ML20058G817
| ML20058G817 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 11/05/1990 |
| From: | Creel G BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20058G821 | List: |
| References | |
| GL-88-17, NUDOCS 9011140013 | |
| Download: ML20058G817 (8) | |
Text
. ~ . . .~ - . . -
o y
, BALTIMORE
. OAS AND ,
ELECTRIC 4 CHARLES CENTER
- P.O. BOX 1475 e ' BALTIMORE. MARYLAND 21203 1475 i i
GroROC C. CRECL vie: p. ..o ~,
Wettaa raian November 5,1990 4 (301) top d e 5 6 i
U. S. Nuclear Regulatory Commission Washington, DC 20555 -;
i ATTENTION: Document Control Desk i
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos, 50-317 & 50-318 '
Reauest for Amendment to Goeratine Licenses
REFERENCES:
(a) Generic Letter 88-17, ' Loss of Decay Ileat Removal," dated ;
October 17, 1988 ,
(b) Letter from Mr. J. A'. Tiernan- (BG&E) to NRC Document Control.
Desk,. dated January .3,1989, sa'me subject s
(c) Letter from Mr. J. .A.t Tiernan -(BG&E); to NRC Document Control Desk, dated January 27, 1989,- same subject (d) NRC Bulletin 88-04, " Potential Safety-Related Pump - Loss," dated -
May 5, .1988 Gentlemen:
The Baltimore Gas and Electric (BG&E) Company hereby requests an Amendment to its Operating License Nos. DPR-53 and DPR-69 for Calvert Cliffs Unit Nos. 1 & 2, respectively, with the submittal of the proposed chariges ' to the Technical i Specifications. This change is requested to make the license conform to a recom-mendation of Generic Letter 88-17 in a . manner thho also provides additional flexibility ;
in facility operations.
l 1
BACKGROUND Reference (a) described concerns and recommended actions ' for operation of the- Reactor Coolant System (RCS) and Shutdown . Cooling (SDC) System during reduced inventory conditions, in response to the Generic Letter, we implemented the expeditious attions described in Reference (b) and .are implementing programmatic enhancements as described in Reference (c). The programmatic enhancements .in Reference (c) indicated that we would- take action to submit an amendment request which would reduce the minimum flow rates, allowed by Technical. Specifications in order to reduce. the likelihord of air.
ingestion into the SDC System as a result of vortexing. pp .
901 nADOCK 4oota05000 9on o$17 0(( M'iq$($ -
{DR PDC
. ..ih.
. c
. ,. y ~;
- Document Control Desk No'vember 5,1990 -
Page 2 ' i r
The Shutdown Cooling Systems for Calvert Cliffs Units I and 2 are independent. of _ each other and consist of Low Pressure Safety injection (LPSI) pumps, Shutdown Cooling 'i IIcat Exchangers (SCHX), portions ' of the: - Reactor- Coolant System (RCS), . and j associated piping, valves and instrumentation.' The SDC - is - designed to reduce the '
temperature of the reactor coolant from 300 F to; refueling temperature (below 130 F) at a controlled rate within approximately 27-l/2 hours ' following shutdown. ' It is 'also ,
designed to maintain reactor coolant . temperature below 1400 F "during ' refueling. In addition to this decay heat removal function, the . SDC System provides adequate .
recirculation flow through the RCS to prevent, boron stratification ~ and to minimize the effects of an inadvertent boron dilution during MODES 5 and' 6.' '
Technical Specification 3.4.1.3, requires at least one: loop (reactor coolant. or shutdown - -
cooling) to be in operation in MODE 5 but does' not specify a minimum flow rate.
