ML20196G210
| ML20196G210 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 02/29/1988 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | |
| Shared Package | |
| ML20196G207 | List: |
| References | |
| NUDOCS 8803070080 | |
| Download: ML20196G210 (15) | |
Text
v -
. a
,> ..u
'Dockst No. 50-346'-
License.No. NPF-3.
Serial No. 1461 n Enclosure -
Page 1 L
L APPLICATION FOR AMENDMENT TO I FACILITY OPERATING LICENSE NO. NPF-3 l
[ FOR l
DAVIS-BESSE NUCLEAR ~ POWER STATION UNIT NO. 1
\
Attached is the requested change to the Davis-Besse Nuclear Power l- Station, Unit No. 1 Facility Operating License No. NPF-3. Also included l are the Safety Evaluation and Significant Hazards Consideration.
(
The proposed changes (submitted under cover letter Serial No. 1461) concern:
Section 3/4.3.2, Safety System Instrumentation Steam and Fesiwater.
Rupture Control System Instrumentation. Table 3.3-11, Steam and Feedwater Rupture Control System %strumentation. Table Notation "*".
By - - - -
D. C. Shelton, Vice President, Nuclear Sworn to and subscribed before me this 29th day of February,1988.
- 1 Notary Public, State of Ohio .
My commission expires /k [
8803070080 880229 PDR F7 P ADOCK 05000346 c
_ggy a
~
r _
UY ,
Docket No.'50-346J
~
License Nb. NPF-3 Serial No. 1461 Enclosure Page 2
'The'following information is provided to support iosuance of the.
requested change (Actachment 3) te the Davis-Besse Nuclear Power Station,.
Unit No. ,1 Operating-License No. NPF-3, Appendix A Technical Speci-fications, Section 3.3.2.2, Table ~3.3-11.-
'A. Time required to implements.This: change is to be implemented within days after NRC issuance of the License Amendment _and prior'to the beginning of Cycle 6. which is presently scheduled for September, 1988.
B'. Reas6n-for change (Facility. Change' Request No. 87-0116A): This change will minimize the possibility if an inadvertent MS low pressure trip occurring during plant cooldown and heatup by modifying the low pressure block permit setpoint from 650 psig to 700 psig and increasing the steam pressure where the block' permit is-automatically _ removed to 750 psig..
C. Safety Evaluation: See attached Safety Evaluation (Attachment.
No. 1).
D. Significant Hazards Consideration: See attached Significant Hazards Consideration (Attachment No. 2) .
l 1
-1 1
i l
_v k e r , - r , 4 v y
Dock:t N . 50-346 License,No. NPF-3 Sepial No. 1461 Attachment 1 Page 1 SAFETY EVALUATION Description The purpose of this Safety Evaluation is to review the proposed change to the Davis-Besse Nuclear Power Station Unit No. 1 Technical Specifications (TS) to ensure that the change does not constitute an unrevieaed safety question. The proposed TS change is to iderease the Steam and Feedwater Rupture Control System (SFRCS) Main Steam (MS) low pressure block permit setpoint specified in TS Table 3.3-11 from 650 psig to 700 psig and to increase the steam pressure when the block permit is automatically removed from 650 psig to 750 psig. This change will increase the pressuce margin-between the SFRCS block permit and the SFRCS MS low pressure trip setpoints; thereby, minimizidg the possibility of an inadvertent MS low pressure trip from occurring during plant cooldown operations.
Systems and CompLnents Affected Steam and Feedwater Rupture Control System (SFRCS)
Documents Affected Eavis-Besse Nuclear Power Station, Unit No. 1, OperatinP License, Appendix A, Technical Specifications Davis-Besse Nuclear Power Station, Unit No.1, Updated Safety Analysis Report, July 1987 Safety Functions Affected The SFRCS is an automatic system designed to detect and mitigate the effects of major upsets in the MS and Main Feedwater (MFW) systems, including MS and MFW line ruptures, loss of MFW events, Steam Generator (SG) overfeed, and a loss of Reactor Coolant System (RCS) forced circu-lation cooling. The SFRCS detects these events through sensing and logic channels and mitigates their consequences by automatically positioning valves in the MS, MFW, and Auxiliary Feedwater (AFW) systems with appropriate actuation signals dependent upon the initiating event.
