ML20059H672
| ML20059H672 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 11/03/1993 |
| From: | Denton R BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20059H675 | List: |
| References | |
| NUDOCS 9311100167 | |
| Download: ML20059H672 (8) | |
Text
p .
. BALTIMORE
! GAS AND ,
ELECTRI !
1650 CALVERT CUFFS PARKWAY . LUSBY, MARYLAND 206574702 -
ROBERT E. DENTON Vict PRESIDENT NcLEAR ENER" November 3,1993 (ato) 200-4455 U. S. Nuclear Regulatory Commission Washington,DC 20555 ATTENTION: Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 License Amendment Request; Removal of the Surveillance Requirement for the Auto-Closure Interlock of the Shutdown Cooline System
REFERENCES:
(a) NRC Case Study Report AEOD/C503, dated December 1985 (b) Generic Ixtter 88-17, " Loss of Decay Heat Removal," dated October 17,1988 (c) Letter from Mr. J. A. Tiernan (BG&E) to NRC Document Control
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Desk, dated January 3,1989, Response to Generic Letter 88-17, " Loss of Decay Heat Removal" Pursuant to 10 CFR 50.90, the Baltimore Gas and Electric Company (BG&E) hereby requests an Amendment to Operating License Nos. DPR-53 and DPR49 by incorporating the changes described -
below into the Technical Specifications for Calvert Cliffs Unit Nos.1 and 2.
DESCRIPTION The proposed amendment would revise the Technical Specifications for both Units 1 and 2 to remove the surveillance requirement for the Auto-Closure Interlock (ACI) of the Shutdown Cooling
- (SDC) System suction line isolation valves. The setpoint for the Open Permissive Interlock (OPI) would also be revised by this proposed amendment.
BACKGROUND At Calvert Cliffs, the SDC System functio u to achieve and maintain the Reactor Coolant System (RCS) in cold shutdown condition by removing the decay heat from the reactor core following pl mt shutdown. The SDC System was designed for a maximum suction pressure of 350 psia while the RCS was designed for a maximum pressure of 2500 psia. When the RCS is operating at high pressures, the SDC System is protected from overpressurization by two isolation valves in series. Each of these isolation valves is capable of maintaining the RCS pressure boundary if the other valve fails.
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. Document Control Desk :
November 3,1993 (
' Page 2 l When the SDC System is in use, the system becomes an extension of the RCS pressure boundary. ;
Since a number of pressurization sources exist within or are connected to the RCS, the low-pressure SDC System must be protected against postulated pressurization transients when the two systems are cenaccted. A relief valve in the SDC System is provided on the SDC System suction line to provide protection against transients that could occur during normal SDC System operation such as i inadvertent charging. The SDC System is protected from low temperature overpressure events by placing administrative controls on the RCPs and HPSI pumps to prevent their inadvertent operation. .
r Should the SDC System be exposed to RCS pressure during power operation, the SDC System could rupture at a point outside the containment causing an interfacing system loss-of-coolant accident (ISLOCA) outside containment. Two instrumentation interlocks are used to prevent the inadvertent connection of the RCS to the SDC System when the RCS is at normal operating temperature and pressure. The function of the interlocks at Calvert Cliffs are similar to the interlocks described in !
Reactor Systems Branch Technical Position (BTP) 5.1. The first interlock, the OPI, is designed to i prevent opening of the SDC System suction isolation valves when RCS pressure is above the SDC System design pressure. The proposed change will not remove the OPI interlock. ;
The second interlock, ACl, provides a close signal to the SDC System suction isolation valves when RCS pressure exceeds a predetermined setpoint. Therefore, should these valves be inadvertently left ,
open during RCS heatup and pressurization, the SDC System suction isolation valves would automatically close upon reaching the predetermined pressure setpoint. Removal of the ACI is being proposed to decrease the probability of loss of shutdown cooling events. Although the ACI ,
initiates an auto-closure of the SDC System suction isolation valves on high RCS pressure, the ACI l function is not intended to isolate the low pressure SDC System from the RCS upon the occurrence -
of a rapid pressure transient, such as a low temperature overpressure event. This is due to the relatively slow stroke time of the large motor operated isolation valves. The intent of the- ACI ,
function is to be a backup to the operator action of closing the SDC System suction isolation valves !
during normal plant heatup and pressurization.
l The ACI function presents a problem of competition between two safety functions. When the SDC System is needed, the suction valves must be open. ACI failures resultire,in valve closure are a safety !
concern due to the resulting loss of decay heat removal. Conversely, when the ACI function is required, failures that leave one of the valves open adversely impact safety by increasing the probability of overpressurizing the SDC System. !
