ML20083K889

Responds to NRC Re Violations Noted in IE Insp Repts 50-456/78-06 & 50-457/78-06.Corrective Actions:Upper Bound Limit on Ratio of Chloride Content to Cement Well Below ACI Limit

ML20083K889
Person / Time
Site:	Braidwood, 05000256
Issue date:	04/10/1984
From:	Swartz E COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20083K869	List: ML20083K889
References
8446N, NUDOCS 8404170065
Download: ML20083K889 (5)

Text

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, [D Comm:nwrith Edison

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) one First National Plaza. Chicago, lilinois O

'"1 Address Reply to. Post Office Box 767 G Chicago Ilknois 60690 ___

April 10, 1984 glPRINQlPAL gggSTAFFy,g g 0/RA DE F 4 l vs m ss RC '/ U A Mr. James G. Keppler ug ses Regional Administrator s a. :it U.S. Nuclear Regulatory Commission Region III

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799 Roosevelt Road Glen Ellyn, IL 60137

Subject:

Braidwood Station Units 1 and 2 Open Item Concerning Total Chloride Ion Content in Concrete NRC Docket Nos. 50-456 and 50-457 Reference (a): R. F. Heishman letter to Byron Lee, Jr.

dated August 7, 1978.

Dear Mr. Keppler:

Reference (a) contains an' unresolved item number 456/78-06-03; 457/78-06-03 concerning total chloride ion content in concrete at Braidwood Station. Specifically, the Region had concern with the impact of the additional chloride ion content contained in the aggregate and admixtures relative to the acceptability of total chloride ion content of the mixing water used for concrete production. Further, the Region had concerns with evidence of mineral and iron oxide deposits on the tendon tunnel walls. The purpose of this letter is to provide information which should allow for the Region's closure in this matter.

On February 17, 1983, Commonwealth Edison made an engineering presentation at the Region concerning these. topics. The Attachment to this letter documents our presentation and in our judgment, provides the technical basis for closing out the open item.

Please address any questions that you or your staff may have concerning this matter to this office.

Very truly yours, ,

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.8404170065 840412 . L.

PDR ADOCK 05000456 G. PDR E. Douglas Swartz Nuclear Licensing Administrator 1m Attachment cc: Region III Inspector - Braidwood 8446N- APR 11 W

P-Attachment 1 Braidwood Station Presentation to NRC Region III February 17, 1983 Chloride Content in Concrete and Evidence of Corrosion in Tendon Tunnels Chloride Content in Concrete ACI Committee 201 (" Guide to Durable Concrete" ACI-201.2R-77, American Concrete Institute, 1977) has recommended, and ACI-318 and ACI-301 have adopted, a lower bound limit on chloride content of 0.06% by weight of cement, for prestressed concrete. This value is based on the premise that the prestressing steel-is in direct contact with the concrete. The prestressing steel at Braidwood is contained in sheathing filled with grease for corrosion protection, and therefore, the 0.06% limit is not appli-cable. The ACI-201 limit for concrete exposed to chloride in service is 0.10%. However, based on current information, ACI-318-83 has adopted a 0.15% limit for concrete exposed to chloride in service. As stated in Section 4.5.4 of the commentary, "The more liberal limits were developed after consultation with ACI Committee 201 on durability and 222 on corrosion, and are con-sidered to represent the best information available at the time of adoption". The 0.15% limit on chlorides in concrete is most

. applicable to Braidwood. -  !

The 0.15% limit for concrete exposed to chlorides is conserva-tive since it is intended for the worst exposure normally expec-ted (bridge decks or seawater exposure) where the chloride ion ,

content may exceed 19,000 ppm. The actual chloride ion content of the groundwater at Braidwood is less than 350 ppm.

