ML17191A587
| ML17191A587 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 01/26/1998 |
| From: | Smith N Seismic Qualification Utilities Group (SQUG) |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML17191A588 | List: |
| References | |
| REF-GTECI-A-46, REF-GTECI-SC, TASK-A-46, TASK-OR NUDOCS 9804160299 | |
| Download: ML17191A587 (12) | |
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.sa*u*G January 26, 1998 Mr; JohnF; Stolz Office of Nuclear Reactor Regulation U.S,Nuclear Regulatory-c;;:ommission 11555 Rockville Pike - Mall Stop 014D07 Rockville,* *MJ? 20555
Subject:
NRC Response to SQUG *Letters on USI A-46 Generic RAis
References:
(1 )NRC (J. Stolz.}JettertoSQUG (N. Smith) dated-:Qecember 2, 1997, Evaluation of Seismic Qualification Utility Group's Responses to Generic Issues Included in NRCs Request for Additional Information
Dear Mr. Stolz:
The. NRC.letter. referenced above.. forwarded.the.staff's evaluation.of £0 U G's responses to six generic RAI items related to implementation of the GIP. The staffs evaluations of three ofthose *responses take *issue with *provisions *of the GlP previ~. approved by the NRC. In addition, the NRC has recently issued RAls to SQUG members requesting justifications for the schedules established for resolving GIP outliers. SQUG members are very concerned *that-the staff is *using the RAI*process to re-revie_w the criteria and guidelines in the GIP which have already been accepted by the NRC in Supplementary Safety Evaluation* Report No. 2 (SSER No.- 2). This has resulted-in new- ~terpretations of the GIP methodology and the addition of new requirements well after the utility members have completed their plant reviews and, in some cases, pfant modifications. The basis for our concerns.is. described.below in four ~neric RAi issues.
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Use of Ground Response Spectra (ORS) fgr EStjmating Seismic Demand The appToved GIP contains two optional methods for estimating seismic demand:
Method A which estimates demand *as -1.5 x*Ground Response Spectrum (ORS) for equipment located at elevations under about 40 feet above the effective grade with fundamentat frequencies greater than &'Hz, and.Method.B"Which-permits use of in-structure response spectra (ISRS).. Method B defines two types of ISRS, "conservative, design" and "realistic, median-centered," and requires higher safety factors for the median-centered specu~
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Mr; John January 26, 1998 SQUG~s understanding of the NRC positions in Reference 1 concerning use of Method A is that the utilities are bound.to the following two conclusions: (1) when SQUG utilities provided information in their 120.:day response lette-F (as requested by the. staff.in.Supplement No. 1 to GL 87-02 and SSER No. 2) on the methods used to calculate ISRS, licensees committed to using those spectra, and only those spectra, for
. all GIP evaluati*ons and {2} that a precautionary statement in the-GIP precludes use of Method A any time the plant's ISRS exceed the Method A spectra. These NRC conclusions are incorrect, inconsistent with the approved GIP, and differ from the understanding.amongSQUG, the.independent expert review panel, SSRAP, and the NRC staff at the time the GIP was developed. Our description of these two issues is provided below:
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PtirposeJOr Sirbrniitjilg ISRS to NRC As explained in SQUG'.s-lettcr of Novcmber-11, 199-7, some.SQUG members submitted information on methods used to calculate ISRS so the NRC could agre-e on whetherthey were 1.'conse~e. design'-' or- realistic median-centered." Neither the information request nor the responses in any way involved the commitment now being inferred by the staff. Further, no changes we-remade to the GIP provis-ionswhic-h give utiHties--the-gp_tion to use~
Method A or Method B.