The industry has experienced a number of spurious valve closure vents during shutdown cooling ;
operation caused at least in part by the presence of the ACI function. A frequent cause of a spurious ACI action is de-energization of a power supply associated with the ACI control circuit during ,
refueling. This would result in a close signal bemg sent to the SDC Sptem suction isolation valves.
A second common cause of inadvertent valve closure is the spurious ACI actuation resulting from l invalid high RCS pressure signals during testing. Both events can result from maintenance work i typically performed during refueling outages. Studies by EPRI and the NRC have identified that t spurious operation of the ACI was the most frequent cause of reported loss of shutdown cooling ,
events at PWRs between 1976 and 1983 (Reference a). While re-design of the pressure- j instrumentation loops and ACI circuit could climinate isolation valve closure resulting from a loss of !
power, it would not protect against invalid pressure signals. ;
s Since ACI has been a contributor to loss of SDC System events at Calvert Cliffs and other plants, BG&E is proposing removal of the feature from Calvert Cliffs Units 1 and 2. The NRC encouraged removal of ACI in Generic Letter 88-17 (Reference b). In that document, the NRC suggests that the utilities seeking removal of ACI consider the approach taken by Pacific Gas and Electric in ;
removing the ACI from the Diablo Canyon units. In BG&E's response to Generic Letter 88-17, we ;
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Document Control Desk l November 3,1993 !
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said we would evaluate removing ACI (Reference c). It should be noted, however, that for Calvert ,
Cliffs, the positive impact of ACI removal on the frequency of loss of decay heat removal events is ,
smaller than for other plants because of the current practice of defeating the ACI function during i approximately 90 percent of the time the SDC System is in operation. This was done as an interim Generic letter 88-17 measure under the 50.59 change control process. ,
I The setpoint for the OPI function was reviewed as part of this proposed change. It was determined-that the value in the Technical Specifications should be the actual pressurizer pressure at the instrument pressure tap location. Revising the OPI action from 300 psia to 309 psia is a result of '
establishing a clear basis for the value. It was raised to ensure that when instrument uncertainties are considered, SDC System pressure cannot be exceeded and shutdown cooling operations will not be hindered.
REOUESTED CIIANGE Change Specifications 4.5.2.e.1 of the Unit 1 and Unit 2 Technical Specifications and associated !
Bases as shown on the marked-up pages attached to this transmittal.
SAFETY ANALYSIS ;
In September 1989, Combustion Engineering (CE) completed a report, CE NSPD-550,' " Risk .!
Evaluation of Removal of Shutdown Cooling System Auto-Closure Interlock," that documents the results of a generic analysis of the impact of removing the ACI from SDC System. This report is - '
generally applicable to Calvert Cliffs Units 1 and 2 and was supplemented by a plant specific evaluation. The evaluation was performed to determine the change in ISLOCA frequency, the change in SDC System unavailability, and the impact on mitigating low-temperature overpressure events due to the removal of ACI. This evaluation addresses the seven guidelines for ACI removal recommended by the NRC in a memorandum from B. W. Sharon (Chief, Reactor Systems Branch) dated January 28,1985. In summary, the following discussion describes how each of the seven items ,
will be met.
- 1. Means available to prevent a LOCA outside containment:
The Calvert Cliffs design provides for a double barrier between the RCS and the SDC System. The design provides a very high confidence that at least one barrier can be established and maintained under postulated conditions. This is accomplished through the ,
use of separate power supplies, independent valve position indication, and the separation of control and indication power sources. Procedural controls, personnel training, automatic .,
audible and visual alarms, and the OPI function will minimize the potential for operator error '
when establishing double isolation or attempting to defeat it once it is established. The OPI ;
will prevent opening of the SDC System suction isolation valves when the RCS pressure :
exceeds the interlock setpoint. ;
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- 2. The alarms to alert the operator of an improperly positioned SDC System isolation valve: '
Prior to the removal of ACI, automatic visual and audible alarms will be provided in the main control room to inform the operator if any one of the SDC System suction isolation valves is .
not fully closed when RCS pressure is above the alarm setpoint. The alarms will be described in the Updated Final Safety Analysis Report and will be tested each refueling outage. ;
- 3. Verification of the adcouacy of relief valve capacity: !
