ML20147B654

Forwards Response to NRC Request for Addl Info (RAI) 121.3. This Info Will Be Included in Amend N12 of the Subj Facils PSAR & Supercedes Matl Filed 780531

ML20147B654
Person / Time
Site:	New England Power
Issue date:	10/03/1978
From:	Devincentis J NEW ENGLAND POWER CO.
To:	Office of Nuclear Reactor Regulation
References
CON-NRC-N-92 NUDOCS 7810110078
Download: ML20147B654 (7)

Text

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NEP 1 & 2 NUCLEAR PROJECT s 66 l NEWENGLAND POWER COMPANY relepHne 617 366-9011 i

, New England Electric System 20 Turnpike Rood, Westborough, Mossochusetts 01581 October 3, 1978 l

NRC-N-92 Director of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Sir:

DOCKET NOS. STN 50-568 and STN 50-569 Enclosed please find the following supplemental information requested by the NRC staff:

Response to NRC staff request for additional information (RAI) 121.3. This information will be included in Amendment N12 of the NEP 1 & 2 PSAR and supersedes material filed on May 31, 1978.

We trust yce "' is information satisfactory; how-ever, should you desi . formation, feel free to contact us.

v truly y urs,

,hv

.avincentis et Engineering Manager JDV/bfm Enclosure i

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NEP 1 & 2 Amendment N12 RAI 121.3 (10.0)

Present'in the NEP 1'and 2 PSAR an evaluation'of your design relative -

to the following criteria and provide justification for any areas of deviation from the recommendations:

Regulatory Guide'1.100 " Seismic Qualification of Electrical Equip-merr; for Nuclear Power Plants" Regulatory Guide 1.124 " Service Limits and Loading Combinations for Class 1 Linear Type Componcat Supports" Regulatory Guide 1.130 " Design Limits and Loading Combinations for Class 1 Plate and Shell Type Component Supports"  !

Regulatory Guide 1.121 " Bases for Plugging Degraded PWR Ste'am Generator Tubes" .

Response

NEP 1 & 2 Design is in conformance with the criteria described in RG 1.100 and RG 1.121.

Regulatory Guide 1.130 Design limits and Loading Combinations for Class 1 ,

Plate-and-Shell Type Component Supports (Revision ,

0, For Comment, July 1977)

1. Westinghouse will use the latest revision of Code Case 1644 as approved by Regulatory Guide 1.85.

2. Paragraph B.1 states that increases are not allowed for bolted connections for emergency  ;

and faulted conditions. The Westinghouse l position is that it is reasonable to allow an increase in the limits for bolted con-nections for these conditions. Further justification concerning this position can  ;

be found in Item 1 of the discussion on Regulatory Guide 1.124.

3. Paragraphs C.3, C.4(a), and C.b(a) state  ;

that the allowable buckling strength should be calculated using a design margin of 2 for flat plates and 3 for shells for normal, l upset, and emergency' conditions.

3:

In the design of plate-type supports, mem-ber compressive axial loads shall be limited per the requirements of Paragraph C.3 for normal upset, and emergency conditions.

There are no Class 2 shell-type supports in the Westinghouse NSSS.

4. In Paragraph C.7, the inclusion of the upset plant' condition in his load combination is inappropriate. The upset plant conditions are properly considered in paragraph C.4.

5. Paragraph C.7(a) references the criterion [

presented in F-1370(c), which states "... loads  ;

should not exceed 0.67 times the critical buckling strength of the support...".

In the design of plate-type component supports, member compressive axial loads should be limited to 0.67 times the critical buckling strength. If, as a result of.more detailed evaluation of the supports the member com-pressive axial loads can be shown to safely exceed-0.67 times the critical buckling strength for the faulted condition, verifica-tion of the' support functional adequacy will ,

be documented and submitted to the NRC for review. The member compressive axial loads will not exceed 0.67 times the critical buck-ling strength without NRC acceptance. The Westinghouse NSSS has no Class 1 shell-type supports.

6. The method described in paragraph C.7(b) of the Regulatorf Guide is overly conservative and inconsistent with the stress limits pre-sented in Appendix F. Westinghouse will use the provisions of F-1370(d) to' ':termine service level D allowable loaes ;or supports designed by the load rating method.

7. The criteria pertaining to the design limits and loading combinations used for other Class 1 component supports will be evaluated as the NEP 1 & 2 design progresses and will be dis-cussed in the FSAR.

Regulatory Guide 1.124 Service Limits and Loading Combinations for Class 1 Linear Type Component Supports (January 1978, Revision 1)

Discussion

1. The Regulatory Guide states in paragraph B.l(b):

" Allowable service limits for bolted connections -

are derived from tensile and shear stress limits and their non-linear interaction; they also

change with the size of the bolt. For this reason,'the increases permitted by NF-3231.1,.

-XVII-2110(a), and'F-1370(a) of Seciion III are.not directly applicable to allowable.

shear stresses and allowable stresses for bolts and bolted connections", and in para-graph C.4: "This increase of level A or B service limits does not apply to limits for bolted connections."

As noted above, the increase in bolt allow-able stress under emergency and faulted conditions is not permitted. Westinghouse belives that the present ASME Code rules are adequate for bolted connections. This position is based on the following:

It is recognized after extensive experimental work by several researchers that the inter-action curve between the shear and tension stress _in bolts is more closely represented by an ellipse and not a line. This has been clearly recognized by the ASME. Code Case 1644-6 specifies stress limits for bolts and represents this tension / shear relationship as a non-linear interaction equation (incor-porated into ASME III Appendix XVII via the Winter 77 Addenda) and has a built-in safety factor that ranges between 2 and 3 (depending on whether the bolt load is_predominantly tension or shear) based on the actual strength of the bolt as determined by test (Ref:

" Guide to Design Criteria of Boited and Riveted Joints," Fisher and Struik, copy-right 1974, John Wiley and Sons, Page 54).

