A05975, Requests NRC Confirmation of Util Interpretation of Reg Guide 1.84 Applicability to plant-specific Use of ASME Code Case N-4111, Alternate Damping Values for Seismic Analysis of Class 1,2 & 3 Piping Sections,Section Iii,Div I

Requests NRC Confirmation of Util Interpretation of Reg Guide 1.84 Applicability to plant-specific Use of ASME Code Case N-4111, Alternate Damping Values for Seismic Analysis of Class 1,2 & 3 Piping Sections,Section Iii,Div I

ML20214Q900
Person / Time
Site:	Millstone
Issue date:	09/17/1986
From:	Opeka J NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	Thadani A Office of Nuclear Reactor Regulation
References
RTR-REGGD-01.084, RTR-REGGD-1.084 A05975, A5975, B12253, TAC-62859, NUDOCS 8609290008
Download: ML20214Q900 (6)

Text

o e NORTIMAST UTILITIES o.nor.i Orric.. . s.io.n str .t. s.riin. Conn.cticut J .we%.sieuens .m cow P.O. BOX 270

.acs . *ia acaea caw HARTFORD. CONNECTICUT 06141-0270 L L J Z7/CE,, ',**"j'7 (203) 665-5000 September 17,1986 Docket No. 50-336 A05915 B12253 Office of Nuclear Reactor Regulation Attn: Mr. Ashok C. Thadani, Director PWR Project Directorate #8 Division of PWR Licensing - B U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Use of ASME Code Case N-411, Alternate Damping Criteria In a letter dated April 15,1986,(I) Northeast Nuclear Energy Company (NNECO) requested authorization from the NRC Staff pursuant to 10 CFR 50.55a(a)3 for use of ASME Code Case N-411," Alternate Damping Values for Seismic Analysis of Class 1, 2 and 3 Piping Sections,Section III, Division 1" at Millstone Nuclear Power Station, Unit No. 2. This code case had been approved by the ASME on September 17,1984.

In a letter dated July 31, 1986,(2) the NRC Staff responded to NNECO's Reference (1) request, stating that the NRC had issued a revision to Regulatory Guide 1.84, " Design and Fabrication Code Case Acceptability ASME Section III, Division 1", whidi endorsed ASME Code Case N-411, subject to certain conditions as outlined in the revised Regulatory Guide. Reference (2) stated that NNECO can now use ASME Code Case N-411 in accordance with the conditions outlined in Regulatory Guide 1.84 without prior NRC approval.

NNECO has reviewed the conditions regarding use of ASME Code Case N-411 outlined in Regulatory Guide 1.84 as they would apply to Millstone Unit No. 2.

Attachment (1) to this letter details NNECO's interpretation of how the

" conditions" apply to Millstone Unit No. 2. It is the intention of NNECO to use ASME Code Case N-411 extensively for future evaluations of piping systems at Millstone Unit No. 2. There is the potential that successful application of these alternate damping criteria could result in removal of snubbers, determined to be unnecessary, throughout the plant. It is NNECO's opinion that there are some ambiguities in the " conditions" outlined in Regulatory Guide 1.84, and there are obvious negative consequences of a misinterpretation of the " conditions" by NNECO (i.e., the removal of snubbers or other piping system changes that might later need to be restored to the previous configuration).

8609290008 860917 $

yDR ADOCK 05000336 L (1)3.F. Opeka letter to A.C. Thadani, dated April 15,1986.

le$ UV Q r

(2)A.C. Thadani letter to 3.F. Opeka, dated July 3,1986. k f

Accordingly, NNECO hereby requests that the NRC Staff review the attached discussion and respond in writing as to whether or not the Staff concurs with ~

NNECO's interpretation of how the Regulatory Guide 1.84 " conditions" regarding Code Case N-411 apply to Millstone Unit No. 2.

Pursuant to the requirements of 10 CFR 170.12(c), enclosed with this request is the requisite fee of $150.00.

To accommodate work planned for the Fall,1986 refueling outage at Millstone Unit No. 2, NNECO would appreciate a response from the NRC Staff by October 31,1986.

Please contact us if you have any questions.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY N b.D J. F. Opeka Senior Vice President A/)-

By: C. F. Sears Vice President Attachment i

Docket No. 50-336 B12253 Attachment 1 Millstone Nuclear Power Station, Unit No. 2 Discussion of Conditions for the Applicability of ASME Code Case N-411 i

i September,1986 r m-r- -- ---

---v - - - -, err ,.my--- , - - , - +.---,=4., e----.- - - - , - - , . . . . = . - - . . =r------=---.--x- - - - , - - - ~ - - - - ----

s Provided below is a detailed discussion of NNECO's understanding of each of the conditions for applicability of ASME Code Case N-411 to Millstone Unit No. 2

~

piping systems analysis. The discussion refers to conditions I through 4 and subparagraphs thereto, as listed in the latest version of Regulatory Guide 1.84.

Condition 1.A(1): Current seismic spectra (Regulatory Guide 1.60 or properly justified site - spectra), with amplified spectra broadened per Regulatory Guide 1.122.

