ML20071G167
| ML20071G167 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities  |
| Issue date: | 07/06/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20071G134 | List: |
| References | |
| IEB-93-003, IEB-93-3, IEIN-93-089, IEIN-93-89, NUDOCS 9407120080 | |
| Download: ML20071G167 (10) | |
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WASHINGTON, D C. 70%$ ac1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.128 TO FACILITY OPERATING LICENSE NO. DPR-19 AMENDMENT NO 122 TO FACIllTY OPERATING LICENSE NO. DPR-25.
AMENDMENT NO.148 TO FACILITY OPERATING LICENSE NO. DPR-29 AND AMENDMENT NO. 144 TO FACILITY OPERATING LICENSE NO. DPR-30 COMMONWEALTH EDISON COMPANY AN,D IOWA-ILLIN0IS GAS AND EL ECTRIC COMPANY DRESDEN NUCLEAR POWER STATION. UNITS 2 AND 3 OVAD CITIES NUCLEAR POWER STATION. UNITS 1 AND 2 DOCKET NOS. 50-237. 50-249. 50-254 AND 50-265 1.0 jfLTRQEUCTION Commonwealth Edison Company (CECO, the licensee) proposed to modify the reactor vessel level instrumentation system (RVLIS) at Dresden and Quad Cities Statinns in response to NRC Bulletin 93-03, " Resolution of Issues Related to-Reactor Water Level Instrumentation in BWRs." The installation of these-
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modifications-will enhance plant safety by assuring that the degassing phenomenon described in Bulletin 93-03 will= not be encountered.
Dissolved-gases in the RVLIS piping may produce uncertainties in the level instrumentation during reactor pressure vessel-(RPV) depressurization, by providing fegassed control rod-drive (CRD) water to the RVLIS reference leg piping this modification will eliminate the uncertainties.
The proposed design and modification ensures that a continuous column of water, free of non-condensible gases, is maintained in the~ RVLIS reference leg piping.
The piping design of the proposed modifications was chosen to-physically-eliminate the consequences of an inadvertent closure of the-instrument rack reference leg-root valve associated with the RVLIS configuration that provides the trip actuation function as described in Informatjon Notice (IN) 93-89
" Potential Problems with BWR Level' Instrumentation Backfill Modifications;"
Concerns over the valve lootion have been previously discussed with the licensee.
The configuration of the modifications connects the non-safety-related CRD system piping to each safety-related division of RPV instrumentation, post l
accident indication and' the feedwater level control s'ystem (FWCS) m 4
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. accictnt indication and the feedwater level control system (FWCS) instrumentation.
The proposed modification includes the installation of redundant check valves to isolate the safety-related piping from non-safety-related piping, thereby limiting the loss of reactor coolant in the event of a postulated failure in the non-safety-related CRD system.
The backfill piping connects into the reference legs inboard of the primary containment isolation valves.
This design categorizes these lines as part of the reactor coolant pressure boundary.
Therefore, the check valves associated with the backfill instrument lines are considered primary containment isolation valves and meet the criteria for inclusion in Technical Specification (TS) Section 3.7 D.1 and 3.7.D.2 for Dresden and Quad Cities.
Technical Specification 3/4.7.D, " Primary Containment Isolation Valves,"
defines the limiting conditions for operation for primary containment isolation valves.
Addition of the reference leg backfill check valves to Technical Specification 3.7,D.1 and 3.7.D 2 will ensure that the valves are r air,t a! red and monitored as primary containment isolation valves.
In addition. the NRC staff is evaluating the proposed modification to meet the intent of the Bulletin, and the licensee's proposed schedule for implementation.
2.0 EU LL4110N Moa:i ustions are being made to add a backfill system for the RVLIS reference legs at Dresden and Quad Cities Stations in response to the Bulletin.
The modifications will connect backfill piping to the RPV reference leg instrument lines.
