ML20078M812
| ML20078M812 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 11/30/1994 |
| From: | Saccomando D COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9412050135 | |
| Download: ML20078M812 (3) | |
Text
[ ]2 Comm:writh Edi::n
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1400 Opus Place Downers Grove. IItnois 60515 November 30, 1994 Office of Nuclear Reactor Regulation U.
S. Nuclear Regulatory Commission Washington D.C.
20555 Attention:
Document Control Desk
Subject:
Request to Use American Society of Mechanical Engineers Code Case N-514 in the Determination of Low Temperature Overpressure Protection System Setpoints.
Braidwood Station Units 1 and 2 NPF-72/77: NRC Docket Nos. 50-456/457 Commonwealth Edison (Comed) requests approval, per Title 10 Code of Federal Regulations, Section 55a, Subsection a, paragraph 3 (10 CFR 50.55a (a)(3)) to use American Society of Mechanical Engineers (ASME)Section XI Code Case N-514, " Low Temperature Overpressure Protection Section XI, Division 1,"
in the determination of Low Temperature Overpressure Protection System (LTOPS) Setpoints for Braidwood Nuclear Station Units 1 and 2.
Code Case N-514 was approved by ASME on February 12, 1992.
Although e use of this Code Case is currently not referenced in Regulatory Guide 1.147, " Inservice Inspection Code Case Acceptability," Revision 10, dated July, 1993, the guidance in Code Case N-514 has been incorporated into the 1993 Addenda to the ASME Boiler and Pressure Vessel Code,Section XI, Appendix G.
Code Case N-514 provides guidance on when LTOPS shall be in effect, and the maximum pressure to which LTOPS shall limit Reactor Vessel pressure.
In particular, Code Case N-514 states:
"LTOP systems shall limit the maximum pressure in the vessel to 110% of the pressure determined to satisfy Appendix G paragraph G-2215 of Section XI, Division 1."
A copy of Code Case N-514 has been included with this request as Attachment 1.
Comed has reviewed Code Case N-514 and determined that its use would provide an acceptable level of quality and safety.
There are many conservatisms incorporated into the pressure-temperature (PT) limits calculated using the current methodology of ASME Code Section XI Appendix G.
The ASME explicitly recognized the amount of margin inherent in the Appendix G PT limits by incorporating Code Case N-514 in the 1993 Addenda to ASME Code Section XI Appendix G.
Use of this code case will not result in any design changes to Braidwood Station.
No new equipment will be installed and no existing equipment will be modified or removed.
The LTOPS system will still function to limit Reactor Pressure Vessel pressure and the use of Code Case N-514 will still ensure that the Reactor Pressure Vessel is protected from brittle fracture.
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7 Document Control Desk November 30, 1994 Compliance with the current requirements for determination of LTOPS setpoints included in 10 CFR 50 Appendix G results in hardships for Braidwood Station without a concurrent increase in the level of i
quality and safety.
Application of the current LTOPS setpoint-determination method reduces operating flexibility by reducing the margin between the maximum allowed Reactor Coolant System (RCS) pressure and the minimum RCS pressure for Reactor Coolant Pump (RCP) operation with no concurrent increase in protection against j
non-ductile failure of the Reactor Pressure Vessel.
The current methodology also increases the likelihood of LTOPS actuation at i
lower setpoints, and reduces the amount of separation of the setpoints for the Power Operated Relief Valves (PORV) used in the LTOPS system.
This endangers the RCP seals as actuation of LTOPS at setpoints determined by the current methodology may cause RCS pressure to drop below the minimum needed to maintain proper RCP seal differential pressure.
Approval of this request to use Code Case N-514 in the determination of LTOPS setpoints is necessary to allow Braidwood Station to obtain approval of new LTOPS Technical Specification curves which will be submitted in a future Technical Specification Amendment request.
These curves allow Braidwood Unit 1 to exceed 5.37 Effective Full Power Years (EFPY) of operation.
Braidwood is currently predicted to reach 5.37 EFPY on July 16, 1995.
Accordingly, Comed requests that this request to use Code Case N-514 in the determination of LTOPS setpoints be approved prior to July 10, 1995.
Please direct any questions to this office.
- incerely, e
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Denise If? Saccomando Nuclear Licensing Administrator j
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Attachment l
cc:
R. R. Assa, Braidwood Project Manager - NRR l
S. G. DuPont, Senior Resident Inspector - Braidwood l
J.
B. Martin, Regional Administrator - RIII Office of Nuclear Safety-IDNS l
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CASE l.
N-514 CASES OF A$ME AOILE3t AND PRESSURE %ISSEL CODE Approval Dote: Fetervary 12,1992 See Numencelindex for expiterion and any reaffirmation dates.
Case N-514 protection against failure dunng reactor start up and Low Temperature Oterpressure Protection shutdown operation due to low temperature over-Section XI, Dirtsion 1 pressure events that have been classi5ed as Service Level A or B events. LTOP systems shall be effective Inquay Section XI, Division 1, IWB-3730, re-at coolant temperatures less than 200'F or at coolant quires that during reactor operadort, load and tem-temperatures 2 corresponding to a reactor vessel perature condidons be maintained to provide pro-metal temperature 8 less than Rbr + 50*F, which.
tection against failure due to the presence of ever is greater. LTOP systems shall limit the maxi.
postulated flaws in the ferritic portions of the reactor mm pressure in the vessel to 110% of the pressure coolant pressure boundary. For those plants having detennined to satisfy Appendix G, para. G-2215 of low temperature overpressure protection (LTOP)
Section XI, Division 1.
systems, what load and ternperature conditions under IWB 3730 may be used to provide protection against failure during reactor start up and shutdown opera.
- The motant temperature is the remaor coolant inlet tempera-tion due to low temperature overpressure events that have been classr5cd as Service Level A or B events?
- h 8*I fn'tal 18"Potam is the impenmre,at a &nace one-founh of the vessel seccon thickness from the insa surface in the venet beltline region. RTur is the highest adjusted refe.
Reply: It is the opinion of the Committee that for resos teciperature for wcld or base metal La ibe belttine repon those plants having LTOP systems the folic, wing load
* "588" '"**""h ! ** '"8*8 **C*** **" f'*"'.'99.
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vessel 1:: side surface, as dete: mined by Regulatory Otude 1 and temperature conditsons may be used to provide Rev. 2.
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