NNECO's Response: Millstone Unit No. 2 FSAR Section 5.8 entitled Seismic Design completely describes the analytical metho.ds used for seismic design of structures and equipment. Section 5.8.1.1 describes the design response spectra utilized for Millstone Unit No. 2. The maximum horizontal ground motion acceleration for OBE is 0.09g and is 0.17g for the SSE event. The vertical ground acceleration is taken as 2/3 the horizontal for both events. The design response spectra for rock-founded structures are shown in Figures 5.8-1 and 5.8-2 of the FSAR. Millstone Unit No. 2 has been licensed in accordance with the requirements of the FSAR, thus the design response spectra described above are considered to be a properly justified site spectra.

The original design response spectra were developed utilizing the time history method of analysis, described within Section 5.8.3 of the FSAR. The response spectr_a to be used for piping system reanalysis using Code Case N-411 damping, will be derived in a manner consistent with the original FSAR analysis.

The only exception ~to the FSAR is that NNECO agrees to peak broaden these design spectra-in accordance with Regulatory Guide 1.222. In summary, as NNECO interprets conditions 1.A(1), the design response spectra to be used in accordance with Code Case N-411 will be based upon the original input design response spectra, and were derived consistent with the methodology stated in the FSAR Section 5.8.3,' with the response spectra curves broadened in accordance with the guidance provided in Figure 1 of Regulatory Guide 1.122,' Revision 1.

Condition I.A(2): The envelope- response spectrum analysis method with Regulatory Guide 1.92 modal and directional combinations, including load contributions from piping system modes with natural frequencies above 33 Hz such that their inclusion does not result in more than a 10% incrementalincrease-in response.

NNECO's Response: Even though FSAR requirements (Section 5.8.3 and 5.8.4) are different than those proposed by this condition, NNECO will use the envelope response spectra with R.G.1.92 modal and directional combinations for piping analysis using Code Case N-411 damping values. Further, load contributions i from system modes above 33 hz will be included using the " square-root-sum-of-the-squares" (SRSS) combination with those under 33 hz.

j NNECO will also commit not to use Code Case N-411 damping values for cases

, where inclusion of system response over 33 hz would cause more than 10% incremental increase in seismic response.

! Condition 1.A(3): Damping values lower than, or equal to, those from Regulatory Guide 1.61.

NNECO's Response: Millstone Unit No. 2 FSAR Table 5.8-1 provides material damping values used in seismic analysis of structures and systems. These values are lower than those allowed by R.G.1.61 and, thus, NNECO complies with this -

condition.

Condition 1.B: For the piping segments of'a piping system, either N-411 damping values or damping va'.ues from A(3) may be used. The mixture of both is not acceptable.

NNECO's Response: NNECO does not intend to mix Code Case N-411 damping values with those from Regulatory Guide 1.61 and thus we will comply with this condition.

Condition 1.C: For equipment only, damping values from A(3), or experimentally determined damping values, may be used. Conversely, if the equipment 'is modeled with the piping using N-411 damping, _the analysis results must show that the equipment have no responses below 20 Hz. For piping systems with different damping values for piping segments, equipment and supports, the modal damping values should be determined usinc; composite damping techniques (ASME Code, Section 111, Appendix N).

NNECO's Response: NNECO will comply with this condition by requiring that the equipment modeled with piping system using Code Case N-411 does not have any natural frequency under 20 hz.

In general, NNECO does not inten'd to recalculate floor / building response spectra curves using higher damping values allowed by R.G.1.61. Instead, Code Case N-

! 411 damping response spectra will be generated by using currently licensed floor i response spectra.

Condition 2: The user shall indicate whether the Code Case will be used for new

, analyses, for reconciliation work, or for support optimization. Due to the

increased system flexibility of the system, the following shall~be checked and' j verified for reconciliation or snubber / support optimization work:

a. Adequate clearance with adjacent structures, components and equipment

{ at alllocations of maximum predicted replacements.

I

b. The capability of mounted equipment to withstand the increased motion.

i-NNECO's Response:

l NNECO intends to use the Code Case N-411 for new analyses, backfit work, and

. snubber-reduction / support optimization work. For piping analyses that use Code Case N-411 damping values, NNECO will check and verify the following:

l a. Existing clearance with adjacent structures, components and equipment is j not exceeded.

b. Allinline equipment can withstand the increased motion.

f Condition 3: Analyses involving the peak shif ting technique per ASME Code l Case N-397 and N-411 damping are acceptable.

NNECO's Response: NNECO will comply with this condition. However, peak shif ting (ASME Code Case N-397) will be used with N-411 damping values only on a case by case basis.

Condition 4: ASME Code Case N-411 is not acceptable for application to piping system analysis under the following conditions:

a. Analysis of piping in which stress corrosion cracking has occurred, unless a case-specific evaluation is made and is reviewed by the staff.

b. Use of the time-history method of dynamic analysis.

c. Analysis of piping system which include energy absorbers designed according to ASME Code Case N-420.

NNECO's Response: As required by this condition, NNECO does not intend to use this Code Case (N-411) for application to piping systems that (i) exhibit / susceptible to stress corrosion cracking, (ii) use time-history method of dynamic analysis (iii) or contain energy absorbers designed per Code Case N-420.

CONCLUDING REMARKS:

It is the conclusion of NNECO that we fully comply with the conditions stipulated for the use of ASME Code Case N-411 in analyzing seismic response of piping systems for Millstone Unit No. 2.