ML20196G933
| ML20196G933 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 03/04/1988 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | |
| Shared Package | |
| ML20196G923 | List: |
| References | |
| 1487, NUDOCS 8803100031 | |
| Download: ML20196G933 (21) | |
Text
T
.i Dockat No. 50-346 License No. NPF-3 Serial No. 1487 Enclosure Page 1 APPLICATION FOR AMENDMENT TO FACILITY OPERATING LICENSE NO. NPF-3 FOR DAVIS-BESSF NUCLEAR POWER STATION UNIT NO. 1 Attached are requested changes to the Davis-Besse Nuclear Power Station.
Unit No. 1 Facility Operating License No. NPT-3.
Also included are the l
Safety Evaluation and Significant Hazards Cowsideration.
The proposed change (submitted under cover letter Serial No. 1487) concern:
Section 3/4.7.1.1 Turbine Cycle-Safety Valves Table 3.7-1 Maximum Allowable High Flux Trip Setpoint With Inoperable Steam Line Safety Valves Table 4.7-1, Steam Line Safety Valves Per Steam Cenerator Bases Section 3/4.7.1.1. Turbine Cycle - Safety Valves For D. C. Shelton Vice President, Nuclear By T.'J M
rs, Nuclear Licensing Director l
1 Sworn and subscribed before me this 4th day of March,198,8 l
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LLLLC LA Notfry)Public,StateofOhio i
My Cornission expires
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.i Dock:t No. 50-346 License No. NPF-3 Serial *No. 1487 Enclosure Page 2 The following informatior. is provided to support ir.stiance of the requested changes to the Davis-Besse Nuclear Power Station, Unit No. 1 Operating License No. NPF-3, Appendix A, Technical Specifications Section 3/4.7.1.1, Tables 3.7-1 and 4.7-1, and Bases Section 3/4.7.1.1.
A.
Time required to Implement: This change will be implemented by the licensee by the end of the fifth refueling cutage. However, expeditious issuance by June 1, 1988 is requested to support the desired main steam safety valve setpoint adjustment during the fifth refueling outage.
B.
Reason for Change:
(DCR 88-0019) Revise the Technical Specifications with regard to: 1) the relationship between the Reactor Protection System High Flux Trip Setpoint and operable main steam safety valves to reflect available main steam system relief capacity in determining the required high flux trip setpoint reduction, and 2) the main steam safety valve required lift settings and number of valves per ASME Code requirements.
C.
Safety Evaluation:
See attached Safety Evaluation (Attachment No. 1).
D.
Significant Hazards Consideration:
See attached Significant Hazards Consideration (Attachment No. 2).
E.
Technical Specification Change Pages (Attachment No. 3) i j
.i Docket No. 50-366 License No. NPF-3 Serial No. 1487 Page 1 SAFETY EVALUATION
1.0 DESCRIPTION
The purpose of this Safety Evaluation is to review the proposed revision to the Davis-Besse Nuclear Power Station (DBNPS), Unit No. 1, Technical Specifications (TS) in accordance with the requirements of 10CFR50.59 to ensure that an unreviewed safety question does not exist.
The revision ',
DBNPS TS 3/4.7.1, Turbine Cycle - Safety Valves, is proposed to, (1) incorporate the TS bases relationship used to derive the reduced b',.. flux trip setpoint into Limiting Condition for Opsration (LCO) 3.7.)
and delete T-ble 3.7-1 "Maximum Allowable liigh Flux Trip Setpoint Oth Inoperable Steam Line Safety Valves", to provide for additional operational flexibility, and (2) incorporate ASME Code requirements into LCO 3.7.1.1 and delete Talde 4.7-1 "Steam Line Safety Valves Per Steam Generator", to allow for enhanced MSSV operability and reliability.
1.1 Reduced High Flux Trip Setpoint Due to Inoperable Steam Line Safety Valves LCO 3.7.1.1 ACTION statement requires, in part, that, "With one or more main steam line code safety valven inoperable, operation in MODES 1, 2 and 3 may proceed provided... the liigh Flux Trip Setpoint is reduced per Table 3.7-1..."
Table 3.7-1 provides a maximum allowable liigh ? lux Trip Setpoint (percent of RATED TIIERMAL POWER, based on four reactor coolant pump operation, "W", as per Table 2.2-1) versus the maximum number of inoperable main steam safety valves (MSSV) on any steam generator (SG).
The reactor t rip setpoint reductions are derived based on the following equation:
(X) - (Y)(V) sp =............ x W Z
where:
SP = Reduced Trip Setpoint in percent of RATED THERMAL P0kIR (Not to exceed W)
V = Maximum number of inoperable safety valves per steam generator J
W = liigh Flux Trip Setpoint for four pump operation as j
specified in Table 2.2-1 X = Total relieving capacity of all safety valves per steam generator in Ibs/ hour (7,087,500 lbs/hr)
Y = Maximuci relieving capacity of any one safety valve in j
lbs/hr (845,759 lbs/hr) 4 Z = Required relieving capacity per steam generator in lbs/hr (6,585,600 lbs/hr)
'.s Dock:t No. 50-316 License No. NPF-3 Serial No. 1487
' Attachment 1 Page 2 This TS bases equation is used to calculate Table 3.7-1 reduced high flux trip setpoint assuming one or more inoperable MSSV with a relieving capacity of 845,759 lb/hr each. Two of the nine MSSVs on each main steam (MS) line have a rated relief capacity of 583,574 lb/hr each and the other seven are rated for 845,759 lb/hr each.
