B15017, Responds to Providing NRC W/Calculations That Documented Technical Justification of Approach for Developing Realistic,Median Centered in-structure Response Spectra for Plant Auxiliary Bldg

Responds to Providing NRC W/Calculations That Documented Technical Justification of Approach for Developing Realistic,Median Centered in-structure Response Spectra for Plant Auxiliary Bldg

ML20149H197
Person / Time
Site:	Millstone
Issue date:	11/04/1994
From:	Opeka J NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
B15017, TAC-M69459, NUDOCS 9411180209
Download: ML20149H197 (8)

Text

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ggg 107 Selden Street, Berlin, CT 06037 Utilities System wro co mue. se comi y

.~ P.O. Box 270 llartford, CT 06141-0270 j

'(203) 665-5000  !

November 4, 1994 Docket No. 50-336  ;

B15017 Re: Generic Letter 87-02 ~!

USI A-46 i U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Millstone Nuclear Power Station, Unit No. 2 ,

Generic Letter 87-02, Supplement 1, USI A-46 Request for Additional Inforreation {

(TAC No. M69459)

Northeast Nuclear Energy Company (NNECO), by letter dated July 7, 1994,tu provided the NRC Staff with-calculations that documented i

the technical justification of. the approach for developing realistic, median centered in-structure response spectra for the Millstone Unit No. 2 Auxiliary Building. The NRC Staff, in a letter dated September 22, 19 94, t2 requested additional information to aid them in completing their review of the USI A-46 submittal. NNECO's response to those questions' is -

contained in Attachment 1.

NNECO trusts that this additional information will assist the NRC Staff in successfully completing their review and issuing the requested Safety Evaluation Report. i i

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(1) J. F. Opeka letter to U.S. Nuclear Regulatory Commission, i

" Millstone Nuclear Power Station, Unit No. 2, Generic  :

Letter 87-02, Supplement 1, USI A-46," dated July 7, 1994.

i (2) G. S. Vissing letter to J. F. Opeka, " Request for Additional  ;

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Information Concerning Generic Letter 87-02, Supplement 1, USI A-46, Millstone Nuclear Power Station, Unit No. 2 (TAC ,

com m. u,4 No. M69459)," dated September 22, 1994.

9411180209 941104 PDR ADOCK 05000336 -

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U.S. Nuclear Regulatory Commission

, B15017/Page 2 November 4, 1994 If you have any questions regarding this information, please contact Mr. G. Papanic Jr. at (203) 440-2069.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY FOR: J. F. Opeka

• Executive Vice President BY: [ t- ' ~

. r d-S{ E. Scac'e Vice President cc: T. T. Martin, Region I Administrator G. S. Vissing, NRC Project Manager, Millstone Unit No. 2 P. D. Swetland, Senior Resident Inspector, Millstone Unit Nos. 1, 2, and 3 s

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1 Docket No. 50-336 j B15017 i Attachment i Millstone Nuclear Power Station, Unit No. 2 Generic Letter 87-02, Supplement 1, USI A-46 Request for Additional Information (TAC No. M69459) l l

November 1994 1

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U.S. Nuclear Regulatory Commission B15017/ Attachment 1/Page 1 November 4, 1994  ;

Millstone Nuclear Power Station, Unit No. 2 ,

i Generic Letter 87-02, Supplement 1, USI A-46 Request for Additional Information (TAC No. M69459)

NRC Request it NRC issued a Safety Evaluation (SE) on the licensee's 120-day response to supplement 1 to the Generic Letter (GL) 87-02 on October 30, 1992.

The commitmento made by the Northeast Nuclear Energy Company (licensee) as enumerated in the SE are different from those contained in the July 7, 1994 submittal. Please provide the rationale for the change.

Response The commitments made by Northeast Nuclear. Energy Company (NNECO) are being maintained since the

- Final Safety Analysis Report (FSAR) spectra will continue to be designated as " conservative '

design." However, ao stated in the Supplemental Safety Evaluation Report (SSER) No. 2,"'

Section II.4.2.4:

"If the licensee intends to use the option of developing or using " median-centered" in-structure response spectra, the licensee is requested to inform the NRC Staff..."