It should also be noted that the ACI limit is on water soluble chlorides. Due to the difficulty in determining the amount of chlorides which are water soluble, the total amount of chlorides l present are compared to these limits. Also, some of the chlor-ides which are initially water soluble are chemically combined with the hydrated cement, further reducing the chlorides avail-able to induce corrosion. 1 i

_ Sargent & Lundy performed an analysis of the total chlorides  !

in the concrete mix for the Containment using conservative values  !

and quantities for the constituent materials as follows: l l

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l Page 2 of 3

' '1 . .The concrete mix with the greatest water and cement contents ware used since these materials contribute the majority '

of the chloride ions.

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2. Chloride contents were less than 350 ppm during the time -

concrete was placed below grade level. (Only concrete below

, grade is exposed to chlorides in the groundwater.) The upperbound value of 350 ppm was used in the analysis.

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3. For admixtures, the maximum amount of chloride allowed by Specification F/L-2722, 1% by weight, was used whereas the actual amount determined by tests did not exceed 0.15%.

4. The chloride content of coarse and fine aggregate was not measurable (less than 1 ppm) and therefore, was taken as 0%.

As shown in Table 1, .the upper bound . limit on the ratio of chlor ,

ide content to cement is 0.027%. This is far below the ACI limit of 0.15% for reinforced concrete exposed to chlorides and evan well below the 0.06% limit'for prestressed concrete.

The limit of 500 ppm on chloride ion in the mixing water found in Specification F/L-2722 provides control on the largest contri-butor to the total chloride content in the concrete. The ASME 1977 edition provided for a limit of 250 ppm for water but had no limit on the total chloride content in the concrete. In the 1980 edition summer 1980 addenda, the limit on chloride content in water was deleted and replaced by a limit of 400 ppm on chlor-ide content in the cement paste. As shown in Table 1, the chlor-ide content, using the same ccnservative assumptions, is 184 ppm. The specification limit on chlorides in water of 500 ppm has limited total chlorides in concrete to acceptable levels.

Iron Oxide Deposits on Tendon Tunnel Walls Mr. Gallagher, after his inspection of the tendon tunnels, noted "the apparent effects of groundwater ~in the form of corrosion of the embedded steel (reinforcing) and by the presence of depo-sits of iron oxide on the walls of the tendon gallery", where groundwater was leaking through cracks in the walls.

On August 22, 1980, a Level III ASME/ACI . Nuclear Engineer Inspec-tor, examined areas in the tendon tunnel. Where the concrete was cracked and iron oxide deposits were present, concrete was removed for approximately 4 inches behind the interior face rein-forcing steel. Examination of these areas yielded no evidence

- of corrosion on the reinforcing steel. In addition, no discolor-ation of concrete was found at the exposed crack approximately 4 inches behind the reinforcing steel, thus-discounting the poten-tial for corrosion of reinforcing steel at the exterior' face-of the tendon tunnel.

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Furthermore, during the inspection, it was determined that a waterproofing system using metallic grout was used to repair cracks. The reddish-brown deposits occurred only at the repaired cracks with the rust confined to areas containing the metallic grout. To minimize future groundwater leakage into the tendon tunnels, these cracks have been repaired using a concrete water-proofing system acceptable for safety related work and which does not contain a metallic grout.

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TABLE 1

. CHLORIDE ION PER CUBIC YARD OF CONCRETE CONSTITUENT LB/CUYD CHLORIDE RATIO CHLORIDE LB/CUYD Water = 315 X 0.00035 = 0.1102 Cement = 680 X 0.00007 = 0.0476

• Admixtures = 2.58 X 0.01 = 0.0258 Total Paste =

997.58 LB/CUYD Total Chlorides = 0.1836 LB/CUYD Ratio of Total Chloride to cement = 0.1836/680 = 0.00027

= 270 ppm

= 0.027%

'N.

Ratio of Total Chloride to Paste = 0.1836/997.6 = 0.000184

= 184 ppm

= 0.018%

• Weight of Chlorides in Admixtures can be Calculated as:

(5+28) = 33 FL.OZ/CUYD Air Entrainment & Water Reducing Admixtures 33 Ounces /Cu.Yd. X 8.33 lbs. X.1.2 (specific gravity) 128 Ounces / gallon gallon

= 2.58 LB/CUYD

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