ML19319D414
| ML19319D414 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 07/06/1976 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19319D412 | List: |
| References | |
| NUDOCS 8003170548 | |
| Download: ML19319D414 (6) | |
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f' STRUCTURAL ENGINEERING BRANCH COMMENTS ON CRYSTAL RIVER UNIT N0. 3 REACTOR BUILDING DOME DELAMINATION INTERIM REPORT GENERAL 1.
For easy reference, provide a list of tables and figures in the Table of Contents.
SECTION 1.2 1.
The staff considers the establishment of the causes of the dome de-lamination to be important in assessing the adequacy of the repair program and in providing assurance that armther. crack will not occur again during the l'ife of the structure.
The potential contributing factors should, therefore, be identified indicating the nagntiude of radial tensile stresses created in the concrete.
2.
The use of radial anchors will enhance the capability of the done to resist radial tension.
However, they will not eliminate tenr:en in concrete, and therefore small cracks may still exist.
Provuje an analysis to indicate that such cracks will not jeopardize che required structural integrity of the dome to resist all combinations of loadings for which it is designed.
SECTION 2.3 AND TABLE 2-2 1.
Clarify the definition of tensile capacity of concrete.
Explain how principal tension is related to shear and diagonal tension as indicated in Section 2.3.1, and.what is the difference between the snsar discussed
,in this section and that in the next section (2.3.2).
2.
Provide and describe with examples of actual design, the conditions under which each of the criteria (a) and (b) in Section 2.3.1 is applied.
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Since the stress / strain distribution is tri-axial, the limits of 6Vf may not be directly applicable to this problem 3 VfI and 6
and their use should be justified.
4.
If 0.8Sf6 as extreme compression in ultimate strength design is used, it may not be directly applicable for the same reason as in the above comment and should be justified.
5.
The shear strength of concrete is influenced by stresses orthogonal to the axis of the element; therefore, this effect should be considered.
SECTION 2.4 1.
In the paragraph in the middle of Page 2-4, you indicated that for structural integrity test and accident condition load ccmbinations, stresses for sustained loads cannot be combined with those due to rapidly applied loads interrally in the program and are combined externally.
Provide an example of actual design to shew how ti:e stresses are combined externally and illustrate the combination en a stress-strain diagram.
2.
On Page 2-5 under Item b; Creep, it is indicated that as a result cf concrete creep there is a reduction in concrete stress and an in-crease in liner stress.
Since the liner is relatively thin and may buckle under prestress, the liner should not be considered to con-tribute any_ strength to the containment vessel.
However,1r the design of the steel liner, strain due to creep of concrete should,be considered to check its leaktightness integrity.
Revise the concrete
. stresses in the report if they have been reduced.
- 3. ~ Provide the procedure which you used in the design of the steel liner.
In Table.2-2, you stated that no criteria on liner strains were used in the original design.
Indicate the criteria you used for the steel liner design.
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4.
Discuss in detail the effects of creep, including the following consideration :
Because of the different level of prestress in the wall in the vertical direction, the wall in the hoop direction, in the
' ring girder and in the dome the E' is different in all these directions and this effect should be considered in the analysis.
The wall acts as an orthotropic element.
The different parts of the structure have simultaneously different E' due to different specific creep.
5.
In Table 2-3 add load combination equation for repairs.
This equation should include the seismic load term.
SECTION 3.1 1.
Discuss the re. liability of direct tensile tests performed on ceras.
Since in the structure the radial tensile stress occurs siccitacacusly with two orthogonal compressions or with two orthogonal tensicas, a more thorough investigation is recuired.
1 Section 3.3 1.
In the list of factors which may have contributed to the delamination problem, add:
creep and stress concentrations (at tendons) inherent in this type of structure.
2.
In Section 3.3.2 it is indicated that by using SAP IV computer pro-gram and the model shown in Fig. 3-16, the effects of materiai properties on radial tension stresses are evaluated.
