ML20148E119

Value/Impact Assessment for Proposed Reg Guide 1.130,Rev 1, Design Limits & Loading Combinations for Class 1 Plate-&- Shell Type Component Supports

ML20148E119
Person / Time
Issue date:	10/05/1978
From:	NRC OFFICE OF STANDARDS DEVELOPMENT
To:
References
REGGD-01.130, REGGD-1.130, NUDOCS 7811060116
Download: ML20148E119 (2)

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c VALUE-IMPACT STATE!!EilT FOR PROPOSED REGULATORY GUIDE 1 Xhr " DESIGN LIMITS AND LOADING COMBINATIONS FOR CLASS 1 PLATE AND SHELL TYPE COMP 0tlEitT SUPPORTS" Statement of Problem Subsection NF of the ASME B&PV Code,Section III contains the rules for the design and construction of component supports which include the Class 1 plate and shell type component s_upports. Like the rest of Section III Codes, Subsection NF provides design limits but does not provide loading combinations to be associated with those design limits.

The need and concern for the subject matter of this guide has been expressed by cognizant technical branches of NRR.

While design rules for Class 1 plate and shell type and Clas.1 i linear type component supports are both provided by Subsection NF, the:. ?rt independently derived and are distinctly different. Design rules for pla nd shell type component supports follow the traditional ASME B&P'! Ccde cc- n:, and those for linear type component supports are modified frcm the .E rules. They are treated in separate guides for the reason of clarity.

Value Issuance and implementation of the subject guide will provide benefits in Mrms of improved safety and efficiency of the review process.

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1his guide clarifies the intent of Subsection NF of the ASME B&PV Code Section III for the design of Class 1 plate and shell type component supports.

It delineates loading combinations and their appropriate design limits for this specific type of component succort, reflecting the philoss;ry of the standard review plant but is considerably more detailed. The suppierentary criteria of this guide clarify the requirements of some NF design limits.

Of particular value is the recommendation that the Code defir.ed Level A Service limits or some other justifiable design limits be used for any 1cading ccmbinations resulted from an accident under which cra service of the supported system is required to mitigate the damage suf# red by the plant during that accident. This recommendation is essential to u sure the proper functioning of safety-related systems and is consistent with sna position of Regulatory Guide 1.48.

When design limits other than the Code defined level A servi: 2 'inits are to be used, justification should be made on the basis that the synin will be able to perform its prescribed function under the action of :r.2 loading combination of that plant condition.

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Impact This guide will have no impact on reactors applying for construction pennits because -

a. This guide merely documents in detail the present licensirg position which has been enforced since July 1975 and is given in the Standard Review Plan 3.3.3.

b. The guide documents current procedures being used by applicants and may be used as guidance in those cases where backfittir.q of the code to Class 1 component supports is considered.

c. The safety related philosophy that the function of a s; c:am which is to mitigate the damage suffered by the plant during ar- 2:ident must be maintained is identifical to that of the Regulator / : vide 1.48. The same philosophy is also adopted by the proposed ME3 ?:s' tion 6.

A case-by-case review will be required for all other reacters en the safety related issue of whether the supports will maintain suf#icient margins of safety under the loading combination of an accident if the supported systea is designed to nitigate the consequence cf that accident. The reactor designers do not have to follow literally the

. details of this guide to satisfy the regulators on this issue. It is possible that scme deficiencies may be discovered during the reviewing process. In that case, modification of the supports will be required.

Alternatives Considered A seeming alternative is to request the ASME to include all requirements of this guide into Subsection NF of its B&P'! Code Section II:. However, sub-section NF will not provide loading combinations for each : eval of design limits it supolied. The supplementary criteria in this cc::::ad guide were l proposed to the ASME WG on Component Supports in a letter ir Dece:nber 1974.

As of this time, the resolution of these issues has not been ir,corporated into the Code. When they are included in Subsection NF, this guide will be l revised as appropriate.

The alternative of modifying the present NF requirement is t: rrecare a complete set of rules for the design of component supports. 'n s would be expensive and unrealistic. .

Discussion Basic regulatory positions of this guide are similar to those cf the guide for linear type component supports. However, some supplemer.tary criteria are applicable only to one type component supports. Thus, the requirements are not identical in the two guides.