ULNRC-03638, Requests Exemption from 10CFR50.60 in Order to Apply Guidance in ASME Code Case N-514, Ltop. Exemption Supports Amend to Ts,Revising Heatup,Cooldown & Cold Overpressure Mitigating Sys Curves
| ML20210P748 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 08/22/1997 |
| From: | Passwater A UNION ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| ULNRC-03638, ULNRC-3638, NUDOCS 9708270332 | |
| Download: ML20210P748 (4) | |
Text
- _.
' 1901 Deuteau Avenue
~ Post Ofixe Ba l49
=s
. St Imis, Masouri63166 s.
314 621 3222 i
August 22, 1997
- b\\70N -
LICLlDCTRKT a
U.
S. Nuclear Regulatory Commission ATTN:
Document Control Desk Mail Station Pl-137 Washington, D. C.
20555-0001 ULNRC-03638 Gentlemen:
l~
CALLAWAY PLANT f
DOCKET NUMBER 50-483 EXEMPTION TO 10CFR50.60,
" Acceptance Criteria for Fracture Prevention for Lightwater Nuclear Power Reactors for Normal-Operation" Union Electric Company herewith transmits a request for exemption to 10CFR50.60 " Acceptance.
Criteria for Fracture Prevention for Lightwater Nuclear Power Reactors for Normal Operation".
We request this exemption in order to apply the guidance in American Society of Mechanical Engineers Code Case N-514, " Low Temperature Overpressure
.otection", in lieu of those specified by 10CFR50, Appendix-G.
This exemption supports-an amendment to-the Callaway Technical Specifications-(to be submitted prior to October 1,-1997) which will revise the heatup, cooldown, and Cold Overpressure Mitigating System curves.
As such, review and approval of this exemption is requested by March 1, 1998 so that it-can-be incorporated consistent with the amendment and prior to Refuel 9.
If you have any questions-concerning this gL I ' '
-request, please1 contact us.
Very truly yours, C70097 d[
g 1
Alan C.
Passwater Manager-Licensing and Fuels
Attachment:
Exemption Request 9708270332 970822 PDR ADOCK 05000483 P
PDR o
s cc: ~
M. H. Fletcher Professional Nuclear Consulting, Inc.
19041 Raines Drive Derwood, MD 20855-2432 Regional Administrator U.S. Nuclear Regulatory Commission Region IV
-611 Ryan Plaza Drive.
Suite 400 Arlington, TX 76011-8064 Senior Resident Inspector Callaway Resident Office.
U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Barry C. Westreich (2)
Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission 1 White Flint, North, Mail Stop 13E16
-11555 Rockville Pike Rockville, MD 20852-2738 Manager, Electric Department Missouri Public Service Commission P.O. Box 360
{
Jefferson City, MO 65102 I
~.
a: 000 _
Attachment to ULNRC-03638 Page 1 of 2 10CFR50. 60 Exemption Request Union Electric requests exemption from the requirements of 10CFR50.60 in accordance with the guidance specified in 10CFR50.12 (a) (2).
This exemption would permit using the safety margins recommended in American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Case N-514, " Low Temperature Overpressure Protection", in lieu of the safety margins required by 10CFR50, Appendix G.
To prevent transients that would result in pressure increases greater than 10CFR50, Appendix G pressure / temperature (P/T) limits while at low temperatures, Union Electric has a Cold Overpressure Mitigation System (COMS).
The pressure actuation setpoint has been established such that if a transient occurred, the COMS would prevent the pressure in the reactor vessel from exceeding the P/T limits of 10CFR50, Appendix G.
The pressure actuation setpoint must also be high enough to prevent the inadvertent actuation of the COMS as a result of normal operating pressure surges.
Application of the various instrument and calculation uncertainties has resulted in a COMS actuation setpoint that established an operating window that-is too narrow to permit reasonable system makeup and pressure control.
To allow for an increased operating band to permit system makeup and pressure control, Union Electric requests use of ASME Code Case N-514, which designates the allowable pressure as 110% of that specified by 10CFR50, Appendix G.
ASME Code Case N-514 is consistent with guidelines developed by the ASME Working Group on Operating Plant Criteria to define pressure limits during low temperature overpressure protection (LTOP) events.
The defined pressure' limits avoid certain unnecessary operational restrictions, provide adequate margins against failure of the reactor pressure vessel, and reduce the potential for unnecessary actuation of pressure-relieving devices used for LTOP.
The
-content of this code case has been incorporeted into Appendix G of'Section.XI of the ASME Code and published in the 1993 Addenda to Section'XI-and has been incorporated into the latest draft of Regulatory Guide 1.147 (Draft DG 1050, dated May 1997).
Pursuant to 10CER50.12, the Commission may, upon applicetion by any_ interested person or upon its own initiative, grant exemptions from the requirements of 10 CFR Part 50 when (1) the exemptions are authorized by law, will not present an undue risk to public-health or safety, and are consistent with the common defense and security and_(2) when special circumstances are present.
According to 10CFR50.12 (a) (2) (ii), special circumstances are present whenever application of the regulation
Attachment'to ULNRC-03638
'Page 2;of 2 i fin' question is not_necessary to achieve the underlying _ purpose'of tthe rule.
It _ is our position-that per 10CFR50.12 (a) (2) (ii), special circumstances are present such that " Application of.the regulation in the.particular. circumstances would not serve the
-underlying purpose of.the rule or is not necessary to-achieve the underlying purpose of the rule...".
The underlying purpose of 10CFR50, Appendix G is to establish fracture toughness requirements for ferritic materials of pressure-retaining components of the reactor _ coolant pressure boundary to provide adequate margins =of safety during any condition'of normal operation.
Appendix G-of ASME'Section XI requires lthat_the P/T limits be
-established (a) using a safety factor of two (2) on the principle membrane _(pressure) stresses; (b) assuming _a flaw at the surface 4
- with a depth of one-quarter (1/4) of the vessel wall thickness and' the length of six -(6) times its depth; and (c) :using a
- conservative fracture toughness curve that is based on the lower-
-band of static,-dynamic, and crack arrest-fracture toughness.
. tests on material-similar to the Callaway reactor vessel-material.
In determining the setpoint for LTOP events, we-propose'to use safety margins ~ based on an alternate methodology consistent with the:ASME Code Case N-514 guidelines.
The ASME Code Case N-514 allows determination of the setpoint for LTOP events ~such that
-the_ maximum pressure in the vessel would not exceed 110% of.the EP/T-limits of;the' existing ASME Code Appendix G..This results in i
a safety: factor of 1.8 on the principle men 6rane stresses.
All other1 factors, including assumed flaw sizefand fracture
= toughness,: remain the same.
Although this methodology would reduce the_ safety factor on the principal membrane stress, the proposed criteria will provide adequate margins of= safety.on the h
< reactor' vessel during LTOP transients,.and thus will satisfy the underlying purpose of 10CFR50.60 for. fracture. toughness requirements.
Further, by relieving the operational restrictions, the potential for undesirable COMS actuation would be reduced, thereby improving. plant _ safety.
.c i
M