ML20148F259
| ML20148F259 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 11/30/1987 |
| From: | Russell M EG&G IDAHO, INC., IDAHO NATIONAL ENGINEERING & ENVIRONMENTAL LABORATORY |
| To: | NRC |
| Shared Package | |
| ML20148F173 | List: |
| References | |
| CON-FIN-A-6808 NUDOCS 8803280101 | |
| Download: ML20148F259 (15) | |
Text
e RESOLUTION OF CONFLICTS BETWEEN THE OC-1 CRITERIA DOCUMENT AND THE JULY 17, 1987 SAFETY EVALUATION REPORT FOR THE YANKEE ATOMIC PLANT M. J. Russell November 1987 IDAHO NATIONAL ENGINEERING LABORATORY EG&G Idaho, Inc.
Idaho Falls, Idaho 83415 Prepared for the U.S. Nuclear Regulatory Commission Washington D.C. 20555 Under 00E Contract No. OE-AC07-76I001570 FIN No. A6808 4
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a
SUMMARY
Oiscrepancies between the July 16, 1987 Nuclear Regulatory Commission (NRC) staff's Safety Evaluation Report, it's supporting Technical Evaluation Reports, and the licensee's criteria document were evaluated and resolutions acceptable to the licensee and the NRC staff were established. The evaluation was limited to issues related to piping and supports. Issues evaluated included: (1) use of 60% SAM in NRC spectrum analysis; (2) use of YCS analyses in future major evaluations of piping; (3) the need for case-by-case review of applications of the square-root-of-the-sum-of-the-squares (SRSS) combination methodology to seismic inertia and SAM loading combination; (4) acceptable methodology for applying deflection criteria to small bore pipe supports; and (5) acceptable computer codes for correct mass distribution. ii
CONTENTS
SUMMARY
.............................................................. 11
- 1. INTRODUCTION ...................................................... 1
- 2. DISCUSSION ........................................................ 1 2.1 Use of 60% SAM in NRC Spectrum Analyses (4) .................. 2 2.2 Use of YCS Analyses in Future Major Evaluation of Piping (5).. 6 2.3 Case-By-Case Review of SRSS Combinacion of Seismic Inertia and SAM Loads (6) ............................................ 6 2.4 Small Bore Pipe Support Deflection Criteria (7) . . . . . . . . . . . . . . 7 2.5 Acceptable Computer Codes for Correct Mass Distribution (10).. 8
- 3.
SUMMARY
.....................................................<..... 9
- 4. REFERENCES ....................................................... 10 TABLE :
- 1. Range of NRC spectrum stress ratios based on strain criteria calculated using stresses based on allowable stresses, use of 60% SAM and stress ratios of 1.0 ................................. 11 iii
I RESOLUTION OF CONFLICTS BETWEEN THE 00-1 CRITERIA 00CUMENT AND THE JULY 17, 1987 SAFETY EVALUATION rep 0RT FOR THE YANKEE ATOMIC PLANT
- 1. INTRODUCTION On July 16, 1987, the Nuclear Regulatory Commission (NRC) staff issued a safety evaluation report (SER) covering the last review cycle for the Yankee Nuclear Power Station (Yankee) of the seismic portion of the Systematic Evaluation Program (Reference 1). The licensee for the plant, Yankee Atomic Electric Company, reviewed the report and found discrepancies in the SER and its supporting technical evaluation reports (TERs), and discrepancies between the SER and TERs, and the criteria document (DC-1) produced by the licensee which the SER governed. In Reference 2, the licensee listed the discrepancies and requested clarification to resolve them. This report is intended to provide the necessary clarification for discrepancies whien deal with technical aspects of the criteria and methodology applicable to piping and supports.