Technical Specification 3.9.8.1 requires at . least one - SDC loop to be in operation in MODE 6, and the associated Surveillance Requirement specifies a minimum flow: rate of a 3000 spm, or - t 1500 gpm when the RCS is drained ito a level below the~ <
mid-plane of the hot leg, regardless of the : decay heat level 'of the core. The Bases for Technical Specification 3.4.1.3 specify that the flow rate must be sufficient .to remove decay heat and to ensure mixing, prevent stratification, and produce gradual reactivity changes during inadvertent boron concentration reductions in the . RCS 'such -
that reactivity changes associated with boron reductions ' are within the capability of 1 operator recognition and control. The Bases for- Technical ~ Specification 3.9.8.1 provide that having at least one shutdown loop in ' operation ensures that: (1) sufficient cooling capacity is available to remove decay heat and maintain the . water in 0
the reactor pressure vessel below 140 F as required during' the' REFUELING MODE, and (2) sufficient coolant circulation is maintained through the reactor core to minimize the effects of a boron dilution incident and prevent boron stratification.
License Amendments No. 38 (Unit 1) and No. 21 (Unit 2) were issued on- April' 24,1979, which allowed reduced SDC flow in MODE 6, from 3000 gpm to 1500 gpm with;the RCS -
drained below the mid-plane of the hot leg. That amendment was . based on operating i experience with SDC flow of less than 3000 gpm and RCS ' levels below the .mid-plane of the hot leg. Observed reductions in SDC flow due to probable vortexing~ were ~ cited by BG&E as the reason for the change.
Generic Letter 88-17, " Loss of Decay lleat Removal," further recognized the problem of vortexing and recommended licensees take several actions. Among .these actions - was the recommendation to review the Technical Specifications and submit appropriate - changes to reflect the concerns identified in the Generic ' Letter. Our - response of
' January 27, 1989 [ Reference (c)], committed . to submit a license amendment to request further relaxation of the SDC flow , requirements when in - a partially drained condition. Subsequent to the Generic Letter, BG&E has : conducted vortex ' testing and participated in a Combustion Engineering Owners Group effort to develop appropriate Technical Specification changes for reducing the shutdown cooling ~ flow rate. - The Owners Group report was received by BG&E in August 1990 and provides the basis for this license amendment request.
The present Technical Specifications satisfy .the Bases described: above, but do not-incorporate measures to provide maximum ~ margin for preventing .vortexing in all potential situations. A condition of full flow from a single LPSI pump (3000 gpm) ,
1
. Docu$ent Control Desk l November 5,1990 l Page 3 l provides a minimum available margin for preventing vortesng with partial RCS i inventories above the mid-loop level. Hence, there would also be a safety benefit to ;
permitting operation with a reduced flow rate when the RCS is at or traversing these' 1 intermediate inventory levels. To take advantage of this . benefit, BG&E proposes . to -)
implement an approach to allow SDC flow to be variable during MODE 6 (as it presently is in MODE 5) to increase the margin for preventing vortexing,' while still performing all design functions. This approach would entall throttling the LPSI pump; ;
discharge valves to gradually reduce or increase' SDC flow for control of ' RCS l temperature, as measured by existing RCS instrumentation. Flow would be- maintained I above a minimum of 1500 spm, which has been determined as adequate to ' protect against boron stratification, minimize the effects of boron dilution ' events, and protect -
against long-term degradation of the LPSI pumps due to continuous pump operation.
l REOUESTED CHANGE l Change pages 3/4 9-g and B3/4 9-2 of the Unit 1 and Unit 2 Technical Specifications as-shown on the marked-up pages attached to this transmittal.
Technical Specification Surveillance Requirement 4.9.8.1 is requened to be revised to allow reduced SDC flow rates during periods when ' the RCS - is partially ' drained. -l Changes to the Bases to reflect this revision are also included.
l SAFETY ANALYSIS l There are four basic safety criteria to be considered when determining appropriate flow-for the SDC System:
- 1. adequate flow to remove decay heat, j
- 2. adequate flow to ensure sufficient mixing, .
- 3. adequate flow to prevent pump damage, and
- 4. adequate flow limits' to prevent :vortexing.
