ML19319D953
| ML19319D953 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 02/27/1969 |
| From: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Davis E FLORIDA POWER CORP. |
| Shared Package | |
| ML19319D939 | List: |
| References | |
| NUDOCS 8003270629 | |
| Download: ML19319D953 (1) | |
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4 Docket No. 50-312 FEB f 7 569
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CPPa-5o Sacramerito Municipal Utilities District Post Of fice Box 15830 Sacramento, California 95813 Attention:
Mr. E. K. Davis Generel Counsel Gentlemen:
On December 15, 1968, you filed Supplement No. I to the Preliminary Safety Analysis Report for the Rancho Seco Nuclear Generating Station Unit No.1.
This supplement descrioed an increase in reactor building diameter, revised reactor building design criteria, new fuel handling method, and revised structural design bases.
.We and our consultants on structural design have completed our review of the contents of this supplement. We have also met with representatives of the Sacramento Municipal Utilities District to discuss ol e qb=a:!ons on its contents.
We conclude that the proposed changes described in Supplement No. I are acceptable under the following con 6f
- ions:
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1.
The load factors proposed for some cases for 01 ass I structures other than the containment are 1.0.
For destin conservatism under these conditiont, we recommended, and y)ur representatives concurred, that the concrete f actors in limit uesign be 0.75 rather than the proposed 0.90 and 0.85.
In areas whers multiple loads of high temperature and pressure are ap plied, such as the reactor supports, the value of 0.75 need not be used, though it i
should be used in all other areas.
2.
With the containmcat design approach, as revised, very close attention must be given to the limitations a td control of cracks in the concrete as well as to the bond and azichorage characteris:ics of the reinforcing steel in a cracked struct ure, such as would result f r'om this design. Anchoring bars wit.1 be avoided in zones where biaxial tension might exist. If unavcidable, we believe a bond stress 3/4 of design value, as suggested by your repra-sentative, to be acceptable.
l 3.
The locations of tendon anchor plates must be analyzed during
-detailed design to ensure that sufficient clearances and edge distances exist.
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A FEB 2 71953 Sacramento Municipal Utilites District 2
4 The results of developmental testing currently underway for the utilities, under Bechtel direction, will be reflected in the detailed design of this plant.
5.
Concrete shear under the liner anchors will be investigated for capacity and effect.
J 6.
Tendon bearing plates must conform at least to silicon killed, fine grain practice in A36 steel if used as listed.
7 Analyses should be submitted as they become available, for the tendon anchorage assemblies and the concrete tendon anchorage zones, as listed in Attachments A and C of this letter. We under-stand that the District (SMUD) is requesting these analyses from tendon anchorage assembly bidders. We will review the approaches, assumptions, and techniques when submitted, to determine whether they are adequate.
8.
It is not clear in the Supplemene whether sufficient compression through prestressing or sufficient reinforcing is available to handle the tangential shears resulting from earthquake loads.
The District has stated that extra prestressing will be available above the criteria levels set forth in Supplement No. 1.
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extra prestress, plus reinforcing ties are to provide sufficient crack restraint to centrol the tangential shears. As the infor-mation is developed, we will be provided information on allowable i
and ultimate shear st resses for t hese tangential ebears.
i 9.
Con cre te tension and flexure limits to be used in design will be completed and these values used will be provided for our review.
10.
The proposed 170-wire BBRV tendon system will be uniformly used for the hoop, the vertical, and the dome post-tensioning systems.
11.
It is stated on pag. 5.1-12 of the Supplement that "... deviations in allowable stresses for the desigr. loading conditions in the working stress method will ca permitted if factored load capacity criteria are fully satisfied...".
The nature of these deviations, for each case, will be recorded and submitted for our review.
12.
It is noted that suf ficient prestressing will be provided to elin.inate memb rane tensile stress under design loads. In this regard, we require the performance of those structural analyses to insure
-that af ter a long period of service, taking into account creep and i
shrinkage stresses and deformations, the structural behavior will be such as to meet the design criteria.
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- 13. Analyses should be submitted on the design of liner anchors as indicated in Attachment B as they become available.
Based on the foregoing, we consider the structural revisions to be accepftable.
Sincerely, (i..
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f, Division of Reactor Licensing Peter A. Morris, Director
Enclosures:
Attachments A, B, & C l
DISTRIBUTION:
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. Assistant Directors, DRL Branch Chiefs, DRL W. Butler ACRS - 18
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Sincerely yours, Peter A. Morris, Director Division of Reactor Licensing
Enclosures:
Attachments A, B, &,C
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Attachment A CRITERIA FOR 1ARGE SIZE PRESTRESSI C TENDONS The use of large size tendons (110 to 164 wires) in containment st ructures is similar to the use of 90 wire tendons. However, their use creates some additional problems.
The design must be based on soecific criteria and procedures to assure resolution of the main construction problems. This applicant will limit the design to ungrouted BBRV (buttonhead) parallel wire tendons and will develop a design in accordance with the following criteria:
1.
The tendons, the anchor blocks, and the sheathing will be defined as Class I elements.
Their design will be in accordance with the general design criteria for the containment structure and with the relevant pro-visions of the ACI and the Prestressed Concrete Institute Codes and Specifications.
2.
For the wire and tendons, analysis or experiments will be performed to assure:
conservative relaxation values; a.
b.
conservative friction f actors; realistic values for the efficiency as a function of curvature; c.
d.
that brittle fracture will not occur; and available wire redundancy per tendon.
e.