- 2. DISCUSSION In regulatory practice, the contents of an SER carry far more weight than the contents of the criteria document of the licensee. This fact was reflected in the review performed in that far more attention was directed toward the production of the applicable portion of the SER and the technical evaluation report (TER) upon which it was based than in the review of the licensee's criteria document. Further, the SER and TER were directed toward establishing that an adequate basis was provided for accepting the criteria and methodology proposed by the licensee. Since the licensee's criteria document does not constitute a valid basis for acceptance, it was not consulted extensively during the writing of the applicable portion of the SER or the TER. Based on this, the fact that the criteria document contains a specific criteria or methodology does not constitute an adequate basis for its acceptance.
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In the following subsections, each of the discrepancies in the scope of this effort are addressed. Clarifications are based on the same documents used in the production of the applicable portion of the SER and the T2R upon which it is based. They are constructed so that the associated discrepancies are resolved in a fashion that results in criteria and methods that have a basis for acceptance by the NRC staff. Numbered entries in Reference 2 are included in parentheses in the subsection titles below to allow easy cross-referencing to that document. 2.1 Use of 60% SAM in NRC Soectrum Analyses (4) The July 1987 SER stated that the 60% SAM methodology (reducing the seismic anchor motion (SAM) stresses to 60% percent when combining them with thermal stresses for evaluations in ANSI B31.1 Equations 13 and 14) could not be used, and that all previous usage of this methodology would be removed by revision of affected calculations on the part of the licensee. The licensee's criteria document allowed the use of this methodology in NRC :pectrum analyses, and hence the licensee intends to use this methodology in the future and does not intend to revise earlier analyses which used it. Two arguments were offered in support of the validity of the 60% SAM methodology. First, the licensee stated that the NRC staff had previously found this methodology acceptable, and identified a document as evidence (Reference 3). This document was retrieved from the docket and found to be a letter transmitting a draft of NUREG-0825. Such a document provides no basis. Further, NUREG-0825 (Reference 4) provides little guidance other than a reference to an earlier SER (Reference 5), which had been previously reviewed in regard to this issue, and found to provide no basis. The earlier SER endorsed Revision 0 of the criteria document, which did not contain the 60% SAM methodology. The previous review established that the formal NRC staff position taken in early 1983 incorporated acceptance of 100% SAM, and did not endorse the use of 60% l SAM. This latest argument made by the licensee is not acceptable. [
- 2 l
t
The second argument is based on the ASME Boiler and Pressure Vessel Code, Section III (the ASME Code). In the ASME Code, SAM stresses require consideration in Level 8 analyses but not in Level 0 analyses. This is significant because the NRC spectrum earthquake is severe and corresponds more exactly with the Level 0 Safe Shutdown Earthquake (SSE) than the level B Operating Basis Earthquake (OBE). Actually, this is an old argument which was discussed several times in the course of the review. The shortcoming with it is that there is no clear correlation between OBE and SSE SAM stresses despite the minimum 1:2 ratio defined in peak ground motion for these two earthquakes. The problem is that Regulatory Guide 1,61 (Reference 6) defines a lower level of damping for the OBE analyses, so that the 1:2 ratio in ground motion would be expected to be shifted toward a 1:1 ratio when comparing stresses generated by analyses using the different damping values. This was reflected in the SEP Guidelines (Reference 7), where 100% of SAM was required to be considered. The licensee has recently attempted to overcome this problem with a reference to NUREG-1061 (Reference 8), where a recommendation was made that OBE SAM stresses be defined as 1/2 the SSE SAM values. NUREG-1061 was checked, and the recommendation found to be made by a consultant, so that it cannot be considered a position of the NRC staff. Recent changes in the NRC staff position concerning acceptable damping levels for OBE and SSE piping analyses made in Regulatory Guide (RG) 1.84, i Revision 24 (Reference 9), do not significantly alter the shortcoming discussed above. Acceptance of ASME Code Case N-411 did allow the use of , the same level of damping (PVRC) for both OBE and SSE piping analyses, but did not change the different damping levels required in the structural analyses used to generate the time histories which are in turn used to l generate the floor spectra for the piping analyses. This change would l admittedly increase the ratio in stresses obtained from OBE and SSE analyses, but it would not increase that ratio to 1:2, nor would it allow quantification of the actual ratio obtained. In the absence of a favorable, well defined ratio of OBE to SSE stress
- for Yankee, any argument based on the ASME Code provides no basis for acceptance of 60% SAM in NRC spectrum analyses.