1
! Shutdown cooling flow must be sufficient c, .4tisfy the criteria specified in Technical
( Specification Bases 3/4.4.1 while in MODE 5 and 3/4.9.8 while in MODE 6. The
- Bases overlap, but contain essentially two criteria. They are
- - (1) to provide sufficient capability for ;-moving decay heat, and (2) to provide adequate flow to l ensure mixing, prevent boron stratification and ' produce gradual reactivity changes during boron concentration reductions in the- RCS such that reactivity changes associated with boron reductions are within the capability of operator recognition .and control.
A third consideration, addressed in Reference (d), is the manufacturer's recommendations for minimum flow to prevent _ damage to the LPSI pumps. The LPSI pump manufacturer recommends that the LPSI pumps not be operated continuously at a flow less than 1340 gpm.
l l
P
' Docu'n$ent Contrcl Desk November 5,1990 !
Page 4 i
Generic Letter 88-17 introduced a fourth consideration not completely accounted ~ for in the Technical Specifications; that is, the possible loss of ' SDC flow - because of vortexing at the SDC suction nozzle during mid-loop evolutions. Vortexing at -the SDC suction nozzle can occur with high SDC flow and/or low: coolant level above .the i nozzle. The vortexing, in turn, can ' result in air entrainment'in the SDC - flow streamL !
and air binding of the LPSI pump (s). Full LPSI pump flow from a single pump (3000 spm) may lead to vortexing at mid-loop conditions.
In setting a balance between adequate flow to meet the Technical ' Specification Bases and the pump - manufacturer's minimum flow criteria, and reducing -flow to prevent vortexing, each of the criteria discussed above must be considered. With regard -to l; maintaining sufficient decay heat removal capability, the design' basis for the SDC System is to reduce the temperature of the reactor coolant at a controlled. rate from -
300 F to refueling temperature (approximately 1300 F) Jwithin 27-l/2 hours after shutdown =
and to maintain these conditions once they are reached, assuming component' cooling water is at its maximum design temperature. - As the time following shutdown increases, !
the decay heat load decreases and less decay heat removal . capability is required.
Presently, flow through .the SCHX is throttled to' match the changing decay heat removal requirements. The excess SDC flow bypasses the SCHX and is mixed with the outlet flow from the SCHX to be injected into-the RCS via the safety injection nozzles. This bypass (excess) flow is not needed for heat removal and could' be reduced -
or eliminated by throttling the LPSI pump discharge valve. This would - help reduce the possibility of vortexing during reduced core inventory conditions.
l Technical Specifications currently require SDC flow to be reduced to 1500 gpm when the RCS is drained to a level below: the mid-plane of the hot leg while in MODE 6.
Operational experience has shown that a pump flow rate- of 1500 gpm is more than adequate to remove decay heat in MODE 6 and to allow the operator sufficient time to control the temperature changes. Allowing reduced flow at ; all intermediate RCS 1 i
levels above the bottom of the hot leg can provide for adequate removal of decay heat and will minimize the possibility of vortexing. The amount . of flow reduction possible l will be limited by Technical Specifications to that necessary to maintain . RCS MODE temperature requirements and to a minimum of 1500 gpm by administrative controls.
Short periods of flow less than 1500 gpm, which may be necessary to prevent vortexing j while making pump shifts or other system alterations, will not significantly impact decay heat removal capability. Technical Specifications currently allow SDC flow to be completely stopped for up to one hour in MODE 6.
The second Bases criterion: to provide adequate flow to ensure mixing; prevent l stratification; and allow the operator sufficient time . to take action on a boron dilution, entails several considerations.' Effective mixing of the- coolant occurs within the LPSI pump, in the SCHX and at the safety injection nozzles into the RCS. A SDC flow rate of 1500 gpm is sufficient to . maintain constant circulation from '
the safety injection nozzles through the reactor vessel and to the LPSI pumps and will thus provide adequate mixing' and will prevent boron stratification within the reactor vessel.
