ML20205H494
| ML20205H494 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 03/23/1987 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | |
| Shared Package | |
| ML20205H491 | List: |
| References | |
| 1354, NUDOCS 8704010078 | |
| Download: ML20205H494 (18) | |
Text
. - - -
- Dock $t No. 50-346 License-No. NPF-3 Serial No. 1354 Attachment APPLICATION FOR AMENDMENT TO FACILITY OPERATING LICENSE NO. NPF-s FOR DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. I t
Enclosed are requested changes to the Davis-Besse Nuclear Power Station, Unit No. 1, Facility Operating License No. NPF-3.- Also included are the-Safety Evaluation and Significant Hazards Consideration.
The proposed changes (submitted under cover letter Serial No. 1354) concern:
i Section 3/4.3.2, Safety System Instrumentation, Table 3.3-13, Steam and Feedwater Rupture Control System Response Times; Bases Sections 3/4.3.1 and 3/4.3.2, Reactor Protection System and Safety System Instrumentation.
l By D. C. Shelton, Vice President, Nuclear Sworn to and subscribed before me this 23rd. day of March, 1987.
0lxuunW.91&dA Notary Public, State of Ohio '
My commission expires /[ [
8704010078 870323 i
Docket No. 50-346 '
License No. NPF-3 LSerial No. 1354-1
' Attachment The following information is provided to support issuance of the requested changes to the Davis-Besse Nuclear Power Station, Unit No. 1 Operating License No. NPF-3, Appendix A, Technical Specification Table 3.3-13 and Bases Sections 3/4.3.1 and 3/4.3.2.
A. Time required to implement: This change is to be effective 30 days after issuance of the License Amendment.
B. Reason for change (Facility Change. Request No. 87-0024): Amend Technical Specifications to revise the overall Steam and Feedwater
, Rupture Control System (SFRCS) response time for the Turbine Stop
- Valves (TSVs) in accordance with Toledo Edison's commitment as stated in its letter to the NRC, dated June 6, 1986 (Serial No. 1280).
C. Safety Evaluation: See attached Safety Evaluation.
D. Significant Hazards Consideration: See attached Significant j Hazards Consideration.
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Dockst No. 50-346 License No. NPF-3 Serial No. 1354 Attachment 1 Page 1 SAFETY EVALUATION DESCRIPTION OF THE PROPOSED ACTIVITY The purpose of this License Amendment Request is to revise the Davis-Besse Nuclear Power Station, Unit No. 1 Operating License, Appendix A, Technical Specification 3/4.3.2.2, Table 3.3-13, Steam and Feedwater Rupture Control System Response Times. This request revises the overall Steam and Feedwater Rupture Control System (SFRCS) response time for the Turbine Stop Valves (TSVs) from less than or equal to .six seconds to less than or equal to o one second. Bases Section 3/4.3.1 and 3/4.3.2, Reactor Protection System and Safety System Instrumentation, is modified to make the Bases consistent with the intent of the Technical Specification.
SYSTEMS AFFECTED
- 1. Main Steam
- 2. Auxiliary Feedwater DOCUMENTS AFFECTED
- 1. Updated Safety Analysis Report (USAR) Section 15.4.4, Steam Line Break
- 2. Technical Specification Section 3.3.2.2 and Bases Section 3/4.3.1 and 3/4.
3.2 REFERENCES
- 1. FCR 85-159, SFRCS Low Stecm Generator Pressure Trip Logic
- 3. ST 5031.27, Response Time Testing of the Main Turbine Stop Valves
- 5. ST 5031.10, Steam Feedwater Rupture Control Instrument Input Response Time SAFETY FUNCTIONS AND FUNCTIONS OF SYSTEMS AFFECTED The safety function of the Auxiliary Feedwater (AFW) System is to provide emergency cooling water to the Steam Generators (SGs) in case the main feedwater is lost due to anticipated transients or postulated accidents.
Dockst'No. 50'-346
, . License No.-NPF-3' Serial'No.'1354 Attachment 1-Page 2-The safety functions' of the 'AW isolation valves AF599. and AF608 are:
~
- 1. Serve as containment. isolation valves for the A W System.
- 2. During a postulated Main Steam Line. Break (MSLB). accident, iAolate.the AW System from the SG connected directly to the main steam line having the break.
, 3. Re-open after a SG repressurization above 600 psig.