The SFRCS consists of four identical sensing and logic channels housed in )
two electrically separate cabinets. Each cabinet consists of two redundant i sensing and logic channels. Logic Channels 1 and 3 are located in Cabinet I and form Actuation Channel 1 (predominantly SG 1). Logic Channels 2 and 4 are located in Cabinet 2 and form Actuation Channel 2 (predominantly SG 2).
i
Dock 3t N3. 50-346 License No. NPF-3 Serial No. 1461 Attachment 1 Page 2 The sensing channels consist of the instrumentation used to monitor the various parameters which provide inputs to the logic channels. These inputs include:
SG high and low water icvel MS low pressure SG to MFW differential pressure RCP high and low motor current The only SFRCS sensing instrumentation relevant to this proposed change is the MS low pressure signal.
A MS low pressure trip of an Actuation Channel of SFRCS during plant operation would be indicative of a main steam line break (MSLB). The MS low pressure trip instrumentation includes pressure switches for all four SFRCS logic channels on each MS header. A trip of single pressure switches in both Logic Channels 1 and 3 on a MS header would cause a trip of SFRCS Actuation Channel 1; whereas, a trip of single pressure switches in beth Logic Channels 2 and 4 on a MS header would cause a trip of SFRCS /.ctuation Channel 2. An SFRCS Actuation Channel trip would cause the complete isolation of the SG cannected to the MS header experiencing the trip signal, the re-alignment of the affected SG's AFW pump to the opposite SG, and the initiation of AFW to the unaffected SG.
It would also isolate the main steam line isolation valve and selected main feedwater valves on the unaffected SG.
The SFRCS also includes a manual low pressure block permissive feature that allows the operator to block the SFRCS MS low pressure trip signal during plant cooldown. This manual operator action is intended to prevent inadvertent actuation and unnecessary challenges to SFRCS and associated systems during plant cooldown. Each MS header contains four pressure switches for the block permissive signal. Two of these pressure switches are associated with a single SFRCS Logic Channel; and the remaining two pressure switches on that MS header are associated with the ermplimentary logic channel in that Actuation Channel. This results in the four pressure switches for the block permit on the MS header for SG 1 being used to block Actuation Channel 1 and the four pressure switches on the MS header for SG 2 being used to klock Actuation Channel 2. Once a block permit for a channel is received, manual action is required to actually block that channel from tripping. As required to comply with IEEE Standard 279-1971 for a protection system and to satisfy the Technical Specification requirements, during plant heatup the SFRCS low pressure block signal is automatically removed. This action ensures that the safety function of the SFRCS MS low pressure trip signal is activated automatically during heat-up operations and remains activated when the plant is criticel in either Modes 1 or 2.
. s
- a Docket No. 50-346 License N'o. NPF-3 Serial No. 1461 Attachment 1 -
Page 3 Effects on Safety DBNPS Technical Specifications, Limiting Condition for Operation 3.3.2.2 requires that:
"The Steam 'and Feedwater Rupture Control System (SFRCS) instrumentation channels shown in Table 3.3-11 shall be OPERABLE with their trip setpoints set consistent with the values shown in the Trip Setpoint column of Table 3.3-12 and with RESPONSE TIMES as shown in Table 3.3-13."
One of the SFRCS sensing instrumentation listed in Table 3.3-11 is the MS low pressure instrumentation channels. Table 3.3-12 lists a trip setpoint for the SFRCS MS low pressure trip signal as greater than or equal to 591.6 psig. A footnote in Table 3.3-11 for the low pressure instrumentation channels states that this instrumentation:
"May be bypassed when steam pressure is below 650 psig. Bypass shall be automatically removed when the steam pressure exceeds 650 psig."
This proposed TS change will increase the steam pressure in the above footnote to 700 psig below which the SFRCS MS low pressure instrumentation can be manually bypassed. Additionally, the steam pressure above which the block permit is automatically removed will be increased to 750 psig.
