ML19339C906
| ML19339C906 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 02/06/1981 |
| From: | Broehl D PORTLAND GENERAL ELECTRIC CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML19339C904 | List: |
| References | |
| TAC-13152, TAC-43449, NUDOCS 8102120287 | |
| Download: ML19339C906 (16) | |
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.._ @_ y PorUand C-eneral BechicCompany 1
223 CccadJ Sten Ass. start Vce Rescent February 6, 1981 Mr.
R. H.
Engelken, Director Nuclear Regulatory Commission, Region V 1990 North California Boulevard Walnut Creek, CA 94596 Re:
Portland General Electric Company et al.
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(Trojan Nuclear Plant) Docket No. T0-T44 (Control Building Proceeding)
Dear Sir:
This letter is a report of instances in which an assumption made by Licensee in the coirse of the Control Building proceed-ing has been proven to be incorrect and two instances in which commitments made by the Licensee in the course of that proceed-
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ing were not met.
In response to a question from the NRC Staff (a copy of which is provided as Attachment I hereto) Licensee represented that based on its past experience, drilling of holes into walls would result '.a maximum damage to the reinforcing steel in those walls of a 1/8-inch nick.
Based on that assumption, Bechtel calculated the maximum total strength loss which would occur if all of the reinforcing steel in the walls suffered such nicks.
bachtel calculated this loss to be 2 percent, and indicated that the reserve capacity of the subject walls, both
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during interim operation and after the modification, is well above this value.
l Recent drilling of the necessary holes indicates that the assumption that the damage would be limited to 1/8-inch nicks was incorrect.
Although the reinforcing steel has been either avoided altogether or only slightly damaged during most of the core drilling, 12 reinforcing bars suffered nicks larger than 1/8-inch and 9 bars were severed.
Bechtel has attributed such damage to changes in the sharpness of the drilling bit as i
drilling is conducted and to some carelessness on the part of certain drill operators.
The damage to the reinforcing steel which has occurred to date has not reduced the structural 8102120 iki$ ~7 121 S W Sa' mon St'eet. Pomano. Oregon 97201
Portland General BectricConwavy 1
Mr.
R.
H. Engelken j
February 6, 1981 j
Page Two capacities of the subject walls any more than 1 percent at any elevation.
(Drilling is virtually complete at El. 45'-61' of the R-line wall where the most significant damage has occurred).
J In an effort to limit the damage to the reinforcing steel, j
Bechtel has assigned an additional Field Engineer to monitor the drilling operation and give direction to the drilling j
Despite this measure, Licensee believes it is no longer crews.
reasonable to rely on the nicks to the reinforcing steel being less than 1/8-inch.
Therefore, Bechtel is keeping a running i
log of the amount of steel damage which has occurred so that the maximum total strength loss due to damage by core drilling i
remains within the 2 percent previously estimated.
Should sufficient damage occur such that severing of one additional rebar would increase the strength loss to greater than 2 per-cent, the core drilling operation will be halted completely for that wall until either (1) previously damaged rebar has j
been repaired, thus reducing the amount of previous capacity reduction, or (2) an additional safety evaluation pursuant to 10 CFR 50.59 has been prepared (and properly submitted to the NRC) assessing the potential impact of further rebar damage.
In the response provided as Attachment 1, Licensee also stated that if it was necessary to abandon a partly drilled hole l
because reinforcing steel had been encountered, the hole would be fully grouted before a replacement hole was drilled *.
In several instances where reinforcing steel was encountered, it was not necessary to completely abandon the hole, but rather to only abandon part of the hole.
(See sketches provided in ).
An evaluation was performed by Dechtel to provide justification for not grouting the portion of the hole i
which was being abandoned.
(This evaluation is being formalized, and it will be transmitted to the Region V office of Inspection and Enforcement as well as the Office of Nuclear Reactor Regulation.)
It is unclear whether License Amendment No. 55 (issued pursuant to the State of Oregon's appeal) would require that this evaluation be submitted to the Region V Office of Inspection and Enforcement, as well as th6 Office of Nuclear
- Licensee condition 2.C (12) (v) places a limitation on the amount of concrete which may be removed from the walls at any one time.
The instances described in this letter have not resulted in a violation of this license condition, which controls the amount of capacity reduction for these walls due to concrete removal.
Portland GeneralBedicCompany Mr. R.
H. Engelken February 6, 1981 Page Three Reactor Regulation, prior to proceeding with the drilling of the slightly moved hole.
In any event, such notification will be provided if a similar uncertainty concerning the reporting requirements occurs in the future.
In two cases a hole was completely abandoned and no.t grouted prior to drilling the replacement hole, in violation of Licensee's commitment.
These holes have been grouted, and steps are being taken to prevent recurrence of the violation.
Licensee has reiterated to Bechtel the nature of this commitment and the importance of complying with it.
