ML20195G872
| ML20195G872 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 11/30/1987 |
| From: | Serb R NCT ENGINEERING, INC. |
| To: | |
| Shared Package | |
| ML20127A683 | List:
|
| References | |
| NUDOCS 8712210073 | |
| Download: ML20195G872 (5) | |
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i SEQUOYAH NUCLEAR POWER PLANT, UNIT 2 TECHNICAL EVALUATION REPORT FOR EMPLOYEE CONCERNS ELEMENT REPORT 218.7(B), REVISION 2 "PIPE STRESS CALCULATIONS Acceptance Criteria for overlap Areas of Calculations"
SUBJECT:
This report sumnarizes the NRC audit of TVA investigation of SQN structural modeling at piping analysis interfaces (overlap) concerns.
By: Robert E. Serb Consultant i
NCT Enginee 'ng, Inc.
Date: November 30, 1987-A jag / 007'> N NCT ENGINEERING, INC.
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l SEQUOYAH NUCLFAR POWER PLANT, UNITS 1 & 2 TECHNICAL EVALUATION REPORT FOR EMPLOYEE CONCERNS ELEMENT REPORT 218.7(B), REVISION 2 "PIPE STRESS CALCULATIONS Acceptance Criteria for Overlap Areas of Calculations" I.
Subject Category:
Engineering (20000)
Subcategory:
Pipe Stress Calculations (21800)
Element:
Acceptance Criteria for Overlap Areas of Calculations (21807)
Concern:
IN-85-039-003 The basis for Element Report 21807 is Employee Concern IN-85
-039-003 which questions the consistency of methods employed at Hatts Bar Nuclear Plant (HBN) for structural modeling of alternate analysis problems at their interfaces with other piping analysis problems.
II. Summary of Issue Although the concern was noted relative to HBN, the ECTG report has addressed it relative to Sequoyah Nuclear Plant (SQN) a and translated it into the following two issues:
a.
There was no consistent policy on what constituted an acceptable lapped region at alterr. ate analysis boundaries.
l
- b. The methods actually implemented for interfacing alternate analysis problems may not Esve been sufficient.
Specific example:2 of improper interface were alleged in the Employee Concern.
The examples are apparently HBN piping problems and as such were not addressed as part of the SQN ECTG program.
Likewise, they were not reviewed during this audit of TVA response to the concern, f
Discussion here is limited to concern regarding interfaces 2,
between alternate and rigorously analyzed piping.
Interfaces between gravity and alternately analyzed piping is one subject of the technical evaluation report for Element Report 21804.
III. Evaluation Issue "a" To investigate concern regarding the consisLency of rigorous to alternate analysis interface requirements, the FCTG reviewed applicable past and present procedures.
The Procedure for Detailed Analysis of Category 1 Piping Performed by TVA, Document Number DED-EP-21.10, was issued in 1975.
Section 8.2.5.2 of that procedure defined rigorous to alternate piping interface requirements which were typical of industry requirements in that time frame.
The procedure required the interface boundary to be specified at an anchor or an effective "3-way restraint."
Overlapping was not a method included in the procedure.
After the USNRC publication of "Dynamic Analysis of Piping Using the Structural Overlap Hethod," NUREG/CR-1980, TVA expanded rigerous to alternate interface requirements in 1983 via Section SQN-RAH-206 of their Rigorous Analysis Handbook (RAH).
The adequacy of these procedutes was addressed by the ECTG and is discussed under Issuo "b" below.
The ECTG report notes that 3 alternate analysis procedures have been applied for SQN piping design.
One of these, TVA Document CEB 76-5, did inappropriately include rigorous to alternate interface recommendations.
During the NRC audit of the TVA employee concerns progra'm, ECTG personnel noted that although the procedure should have defered to rigorous analysis procedures for interface requirements, it is reasonable to expect experienced analysts not to have been confused and to have applied the rigorous analysis procedural requirements.
Issue "b"
ECTG investigation of concern regarding rigorous to alternato interface methodology included review of a TVA study and follow-up evaluation conducted in response to TVA Nonconformance Report (NCR) SQHCEB8303.
The NCR which was written in 1983 identified deficient rigorous to alternate analysis interfaces for analyses performed prior to issuance of RAH Section SQU-RAH-206.
Results of the study are contained in the TVA report "Finding of the Design Study of Analysis LappinJ and j
Termination Techniques (NCR SQNCEB8303) for Sequoyah Nuclear Plant dated January 11, 1985.
The study included review of 358 analyses for adequate interface definitions.
Thirty-eight (38) rigorous to alternate interfaces were found not to terminate at anchors or 3-way (or effective 3-way supports) as was required by the procedure applicable priot to 1983 (TVA Document No.
