ML19263D733
| ML19263D733 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 04/12/1979 |
| From: | Vandenburgh D Maine Yankee |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19263D734 | List: |
| References | |
| WMY-79-31, NUDOCS 7904130201 | |
| Download: ML19263D733 (5) | |
Text
,
MAIRE HARHEE
, u n,_ n u A u m n Q
/
ENGINE E HING oF FICE V.EST BCHO, M ASS ACHUSF T TS 01581 G 1 7-366 - 9011 O
WMY 79-31 B 3.2.1 April 12, 1979 United States Nuclear Regulatory Commission Washington, D.C.
2055S Attention: Office of Nuclear Reactor Regulation Referencea!
(a) License No. DPR-36 (Docket 50-309)
(b) Maine Yankee Letter WMY 79-27, April 2, 1979.
(c) Maine Yankee Letter WMY 79-29, April 3,1979.
(d) USNRC Letter to Maine Yankee, April 10, 1979.
Dear Sir:
Subject:
Maine Yankee Piping Seismic Analysis This letter supplements and clarifies information provided in References (b) and (c) as well as submitting responses to NRC questions contained in Reference (d).
Subsequent to the submittal of References (b) and (c), Maine Yankee continued its investigation into the piping analysis methods utilized in the design of Maine Yankee. This investigation consisted of a records search and discussions with Stone and Webster engineering personnel who were personally involved in the original design.
No new information has been learned, but clarification of some information is provided below.
The choice of analysis methods was primarily one of economics.
Large piping, arbitrarily defined as greater than six inches nominal size, was computer analyzed, using PSTRESS/ SHOCK 1 or PSTRESS/ SHOCK 2 to allow optimum placing of supports. The cost of computer analysis was warranted to reduce the number of supports since large pipe supports were expensive.
Small piping was supported based on a static analysis method. This method generally resulted in more supports than if a computerized dynamic analysis was employed, but these supports were relatively inexpensive; the cost of the computerized analysis did not offset the savings from reduced supports.
A further subdivision of the static method existed. As described in FSAR Question 4.1, piping 2 inches nominal pipe size and smaller was supported by the Field Engineering forces. Using a chart based on pipe O
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Nuclear Regulatory Commission April 12, 19'/9 Attn: Office of Nuclear Hecctor Regulation Page 2 size the engir.eer would know the maximum permissible span between supports; he could easily establish hangar locations, resulting in a significant saving in construction time.
We have observed exceptions to this basic criterion.
Some sections of large pipe were not dynamically enalyzed; however, they were simple geometries that could easily be analyzed by hand, in many cases, the piping layout provided inherent support for seismic - a short run of large pipe between a pump and heat exchanger has inherent support from the two equipment, nozzles.
If the pump and heat exchanger nozzles can accept the conservatively calculated forces and moments no additional pipe support is required.
Conversely, sometimes the required routing of small pipe would not allow support spacing based on simplified nethods; in these cases a dynamic analysis was performed.
Maine Yankee has performed an evaluation of the static analysis methods employed by Stone and Web 3ter and has concluded that the method is conservative.
A report describing our study is attached (Enclosure (1)).
The previously mentioned PSTRESS/Sil0CK) and PSTHESS/Sil0CK2 dynamic analysis methods were also evaluated by Maine Yarkee.
All safety related piping analyzed using the PSTHESS/Sii0CK2 program have been reanalyzed using hand calculation methods, PSTHESS/SliOCKJ or NUPIPE-SW.
Some non-safety related piping was supported based on PSTHESS/Sil0CK2; we cannot ascert.ain as to why this piping was analyted in that manner, but we have proceeded to also reanalyze all this piping. We expect the last of that piping to be completed within a week or so.
Thus, no piping in Maine Yankee will be supported based on a PSTRESS/Sil0CK2 analysis.