Thcrefore, Table 3.7-1 imposes a greater reduction in reacter power than is required for MS system overpressure protection with one, or both, lower relief capacity MSSVs inoperable. Further, potential future replacement of the existing MSSVs with new safety valves to enhance system operability and reliability is limited to an individual valve relief capacity which does not exceed the 845,759 lb/hr assumed for Table 3.7-1.
Consequently, a revised combination of MSSV relief capacities that complies with ASME Code and total relief capacity requirements, may be restricted by the existing TS table assumptions.
The proposed revision to LCO 3.7.1.1 incorporates the TS bases equation discussed above, rearranged to utilize total operable MSSV relief capacity per SG as the independent variable. The resulting relationship, Equation 3.7-1, is:
Y SP = ----- x W Z
where:
SP = Reduced high flux trip setpoint in percent of RATED THERMAL POWER (Not to exceed W)
W = High Flux Trip Setpoint for four pump operation as specified in Table 2.2-1 Y = Total OPERABLE relieving capacity per steam generator based on a summation of individual OPERABLE safety valve relief capacities per steam generator in Ibs/hr Z = Required relieving capacity per steam generator of 6,585,600 lbs/hr Trip setpoint reductions determined in this manner offer the following enhancements, while maintaining the required level of MS system overpressure protection:
1 1.
High Flux Trip Setpoint levels which allow for optimization of the operable MSSV relief capacity combinations.
l l
2.
Increased flexibility for replacement of two or more of the I
existing MSSVs with a combination of safety valves which individually have a higher and lower relief capacity than the l
currently assumed Table 3.7-1 capacity of 845,759 lbs/hr.
l l
~
Dock:t No. 50-346 License No. NPF-3 Serial No. 1487
' Attachment 1 Page 3 Total operable MSSV relief capacity per SG can be determined based on a summation of the individual operable MSSV rated capacities. Using the proposed trip setpoint reduction equation and this relief capacity, a maximum liigh Flux Trip Setpoint can be determined.
1 Attachment A to the Safety Evaluation illustrates this process for the existing set of MSSVs for all possible combinations of inoperable valves.
1.2 ASME Code Requirements for Steam Line Safety Valves Surveillance Requirement (SR) 4.7.1.1 refers to the mai.n steam line code safety valves of Table 4.7-1, "Steam Line Safety Valves Per Steam Generator". Table 4.7-1 lists the number of MSSVs per SG and toe j
corresponding lift setting as follows:
Number Per SG Lift Setting A. 2 1050 psig B. 2 1070 psig C. 3 1090 psig D. 2 1100 psig The TS bases for the MSSVs is to,
"... ensure that the secondary system pressure will be limited to within 110% of its design pressure of 1050 psig during the most severe anticipated transient."
It also states that, l
"The specified valve lift settings are in accordance with requirements of Section III of the ASMS Bailer and Pressure Vessel Code, 1971 Edition."
j The specified number of MSSVs and lift settings of Table 4.7-1 are actually in excess of the requirements of Section III of the ASME Boiler end Pressure Vessel (B&PV) Code.Section III of the ASME S&PV Cede, 1971 Edition requires:
1.
At least two pressure-relief valves are required to pre. vide relieving capacity for steam systems.
(This is currently met by the use of nine MSSVs per SG.)
2.
The capacity of the smallest pressure-relief valve shall not be less than 50 percent of that of the largest pressure-relief device.
(This is currently met by the use of two 5 percent and seven 7 percent capacity MSSVs per SG.)
F=
4 Dockst Ns. 50-346 License No. NPF-3 Serial No. 1487
' Attachment 1 Page 4 3.
The set pressure $f one of the pressure-relief devices shall not be greater than ths maximum allowable working pressure of the system at design temperature.
(This is currently met with two 7 percent capacity MSSVs per SG set at the design pressure 1050 psig.)
4.
Total rated relieving capacity of the pressure-relief devices shall prevent a rise in pressure of more than 10 percent above systers design pressure at design temperature under any pressure transients antielpated to arise.
(This is currently met by having a total MS system relief capacity of 120 percent of rated thermal power and a maximum MSSV setpoint pressure of 1100 psig. This setpoint, allowing for a 1 percent tolerance, assures MS syscem pressure remains belon 110 percent of design pressure, or 1155 psig.)
The following ASME Code requirements are proposed to be incorporated into the ACTION statement for LCO 3.7.1.1 in place of TS Table 4.7-1:
1.
A minimum of two OPERABLE safety valves per Steam Generator, one with a setpoint not greater than 1050 psig (+/- 1%), and, 2.
A maximwn setpoint of 1100 psig (t/- l'A,) for any OPERABLE safety valve.
Other administrative controls will require that two MSSVs per SG shall be set at 1050 psig (+/- 1%) per the current practice. This practice of setting t o MSSVs per SG provides flexibility to satisfy the ASME Code requirement of one valve at 1050 psig by allowing one 1050 psig MSSV per SG to be declared inoperable.
These requirements will provide continued assarance that:
1.
The valve lif t settings and syntera everpressure protection are in accordance with the requirenents of Section III of the ASME B&PV Code, 1971 Edition.
2.
The secondary system pressure will be limited to 110 percent of MS system design pressure of 1050 psig (including 1 percent I
set pressure tolerance) for the most revere anticipated system operational transient, as previcusly analyzed.
3.
