ML20084D789
| ML20084D789 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 04/10/1984 |
| From: | Swartz E COMMONWEALTH EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| Shared Package | |
| ML20084D735 | List: |
| References | |
| 8446N, NUDOCS 8405010477 | |
| Download: ML20084D789 (5) | |
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t April 10, 1984 Mr. James C. Keppler Regional Adninistrator U.S. Nucleer Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, IL 60137
Subject:
Oraidwood Station Units 1 and 2 Open. Iten Concerning Total Chloride Ion Content in Concrete NRC Decket Nos. 5C-456 and 50-457 Refere'nce (a):
R. F. Heishman letter to Byron Lee, Jr.
cated August 7 1978.
Dear Mr. Keppler:
./ d Reference (a) contains an unresolved item number 456/78-06-03; 457/78-06-03 concerning total chloride ion content in concrete at Braidwooc Station.
Specifically, the ReDion 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 ceide deposits on the. tendon tunnel walls.
The purpose of this letter 1s-to provide infernation which should allow for the Region's closure in this natter. -
On February 17, 1983, Commonwealth Edison made an engineering presentation at'the Region concerning these topics.
The Attachment to i
this letter occur.ents our cre4entation and in our judgment, provides the tecnnical oesis for closing out the open iten.
Please eddress any questions that you or your staff may have-concerning this natter to this office.
Very truly yours, f,.<*
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E. Douclas Swartz Nuclear Licensing Adninistrator l
Im 8405o10477 840427
{DRADOCK05000 g Attachr.ent cc Region III Inspector - Braidwood 1
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Braidwood Station Presenta'tiDn to'NRC Eeilen III February"17, 1983 Chloride Content in Con $ rete and Evidence of Corrosion in _ Tendon Tunnels Chloride Content in Concrete ACI Committee 201
(" Guide to Durable Concrete' ACI-201.2R-77, American Concrere Institute,1977) has recommended, and ACI-312 and AC:-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 prestressine 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%.
Mcuever, based on current inforMation, ACI- /
318-83 has adopted g 0.15% limit for concrete exposed to chicride in service.
As stated in Section '4.5.4 of the commentary, "The core liberal limits were developed after consultation with ACI Committee 201 on durability and 222 on corrosion, and are con-sidered to rep. resent the best information available at the time of adoption".
The 0.15% limit on chlorides in concrete is most applicable to Braidwood.
The 0.154 limit for concrete expcsed to chicrides is conserva-tive since it is intended for the worst exposure normally expec-ted (bridge decks or seawater expcaure) where the chloride ion content may exceed 19,000 ppm.
The actual chloride ion, content of the groundwater at Brelduced is less than 250 ppm.
It should also be noted that the ACI limit is on water soluble chlorides.
Due to the dif ficulty in determining the amount of chierides which are water soluble,'the total amount of chlorides precent are compared to these limits.
Also, some of the chlor-idea whien are initially water soluble are chemically combined with the hydrated cement, further reducing the chlorides avail-able to induce corrosion.
satgent & Lundy performed an analysis of the total chlorides in the concrete mix for the Containment using conservative valuca and quantities for the constituent materials as follows:
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The concrete mix with the greatest water and cement contents were 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
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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.
3.
For admixtures, the maximum amount of chloride allowed by Specification F/L-2722, 14 by weight, was used whereas the actual amount determined by tests did not exceed 0.154.
4.
' The chloride content of coarse and fine aggregate was not censutable (less than 1 ppm) and therefore, was taken as 04.
As shown in Table 1, the upper bound. limit on the ratio of, chlor.
ide content to cement is 0.0274.
This is far below the ACI limit of 0.154 for reinforced concrete erposed to chlorides and even well below the 0.064 limit *for prestressed concrete.
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The' limit of 500 ppm on chloride ion in the mixing, water found e 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 1960 edition suT.er 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 conservative assumptions,- is 184 ppm.
The specification limit en chlorides in water of 500 ppm has limited total chlorides in concrete to acceptable levels.
Iron Oxide Deposits on Tendon Tunnel Wells s
Mr. Gallagher, after his inspection of the tendon tunnels, ncted "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 thrcugh 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 appcoximately 4 inches behind the interior face rein-forcing steel.
Examination of these areas yi'elded 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 ste'el, thus discounting the poten-tial for corrosion of reinforcing steel at the exterior face of the tendon tunnel.
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,l D F 3 Furthermore, during the inspection, it was determined that a waterproofing system using metalMc grout was used.to repair cracks.
The reddish-brown deposits occurred.c'nly 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-proof ~ing system acceptable for saf ety related work and which does not contain a metallio grout.
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TABLE 1
. CHLORIDE ION _PER CIIBIC YARD OF COMCRETE CONSTITUENT LB/CUYD CHLORIDE RATIO CHLORIDE LB/CUYD 0.1102 Water
,=
315 X
0.00035
=
0.0476 680 X
0.00007
=
=
Ce nent 0.0258
=
=
2.58 X
0.01
- Ad:nixture s.
Total Chlorides = 0.183G LB/CUYr 997.58 LB/CUYD Total Paste
=
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0.00027 0,1836/680
=
Ratio cf Total chloride to Cenent =
270 ppm
=
0.0274
=
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0.1936/097.6
0.000184 y.atio of Total Chloride to Paste 184 ppm
=
=
0.0184 4
- Weight of Cr.lorides in Admixtures can be Calculated as t
= 33 FL.0Z/CUYD Air Entrainment & Water Reducing A:1miv ures (5+28) lbs. _ X 12 (specific gravity) 33 Ounces /Co.Yd.' X B.33 128 Ounces / gallon gallon
= 2.58 LB/CtND e
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