ML20030B365
| ML20030B365 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 05/28/1981 |
| From: | Stello V NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | Drey L AFFILIATION NOT ASSIGNED |
| Shared Package | |
| ML20010B232 | List: |
| References | |
| NUDOCS 8108140244 | |
| Download: ML20030B365 (8) | |
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50 _u 9s IE FILE COPY MAY 2 8 1981,
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$h Mrs. Leo A. Drey y
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Dear Mrs. Drey:
This is in final response to your letters of u 979, June 9, 1980, and June 23, 1980, regarding the embedded steel anchor plates at the Callaway Nuclear Power Plant.
Previous NRC letters that were sent to you on this subject were dated October 30, 1979 and July 8, 1980.
In addition, a copy of IE Raport 50-483/90-14, dated September 16, 1980, was also sent to you.
A final review of this matter by NRC Headquarters staff has now been completed.
While that review was underway the Atomic Safety and Licensing Board for the OL proceeding issued a Special Prehearing Conference Order (dated April 21, 1981).
That Order outlines the petitions submitted, defines the intervenors and describes the contentions that have been admitted for the hearing.
Joint Intervenors' Contention 1A stating that, " inadequate and incomplete inspection and teccing on embedded plates were performed during the plant's construction" hae. been admitted. This contention will assure Board review of the resolutio.. of the matter of embedded plates.
This reply will provide you with the staff position on this issue. While preparing this response and the specific items in the enclosure, a review was made of the various questions and conccrns that you had expressed in the past related to the embedded steel anchor plates that may not have been specifically addressed.
These items are listed and a response or the reference to a document you have received previously is provided.
We hope that this information will satisfactorily answer your questions and concerns. We are of the opinion that the questions and concerns related to the concrete embeds installed prior to June 1977 at the Callaway facility ha're now been resolved to the satisfaction of the staff.
Sincerely, Original signed by victor Stello Victor Stello, Jr., Director Office of Inspection and Enforcement fd
Enclosure:
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4 Enclosure SPECIFIC RESPONSES Q1.
Isn't it possible that some anchor plates embedded prior to June 1977 are defective?
A1.
Yes.
It was NRC's continuing concern about the integrity of the anchor plates embedded prior to June 1977 that caused the initiation of the random in place test and representative test programs that were reported in IE Inspection Report 50-483/80-14, dated September 16, 1980 (see 3rd paragraph' on page 6).
Considering the small number of defective embeds detected by the re-inspection and testing effort, the NRC has concluded that an equal proportion of defects in installed plates would be well within the tolerance limits of the system design and no more special efforts are i,
required for the installed plates.
Q2.
Is it possible to find and replace defective anchor embedments already installed into the concrete?
A2.
The use of a visual examination is precluded when embedments such as these in question have, in fact, had the concrete placed around them, unless destruction of the surrounding concrete and reinforcing steel matrix is accomplished.
No nondestructive techniques we are aware of could, in this instance, be utilized to provide meaningful results.
Therefore, in this case, the first action we deemed necessary was an examination of anchors not already embedded. We concluded that the data obtained in July and August 1977, supplemented by some later information on embeds not yet cast-in concrete, could be considered representative of those anchors already embedded.
Consequently, a destructive program would become necessary only after it was evident that the failure rates in the ability to carry and respond satisfactorily under load were too high in a similar and representative sample. With high failure rates, it would become necessary to execute extensive load tests or complete the removal of concrete to obtain samples on which to base a conclusion.
Although removal of concrete and replacement of embedments is possible, it is a difficult task and requires close control and consiceration of.
the potential for additional damage.
In the past, NRC has required the removal of some very complex concrete structural components consisting of many cubic yards of concrete.
This situation was certainly not precluded in this case.
Q3. What assurance is there that anchor embeds not already cast into concrete are recresentative of those already embedded?
A3.
From the records available revealing that the anchor embeds had been fabricated, inspected, released, and accepted under the same specifica-tions, contract, and work procedures with the only variable being the time the work was completed, we concluded that those units not yet embedded were representative of those already embedded.
i Q4. With regard to the results of inspections performed on manually welded anchor rods for embeds, did the NRC believe Daniel or Bechtel?
. Enclosure A4.
The reinspection performed by a team of inspectors consisting of personnel from Daniel, Bechtel, and Union Electric Company, in order to identify the cause for the original rejections made by Daniel, was accepted by the NRC as representing the facts.
The findings were discussed in IE Inspection Report 50-483/80-14, dated September 16, 1980 (see cages 8 and 9).
QS.
Compare ASME, AWS and Union Electric criteria on wald undersize for accepting manual welding of anchor rods for anchor eebeds.
AS.
As noted in the March 10, 1978 letter from Union Electric to which you referred, the ASME Code does not apply to this type of safety-related component.
In referring to the ASME Code, the licensee was addressing the ASME Boiler and Pressure Vessel Code,Section III, Division 1 which addresses Class 1, 2 & 3 components, metal containments, component supports and core support structures. These components do not include general structural framing supports, of which these manually welded anchor embeds consisted.
The comparisons of AWS and Union Electric criteria were provided in IE Report 50-483/80-14, dated September 16, 1980 (see page 7).
NRC accepted the criteria used by Union Electric.
Q6.
What is the applicability of AWS D.1.1-75 for machine stud welding?
A6.
As noted in Answers to Questions 6 and 7 of Attachment B, IE Inspection Report 50-483/80-14, dated September 16, 1980, the above standard was intended for application to machine stud welding and acceptance testing.
Q7.
