ML18046B401
| ML18046B401 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 04/29/1974 |
| From: | Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8101100285 | |
| Download: ML18046B401 (2) | |
Text
.
\\
- ~*
((p,
.. - /
REF
~
consumers Por1er company I
Generol Offices: 212 West Michigan Avenue, Jackson, Michigan 49:201 *Area Code :i17 788*0550 Mr. John F. O'Leary, Director Directorate of Licensing.
US Atomic Energy CoI:imission Washington; DC 20545
Dear Mr. O'Leary:
April 29, 1974 Re:
Docket 50-255 License DPR 20 Attached is a copy of report titled "Consumers Power Company Palisades Nuclear Power Plant Containment Building Post Tensioning System Three-Year Surveillance," dated February 1974.
This report, pre-pared by Bechtel Corporation; describes the surveillance of the Palisades containment building post tensioning system.
This report bas been revie*wed in detail by Consumers Power Co:npany.
We feel that.the testing performed demonstrates that the exist-ing tendon forces are in accordance with the design objcctive3 er the contaimtlent structure. In addition, there were no broken wires since the last inspection and there were no significant chaDges in ~he corrosion con-ditions or grease properties. However, the testing performed to date has not been adequate to determine a force-time trend line for each tendon ~s required by Technical Specification 4.5.4d2.
- Studies were performed to determine variations that might be expected due ~o the measurement technique used in the tendon surveillance.
~he measurement technique used in the first year surveillance as well as the scheduled three-year surveillance showed ten percent variations in stress in tendons, except that the stress in Tendon V 204 was measured to be 44 percent below the predicted stress.
(Tendon V 204 was evaluated to be below th c required force level in the first year surveillance as well. )
The ori&inal testing techniques provided for increasing the tension in a tendon until one of a pair of shims.came loose.
The variations were in part due to the differences in thickness of the two shims.in a pair. The thinner shim would be relieved of load while the thicker shim still ca:!'"-
ried a portion of the tendon load. A description of the problems asss=?i-ated 'With this test method is contained in Appendix F of the report. ~
c.o Because or the apparent variations in tendon lift-off fore~
cnuscd by the measurement technique, an additional tendon surveillan~
effort \\-ms w1dcrtaken in the fo.11 of 1973*
This effort included dette:>*
'mining the li"ft-off forces of the jack when all shims in the stn.ck becwuc
. Mr. John F. ~'Leary,.ector Docket 50-255 License DPR 20 April 29, 1974 2
loose as well as verification of the lift-off measurements by deter-'
mining gage pressure versus tendon elongation..Consumers Power Comi)any feels lift-off forces measured by the "all shims loose" method indicate
- that the tension in the tendons varies less than 3.0 percent above or
. below the expected tension. This range of measurements is relatively "Small considering the tolerances in the measuring and calibrating devices (expected to be abo..it +/-~) and considering the judgment factor inherent in the testing method itself. Although it has been concluded that the contain.~ent prestress is at adequate levels, the methods used to date do
~ot pennit predicting trends, since their results do not tend to be re-peatable. It is our intention tp develop a measuring technique that will eliminate human error insofar as it is possible. The results of measure-ments 'Will hopefulJy pernj t extrapolation Of the. force-time curves in the futur~ when the tendon surveillances are made at five-year intervals.
~ecause of. the inability to determine a force-time trend line
~~~don the 9ne-year and.three-year surveillance tests already performed, the tendon surveillance program will be changed to include surv.eillance
~~sting in 1974 and.1976 before adopting a five-year interval. Testing techniques are being reviewed in an attempt to develop a techriique that giyes repeatable results with an acceptable degree of accuracy.
The attached report has been reviewed by the Safety and Audit
~eview Board.
Thei~ findings are also attached..
Yours very truly, Ralph B. *Sewell (Signed)
'RBS/pb Ralph B. Sewell Nuclear Licensing Administrator CC:
JGKe:ppler, USAEC r:.
-