We have had extensive discussions with Stone and Webster concerning the PSTRESS/Sii0CK1 analysis method. We have been informed by Stone and Webster (Enclosure (2)) that their review of the PSTRESS/S110CK1 analysis method shows the method is adequate to ensure that seismic-category 1 systems can fulfill their safety function in the event of a design basis earthquake.
We have concluded that piping systems analyzed by the static nethod, PSTRESS/3110CK3 or NUPIPE-SW will satify that criteria.
While we concur with Stone and Webster that piping analyzed using PSTRESS/S!!OCK1 will properly perform its intended function in the event of a design basis earthquake we are unable to state conclusively at this time that the FSAR criteria are satisfied with respect to stress limits.
We are conducting an independent review of the Stone and Webster PSTHESS/SlioCK1-NUPIPE comparison; we will report the results of that effort in a subsequent letter.
Nuclear Regulatory Commission April 12, 1979 Attn: Office of Nuclear Reactor Regulation Page 3 We trust this information adequately explains the analysis methods utilized in the design of Maine Yankee.
It is important to recognize that there was no licensing requirement with respect to analysis methods; the commitment was with respect to compliance with certain allowable stress limits.
Enclosure (3) to this letter submits oJr response to NRC questions transmitted via Reference (d).
As discussed in Reference (c), Maine Yankee was reanalyzing supports H-51 and H-53 considering base plate flexibility. We have determined that modifications are necessary. They will be performed prior to plant startup.
New calculations are enclosed (Enclosure (D)).
We are also conducting a field check of all pipe supports in the affected problems. Any discrepancies will be evaluated to ensure that the analysis results are not affected.
Any required modifications will be completed prior to plant startup.
Should you have any questions on this material, please feel free to contact Mr. J. R. Hof fman of this of fice.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY v
D. E. Vandenburgh Vice President JRH/slw
ENCLOSURE 3 Responses to NRC Questions contained in NRC letter to Maine Yankee dated April 9, 1979:
1.
The computer code listings requested by NRC have been submitted in a letter from Stone and Webster to NRC dated April 6, 1979.
2.
The basis of our conclusion concerning the static method of analysis is contained in the text of this letter and Enclosure (1) to this letter.
3.
Our response to this question is contained in the text of this letter.
4 FSAR Question 1.3 is the listing of all Seismic Category 1 systems, structures and components at Maine Yankee. Amendment 35 to the FSAR lists the Stone and Webster designed piping that was re-evaluated in 1971-1972 during the " Robinson Fix" study. Question 1.3 describes the Seismic Category 1 piping by function.
Ascertaining the actual method of analysis for each line is an extremely time-consuming process if we attempt to do that by a record search. The Stone and Webster files list all the computer analyses; piping not analyzed by computer methods was statically analyzed.
Records for such piping were not indexed and are difficult to retrieve.
Since we have established that the static analysis method is conservative in all cases, we do not believe that a listing showing the method of analysis of each line is necessary.
S.
The Seismic Category 1 piping systems identified in response to Question 1.3 of the Maine Yankee FSAR includes all of the piping systems required to assure:
(a) The integrity of the reactor coolant pressure boundary.
(b) The capability to shutdown the reactor and maintain it in a safe shutdown condition; and (c) The capability to prevent or mitigate the consequences of accidents which could result in potential offsite exposures comparable to the guideline exposure of 10CFR Part 100.
6.
Table 1 provides the requested list.
7.
SHOCK 2 is not utilized as the analysis of record for any safety related piping systems.
8.
Stone and Webster incorporated stress intensification factors into
all analyses.
9.
Stone and Webster received concurrence from manufacturers if loads on the components increased.
10 We will submit under separate cover the information we have found in our and Stone and Webster files concerning the " Robinson Fix".
We have not been able to find information supporting the basis for the factor 22 other than the discussion contained in Amendment 35.
11.
Piping interfaces with the reanalyzed piping have been evaluated to ensure that the stress analysis of those lines remains valid.