamber differential pressure of above 30 psid, which envelopes the maximum drywell-to-suppression chamber differential pressure postulated to occur ,
during LOCA conditions.
There have been six Unit I and three Unit 2 bypass leak tests performed in accordance with TS Surveillance Requirement 4.6.2.1.d. These tests were conducted at a drywell-to-suppression chamber differential pressure of at least 4.0 psid. The measured leakage area includes leakage from both the vacuum breakers and sources other than vacuum breakers.
In all cases, the measured leakage is significanny less than the TS and design values. The maximum measured leakage areas are 0.0400 in' and 0.0114 in' for Unit 1 and Unit 2, respectively; or 5.56% and 1.55 %,
respectively, of the TS limit. The average values are 0.0180 in' for Unit I and 0.0107 in' for Unit 2; or 2.5% and 1.49%, respectively, of the TS limit of 0.720 in'. The minimum measured leakage areas are 0.0 in' and 0.0100 in' for Unit I and Unit 2, respectively, or 0% and 1.3 %,
respectively, of the TS limit. Clearly, the test data confirm that the bypass leakage measured to date at LGS has been negligible.
In addition, we have obtained bypass leakage data from the Pennsylvania Power and Light Company, Susquehanna Steam Electric Station (SSES),
Units 1 and 2, which also has Mark 11 containments with the Anderson Greenwood vacuum breakers (i.e., the same manufacturer as the vacuum breakers installed in the LGS, Unit I and Unit 2 containments) and therefore the dita is applicable to LGS. The maximum bypass leakage
. area for the SSES Unit I containment was 0.037 in', and 0.009 in' for the SSES Unit 2 containment, or 4.81% and 1.17%, respectively, of the SSES ,
TS limit. Approval for a similar TS chaw for SSES, Units I and 2 was !
issued by the NRC by letter dated Aumn ., 1993. j The remaining and most likely source m potential bypass leakage is the l four sets of drywell-to-suppression chamber vacuum breakers. Each set consists of two vacuum breakers in series, flange mounted to a tee off the downcomers in the suppression chamber airspace. The drywell-to-suppression chamber bypass leak test is currently required by TS l
'. \
. l 1 .
4 PAGE 10
' Surveillance Requirement 4.6.2.1.d to be completed during each refueling outage and the results are used to verify that the total bypass area, including that due to the vacuum breakers, meets the TS limit. If maintenance has been performed on the vacuum breakers, this test also serves as a post-maintenance vacuum breakers leakage area test, j The proposed TS changes decrease the frequency of the drywell-to-suppression chamber bypass leak test. The drywell-to-suppression ,
chamber bypass leak test data obtained following vacuum breakers i maintenance can not be utilized to determine vacuum Lreakers leakage l reliability over the duration of the propose test interval extension.
To address this concern and collect additional vacuum breakers leakage data, the proposed TS changes include an additional requirement to perform a vacuum breaker leakage test as described below.
The leakage test will be conducted on each set of vacuum breakers (i.e.,
four vacuum breakers sets per unit) during each refueling outage when the drywell-to-suppression chamber bypass leak test would not be required to be performed. If maintenance is performed on the vacuum breaker assemblies, this additional test will be performed post-maintenance to verify that the leakage is acceptable. This test will be conducted at a drywell-to-suppression chamber differential pressure of 4.0 psid (i.e., the same as differential pressure required for the drywell-to-suppression chamber bypass leak test) by either pressurizing the drywell side of the vacuum breakers or inducing a vacuum on the suppression chamber side of the vacuum breakers. The acceptance criteria for the vacuum breaker leakage tests will be as follows. The ;
total vacuum breaker leakage areas for all four sets of vacuum breakers will be less than or equal to 24% of the TS limit (i.e., 0.24 x 0.720 i n' - 0.173 ' n') . This proposed acceptable vacuum breaker leakage area provides a N% margin to the TS limit to account for the leakage paths other than ine vacuum breakers. As described above, previous bypass leakage testing measured a maximum bypass leakage area of 5.56% of the TS limit. The 76% margin is sufficiently large to accommodate the other expected leakage sources. In addition, each set of vacuum breakers will be limited to a leakage area twice the assumed leakage from a single vacuum breaker set, assuming the leakage area is evenly distributed among the four sets of vacuum breakers (i.e., four sets equate to 24% of the TS Limit where each set is 6% and twice this total is 12% of the TS Limit). This allows a leakage of less than or equal to 0.0865 in' (i.e., (0.173 in' + 4 sets of vacuum breakers) x (a factor of 2 times the acceptable total) - 0.0865 in') for an individual set of vacuum breakers. This criterion is stipulated to identify individual sets :f '
vacuum breakers with higher leakage area.