The SFPCS MS low pressure instrumentation utilizes pressure switches to sense a low pressure condition in the MS piping. To ensure that these pressure switches actuate to satisfy the 591.6 psig TS requirement, an actua.1 field setpoint of 612 psig is used for these components. The hick . field setpoint accounts for instrument tolerance error and settability. Separate pressure switches are used for the MS low pressure block permit feature. These pressure switches allow the operator to manually bypass the SFRCS MS low pressure instrumentation during plant cooldown when the steam line pressure falls below 650 psig. Additionally, the pressure switches must automatically reset when MS line pressure exceeds 650 psig. Because the existing block permit setpoint and auto-recoval setpoint is the sare, no margin is provided for the reset dead band of these pressure switches in the Technical Specification.
As noted above, there are two block permit pressure switches for each SFRCS MS low pressure logic channel. Both switches associated with one Logic Channel need to actuate before the block permit so that the channel can be manually blocked by the operators. Since the block permit for an Actuation Channel utilizes pressure switches that are all located on one MS header while the MS low pressure trip instrumentation for the same Actuation Channel exists on both MS headers, the plant operators need to maintain approximately the same pressure in both SC's during plant cooldown. Failure to do this could cause the SG with the lower pressure
Dock:t No.'50-346 License No. NPF-3 Se, rial No. 1461
- Attachment 1 Page 4~
to experience MS low pressure trip of the SFRCS before the. block permissive for the Actuation Channel on the opposite SG-is allowed. Further, the
- block permit in both logic channels associated with an Actuation Channel needs to reset to automatically remove the block permit in its associated Actuation Channel; however, only one of the two pressure switches in each logic channel needs to autonatically reset to-re-activate the MS low pressure trip functions during plant heat-up.
With the present block permit-value of 650 psig, the nominal pressure margin between it t.nd the 612 psig field setpoint for the MS low pressure instrumentation is only 38 psi. Due to instrument inaccuracy, settability and drift associated with the pressure switches this.small pressure margin l creates the possibility of an inadvertent and spurious SFRCS MS low pressure actuation during plant cooldown and heatup operations. This, along with the need to depressurize both SGs together during cooldown as discussed above, places an unnecessary burden upon the operators to l initiate the manual block permit as soon as allowable. The increased-pressure margin-obtained by raising the block permit value.to 700 psig therefore minimizes the possibility of inadvertent and spurious SFRCS trips during both normal cooldown and emergency cooldown (e.g SG tube rupture event) scenarios. This would minimize the potential for isolating all main and auxiliary feedwater flow to one SG and initiating AW flow to the other SG, thereby, minimizing challenges to safety equipment.
The primary purpose of the MS low pressure insttumentation of the SFRCS it steam line break detection and mitigation in Modes 1 and 2. During plant cooldown oparations, the RCS temperature closely approaches the saturation temperature associated with the SG secondary side pressure. Consequently, the present block permit value of 650 psig corresponds to an RCS tem- ,
l perature of ~ 498*F. Since the nominal RCS temperature in Mode 3 innediately following a reactor trip is ~ 545*F which corresponds to the saturation temperature for the post-trip turbine bypass valve setpoint of 1015 psig, SFRCS main steam line break protection is available only for a duration associated with an approximately 50*F cooldewn in Mode 3. Thus, the present block permit setpoint results in the SFRCS MS low pressure instrumentation channels being blocked over most of the RCS temperature range associated with Mode 3.
By raising the block permit setpoint to 700 psig, the RCS temperature at ,
l which the MS low pressure instrumentation can be blocked is increased
- from ~ 498*F to ~ 506*F. This represents increasing by only 8*F the ,
range of RCS temperatures in Mode 3 where the MS low pressure l
l instrumentation would be unavailable during cooldown operations. The RCS temperatures from 498'F to 506*F represent a range of transient plant operations in Mode 3 and do not represent temperatures in Mode 3 where the RCS wculd be stabilized for any long periods of time. Using a nominal cooldown rate of 15'F/hr, the raising of the block permit value to 700 psig would increase by less than 1 hr the period of time in Mode 3 where the MS low pressure instrumentation would be unavailable during a normal plant cooldown operation. Tine probability that a MSLB would occur ,
in this short time period is extremely low.