The primary consideration of this second criterion is to provide sufficient. flow to.
ensure adequate circulation and mixing so that any inadvertent boron concentration !
changes in the RCS occur gradually enough to allow the operator time to recognize and i
u_
=
JDocu'm, ent Control Desk i November 5,1990 Page 5 l
correct them. During MODE 6. the normal source of makeup is the' Refueling' Water Tank with a minimum boron concentration of 2300 ppm. Planned - boron dilutions are already covered by Technical Specification 3.1.1.3 which requires- flow to be a 3000- spm .
whenever a reduction in RCS boron concentration is being ' made. Inadvertenti boron. I dilution could occur via gravity feed from the make-up water tank or by charging to' the RCS with charging pumps misaligned to the make-up . water _ tank. These events are '
unlikely during mid-loop operations; however, they. arc analyzed in the Final l Safety l Analysis Report (FSAR) Chapter 14.3, ' Boron ' Dilution' Event." The' analysis ~ assumes j
that the RCS boron concentration is uniform at all times when operating- with . reduced-inventory in MODE 6. In both cases, the analysis concludes that- the ' operator has-sufficient time to take appropriate actions to mitigate . the consequences of this event, q A SDC flow rate of 1500 gpm will' provide adequate circulation and mixing to satisfy. ~j the assumption- of uniform RCS boron concentration should -. an inadvertent boron dilution occur. Therefore, it can be concluded that: boron dilution will not occur in such a way that the operator does not have time to recognize; and correct . the situation. ,
The third consideration is that of- the pump manufacturer's recommendations' for minimum I flow. The manufacturer recommends that the LPSI pumps not be operated continuously -
at a flow less than 1340 gpm. Consequently, a minimum flow of 1500 spm is specified in BG&E operating procedures.
The last consideration, that of reducing flow sufficiently to. prevent vortexing, is ,
dependent upon .the level in the. RCS as well .as the flow rate. Any reduction in pump 'l flow, however, will help reduce - the possibility' of vortexing. The: more reduction, the greater the benefit.
Removing the minimum flow requirements in MODE 6 is consistent with the - current Technical Specification Surveillance Requirement 4.4.1.3.3. for MODES 14 and 5, the proposed CE Owners Group Restructured . Standard Technical'. Stecifications (E. C. Sterling to NRC - Document Control Desk, dated May 26, .1989), ar.d . the stated l objectives of Generic Letter 88-17 (Enclosure 2, Section 3.5.2) to '~ simplify Technical '
Specifications for non-power operation - and consider alternatives suc'. as- procedural: i requirements when such alternatives achieve the same purpose. A minirr.um value of;1500 '
spm will satisfy all of the criteria discussed above and -is therefete - specified in the:
Calvert Cliffs Operating Instructions as the minimum continuous r'.te of; SDC flow in MODE 6 during operations with reduced water levels.
DETERMINATION OF SIGNIFICANT HAZARDS This proposed change has been evaluated against the standards in .0 CFR 50.92 and has been determined to involve no significant hazards considerations, . in that operation of the facility in accordance with the proposed amendment would not:
(i) involve a significant increase in. the probability or consequences of an accident previously evaluated; or Previously evaluated accidents which could; be impacted by SDC' flow:
~
changes include a (1) boron dilution event, and a (2) loss of - coolant flow.
Sufficient flo,w for mixing will continue to be provided and the- assumptions and conclusions of the Boron Dilution Event analysis presented in the FSAR:
(Section 14.3) will be preserved. Also, two SDC loops will continue. to j u_ _ _ . __m _ _ _ _ _-- _m
'L DocuYnent Control Desk November 5,1990 Page 6 provide the . level of protection previously established by the safety-analysis when there is less than 23 feet of water above 'the core, thereby ensuring that a single.: failure of the operating SDC loop will not ! result '
in a complete loss of decay heat removal capability.