DED-EP-21.10).
The improper incerfaces appear to have resulted i
in part from the lack of detailed instructions provided by that i
TVA procedure.
Subsequently, the improper interfaces were evaluated by TVA via the OE Calculation "Review of Piping Analysis for Adequate Termination - SDR - SO48" dated February 27, 1986.
For interfaces which comply with the intent of the DED-EP 21.10 procedure and an associated informal handout dated August 14, 1975, TVA states in that calculation that: "these procedures provided piping boundary conditions wnich prevented significant problem interaction and provided either conservative stresses and support loads or stresses and support loads representative of an encompassing analysis." On that basis TVA found all but 16 of the identified discrepant interfaces to be acceptable.
During the NRC audit it was determined that the SQN Alternate Analysis Review Program, TVA Document SQN-AA-001 dated March 30, 1987, identifies evaluation of these 16 problems as a post restart effort.
During the NRC audit ECTG personnel noted that their investigation included review and evaluation of SQN rigorous to alternate analysis interface structural modeling methods.
Their review resulted in discuscion with TVA regarding the adequacy of terminating rigorous analyses at interfaces with alternate analysis scope piping at 3-way, or effective 3-way supports.
TVA noted that since alternate analysis scope piping is supported such that piping dynamic response is limited to the rigid range
( i. e., > 33 hertz), a 3-way support is adequate to isolate the alternate analysis piping response.
However, the ECTG has demonstrated that alternate analysis piping is not always rigidly supported.
This matter was not resolved at the time the ECTG report was issued and was the subject of further review and discussion between the ECTG and TVA.
Resolution to the satisfaction of the ECTG is addressed in the ECTG verification closecut checklist for the subject element repo'rt, CATD No. 218 07 SQN 01 dated July 24, 1987 which was also reviewed during the NRC audit of the TVA employee concerns program.
The ECTG verification closecut checklist summarizes corrective actions taken which meet the TVA corrective action plan l
requirements and which include additional actions identified by I
the ECTG subsequent to issuance of that plan.
Initially, TVA screened all SQN rigorous analysis problems for critical examples i
of rigorous to alternate interfaces at 3-way restraints.
Eight i
example interfaces based on pipe size and span, branch pipe locations, pipe routing, support types and locations, and concentrated weights and locations were selected for reanalysis.
Subsequently, TVA screened all such interfaces at the request of the ECTG to identify analyses for which in the vicinity of the subject interfaces, small increases in stress over the then current analysis results would result in exceeding stress allowables.
TVA identified twelve worst cases of thic low stress margin condition.
The ECTG evaluated the twelve problems and identified one for inclunion in the critical interface sample, i
The nine problems were rennelyzed by TVA.
The results of these reanalynes met plant design criteria.
The ECTG verification closecut checklist also summarices._
t
chsuges made to the RAH to avoid future problems with analysis interface locations.
Section SQN-RAH-206.of the handbook now l
prohibits interfaces defined at other than structural' anchor locations without technical supervisory approval..For cases in which anchors are not feasible, rigid region and overlap i
guidelines are specified.
Based on the reanalysis results and RAH revision discussed above, and the understanding that additional systems will be evaluated as part of the'TVA Alternate Analysis Review Program the ECTG concluded that concern regarding rigorous to alternate interfaces and, in particular, the-adequacy of using of 3-way restrainto at rigorous to alternate interf aces had been adequately addressed.
1 IV. Conclusions Issue "a" Alternate to rigorous piping analysis interface modeling and evaluation instructions have been available for use by SQN analysts.
The failure of one of the alternate analysis criteria documents to defer to the rigorous procedure for interface requirements is not likely to have resulted ir confusion to an experienced analyst.
The NCR and employee concerns program corrective actions which are addressed in this report relative to Issue "b" and the TVA alternate analysis review program (TVA Ducument NO. SQN-AA-001) assure that this issue does not pose a safety concern.
Therefore, TVA investigation of this issue is considered adequate and resolution as described in Element Report 218.7(B), Revision 2, is acceptable, j
Issue "b"
The resolution of discrepant interfcces identified via HCR 8303 has been adequately addressed provided designating evaluation of the 16 "unacceptable" interfaces as a post restart function is confirmed to be acceptable.
Concern regarding rigorous to alternate analysis interface procedure is resolved based on the corrective actions summarized in the ECTG verification closeout checklist and discussed in Section III of this evaluation.
Therefore, TVA investigation of concerno regarding this issue is acceptable provided post restart evaluation of the noted 16 interfaces is confirmed to be acceptable by the NRC.
Review of the SQN alternate analysis review program (TVA Document SQN-AA-001), including designation of requirements as pre or post restart, is the subject of a separate NRC evaluation.