ML20011A535

Requests NRC Confirm Design Requirements for Util Containment Structures as Soon as Possible Because of Impact on Const

ML20011A535
Person / Time
Site:	Wolf Creek, Callaway, Sterling, 05000484
Issue date:	02/13/1978
From:	Petrick N STANDARDIZED NUCLEAR UNIT POWER PLANT SYSTEM
To:	Case E Office of Nuclear Reactor Regulation
Shared Package
ML20011A456	List: ML20011A535 ML20011A550
References
SLNRC-78-3, NUDOCS 8110130528
Download: ML20011A535 (9)

Text

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555' SNUPPS 5 Standardized Nudear Urst

• Power Pia S,ystem {

{~ e choke Cherry Road Nicholas A. Petncst ==

Roca viina, M.aryland 20850

. flav ass aoto Executive Director 5

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February 13, 1978 M EEE SLNRC: 78- 3 FILE: 0541 EE SUBJ: Concrete Cover Recuirements EE For Reinforcino Steel in E Reactor Containment g 5E M

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Mr. Edson G. Case, Acting Director E Office of Nuclear Reactor Regulation -

M U. S. Nuclear Regulatory Comission EE Washington, D. C. 20555 E

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References:

STNe50-482 5 STN 50-483 IEE STN 50-484 @

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STN 50-486 EE

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( Cear Mr. Case:

g Representatives of the Union Electric Company, SNUPPS Staff, Bechtel Power Corpora icn, and Daniel International Corporation met with the NRC Staff EE on January 23, 1978 in a meeting chaired by a representative of the Com- Ei mission's Division of Inspection and Er.forcemant. The meeting resolved a si number of issues associated with the design basis and design documents for Er <

the reactor containment for the SNUPPS plants as well as specific construc- EE tion activities for Callaway Unit #1. One issue associated with interpre- gg tation of the design bcsis and construction specifications has not been E+

resolved. The purpose of this letter is to present the position of the EE SNUPPS Ut'ility applicants and request prompt review and resolution of the 5" issue. "E E=-

i The NRC represe.ntative stated, at the meeting on January 23, 1978, that M the applicant (Union Electric Company) was required to maintain a minimum EE concrete cover of two (2) inches over reinforcing steel on the outer face .EE of tbe reactor containment, with no placement tolerance allowed on that E"-

minimum dimension. In addition, no placement tolerance was to be allowed gg on the maximum cover dimension. The construction activities for Callaway EE Uni !1 were to be in coformance with this requirement by the sixth lift gE of the containment exterior concrete. Preparation of the fourth lift was E~

underway at the time of the meeting. E 5

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, T,he SNU'P'PS Utility applicants object to this requirement on the basis that:

1) maintenance of a two (2) inch concrete cover without fabrication 5 and construction tolerinces is not required for technical reasons. -

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2) the current design conforms to commitments of the PSAR which pro- E vide that placing tolerances permit reduction of the specified E

' cover by one-third (Sec. 3.8.1.6.6.1). E E

The background fcr and technical justification for the SNUPPS design basis E is presented in Attachment 1, which demonstrates that the current c'esign M basis is adequate.

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In addition to the technical considerations presented in the attachment, -

E imposition of this requirement will necessitate revision of the reinforcing M steel detail drawings, thus forcing redesign of the containment. A major E advantage of the SNUPPS concept is that detailing errors and other prob- E lems associated with interferences and congestion are resolved during con- EE struction of the first unit. Revision of the design after partial construc- E tion of the containment for Callaway Unit #1 negates this advantage. EE E

Although the SiiUPPS applicants consider the PSAR commitments to be clear, g a clarification of the commitment is submitted as a PSAR revision in EE Attachment 2 to eliminate possible alternate interpretation of the design 5 g

,. requi rements .

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( The SNUPPS aoplicants request that the NRC confirm the design requirements E for the SNUPPS containment structure as soon as possible, because of the si impact on construction at the Callaway Unit !1 and Wolf Creek Generating E S ta ti on. The SNUPPS applicants are )repared to meet'with the NRC Staff on _

short notice to discuss or clarify tnis position. [5 5

Veryhruly yours, t M Y:

s -C hT \C h Nicholas A. Petrick 5 EFB/lc sf 9

Attachments E

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cc: w/ Enclosures (See Attached List) {.-

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SLNRC 78 3 [y[.=

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Attachment 1  :=_=

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. gg" Reinforcino Steel Cover Tolerances in Reactor Buildina .