The purpose of the backfill piping is to provide a continuous flow of degassed CRD system water to the RVLIS reference leg piping.
This will ensure that a continuous column of water, free of any non-condensible gases, is maintained in the reference leg piping.
This modification will eliminate the occurrence of the " notching" effect in the RPV level instrumentation during RPV depressurization due to the presence of dissolved gases.
The design of the backfill system injects water from the CRD system to the instrument reference legs between the containment penetration and the existing primary containment isolation valves (excess. flow check valves).
Figure 1 provides a simplified diagram of the backfill modification.
2.1 Basis of the Backfill Line Reference Lea Modifications The connection incation of the backfilled reference leg piping physically eliminates the consequences of an inadvertent RVLIS reference leg root valve manipulation error as desu ibed in Information Notice (IN) 93-89, " Potential Problems with BWR Level Instrumentation Backfill Modifications."
-The backfill lines are connected in such a manner that they do not have an' adverse effect on the capability of the connected instruments to perform their intended function.
The backfill lines have no effect on the response time and
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, ificant impact on instrument accuracy.
The design of the backfill systen does not impact the redundancy, independence and testability requirements of the reactor protection system.
The backfill lines are
- 2. gm to the same level of quality as the existing instrument lines.
The chck valves will not close inadvertently during normal operation, but ha eG; :wlate when the backfill instrument line integrity is challenged during arra) er accident conditions.
The backfill line check valves will isolate if CnD syster pressure falls below reactor pressure and will re-open under m di' ins that necessitate re-opening because the CRD water pressure is 9 eater than reactor pressure.
Dr.e of the effects of the proposed addition of the backfill lines which inject c eted of the root valve is to extend the containment pressure boundary out safety-related backfill lines to the containment isolation devices
, the backfill lines from the non-safety-related CRD system.
The a
' n proposed installing two check valves, in series, in each of these backfill lines as the containment isolation devices required by
' ion criterion (GDC) 55 of Appendix A to 10 CFR Part 50.
GDC 55 four specific containment isolation valve arrangements for lines a.
a t r+
containment, but also allows for alternate containment isolation Since the licensee's present proposal does not conform with any se arrangements prescribed in GDC 55, the licensee has proposed an W
.3 1 torm W compliance as provided for in GDC 55.
+:ge of extending the containment pressure boundary out to the two valves in the four reference legs which provide. engineered
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5t'2t fett rt (ESF) actuation signals is offset by eliminating the pe;:ib'1,t_, of inadvertently isolating the instrument racks from the reactor-iressun sessel by closing the manual root valve, thereby potentially-sao;ect U.g these instruments to the CR0 system pressure of 1300 psi, which could result in a severe-transient at the Dresden and Quad Cities Stations, For the reference leg backfill lines, the criteria for acceptable containment iritegrity is: 1) maintenance of the integrity-and functional performance of-the seccndary containment system; 2) maintenance of the rate and extent ~of coolant loss within makeup-capability; and 3) ensuring that the calculated offsite exposures from a single failure during-normal operations are-suDstantially below 10 CFR 100 limits.
The instrument line break accident,-as described -in Updated Final Safety Analysis Report (UFSAR) Section 15.6.2, limits reactor coolant leakage below 10 CFR 100 limits for line breaks inside or outside the containment.
The addition of the reference leg backfill lines does not change the description or consequences of the instrument line break scenario.
Outside of containment, isolation is provided by two new simple check valves located as 3
close as practical to the containment (within 15 feet).
The same provisions are made for visual inspection of the backfill piping as for the original o
N trun nt lines up to and including the new containment isolation check-valves.
The new check valves will be leak tested by use of procedural methods i
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-t 3 u e adequate to accurately verify leakage below the chosen criteria.
lhis :eak testing method will account for measurement accuracy effects at the low flow rnes needed to preserve reference leg inventory.
The new r. neck valves themselves provide greater leak tightness than other-vahes used on similarly sized lines.