Are the requirements for the acceptance of machine stud welding on bridges more stringent than those applied to nuclear power plants?
A7.
The following comments are based on a comparison of specifications of the American Welding Society (AWS D.1.1-75) and the American Association of State Highway and Transportation Officials (AASHTO Interim Bridge Specifi-cations for 1975).
These listed items constitute the primary differences.
a.
AASHTO allows welding when base metal is below 0 F but requires oreheating to 70 F and maintaining the base metal above 32 F during stud welding.
Two additional 45* angle bend tests are required per 100 studs.
AWS allows no welding when the base metal is below 0 F and imposes additional inspection / test requirements when the base metal is below 32 F.
b.
AASHTO requires the contractor to submit the following informa-tion to the engineer for approval:
(1) name of manufacturer, (2) detailed description of the stud and arc shield,
. Enclosure (3) certification from the manufacturer that the stud has met AASHT0 qualification tests, and (4) notarized copy of the qualification test report as certified by the testing laboratory.
The purpose of the qualification testing is to prescribe weldability and strength tests for a given type, size, and arc shield.
If all factors that could affect stud performance remain unchanged, such initial qualification tests remain valid.
AWS does not require qualification testing, unless requested by the engineer.
Such a request would typically be done in the written specification.
The number of tests to be performed is left to the engineer to specify.
c.
AASHTO production acceptance inspection for the first two studs on a beam requires bending to 45, whereas AWS requires only a 30 bend.
d.
AASHTO, as you indicated, requires that "each stud shall be given a light blow with a hammer" and "any stud which does not emit a ringing sound when given a light blow with a hammar...
shall be struck with a hammer and bent 15* from 'he correct axis of installation.
Studs that crack e:ther in the weld or in the shank shall be replaced."
In summary it can be stated that there are only minor differences between the AASHTO Standard Specification for Highway Bridges and the AWS Structural Welding Code and that the AASHTO specificction is a bit more stingent, undoubtedly because of the need for fatigue life.
The two specifications / codes are intended for different types of structures which undergo distinct service conditions.
Fatigue is a major concern in the use of studs in composite bridge design as a result of the many load repetitions a bridge receives ar, opposed to a building structure.
It is NRC's position that the requirements placed on a licensee (in conjunction with use of the AWS Code) that include operator training and qualification, quality control, inspection, and correction of identified deficiencies are more than adequate to assure the proper level of safety.
Q8.
Will manually welded anchor rods with undersized welds be able to withstand the maximum design load, vibration, and durability requirements?
A8.
The analytical calculations completed by the licensee as reported in IE Inspection Report 50-483/80-14, dated September 16, 1980 (see page 8), as well as the additional testing requested by NRC (see page 9 of the above-referenced report), demonstrate quite clearly that the maximum design load can be met.
The load-strain curves that reflect the behavior of the six specimens cut from actual anchor embeds clearly illustrate a ductile behavior under load that provides the energy-absorbing capability for response to dynamic loading.
Vibratory loads with respect to fatigue-related problems are not considered to be of sufficiently high numbers of
. Enclosure repetitions for these embedded elements to be of significance.
Durability is not a major problem with these anchors since the backs of the embedded plate, the weld and the anchor rods are embedded in concrete and are not subjected to an adverse environment.
Q9.
Have specifications changed to meet the deviations which were found?
A9.
As noted in IE Inspection Report 50-483/80-14, dated September 16, 1980 (see page 7), certain revisions were made by the licensee as Revision 9 to Specification C-131.
We do not know the motive for the change, but we have established the technical validity of the revision as noted in the response to Question 8 herein.
Q10. A dangerous percentage of the manual and machine made welds are defective.
A10. During the reinspection of over 81,500 machine-welded studs on 7543 anchor embedments not yet installed, only 0.0?% of :he studs failed the bend test.
It was also found that 0.13% of the ancnor embedments had more than one stud failing during the bend test.
Testing a sample of 2.5% of the embedded anchors with machine-welded studs to design loads resulted in no signs of distress or indications of inadequacies.
There was no evidence to suggest a difference in the frequency of studs failing the bend test on anchors that were embedded or on those anchors that were not embedded in concrete.
Our conclusion is that the failure rate to bend tests on individus1 machine-welded studs was low and would not cause technical questions related to the functioning of an individual anchor'as shown by the in place testing program.
We determined that 10% of the manually welded anchorage rods remained in question and required further study.
The further study included actual testing of individual welds of the anchor rod to the embed plate that were cut from the group of anchor embeds that had been on hold since August of 1977.
The welds sustained the ultimate failure loads of the base material.
Analysis of the weld deficiencies also indicated that the embedments as built would sustain the design loads.
There was no evidence to conclude that manually welded anchorage rod to anchor embeds already cast in concrete in June 1977 contained any different or more frequent weld deficiencies than the group examined and tested.
Our conclusion is that there is no danger in the manual or machine-made welds in the anchors embedment cast into concrete orior to June 1977.
Q11. Does Bechtel have a lack of faith in the ability of Daniel inspectors in areas other than the inspection of manually welded anchor rods?
All. In this case, the Daniel inspectors were being more cautious than necessary, so the problem they identified was brought to the attention of the licensee who in turn obtained the design expertise of the engineering disciplines who resolved any safety questions to the satisfaction of the NRC.
We are unaware of any Bechtel concerns; however, we are certain that if there were concerns, Bechtel would report them under 10 CFR 21.
. Enclosure Q12. Who bears tne burden of proof regarding safety at the OL proceedings?
A12. As defined in the NRC regulations, the burden of proof rests with the licensee.
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