J
Dock;t N). 50 346.
License,No. NPF -Scrial_No.'1461
' Attachment 1 Page 5 By ra "ng the automatic reset pressure of the MS low pressure trip i instrumentation to 750 psig from 650 psig, the dead band associated with l the resetting of the pressure switches does not become a limitation upon the block permit setpoint. Based upon past surveillance. tests of the
, . pressure switches, the switches used for the block permit feature L typically reset within 20-30 psi above the block permit setpoint.
Consequently, the proposed 50 psi difference between the block permit and l automatic' reset setpoints allows the block permit setpoint to be satisfied I
without'havingito lower its actual field setpoint due to the reset-
~
setpoint.requirementsfof the Techr.ical Specifications.
l-By raising the automatic reset value to -750 psig, the RCS temperature at which the block permit automatically resets is increased from ~ 498'F to l ~ 513 F. This increases by 15'F the range of RCS temperature.in Mode 3 where the MS low pressure instrumentation would be unavailable during-
! heat-up operetions. However, it still ensures that the automatic reset
! occurs before the plant enters Mode 2 since per T.S. 3.1.1.4 the plant is not allowed to go critical until RCS T is greater than or equal to 525*F. "V8 Using a nominal heat-up rate of 15'F/hr, the raising of.the automatic :
reset setpoint *.o 750 psig would increase the time period during heat-up l where the MS low pressure instrumentation is blocked by approximately l 1 hr. As with the increased time period associated with plant cooldown operations, this time period is so short that the probability of a MSLB during this interval is extremely low.
Since during normal plant operation in Modes 1 and 2 the MS line presr.are is typically 870 psig, the raising of the block permit pressure to 700
' psig and the automatic reset to 750 psig has no impact upon plant operation in Modes 1 and 2. Use of the block permit in Modes 1 and 2 is not possible due to the large difference in pressure between its setpoint and the normal MS operating pressure. Consequently, the protection against MSLBs during power operation provided by the MS low pressure instrumentation is unaffected by the proposed change.
Unreviewed Safety Question Evaluation Revising :ae Technical Specifications as proposed and changing tLe SFRCS MS low prt:ssure trip block permit and automatic reset setpoints will not increase the probability of an accident previously evaluated in the USAR because the associated pressure switches, do not initiate any accident previously analyzed in the USAR. The pressure switch only allows a manual bypass function for the MS low pressure trip switches to be performed by the operators. Additionally, the potential for an' inadvertent SFRCS MS low pressure trip which can cause a loss of main acd auxiliary feedwater to one steam generator, during plant cooldown operaticas will be reduced '
l l
l l
- c
' Dockct No. 50-346 License No. NPF-3 Serial No. 1461
,J Attachment ~1 Page 6.
Revising the Technical Specifications as proposed and changing the SFRCS
.MS low pressure block permit and automatic reset setpoints will not increase the consequences of an accident previously evaluated in the USAR because the setpoint change does not affect the assumptions or effects of.
the USAR accident analysis. The bounding USAR analysis for this SFRCS ,
instrumentation is a MSLB at full power operation. The MS low pressure '
trip function of the SFRCS instrumentation is automatically reset during startup and power operation. The proposed setpoint change does not reduce the ability of SFRCS to mitigate the consequences of the MSLB accident analysis provided in the USAR. The setpoint changes do increase the time
-in Mode 3 where the MS low pressure trip. protection is not available. t However, as evidenced by the present setpoint, this SFRCS trip'is not required in Mode 3, cince the period of time the plant.is in Mode 3 is small and the likelihood of an MSLB in Mode 3 is extremly low ,
(10CTR50.59 (a) (2) (i)) .
Revising the Technical Specifications as proposed will not increase the probability of a malfunction of equipment important to safety because this '
setpoint change does not alter the safety function of SFRCS or related equipment. No equipment modifications are required. The setpoint of the existing instrumentation will be reset to the new value. SFRCS sur-
- veillance requiremener.'will be revised to reflect the setpoint change. t Redundancy and reliability of SFRCS instrumentation has not been reduced.
The probability of malfunction of equipment important to safety is actually reduced because inadvertant challenges to the SFRCS and AFWS are i minimized during plant heat-up and cooldown (10CFR50.59(a)(2)(i)).