It is noteworthy that the NRC did not request ISRS information from some SQUG members (e.-g.~ SEP plants) because they had-previom!.y reviewed them on other projects or already had the ISRS information in their files. With this previously obtained information, the NRC concluded in SSER, No. 2 (page 14) that* the-ISRS in the licensing-basis-documents of-these 15-plapts "may be used as 'conservative, design' in-structure response spectra." SSER No. 2 does not require these pl-ants-to use ISRS (Method-B} exclusivcly. oor does it draw a
- distinction between tht!se plants and the other USI A-46 plants, except with respect to whetlier the ISRSshouldbe cfassified:as <<--conserxative, design" or "realistic, median-centered."
There is nothing in GIP-2 or SS-ER No. 2 whiGb limits.-'t1se of the GIP to Method B. GIP-2 clearly states, in Part II, Section 4.2, that either Method A or Method B may be used to compare seisinic capacity tQ, seismic demand:
"The seismic capacity of an item of equipment can be compared to a seismic demand-which is-defined in terms--ofeithe:i;.~ ground response spectrum or an in-structure response spectrum. Table 4-1 outlines these types of comparisons as either Method A or B-. Method A is for making a comparison with a ground response spectrum; Section 4.2.3 discusses this type of comparison. Method B is a comparison with an in-structure
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Mr. John E StOlz
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January 26, 1998 respopsespectr~ Section 4.24discusses this*fyp_e of comparison.
Method A comparisons are generally easier to apply than Method B comparisons."*
(GIP-2, pg. 4-8)
SSERNo. 2 does not take exception to this provision in.the.. GIP but concludes that the screening procedures and criteria are adequate and acceptable:
"The staff has reviewed the screening procedures ami-~riteria. Based on the evaluations and findings described in Sections 11.4.2, 11.4.3, and II.4.4 below, the staff concludes*thatthe screening proc-edure.~ and criteria are adequate and acceptable only for verifying seismic adequacy of equipment in lJSl A-46 plants; subje~t to-the staff clarificatio~ interpretations, exceptions and positions described in the sections that follow."
. (S~R.No. 2,.pg. 12)
There are no *staff clarifieations,: interpretations-,: except~s, or positions in SSER No.* 2 which contradict our conclusion that licensees may use either Method 'A or Method B:
- The above interpretation ofNRCs positiOn on GIP~2; as CQntained in SSER No..2, is sup.p.orted by the. NRC.position.in GL 87"'.0l which.clearly allows use of 1.5 times ground response spectra (later called GlP Method A) in lieu of plant floor respons~ si:>ectra (also catted ISRS): *
When horizon tar floor spectra exist; -these spectra may be used to obtain the eq\\Jipment spectral acceleration. Alternatively, for equipment mounted less than about 40 feet above grade, one-and-a-half times the free-field horizontal design ground spectt~ may be used to conservatively estimate the equipment spectral acceleration. For equipment mounted more than about 40 feet above 'grade, floor spectra must be*used:"
(GL 87~02, Enclosurel Section 3, page 5)
Therefore, we conclude that the NRC's request for information in GL 87-02, Suppfement No. l andSSER No. 2; and their review oftliese 1,..B ISRS, was for the purpose of.evaluating* the adequacy of these spectra-fof ~e in GIP Method B and for deciding whether to classify them as either "conservative, design" or "realistic~ median-centered;" The licensee submittal of the :I:SRrS in the 120-day response does not imply a commitment to use these ISRS exclusive of Method A GlP Method A is dearly an alternative tG-Method B, and no requirement to use the more conservative of Method A or Method B is stated or implied.
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Mr. John January 26, 1998 b *.
Restrictions and I imitations on Use of GIP Method A
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In Reference 1, the NRC quotes a precauti-Onary n-0te in the GIP that Method Ais not intended for structures.where amplification is.expected to be more than about 1.5 times the free field ground response spectrum, and then the NRC concludes that if the plant's ISRS show.calculated*amplification :greatert:l,lan. l.5, use of Method A is precluded. The NRC has taken this precaution out of context. The fuJI text of the precaution makes clear that it is intended to alert reviewers not* to*use *Method A *for* alV,pjcal structures,, and~~rly indicates that Method A is intended for use on reinforced concrete frame and shear wall structures and heavily-5raced steeHJ".ame structures which~ typicaUy.w.ed in commercial nuclear plants. The remainder of the text in GIP-2 reads as follows:
"Seismic Capability Engineers. should be alert for u~ual, plant-specific situations which could cause the amplification factor to be greater than that of typical nuclear plant* structures. **The ISampiification* factor is only applicable to.reinfurcedconcretc_fram~ an.cl shear.wall structures and to heavily-braced steel frame structures.