The miniman hSSV relieving capacity la available as described in the TS bases. The nominal MSSV relief capacit>'of two valves per header, set at the design pressure of Iv50 psig (first bank of safety valves), is available as evaluated in the Safety Evaluatic,n for FCR 87-0109, (Reference 8.4.)
which increases the Anticipatory Reactor Trip System (ARTS)
J turbine trip arming setpoint.
Dockst No. 50-346 License No. NPF-3 Serial No. 1487
' Attachment 1 Page 5 2.0 SYSTEM AND COMPONENTS AFFEC,'(FJ Main Steam System 3.0 DOCUMENTS AFFECTED Davis-Besse Nuclear Power Station, Unit No. 1, Operating License, Appendix A, Technical Specificatior.s.
Davis-Besse Nuclear Power Station, Unit No. 1, Updated Safety Analysis Report, July 1987.
Davis-Besse Nuclear Power Station, System Procedure, SP1106.24 - Main Steam System Operating Procedure, Revision 09.
i 4.0 SAFETY FUNCTIONS AFFECTED The main ateam system receives steam from each of two steam generators (SG) and supplies it to the turbine generator.
The MS system design rating is 1050 psig at 600 degrees F.
Pressure relief for the MS system is provided by the turbine bypass valves (TBV), atmospheric vent valves (AVVs) and MSSVs. The AVVs and the MSSVs are located on the MS header between each SG and its associated mat,. steam isolation valve (MSIV). This configuration ensures overpressure protection of the SG even when it is isolated with the l
MSIV tlosed and the TBVs unavailable. The MSSVs are designed in accordance l
with the requirements of ASME Boiler and Pressure Vessel Code,Section III, 1968. The AVVs and TBVs open at lower pressures than the MSSVs.
The safety function of the MSSVs is to provide the pressure relief capacity 1
J necessary for the SGs to dissipate the primary system energy generated at j
the reactor high power level trip setting. The MSSVs are part of the secondary system pressure boundary. There are nine spring operated Mf3Vs in each MS line. The nine valves have a total capacity of 120 nercent j
(7,067,461 lbs/hr) of the rated steam flow of one SG operating at 100 percent (5,880,000 lbs/hr) of rated power.
The MSSV capacities per SG are as follows:
j 7 MSSVs at 845,759 lbs/hr each (Appron. 7% of rated capacity) 2 MSSVs at 583,574 lbs/hr each (Approx. 5% of rated capacity) i 9 MSSVs at 7,087,461 (*) lbs/hr total (60% of total secondary system steam flow, and 120% of rated SG capacity)
- rounded to 7,087,500 lbs/hr in the TS bases Each AVV provides a relief capacity of 5 percent of rated thermal power.
I
Dock 2t No. 50-346 License No. NPF-3 Serial No. 1487
' Attachment 1 l
page 6 The TS bases for ARTS (Section 3/4.3.1 and 3/4.3.2) states:
"Safety grade anticipatory reactor trip is initiated by a turbine trip above 25 percent rated thermal power. This anticipatory trip will operste in advance of the reactor coolent system high pressure reactor trip to reduce the peak system pressure and thus reduce the challenges to the power operated relief valve. This anticipatory reactor trip system was installed to satisfy Item II.K.2.10 of NUREG-0737."
Reference 8.4 proposes increasing the ARTS turbine trip input arming level from 25 percent to 45 percent. That evaluation considers secondary side reli:f capacity te m ort a successful turbine runback.
The TBVs and first bank of MS'-
-ride the relief capacity evaluated for the proposed ARTS arming lese'
- ase, j
5.0 EFFECTS ON SA. n The proposed revisions to TS 3/4.7.1 are evaluated below for impact on USAR analyzed events and the TS bases.
5.1 TS Table 3.7-1 Deletion The proposed revision to LCO 3.7.1.1 anu ueletion of TS Table 3.7-1, i
does not impact any USAR analyzed events or TS bases. The existing tabular presentation of reduced high flux trip setpoint due to I
inoperable MSSVs is determined using the TS bases relationship between SG design parameters, inoperable MSSVs, maximum existing MSSV relief capacity and the High Flux Trip Setpoint for four pump operation. The right hand side of this equation can be rearranged to utilize total operable MSSV relief capacity per SG as the independent variable.
This revised relationship is provided in the proposed revision to LCO 3.7.1.1 and the associated TS bases section. A graphical representation of this revised equation is also provided in the TS baoes. The curve illustrates appropriate reductions in reactor power bared on an actual reduction of MSSV rated relief capacity. Mininium operability of liSSV relief capacity is maintained per ASME Code requirements with at least one MSSV per SG with a setpoint not greater than MS system design pressure and at least one with a maximum setpoint of 1100 psig (+/- 1%). Consequently, unnecessary conservatism can be removed from this TS requirerent and plant operability and efficiency can be enhanced.
5.2 TS Table 4.7-1 Deletion The bases for TS 3/4.7.1 considers that the bounding event for MSSV relief capacity is a turbine trip from 100 percent rated thermal power coincident with a losa, of condenser heat sink.
This is analyzed in USAR Chapter 15, Section 15.2.9, "Loss of All AC power to Station
Dockst No.50-34o License No. NPF-3 Serial No. 1487
' Attachment 1 Page 7 Auxiliaries (Station Blackout)". For this event, the condenser circulating water system is lost and, therefore, the TBVs are not available to relieve MS system pressure. The proposed deletion of TS Table 4.7-1 and incorporation into LCO 3.7.1.1, as discussed in Section 1.2 above, does not affect MS system overpressure protection required by ASME B&PV Code and the total rated MSSV relief capacity.