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Since the recent arguments in favor of 60% SAM with NRC spectrum analyses are not acceptable, the proposal was evaluated on its own merits. A comparison was made between NRC spectrum analyses using strain criteria (which are acceptable to the NRC staff) and analyses using criteria incorporating the 60% SAM methodology (currently under question). Ranges of all limiting combinations of normal operating (weight plus pressure) stress, thermal stress and seismic inertia and SAM stresses were used to calculate the corresponding stress ratio based on strain criteria. This was done for three materials: cold (room temperature) carbon steel, and cold and hot (550*F) stainless steel. Normal operating stress was varied between zero and a maximum value defined by ANSI B31.1 Equation 11. Given a value of normal operating stress, the thermal stress was varied between zero and a value that was limited by Equation 14. For each pair of normal operating and thermal stresses, seismic inertia and SAM stresses were calculated which placed the Equation 12 value (for inertia) and equation 14 value (for 60% of SAM) at their limits. The result was a series of stress combinations of normal operating, thermal, seismic inertia and SAM stresses that covered all combinations of such stresses that can occur. Further, each combination was defined so that a maximum allowable stress state was obtained per the criteria under question (both equation 12 and 14 yielded a stress ratio of 1.0). For each combination, a stress ratio was calculated based on strain criteria. Since the 60% methodology is not intended for use with strain criteria, the seismic stress used in the strain calculation was a square root of the sum of the squares (SRSS) combination of inertia and SAM stress. The results are presented in Table 1, and are interpreted as follows: If all the calculated strain based stress ratios are 1.0, then the criteria yield identical results for all acceptable combinations of stress. Strain based stress ratios that fall above 1.0 indicate stress combinations that are acceptable using the 60% SAM methodology, but are l 4
i-not acceptable using strain criteria. With this in mind. Table 1 indicates that the 60% SAM methodology allows significantly higher strain ; levels in the piping than strain criteria in cases where normal operating stress and thermal stress are small, particularly for stainless steel. Therefore, acceptance of 60% SAM represents a reduction of seismic requirements in addition to that already provided by acceptance of strain criteria. Further, acceptance of the 60% SAM methodology reduces margin in areas of the piping subject to damage from seismic differential anchor motion. This is not advisable in view of the evidence of damage to piping systems subjected to seismic differential anchor motion cited in the Addendum to Volume 2 of NUREG-1061 (Reference 10). The 60% SAM methodology is not acceptable in NRC spectrum analyses. Upon rejection of the use of 60% SAM in NRC spectrum analyses, the licensee proposed an alternative (Reference 11). This involved the use of 100% of the SAMs generated in YCS analyses. The basic idea was to treat the YCS earthquake as comparable to an OBE event. The shortcoming to this, as discussed above, is that the YCS building analyses were done with damping levels commensurate with those defined in NUREG-0098 (Reference 12), which are significantly higher than the damping levels defined by the staff as acceptable for use in OBE analyses. This shortcoming was compensated by the proposed use of YCS piping analysis results generated using damping levels at or less than those specified in NUREG-0098 for i vital piping rather than those using PVRC damping (which is currently acceptable to the NRC staff for OBE piping analyses). This would include a measure of conservatism in the piping analyses to compensate that lost with the use of higher damping levels in the building analyses. Implicit in the proposal to use criteria and methodology previously accepted for YCS analyses is the use of the absolute summation method in combining SAM with seismic inertia stresses for evaluation in ANSI B31.1 Equation 12. The licensee's proposal to use 100% of YCS SAMs in analyses uniformly applying damping specified in NUREG-0098 is acceptable. ,}
. 4 1 '
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2.2 Use of YCS Analyses in Future Major Evaluation of Pipina (5) The licensee has stated that the earlier commitment to use NRC spectrum analyses in future major modifications does not include a commitment to use NRC spectrum analyses in any future major evaluations. Commitment or not, the licensee should be required to use NRC spectrum analyses in future major evaluations. The NRC staff made clear to the licensee their preference for NRC spectrum /SEP guidelines analyses du:ing the second meeting of the current review cycle, and many times during subsecuent meetings. It is clear that qualification of piping using lower spectra (YCS), compensated by more stringent criteria (Code Criteria), adds needless complexity with attendant risks of misunderstanding: witness the document in hand. A major evaluation would not be required by the NRC staff without the expectation that the evaluation would result in significant modifications. In a limited number of cases, the licensee used modified YCS loadings with SEP guidelines criteria. In these cases, the