(GIP-2, pg. 4-16)
The criteria for deciding whether this conditiOn is met are., not whether the calculatedISRS.fora.structure.are more than 1.5 x.GRS, but whether the structure is similar to commercial nuclear plant structures, i.e., reinforced concrete frame and shearwall structures*and heavily-~aced steel frame structures for which Method A was specifically intended.
This interpretation of the GIP is.consistent with the SSRAP report (GIP-2, Reference 5), upon which the GIP is based, and the NRC's review of this report in Generic Leuer (GL) 87*02. SSRAP's position in *this -repon. is that calculated ISRS (1) are known to have excessive conservatism, (2) are expected to exceed.
1.5 x GRS (GIP.Method A spectra); and(3) should not be ~d when assessing seismic ruggedness of floor-mounted equipment. Their position on this issue is as follows:
"Often floor spectra for nuclear power plants are very conservatively computed; In such" cases *an-amplification greater than. 1.5 may be found even at elevations below 40 feet above grade. However, when more median-centered analyses are performed that use reasonable damping levels for the structure and account for embedrnent and wave-scattering effects, these high amplifications are not observed with most earthquake ground motion.records. The Seismk Safety.Margin.Research Program
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Mr. John*F~ Stolz January 26, 1998
- (SSMRP) (References 31and32)1 has.delllQnstrated the large conservatism which exists in traditionally computed floor spectra versus median floor spe-ctra, Further; flOOf spectra measure(l less than 40 feet
- above the grade on moderately stiff portions of the Pleasant Valley Pump Station; the Humboldt Bay Nuclear Power Plant* f~ference 33), and Fukushima Nuclear Power Plant do not show amplifications over the ground spectra of more than I.5for frequencies aoove a:Oput 6 Hz. In fact, on floors corresponding to near grade level, the-floor spectra are less than or about equal to the ground spectra at frequencies above about 6 Hz.
Thus; it is SSRAP'sjudgment:thatamptifica:tions.gre~.than a.factor.of 1.5 are unlikely in stiff structures at elevations less than 40 feet above grade, except possibly at the fundamental frequency of ttie building where higher amplifications might occur when such a frequenc.y. is less than about 6 Hz. Thus, for equipment with fundamental frequencies greater than about* 8 *Hz in their as~anchored *condition~ it was. judged tpat floor.spectral amplifications within 40.feet of grade would be less than 1.5 when reasonably computed using more median-centered approaches."
. "It was judged by SSRAP lhat the use ofvery conserva~ive floor spectra should be avoided when assessing the seismic ruggc;:dness of floor-mounted equipment. It was also the opinion of SSRAP that many of the operating plants may only-have these very conservatively-computed floor spectra available. To avoid the burden of having fo compute.more reaJistic floor spectra; SS RAP decided to anchor its conclusions to.ground spectra at the nuclear plant sites in those cases where this was judged to be reasonable."
(SSRAPReport(GIP..:z*Re-ference5), pgs. 101-103]
The NRC came to a *similar conclusion in:GL 87~92 wft.fre they state the following:
"The comparison-of these seismic bouoos-withthG ~esign horizontal ground response spectrum [GIP Method A] is judged to be acceptable for equipment mounted less than about 40 feet above graqe (the top of the ground surrounding the building) and for moderately stiff structures."
(GL 87-02, Enclosure, pg. 9) 1NRC contractor, LLNL, presents the results of their work* in Ni)REG/CR-1489 in which ISRS are. estimated to.have factors of conservatism rangmg from 1.5 to 8.