Similarly, MSSV relief capacity is utilized in the USAR for mitigation of the following events; 1) Loss of Normal Feedwater, 2) MS Line Break, 3) SG Tube Rupture, and 4) Excessive Heat Removal Due to Feedwater System Malfunction. The USAR safety evaluation criteria for these events are not affected by this TS revision.
The feedwater system malfunction analysis states that the two lowest setpoint safety valve banks alone can provide secondary system pressure protection for this event. This TS revision allows for changes in MSSV setpoint pressures from those assumed in the USAR analysis, but the total rated relief capacity is unchanged.
Consequently, equivalent secondary system pressure protection is provided for this event.
The requirements of Section III of the ASME B&PV Code, 1971 Edition, are met since, 1) the existing MSSV relief capacity is adequate and unchanged by this revision, and 2) provisions of operability are ir corporated into the proposed revisions to LCO 3.7.1.1 requiring a minimum of two operable MSSVs per SG, at least one with a setpoint not greater than MS system design pressure, and the other MSSVs with a maximum setpoint of 1100 psig (+/- 1%).
Consequently, SG overpressure protection is assured for all anticipated transients. Other administrative controls will also require that two MSSVs per SG shall be set at 1050 psig (+/- 1%). The ASME Code requirements for MS system design pressure protection is, therefore, satisfied even with one MSSV set at 1050 psig per SG inoperable.
The Reference 8.4 safety evaluation discusses the effects on safety due to increasing the ARTS turbine trip input arming level from 25 percent to 45 percent. The limiting case analyzed allows for an end of life thermal power prior to the turbine trip to exceed the steam relief capacity assumed to be available from the TBVs and the MSSVs set at 1050 psig. The installed MS system steam relief capacity was arbitrarily limited, in the Reference 8.4 evaluation, to the first bank (2 MSSVs per SG set at 1050 psig) of MSSVs. Since this TS revision evaluation allows for a first bank relief capacity of 20 percent, it potentially affects the Reference 8.4 safety evaluation which is based on the existing MSSV first bank relief capacity of 30 percent.
However, the existing 30 percent first bank relief capacity provides a 10 percent excess steaming capacity margin per the Reference 8.4 evaluation.
Therefore, with the potential reduction in MSSV first bank relief capacity to 20 percent, the ARTS arming level of 45
~
Dockrt No. 50-346' License No. NPF-3 Serial No. 1487 -
Page 8 percent still does not exceed the combined total MS relief caphcity available from the TBVs (25%) and the first bank MSSV capacity (20%).
Additionally, the Reference 8.4 evaluation conservatively ignored the 10 percent steaming capacity available from the AVVs. Therefore, the Reference 8.4 safety evaluation conclusion remains valid.
6.0 UNREVIEWED SAFETY QUESTION EVALUATION The proposed TS 3/4.7.1 revision, which:
1.
incorporates the TS bases relationship used to derive the reduced high flux trip setpoint into LCO 3.7.1.1 and deletes Table 3.7-1,
- and, 2.
incorporatesSection III of ASME B&PV Code, 1971 Edition requirements into LCO 3.7.1.1 and deletes Table 4.7-1.
is evaluated below for the existence of an unreviewed safety question.
Revising the TS, as proposed, will not increase the probability of an accident previously evaluated in the USAR.
The MSSVs do not contribute to the initiation of any accident. Operation and malfunction of MSSVs is considered in the USAR as part of various accident scenarios. However, operation and function of the MSSVs is not affected by this change. ASME Code requirements for MSSV setpoint, relief capacity and operability are maintained. (10CFR50.59(a)(2)(i))
Revising the TS, as proposed, will not increase the consequences of an accident previously evaluated in the USAR. Equivalent reduction of the High Flux Trip Setpoint due to inoperable MSSVs is provided by this TS revision. MS system relief capacity requirements for power operation have not been changed.
Revising the Io, as proposed, will not increase the probability of a malfunction of equipment important to safety. Redundancy and single failure assumptions are not affected by this change and remain valid.
Revising the TS, as proposed, will not increase the consequences of a malfunction of equipment important to safety. This TS revision will not affect any USAR safety evaluation criteria. (10CFR50.59(a)(2)(i))
Revising the TS, as proposed, will not create the possibility for an accident of a different type than any previously evaluated in the USAR.
MSSV function has not been altered. (10CFR50.59(a)(2)(ii))
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$'5 Docket No. 50-346 License No. NPF-3 Serial No. 1487
' Attachment 1 Page 9 Revising the TS, as proposed, will not create the possibility of a malfunction of equipment of a different type than any evaluated previously in the USAR.
System operation and component performance will not be changed and the existing assumptions of the USAR analysis remain valid.
Revising the TS, as proposed, will not reduce the margin of safety as e
defined in the bases for any Technical Specification. TS bases 3/4.7.1 equation has been revised to utilize total operable MSSV relief capacity per SG as the independent variable to determine reduced high flux trip setpoint.
The requirements for MSSV lift settings and secondary system overpressure protection per Section III of ASME B&PV Code, 1971 Edition are not affected by this TS revision.
7.0 CONCLUSION
Based on the above evaluation, the proposed TS revision does not constitute an unreviewed safety question.
