ML19309E144
| ML19309E144 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 04/14/1980 |
| From: | Broehl D PORTLAND GENERAL ELECTRIC CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19309E145 | List: |
| References | |
| TAC-07551, TAC-11299, TAC-7551, NUDOCS 8004180466 | |
| Download: ML19309E144 (12) | |
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April 14, 1980 Trojan Nuclear Plant Docket 50-344 License NPF-1 Director of Nuclear Reactor Regulation ATTN:
Mr. A. Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Sir:
Attached are 40 copies of responses prepared by Bechtel to questions from your staff relating to the proposed modifications to the Trojan Control Building.
The results of the additional evaluations performed by Bechtel to respond to these questions have not altered Bechtel's previous conclusions and statements with respect to the appropriateness of the proposed construction sequence.
Included as Attachment 6-1 to Question 6 is Licensee 's proposed Technical Specification and Bases relative to the Control Building modification connection bolts.
Also included as Attachment 21-1 is Licensee 's proposed revision to Technical Specification 5.7.1.
Sincerely, P
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Mr. R. H. Engelken, Director l
U. S. Nuclear Regulatory (.ommission Region V i
Mr. Lynn Frank, Directo'.
State of Oregon Department of Energy Control Building Service List n :- n-e r: on-- r:::
800.4180466
NRC Staff Questions (4/3/80)
Q. 1 Page 1 of 1 With respect to the adequacy of the initial welding of Plate 8 described at pp. 4314-17 and 4321-25 of the transcript:
a.
What is the f actor of safety on the weld?
b.
Is this based on a code allowable or an ultimate value?
c.
What type of weld will be utilized:
- fillet, partial penetration or tack?
Answer:
a.
Thirty-three in. of weld would provide a factor of safety of 5 to resist the North-South SSE forces.
Since forty-eight in. of weld will be provided, the factor of safety will be approxi-mately 7.
I b.
The factor of safety is based on the allowable stress givsn in Table 1.5.3 of the AISC Specifi-
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cation.
No 11 crease in the allowable stress has been taken for dynamic loading.
c.
The weld will be 1/4-in. thick, root pass.
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2 NRC Staff Questions (4/3/80)
Q. 2 Page 1 of 1 Identify the code that will be complied with in the welding of Plate 8.
What code or procedures will be used in qualifying the welders?
Answer:
a)
Welding will be performed in accordance with AWS Dl.1-1979, Structural Welding Code.
b)
Welder qualification and visual inspection will be in accordance with AWS Dl.1.
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O NRC Staff Questions (4/3/80)
Q. 3 Page 1 of 2 When exposing the columns, what magnitude of vertical shear is required to be redistributed and what is the load path?
Answer:
The construction sequence and reduction in vertical shear capacity resulting from exposing the columns have been investigated.
The vertical shear capacity was based on the shear friction resistance developed by the horizontal reinforcing steel in the block and the frictional resistance of the beam-column connections.
These vertical shear capacities are consistent with the discussion given in Licensee's response dated December 22, 1979 to NRC Staff Question 6 dated October 2, 1979.
The vertical shear loads used in the evaluation were for the 0.25g SSE and the structure in the existing or unmodified condition.
There will be a reduction in the vertical shear in the existing elements due to the presence of the new struc-tural elements which precede ecctain column exposures but this has been neglecteo in this investigation.
As indicated in the response to Question 6 submitted March 17, 1980, the vertical shear is the important quantity during construction since this is the capacity being removed by exposing the columns.
As indicated in this referenced response, the influence of gross bending and reduced dead load due to creep and shrinkage on the vertice.1 shear will only be minor and will not affect the final conclusions.
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9 NRC Staff Questions (4/3/80)
Q. 3 Page 2 of 2 This investigation indicates that exposing the column from el. 65' to 77' on the R wall causes the largest reduction in capacity.
This is due to 12 feet of column being exposed at two locations, R-41 and R-46, and the vertical shear in the R wall being greater than that in the N wall.
Above el. 77 ' in the R wall, only 8 feet of the column will be exposed.
On the N wall, the blocks are only partially removed.
The accumulated '?ertical shear force at R-41 is 1650 kips from el. 65' to 117'.
The vertical shear capacity is 1850 kips
- at and above el. 77'; therefore, no redistri-bution is required.
If the actual reinforcing steel yield stress of 45 ksi was used, the vertical shear capacity at i
and above el. 77' would be 1900 kips.
Thus, we continue to believe that the construction sequence we have proposed is appropriate with respect to maintaining the seismic capability of the Complex.
- This capacity value reflects application of a capacity reduction factor of 0.85.
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NRC Staff Questions (4/3/80)
Q. 4 Page 1 of 2 a.
Your testimony indicated that test specimens with embedded columns exhibited no delaminat' ion.
The steel in those test specimens was not the same as in the actual structure.
In addition, the actual walls house an encased steel bear in the core and the beam induces t
shear stresses on the masonry-core interface.
- Also, the loading paths differ between the test specimen and actual walls.
In view of these differences, what do these two specimens indicate about potential delamina-tion of the actual walls?
b.
What kind of steel ties were in the test specimens?
How do they compare to the steel in the walls (distri-bution, thickness, etc.)?
Answer:
When bond strength between the embedded columns and a.
the concrete core is considered, the shear walls will i
act monolithically to resist the lateral forces resulting from an earthquake.
In this instance, the behavior of the test specimens ('L1 and L2) and the actual structure will exhibit the same behavior.
If the bond strength between the above components is conservatively neglected, the load paths in the actual walls will differ from those in the test specimens.