In " Licensee's Testimony on Matters Other than Structural Adequacy of the Modified Complex", Licensee testified that drilling along column line N' in the electrical auxiliaries room so that rebar U-bends could be inserted would not affect the tendons in the precast panels of the floor slab because the tendons are located at regular intervals and their location would be established and avoided during the drilling.
This testimony was based on Licensee's plan at that time to drill holes one inch in diameter.
Bechtel field construction engi-neering personnel requested that additional holes five inches in diameter be drilled to facilitate concrete placement.
This size hole necessarily required that two tendons be severed during the drilling process.
An evaluation was performed by Bechtel prior to drilling which concluded that the severing of j
these two tendons would not have adverse safety consequences; however, a formal safety evaluation should have been prepared and transmitted by Licensee to the Region V Office of Inspec-tion and Enforcement, as well as the Office of Nuclear Reactor Regulation, prior to the performance of this work.
(Such l
an evaluation is being formalized, and it will be transmitted to these two offices of the NRC.)
Licensee has taken the following steps, both as a result of the occurrences described above and to prevent recurrence of similar incidents in the future:
(1) The drilling crew respon-sicle for the damage to 9 of the reinforcing bars has been terminated; (2) Bechtel has taken steps, described above (p.
2), to limit damage to reinforcing bars and to assess further damage to reinforcing bars should it occur; (3) Licensee has emphasized once again to Bechtel the importance of the trans-mittal of safety evaluations involving changes in the modifica-tion program in accordance with L' cense Amendment No. 55; and (4) Licensee has directed Bechtel that no changes in the modification program take place before (a) such changes have been submitted to Licensee personnel who were directly involved l
in this NRC proceeding and (b) such Licensee personnel have reviewed the relation of any such changes to the commitments l
made by Licensee in the course of this proceeding and have t
Po:tland Genera! ElectricCompany Mr.
R.
H.
Engelken February 6, 1981 Page Four determined that all requirements for reporting such changes in accordance with License Amendment No. 55 have been satisfied.
Licensee believes that the measures described above are adequate to prevent the recurrence of similar situations.
Sincerely, W
Attachments c:
Director, Office of Inspection and Enforcement Nuclear Regulatory Commission Washington, DC 20555 Director, Office of Nuclear Reactor Regulation Attention Mr.
R.
L. Clark Washington, DC 20555 Mr. Lynn Frank, Director Oregon Department of Energy
ATTACHMENT 1 i
NRC Ouestions (10/2/79)
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Q. 1 Page 1 of 7 Your motion for summary disposition indicates that a core drill is to be used to drill holes in the existing walls.
Previous indications were that a core drill was not to be used, but rather a star drill.
a.
Provide a detailed basis for your conclusion that the reinforcement will not be significantly damaged by contact of the core drill and that contact will be immeolately detected by the drill operator considering the strength of the concr te and aggregate used for the construction of the in-situ walls, b.
Include a detailed discussion of how the safety-related
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conduits embedded in the R wall will be avoided.
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c.
Additionally, your June 29, 1979 response to question 30 indicates that abandoned holes will be fully grouted before replacement holes are drilled.
d.
Verify that the grout will have attained its required strength before replacement holes are drilled.
- Also, provide the properties of the grout which will be used and justify the acceptability of the grout for the proposed application and your procedure for determining that the grout has attained its required properties before.the replacement hole is drilled.
e.
Also, state how many holes can be drilled before a wall is degraded significantly if the grout has not been allowed 4
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NRC Ouestions (10/2/79)
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Q. 1 Page 2 of 7
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to develop the required strength and justify all assump-tions and conclusions.
Answer:
a.
The holes in the existing walls for the bolts which will connect the new elements with the existing ones will be drilled with a core drill.
There is an increased drag on the drill when reinforcing steel is encountered and the water that is being used to lubricate the drill becomes less turbid due to the reduced cutting rate.
This was confirmed by observing typical core drilling on a similar wall at Trojan.
It was observed that the maximum damage sustained by a reinforcing bar was a nick g,
of 1/8".
It was also shown that the operator was capable of detecting a reinforcing bar during the drilling and stopping the drill without any further damage than the mentioned 1/8" nick.
Reinforcing steel in the masonry wythes can be readily located with the magnetic rebar locator presently in use at the Plant, and thus can be avoided in the drilling
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operation.
Reinforcing steel in the. concrete core of composite walla cannot be easily located in this manner due to its distance from the wall surface.
The smallest size bar in the cores of existing composite walls is a No. 6 bar for verticals and a No. 9 bar for horizontals.
Therefore the smallest size bar that can be damaged by l
1 drilling in the walls is a No. 6 bar which has a nominal s-l k.