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g99 A. Statement of the Problem & Backcround =

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As a result of a recent irsoection of the Callaway Unit #1 reactor gg" building, the NRC Division of Inspection & Enforcement has raised Egg a question regarding minimum and maximum concrete cover for Eg reinforcing steel on the outside face of the reactor building shell. p,_::

Egg The design criteria (BC-TOP-5) for the reactor building inc?udes '

igi both minimum and raximum cover requirements. This criteria has gg been met throughout the design and is shown on the design and ==

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placing drawings.  :=.

EE A review of the drawings shows that the rebar on the outside face of the reactor building shell is normally detailed to provide a two g@

gg (2) inch cover, which is consistent with the minimum design require- gg ment in BC-TOP-5. The maximum design cover for the reactor building gg walls is approximately 10 inches. In the design of the wall there EE are 1; cal areas adjacent to the two electrical penetration block-55 outs and the two purge line penetrations where, due to the geometry EE

/'" of the blockout, the rebar is locally two to ten inches from the jj l surface. A similar situation occurs' at the purge line penetrations, =-

N The clearances shown on the design and placing drawings meet the  ![

design requirements. As a normal construction practice however, E#

EE placing tolera.:ces are granted to field forces transverse to the wall section of t 1 1/2" (with the exception that the cover shall not EE be reduced by more than 1/3 of that specified). The incorporation hi of these field tolerances in the olacement of rebar may result in !B EE 5F the cover being 1 1/3 inches minimum and 11 1/2 inches rGalkv>n l

extreme conditions. The issue being rai;ed by the NRC is whether Mi l

placement tolerances can be imposed upon the minimum and maximum g[.r l design cover. E.

5" The requirements in the de.iign document are intended solely to be T the criteria necessary to prepare the design. Design requirements if do not exclude the possibility of providing reasonable tolerances g;

. to the field as an aid in construction. ,

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B. Licensino Commitment 1;-

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The introduction to Section 3.8.1 of the PSAR states, in part, that =

" . . . Topical Report BC-TOP-5. . . .provides the basis for design, con- r struction, testing, and surveillance ior the prestressed concrete '

i reactor bu lding". Conformation that BC-T0P-5 is the basis for i -

i design comes from the Callaway SER, Section 3.8.1, which says in .

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part "The containment will be designed"We in accordance have reviewed with the Topical E

l methods described in . . . .BC-TOP-5" . .

Repgrt... B?-TOP. 5 and found it acceptable. . ."

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E SLNRC 78- 3 l

1sttachment 1 {h Page 2

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The topical however, is limited to design aspects only. This was recognized by the NRC evaluation of the topical which accompanied E E

the letter of approval, stating that, "It (the topical report) is an at.ceptable reference for all subsections of Section 3.8.1 E except subsections 3.8.1.1, Descriotions and 3.8.1.6, Materials, E Ouality Control, and Soecial Construction Technioue". ACI 316-71, 5 E

along with other coces and :,tancarcs were referencec to cover those areas of fabrication and construction not included in the Topical'. E Specifically, as stated in SNUPPS PSAR Section 3.8.1.6, ACI 318-71 E is utilized in matters associated with the placing and splicing of E reinforcing steel (see subsection 3.8.1.6.2).

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Although ACI 318-71, subsection 7.3.2, establishes placing toler- E ances, minor exceptions have been taken to these tolerances in PSAR E subsection '.8.1.6.6.1, which further amplify the project intent to E specify placing tolerances. The concrete cover tolerances were E revised in Revision 11 as a result of design evolution. These E revisions are consistent with BC-TOP-5, project design drawings, and project specifications. [E

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C. History of Tooical Develcomert =

At the time the initial design work comenced and the licensing effort was under way for SNUPPS, no national code or standard E existed for reactor building containments. To fill this void a E topical report (BC-TOP-5), prepared by Bechtel Power Corporation, . jE was approved by the NRC for use on SNUPPS. The design criteria E in the topical utilized tne latest draft information of the joint E ACI-ASME Comittee. As previously indicated the topical report, g

as approved, included no infcmation in regard to construction. 5;'

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The ACI 318-71 code, with the exceptions noted in the PSAR, was l

i utilized as the appropriate standard for fabricV." and h cons truction. E f

Presently there is a national code (ASME Section III, Division 2) G which covers all matters associated with design and construction. L The issue - the application of field tolerances to design cover E requirements - is under discussion within the various subcommittees 2.

