ML20086P978
| ML20086P978 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 12/18/1991 |
| From: | Shelton D CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20086P980 | List: |
| References | |
| REF-GTECI-070, REF-GTECI-094, REF-GTECI-NI, TASK-070, TASK-094, TASK-70, TASK-94, TASK-OR 1970, GL-90-06, GL-90-6, NUDOCS 9112270306 | |
| Download: ML20086P978 (4) | |
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CENTERIOR ENEf1CY Donald C Shelton
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Docket Numbet 50-246 License Number NPF-3 Settal Number 1970 December 18 1991 linited States Nuclear Regulatory Commission Document Conttol Desk Vashington, D.C. 205$5
Subject:
Change to Technical Specification Banes 3/4.4.11, liigh Point Vents Gentlemen The attached ptovides a proposed change to the Davis-Besse Nuclear Power Station (DBNPS) Unit No. 1, Operating Licenso Number NPF-3, Appendix A, Technica. Specifloation (TS) Bases Section 3/4.4.11, liigh Point Vents. The proposed change adds a discussion of the overall operabi.lity requirements for the pilot-oper ted relief valve (PORV) and block valve in the DBNPS sy0 tem configura.on.
TbAs change is submitted in acentdance with Toledo Edison's (TF) casponse (TE letter Serial Number 1884, dated December 21, 1990) tn intC Generic Letter 90-06. Resolution of Generic Issue 70, " Power Opetated Relief Valve and Dlock Valve Reliability." Generic Letter 90-06 stated that although PORVs may not have been classified as sniety telated components that are used to mitigate a design basis accident, and therefore, may have not been included in the TS as part of the licensing basis, this was not an acceptable basis for rot incorporating TS requirements for the PORV.
As described in TE letter settal 1884, TL has appropriate shutdown requirements for the PORV and block valve, however, the Bases discussion should be expanded. The attached proposed change provides a description of the overall operability requirernents for the PORV and block valve in the DBNPS configuration.
Background
The pressurizer is a cylindrical vessel that is connected by the pressutizer surge line to the Reactor Coolant System (RC3) loop 2 hot leg (see attached figure). The pressurizer establishes and maintains RCS pressure within prescribed limits and provides a surge chamber and a vater reserve to accommodate changes in reactor coolant volume during operation.
RCJ pressure is decreased by injection of teactor coolant irom the Reactor Coolant Pump (RCP) 2-2 discharge via the ptissurizer spray nozzle.
RCS pressute is increttsed by energizing immersion type l
ptessut izer heaters.
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Page 2 Two ASHE code safety valves (RC 13A and RC 13B) and the PORV (RC 2A) are connected to the top of the pressurizer, and provide overpressure ptotection for the RCS.
Each of the code safety valves discharges to the containment atmosphere. The PORV dischanges to the pressurizer quench tank.
As described in TS Bases 3/4.4.2 and 3/4.4.3, Safety Valves, the PORV lift setpoint is higher than the Reactor Protection System (RPS) high pressur e trip setpoint, but lover than the lif t setpoint for the code safety valves. Therefore, the PORV should not open on any anticipated transient.
The control rod group vithdrawal accident vill result in the most limiting high pressure in the RCS. The analysis of this i
transient does not take credit for the PORV opening.
Therefore, the PORV provides additional margin for an overpressure transient and limits the lifting frequency of the code safety valves.
The motor-operated PORV block valve (RC 11) provides the capability to manually isolate the PORV in the event that it falls open, falls to rescat, or is leaking. This prevents uncontrolled depressurization and excessive leakage of reactor coolant.
The primary means_of-depressurization during a steam generator tube rupture (SGTR) accident is the pressurizer spray.
If pressurizer spray is not available, then the DBNPS Emergency Procedures direct the use of the pressurizer vent line (RC 239A and RC 200) as the means of RCS pressute reduellon. The use of the pressurizer vent line for recovery from a SGTR or for a__ natural circulation cooldown (pressurizer spray not available) has been chosen because a restricting orifice in the vent line limits flev to provide a controlled pressure reduction and prevent rupture of the pressurizer quench tank rupture disk.
Although not the pri. nary or s s ondary means to depressurize during a SGTR, t1.3 capability to manually open the PORV from the control room provides a backup method of depressurizing.
The DBNPS has two steam driven main feedvater pumps, two steam driven auxiliary feedvater pumps, and an electric motor driven feedvater pump to ensure that water can be delivered to the secondary side of the steam generators.
During an off design basis total loss of feedvater event, the PORV flow path (RC 2A and RC 11) is one method of providing a relief path during " feed and bleed" cooling.
As described in Section 3.6.6 of the DBNPS Fire llazards Analysis Report (filar), in the event of a serious station fire, the PORV is the preferred means of depressurizing the RCS to a pressure below the operating pressure of the liigh Pressure Injection System, however the pressurizer vent line (RC 239A and RC 200) can be used.
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Docket Number 50-346 License Number NPF-3 Serial Number 1970 Page 3 Proposed Bases change Based on the apove discussion, the proposed Bases change reflects the following operability considerations 1.
Section 5.5.10.1 of the DBNPS Updated Safety Analysis Repott (USAR) statest "The Reactor Coolant System (RCS) liigh Point Vent System provides vents on each of the two hot legs and on the pressurizer to "ent non-condensible gases to aid in refilling the RCS and promotes natural circulation-flow for core cooling." The cristing Bases wording reflects the USAR.
flovever, the existing wording is clarified in the proposed Bases change.
2.
The PORV flow path (RC 2A and RC 11) provides a relief path during the feed and bleed mode of operation.
A discussion of this function has been added to the proposed Bases.
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3.
If pressurizer spray is not available, the pressurizer vent line (RC 239A and RC 200) is the preferred means for a Reactor Coolant System pressure reduction for tecovery from a steam generator tube rupture or natural circulation cooldown.
If this flow path is not available, or too slov, the PORV flov-path is availabic for use.
A discussion of this function has been added to the proposed Bases.
l 4.
In the event of a serious station fire, the PORV is the preferred means of depressurir'ng the RCS to a pressure below the operating pressure of the High Pressure Injection System, however, the pressurizer vent line (RC 239A and RC 200) can be used. A discussion of this function has beca added-to the proposed Bases.
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The PORV limits the lifting frequency of the pressurizer code safety relief valves.
The PORV block valve provides positive shutoff capaoility should the PORV become inoperable.
A discussion of these functions have been added to the proposed Bases.
6.
The title of the proposed Bases section change has been revised to be consistent with that:of the associated TS, and its numbering corrected.
Conclusion This proposed Bases change to TS 3/4.4.11 provides an expanded i
discussion of the overall operability requirements for the PORV and block valve in the DBNPS_ system configuration, and completes TE's response'to Generic Letter 90-06.
Toledo Edison requests-that.this TS Bases change be issued by the Nuclear Regulatory Commission (NRC) Staff by April 30, 1992.
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Docket Idumber 50-346 License Number NPF-3 i
Serial Number 1970 Page 4 If you have any questions, please contact Mr. R. V. Schrauder, j
Hanager - Nuclear Licensing at (419) 249-2366.
Very trul yours,
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J. Davis, Regional Administrator, NRC Region III J. B. Ilopkins, NRC/NRR DB-1 Senior Project Manager V. Levis, NRC Region III, DB-1 Senior Resident Inspector J. R. Villiams, Chief of Staff, Ohio Emergency Management Agency, State of Ohio (NRC Liaison) 4 Utility Radiological Safety Board t
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