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NRC Ouestions (10/2/79)
O. 1 Page 3 cf 7 area of 0.44 in.2 A 1/8" nick would reduce this area by.05 in.2 In terms of loss of strength this amounts to. 0 5/. 4 4 =.11, o r 11 %.
If it is assumed that all of the vertical bars between column lines 41 and 46 (or 1 panel in 4, or 25%) are damaged, and considering that the vertical bars provide 75% of the wall capacity, the =aximum total strength loss due to damage by core drilling to reinforcing bars is 0.11 x 0.25 x 0.75 =.02, or 2%.
The reserve capacity of these walls both during interim opera-tion and af ter the modification is well above 2%.
The assumption that all vertical bars are damaged is very conservative, since once a bar is encountered, the loca-tion of other vertical bars can be established based on their known spacing, and damage to other bars can be avoided.
b.
There are no electrical conduits embedded in the M line wall where drilling will be performed.' There are two electrical conduits embedded in the R line wall where core drilling will be performed.
Their approximate location will be marked on the surface of the walls where the core drilling will be performed.
This procedure should reduce l
the possibility of the drill bit striking the conduit; however, experience has shown that should the drill bit strike the conduit, the enclosed cable would not be harmed.
The conduit i s made of steel and has a wall thickness of 0.145 inches (slightly larger than 1/8 of an inch).
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NRC Ouestions (10/2/79)
Q. 1 Page 4 of 7 Previous observations with regard to the ef fect of the drill bit striking reinforcing steel has shown that the smaller diameter reinforcing steel would only be nicked by a maximum of 1/,8 inch before the drill operator, upon detecting he had struck the steel, could pull back the drill bit.
Since the conduit diameter (1-1/2" nominal rigid steel) is much larger.than the 5/8" diameter rein-forcing bar discussed above, the depth of penetration into the conduit wall before the drill operator detects that he has contacted conduit should be much less due to the larger. surface area presented.
Nevertheless, as added assurance that there is no sig-nificant safety concern, we have further reviewed the consequences of the encased wiring being completely cut.
Our review has shown that two existing conduits, CB1910 and DB1937, are routed in the Control Building from the Electrical Auxiliaries Room (el. 65') to the Control Room (el. 93 ' ).
The major portion of these conduits is embedded in the Control Building wall as shown on the
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attached Figure 1-1.
Each conduit contains two cables that perform the following f unctions :
CB1910 Power for the instruments in the Nuclear Instr-umentation (NIS) Channel C Cabinet C31C Power for the Control Circuits in the NIS Channel C Cabinet C31C l
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e 1
NRC Ouestions (10/2/79)
O. 1 Page 5 of 7 DB1937 Power for the instruments in the NIS Channel D Cabinet C31D Power for the Control Circuits in the NIS Channel D Cabinet C31D Nuclear Instrumentation Cabinets C31C and C31D contain redundant safety-related circuitry for the ex-core neutron power range flux detectors (Channels A and B are not affec-ted).
The Channel D Cabinet C31D contains additional circuitry that consists of the power range neutron flux comparator circuit, source range neutron flux rate cir-cuitry, and an audio display of the source range flux levels.
These two NIS cabinets and their associated elec-trical circuitry generate the following reactor trip s ignals :
1.
Power Range high neutron flux (high and low setpoint) 2.
Power Range high positive neutron flux rate trip 3.
Power Range high negative neutron flux rate trip The loss of Channel C power range detector would not cause a reactor trip since the reactor trip logic (2 out of 4) i would not be satisfied.
Activation of Control Room alarms (power range loss of detector voltage, NIS high neutron flux power range, and power range comparator deviation) would reault from damage to conduit CB1910.
Loss of MIS
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NRC Questions (10/2/79)
Q. 1 Page 6 of 7 cabinet C31C would not affect any other safety-related circuits or-equipment.
The effect of damage to conduit DB1937 would be the sa'me as for CB1910 except that Channel D NIS would be involved and the startup rate count meters on the main control board would be lost.
If both conduits CB1910 and DB1937 were damaged, a reactor trip may occur since two of the four NIS channels are affected.
c.
If it is necessary to abandon a partly drilled hole because reinfercing steel has been encountered, the hole will be
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fully grouted befora a replacement hole is drille*d. Since the reduction in shear area owing to any such abandoned hole would be insignificant (see "e." below) the replace-ment hole may be drilled even if the grout in the abandoned hole has not yet developed its design strength.
d.
The grout to be used to fill the abandoned holes is Five I
Star Grout manufactured by U.S. Grout Corp.
Tests per-formed in accordance with ASTM C109 established that this grout attains at least 5000 psi compressive strength in 7 days and at least 8000 psi in 28 days.
Since this strength is greater than the strength of the block material (2000 psi) or the strength cf the concrete core (5000 psi) and because it is non-shrink grout, its use to grout the l
abandoned holes in these materials is acceptable.