! The. safety function of.the Main Steam-Isolation Valves (MSIV) is to isolate 7
steam lines during certain postulated accidents.
j i The function of the TSVs is to isolate the SG from the main turbine to
! prevent continuous blowdown of both SGs during a postulated MSLB.
PROPOSED AMENDMENT REQUEST DISCUSSION
! Following a MSLB in the steam line between a SG and a MSIV, both SGs begin l to depressurize. The blowdown from the unaffected SG occurs through the j equalizer piping section located between the TSVs and turbine control valves. The accident analyses assume that when the pressure in either steam line at an SFRCS pressure tap location drops below 600 psig an SFRCS l low pressure trip signal is actuated for the appropriate SG. The SFRCS i pressure switches used to detect low SG pressure are located-just upstream j of the respective MSIVs.
- Although both MSIVs receive close signals, the MSIV on the affected SG j may not close because the reverse flow condition (a direct result from the break) may prevent it from closing. Assuming a single failure of the MSIV
] on the unaffected SG, credit for the closure of TSV is taken to prevent
, blowdown from both of the SGs. The MSIVs require about six seconds to close after the steam line pressure drops below 600 psig whereas TSVs require less than one second to close. The six-second closure time is based on the overall SFRCS response time for the MSIV closure including response time of the SFRCS low steam pressure circuitry. Since the MSIVs take longer'to
.close than'the TSVs, the analyses presented in USAR Section 15.4.4 considered
+
the failure of a TSV to close as a single failure. Accordingly a Technical Specification limit of six seconds as the overall SFRCS response time is
- closure.
a .
i During the NRC Fact Finding Team review of the June 9, 1985. event, the NRC
( Team expressed a concern that the operation of the AW isolation valves l (AF599 and AF608) may not have been completely investigated for single failures. This concern arose after review of USAR Figure 15.4.4-3;which
- shows that.both SGs.depressurize below the 600 psig SFRCS low pressure trip setpoint following a MSLB upstream of_a MSIV.
L
Docket No. 50-346
' License-No. NPF-3 Serial No. 1354
. Attachment 1 Page 3:
Evaluation Of The Design That ' Existed At ' Thi Time Of The June - 9, 1985 Event When the pressure in.only one steam line at an SFRCS pressure tap
' location drops below 600 peig, SFRCS low. pressure trip signals will-be actuated for the appropriate SG. An SFRCS low pressure trip will
. initiate the following actions:
Close AFW isolation valve connected to the faulted SG (AF599 or AF608)
Close both MSIVs Close other appropriate isolation valves connected to both SGs Trip the main turbine Trip Anticipatory Reactor Trip System (ARTS) which trips the reactor Align AFW to unaffected SG For other operating conditions and accidents, the AFW isolation valves remain in their open position.
A subsequent low pressure trip on the steam line of the unaffected SG would initiate isolation of that SG and would attempt to align the auxiliary feed pumps to the first SG. However, if the first SG had not repressurized above 600 psig, AFW would not be fed to either SG.
The AFW isolation valves would re-open only when the corresponding SG repressurized above 600 psig and another SFRCS trip is present.
During a postulated MSLB between the SG and the MSIV, if the TSVs did not close until six seconds as currently stated in the Technical Specifi-cations, the AFW to the unaffected SG would be isolated if the unaffected SG pressure falls below 600 psig. A single failure of the AFW isolation valve associated with the unaffected SG (SG not directly connected to break) to re-open after this SG repressurized above 600 psig would result in a complete loss of feedwater to the unaffected SG.
Although the Technical Specification requirement for TSV closure is six seconds, past-testing has demonstrated that the actual TSV closure time is less than one second. Therefore, blowdown of the unaffected SG would normally be terminated before its pressure drops below 600 psig by closure of the TSV due to its more rapid response time.
Additional accident analyses (Reference 2) were performed to show that a rapid TSV closure prevents pressure falling below 600 psig at the SFRCS low pressure tap location for the unaffected SG. Since this tap location is further from the MSLB than the SFRCS low pressure tap location for the affected SG, the pressure at this location decreases at a slower rate. To demonstrate that the pressure at the SFRCS. low pressure tap location for the unaffected SG does not fall
Dockst No.1 50-346
' License No. NPF-3 Serial No.'1354 Attachment 1.