Revising the Technical Specifications as proposed will not increase the
, consequences of a malfunction of equipment important to safety because ,
all previously analyzed events, with appropriate failures included, remain within the bounds of the USAR. The reset value of the pressure switches has not been increased above the minimum operating pressure of the MS.
The SFRCS low presue trip continues to be automatically reset during startup and power operation. Therefore, the consequences of a malfunction of equipment important to safety have not been af fected (10CFR50.59(a)(2)(1)).
Revising the Technical Specifications as proposed will not create a possibility for an accident of a different type than any previously ;
evaluated in the USAR because the setpoint change does not alter the safety function of SFRF, or any associated systems. The revised setpoint provides the same function as before and does not introduce failure modes i
that are not bounded by existing USAR analyzed events (10CFR50.59(a)(2)(ii)). ;
Revising the Technical Specifications as proposed will not create the possibility of a malfunction of a different type than any evaluated previously in the USAR because the new setpoint provides the same reset safety function as before. 2FRCS instrumentation function is not changed by this setpoint revision. The SFRCS and associated systems will continue to provide the safety functions presently disenssed in the USAR (10CFR50.59 (a) (2) (ii)) .
t .
p o
! i
+
- , 6 . . . . . .
, E M * ' -
- Dockst N n 50-346
~
, License lNo1 NPF-3 Serial No1461- . _ .
- Attachment 1 Page 7~
i
. Revising the Technical Specifications as-proposed and~ changing the SFRCS--
l low pressure permissive; bypass setpoint will not reduce the margin' of safety as defined in the bases for any Technical' Specification because =
l' Lthe setpoint' change .does not . affect any of the -bases for TS 3.3.2.2 and .
- .is not associated.with the bases for any.other Technical Specifications. ;
L The operability requ'irement of TS 3.3.2.2 bases have not been affected. '
All TS surveillance requirements will be net by revising' the appropriate -
. plant surveillance procedures to reflect a. setpoint change of 700 psig for
~
the . block permit and. 750 psig for;the automatic reset.' . - In addition,.the
~
potential:for inadvertent challenges to the SFRCS-and AFW system is i reduced _by this'setpoint change. The reset value of'the pressure switches- ,
has not been increased above the minimum operating pressure of the MS.' :
The SFRCS low pressure trip continues to be automatically reset during startup-and. power operation. (10CFR50.59(a)(2)(iii)).
I~
Conclusion
' Based on the above evaluation, the proposed TS change does not constitute an unreviewed safety question. I References !
i Davis-Besse Nuclear Power Station, Unit No. 1,' Operating License, ,
Appendix A, Technical Specifications !
Davis-Besse Nuclear Power Station, Unit No. 1, Updated Safety Analysis -N Report, July 1987- '
IEEE Standard 279-1971 Criteria for Protection Systems for Nuclear Power Generating Systems Decay Heat Removal Task Force Final Report of October 15, 1985 j l
~
j i
,i
't 5
_L___.___.a'_ . _ _ - _ _ _ _ _ _ . _ - _ - - _ _ - _ _ - - . _ - . - _ _ - - _ _ - . _ _ _ . . _. :- . - __ __ '
- Dock;t NL. 50-346 License No. NPF-3 Serial No. 1461 Attachment 2 Page 1 SIGNIFICANT HAZARDS CONSIDERATION Description The purpose of this Sip,nificant Hazards Consideration is to review the proposed change to the Davis-Besse Nuclear Power Station Uni No. 1 Technical Specifications (TS) to ensure that the change does not con-stitute a significant hazards consideration. The proposed TS change is to increase the Steam and Feedwater Rupture Control System (SFRCS) Main Steam (MS) low pressure block permit setpoint specified in TS Table 3.3-11 from 650 psig to 700 psig and to increase the steam pressure where the block permit is automatically removed from 650 psig to 750 psig. This change will increase the pressure margin between the SFRCS block permit and the 5FRCS MS low pressure trip setpoints; thereby, minimizing the possibility of an inadvertent MS low pressure trip from occurring during plant cooldown operations.