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v Vv Mr. John F. Stolz* ~anuary 26, 1998 The NRC also endorsed SSRAP's approach in their Regulatory Analysis of the USI A-46 program where NUREG-'-121 t sta,tes the following:
"The NRC staff has closely followed the ~RAP work and is in broad agreement with its conclusions. "
(NUREG-1211, Se__ction V.1, pg. 17)
We have reviewed this matter with the chairman of SSRAP (Dr. R. P.
Kennedy), the group which developed Method A and obtained NRC staff agreement on its applicability. Iii conversationswe have had~th Dr. Kennedy, he indicated that he agrees with SQUG's position on the interpretation of SSRAP's precautionary note in the GIP.. He has indicated that the SQUG
.position is consistent with the 5_SRAP-r,ecommendation.
In summary, the NRC staffs recent interpretation on use of GIP Method A represents a new position which. is inconsistentwith-thell-dpcumented safety evaluations. Considering that most A-46 plants have completed the A-46 program reviews at a cotareost in excess of $100.mirrion, exctusive of the costs of modifications, and most have utilized the Method A option in accordance with the intent and lan&'llage of the GIP and the SSRAP report, such a change in requirements would have a significant program anc!,c_ost impact for no meaningful increase in safety:
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Lateral.Load Ductility. Evaluation of Cable Trays
- The staff has questioned the approved GIP methodology for cable trays and requested justification of keyelements*ofthis experience-based-method involving lateral load ductility and treatment of longitudinal loads. SQUG described the basis for these elements of the GIP method in *letters dated April 18 and june 11, 1997, and noted that these* areas were thoroughly-reviewed by* the staff and 4ccepted in SSER No. 2. In response to subsequent questions, SQUG is providing a copy of a report that was *originally usect by the-NRC staff in their-revieW and apprpval of the cable tray methodology. We are also providing two other documents to assist the current NRC staff members in understanding the basis for the NRCorigfnaJ position that the GIP provides an acceptable evaluation method for resolution of USI A-46. This information was transmitted.by separate correspondence dated January 23, 1998.
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Seismic Adequacy. of Re.13.¥s Mounted on.Diesel Generators and Air C.ornpressor!'\\
The GIP contains a provision which permits acceptance of relays mounted on equipment such *as diesel generators and air compressors*withe\\lt explicit seismic qualification by separate testing or analysis. This provision is based on substantial experience with such equipment in transportation a~d inll:fine industries. Specifically,
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January 26, 1998 experience with such equipment as diesel drive locomotives, shipboard diesels, and compressors supports the judgment of SQUG and SSRAP that relays which are rugged enough*towithstandthis"service, including the consider~ vibration during normal, startup and transient operation, without chatter, will not be affected by earthquakes equivalent to the Reference Spectra. Actual eartl1quake experience also supperts this judgment.
The Senior Seismic Review and Advisory Panel's-(SSRAP's) position on this issue is provided in their report as follows:
"Relays for which cbaHer is not-acceptable on the engine ()(motor generator
- must be separately evaluated in accordance with the guidance given in Section 5 with the exception of relays on reciprocating engines thanputinely see high vibration due to operation."*
- (SSRAP Report(GIP-:-2 Reference 5) pg. 81]
"Relays for which chatter is not a~ceptable-mnst be separa~valuated in accordance with the guidance given in Section 5 with the exception of relays on air compressors that routinely see high vibration due -to operation."
[SS RAP* Repert :~GIP-2R~rence $)pg. 82]
The NRC reviewed GIP~2 and its associated reference, EPRfN.f-7148, which are based on. the.SSRAP.reportand concluded the following:
"In-conclusio~ on the basis. ofits. *review -of Section.6 of :ean U, the staff agrees with the approach of evaluating systems and electrical circuits to determine the.
effect* of relay chatter and*e-nElorses the review*prooedure.~s given in GIP-2.