This change will ' allow a variable SDC flow ~ to. be' established when the RCS is partially _ drained to prevent ' vortexing. The established flow will l provide SDC System performance commensurate with -its' design functions of ;
0 removing . decay heat and maintaining . RCS - - temperature sl40 F 'in 1 MODE 6. Further, this change _ will provide - a . net ' improvement in SDC System reliability by reducing the probability of common mode failure- due to .vortexing during partially drained RCS conditions. Therefore, this >
change will not increase the probability or the ' consequences of an accident ,
previously evaluated. 1 (ii) create the possibility. of a new or different type- of accident from any accident previously evaluated; ' or - l This change does not~ represent a significant change -in the configuration ' or l operation of the plant. Specifically, no new hardware 'is -. being _ added to !
the plant as part of the proposed change, no existing equipment is being modified, nor are any significantly different ' types of operations-- being '
introduced. Variable flow .of SDC is currently allowed :in : MODE . 5 and .
will be similarly controlled in MODE 6. ;
l (
i The SDC System will still beLoperated in the same ' manner as. before with l the exception that ' the LPSI pump flow will. be throttled -to match' decay 'I l heat removal requirements.- The system will 4 maintain the same capacity for
- l decay . heat removal as before.' No. new or< different kinds of accidents than . ,
any previously- evaluated are being' created.' This change will actually help prevent a possible common' mode failure of both 1. PSI- pumps caused by vortexing and air entrainment" while E at partially ~ drained conditions. l (iii) involve a significant reduction in a margin of' safety.
7
. This change 'will ensure that< the. margin of. ' safety > is maintained. The i system configuration will remain the 'same, 'and it will be' operated in a manner less likely to. cause vortexing. The system's - capability - _ for decay heat removal and mixing will be maintained, as will system: redundancy. :
Administrative control minimum flow in MODE 6 is consistent with- the philosophy of cc, trol currently applied in MODE 5' and promoted in Generic Letter 88-17, Enclosure 2, Section 3.5.2. Therefore, the proposed change-will not reduce the margin of safety associated with this system.
l q
e Doc $ ment Contr :1 Desk November 6,1990 Page 7 SAEETY COMMITTEE REVIEW These proposed changes to the . Technical Specifications and our ~ determination of significant hazards have been reviewed _ by our Plant Operations and.: Safety. Review i Committee and Off-Site Safety Review Committee, and they have concluded ~ = that I implementation of these changes will not result in an undue risk to the health ;and:
safety of the public. l Should you have any questions regarding this matter, we will be pleased- to discuss them -
~
with you.
Very truly yours, l
- /
l-STATE OF MARYLAND :
- TO Wrr : 2 COUNTY OF CALV~cR's :
I hereby cerG.*, that on the day of of ,1990, before me, the subscriber, a Notary Public of the State of' Maryland in and for C4/d fM , personally = appeared George C. Creel, being- duly sworn, and states that he is' Vice President of' the Baltimore Gas and Electric Company, a corporation -of the State of Maryland; that. he provides the foregoing - information for 'the purposes therein set forth; that the statements made are true and correct, to the best of his knowledge, information, and' belief; and- that he was - authorized to - provide the .
information on behalf of said Corporation.
WITNESS my Hand and Notarial Scal:
Notary Public i
( -!
My Commission Expires:
We ;
GCC/ ERG /dtm ,
Attachments: (1) Unit 1 Revised Technical Specifications and Bases Pages ,
(2) Unit 2 Revised Technical Specifications and Bases Pages l l
.\
l l
1 . !
1 Doc 0 ment C@ntrol Desk November 6,1990 :
Page 8
+
1 cc: D. A. Brune, Esquire J. E. Silberg,- Esquire. l*
R. A.Capra,NRC D. G. Mcdonald, Jr., NRC -
- i T. T. Martin, NRC - '
L. E. Nicholson, NRC '
R. I. McLean, DNR
-l I
1 i
i 1
t I
'l t