They have low opening pressure and a soft teat which will not cause pressure spikes in the downstream instruments.
The isolation capability of the backfill line check valves will be cerirdically verified by testing to leak rate criteria that is significantly more restrictive than-the 10 CFR 50, Appendix J, minimum leak rate testing-rcm irements.
In addition, inclusion of all the new check valves into TS Section 3.7/4.7.D requires that these valves be subject to Type C testing in accordante with 10 CFR 50, Appendix J.
% i. c ;- sed plant modifications for the reference leg backfill check valves cr mcrease the radiological consequences of any previously evaluated The radiological impact from a reference leg backfill instrument a.
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A is bounded by Dresden and Quad Cities' Instrument Line Break (UFSAR Section 15.6.2).
Therefore, the offsite exposures from-a line sm,-
t u t.. useclated with the backfill lines during normal operations are sum'
Gly below 10 CFR 100 limits.
2.2 ( ~ 'ian;e to General Desian Criterion (GDC) H
"' ciping connects into the reference instrument line legs on each un't w ro of the existing containment isolation valves.
These new lines are part of the reactor coolant pressure boundary.
Therefore, the intent'of CD: 55 is applicable to these reference leg backfill lines.
GDC 55 requires each-line that is part of-the reactor coolant pressure-boundary and penetrates primary reactor containment be provided with-c or.t a inment isolation valves meeting specific criteria.
GDC 55 allows--
deviation from these specific criteria, if it can be demonstrated that the containment isolation provisions for a specific class of lines are acceptable-on some-other defined b6 sis.
The licensee's defined ba is, as required by GDC 55, for the acceptability of the two subject check valvis separating the safety-related portion of the--
backfill lines from the non-safety-related CRD system is based on the-following:
1 )--
The backfill piping is not a part of a protection system.
2)
The safety-related portion of the backfill piping is designed to the same quality requirements of the current' instrument lines.
The piping and supports on the containment-side, including the check valves, are safety-related and seismically qualified.
3)
The reference leg backfill line check valves for all four (4) reference-legs are located as close as practical to the containment penetration.
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In all cases, the check valves will be located within 15 feet of the-containment penetration.
4}
The same provisions are made for visual inspection of the backfill ciping as for the original instrument lines up to and including the-containment isolation check valves.
Thest valves are being added to the inservice test (IST) _ and local leak-rate test (LLRT)- programs.
5)
The backfill line connection made to the reference legs is such that the-response time of the connected instrumentation is not-affected.
6; Tne backfill lines will not close accidentally during normal reactor operation because CRD drive water flow will keep the check valves open.
lhe TRD drive water flow is checked daily on operator rounds.
7; TL Dackfill line will be isolated by the use of simple check valves if (c' sistem pressure is lost during normal reactor operation or under ac" Rnt conditions.
Tr tackf111 lines will re-open under conditions that necessitate re-e 9erirg because the_CRD water pressure is greater than reactor pressure.
+6 (;0 pump is not operating, the backfill check valves will remain closed and cannot be re-opened until a CRD pump is operating with acequate water pressure to re-establish backfill flow.
- j in-is..ation capability of the check valves will be periodically verified by testing to leak rate criteria that exceeds the 10 CFR 50, Appendix J, minimum requirements.
10)
The offsite exposure due to a line break in the backfill system is below 10 CFR 100 limits. -The leakage from the reactor pressure vessel assuming a's' ingle failure of a check-valve in addition to the line break-is substantially less than the. instrument line break evaluated in UFSAR Section 15.6.2.
Based upon the previous discussion, the proposed. modifications do not
-adversely affect the function that_the reference leg performs, and maintain containment leakage within' established limits for Dresden Station-and _ Quad Cities Station.
The function of_ the RVLIS is not impaired because the backfill piping is designed to the same quality as the existing _ instrument lines and does not have a significant impact on existing instrument accuracy.