8.0 REFERENCES
8.1 Davis-Besse Nuclear Power Station, Unit No.
1, Operating License, Appendix A, Technical Specifications 8.2 Davis-Besse Nuclear Power Station, Unit No. 1, Updated Safety Analysis Report, July 1987 8.3 ASHE Boiler and Pressure Vessel Code, 1971 Edition 8.4 Safety Evaluation for Facility Change Request 87-0109, "RPS High Pressure Setpoint and ARTS Threshold Power", dated December 10, 1987 8.5 NUREG-0737, Clarification of TMI Action Plan Requirements, dated November 1980.
l
,Docke,t No. 50-346 License No. NPF-3
' Serial No. 1487 Attachement 1 Page 10 ATTACHMENT EOUATION 3.7-1 MATRIZ (EQ 3.7-1)
SP=Y/IxW NUMBER OF OPERABLE MAIN STEAM SAFETY VALVES HODEL NO. 3777 QA (5 PERCENT OF RATED THERMAL CAPACITY) 0 1
2 (NOTE 1)
N~
s, 0.177W 0
NOTE 2 NOTE 2 g
(1,167,148)
U g
0.217W 0.306W 1
NOTE 2 (1,429,333)
(2,012,907) b$
gN 0.257W 0.345W 0.434W o
2 Dy (1,691,518)
(2,275,092)
(2,858,666) m<
0.385W 0.474W 0.563W 3
gg (2,537,277)
(3,120,851)
(3,704,425) mz 0,514W 0.602W 0.691W m
4 (3,383,036)
(3,966,610)~
(4,550,184) x t-O.642W 0.731W 0.819W a.s:
5 (4,228,795)
(4,812,369)
(5,395,943) a r-0.771W 0.859W 0.948W om 6
g g*
(5,074,554)
(5,658,128)
(6,241,702)
M
$a 0.899W C.988W nm 7
NOTE 2 (5,920,313)
(6,503,887)
Oz NOTES:
- 1. This column represents the existing Table 3.7-1 requirements for maximum High Flux Trip Setpoint (3 significant digits).
2.
High Flux Trip Setpoint reductions are not applicable
- 3. Top figure - Maximum allowable High Flux Trip Setpoint Botton figure ( ) - Operable MSSV relief capacity per SG in lbs/hr 4.
The allowable increase in trip setpoint for an inoperable 5 percent capacity HSSV can be read along a diagonal from upper right to lower left.
Docket No. 50-346 License No. NPF-3 Serial'No. 1487 Page 1 Significant Hazards Consideration
1.0 DESCRIPTION
The purptae of this Significant Hazards Consideration is to review the proposed revision to the Davis-Besse Nuclear Power Station (DBNPS), Unit No. 1, Technical Specifications (TS) in accordance with the requirements of 10CFR50.92 to ensure that this change does not involve a significant hazards consideration. The revision to DBNPS TS 3/4.7.1, Turbine Cycle -
Safety Valves, is proposed to, (1) incorporate a more realistic TS bases-derived relationship used to establish the reduced high flux trip setpoint into Limiting Condition for Operation (LCO) 3.7.1.1 and delete Table 3.7-1, "Maximum Allowable High Flux Trip Setpoint With Inoperable Steam Line Safety Valves", to provide for additional operational flexibility, (2) incorporate ASME Code requirements into LCO 3.7.1.1 and delete Table 4.7-1, "Steam Line Safety Valves Per Steam Generator", to allow for enhanced MSSV operability and reliability and (3) incorporate the basis for these changes into a revised Bases Section 3/4.7.1.1, Turbine Cycle -
Safety Valves.
1.1 Reduced High Flux Trip Setpoint Due to Inoperable Steam Line Safety Valves LCO 3.7.1.1 ACTION staten?nt requires, in part, that, "With one or more main steam line code safety valves inoperable, operation in MODES 1, 2 and 3 may proceed provided... the High Flux Trip Setpoint is reduced per Table 3.7-1..."
Table 3.7-1 provides a maximum allowable High Flux Trip Setpoint (percent of RATED THERMAL POWER, based on four reactor coolant pump operation, "W", as per Table 2.2-1) versus the maximum number of inoperable main steam safety valves (MSSV) on any steam generator (SG).
.he reactor trip setpoint reductions are determined based on the rollowing equation:
(X) - (Y)(V)
SP = ------------ x W Z
where:
SP = Reduced Trip Setpoint in percent of RATED THERMAL POWER (Not to exceed W)
V = Maximum number of inoperable safety valves per steam generator W = High Flux Trip Setpoint for four pump operation as specified in Table 2.2-1 X = Total relieving capacity of all safety valves per steam generator in 1bs/ hour (7,087,500 lbs/hr)
Y = Maximum relieving capacity of any one safety valve in 1bs/hr (845,759 lbs/hr)
Z = Required relieving capacity per steam generator in Ibs/hr (6,585,600 lbs/hr)
s-
' Docket No. 50-346 License.No. NPF-3 Serial No. 1487 Page 2 This TS bases equation was used to calculate the Table 3.7-1 reduced high flux trip setpoint assuming one or more inoperable MSSV with a relieving capacity of 845,759 lb/hr each. However, two of the nine MSSVs on each main steam (MS) line have a rated relief capacity of 583,574 lb/hr each and the other seven are rated for 845,759 lb/hr each. Therefore, Table 3.7-1 imposes an unnecessarily greater reduction in reactor power than is required-for MS system over-pressure protection with one, or both, lower relief capacity MSSVs inoperable. Further, potential future replacement of the existing MSSVs with new safety valves to enhance system operability and reliability is limited to an individual valve relief capacity which does not exceed the 845,759 lb/hr assumed for Table 3.7-1.