- Page 4-F lbelow 600 psig. B&W has analyzed a MSLB at Davis-Besse with.a more:
detailed model of the main steam line piping than was used to calculate
- the present USAR Chapter.15 results. .The new B&W model includes all frictional effects for valves and fittings in the steam line.- No '_
4 credit is taken for operation of the non-return valves between the
-MSIVs and TSVs.
. With this model, B&W has analyzed (B&W Document 86-1158463-00) the
! following cases with the TRAP computer code and using USAR Chapter 15' ,
assumptions: ,
. Case 6A - MSLB with TSV Closure f - Case 6B - MSLB without TSV Closure
- Both cases assume a low pressure SFRCS trip at 600 psig; however, for j Case 6B a single failure of the TSV to close is assumed.
For Case 6A the TSVs are assumed to be closed one second after the initial'SFRCS low pressure trip setpoint is reached.- The pressure j transient results for Case 6A at the SFRCS low pressure tap location-are shown on Figures 1 and 2 (attached). The results indicate that r
closure of the TSV within one second following SFRCS low pressure-
, below 730 psia. Therefore, no low pressure SFRCS trip will occur on-t the unaffected SG. Consequently, the AFW isolation valve to the unaffected SG will not close and the AFW flow path to the unaffected SG will not be isolated.
Comparable pressure transient results are shown for Case 6B on Figures 3 and 4 (attached). These results indicate that using the
, MSIVs to isolate blowdown from the unaffected SG results in a minimum j unaffected SG pressure of 580 psia. This transient, although not as l' severe as the USAR Figure 15.4.4-3 transient, indicates that the
- pressure in both SGs could fall below 600 psig, thus resulting in a-
- closure of both AFW isolation valves. This could possibly occur if a 2 single failure of the TSV is assumed. 7 The above evaluation demonstrates that closure of.both AFW isolation' valves would only occur following failure of.the'TSV to close on a
- low pressure SFRCS trip for the affected SG. Since failure of the TSV to close represents a single failure, the single failure concern <
i of the good AFW isolation valve to re-open is beyond the single 'I
} failure criteria. Closure of the TSVs within one second of an SFRCS low pressure trip signal will prevent the unaffected SG pressure .f rom falling below 600 psig thereby preventing closure of its AFW isola-I tion valve. Also, no common cause failure exists that could prevent the TSV from closing and also prevent the re-opening of the AFW j isolation valve. These analytical results meet the USAR Chapter 15 j acceptance criteria for accident analyses.
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-Dockst Ns. 50-346 License No. NPF-3 Serial No. 1354 Attachment 1 Page 5 Current Design In order to further improve the reliability of the AFW System, the SFRCS logic was modified during the 1985-86 outage (FCR 85-159) such that low pressure in one SG would continue to isolate that SG, and initiate AFW to the other SG. However, a subsequent low SG pressure trip on the other SG is blocked and will have no effect on the AFW System. If the pressure on the first SG recovers above 600 psig, the SFRCS will respond according to the conditions in the second SG. If both SGs recover, then SFRCS will respond based upon other plant conditions. Thus the potential for the total loss of AFW to the SGs under multiple failure conditions is reduced.
The fast closure of TSVs limits the steam blowdown from the unaffected SG into the containment thereby limiting containment temperature and pressure for steam line breaks inside the containment. The TSV closure time specified in Technical Specification Section 3.3.2.2, Table 3.3-13 is revised to less than or equal to one second. This ensures that actual TSV closure times at Davis-Besse conform with the assumptions made in the MSLB analyses. This response time requirement is applicable only for the SFRCS low pressure trip. For this reason the Bases Section 3/4.3.1 and 3/4.3.2 is modified to make the bases consistent with the intent of the Technical Specification.
Based upon a review of past testing at Davis-Besse, a one-second response time for the TSV can be met without any plant modifications. The SFRCS response time consists of summing of the response times for low pressure sensing devices, the SFRCS cabinet logic and the TSV closure. The mea-sured response time for the main steam line pressure switches (ST 5031.10) is less than 0.050 seconds. The measured cabinet logic response time (ST 5031.09) for the low steam line pressure signals is approximately 0.035 seconds. The longest measured TSV closure time (ST 5031.27) is 0.576 seconds. Thus, the overall SFRCS response time for the closure of TSV when a low pressure is detected in the main steam lines is less than one second.
