ML20010H823
| ML20010H823 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 09/18/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21-81 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8109290324 | |
| Download: ML20010H823 (3) | |
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.D TENNESSEE VALLEY AJTHORITY CH ATTANOOGA.-TENN ESSEE 37401.
400 Chestnut Street Tower II 7"
Septeyberi58l 1981
'I BLRD-50-438/81-49 S~, &p
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Mr. James P. O'Reilly, Director t7 O
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s 101 Marietta Street VA Atlanta, Georgia 30303 f_
Dear Mr. O'Reilly:
BELLEFONTE NUCLEAR PLANT UNIT 1 - LOOKOFF PRESSURE ON POSTTENSIONINO SYSTEM - BLRD-50-438/81 SECOND INTERIM REPORT The subject deficiency was initially reported to NRC-0IE Inspector R. V. Crlenjak on July 17, 1981 in accordance with 10 CFR 50.55(e) as NCR BLN CEB 8104. This was followed by our first interim report dated August 17, 1981. As discussed with J. Lenahan by telephone on August 20, 1981, enclosed is our second interim report. We expect to submit our next report by November 24, 1981. We consider 10 CFR Part 21 applicable to this deficiency.
If you have any questions concerning this matter, please get in touch with D. L. Lambert at FTS 857-2581.
Very truly yours, TENNESSEE VALLEY AUTHORITY
. M. Mills, Manager Nuclear Regulation and Safety Enclosure cc:
Mr. Victor Stello, Jr., Director (Enclosure)
Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission
,N Washington, DC 20555 J
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8109290324 810918 i PDR ADOCK 05000438 S
PDR-An Equal Opportunity Employer
ENCLOSURE BELLEFONTE NUCLEAR PLANT UNIT 1 LOCK 0FF PRESSURE ON POSTTENSIONING SYSTEM BLRD-50-438/81-49 10 CFR 50.55(e)
SECOND INTERIM REPORT Description of Deficiency Inryco, Incorporated has been contracted (contract 75C53-85380) to supply and install the posttensioning system for the primary containment structures. Allowable lockoff stresses for each tendon have been established by Inryco in accordance with the April 1973 Trial Use Version of the ACI 359 code and the contract specifications. These lockoff stresses are required to provide assurance that the containment structure will have adequate prestress force to perform its intended safety function.
In order to resolve a problem with certain stressing gauges being out of calibration, Inryco performed liftoff tests on several horizontal tendons.
These lif toff tests revealed that, in several cases, lockoff stresses were substantially lower than predicted.
Interim Progress In the first interim report on this deficiency, Inryco's program for investigation was outlined. Following is a brief summary of the findings to date.
Inplace tendon liftoff readings taken on a random sample basis on unit 1 revealed that the majority of the tendons are exhibiting liftoff stresses substantially lower than the allowable lockoff range durf ng original stesssing of the tendon. A review of the material certi.'ications for the tendon wire revealed that the tendons sampled were fabriaated with wire manufactured by NDI or by Florida Wire and Cable Compan) (FWC). The NDI wire is 4-percent relaxation w1re while FWC wire is 8-1,2 percent relaxation wire. As would be expected, the tendons fabr icated with FWC l
wire exhibit lower liftoff stresses than the tendons fat ricated with NDI wire. However, the differences are not substantial.
Steps have been taken to perform physical and chemical testing of the FWC and NDI wire. To date, no results have been submitted to TVA.
Further testing has been initiated since the first interim report on this deficiency. Inryco attributes the low liftoff readings to " load equalization." In short, their theory states that with time the stress in a tendon will equalize lengthwise. Because of the initial loss in stress lengthwise in a tendon because of friction, it would be expected that the stress in the lengthwise center of the tendon would increase in time and the anchorage stress would decrease. TVA required that Inryco substantiate their theory with physical evidence. To this end, Inryco has performed a friction test to verify the assumed friction coefficient and is currently performing tests to ascertain whether or not " load equalization" does ocottr.
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The friction test has been completed and has served to experimentally verify the friction coefficient. Inryco had expected the coefficient to be 0.08 while TVA used a conservative value of 0.13 in preliminary design calculations. The experimental value was 0.10 with a standard deviation of 0.062. Therefore, the friction test produced uniform results and exhibited a normal distribution since the largest difference in values was 0.02.
Currently consideration is being given to why tha experimental value differs from that found on other nuclear projects.
In addition, the " load equalization" test is being conducted. Additional information will be provided upon completion of this testing. At this point, no corrective action has been established.
The stressing gauges and stressing jacks have been checked for calibration and repeatability. TVA has not been notified of any problems with the stressing equipment. However, equipment problems or procedural problems with tendon stressing have not been ruled out at this time as being a possible contributor to the low liftoff problem.
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