Conse-quently, a revised combination of MSSV relief capacities that complies with ASME Code and total relief capacity requirements may be restricted by.the existing TS table assumetions.
The proposed revision to LCO 3.7.1.1 incorporates the TS' bases equation discussed above, rearranged to utilize total operable MSSV relief capacity per SG as the independent variable. The resulting relationship, Equation 3.7-1, is:
Y SP = ----- x W Z
i 1
where.
SP = Reduced high flux trip setpoint in percent of RATED THERMAL POWER (Not to exceed W)
W = High Flux Trip Setpoint for four pump operation as specified in Table 2.2-1 Y = Total OPERABLE relieving capacity per steam generator based on a summation of individual OPERABLE safety valve relief capacities per steam generator in Ibs/hr Z = Required relieving capacity per steam generator of 6,585,600 lbs/hr Trip setpoint reductions determined in this manner offer the following enhancements while maintaining the required level of MS system overpressure protection:
1.
Operable MSSV relief capacity combinations which allow for optimization of the High Flux Trip Setpoint levels.
2.
Increased flexibility for replacement of two or more of the existing MSSVs with a combination of safety valves which individually have a higher and lower relief capacity than the currently assumed Table 3.7-1 capacity of 845,759 lbs/hr.
j
Docket No. 50-346 License No. NPF Serial' No. 1487 Page 3 Total operable MSSV relief capacity per SG can be' determined based on a summation of the individual operable MSSV rated relief capacities.
Using the proposed trip setpoint reduction equation and-this relief capacity, a maximum High Flux Trip Setpoint can be determined.
Table 1 of the Significant Hazards Consideration illustrates this process for the existing set of MSSVs for the possible combinations of inoperable valves.
1.2 ASME Code Requirements for Steam Line Safety Valves Surveillance Requirement (SR) 4.7.1.1 refers to the main steam line code safety valves of Table 4.7-1, "Steam Line Safety Valves Per Steam Generator".
Table 4.7-1 lists the number of MSSVs per SG and the corresponding lift setting as follows:
Number Per SG Lift Setting A. 2 1050 psig B. 2 1070 psig C. 3 1090 psig D. 2 1100 psig The TS bases for the MSSVs is to,
"... ensure that the secondary system pressure will be limited to within 110% of its design pressure of 1050 psig during the most severe anticipated transient."
It also states that, "The specified valve lift settings... are in accordance with requirements of Section III of the ASME Boiler and Pressure Vessel Code, 1971 Edition."
The specified number of MSSVs and lift settings of Table 4.7-1 are actually in excess of the requirements of Section III of the ASME Boiler and Pressure Vessel (B&PV) Code.
Section III of the ASME B&PV Code, 1971 Edition requires:
1.
At least two pressure-relief valves are required to provide relieving capacity for steam systems.
(This is currently met by the use of nine MSSVs per SG.)
2.
The capacity of the smallest pressure-relief valve shall not be less than 50 percent of that of the largest pressure-relief device.
(This is currently met by the use of two 5 percent and seven 7 percent capacity MSSVs per SG.)
~..
,- v-Docket No. 50-346 License No. NPF-3 Serial'No. 1487 Page 4 3.
The. set pressure of one of the pressure-relief devices shall not be greater than the. maximum allowable working pressure of the system at design temperature.
(This is currently. met with two 7 percent capacity MSSVs per SG set at the design pressure of 1050 psig.)
4.
Total rated relieving capacity of the pressure-relief devices shall prevent a rise in pressure of more than 10 percent above system design pressure at design temperature under any pressure transients anticipated to arise.
(This is currently met by having a total MS system relief capacity of 120 percent of rated-thermal power and a maximum MSSV setpoint pressure of 1100 psig.
This setpoint, allowing for a 1 percent tolerance, assures MS system pressure remains below 110 percent of design pressure, or 1155 psig.)
1 The fo11 ewing ASME Code requirements are proposed' to be incorporated into the ACTION statement for LCO 3.7.1.1 in place of TS Table 4.7-1:
1.
A minimum of two OPERABLE safety valves per Steam Generator, one with a setpoint not greater than 1050 psig (+/- 1%), and, 2.
A maximum setpoint of 1100 psig (+/- 1%) for any OPERABLE safety valve.
Other administrative controls will require that two MSSVs per SG be set at 1050 psig (+/- 1%) per the current practice. This practice of setting two MSSVs per SG at 1050 psig provides flexibility in i
satisfying the ASME Code requirement of one valve at 1050 psig by allowing one 1050 psig MSSV per SG to be declared inoperable.
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These requirements will provide continued assurance that:
4 1.
The valve lift settings and system overpressure protection are in accordance uith the requirements of Section III of the ASME B&PV Code, 1971 Edition.
2.
The secondary system pressure will be limited to 110 percent of MS system design pressure of 1050 psig (including 1 percent set pressure tolerance) for the most severe anticipated system operational transient, as previously analyzed.
3.
The minimum MSSV relieving capacity is available as described in the TS bases.
The nominal MSSV relief capacity of two valves per header, set at the design pressure of 1050 psig (first bank of safety valves), is available to satisfy the 2
evaluation of Serial 1464 (Reference 8.4) which proposes'to increase the Anticipatory Reactor Trip System (ARTS) turbine trip arming setpoint.