UNREVIEWED SAFETY QUESTION EVALUATION The proposed action would not increase the probability of an accident previously evaluated in the USAR because the proposed changes do not involve a test or an experiment, or a modification to a system. The Technical Specification limit on TSV response time has been chosen based upon measured test data and is commensurate with the analyses submitted to the NRC in the Davis-Besse Course of Action document (10CFR50.59 (a) (2) (i)) .
Docket No. 50-346 License No. NPF-3 Serial No. 1354 Attachment 1 Page 6 The proposed action would not increase the consequences of an accident previously evaluated in the USAR because the proposed changes do not involve a test or an experiment or a modification to a system. The proposed changes do not alter the assumptions used in the accident analysis given in the USAR (10CFR50.59(a)(2)(1)) .
The proposed action would not increase the probability of a malfunction of equipment important to safety because the proposed changes do not involve a test or an experiment, or a modification to a system. The Technical Specification limit on TSV response time has been chosen based upon measured test data and is commensurate with the analyses submitted to the NRC in the Davis-Besse Course of Action document (10CFR50.59 (a) (2) (1)) .
The proposed action would not increase the consequences of a malfunction of equipment important to safety because the proposed changes do not involve a test or an experiment, or a modification to a system. The Technical Specification limit on TSV response time has been chosen based upon measured test data and is commensurate with the analyses submitted to the NRC in the Davis-Besse Course of Action document (10CFR50.59 (a) (2) (i)) .
The proposed action would not create a possibility for an accident of a different type than any evaluated previously in the USAR because the proposed changes do not involve a test or an experiment, or a modification to a system. The Technical Specification limit on TSV closure time has been chosen based upon measured test data and is commensurate with the analyses submitted to the NRC in the Davis-Besse Course of Action document.
I The proposed action would not create a possibility of a malfunction of a different type than previously evaluated in the USAR because the proposed changes do not involve a test or an experiment, or a modification to a system. The Technical Specification limit on TSV closure time has been chosen based upon measured test data and is commensurate with the analyses submitted to the NRC in the Davis-Besse Course of Action document.
The proposed action would not reduce any margin of safety as defined in the basis for any Technical Specification because credit for closure of TSV is not considered in the USAR analyses. The response time for TSV listed in the existing Technical Specifications is based on the response time for the MSIV. Since the MSIV responsa time is not changed by chang-ing the TSV response time in the Technical Specifications, the margin of safety defined in the basis for the Technical Specification is not re-duced. Since the fast closure of TSVs will prevent the unaffected SG pressure from falling below the SFRCS low pressure trip, the margin of safety is actually improved. The limit on response time for TSV is based on the actual periodic measurements at the Davis-Besse Nuclear Power Station, Unit No. 1 (10CFR50.59(a)(2)(iii)) .
Based on the above evaluation, it is determined that this change does not involve an unreviewed safety question.
i
FIGURE I Docket No. 50-346 CASE 6A PRESSURE TRANSIENT AT SFRCS License No. NPF-3 PRESSURE TAP LOCATION FOR UNAFFECTED SG Sprial No. 1354 Page 7 12.000 -
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Docket No.' 50-346 FIGURE 2 License No. NPF-3 CASE 6A PRESSURE TRANSIENT AT SFRCS Serial No. 1354 PRESSURE TAP LOCATION FOR AFFECTED SG Page 8 ,,
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Dockst No, 50-346 i
LicsInza No. NPF-3 FIGURE 3 '
Strial No. 1354 CASE 6B PRESSURE TRANSIENT AT SFRCS Attrchment 1 PRESSURE TAP LOCATION FOR UNAFFECTED SG Page 9 12.000 -
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Dockat' No.' 50-346 FIGURE 4 Licines No. NPF-3 CASE 6B PRESSURE -TRANSIENT AT SFRCS S: rial No. 1354 PRESSURE TAP LOCATION FOR AFFECTED SC Attachment 1
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- . Docket No 346-License
- No.'NPF-3 ,
- . Serial No.-1354 Attachment 2 Page 1.