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I NRC Ouestions (10/2/79)
Q. 1 Page 7 of 7 e.
The reduction in area due to the drilling of bolt holes at any period of time will not be more than that described in Licensee's response dated June 29, 1979 to NRC Question No. 30.
The above condition will be assured by stopping the drilling whenever the area reduction percentages reach the limits set in the above referenced response.
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ATTACHYENT 2
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I BechtelPowerCorporation Interoffico Memorandum l
M. Daubenheyer ee.w. 274
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we.cs Portland General Electric Co.
one December 31, 1980 I
Trojan Nuclear Plant C
Bechtel Job No.13097 s-P. Chang-Lo Spec. C-501 es SFPD o.s c =
J. F. O' Leary 221/5/A-03 sv. 0211 a
J. C. Kotler W. Lang As a further clarification of Spec. C-501, please find belov the ground-rules for drilling bolt holes in the Control Build-j ing R & M wall, above elevation 65'-0*:
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1.
Definition of terms as used in these ground-rulest
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Hole A void resulting from material removed with a core drill from the wall.
A hole filled with grout (or bolt and grout) that has attained 5000 pai, shall not be considered a hole as defined above.
Mola Projections see sketch below.
Iforizontal or vertical band A horisontal or vertical band of the wall not to exceed 6 inches in width, i
centered on bolt lines, shown in elevation 7
on dwg. C-1213.
2.
Ground-rules:
a.
The hole projection shall not be larger than 7.5 inches.
b.
The sum of the horizontal projections of the bolas In a horisontal band shall not exceed 67 inches.
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IO!!, Spec. C-501 Pago 2 of 2 c.
The sum of the verticc1 projections of the holes in a verticci bcad sht.11 not exceed 45 inches.
Cases not fc111ng excetly in one of the above categories shall be verified with the Project Engineer.
.h-P. Chang-L Project Engineer who d
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2/A-19 e
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING APPEAL BOARD In the Matter of
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Docket 50-344 PORTLAND GENERAL ELECTRIC COMPANY,
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et al
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(Control Building Proceeding)
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(Trojan Nuclear Plant)
)
CERTIFICATE OF SERVICE I hereby certify that Licensee's letter dated February 6,1981 to the Atomic Safety and Licensing Appeal Board, with attachments, has been served upon the persons listed below by depositing copies thereof in the United States mail with proper postage affixed for first class mail.
Alan S. Rosenthal, Esq., Chairman Dr. Kenneth A. McCollom, Dean Atomic Safety and Licensing Appeal Division of Engineering, Board Architecture and Technology U. S. Nuclear Regulatory Commission Oklahoma State University Washington, D. C.
20555 Stillwater, Oklahoma 74074 Dr. John H. Buck, Member Dr. Hugh C. Paxton Atomic Safety and Licensing Appeal 1229 - 41st Street Board Los Alamos, New Mexico 87544 U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Atomic Safety and Licensing Board Panel Dr. W. Reed Johnson, Member U. S. Nuclear Regulatory Commission Atomic Safety and Licensing Appeal Washington, D. C.
20555 Board j
U. S. Nuclear Regulatory Commission Atomic Safety and Licensing Appeal Washington, D. C.
20555 Panel (5)
U. S. Nuclear Regulatory Commission Marshall E. Miller, Esq., Chairman Washington, D. C.
20555 Atomic Safety and Licensing Board U. S. Nuclear Regulatory Commission Washington, D. C.
20555
CERTIFICATE OF SERVICE Docketing and Service Section (4)
Ms. Nina Bell Office of the Secretary 3920 N. E. 12th Avenue U. S. Nuclear Regulatory Commission Portland, Oregon 97212 Washington, D. C.
20555 Mr. John A. Kullberg Joseph R. Gray, Esq.
15523 S. E. River Forest Drive Counsel for NRC Staff Partland, Oregon 97222 U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Mr. David B. McCoy 348 Hussey Lane Lovenstein, Newman, Reis, Axelrad &
Grants Pass, Oregon 97526 Toll 1025 Connecticut Ave., N. W.
Ms. C. Gail Parson Suite 1214 P. O. Box 2992 Washington, D. C.
20036 Kodiak, Alaska 99615 Frank W. Ostrander, Jr., Esq.
Mr. Eugene Rosolie Assistant Attorney General Coalition for Safe Power State of Oregon 215 S. E. 9th Avenue Department of Justice Portland, Oregon 97214 500 Pacific Building 520 S. W. Yamhill Columbia County Courthouse Portland, Oregon 97204 Law Library Circuit Court Room William Kinsey, Esq.
St. Helens, Oregon 97051 Bonneville Power Administration P. O. Box 3621 Portland, Oregon 97208 i
t RonaldW//ohnson Assistant Ge,zferal Counsel Portland General Electric Company Dated:
February 6, 1981 66.27B13