ML20138P895
| ML20138P895 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 12/05/1985 |
| From: | Hufham J TENNESSEE VALLEY AUTHORITY |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21-85, REF-PT21-86-015-000 PT21-86-015-000, PT21-86-15, NUDOCS 8512260333 | |
| Download: ML20138P895 (4) | |
Text
"
TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 37401 SN 1578 Lookout Place DekekeAO,*1($
BLRD-50-438/84-20 BLRD-50-439/84-19
.U.S. Nuclear Regulatory Commission Region II Attn:
Dr. J.. Nelson Grace, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Dear Dr. Grace:
BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 - ITT GRINNELL PIPE SUPPORTS DESIGNED WITH SWAY STRUTS INSTEAD OF REQUIRED GAPS - BLRD-50-438/84-20 AND BLRD-50-439/84 FINAL REPORT The subject deficiency was initially reported to NRC-01E Inspector P. E. Fredrickson on February 16, 1984 in accordance with 10 CFR 50.55(e) as
-NCR BLN BLP 8404. Our interim reports were submitted March 13, 1984 and February 22, 1985.
Enclosed is our final report. We consider 10 CFR Part 21 applicable to this deficiency.
If you~have any questions, please get in touch with R. H. Shell at FTS 858-2688.
Very truly yours, TENNESSEE VALLEY AUTHORITY
. W. Hufham, Manager Licensing and Risk Protection Enclosure cc: Mr. James Taylor, Director (Enclosure)
Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Records Center (Enclosure)
Institute of Nuclear Power Operations 1100 Circle 75 Parkway, Sulte 1500 Atlanta, Georgia 30339 8512260333 851205 PDR ADOCK 05000438 S
PDR An Equal Opportunity Employer
\\ \\
ENCLOSURE BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 ITT GRINNELL PIPE SUPPORTS DESIGNED WITH SWAY STRUTS INSTEAD OF REQUIRED GAPS BLRD-50-438/84-20 AND BLRD-50-439/84-19 10 CFR 50.55(e)
NCR BLN BLP 8404 FINAL REPORT Description of Deficiency Seismic pipe supports designed by ITT Grinnell, Providence, Rhode Island, --
which are used on safety-related systems--have sway struts specified where the piping analysis load tables generated by TVA require gaps ranging from 1/16 to 1/8 inches in the restrained direction.
The sway struts (ITT Grinnell Figure 211) do not specify any allowable movements in the restrained direction in the load capacity data sheets.
The deficient supports which have been identified are as follows:
1 RT-MPHG-A052 Sh3 1 RT-MPHG-A052 Sh4 1 RT-MPHG-B052 Sh3 1 RT-MPHG-B052 Sh4 0 RF-MPHG-0300 Sh1 The cited supports were designed for use on the standby diesel generator and controls (RT) system and the high-pressure fire protection (RF) system.
The cited deficiency is potentially applicable to TVA's nuclear plants at Browns Ferry (BFN), Sequoyah (SQN), and Watts Bar (HBN).
This deficiency may be attributed to a failure by support designers and pipe analysts to recognize limitations on constructing very small gaps into pipe supports.
Safety Implications Failure to provide the gaps specified on the load tables would result in piping stresses which were not evaluated.
When evaluated, these stress factors could require support modifications in order to meet design allowables.
Failure to meet design allowables would reduce the margin of safety intended for these components.
Corrective Actions TVA has reviewed the design philosophy governing the use of thermal gaps in support designs and reached the following conclusions.
It is considered a reasonable and prudent analysis technique to investi-gate the effect of a small gap (1/16 inch or 1/8 inch) on pipe secondary stress qualification.
If significant relief is obtained in the computed stress, it is an indication that the pipe is very rigidly supported.
Any reasonable flexibility in the support, flexibility of the pipe wall or shakedown of the pipe (plastic deformation during the first few cycles of operation), would provide the relief simulated by the gap.
T
\\
g
)
1
)
It is not practical, however, to expect a piping system to be fabricated with these small gaps in a specified direction for the following reasons:
1.
It is not possible to align pipe and supports to maintain a gap c
1/8-inch or less in a specified direction.
2.
It is not practical to have a pipe insulated and filled with water during alignment and installation of pipe and supports. When the pipe is insulated and filled with water, the pipe will change position in the support.
3.
The initial few cycles of operation will relieve residual stress, code allowable plastic deformation will occur, and friction forces will be established. As a result, the pipe will shift position in the supports.
With these conclusions and observations in mind, a design review was conducted by TVA to determine which support designs specified a gap in a restrained direction.
The affected designs were reviewed as follows.
Support designs for which a 1/16-inch gap in the restrained direction was specified in the load tables were acceptable without the gap due to the inherent flexibility of suppo s and pipe walls and the plastic deforma-tion of pipe which occurs dur g the first few cycles of operation.
I Support designs for which a 1/8-inch gap in the restrained direction was specified in the load tables were not uniformly accepted.
The designs were reviewed on the basis of the following guidelines wh.ich have been incorporated into the Bellefonte Nuclear Plant Rigorous Analysis Handbook.
1.
On reanalysis, first inves:igate the possibility of eliminating the support.
If the support cannot be eliminated, investigate the possibility of accepting the gap tolerance in General Construction Specifica-tion C-43 and standard snubber free travel and spring rates should be accepted as adequate (i.e., the free travel--plus deformation under load
{
of a snubber--based on engineering judgment--should be specified without regard for the 1/8-inch gap considered in the analysis).
2.
In extreme situations where--in the judgment of the analysts--item I was not practical or adequate, special designs and fabrication ren trements must be developed and specified.
3.
If a 1/8-inch gap is used to qualify a pipe and normal (G-43) fabrication tolerances are acceptable, a gap should not be specified on analysis documents.
I
?
_. -,, _ _. _, _, _., _ ~ _ _ _. _. _ _ _ _ _ -.... _
f As a result of the design review described above, 49 supports were identified that required rework.
TVA has revised the affected support drawings and added guidelines to ensure that gaps specified in pipe support designs are maintained during construction and properly inspected. Support rework will be complete no later than six months before fuel load of the unit affected.
ITT Grinnell personnel have been instructed on the approved TVA procedure for handling gaps.
This re-training, in conjunction with the changes in the BLN Rigorous Analysis liandbook, should prevent recurrence of this deficiency.
TVA has reviewed the design practices at BFN, SQN, and WBN and found that the criteria used on these plants specify the use of gaps less than, or equal to 1/16-inch. Consequently, the design criteria on these plants is considered to be conservative and does not rer esent a condition adverse to quality.
M J
r 4
1 4
i
-