l l Systems and Components Affected l Steam and Feedwater Rupture Control System (SFRCS)
Documents Affected Davis-Besse Nuclear Power Station, Unit No. 1, Operating License, Appendix A, Technical Specifications Davis-Besse Nuclear Power Station, Unit No. 1, Updated Safety Analysis Report, July 1987 Safety Functions Affected The SFRCS is an automatic system designed to detect and mitigate the effects of major upsets in the MS and Main Feedwater (MFW) systems, including MS and MFW line ruptures, loss of MFW events, Steam Generator (SG) overfeed, and a loss of Reactor Coolant System (RCS) forced circu-lation cooling. The SFRCS detects these events through sensing and logic channels and mitigates their consequences by automatically positioning valves in the MS, MFW, and Auxiliary Feedwater (AFW) systems with appropriate actuation signals dependent upon the initiating event.
The SFRCS consists of four identical sensing and logic channels housed in two electrically separate cabinets. Each cabinet consists of two redundant sensing and logic channels. Logic Channels 1 and 3 are located in Cabinet I and form Actuation Channel 1 (predominantly SG 1). Logic Channels 2 and 4 are located in Cabinet 2 and form Actuation Channel 2 (predominantly SG 2).
Dockot No.: 50-346
. License No. NPF-3 Serial No. 1461 Actachment 2 Page 2 The sensing channels consist of the instrumentation used to monitor the various parameters which provide inputs to the logic channels. These inputs include:
SG high and low water level NS low pressure SG to MFW differential pressure RCP high and low motor current The only FFRCS sensing instrumentation relevant to this proposed change is the MS low pressure signal.
A MS low pressure trip of an Actuation Channel of SFRCS during plant operation would be indicative of a main steam line break (MSLB), The MS low pressure trip instrumentation includes pressure switches for all four SFRCS logic channels on each MS header. A trip of singla-pressure switches in both Logic Channels 1 and 3 on a MS header would cause a trip of SFRCS Actuation Channel 1; whereas, a trip of single pressure switches in both Logic Channels 2 and 4 on a MS header would cause a trip of STRCS Actuation Channel 2. An SFRCS Actuation Channel trip would cause the complete isolation of the SG connected to the MS header experiencing the trip signal, the re-alignment of the s.ffected SG's AFW pump to the opposite SG, and the initiation of AFW to the unaffected SG.
It would also isolate the main steam line isolation valve and selected main feedwater valves on the unaffected SG.
The SFRCS also includes a manual low pressure block permissive feature that allows the operator to block the SFRCS MS low pressure trip signal during plant cooldown. This manual operator action is intended to prevent inadvertent actuation and unnecessary challenges to STRCS and associated systems during plant cooldown. Each MS header contains four pressure switches for the block permissive signal. Two of these pressure switches are associated with a single SFRCS Logic Channel; and the remaining two pressure switches on that MS header are associated with the complimentary logic channel in that Actuation Channel. This results in the four pressure switches for the block permit on the MS header for SG 1 being used to j block Actuation Channel 1 and the four pressure switches on the MS header for SG 2 being used to block Actuation Channel 2. Once a block permit for a channel is received, manual action is required to actually block that ,
channel from tripping. As required to comply with IEEE Standard 279-1971 j for a protection system and to catisfy the Technical Specification l requirements, during plant heatup the SFRCS low pressure block signal is '
automatically removed. This action ensures that the safety function of the SFRCS MS low pressure trip signal is activated automatically during heat-up operations and remains activated when the plant is critical in either Modes 1 or 2.
Dockct N). 50-346 License No. NPF-3 Ser'ial No. 1461 Attachment 2 Page 3 Effects on Safety DBNPS Technical Specifications, Limiting Condition for Operation 3.3.2.2 requires that:
"The Steam and Feedwater Rupture Control System (SFRCS) instrumentation channels shown in Table 3.3-11 shall be OPERABLE with their trip setpoints set consistent with the values shown in the Trip Setpoint column of Table 3.3-12 and with RESPONSE TIMES as shown in Table 3.3-13."