SIGNIFICANT HAZARDS CONSIDERATION DESCRIPTION OF THE PROPOSED ACTIVITY The purpose of this License _ Amendment Request is to revise the Davis-Besse Nuclear Power Station, Unit No. 1 Operating License, Appendix A, Technical Specification 3/4.3.2.2, Table 3.'3-13, Steam and Feedwater Rupture Control System Response Times. This request revises the overall Steam _and Feedwater Rupture Control System (SFRCS) response time for the Turbine Stop Valves (TSVs) from less than or equal to six seconds to less.than or equal to one second. Bases Section 3/4.3.1 and 3/4.3.2, Reactor Protection System
, and Safety System Instrumentation, is modified to make the Bases consistent with the intent of.the Technical Specification.
SYSTEMS AFFECTED
- 1. Main Steam h 2. Auxiliary Feedwater 1 DOCUMENTS AFFECTED 1
i 1. Updated Safety Analysis Report (USAR) Section 15.4.4, Steam Line Break
- 2. Technical Specification Section 3.3.2.2 and Bases Section 3/4.3.1 and 3/4.
3.2 REFERENCES
- 1. FCR 85-159, SFRCS Low Steam Generator Pressure Trip Logic
- 3. ST 5031.27, Response Time Testing of the Main Turbine Stop Valves i
}' 4. ST 5031.09, Steam and Feedwater Rupture Control System Refueling Test i 5. ST 5031.10, Steam Feedwater Rupture Control Instrument Input Response Time.
SAFETY FUNCTIONS ~AND FUNCTIONS OF SYSTEMS AFFECTED The. safety function of the Auxiliary Feedwater (AFW) System is to provide emergency cooling water to the Steam Generators (SGs) in case the main _
1 feedwater is lost due to anticipated transients or postulated accidents.
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Dock;t No. 50-346 License No. NPF-3 Serial No. 1354 Attachment 2 Page 2 The safety functions of the AFW isolation valves AF599 and AF608 are:
- 1. Serve as containment isolation valves for the AFW System.
- 2. During a postulated Main Steam Line Break (MSLB) accident, isolate the AFW System from the SG connected directly to the main steam line having the break.
- 3. Re-open after a SG repressurization above 600 psig.
The safety function of the Main Steam Isolation Valves (MSIVs) is to isolate steam lines during certain postulated accidents.
The function of the TSVs is to isolate the SG from the main turbine to prevent continuous blowdown of both SGs during a postulated MSLB.
PROPOSED AMENDMENT REQUEST DISCUSSION Following a MSLB in the steam line between a SG and a MSIV, both SCs begin 4 to depressurize. The blowdown from the unaffected SG occurs through the equalizer piping section located between the TSVs and turbine control valves. The accident analyses assume that when the pressure in either steam line at an SFRCS pressure tap location drops below 600 psig an SFRCS low pressure trip signal is actuated for the appropriate SG. The SFRCS pressure switches used to detect low SG pressure are located just upstream of the respective MSIVs.
Although both MSIVs receive close signals, the MSIV on the affected SG may not close because the reverse flow condition (a direct result from the break) may prevent it from closing. Assuming a single failure of the MSIV on the unaffected SG, credit for the closure of TSV is taken to prevent blowdown from both of the SGs. The MSIVs require about six seconds to close after the steam line pressure drops below 600 psig whereas TSVs require less than one second to close. The six-second closure time is based on the j overall SFRCS response time for the MSIV closure including response time of the SFRCS low steam pressure circuitry. Since the MSIVs take longer to close than the TSVs, the analyses presented in USAR Section 15.4.4 considered the failure of a TSV to close as a single failure. Accordingly a Technical Specification limit of six seconds as the overall SFRCS response time is used in the current Technical Specification for both the MSIV and TSV closure. ;
During the NRC Fact Finding Team review of the June 9, 1985 event, the NRC Team expressed a concern that the operation of the AFW isolation valves (AF599 and AF608) may not have been completely investigated for single failures. This concern arose after review of USAR Figure 15.4.4-3 which shows that both SGs depressurize below the 600 psig SFRCS low pressure trip setpoint following a MSLB upstream of a MSIV.
l
Dockat No. 50-346 License No. NPF-3
- Serial No. 1354 Attachment 2 Page 3 Evaluation Of The Design That Existed At The Time'Of The' June 9, 1985 Event When the pressure in only one steam line at an SFRCS pressure tap location drops below 600 psig, SFRCS low pressure trip signals will-be actuated for the appropriate SG. An SFRCS low pressure trip will initiate-the following actions:
Close AFW isolation valve connected to the faulted SG (AF599 or AF608)
Close both MSIVs
- Close other appropriate isol'ation valves connected to both SGs Trip the main turbine . . .
