AECM-83-0732, Responds to Questions Raised During Special Safety Insp on 830322-25 Re IE Bulletin 80-11 That Three Mortar Cube Compression Tests Did Not Meet Min Compressive Strength Requirements.Structural Integrity Unimpaired

Responds to Questions Raised During Special Safety Insp on 830322-25 Re IE Bulletin 80-11 That Three Mortar Cube Compression Tests Did Not Meet Min Compressive Strength Requirements.Structural Integrity Unimpaired

ML20086U457
Person / Time
Site:	Grand Gulf
Issue date:	12/30/1983
From:	Dale L MISSISSIPPI POWER & LIGHT CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
AECM-83-0732, AECM-83-732, IEB-80-11, TAC-49996, NUDOCS 8403070268
Download: ML20086U457 (6)

Text

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E MISSISSIPPI POWER & LIGHT COMPANY

( Helping Build Mississippi P. O. B OX 164 0 J AC K S O N MIS SIS SIP PI 3 9 2 05 7 { *, 1 b December 30, 1983 NUCLE AR PRODUCTION DEP ARTMENT U. S. Nuclear Regulatory Commission Region II 101 Marietta St., N.W., Suite 2900 Atlanta, Georgia 30303 Attention: Mr. J. P. O'Reilly, Regional Administrator

SUBJECT:

Grand Gulf Nuclear Station Units 1 and 2 Docket Nos. 50-416 and 50-417 License No. NPF-13 File: 0260/0277/L-860.0 Ref: I&E Bulletin 80-11 CMU Walls - Evaluation of Low Mortar Strength Tests AECM-83/0732 This letter is provided in response to questions raised during a special safety inspection conducted on March 22-25, 1983, at Grand Gulf Nuclear Station Unit 1 (CGNS-1), by J. J. Lenahan of NRC, Of11ce of Inspection and Enforcement, Region II. Mr. Lenahan identified as unresolved item 416/83-12-02 that three mortar cube compression tests did not meet the minimum specified compressive strength requirements.

The results of an evaluation of the low cortar strength tests are provided as an attachment to this letter. The evaluation indicates that the structural integrity of the concrete masonry unit walls affected by the aforementioned tests is not impaired. Mississippi Power & Light Company considers that the evaluation presented in the attacheent adequately answers unresolved item 416/83-12-02.

Contact this office if further information is desired.

Yours truly, L. . Dale Ma ger of Nuclear Services MLC/JGC:rg Attachment cc: See next page 8403070268 831230 PDR ADOCK 05000416 PDR G \

Member Middle South Utilities System k , '

, AECM-83/0732 MlZ,'_'ISS:PPI POWER Q Ll2HT COMPANY cc: Mr. J. B. Richard (w/a)

Mr. R. B. McGehee (w/o)

Mr. T. B. Conner (w/o)

Mr. G. B. Taylor (w/o)

Mr. Richard C. DeYoung, Director (w/a)

Office of Inspection & Enforcement U. S. Nucleat Regulatory Commission Washington D. C. 20555 I

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Page 1 of 4 Attachment to AECM-83/0732 i

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REPORT ON THE i r 4 REEVALUATION OF CONCRETE MASONRY UNIT WALLS

, LOW MORTAR STRENGTH l

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GRAND GULF NI! CLEAR STATION OCTOBER, 1983 3

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P2ge 2 of 4 It7rRODUCTION In May 1980, the Nuclear Regulatory Ccmnission (NRC) issued I&E Bulletin 80-11,

" Masonry Wall Design," which prcrpted an extensive Concrete Masonry Unit (00) wall reevaluation effort by Mississippi Power and Light Ccmpany (MP&L) for the Grand Gulf Nuclear Station Unit 1. This effort consisted of multiple on-site as-built surveys, sanpling programs, and reanalyses; reports were prepared for review by the NBC, and questions raised by the NRC dealing with the submitted reports were addressed. Subsequently, site audits were performed by the NRC's Office of Inspection and Enforcement, Region II, Atlanta, Georgia.

During a site audit performed on March 22 - 25, 1983, by Mr. J. J. Ienahan of the NRC, unresolved item 416/83-12-02 was reported and documented in Inspection Reports 50-416/83-12 and 50-417/83-04. The unresolved item cited three mortar cube ccepression tests which did not meet the minimum 28-day ccupressive strength of 2500 psi for type "PL" nortar, as specified in the Grand Gulf specification. Mortar is classified as type "PL" and "M", "S" or "N" based on minimum average 28-day ccupressive strength of 2500 psi,1800 psi and 750 psi, respectively, according to AS'1M Specifications C-270-71 and C-476-71.