• responsible for the new code. These various subcomittees are l=

presently not in agreement as to the requ ements of the code. E E

The design working group had prepared a draft response to a quas-tion concerning minimum cover, which essentially acreed with the E position taken by HRC during the January 23 meeting. However, i

during a January 26, 1978 code committee meeting of the materials g subcomittee, a response consistent with the SNUPPS position was 5 l

• l taken. The result is that no formal action has occurred but efforts Although the =

are undoubtedly underway to resolve this question.

f final resolution of this issue will provide guidance for future plants it is not applicable to SNUPPS. g

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6. Technical Basis =

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l. Minimum Cover' E_E In reinforced concrete members the concrete cover for rein-  !$

forcing steel serves two specific purposes: (1) to protect Ei the steel from corrosion in an adverse environment; and (2) Ei to provide adequate bond for rebar development. 53 -

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a. Corrosion Protection ,

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To minimize the corrosion problem over a long period of 5's time it is necessary to control cracking throuch the E7 concrete cover. Crack control is within the scope of Ei ACI Committee 224. Reference 1 prepared by the Committee g.

- indicates: Eg EI "the cracking mechanism in two-way action slabs and plates si is controlled primarily by the steel stress level and the [;

scacing of tha reinforcement in the two perpendicular EE

<- directions and only to a small extent by the maanitude of g the concrete covar" (underlining adaed). EE

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E Further, according to Reference 1, crack width is prcpor- @

E tional to the state of tension stress. The reactor build-ing is prestressed so that the concrete is generally in f significant compression under normal operating conditions. (.-

The state of stress therefore ensures c.losure of any h hairline cracks that developed prior to prestressing or T daring transient load conditions, and renders crack prop- -

acation throuch the concreta imoossible. In the absence E I

of any significant crack opening, moisture migration will -

be impossible and corrosion i; not a problem during the operating life of the reactor building.

b. Bond Development .

. The second consideration in regard to determining minimum -

concrete cover is to assure reinforcing steel near the surface has sufficient cover so that failure will not occur due to insufficient bond caused by a cor. crete failure -

between the bee and t'e concrete surface.

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- The foremost c:scussion on this subject is presented in Reference 2. Using the empirical expressions formulated f rom that work, together with the absolute minimum cover f (including placement tolerances) and appropriate rebar spacing, the development lengths provided in the shell are acceptable.

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2. Maximum Cover _ g.

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as discussed above it is only at very local areas (and then E only when the . field tolerances are utilized inwardly) that EE the requirements specified in the design document for maximum L}

cover will be exceeded. g

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- The purpose of the crack control provisions in the topical is Ef primarily intended to be applicable for the main body of the E shell "to control ceneral face cracking" (emphasis added). E Over local areas however, a strict adherence to the placing '

E provision is neither intended nor technically required. None EE of the areas affected by increased reinforcing cover are E exposed to outside environmental conditions. Rather, the Ei exterior wall of the reactor building shell in these areas E is enclosed within the environment of the auxiliary building. E E

Although the crack control criterion of Reference 1 is not a E requirement for the reactor building shell, it is satisfied. E Using the analytical methods included in that report for the E E;

local areas under question and considering the case where field tolerances increase the cover bayend that indicated s

.- ' in the topical, crack width is again of no consequence. g

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' Considering the fact that the building is prestressed it is E inconceivable that the structural integrity of the contain- E-ment shell will be compromised in any way where the maximum g~i cover design limits are exceeded in these local areas. 5 E

E. Suma ry .

Based on the above discussion and the intent of the PSAR, the rebar cover and field placing tolerances as they presently exist in the g project drawings and specifications for the SNUPPS Units satisfy all necessary design conditions.

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References E:

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4. Control of Cracking in Concrete Structures - ACI Comittee 224 Report, ACI Journal, Dece:ter,1972. 5 EEE 2.

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"A Reevaluation of Test Data on Developreent Length and Splices" by iii.i

. O. C. Orangun, J. O. Jirsa and J. E. Brown, ACI Journal, March,1977. g 4

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• • SLNRC 78-3 Attachment 2 SNUPPS M.

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industry codes such as AS.'C B&PV Code for nuclear piping, I

T SI B31.1 for nonnuclear power piping, and the applicable [=-

' state or local plumbing codes. Where no such codes cr 10 f:

. code cases govern a particular pipe embedded in structural g concrete, the requirements of ACI 318-71, Paragraph 6.3.2.4 -

g will be implemented. iiE In place of Paragraph 7.3.2, Tolerances, the following Er requirements shall apply: fi

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1. Placement of reinforcing steel: E E*

The reinforcing steel shall be placed within the E

following tolerances, but the cover shall not be E~

reduced by more rhan ona-icird of the minimum specified .

lE .2 design cover: =

E Tolerance (in.) E

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Base C ab tl-1/2, -1/2 g" E

Exterior walls and dome s No. 14 and No. 18 bars tl-1/2 11 EE All other bars 1 E E

Cadwelds and other connectors shall not be censidered E

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( Variation in spacing shall be 2 bar diameters $

except where these requirements would violate ACI Es 318-71, Sections 't.4.1 and 7.4.5, in which case the $

requirements of Sections 7.4.1 and 7.4.5 will govern. E

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