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Docket No. 50-346 License No. NPF-3 Serial'No. 1487 Page 5 2.0 SYSTEM AND COMPONENTS AFFECTED Main Steam System 3.0 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.
Davis-Besse Nuclear Power Station, System Procedure, SP1106.24 - Main Steam System Operating Procedure, Revision 09.
4.0 SAFETY FUNCTIONS AFFECTED The main steam system receives steam from each of two steam generators (SG) and supplies it to the turbine generator. The MS system design rating is 1050 psig at 600 degrees F.
Pressure relief for the MS system is provided by the turbine bypass valves (TBV), atmospheric vent valves (AVVs) and MSSVs. The AVVs and the MSSVs are located on the MS header between each SG and its associated ::in steam isolation valve (MSIV). This configuration ensures overpressure protection of the SG even when it is isolated with the MSIV closed and the TBVs unavailable.
The MSSVs are designed in accordance with the requirements of ASME Boiler and Pressure Vessel Code,Section III, 1968. The AVVs and TBVs open at lower pressures than the MSSVs.
The safety function of the MSSVs is to provide the pressure relief capacity necessary for the SGs to dissipate the primary system energy generated at the reactor high power level trip setting. The MSSVs are part of the secondary system pressure boundary. There are nine spring operated MSSVs in each MS line. The nine valves have a total capacity of 120 percent (7,087,461 lbs/hr) of the rated steam flow of one SG operating at 100 percent (5,880,000 lbs/hr) of rated power. The MSSV capacities per SG are as follows:
7 MSSVs at 845,759 lbs/hr each (Approx. 7% of rated capacity) 2 MSSVs at 583,574 lbs/hr each (Approx. 5% of rated capacity) 9 MSSVs at 7,087,461 (*) lbs/hr total (60% of total secondary system steam flow, and 120% of rated SG capacity)
- rounded to 7,087,500 lbs/hr in the TS bases Each AVV provides a relief capacity of 5 percent of rated thermal power.
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'Do kat No. 50-346 License No NPF-3 Serial' No. 1487 Page 6 The TS bases for ARTS (Section 3/4.3.1 and 3/4.3.2) states:
"Safety grade anticipatory reactor trip is initiated by a turbine trip above 25 percent rated thermal power. This anticipatory trip will operate in advance of the reactor coolant system high pressure reactor trip to reduce the peak system pressure and thus reduce-the challenges to the power operated relief valve. This anticipatory reactor trip system was installed to satisfy Item II.K.2.10 of NUREG-0737."
Reference 8.4 proposes increasing the ARTS turbine trip input arming level from 25 percent to 45 percent. That evaluation considers secondary side relief capacity to support a successful turbine runback. The TBVs and first bank of MSSVs provide the necessary relief capacity evaluated for the proposed ARTS arming level increase.
5.0 EFFECTS ON SAFETY i
The proposed revisions to TS 3/4.7.1.1 are evaluated below for impact on USAR analyzed events and the TS bases.
5.1 TS Table 3.7-1 Deletion The proposed revision to LC0 3.7.1.1 and deletion of TS Table 3.7-1, does not impact any USAR analyzed events or TS Bases. The existing tabular presentation of reduced high flux trip setpoint dt.e to inoperable MSSVs is determined using the TS Bases relationship between SG design parameters, inoperable MSSVs, maximum existing MSSV relief capacity and the High Flux Trip Setpoint for four pump operation. The right hand side of this equation can be rearranged to utilize total operable MSSV relief capacity per SG as the independent variable.
This revised relationship is provided in the proposed revision to LCO 3.7.1.1 and the associated TS Bases section. A graphical representation of this revised equation is also provided in the TS Bases. The curve illustrates appropriate reductions in reactor power based on an actual reduction of MSSV rated relief capacity. Minimum operability of MSSV relief capacity is maintained per ASME Code requirements with at least one MSSV per SG with a setpoint not greater than MS system design pressure and at least one with a maximum setpoint of 1100 psig (+/- 1%). Consequently, unnecessary conservatism can be removed from this TS requirement and plant availability can be enhanced.
5.2 TS Table 4.7-1 Deletion The bases for TS 3/4.7.1.1 considers that the bounding event for MSSV relief capacity is a turbine trip from 100 percent rated thermal power coincident with a loss of condenser heat sink. This is analyzed in USAR Chapter 15, Section 15.2.9, "Loss of All AC Power to Station s
Docket No. 50-346 License No. NPF-3 Serial'No. 1487 Page 7 Auxiliaries (Station Blackout)".
For this event, the condenser circulating water system is lost and, therefore, the TBVs are not available to relieve MS system pressure. The proposed deletion of TS Table 4.7-1 and incorporation into LCO 3.7.1.1, as discussed in Section 1.2 above, does not affect MS system overpressure protection required by ASME B&PV Code and the total rated MSSV relief capacity.
Similarly, MSSV relief capacity is utilized in the USAR for mitigation of the following events; 1) Loss of Normal Feedwater, 2) MS Line Break, 3) SG Tube Rupture, and 4) Excessive Heat Removal Due to Feedwater System Malfunction. The USAR safety evaluation criteria for these events are not affected by this TS revision.
The feedwater system malfunction analysis states that the two lowest setpoint safety valve banks alone can provide secondary system pressure protection for this event. This TS revision allows for changes in MSSV setpoint pressures from those assumed in the USAR analysis, but the total rated relief capacity is unchanged.
