ML17263A679
| ML17263A679 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 05/27/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17263A678 | List: |
| References | |
| NUDOCS 9406070259 | |
| Download: ML17263A679 (4) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055&4001 Enclosure i SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION STRUCTURAL INTEGRITY OF THE CONCRETE CONTAINMENT
~0 ROCHESTER GAS AND ELECTRIC CORPORATION R.E.
GINNA NUCLEAR POWER PLANT DOCKET NO. 50-244
- 1. 0 INTRODUCTION The R.E. Ginna concrete containment is unique in that it is prestressed only in the axial direction of the cylinder with the lower ends of the prestressing tendons anchored in rock.
Reinforcing steel bars (rebar)
} ather than prestressing tendons are used in the hoop direction of the cylinder and in the dome.
The lower end of the cylinder is designed as a hinge, which is made up of laminated elastomer pads to permit rotation, radial tension bars to transfer the horizontal reaction to the foundation mat, and the prestressing tendons and the rock anchors for the vertical reaction.
For some time the hinge was submerged in water.
The NRC staff has been concerned about the potential damage done to the hinge, specifically the lower end anchorage of the tendons.
We requested that the licensee make radial displacement measurements of the containment near the hinge when performing pressure tests to assure that the integrity of these components, on which the structural integrity of the containment
- depends, is maintained.
During the first half of April 1993, the licensee performed an integrated leak rate test
(=ILRT) of the containment and used the opportunity to take radial displacement measurements as well as rebar strain gage measurements at locations away from the hinge.
The results of these measurements are contained in Technical Report No. 50016-7, dated May 17, 1993.
The licensee indicated in a letter dated November ll, 1993, that the measurements were made at approximately the same locations used during the preoperational
- test, and that the data collected during the 1993 ILRT were consistent with the data collected during the 1969 structural integrity test.
The licensee did not make any statement as to the results of these measurements.
Because the measurements were made at some distance from the hinge, these results cannot be used to represent the condition of the hinge.
This staff review attempts to interpret the results and evaluate their significance as far as the integrity of the containment is concerned.
9406070259 940527 PDR ADOCK 05000244 I,
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A careful examination of the design of the base reveals that the base, as
- designed, cannot be classified as either totally fixed or hinged.
The licensee realizes this condition and has performed an exhaustive analysis of the containment, taking into consideration a large number of combinations of
- boundary, loading, wall cracked and uncracked conditions to envelope the potential maximum stresses and deflections (Reference 5).
From the results of the analysis, the licensee concluded that the cylinder/ring beam is insensitive to the possible variations of structural boundary conditions.
In Reference 3, the licensee indicated its decision to monitor during the scheduled ILRT in 1993, the radial displacement of the containment at approximately the same locations monitored during the preoperational
- test, and not to make more extensive 'additional measurements which would not be cost effective.
The measurements performed demonstrated the integrity of the containment up to the tested pressure of 35 psi, but they cannot give any indication of the condition of the hinge.
Through its elastic
- behavior, the integrity of the containment may be extrapolated to its design pressure of 60 psi with some degree of uncertainty resulting from the lack of knowledge of the condition of the tendon and rock anchor near the base.
Since both the portion of the tendons near the base and their rock anchorages were submerged in water, there is a potential for corrosion of these elements vital to the structural integrity of the containment.
Unfortunately, they are not easily accessible for direct inspection.
It appears that the only realistic way to assure the integrity of the tendons, their anchorages and the containment is through tendon surveillance.
However, since the tendons are connected to the rock anchors, it becomes very difficult to determine which element is at fault in case any abnormality is detected in the tendon lift-off forces.
In view of this observation, it appears that the surveillance program as -used for tendons with both end anchors accessible for inspections as described in Regulatory Guide 1.35 may need some modification. Specifically, the relation between lift-offforces and elongation should be carefully monitored.
3.0 CONCLUSION
The staff has reviewed the radial measurements of the cylinder portion of the containment at various locations and strain measurements of various rebars.
Based on these measurements, we conclude that the containment behaves elastically up to the maximum ILRT pressure of 35 psi, which may be extrapolated to the design pressure of 60 psi with some degree of uncertainty resulting from the lack of knowledge of the condition at the base where the tendons and the rock anchors may be damaged by corrosion as a result of submergence in water.
It appears that the best way to assure the structural integrity of the containment is through a well-planned tendon surveillance program.
Principal Contributor:
C.P.
Tan Date:
Nay 27, 1994
Enclosure 2
RE ERENCES 1.
Letter dated November 11,
- 1993, from RG&E (Hecredy) to NRC (Johnson)
Subject:
Technical Report 500167-7.
.r 2.
Letter dated October 23,
- 1991, from NRC (Johnson) to RG8E (Hecredy)
Subject:
Ginna Containment Integrity - Request for Additional Information R.E.
Ginna Nuclear Power Plant.
(TAC No. H80494) 3.
Letter dated December 3,
- 1991, from RG&E (Hecredy) to NRC (Johnson)
Subject:
Ginna Containment Integrity Request for Additional Information.
4.
Letter dated July 11,
- 1991, from RG&E (Mecredy) to NRC (Johnson)
Subject:
Ginna Containment Integrity Request for Additional Information.
5.
Letter dated April 15,
- 1991, from RG&E (Mecredy) to NRC (Johnson)
Subject:
Additional Information of Structural Integrity.