Therefore, the staff concludes that the procedure, if properly implemented, is an acceptable metfiod'C>fverifying the seismic adequacy of relays for this resolution of USI A-46 subject to the following:... "
(~ER No. 2, pg. 24)
Nothing in the remainder of SSER No. 2 limits or excludes the GIP method which permits acceptance of relays mo anted on diesel generators* anq air compressors without explicit seismic qualificaJion by. separate testing or analysis.
In summary, the NRC staff appears to be taking a new position in Reference 1 which is inconsistent with GIP-2 and EPRI NP-7148, as approved for use in SS.ER No. 2.
The -types *of additional tests-and/or* analyses-requested-m ~ference 1 are not warranted and would have signific'ant program and cost impact for no measurable increase in safety.
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Mr: John F. Stolz*
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January 26, 1998
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Justification for.Schedules.to Res?Jve GIP Outliers The NRC has asked certain SQUG members in RAis to justify their schedules for resolving A-46 outliefS; This *is. a *significant co~em to S~
since the plants affected by USI A-46 are committed by Generic Letter 87-02, Supplement 1 to only perfrirm a seismic adequacy review and report the results to the ~C staff in response.to a5Q54(f).informatjon request... The NRC backfit analysis used to support this request for information is contained*in NUREG-1211 where it specifically excludes* correction of deficiencies id.entified*in the review from-~. backfit analysis; separate plant-specific backfit analyses by the NRC are required if utilities choose not to voluntarily correct deficiencies. Spc:cificaUy, NUREG-1211 states that:
"The backfit analysis which is presented in the following paragraphs presents
. justific~tion for*per.f~ng-th~ seismic adequacy review, ~ckfit a1~al~sis fo~
correction of any deftc1cncy will be performed on a case by case basis if required folfowirig completioi1 oftfie review.~*
(NUREG-1211, page 16)
Therefore, absent plant-specific backfit analyses, the utilities have no obligation to remain* committed to* resolve A-46 outliers* unless; of course,: there-a_re licensing basis violations which are required to be reported and addressed under existing regulations and plant procedures. Clearly, the NRCs demand for justificatio11>of schedules for outlier resolution is inappropriate when tl:ie utilities.' plans for outlie.r resolution are completely voluntary. Itis also inappropriate to expect licensees to resolve outliers wficn the NRChas not iS:Suedj>fant-specific sERs validating the u~ties' methods for implementing the A-46 program. This is of particular concern since the NRC appears
- to be challenging fundamental clements of the GIP review process, e.g., the other generic* RAJ* issues *discussect*earlierin this, letter.
The NRC positions*reflected in* the above generic* RAls rontai_n new, additional requirements beyond those contained in GIP-2 as approved in SSER No. 2. The impact of these *changes in NRC positron would canse significant re-work of the ~w complete A-46 programs.
In SQUG's view, the foregoing generic RAI issues are examples where the NRC staff is changing positions which are central elements*of the *approved SOW program and on which the industry based its commitment to undenake and to implement the A-46 reviews.
As a result, these NRC positions represent a fundamental problem in acliieving a timely and cost~eff ectiveclosure of-the A-46 program.
Mr. John January 26, 1998 We request your assistance to resolve these* issues so that the USIA-~ program can be closed out.in. a.timely fashion,.. as.outlined.in.Supplemental Safety Evaluation Report No. 2.
We look forward to reaching agreement with you on the generic issues discussed in this letter so that the investments.made by -Industry and the NRC in *thi&-~ogram during the past 15 years are preserved.
cc:* D. H. Dm:man.,..NRC, MS: 0-14C7 R. Wessman, NRC, MS: 0-7E23 K Manoly, NRC, MS: 0-7E23 P. Y. Chen, NRC, MS: 0-7E23 R. P. ~assawara, EPRI SQUG Steering Group Sincerely,
- N. P: Smith, Chairman Seismic Qualification Utility Group SQUG Representatives, Alternates, and* licensing Personnel
ATTACHMENTC SQUG Letter (1/26/98) to USNRC
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