This report deals with the resolution of the OU wall low nortar strength issue, as identified in the aforementioned Inspection Reports.

DISCUSSION Samples of mortar and grout were periodically taken by Pittsburgh Testing Laboratory (PTL) to determine their cmpressive strenoths. Grout and nortar cube test reports were subnitted by PrL and are available at the Grand Gulf jobsite. Upon inspection of these reports, NBC identified three mortar cube ccnpression test reports that did not meet the specified minimum average 28-day cmpressive strength of 2500 psi.

For the periods during which the low strength mortar was placed (March 10 to March 25, 1977 and June 3 to August 1, 1977), a review of the available work time records indicates that the only CMU walls constructed in a safety-related building were in the control building at elevations 93'-0", 133'-0", 148'-0",

and. 166'-0". The only 0 0 walls erected on elevation 93'-0" were the south corridor walls in area 25A. These walls fall into the June 3 to August 1, 1977 period corresponding to the August 8, 1977 test report only. On the other floors, identification of which specific OU walls were erected within the 1%rch 10 to March 25, 1977 time period (corresponding to the April 13 and April 19, 1977 test reports) was not possible. Accordingly, at elevations 133'-0",

148'-0" and 166'-0", the existing OU walls having the highest masonry and reinforcement stress levels were identified. It was noted that these selected OU Walls had significantly higher stress levels than the remaining GU walls on each floor elevation. It was concluded, therefore, that if the structural integrity of these walls is not impaired with the lower mortar strength, then the other walls will also be structurally adequate.

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EVAIDATION 00 WALLS ON ELEVATION 93'-0" We average 28-day cmpressive strength of mortar on elevation 93'-0" is 2265 psi, based on results of the August 8, 1977 test report as shown in Table 1. The value of 2265 psi is between the compressive strength values of type "PL" (2500 psi) mortar and type "S" (1800 psi) mortar. If it is assumed that the strength characteristics are similar to type "S" mortar, then the masonry cm pressive strength value remains 1350 psi, as allowed by ACI 531-79, Table 4.3, and the original analysis of these walls is unchanged. %erefore, these walls are structurally adequate. In addition, they are not required to be seismically designed since they are not in the proximity of any safety-related equipment.

0 0 WALLS ON ELEVATION 133'-0", 148'-0", AND 166'-0"

, he 28-day average cmpressive strength of nortar placed at elevations 133'-0", 148'-0" and 166'-0" is 1343 psi and 1916 psi corresponding to the April 13, 1977 and April 19, 1977 test reports as shown in Table 1.

Therefore, for re-evaluation of OU walls on these elevations, the lower average cmpressive strength value of 1343 psi is used. According to A?IM Specification C-270-71 this tested strength falls between type "S" (1800 psi) and type "N" (750 psi) mortar. If the strength characteristics of the type "N" mortar are assumed, then the masonry cmpressive strength should j be 1000 psi, in accordance with ACI 531-79, Table 4.3. Reanalysis at elevations 133'-0",148'-0", and 166'-0" shows that the OU walls with this reduced value remain within allowable stress limits and are, therefore, structurally adequate.

RESULTS OF THE EVAIDATION The results of the evaluation indicate that the structural integrity of the 00 walls in the control building which are affected by the low mortar strength, as documented by the mortar cube compression tests of April 13, 1977, April 19, 1977, and August 8,1977, is not inpaired. Results of the reanalysis

show that the changes in stresses resulting frun the use of reduced mortar strength are not significant for the most highly stressed walls that were evaluated.

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Page 4 of 4 TABLE 1 MORTAR CUBE , AVERAGE

• COMPRESSION TEST 7 DAY COMPRESSIVE 28 I T COMPRESSIVE .28. DAY COMPRESSIVE REPORT DATE STRENGTH, PSI STRENGTH, PSI ~ STREiGTH, PSI April 13, 1977 880, 980, 1110 1300, 1480, 1250 1343 April 19, 1977 1140, 1180, 1150 2000, 1900, 1850 1916 August 8, 1977 880, 890, 80 2130, 3130, 2400 2265** ,

These average, values have been added for clarity. They were not included in the NRC Inspection Reports 50-416/83-12 and 50-417/83-04

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• • This average value disregards the unusually high test result of 3130 psi.

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