As such, NNECO's July 7, 1994, 2) submittal is I specifically intended for compliance with SSER .

No. 2. and is consistent with our September 21, 1992,"I response which stated (page 2, last paragraph):

i (1) U.S. Nuclear Regulatory Commission letter, " Supplement No. 1 to Generic Letter (GL) 87-02 that Transmits Supplemental j Safety Evaluation Report No. 2 (SSER No. 2) on SQUG 1 Implementation Procedure, Revision 2, as Corrected on l February 14, 1992 (GIP-2)," dated May 22, 1993.

(2) J. F. Opeka letter to U.S. Nuclear Regulatory Commission, l

" Millstone Nuclear Power Station, Unit No. 2, Generic Letter 87-02, Supplement 1, USI A-46," dated July 7, 1994.

(3) J. F. Opeka Letter to U.S. Nuclear Regulatory Commission, "Haddam Neck Plant, Millstone Nuclear Power Station, Unit Nos. 1 and 2, Plant Specific Response to Supplement 1 of Generic Letter 87-02," dated September 21, 1992.

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r-U.S. Nuclear Regulatory Commission B15017/ Attachment 1/Page 2 November 4, 1994

" ...NNECO will provide technical justification of the spectra generation methods where required by SSER-2,Section II 4.2.4."

NRC Request 2: The licensee nas indicated that because of the 40 foot rule cited in the Generic Implementation Procedure (GIP), Section 4.2, the licensee will apply Method B, Section 4.2.4, of the GIP. This section, among others, enumerates the types of input motion that may be used for generating in-structure response spectra, all of which are to be evaluated at the 84 percentile ncn-exceedance probability. Please explain in detail how the information provided in your July 7, 1994 submittal conforms with the GIP guidelines.

Response: The selection of the input motion for the Millstone Unit No. 2 USI A-46 evaluations is in full conformance with the GIP-2 requirements. In particular, the GIP-2 requirements of Section

4.2.4 state

"The in-structure response spectrum associated with SSE can be used to represent the seismic demand applied to nuclear plant equipment when one of the following three comparisons is made:

+ 1.5 X Bounding Spectrum envelops the realistic, median-centered, in-structure response spectrum (or conservative, design in-structure response spectrum) (5% damping).

. The GERS envelops the conservative, design, in-structure response spectrum (5% damping).

• The GERS envelops the 1.5 X the realistic, median-centered, in-structure response spectrum (5% damping)."

For the Millstone Unit No. 2 USI A-46 evaluations, the first of the above options (comparisons) was selected. The licensed Safe Shutdown Earthquake (SSE) rock motion of Millstone Unit No. 2, as documented in the Millstone Unit No. 2 FSAR, was selected as the control motion to be applied on rock.

The seismic fixed-base analysis of the Auxiliary l Building was performed using a suite of 30 time

U.S. Nuclear Regulatory Commission B15017/ Attachment 1/Page 3 ,

November 4, 1994 histories. The median 5% damped spectra of the 30 time histories closely approximate the SSE rock motion. Therefore, the median of the 5% damped in-structure response spectra that are generated from the fixed-base analyses is compared to 1.5 X Bounding Spectrum, thus conforming to the first option above.

As stated by the NRC Staff Reviewer in the telephone conversation between NNECO and the NRC Staff on August 10, 1994, the licensed SFE FSAR rock motion is by definition the 84th percentile motion for the Millstone Unit No. 2 site. This defined motion was also used as the control motion for the USI A-46 analyses. This _ structural analysis approach is consistent with Standard Review Plan (SRP) 3.7.1 guidelines for multiple time history analysis. The median value of structural damping is consistent with Regulatory Guide 1.61. As stated on page 4-18 of the GIP-2, such spectra may be treated as " conservative, design." For purposes of the Millstone Unit No. 2 USI A-46 work, these generated in-structure spectra will be exclusively used as " median-centered." The original FSAR spectra will continue to be used and designated as

" conservative, design" for consistency.