The design of-the backfill-system satisfies the redundancy, independence 1and
~testabil'ty requirements of the reactor _ protection system.
The containment integrity is maintained because the radiological impact from a reference leg backfill instrument-line break is bounded by Dresden and Quad Cities' Instrument Line Break analysis (VFSAR, Section 15.6.2). The design of the check valves provides greater leak tightness than other valves used on similarly; sized-lines.
The isolation capability of the backfill check lines-
-will be-periodically verified _to stringent'requiremtnts that ensure the integrity of the lines are maintained.
The radiological impact of the
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= p a act modification is insignificant as existing line break analyses bound the consequences of a loss of backfill line integrity.
Based on the above, the staff finds the design of the proposed modifications meets the intent of CDC 55 and also meetsBulletin 93-03, and are, therefore, acceptable.
2.3 Peference lea Intearity with CRD System Flow The non-safety-related CRD system piping will be connected to each of the safety-related divisions of RPV and FWCS instrumentation.
The connection of the non-safety-related backfill piping to the safety-related vessel instrumentation line requires the establishment of an isolation boundary.
The-isolation boundary will ensure that the vessel reference leg piping remains
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filled in the event of-challenges to the piping integrity or dem uurization of the CRD system piping. This boundary is provided by two J: fafe., related check valves in series. The backfill check valves will (1;r v o t ne potential for reference leg leakage if CRD piping integrity is N e check valves are designed for use in an instrument application n.,
s:" seats which provide for very tight backseating and low leakage v:
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.ne check valves allow flow to the vessel instrumentation reference o a,;w ny and prevent flow out of the reference leg piping, t eac ce mteria has been established to provide assurance that vessel level instrurentation integrity is adequately maintained in the event of CRD system cepre.surization.
The basis for the check valve leakage is provided below:
<ti i;e.nas calculated the criti:4 seat leakage rate for the.RVLIS nackfill instrument check valves to be 3J ml/hr.
To establish a comfortable marg 1r of safety, the licensee has established a maximum test leakage rate of 3.0 H hr for the RVLIS backfill check valves.
This provides signifit. ant leak rate margin for assurance that instrument accuracy will be maintained.
teasage criteria was established-to provide assurance that vessel level
-instrumentation integrity is adequately maintained in the event of CRD system
-depressurization. The basis'for the check valve leakage is the maximum -
4 leakage which ensures that the-loss of water inventory from the reference leg piping over an acceptable time period is limited to that corresponding to a 6" level change.
This ensures that adequate vessel level indication is provided to the operator for assessing plant operating conditions.
The level change criteria (six inches) is based upon the total instrument calibration tolerance from sensor to control room indicator.
The-time criteria (ten hours) is based upon the detection of a level gauge discrepancy by the 'ontrol room operator within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, and implementation of' corrective actions (isolation of the potentially leaking backfill system) within an additional 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
Based upon the inputs described above, licensee determined the volume of water in the condensate pot and reference leg that, if lost, would provide-a 6"
-level discrepancy. This value was then divided by-10, hours.
This yielded a
o critical seat leakage rate for the RVLIS backfill instrument check valves of 30 m1 hr.
However, in order to establish a margin of safety, the licensee has f
established a maximum test leakage rate of 3.0 ml/hr, which is a factor of 10 less than the critical seat leakage.
The RVLIS backfill instrument check valves will be periodically tested as part of the IST program.
The Dre, den station and Quad Cities Station IST programs are committed to the 1986 Edition of ASME Section XI.
Per this edition of ASME Section XI, the leakage rate for check valves will be " owner supplied", or as calculated using the following formula, 2*30*D (ml/hr), where D is the check valve nominal valve size.
Given the nominal valve size of 3/8", the calculated leakage (22.5 ml/hr) is consistent with the critical seat leakage calculation (30 ml/hr) described above.
