ML18064A616

Requests Exemption from Certain Requirements of 10CFR50,App G & Application of ASME Code Case N-514, Ltop, in Determining Acceptable Ltop Sys Setpoint for Plant

ML18064A616
Person / Time
Site:	Palisades
Issue date:	02/10/1995
From:	HAAS K M CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9502210167
Download: ML18064A616 (5)

Text

• consumers Power POWERING MICHIGAN'S PROGRESS Palisades Nuclear Plant: 27780 Blue Star Memorial Highway, Covert, Ml 49043 February 10, 1995 Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 DOCKET 50-255 -LICENSE DPR-20 -PALISADES PLANT REQUEST FOR EXEMPTION

-ASME CODE CASE N-514 KurtM. Haas -Plant Safety and Licensing Director -Pursuant to the regulatory requirements of 10 CFR 50.12, "Specific exemptions", an exemption from certain requirements of 10 CFR 50 Appendix G is hereby requested for the Palisades Plant. This exemption is requested to allow the application of American Society of Mechanical Engineers (ASME) Code Case N-514, "Low Temperature Overpressure Protection", in determining the acceptable low temperature overpressure protection (LTOP) system setpoint for Palisades.

Regulatory Guides 1.84, 1.85, and 1.147 list the ASME Code Cases that have been approved by the NRC. Code Case N-514 has not yet been added to those Regulatory Guides, although its use has been approved for other facilities.

Code Case N-514 is discussed in the attachment to SECY-94-267, Section 4.5.2, "Status of Low-Temperature Overpressure Protection limits Issue". That discussion concludes with the statement "The content of Code Case N-514 has been incorporated into Appendix G of Section XI of the ASME Code and published in the 1993 Addenda to Section XI. The NRC staff is currently developing a revision to 10 CFR 50.55a that will endorse the 1993 Addenda and Appendix G of Section XI in the regulations." Using Code Case N-514 in calculating the setting limit curve for the variable LTOP provides the maximum acceptable operating band between the minimum pressure for Primary Coolant Pump (PCP) seal operation and the opening pressure for the Power Operated Relief Valves (PORVs). As the reactor vessel has ag*ed, this operating band has-become narrower.

-A wider band reduces* the* probability of an inadvertent opening of the PORVs and the consequent loss of Primary Coolant System (PCS) inventory.

The following discussion shows tbat the wider pressure band obtained by use of the Code Case N-514 LTOP limits instead of the Appendix G LTOP limits attains that wider band without a significant reduction in the margin of safety. 1 I A CMS' ENERGY COMPANY l ;..,. * .

• 2 Title*lO CFR 50.12(a) requires the following for an exemption to be granted: 1) 2) 3) 4) The exemption be authorized by law, The exemption will be consistent with the common defense and security, The exemption will not present an undue risk to the public health and *safety, and Special present. Consumers Power Company believes that each of these requirements is met in the case of this exemption request and provides a discussion of each. 1) The granting of an exemption to certain portions of 10 CFR 50 Appehdix G is authorized by law: *The.source of the requirement to be waived is 10 CFR 50.60(a) which that all light water nuclear power reactors must meet the fracture toughness program requirements for the reactor coolant pressure boundary as set forth in 10 CFR 50 Appendix G. 10 CFR 50.60(b) however, allows use -0f alternatives to the requirements of or portions.

thereof, when an. exemption is by the Commission under 50.12. 2) The exemption will be consistent the common defense and security:

The requested exemption would nqt affect the common defense and security.

3) The exemptioh will not present an risk to the public health and safety, and 4) Special circumstances are present: The following discussion discusses both the fact that granting the exemption would not present an undue risk to the public health and safety, and demonstrates that special circumstances are present. 10 CFR 50.12(a)(2)(ii) lists, as a special circumstance:

• Application of the regulation in the would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule. There are conservatisms in the development of Appendix G pressure/temperature curve calculations.

These conservatisms

1. A factor of safety of 2;0 on the primary membrane (pressure) stresses.

2. A margin factor of one or two standard deviations; to the shift in RTndt by Regulatory Guide 1.99, Rev 2. 3. The use of the stress intensity curves (K 1 R) by ASME Section III and XI, Appendix G, bounds the dynamic crack initiation and crack toughness.

Further, the use of the reference

• stress intensity curve bounds crack initiation fracture

.. 4. * . tbughness

{K 1 c) properties by a factor of to 2.5, depending on vessel temperature and RTndt" * -* Lower bound material properties are used in the analjsis.

increased mechanical properties of the vessel which accdmpany material embrittlement are not considered (increased yield strength and flow stress). ASME Code Case N-514 allows setting the LTOP actuation setpoint that the ASME Section XI, Appendix G limits are not exceeded by more than 10%. *Application of this Code Case at Palisades would allow a significantly wider pressure band between the minimum Primary Coolant Pump (PCP) operating pressure and the variable LTOP actuation point. Tris wider pressure band reduces the probability of an inadvertent opening of the Power Operated Relief Valves or of reduced pump seal life due to operation at reduced differential pressure.

The attached figure illustrates.the minimum PCP operating pressure and the necessary variable LTOP settings as they would be with and without use of Code Case N-514. 3 Establishing the LTOP limit curve in accordance with ASME Code Case N-514. criteria satisfies the underlying purpose of the ASME Code and the NRC regulations to ensure nuclear power plants and components are operated to ensure an acceptable level of safety .. Therefore, 1) there will be no undue risk to the public health and safety caused by issuance of the requested exemption, and 2) application of regulation in the particular circumstances is not necessary to achieve the underlying.

purpose of the rule.

• A Technical Specification change request, submitted on October 5, 1994, proposed revisions to the PCS Pressure-Temperature limits, LTOP setting limits, and PCP starting limits. The calculations which support the proposed . LTOP limits proposed in that submittal utilized ASME Code Case N-514. At the time of that submittal, it was not realized that ah was necessary for use of the code case.

SUMMARY

OF COMMITMENTS This letter contains no new commitments or revisions to former commitments.

Kurt M. Haas Director, Plant Safety & Licensing CC Administrator, Region III, USNRC Resident Inspector, Palisades State of Michigan

.. ATTACHMENT 1 Consumers Power Company Palisades Plant Docket 50-255 ** REQUEST FOR EXEMPTION

-CODE CASE N-514 . COMPARATIVE LIMITS FIGURE 1 Page _, ,*

.,, 'iii c. ::I II) rn. ) TOP w/o Code Case _._PCP Limit 600 +--------1-L TOP Limit LTOP Limit without ASME Code Case N-514 £

______ --+--------l

... Cl) N *;: ::I II) II) Cl. 200 +-----------+-----------+-------------'I------------+-----------+----'

50 100 150 200 250 300 Temperature, F " ' 219195 .. > t-3 t-3 > (") z t-3 I-'