One of the SFRCS sensing instrumentation listed in Table 3.3-11 is the MS low pressure instrumentation channels. Table 3.3-12 lists a trip setpoint for the SFRCS MS low preseire trip signal as greater than or equal to 591.6 psig. A footnote in Table 3.3-11 for the low pressure instrumentation channels states that this instrumentation:
"May be bypassed when steam pressure is below 650 psig. Bypass shall be automatically removed =*.m the steam pressure exceeds 650 psig."
This proposed TS change will increase the steam pressure in the above footnote to 700 psig below which the SFRCS MS low pressure instrumentation can be manually bypassed. Additionally, the steam pressure above which the block permit is automatically removed will be increased to 750 psig.
The SFRCS MS low pressure instrumentation utilizes pressure switches to sense a low pressure condition in the MS piping. To ensure that these pressure switches actuate to satisfy the 591.6 psig TS requirement, an actual field setpoint of 612 psig is used for these components. The higher field setpoint accounts for instrument tolerance error and settability. Separate pressure switches are used for the MS low pressure block permit feature. These pressure switches allow the operator to manually bypass tha SFRCS MS low pressure instrumentation during plant cooldown when the steam line pressure falls below 650 psig. Additionally, the pressure switches v.ust automatically reset when MS line pressure exceeds 650 psig. Because the existing block permit setpoint and auto-removal setpoint is the same, no margin is provided for the reset dead band of these pressure switches in the Technical Specificatien.
As noted above, there are two block permit pressure switches for each SFRCS MS low pressure logic channel. Both switches associated with one Logic Channel need to actuate before the block permit so that the channel can be manually blocked by tc operators. Since the block permit for an Actuation Channel utiliues pressure switches that are all located on one MS header while the MS low pressure trip instrumentation for the same Actuation Channel exists on both MS headers, the plant operators need to maintain approximately the same pressure in both SG's during plant cooldown. Failure to do this could cause the SG with the lower pressure 1
- - Dock;t No. 50-346 License,No. NPF-3 Serial No. 1461 Attachment 2 Page 4 to experience MS low pressure trip of the SFRCS before the block permissive for the Actuation Channel on the opposite SG is allowed. Further, the block permit in both logic channels associated with an Actuation Channel needs to reset to automatically remove the block permit in its associated Actuation Channel; however, only one of the two pressure switches in each logic channel needs to automatically reset to re-activate the MS low pressure trip functions during plant heat-up.
With the present block permit value of 650 psig, the nominal pressure margin between it and the 612 psig field setpoint for the MS low pressure instrumentation is only 38 psi. Due to instrument inaccuracy, settability and drift associated with the pressure switches this small pressure margin creates the possibility of an inadvertent and spurious SFRCS MS low pressure actuation during plant cooldown and heatup operations. This, along with the need to depressurize both SGs together during cooldown as discussed above, places an unnecessary burden upon the operators to initiate the manual block permit as soon as allowable. The increased pressure margin obtained by raising the block permit value to 700 psig therefore minimizes the possibility of inadvertent and spurious SFRCS trips during both normal cooldown and emergency cooldown (e.g SG tube rupture event) scenarios. This would minimize the potential for isolating all main and auxiliary feedwater flow to one SG and initiating AFW flow to the other SG, thereby, minimizing challenges to safety equipment.
The primary purpose of the MS low pressure instrumentation of the SFRCS is steam line break detection and mitigation in Modes 1 and 2. During plant cooldown operations, the RCS temperature closely approaches the saturation temperature associated with the SG secor_dary side pressure. Consequently, the present block permit value of 650 psig corresponds to an RCS tem-perature of ~ 498*F. Since the nominal RCS temperature in Mode 3 immediately following a reactor trip is ~ 545'F which corresponds to the saturation temperature for the post-trip turbine bypass valve setpoint of 1015 psig, SFRCS main steam line break protection is available only for a duration associated with an approximately 50*F cooldown in Mode 3. Thus, the present block permit setpoint results in the SFRCS MS low pressure instrumentation channels being blocked over most of the RCS temperature range associated with Mode 3.