Study of three interaction curves of allow-able tension and shear stress based on the ASME Code (cuergency condition allowables per XVII-2110 and faulted condition allow-ables per F-1370) and the ultimate tensile and shear strength of bolts (obtained from experimental work published by E. Chesson, Jr., N. L. Faustino, and W. H. Munse, "High Strength Bolts Subjected to Tension and Shear,"

Journal of the Structural Division, Proceed-ings of the American Society of Civil Engineers, October 1965, Pages 155-180) indicates that there is adequate safety margin between the emergency and faulted condition allowables and failure of the bolts.

c 1

During their tests to determine the strength

-and behavior characteristics of single high strength bolts subjected to various combina-tions of tension and shear (T-S), Chesson, et. al. used a total of 115 bolts to ASTM specification A325-61T and A354-Crade BC.

The A325-61T, which is a medium' carbon steel, had a yield point of 77000 psi to 88000 psi and ultimate strength of 105000 psi to_120000 psi, depending upon the bolt diameter. The A354-Grade BC, which is a heat treated carbon steel, had a yield point of 99000 psi to 109000 psi and ultimate strength from 115000 psi to 125000 psi, again depending upon the bolt diameter.

Figure 3A-2 shows the interaction curves for T-S loads on SA325 bolts. Curve (1) repre-sents the interaction relation (ellipse) permitted by Code Case 1644 (ASME III Appen-

~

dix XVII Winter 77 Addenda) for service lev-els A, B and design condition. Curve (2) represents the interaction curve which con-siders the Code Case 1644 allowables and the increase permitted by XVII-2110(2) for ser-vice level C. Curve (3) represents the interaction curve which considers the Code Case.1644 allowables and the increase per-mitted by F-1370(a) for service level D. ,

Curve (3) is the upper limit of the a110w-able stresses.

The design stress limits represented by Curves 1, 2, and 3 for A325 bolts are then compared against the ultimate strength of the bolts represented by Curve 4, which is based on Chesson's test results. The area between Curve 3 and Curve 4 is the safety margin between the maximum bolt stress under service level D and minimum ultimate strength of the bolt.

Factor of safety against failure ofr A325 bolts for various T-S ratios is shown in Figures 3A-3. The safety factor varies be-tween a minimum of 1.36 and a maximum of 2.29 depending upon the value of T-S ratio. This is based upon the ultimate strength of the bolts from Chesson's test and the allowables obtained from Code Case 1644 and the increase permitted'by F-1370(a) for service level D.

Figure 3A-3 demonstrates that there exists an adequate factor of safety for the complete range of T-S loadings.

From this study it is observed that: ,

(1) For the emergency condition, the safety factor (ratio of ultimate strength to allowable stress) varies between a mini-mum of 1.63 and a maximum of 2.73 depend-ing upon the actual tensile stress / shear stress (T/S) ratio on the bolt.

(2) For the faulted condition, the safety factor varies between a minimum of 1.36 to a maximum of 2.29, again depending upon actual T/S ratio on the bolt.

It is thus reasonable to allow an increase in these limits for the emergency and faulted conditions.

Based on the above discussion, for the emer-gency and faulted conditions, Westinghouse l will use allowable bolt stresses specified in Code Case 1644-6, as increased according to the provisions of XVII-2110(a) and F-1370(a),

respectively.

2. The increased design limit for the stress range identified in NF-3231.l(a) shall be ,

limited to the smaller of 2 Sy or Su ""1888 r otherwise justified by shakedown analysis.

3. In paragraphs B.5 and C.8 of the Regulatory Guide, Westinghouse takes exception to the requirement that systems whose safety-related funct1on occurs during emergency or faulted plant conditions must meet level B limits.

The reduction of allowable stresses to no greater than level B limits (which in reality are design limits since design, level A and level B limits are the same for linear sup-ports) for support structures in those sys-tems with safety related functions occurring during emergency or faulted plant conditions is overly. conservative. The primary concern is that the system remains capable of per-forming its safety function. For active com-ponents, this is accomplished through the operability program as discussed in Section 3.9.2.4. . In the case of Class 1 piping, main-taining the pipe stresses within level D limits assures that piping geometry is main-tained and that required flow is not impeded (This is further discussed in the response to question 110.34.) The selection of more re-strictive stress limits for component supports is not necessary to assure the functional capability of the system.

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4. Paragraph C.4 of the Regulatory Guide states:

"However, all increases (i.e., those allowed by NF-3231.1(a), . XVII-2110(a), and F-1370(a))

should always be limited by XVII-2110(b) of Section III". Paragraph XVII-2110(b) speci-fies that member compressive axial loads shall te limited to 2/3 of critical buckling.

In the design of component supports, mer.ber compressive axial loads shall be limited.to 0.67 times the critical buckling strength.

If, as a result of more detailed evaluation of the supports the member compressive axial loads can be shown to safely exceed 0.67 times the critical buckling strength for the faulted condition, verification of the sup-port functional adequacy will be documented and submitted to the NRC for review. The member compressive' axial loads will not ex-ceed 0.67 times the critical buckling strength without NRC acceptance. In no case shall the compressive load exceed 0.9 times the critical buckling strength.

5. The criteria pertaining to the design limits and loading combination used for other Class 1 component supports will be evaluated as the NEP 1 & 2 design progresses and will be dis-cussed in the FSAR.

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