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A review of the original design basis of the SDC System relief valve indicated that the ACI has not been credited in the selection of the limiting events or mitigation of the resulting transients. The use of the SDC Syste n relief valve along with administrative controls provide -
overpressure protection on the SDC System. As a result, the removal of ACI will have no adverse impact on SDC System overpressure protection prosisions. ;
The setpoint for the OPI function was reviewed as part of this proposed change. It was j determined that the value in the Technical Specifications should be the actual pressurizer j' pressure at the instrument pressure tap location. Revising the OPI action from 300 psia to 309 psia is a result of establishing a clear basis for this value. It was raised to ensure that I when instrument uncertainties are considered, SDC System pressure cannot be exceeded and shutdown cooling operations will not be hindered. ;
- 4. Means other than ACI to ensure that both isolation valves are closed:
Closure of both isolation valves prior to pressurizing the RCS remains primarily an operator function, with or without ACI. The ACI or the alarm provides backup if the operator fails to close both valves. In addition to the alarms described in Item 2 above,. the proposed modification will use position indication, operating procedures, and personnel training to ensure that the double barrier is established when needed. '
- 5. Assurance that the OPIis not affected by ACI removal:
The OPI function will be maintained in its present form. Assurarce that the OPI function is not affected will be confirmed by testing the operability of the OPI function after the ACI is removed. .'
- 6. Assurance that valve position indication will remain available in the control room after ACI j removal:
There is continuous valve position indication on the main control board. The indication for the valve position utilizes DC control power. Power for valve position indication has been l separated from control power. Circuit operability will be verified after the ACIis removed. ;
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- 7. Assessment of the effect of ACI removal on SDC System availability and low-temperature overnressure event: :
i The effect of ACI removal on low temperature overpressure protection (LTOP) for the reactor vessel was not assessed since no portion of the SDC System at Calvert Cliffs is used for this purpose. The LTOP system at Calvert Cliffs makes use of a lowered setpoint on the Power-Operated Relief Valves (PORVs) located on the pressurizer, along with ,
administrative controls, to provide protection against brittle fracture of the reactor coolant ;
pressure boundary. As a result, ACI removal has no effect on LTOP. The use of the SDC t System relief valve along with administrative controls provide protection against overpressurizing the SDC System.
A plant specific evaluation has been performed to evaluate the effect of the proposed change on the probability of ISLOCA, SDC System availability, and potential mitigation of slow acting pressure transients. It should be noted that the use of the ACI for isolation of the SDC System from the RCS during slow acting pressure transients is not in the original plant ,'
design basis. However, considering that the potential for using the ACI for this purpose exists, BG&E evaluated the impact of ACI removal on this type of overpressure protection.
The evaluation considered the effects of the proposed change on plant safety for power ,
operation as well as shutdown conditions. For power operation, the proposed change .esults -
in a very small increase in the probability of a ISLOCA via the SDC System suction line.
However, this represents a very small fraction of the total ISLOCA contribution to the total ;
offsite release frequency.
For shutdown conditions, the proposed change eliminates the possibility ofinadvertent ACI actuations which contribute to the frequency ofloss of decay heat removal events. However, these contribution of these events to core boiling and core uncovery is very small and the !
proposed change will result in a small improvement in the plant's shutdown safety. This is due to our current practice of defeating the ACI during approximately 90 percent of the time the SDC System is in operation. However, the improvement in shutdown safety is larger if the proposed configuration is compared with the original plant design that left the ACI in operation during the entire shutdown cooling operation.
l The proposed change eliminates automatic isolation of the SDC System from the RCS during ;
a slow-acting pressure transient. As a result, there is a small increase in the probability of t exposing the SDC System to high RCS pressure due to failure of the operator to detect the transient and isolate the SDC System. However, the contribution of SDC System piping ,
rupture resulting from overpressurization to core boiling and core uncovery is very small.
Consequently, the proposed change will not result in a significant change in shutdown safety.
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Document Control Desk November 3,1993 Page 6 DETERMINA FION OF SIGNIFICANT llA7ARDS The proposed change has been evaluated against the standards in 10 CFR 50.92 and has been determined to not involve a significant hazards consideration, in that operation of the facility in accordance with the proposed amendments:
- 1. Would not im>olve a significant increase in the probability or consequences of an accident .
pmiously evaluated.
The Calvert Cliffs Shutdown Cooling (SDC) System is used to achieve and maintain the Reactor Coolant System (RCS) in cold shutdown condition by removing the decay heat from the reactor core following plant shutdown. He Auto-Closure Interlock (ACI) is designed to provide a close signal to the SDC System suction isolation valves when the RCS pressure exceeds the predetermined pressure setpoint. His proposed change would modify Technical Specification Surveillance Requirement 4.5.2.e.1 to reflect removal of the ACI function. The Open Permissive Interlock (OPI), which is designed to prevent opening cf the SDC System suction isolation valves when RCS pressure is above the pressure setpoint, would remain.