Therefore, there is conservatism included in the results, since the USI A-46 in-structure spectra are treated as median-type spectra.

Finally, as shown in Figure 4.3 of Calculation 0024-00099-A46-1, the median of the 30-times histories used in the analyses closely matches the SSE control motion (an 84th percentile motion).

The 84th percentile of the 30-time ..istories used in the analyses is at least 20% higher than the SSE rock motion (Figure 4.3 and 4.4).

NRC Request 3: Method B.1 of the GIP, Section 4.2.4 stipulates that a spectrum equal to 1.5 times the Bounding Spectrum (GIP, Section 4.2, p. 4-8) shall envelop the in-structure response spectrum. This does not appear to be the case in the subject submittal as shown in figures on page C-12, C-14, and C-15.

Please provide an explanation and a justification for the deviation.

Q.

U.S. Nuclear Regulatory Commission

, B15017/ Attachment 1/Page 4 November 4, 1994 Response The in-structure response spectra shown in the '

figures on pages C-12, C-14, and C-15 of Calculation 0024-00099-A46-1 corresponds to ,

elevation +71'6" and +86'6" of the Auxiliary Building. These figures were shown for completeness. As dictated by GIP-2 rules, for these elevations, the screening criteria do not apply and other approaches are used. (It must '

also be noted that currently no USI A-46 equipment are identified at those elevations.) 1 NRC Request 4: The licensee has invoked tc.e use of risk based seismic design criteria (annual probabilities of exceeding the spectral accelerations used). The ,

GIP document makes no reference to this practice i and NRC regulations do not provide for reducing seismic design criteria based on probabilistic estimates. Please provide the rationale and justification for the use of this method.

Response The comparison of the probabilities of exceedance of the spectral accelerations with the Electric Power Research Institute -(EPRI) and Lawrence Liverpool Nuclear Laboratory (LLNL) results is performed purely for demonstrating that the rock control motion is similar in conservatism to the average of the 69 U.S. sites studied by EPRI and LLNL, and serves no other purpose. This comparison does not affect the selection of the licensed SSE rock spectrum for USI A-46 evaluations. Therefore, the selection of the rock spectrum is not associated with any ris!: based methods and no reduction in the seismic design criteria was sought for the USI A-46 evaluation of i Millstone Unit No. 2.

i NRC Request 5: The licensee makes use of a ground motion deconvolution method (SHAKE computer program) to justify the seismic input motion for soil based ,

Category 1 structures. The FSAR specifically provides a design spectrum for soil based structures which, according to the FSAR, was applied at the base of the soil founded structures to produce in-structure response spectra. The soil analysis discussed in the subject report makes use of seed & Idriss type soil stress-strain relations which are no longer considered appropriate by the staff. In addition the' soil

U.S, Nuclear Regulatory Commission B1f,017/ Attachment 1/Page 5 Nc,vember 4, 1994 profile submitted in Table 4.1 of the subject '

report is not acceptable without a detailed in situ shear wave analysis of the Millstone 2 backfill used at the plant site. Please provide an explanation and a justification.

Response: The convolution of the rock outcrop motion at the surface was performed for comparison purposes with the SSE surface motion (in the FSAR) and the NUREG-0098 84th percentile motion. Note that no deconvolution was made. The soil analysis involved assigning the rock motion as a rock outcrop motion and propagating this motion upwards to the surface. This is the reason for the amplified surface spectra (with respect to the rea motion) shown in Figure 4.3 of Calculation 0024-00099-MOT-01. Because of the limited soil data on the backfill, the soil properties are varied as half the stiffness for lower bound and twice the stiffness for upper bound of the best estimate soil, thus conforming to SRP guidelines.

The stiffness degradation and damping relationship with soil strain used in this analysis are the latest relationships that exist in the industry and they were provided by Dr. I. M. Idriss through personal communication.

Since the above analysis was performed for comparison purposes, as discussed during the telephone conversation on August 10, 1994, between NNECO and the NRC Staff reviewers, it was decided to use the existing FSAR SSE soil spectrum to be applied at the base of structures that are founded on the soil surface.

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