Trip Anticipatory Reactor Trip, System (ARTS) which trips the reactom Align AFW to unaffected SG
- For other operating conditions and accidents, the AFW isolation valves j remain in their open position.
I A subsequent low pressure trip on the steam line of the unaffected SG would initiate isolation of that SG and would attempt to align the
. auxiliary feed pumps to the first SG. However, if the first SG had i not repressurized ab1ve 600 psig, AFW would not be' fed to either SG.
The AFW isolatic,n valves would_re-open only when the corresponding SG repressurized above 600 psig and another SFRCS trip is present.
] During a postulated MSLB between the SG and the MSIV, if the TSVs did
! not close until six seconds as currently stated in the Technical Specifications, the AFW to the unaffected SG would be isolated if the i unaffected SG pressure falls below 600 psig. A single failure of the
! AFW isolation valve associated with the unaffected SG (SG not directly connected to break) to re-open after this SG repressurized above 600 psig would result in a complete loss of feedwater to the unaffected SG.
4 Although the Technical Specification requirement for TSV closure is six seconds, past-testing has demonstrated that the actual TSV closure time is less than one second. Therefore, blowdown of the unaffected SG would normally be terminated before its pressure drops below 600 psig by closure of the TSV due to its more rapid response time.
Additional accident analyses (Reference 2) were performed to show
- that a rapid TSV closure prevents pressure falling below 600'psig at ;
, the SFRCS low pressure tap location for the unaffected SG. Since this tap location is further from the MSLB than the SFRCS low pressure tap location for the affected SG, the pressure at this location decreases at a slower rate. To demonstrate that the pressure at the l SFRCS low pressure tap location for the unaffected SG does not fall 4
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-D ckat No. 50-346 License No. NPF-3 Serial No. 1354
. Attachment 2
.Page 4 .
i Thelow 600 psig, B&W has analyzed a MSLB at Davis-Besse with,a more
- detailed model of the main steam line piping than was'used to calculate the present-USAR Chapter 15 results. The new B&W model includes.all
, frictional effects for valves and fittings in the steam line...No.
credit is taken for operation of the non-return valves between.the MSIVs and TSVs.
With this model, B&W has analyzed (B&W Document 86-1158463-00) the following cases with the TRAP computer code and using USAR Chapter 15 i assumptions:
Case 6A - MSLB with TSV Closure Case 6B - MSLB without TSV Closure Both cases assume a low pressure SFRCS trip at 600 psig; however, for Case 6B a single failure of the TSV to close is assumed.
l For Case 6A the TSVs are assumed to be closed one second after the j-initial SFRCS low pressure trip setpoint is reached. The pressure transient results for Case 6A at the SFRCS low pressure tap location are shown on Figures 1 and 2~of the Safety Evaluation. The results indicate that closure of the TSV within one second following SFRCS low pressure trip on one SG will prevent the unaffected SG from l depressurizing below 730 psia. Therefore, no low pressure SFRCS trip will occur on the unaffected SG. Consequently, the AFW isolation valve to the unaffected SG will not close and the AFW flow path to the unaffected SG will not be isolated.
Comparable pressure transient results are shown for Case 6B on
- Figures 3 and 4 of the Safety Evaluation. These.results indicate l that using the MSIVs to isolate blowdown from the unaffected SG i results in a minimum unaffected SG pressure of 580 psia.- This trans-j ient, although not as severe as the USAR Figure 15.4.4-3 transient,
{ indicates that the pressure in both SGs could fall below 600 psig, 1 thus resulting in a closure of both AFW isolation valves. This could j possibly occur if a single failure of the TSV is assumed.
I
- The above evaluation demonstrates that closure of both AFW isolation
[ valves would only occur following failure of the TSV to close on a J low pressure SFRCS trip for the affected SG. Since failure of the i TSV to close represents a single failure, the single failure concern 4 of the good AFW isolation valve to re-open is beyond the single
, failure criteria. Closure of the TSVs within one second of an SFRCS low pressure trip signal will prevent the unaffected SG pressure from falling below 600 psig thereby preventing closure of its AFW isola-i tion valve. Also, no common cause failure exists that could prevent
- the TSV from closing and also prevent the re-opening of the AFW isolation-valve. These analytical results meet the USAR Chapter 15
- acceptance criteria for accident analyses.