l The artwell-to-suppression chamber bypass leak test data obtained during l previeus testing at LGS demonstrates conformance by a large margin ;
compared to the TS and design leakage requirements. The test data !
indicates that there is negligible risk that the bypass leakage will change adversely in future years. Furthermore, the proposed test frequency is judged to be acceptable based on the risk of the leakage sources other than the vacuum breakers being essentially equivalent to that of the rest of the primary containment structure, which is leak l
l
1 .
l PAGE 11
' tested (i.e., CILRT) every 40 +/- 10 months as required by TS Surveillance Requirement 4.6.1.2.a. A bypass leak test will be deseloped and conducted to verify acceptable vacuum breaker bypass leakage areas for those outages when the bypass leak test'will not be required to be performed. The proposed vacuum breaker leakage test with stringent acceptance criteria, combined with other negligible leakage areas, provide an acceptable level of assurance that the bypass leakage can be measured and an adverse condition can be detected and corrected such that the existing level of confidence that the primary containment will function as required during a LOCA is maintained.
Therefore, the proposed TS changes will not involve an increase in the probability or consequences of an accident previously evaluated. ,
- 2. The proposed TS Chances do not create the possibility of a new or .
different kind of accident from any accident oreviousiv evaluated.
The proposed TS changes involve the drywell-to-suppression chamber bypass leak test frequency. There are no physical or operational changes as a result of these proposed changes. These proposed changes include the requirement to perform an additional surveillance test on the vacuum breaker assemblies, applying a differential pressure of 4.0 psid which is the same differential pressure as currently required by TS for the drywell-to-ruppression chamber bypass leak test. This required test will ensure that acceptable vacuum breaker leakage is maintained during those intervals when the drywell-to-suppression chamber bypass leak test is not required to be performed. Furthermore, the affected !
structure (i.e., primary containment) acts as an accident mitigator and not as an accident initiator. Accordingly, the possibility of a different type of malfunction of equipment or the possibility of an accident of a different type is not introduced.
Therefore, the proposed TS changes do not create the possibility of a new or different kind of accident from any accident previously evaluated.
- 3. The oroposed TS chanaes do not involve a sianificant reduction in a marain of safety.
The drywell-to-suppression chamber bypass leak test data obtained during previous testing at LGS demonstrates conformance by a large margin to the TS and design leakage requirements. The test data 1 indicate that there is negligible risk that the bypass leakage will j change adversely in future years. Furthermore, the proposed test frequency is judged to be acceptable based on the risk of sources of leakage other than the vacuum breakers being essentially equivalent to that of the rest of the primary containment structure, which is tested every 40 +/- 10 months. A bypass leak test will be developed and conducted to verify acceptable vacuum breaker bypass leakage areas for those outages when the bypass leak test will not be required to be performed. The proposed vacuum breaker leakage test with stringent ,
acceptance criteria, combined with the other negligible potential j leakage areas, provide an acceptable level of assurance that the bypass i leakage can be measured and an adverse condition can be detected and I corrected such that the existing levels of confidence that the primary i containment will function as required during = LQCA is maintained. j i
l
PAGE 12 s
Therefore, the consequences of an accident are not impacted by this change and containment integrity during a LOCA will be maintained.
Therefore, the proposed TS changes do not involve a reduction in a margin of safety.
Jnformation Supportina an Environmental Assessment An Environmental Assessment is not required for the Technical Specifications (TS) changes proposed by this Change Request because the requested changes to the Limerick Generating Station (LGS), Units 1 and 2, TS conform to the criteria for " actions eligible for categorical exclusion," as specified in 10CFR51.22(c)(9). The proposed TS changes do not involve a Significant Hazards Consideration as discussed in the preceding safety assessment section. The proposed changes do not involve a significant change in the types or significant increase in the amounts of any effluent that may be released offsite. In addition, the propt ed TS changes do not involve a significant increase in individual or curoulative occupational radiation exposure.
fonclusion The Plant Operations Review Committee and the Nuclear Review Board have reviewed these proposed changes to the Limerick Generating Station (LGS), Units 1 and 2, Technical Specifications (TS) and have concluded that they do not involve an unreviewed safety question, and will not endanger the health and safety of the public.