Identify in the model:
(1) the steel elements, such as reinforcing steel, and. tendon
- conduits, (2) the manner in which the prestressing force is applied. indi-cating if the prestressing force component tangent to thy dome curvature is considered.
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3.
Provide the hand calculation which you made to obtain the radial tension.
4.
In Section 3.3.4, transient thermal gradients may generate shear stresses, and should be considered in the analysis.
Similar effect exists for localized thermal gradients.
5.
The solution for stress concentrations as shown in Fig. 3-17 & 3-18 is incomplete.
It should be noted that compression exists also in the direction parallel to the conduit (d'1).
This stress generates additional stress concentration in the plane (d'25c) rth ') nal to 3
the tendon, which should be added to the stresses shown in Fig. 3-18.
6.
When the effect of tendon conduits is analyzed, it should be acted that this effect is different when evaluated in the direction parallel to the tendon and orthogonal to the tendon.
In the direction parallel to the tendon a 4" thick pipe (5"0) approximately replaces the removed concrete.
But in the direction perpendicular to the tencon, tne pipe introduces a flexible link which modifies the average propr ties of the concrete section.
SECTION 4.4 1.
In Sections 4.4.1 and 4.4.2 you indicated that in order to censider tne containment structure serviceable for the two loading conditions the shear capacity of the tendon conduit would have to be considered.
Such consideration may not be possible, unless the bond stress betwee1 the
. con u t and concrete can be justified to be adequate.
di SECTION 5.3 1.
In releasing the prestressing force as a result of tendon detensicning, strain recovery will occur.
However, most likely the strain recovery in concrete will be resisted by the steel reinforcing bars and steel liner, because of creep effects, and tension may result in the cencrete.
Provide an analysis to show that the resulting cracking in come concrete will not jeopardize the structural integrity of the dome particularly in the region of the liner anchors.
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The behavior of the detensioned dome is strongly influenced by tre 2.
creep of the prestressed structure which has taken place after pre-stressing and up to this date.
The detensioning of the dome will
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not return the structure to a previously unprestressed state, what-ever the sequence of operations.
It is therefore imperative to Present analyze the detensioned dome for the influence of creep.
such' an analysis and demonstrate that the integrity of the detensioned dome will not be impaired.
The analysis should include the ring girder and the top of the cylindrical wall.
Provide a 3.
The figures 5-11 to 5-14 do not include a study on shears.
detailed analysis of shear stresses in the detensioned dame and demon-strate that these shear stresses, acting simultaneously with normal stresses, do not endanger the stability of the de;ae.
Special attantion
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should be given to radial shears.
4.
Either justify in detail the use of 24" for the dome thickness in the present analysis, or present a parametric stuJy for diff ercmt thick-nesses; for instance 24"; 18"; 15".
5.
Demonstrate that the detensioned dome and the steel liner can tai.;
the load applied during the repair operations.
6.
Present a detailed discussion of the provision made to mor. iter the behavior of the dome, the ring girder, and the top part of :he cylin-drical wall during repair operations.
Indicate:
(a) the acceptance criteria for safety in such operations, and (b) the provisions made to safely stop the repair procedures it the acceptance criteria for safety are not met.
7.
Describe in detail the methods, acceptance criteria and mecnods of inspection for the grouting of the cap on the dome, the radial anchors to be installed and the grouting of these anchors.
Tresent the planned testing of these anchors.
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Provide a commitment that sufficient strain instrumentation will be i'nstalled at the top and bottom of the dome to assure that during retensioning of tendons the upper portion of the doma (above the crack) will be participating in developing compressive stress at the same rate as the lower portion.
4 9.
Indicate in more detail the planned method of water proofing of the repaired dome and its protection against detrimental environmental conditions.
10.
Describe the acceptance testing of the repaired dome and the inservice monitoring of the structure.
- 11.. Investigate the influence of possible cracking in the hoop direction j
on the dome tendon' conduits.
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