Consequently, equivalent secondary system pressure protection is provided for this event.
The requirements of Section III of the ASME B&PV Code, 1971 Edition, are met since, 1) the existing MSSV relief capacity is adequate and unchanged by this revision, and 2) provisions of operability are incorporated into the proposed revisions to LCO 3.7.1.1 requiring a minimum of two operable MSSVs per SG, at least one with a setpoint not greater than MS system design pressure, and the other MSSVs with a maximum setpoint of 1100 psig (+/- 1%).
Consequently, SG overpressure protection is assured for anticipated transients. Other administrative controls will also require that two MSSVs per SG be set at 1050 psig (+/- 1%). The ASME Code requirements for MS system design pressure protection are, therefore, satisfied even with one MSSV, set at 1050 psig, per SG inoperable.
Reference 8.4 discusses the effects on safety due to the proposed increase of the ARTS turbine trip input arming level from 25 percent to 45 percent. The limiting case analyzed for that proposed change allows for an end of life thermal power prior to the turbine trip in excess of the steam relief capacity assumed to be available from the TBVs and the MSSVs set at 1050 psig. The installed MS system steam relief capacity was arbitrarily limited, in the Reference 8.4 evaluation, to the first bank (2 MSSVs per SG set 1050 psig) of MSSVs. Since this proposed TS revision evaluation allows for a first bank relief capacity of 20 percent, it potentially affects the Reference 8.4 safety evaluation which is based on the existing MSSV first bank relief capacity of 30 percent.
However, the existing 30 percent first bank relief capacity provides a 10 percent excess steaming capacity margin per the Reference 8.4 i
evaluation. Therefore, with the potential reduction in MSSV first i
bank relief capacity to 20 percent, the proposed ARTS arming level i
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' Dockst No. 50-346 License No. NPF-3 Serial No. 1487 Page 8 increase to 45 percent still does not exceed the combined total MS relief capacity available from the TBVs (25%) and the first bank MSSV capacity (20%). Additionally, the Reference 8.4 evaluation conservatively ignored the 10 percent steaming capacity available from the AVVs. Therefore, the Reference 8.4 evaluation conclusion remains valid.
6.0 Significant Hazards Consideration The Commission has provided standards in 10CFR50.92(c) for determining whether a significant hazards consideration exists. A proposed amendment to an Operating License for a facility involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not: (1) involve a significant increase in the probability or consequences of an accident previously evaluated, (2) create the possibility of a new or different kind of accident from any accident previously evaluated, or (3) involve a significant reduction in the nargin of safety. Toledo Edison hac reviewed the proposed change and determined that:
1.
The proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated because the MSSVs do not contribute to the initiation of any accident. Though improper operation and malfunction of MSSVs are considered in USAR analyses as part of accident scenarios, no change in the operation or function of the MSSVs is effected by this proposed change. ASME Code requirements for MSSV setpoint, relief capacity and operability are maintained.
The proposed change to the revised relationship between RPS high flux trip setpoint reduction and inoperable MSSVs does not involve a j
significant increase in the probability or consequences of an j
accident previously analyzed because the high flux trip setpoint does not contribute to the initiation of any accident. The main steam system relief capacity requirements are not changed.
The proposed relationship provides a reduction in the RPS high flux trip setpoint based on the available main steam system relief capacity; therefore, the consequences of any accident previously analyzed are not affected. (10CFR50. 92 (c) (1))
2.
The proposed change does not create the possibility for a new or different kind of accident than previously evaluated because the function of the MSSVs or the RPS high flux trip is not affected.
(10CFR50. 92 (c) (2))
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-Sdrial No. 1487 Attachnent 2 Page 9 3.
The proposed change does not involve a significant reduction in a margin of safety. The proposed revised relationship between the available main steam safety valve relief capacity and the RPS high flux trip setpoint results in a reduction in the relationship's margin from the previously calculated setpoint which was based on the maximum safety valve relief capacity (rather than the actual capacity of the inoperable safety valves)..However, the reduction in the margin is the result of removing unnecessary conservatism. The reduction in the margin associated with the high flux setpoint and MSSV relief capacity is not significant in that adequate and proper relisf protection is still provided.
This is because the RPS high flux trip setpoints which are generated by the proposed relationship will yrovide trip setpoint reductions based on actual operable main steam ystem relief capacity.
The req,irements for MSSV lift setting and secondary overpressure protteti n requirements are not affected by the proposed change in thi-ASME B&PV Code,Section III, 1971 Edition requirements are
..m still met. (10CFR50.92 (c) (3))
7.0 Conclusion Based on the above Toledo Edison has determined that the proposed change does not involve a significant hazards consideration.
8.0 References 8.1 Davis-Besse Nuclear Power Station, Unit No. 1, Operating License, Appendix A, Technical Specifications 8.2 Davis-Besse Nuclear Power Station, Unit No. 1, Updated Safety Analysis Report, July 1987 l
8.3 ASME Boiler and Pressure Vessel Code, 1971 Edition 8.4 Serial No. 1464, dated February 1, 1988, "License Amendment Application Regarding Changes to Setpoints for Anticipatory Reactor Trip System Arming, Reactor Protection System High Pressure Trip and Pilot Operated Relief Valve Trip", (TAC No. 66727) 8.5 NUREG-0737, Clarification of TMI Action Plan Requirements, dated November 1980.
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