YCS loadings were doubled to obtain a conservative representation of NRC spectrum loadings. This was found acceptable in the July 16, 1987 SER. These cases do not exhibit the additional complexity associated with a second set of acceptable criteria and methodology, and as such are acceptable for future use. Such acceptance is applicable only to the cases where such an approach has been previously accepted by the NRC staff as documented in the July 16, 1987 SER. 2.3 Case-by-Case Review of SRSS Combination of Seismic :nertia and SAM Loads (6) Passages in the SER and TER that discuss square root of the sum of the squares (SRSS) combination of seismic inertia and SAM loadings in the analyses of pipe supports are inconsistent in that some require case-by-case review and some do not. Those passages that do not are in 6
error. The basis for acceptance of SRSS combination is found in the San Onofre Nuclear Generating Station Unit 1 (SONGS 1) 3ER (Reference 11), and acceptance of SRSS combination there was conditional, based on a positive finding of a case-by-case review by the NRC staff. All applications of the SRSS combination methodology in the analyses of Yankee pipe supports require a case-by-case review by the NRC staff. The purpose of the case-by-case reviews is to ensure that an acceotable overall level of margin is achieved for piping and supports in the area of application of the SRSS methodology. Such reviews should include consideration of quantifiable factors, such as: (1) the margin available in excess of that required by the applicable criteria; (2) whether or not other alternate criteria were required in the area (such as strain criteria); and (3) whether the piping and supports in the area are of the type which would be expected to exhibit substantial ductile response before failure (such as an all-welded pressu*e boundary, welded supports without concrete anchor bolts, etc.). In the ideal case, all components which could suffer from load redistribution resulting from degraded performance of the component qualified using the SRSS methodology would have substantial excess margin. In the worst case, the components subject to load redistribution would have so little excess margin as to require alternate criteria, or would be of a type with lesser potential for ductile response (such as a threaded fitting in the piping). It is the reviewers responsibility te establish that the weakness of a piping system represented by the need for the SRSS methodology is compensated by strengths in other areas that would compensate for the weakness. 2.4 Small Bore pioe Suecort Deflection Criteria (7) The licensee took exception to the requirement in the SER that support deflection be "less than 1/16" for the se:smic loading" for the support to be considered acceptable. The wording in the licensee's criteria document was semantically identical, except that "primary loading" was used in 7
place of "seismic loading." The difference between these two terms was discussed during the January 1987 meeting, and the conclusion was drawn that they have meanings sufficiently close to be interchangeable in the requirement. Further reflection indicates that there is significant difference. "Primary loading," in terms of the ASME Code is generally the combination of weight and seismic inertia alone. "Seismic loading" is specifically the combination of seismic inertia and SAM loadings. If the underlying need for this requirement is examined, the restriction need only apply to the seismic inertia loading. The deflection restriction is intended to ensure the accuracy of the response spectra analyses done to generate the seismic inertia loads. From this perspective, "primary loading" is the preferred term. Inclusion of the SAM loading under the 1/16" deflection limit would result in relatively stiffer supports in the area of significant SAM loadings. This would result in relatively higher strain levels in the associated piping. The SAM load would still be limited by the stress limits applied to the supports, so support functionality would be ensured. In light of this, it.would be preferable to allow the support to take the 1/16" displacement under dispute rather than the associated piping. ! One restriction must be placed on acceptance of the term "primary loading." This is an ASME Code term which currently includes seismic inertia loading. If the ASME Code definition is changed in the future to remove the seismic inertia loading, the term "primary load" would no longer be acceptable. From the above discussion, it is clear that the seismic inertia load must meet the 1/16" deflection limitation regardless of the wording used to define the requirement. l 2.5 Acceotable Comouter Codes for Correct Mass Distribution (10) l l The licensee stated that the correct piping computer code in the discussion of automated masseoint spacing was ADLPIPE and not SUPERPIPE, as stated in the TER. Actually the discussion should not have been in l l 8
< --- ~ -r, , , - - ,,,-w,-m-- ---e-, e->----,,n-,-<-----,,,r-, m ---- - - -- - - , -- , - . - ---,.----r, ,---
e u. terms of specific computer codes. If AOLPIPE, or any code the licensee chooses to adopt in the future, has an automated check for adequate masspoint spacing, and the check is performed, then no manual checking is required. If the computer code used does not perform the check, then the manual check must be performed, using the method defined in the criteria document.
