ML17321A462
| ML17321A462 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 02/21/1985 |
| From: | Varga S Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17321A461 | List: |
| References | |
| NUDOCS 8502280524 | |
| Download: ML17321A462 (4) | |
Text
EVALUATION REPORT ON 0.
C.
COOK CONTAINMENT ULTIMATE CAPACITY OOCKET NOS. 50-315 and 50-316 The D. C. Cook containment ultimate capacity was initially evaluated by staff's consultant, Gunnar Harsted.
The evaluation was based on the code specified design strengths for concrete, reinforcing steel, liner steel and structural
- steel, and on simple hand calculation.
On the basis of this evaluation it was identified that the containment capacity is limited by the strength of the equipment hatch closure plate and equipment hatch door, and the limiting in-terna1 pressure is 23.5 psig.
An independent evaluation was made by Structural Mechanics Associates (StlA),
the D. C.
Cook licensee's consultant, and is contained in the two referenced
~
~
reports.
The SMA analyses were based on the "as bui lt" strengths as well as.the code specified values and more detailed computer analyses were employed.
The "as built" strengths consisted of the lowest sample value and the mean sample value of the materials.
Containment internal pressures corresponding to the code specified and "as built" values were calculated for different limiting sections of the containment.
In order to measure the anticipated degree of dispersion in the calculated results, a probabilistic de'scription
~ I of the ultimate internal pressure capacity of the containment was developed.
The evaluation identified four limiting modes of failure.
They are shear failure in base
- mat, membrane hoop tension failure of containment cylinder, bending failure of equipment hatch, and bending failure of personnel hatch.
~
~
The corresponding failure pressures are respectively 49.6, 61.2, 42.6, and 42.6 psig.
These pressures are based on the lowest as-built material properties.
These results confirm the finding of staff's consultant that 8502280524 850221 PDR ADOCK 05000315 P
0 P
equipment hatch limits the pressure capacity of D. C.
Cook containment.
- However, on the basis of the licensee's detai led.analysis the limiting pressure should be 32.3 psi rather than 23.5 psi, if the same code specified values are used.
This is to be expected, since the 23.5 psi limiting pressure is hand-calculated with simplifying assumptions while the 32.3 psi value is obtained'hrough finite element analysis.
The Sf% analysis also included the limiting pressures for the four failure modes computed on the basis of the mean va1ues of the as-built material properties.
In the probabilistic evaluation the concept of "fragility" is employed.
Fragility is defined as the cumulative frequency or probability that the capacity is less than a specified prcssure.
The curve giving the cumulative frequencies for different pressures is known as fragi lity curve.
In the evaluation the fragi lity curve and the uncertainty in that curve are ex-pressed in terms of the median ultimate pressure capacity and two random variables.
All uncertainty in the fragility curve is expressed through uncertainty in the median alone.
Through a series of assumptions, judgr;.ents and computations, SMA established that the median limiting pressure capacity of the containment is 57.8 psi.
It was further concluded by StN that (1)
The pressure capacity that is exceeded with 95 percent frequency considering on ly the inherent randomness about the median is 46 psi, and (2)
The pressure capacity that is exceeded with 95 percent frequency at 95 percent confid nce considering both the inhereht randomness about the median and the uncertainty in the median itself is 36.0 psi'.
On the basis of staff's review of the findings of the staff's consultant and the licensee's, we conclude that the ultimate capacity of D. C.
Cook containment should be taken as 36.0 psig.
The use of this seemingly conservative value is justified on the basis of the observation that only limited test data have been used in the licensee's evaluation.
REFERENCES 1.
"Evaluation of D. C. Cook Containment to.Determine Limiting Internal.
Uniform Pressure Capacity," Report No. 80C129-1 Dated b1arch 16, 1981.
2.
"Containment Internal Pressure
- Capacity, D. C.
Cook Nuclear. Generating Station - Phase II, Probabilistic evaluation," Report flo, 80C129-2 Dated April 6, 1981.