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11n order to' furt'her improve the ireliability of the An System, thg y, 3 t;
'i SFRCS logic'was modified during the 1985-86 cutage (FCR f5'-159) agh s,,
that low pressure in one SG would conyinue tp. isolate thac SGiand \ s-initiate AFW to the other SG. However,a(sufaequentlowSGpressure trip.on the other SG is blocked and will have no effect on the AFW System. If the-pressure'on the firet SG gecovers above 600spsig, the SFRCS will respond according to the condiVions in ty second SG. If both SCs recover, then SFRCS yill'reapond baced upon %ther plant q /
conditions. Thus the potential forethe total Loss of'AFA* to the SGr ?
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under multiple failure cdnditions is Oeduced.'$ ,
The fast closure of TSVs limits the steam blowdoyn from'the unaffected SG e.
into the containment thereby limiting 1 containment temperature and pressure for steam line breaks insid,e the concainment. The.TSV closure time s specified in Technical Specificatior Section 3.3.2.2, Table 3.3-13 is proposed to be revised ~to less, thai or equal to one seco'nd. This enii.res that actiial TSV closure times at Davis-Besde' conf orm with the assunytions made in'the MSLB analyses'. This response ttme @ uires mt is; applicable only for the SFRCS low pressure trip. Fof this nason 'the Bases Section' 3/4.3.1 and 3/4.3.2 is modified to make the' bas'wa consist +nt with the intent of the Technical,Spr.hificatir.n. < ' '
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Based upon a review of past, testing at Davis-Bcsse, a one-second response ,
time for the TSV can be met without eny plant modifications. The SFRCS ,
response time consisto of summing of the respones times for low pressure sensing devices, the SFRCS cabinet logic and ths TSV closure. The mea- l sured response time for the main steam line pressure switches-(ST 5031.10) M is less than 0.050 seconds. The measure'd c.1 binet logic response time ,
(ST 5031.09) for the low steam line pressurk signals is approxivnacely ~
O.035. seconds. The longest measured TSV closure time (ST 5031.27)visi 0.576 seconds. Thus, the overall SFRCS response tiue Io' r 'the closure of TSV when a low pressure is detected in the main stdam lines Lis less than one second. -
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/c The proposed changes do not innlve n significant hazards', cons'ideration becencetheoperationofthMDavis-BesseNuclearPower/St'Etio.1, Unit, '
No. 1, in accordance with these changes would vet: -
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- 1. Involve a significant increase in thel drobability or consequences of an accident previously evaluated because the proposed changes dp not it involve a test or an exoeriment, or a modiffeation ti a systdn. The , g Technical Specificatfog yimit, on TSV responte time $as bee'tQhsen based upon measured test data' and is commenadrate with the anal tses t.' ,
V submitted to the NRC in che Davis-Besse Course of Act3on docundat.
The proposed changes do,not al er the assumptions b ed j'ct the accident annlysis given,in the USAR (10CFR50.'92 0c)(1)).
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- h. A w: Dockst No. 50-34'6 License No. NPF Serial No. 1354 Attachment 2 C Page 6
- 2. Create the possibility of a new or different kind of accident from any accident previously evaluated because the proposed changes do not involve a test or an experiment, or a modification'to a system.
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. The Technical Specification limit on TSV response time has been
,? _ chosen based upon measured test data and is commensurate with the
)) ' analyses submitted to the NRC in the Davis-Besse Course of Action document (10CFR50.92(c) (2)) ..
- 3. . Involve a significant reduction in a margin.of safety because credit for closure of TSV is not considered in the USAR analyses. The response time for TSV listed in the existing Technical Specifications is based on the response time for the MSIV. Since the MSIV response time is not changed by changing the TSV response time in the Technical Specifications, the margin of safety defined in the basis for the Technical Specification is not reduced. Since the fast closure of TSVs will prevent the unaffa.cted SG pressure from falling below the SFRCS low pressure trip, the margin of safety is actually improved.
The limit on response time for.TSV is based on the actual periodic measurements at the Davis-Besse Nuclear Power Station, Unit No. 1.
On the basis of the above, Toledo Edison has determined that the Amendment Request does not involve a significant hazards consideration.
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