The maximum test leakage rate of 3.0 ml/hr provides margin to both values.
Based on a review of the predicted flow rates calculated in the licensee's conservative analysis, the staff agrees with the licensae's conclusion, that a single failure consisting of a potential line t.reak in the non-safety-related CRD system would result in a leakage rate far below that previously found acceptable for the present RVLIS design
- n f. p ation.
Therefore, the staff finds that the proposed addition of the subject bacr. fill lines and their associated check valves will not increase potential primary containment leakage or discharge under faulted conditions therefor e, is in compliance with 10 CFR 100 as discussed above.
and.
- n summary, the staff finds that the proposed addition of the two subject backfill linos and their associated check valves have a defined basis which the intent of GDC 55 is met and, therefore, is in compliance with u st
.r.a t its requirerents.
We also find that the licensee's proposal is in compliance with Appendix J to 10 CFR 50, and 10 CFR 100, as discussed above.
2.a Basis lqt_.C!tances to the Technical Soecifications The backfilled reference legs and associated piping connect into the RPV and FWCS instrumentation lines ahead of the existing primary containment isolation valves.
Such a configuration requires the establishment of an isolation boundary by the requirements of GDC 55.
Therefore, the check valves associated with the active trip backfill instrument lines are considered primary containment isolation valves and meet the criteria for inclusion into TS 3/4.7.0 " Primary Containment Isolation Valves".
Based on the above evaluation, the staff finds the design of valves is adtguate as containment isolation valves. Adding the valves to the TS assures ita valves will be operable and are maintained and monitored as primary containment isolation valves.
Therefore, the staff f4nds the proposed change acceptaoie.
2.5 Compliance with NRC Bulletin 93-03 The staff has reviewed the licensee's modifications to meet the Bulletin and finds the hardware modifications meet the intent of the Bulletin.
Region III will inspect the backfill system including such aspects as the applicable
o cuality assurance program in accordance with a forthcoming Temporary Instruction (TI) module, af ter implementation of the hardware modifications.
Schedule Qyad Cities Unit 1:
CECO will fully install the backfill modification during the 13th refuel outage (QlR13 March 1994).
Quad. Cities Unit 2:
Interim modifications to meet the Bulletin are adequate and acceptable.
Final modifications, spring 1995 (Q2R13).
Qte. gea_ Unit 2:
CECO vil fully install the backfill modification during the 14th refuel outage D2R14 planned for March 1995 or during the first Cold Shutdown after June 30. 199a.
Cresder. Unit 3:
CECO will fully install the backfill modification during 13th refuel outage
'7F'! %q a 1994).
The staff has reviewed the above proposed modification schedule and finds it acc ep t abl e.
2.6 Conclusion Basea on the above evaluation, the staff finds the proposed changes to the TS are acceptable, in addition, the staff finds the modifications and the schedule to meet the Bulletin are also acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois tate official was notified of the proposed issuance of the amendments.
The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements.
The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
Ti.a Commission has previously issued a
e ~o
-g.
- r.pote; finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (59 IR 17E93).
Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR
.'2 r). no environmental impact statement or environmental assessment need prarared in connection with the issuance of the amendments.
5.0 00t4LLU510N ihe Comnission has concluded, based on the considerations discussed above, th2 -
'1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such
,:'i', a: will be conducted in compliance with the Commission's regulations, issuance of the amendments will not be inimical to the common
.c>>- ;ra security or to the health and safety of the public.
.nc
..e e:
.eckfill Modification P~rcipai Contributor:
John F. Stang, NRR Date:
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FIGURE 1 DRESDEN STATION UNITS 2 'i 3 OU.AD CIT!ES STAT!ON UNIT 4 : & :'
e BACKFILL MOUlFIC%T!ON j
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S AF E T Y RELAIED NON-SAFETY RELATED l
t NEEDLE VALVES FILTERS CONTAINMENT (FLOW METERING)
ISOLATION
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