ML19319D250
| ML19319D250 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 04/20/1977 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19319D247 | List: |
| References | |
| NUDOCS 8003130876 | |
| Download: ML19319D250 (3) | |
Text
-
4 ENCLOSURE 2 O
COMMENTS AND POSITION ON CRYSTAL RIVER UNIT NO. 3 CONTAINMENT DOME SURVEILLANCE STRUCTURAL ENGINEERING BRANCH I.
GENERAL COMMENT
AND POSITION Regulatory Guide requirements are for structures which have not exhibited any structural defect due to design and/or construction deficiencies.
For those which do exhibit such defect, the staff had to impose additional requirements for structural integrity test and inservice surveillance.
This is because Regulatory Guide requirements are not designed to uncover all kinds of defects, and prudence and good engineering practice demand requirenents in addition to 'those of the Regulatory Guides in order to assure that the integrity of the structure which did exhibit iefects and is repaired is maintained throughout its life.
This is particularly required in the case of the Crystal River Unit No. 3 containment structure, the dome of which experienced delamination and was repaired.
The cap of the dome thus repaired is quite different frca the original design.
Originally it was prestressed.
After the reapir the cap is only partially prestressed and is basically reinforced concrete.
There is no experience with the behavior of such a hybrid structure.
The need of monitoring of its behavior during the life span of the plant is obvious.
The three items of inspection as indicated on j
the first page of the referenced letter for the surveillance program do not include any inspection of the dome, which the staff finds to be insufficient under the circumstance.
The arguments against any inservice inspection of the dome as given 8003130f
. on Page 2 of the referer-ad letter are at best tenuous, and the following are the staff's comments en the arguments.
II.
COMMENTS ON ARGUMENTS AGAINST ADDITIONAL INSERVICE INSPECTION
}
1.
In order to keep the stresses and strain the dome within the design limits and to maintain acceptable containment integrity it is essential that interaction between the "new" cap and the lower structure exists so that the dome behaves as an integral structure.
This is because the dome is designed to resist not only prestress and pressure loads but also dead, thermal, seismic' and other loads.
There is bending in.the dome at point of discontinuity or as a whole due to loading characteristics.
In order to resist bending interaction between the two is required, even if the radial tension is relatively small.
This interaction depends primarily on the bond between the new and old concrete.
The radial reinforcement as designed plays only a secondary role.
2.
The hoop and meridional reinforcement in the new cap will function most effectively cnly if interaction between the "ned' cap and old structure exists, otherwise the contri-bution of this reinforcement to the strength of the dome will be in doubt.
3.
When the. plant is shut-down and outside temperature is higher than that inside, tensile radial stresses is introduced in the dome.
This will give rise to the possibility of de-lamination.
4.
The decrease of prestress forces in the old structure will introduce tension in the "new" cap wherein cracking may result.
5.
The purpose of SIT is to confirm that the design and the configuration of the _ containment are adequate to withstand the pressure loading as indicated by design analysis.
If i
l
~ _.
~*
' there is good correlation between the measured and predicted values for the pressure loading, one can surriise with reasonable assurance that the design of the containment for other loadings should be adequate.
Therefore the capability of the containment structure to withstand all design load combinations is not demonstrated directly through SIT, since SIT consists of only pressure loading.
Furthermore as indicated in the general comment SIT has its limitations.
I P