By raising the block permit setpoint to 700 psig, the RCS temperature at which the MS low pressure instrumentation can be blocked is increased from ~ 498'F to ~ 506*F. This represents increasing by only 8'F the range of RCS temperatures in Mode 3 whe e the MS low pressure instrumentation would be unavailable during cooldown operations. The RCS temperatures from 498'F to 506'F represent a range of transient plant operations in Mode 3 and do not represent temperatures in Mode 3 where the RCS would be stabilized for any long periods of time. Using a nominal cooldown rate of 15'F/hr, the raiaing of the block permit value to 700 psig would increase by less than I hr the period of time in Mode 3 where the MS low pressure instrumentation would be unavailable during a normal plant cooldown operation. The probability that a MSLB would occur in this short time period is extremely low.
T Docket N;. 50-346 License; No. NPF-3 Serial No. 1461 Attachment 2 Page 5 By raising the automatic reset pressure of the MS low pressure trip instrumentation to 750 psig from 650 psig, the dead band associated with the resetting of the: pressure switches does not become a limitation upon the block permit setpoint. Based upon past surveillance tests of the pressure switches, the switches used for the block permit feature typically reset within 20-30 psi above the block permit setpoint.
Consequently, the proposed 50 psi difference between the block permit and automatic reset setpoints allows the block permit setpoint to be satisfied without having to lower its actual field setpoint due to the reset setpoint requirements of the Technical Specifications.
By raising the au.omatic reset value to 750 psig, the RCS temperature at which the block permit automatically resets is increased from ~ 498'F to
~ 513'F. This increases by 15'F the range of P.CS temperature in Mode 3 where the MS low pressure instrumentation would be unavailable during heat-up operations. However, it still ensures that the automatic reset occurs before the plant enters Mode 2 since per T.S. 3.1.1.4 the plant is not allowed to go critical until RCS T is greater than or equal to 525'F. "V8 Using a nominal heat-up rate of 15*F/hr, the raising of the autocatic reset setpoint to 750 psig would increase the time period daring heat-up where the MS low pressure instrumentation is blocked 1.y approximately I hr. As with the increased time period associated with plant cooldown operations, this time period is so short that the probability of a MSLB during this interval is extremely low.
Since during normal plant operation in Modes 1 and 2 the MS line pressure is typically 870 psig, the raising of the block permit pressure to 700 psig and the automatic reset to 750 psig has no impact upon plant operation in Modes 1 and 2. Use of the block permit in Modes 1 and 2 is not possible due to the large difference in pressure between its setpoint and the normal MS operating pressure. Consequently, the protection against MSLBs during power operation provided by the MS low pressure instrumentation is unaffected by the proposed change.
,i' ; u, .
Dock;t No.: 50-346 ' ;
License Ro.' NPF-3 Ser'ial No.-1461
' Attachment 2
'Page 6.
Significant Hazards Consideration The proposed' change does not involve a significant hazards consideration because the operation of the Davis-Besse Nuclear Power Station, Unit No.'1, in accordance with these changes would not:
- Involve a significant increase.in the probability or consequences of an accident previoualy. evaluated because the pressure switches associated with the change do not initiate any accident previously
' analyzed. The pressure switches only allow a manual bypass function for the MS low pressure trip switches to be performed by the operators. -These trip switches provide a mitigating function in the event of a MSLB. Additionally..the potential for an inadvertent SFRCS MS low pressure trip during plant cooldown operations will be reduced (10CFR50.92(c)(1)) .
Create the possibility of a new or different kind of accident'from any accident previously evaluated because the setpoint change does not alter the safety _ function of SFRCS or any associated systems.
The revised setpoints provide the same function as before and do not introduce failure modes that are not bounded by existing analyzed events (IOCFR50.92(c)(2)) .
Involve a significant reduction in a margin of rafety because the change minimizes the possibility of an unnecessary actuation of the-AFW system during plant cooldown and heat-up operations. The change
(
in the setpoints has no impact upon the'availabilAty of SFRCS during plant power operations and does not appreciably increase the time period in Mede 3 where the SFRCS main steam low pressure trip signal is blocked (10CFR50.92(c)(3)) .
Conclusion On the basis of the above, Toledo Edison has determined that the amendment request does not involve a significant hazards consideration.
l ;
i l
l l l 1 i l l
l l
!