- 3.
SUMMARY
Review of the discrepancies has established the following clarifications:
- 1. The use of the 60% SAM methodology in NRC spectrum analyses is not acceptable. An acceptable alternative based on YCS SAMs with NUREG-0098 damping for both building and piping analysis was developed.
- 2. YCS analyses are not acceptable for future major evaluations except in those cases previously established where twice the YCS load was used to estimate an NRC spectrum load.
- 3. All applications of SRSS combination of seismic inertia and SAM '
loading in support analyses must be identified to the NRC staff for case-by-case review.
- 4. The deflection check for adequate stiffness of small bore supports must ensure that the seismic inertia loading results in a support deflection less than 1/16". The use of the term "primary load" is acceptable as long as the definition of this term includes seismic inertia loading.
- 5. If any computer piping analyses do not include an automated check for adequate mass distribution, then manual checks, as defined in the criteria document, must be performed.
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- 4. REFERENCES
- 1. USNRC Safety Evaluation Report dated July 16, 1987,
Subject:
Safety Evaluation by the Office of Nuclear Reactor Regulation Relating to the Seismic Reevaluation Program, NUREG-0825 Section 4.11, Yankee Atomic Electric Company, Yankee Nuclear Power Station, Occket No. 50-029.
- 2. Letter from G. Papanic (YAEC) to M. Fairtile (NRC) dated August 31, 1987,
Subject:
Clarification of Staff Position, SEP Topic III-6, Safety Evaluation Report.
- 3. Letter from O. Crutchfield (NRC) to J. Kay (YAEC) dated February 10, 1983,
Subject:
Yankee Nuclear Power Station - Oraft (NUREG-0825) Integrated Plant Safety Assessment Report.
- 4. NUREG-0825, "Integrated Plant Safety Assessment Report, Systematic Evaluation Program, Yankee Nuclear Power Station, Docket No. 50-029,"
dated June 30, 1983.
- 5. Letter from D. Crutchfield (NRC) to J. Kay (YAEC) dated February 1, 1983,
Subject:
SEP Topic III-6, Seismic Design Considerations, Yankee Nuclear Power Station.
- 6. USNRC Regulatory Guide 1.61, "Damping Values for Seismic Design of Nuclear Power Plants," dated October 1973.
- 7. Letter from R. Caruso (NRC) to J. Kay (YAEC) dated September 20, 1982,
Subject:
Revision 1 to Reevaluation Guideline Seismic Criteria for SEP Group II Plants (Excluding Structures).
- 8. NUREG-1061, Volume 2, "Report of the U.S. Nuclear Regulatory Commission Piping Review Committee, Evaluation of Seismic Designs - A Review of Seismic Design Requirements for Nuclear Power Plant Piping,"
dated April 1985.
- 9. USNRC Regulatory Guide 1.84, "Design and Fabrication Code Case Acceptability, ASME Section III Division 1," Revision 24, Dated June 1986.