Under this assumption, the test specimens would not provide information on the interface stresses between the masonry and the concrete core.
However, as indicated in Licensee's response to NRC Staff Request No. 3 dated January 28, 1980, these stresses are i
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NRC Staff Questions (4/3/80)
Q. 4 Page 2 of 2 significant only in a very local zone and that there is ample reserve capacity in the walls to resist the associated forces.
As indicated in Licensee's Testi-mony on the Structural Adequacy of the Modified Complex, Q(130), the capacity of these specimens was not used in our evaluation.
b.
In test specimens L1 and L2, No. 3 ties at 3'-4" horizontal and 2'-0" vertical spacing were used.
In the actual structure, both the double wythe and the composite walls have a square pattern of No. 3 ties at 4-ft. spacing, in both the vertical and horizontal directions.
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NRC Staff Questions (4/3/80)
Q. 5 Page 1 of 2 Your testimony discussed the coefficient of friction between steel plate and concrete.
There is also a question concerning the coefficient of friction on the N-line wall of the Complex where new concrete is being added.
What coefficient of friction is necessary at this location?
Answer:
In the design of the bolts for the N line wall, an effec-tive coefficient of friction between block and concrete of 0.50 was used and a capacity reduction factor of 0.85 was applied to that value, yielding a resultant of 0.59.
The minimum factor of safety for these bolts, due to unfactored OBE forces and considering the potential ef fects of gross bending, potential dead load reduction
- and thermal stresses, is 1.60 relative to initial slippage.
Appli-cation of a capacity reduction factor of 0.85 reduces this value to 1.36.
However, as indicated in Licensee's response to NRC Staff Question 1 dated March 30, 1980, dead load will remain on the wall panels since the wall panel deformations will compensate for creep and shrinkage effects under dynamic conditions.
Based on this consider-ation, the minimum factor of safety for the bolts due to unf actored OBE forces and considering gross bending and thermal effects is 1.68.
Application of a capacity reduction factor of 0.85 reduces this value to 1.43.
This latter value implies that a coefficient of friction value
- In all responses to this set of questions, whenever it is stated that potential dead load reduction has been con-sidered, such statement also implies that the contribution of the beam-column connections to stiffness has been disregarded.
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9 NRC Staff Questions (4/3/E0)
Q. 5 Page 2 of 2 of only 0.70 is needed to develop required frictional resistance between the block and the concrete.
To further assure that the necessary friction is obtained, the existing block face will be roughened by bush hammering, heavy sand blasting or other appropriate means.
NRC Staff Questions (4/3/80)
Q.
6 Page 1 of 3 Discuss the acceptability of A 354 bolts with respect to stress corrosion and provide your proposed Technical Specification for the bolts.
t Answer:
The bolts to be used to fasten the 3-in. thick plate to wall R and the new concrete walls to the existing walls N and R are in accordance with the requirements of ASTM A 354 Grade BD.
These bolts have similar mechanical prop-erties to ASTM A 490 bolts and they will comply with the additional requirements of maximum tensile strength, nut size and strength, washer hardness, tests, and inspection contained in Specification A 490.
An aspect which has been given careful consideration during the selection of this material is stress-corrosion resistance.
Literature (ref. " Factors Affecting Environ-mental Performance of High Strength Bolts" by Walter K.
Boyd and W. S. Hyler, A'SCE Journal of the Structural Division, July 1973) and other investigations in this field have indicated that for stress corrosion to occur three factors are required, namely, high strength level, high stress level, and the presence of a corrosive agent.
The strength level is specified (and will be verified) l to be below the level where the bolt materials are sus-ceptible to stress corrosion cracking.
The relatively low stress levels and the mild environment at Trojan make the probability of stress corrosion cracking low, even for susceptible materials.
NRC Staff Questions (4/3/80)
Q. 6 Page 2 of 3 The findings in 'he referenced article indicate that t
materials with tensile strength below 170 ksi did not create a stress-corrosion problem.
It is in accordance with this conclusion that ASTM A 490 specifies a 170-ksi maximum tensile strength.
In the same article it is also stated that at stress levels 20 percent below the material yield strength, corrosion-related problems should not be anticipated.
The design of the fasteners is based on a 1-3/4-in diameter bolt with a maximum tension load of 200 kips.
In order to further reduce the stress level in the bolts, a 2-in. diameter bolt will be used with the same maximum load of 200 kips.
For that bolt diameter, the maximum stress level is 80 ksi, which is well below the recommended 80 percent of 130 ksi (yield strength),
which equals 104 ksi level.
The only potential corrosive agent present at Trojan is the moisture in the air.
Moisture has been shown to cause stress-corrosion cracking only in highly susceptible materials at relatively high stress levels.
The stressed portions of the bolts are provided protection from the outside atmosphere in the applications used in the modi.
fication, and neither the susceptible material nor the high stress levels will be present.
In accordance with additional recommendations of the referenced article, other precautions will be taken to preclude mechanisms which might induce stress corrosion.
The A 354 Grade BD bolts will not be galvanized.
Each bolt will be tested to verify.that its hardness falls
NRC Staff Questions (4/3/80)
J Q. 6 Page 3 of 3 between the limits required by the specification (33 to 38 Rockwell C).
The base material from which the bolts i
will be manufactured is specified as AISI 4340 material.
l In light of the above considerations, it is concluded that use of the ASTM A 354 Grade BD bolts for the intended application is acceptable from the standpoint of stress Corrosion.
Licensee's proposed Technical Specification and bases are I
provided as Attachment 6-1.
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