3 For the anchor block (i.e., bearing plateg washers, washer nuts, composite washers, split shims), the brittle fracture characteristics and the capability of the anchor blocks to develop the ultimate strength of the tendon will be established by either analysis or experiment.
4 A detailed stress analysis (including a determination of stress concen-tration) of the different elements of the anchor block assembly will be performed, and an evaluation will be made of the bearing stresses in the concrete immediately under the plate.
5.
The most unfavorable loads and load combinations will be considered.
Transient thermal gradients will be used in all cases where the use of steady state gradients underestimates the stresses and strains.
The design will cover not only.the accident condition, but also other cases such as:
start-up during very cold weather af ter protracted shutdown; and an accident occurring towards the end of the useful life of the structure.
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B 4 6.
It will be established by direct experimental methods on the structure, on full scale mockups, or by observation in similar structures, using the same tendons, with the same. curvature, that the v lue of the friction factor and the efficiency mentioned in item 2, above, are realistic.
7.
The following additional provisions will be adhered to:
a.
All materials for sheathing, bearing plates, split shims, washers, washer nuts, composite washers, and, in general, all material.s used in the anchor block assemblies will be defined by their ASTM specification numbers in addition to the AISI and SAE numbers.
Their brittle fracture and notch properties and their chemistry will be indicated; b.
Provisions made for corrosion protection will be indicated not only for the tendons, but for the buttonheads and for all elements of the anchor block assemblies, including threads; c.
The ef fect of welding (for instance:
trumpet to bea ring ninte) will be indicated; d.
The fabrication methods of different elements of the anchor block assembly, such as burning to shape, heat treating, quenching, tempering, hardening, saw cutting, etc., will be described in full; and Quality control methods and procedures will be described completely.
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A Attachment B CRITERIA FOR DESIGN OF LINER ANCHORS The design of the liner anchors will be in accordance with the following crite ria:
3 1.
The anchors, the welds attaching the liner plates to the anchors, and the concrete around the anchors, will be defined as Class I elements and will' be designed in accordance with the general design criteria for the containment.
Specifically, the allowable stresses in the welds' will not be higher than the allowable stresses in the connected materials and the local stresses in the concrete encasing the anchors will be such that massive failure of the anchor cannot occur-2.
The most unfavorable loads and load combinations will be considered.
Transient thermal gradients will be used in all cases where the use of steady state gradients underestimates the stresses and the. strains.
design will cover not only the accident candition,'but also other cases The such as:
start-up during very cold weather and after protracted shutdown; and, an accident occurring towards the end of the useful life of the structure.
3.
For the determination of the unbalanced load or the anchors, and the resultant stresses and strains, the following elements will be considered:
4 the case of a buckled panel adjacent to an unbuckled panel; a.
b.
the. unbalanced bending moment, and the axial force acting on the anchor;the tangential force, the radial force, variation of thickness of adjacent plates; c.
d.
variation of yield point of liner steel (in such cases where strains reach the yield point);
influence of Poisson's ratio, e.
in steel and concrete; for two-dimensional stress distributions f.
erection inaccuracies for plate's, anchors, and concrete (local bulges, l
of fsets at seams, wrong anchor locations, local anchor deformations, faulty anchor welding, etc.)
axial, radial, and tangential creep of concrete unoer prestrer,ing g.
load and its influence on plates and anchors; h.
axial, radial, and tangential shrinkage of concrete and ims influence on plates and anchors; 1
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cracking of concrete ;
- j. vacuum loads.or hydrostatic pressure on the back side of the liner; and-1 k.
elasticity of the anchors, All assumptions on anchor elasticity will be fully. documented.
If they are based on analytical con-siderations, conservative values will be used.
If they are based on experiment.a1 evidence, tests will be performed to reproduce the actual arrangement used in the containment structure, i
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Attachment C CRITERIA FOR DESIGN OF A'ICl!0 RACE ZONE OF FRESTRESSING TENDONS The design of concrete and robars in the anchorage zones of prestressing tendons must consider two main problems:
a.
Evaluation of bearing stresses under the enchor bearing plate; and b.
Determination of the transverse tensile forces (bursting forces) and the design of the corresponding reinforcing bars.
To provide an adequate margin of safety, the design of the anchorage zone shall be in accordance with the following criteria:
1.
The tendon anchorage zone will be defined as a Class I element as is the structure itself.
Its design will be accordance with the general design criteria for the containmant structure and wi the requirements of the current ACI Code.
2.
The following will be established on a conservative basis by analytical, and, or, experimental evidence:
a.
That there is no danger of delayed rupture of the concrete under sustained load, due to local overstress and micro-cracking; b.
That reinforcing bars located in the anchorage zone are adequate to carry the tension stresses existing in this zone, with a safety factor similar to the safety factors provided in the design of the containment structure in general, and that the cracking in this zone will be safely controlled; c.
That the possibility of concrete breaking along shear planes is excluded, 3.
The most unfavorable loads and load combin.tions will be considered.
Transient thermal gradients will be used in all cases where the use of steady state gradients underestimetes the stresses and strains.
The design will cover ndt only the accident condition alone, but als3 other cases such as: start-up during very cold weather and after protracted shut-down; and an accident. occurring towards the end of the useful life 'of the structure.
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The design analyses will decernine the three-dimensional stress distribution in the anchor.zenes in sufficient detail to permit the rational evaluation of stress concentrations and of ' maximum tension 4
and shear stresses. Standard design methods (Guyon, Leonhardt, Taylor, etc) will be modified to take care of three-dimensional stress distributions similar to the most unfavorable stress distribution existing in the actual structure. Three-dimensional creep and shrinkage of conrate will also be considered.
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