- 10. NUREG-1061, Addendum to Volume 2, "Report of the U.S. Nuclear Regulatory Commission Piping Review Committee, Summary and Evaluation of Historical Strong-Motion Earthquake Seismic Response and Damage to Aboveground Industrial Piping," dated April 1985.
- 11. Letter from G. Papanic (YAEC) to M. Fairtile (NRC) dated November 23, 1987,
Subject:
Seismic Evaluation of Piping - Seismic Anchor Motions. l
- 12. NUREG-0098, "Development of Criteria for Seismic Review of Selected Nuclear Power Plants," dated May 1978.
- 13. Letter from T. Novak (NRC) to K. Baskin (SCE) dated September 19, 1985,
Subject:
Long Term Service (LTS) Seismic Criteria and Methodology - San Onofre Nuclear Generating Station Unit 1. l l 10 l l
4 TABLE 1. RANGE OF NRC SPECTRUM STRESS RATIOS BASE 0 ON STRAIN CRITERIA CALCULATED USING STRESSES BASED ON ALLOWABLE STRESSES. , USE OF 60% SAM AND STRESS RATIOS OF 1.0 PROBLEM HOT CS HOT SST COLO SST PARAMETERS MATERIAL A106 Gr8 A376 TP304 A376 TP30 T(OP) 550F 550F 120F E(HOT) 26640 25750 28070 S(cold) (KSI) 15 18.8 18.8 S(hot) (KSI) 15 15.9 18.6 SA (KSI) 22.5 39.65 42.35 SA+SH (KSI) 37.5 55.55 60.95
----------------------------- HOT CS -----------------------------
THERMAL STRESS FACTOR
- NOPSTREjj 0.00 0.25 0.50 0.75 1.00 FACTOR 0.00 1.23 1.01 0.82 0.67 0.62
> 0.25 1.10 0.96 0.75 0.59 0.53 0.50 0.96 0.92 0.70 0.44 0.44 0.75 0.83 0.83 0.64 0.36 0.36 1.00 0.70 0.70 0.27 0.27 0.27 i
............................. HOT SST ----------------------------
THERMAL STRESS FACTOR t NOP STRESS 0.00 0.25 0.50 0.75 1.00 1 FACTOR 0.00 1.71 1.35 1.03 0.76 0.65 0.25 1.57 1.31 0.97 0.69 0.56 O.50 1.44 1.28 0.92 0.62 0.47 i 0.75 1.30 1.25 0.88 0.38 0.38 1.00 1.17 1.17 0.84 0.37 0.37
------------------------------ COLO SST -------------------------- ,
THERMAL STRESS FACTOR NOP STRESS 0.00 0.25 0.50 0.75 1.00 FACTOR 0.00 1.90 1.51 1.16 0.88 0.76 0.25 1.73 1.46 1.09 0.79 0.66 0.50 1.57 1.41 1.03 0.70 0.55 0.75 1.41 1.38 0.98 0.45 0.45 - 1.00 1.25 1.25 0.93 0.40 0.40
?
11 ,
? li NOTES TO TABLE 1 "THERMAL STRESS FACTOR" is the ratio of thermal stress used in the strain based stress ratio calculation to the maximum allowed given the value of normal operating stress (determined as discussed in the paragraph below) and the ANSI B31.1-1977 Equation 14 limit with SAM stress reduced to 60% of its value. When this factor is zero (the left most column of each of the three tables), thermal stress is zero, and SAM stress is at a maximum, defined by the value of normal operating stress and the Equation 14 limit with SAM stress reduced to 60% of its value. When this factor is 1.00 (the right most columns),
thermal stress is at the maximum allowed value, and SAM stress is consequently zero.
"NOP STRESS FACTOR" is the ratio of normal operating stress used in the strain based stress ratio calculation to the maximum allowed by the ANSI B31.1-1977 Equation 11 limit. When this factor is zero (the top row of each of the three tables), normal operating stress is zero, and seismic inertia stress is at a maximum, defined by the Equation 12 limit. When this factor is 1.00 (the bottom rows),
normal operating stress is at the maximum allowed value, and seismi: inertia stress is at a minimum, i l 12}}