The removal of ACI was evaluated generically in the report CE NSPD-550 in terms of the availability of the SDC System. This generic evduatien has been supplem:nted by a plant-specific evaluation for Calvert Cliffs. The evaluation demonstrated that removing ACI and -
replacing it with a valve position alarm will reduce the number of spurious closures of the SDC System suction isolation valves and thus increase the availability of the SDC System, resulting in a corresponding decrease m shutdown risk. Revising the OPI action from 300 psia to 309 psia is a result of establishing a clear basis for this value. Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.
- 2. Would not create the possibility of a new or different type of accident from any accident previously evaluated.
! The report CE NSPD-550 also evaluated the removal of the SDC System ACIin i: tms of the frequency of an inter-system Loss of Coolant Accident (ISLOCA) and thv effect on l.
i ovetpressure transients. The plant-specific evaluation for Calvert Cliffs showed a negligible change in the calculated probability of an ISLOCA event associated with ACI removal. The proposed change to remove the ACI surveillance requirement and the setpoint change will not alter the effect of an overpressure transient at cold shutdown conditions. The ACI was intended to ensure that the SDC System is properly isolated from RCS pressure during start-up operations. The ACI function does not protect against a malfunction of the valve which results in its failure to close. De valve position alarm will warn the operator of a failure to manually close the valve as well as a valve malfunction. While it is true that the ACI initiates an auto <losure of the SDC System suction isolation valves on high RCS pressure, overpressure protection of the SDC System is provided by the SDC System relief valve and administrative controls, and not by the slow. acting suction isolation valves that isolate the SDC System from the RCS. The possibility of a loss of SDC System is reduced by the proposed change because the potential of the SDC System suction isolation valves being closed by a spurious signal will be climinated. No other failures are introduced by remosing ACL Derefore, the proposed change does not create the possibility of a new or different type of accident from any accident previously evaluated.
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- 3. Would not involve a significant reduction in a margin ofsafety. i i
The ACI function is not credited in a margin of safety for any accident previously evaluated 3 and is not discussed in the basis for Technical Specification 3/4.5.2. The ACI function is !
intended to provide a backup to the operator action of closing the SDC System suction f isolation valves during plant pressurization. The evaluation of CE NSPD.550 and the Calvert l Cliffs plant-specific evaluation indicates that the availability of the SDC Eystem is increased l with removal of ACI. In place of ACI, the installation of new visual and audible alarms in the :
control room, along with procedural changes and operator training, will reduce shutdown risk i for the plant by eliminating the possibility of a spurious signal closing the SDC System suction ;
, isolation valves during shutdown cooling operation. Revising the OPI action limit is a result of establishing a clear basis for this value. Therefore, the proposed change does not involve a significant reduction in a margin of safety.
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, ENVIRONMENTAL ASSESSMENT !
The proposed amendment would change requirements with respect to the installation or use of a j facility component kicated within the restricted area as defined in 10 CFR Part 20 or changes to an l inspection or surveillance requirement. We have determined that the proposed amendment involves l no significant hazards consideration, and that operation with the proposed amendment would result i in no significant change in the types or significant increases in the amounts of any effluents that may be released offsite, and in no significant increase in individual or cumulative occupational radiation :
exposure. Therefore, the propcsed amendment is eligible for categorical exclusion as set forth in !
10 CFR Part 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no emironmental impact statement or {
emironmental assessment is needed in connection with the approval of the proposed amendment. !
SCIIEDULE !
This change is requested to be approved and issued by May 1,1994. However, issuance of this !
- amendment is not currently identified as impacting outage completion or continued plant operation. ;
4 SAFETY COMM11 TEE REVIEW !
These proposed changes to the Technical Specifications and our determination of significant hazards have bee 1 reviewed by our Plant Operations and Safety Review Committee and Offsite Safety Review Committee. They have concluded that implementing these changes will not result in an i undue risk to the health and safety of the public.
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- . Document Control Desk November 3,1993
- Page 8 Should you have any further questions regarding this matter, we will be pleased to discuss them with l you. !
t Me
- truly yours,
(
I STATE OF MARYLAND :
- TO WIT :
COUNTY OF CALVERT :
I hereby certify that on the 3 day of h/overn h r ,1993, before me, the subscriber, l a Notary Public of the State of Mar 31 and in and for Calvert OcuntV personally appeared Robert E. Denton, 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 response 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 response on behalf of said Corporation. ,
WITNESS my Hand and Notarial Scal:
Notory Public My Commbsion Expires:
Iyate RED /DJM/d!m i
Attachments: (1) Unit 1 Technical Specification Revised Pages (2) Unit 2 Technical Specification Revised Pages ;
cc: D. A. Brune, Esquire '
J. E. Silberg, Esquire ,
R. A. Capra, NRC '
D. G. Mcdonald, Jr., NRC T. T. Martin, NRC P. R. Wilson, NRC -
R. I. McLean, DNR ,
J. H. Walter, PSC
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