ML19274E704

Forwards Info Requested at 790315 Meeting Re Program to Investigate Reactor Bldg Base Mat Concrete & Jj Shidelers Responses to Questions Re 790227 Rept

ML19274E704
Person / Time
Site:	Wolf Creek
Issue date:	04/11/1979
From:	Koester G KANSAS GAS & ELECTRIC CO.
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
NUDOCS 7904170197
Download: ML19274E704 (25)

Text

{{#Wiki_filter:., o KANSAS GAS Ah3 ELECTRIC COMPANY THE ELS CTR*C COMPnntY .,....n. s April 11, 1979 Mr. Karl V. Seyfrit . Director, ingion IV Office of In:;pection r. I:nforcement U.S. !iuclear Pequlatory Conni! sion Gil Ryan Plaza Drive, ':uite 1000 rirlington, Texa:. 76012 He Dochet 'o. STil 50-482 Subi: Wolf Creek Reactor Building ILwe Mat

Dear Mr. Sey[rit:

Attached in the additional information rectuented during our reeting with you and membern of your ntaf f at Arlington on March IS, 1979 The requented information in contained in th.' attachod two documentt Program To Investigate Reactor Buil ding Ban < tfa t Concre te, and Mr. Sh i d e l er ' <, renponses to <1ue n t ions regarding the February 27, 1979 PCA Report. Pleane advise if you have any quostionn regarding thene documents. Yours very truly, / / l c [L,L A ff Y Glenn I, Koenter Vice President-Operations GiK:l'b Attach cc: "r. Poqe r ti. Boyd, Director Division o f Pro ject Managiment Office of *1uclear 1:ract or Hequlat ion

11. ', !Juclear Requlatory C<,mmirnion Washington, D.C.

20555 Att ach 7901170 /7'/ k 201 tL Afarket - Woch!!3, Kansas - Mad AJdwsv P. 0 Box 208 / Wrchita. Kansas C7201 - Telephone: Area Code (316) 2C&lill

I PROGRAM TO INVESTIGATE PEACTOR DUILDING BASE MAT CONCRCTE Backcround: On March 13, 1978, the 90-day compressive strength tests for the reactor building base mat concrete were made. The strength data obtained indicated the concrete had a strength less than the 5000 psi design strength. The Program: r The reviews, analyses and additional tests which were needed to investigate the concrete strength were not immediately apparent. The actions which were carried out evolved over a period of time. Numerous meetings were held with our Contractor, A/C, Concrete Consultant, etc., to decide on specific actions. The program has been developed to find answers to the following questions: 4 (1) Were the original test results accurate? (2) If accurate, what caused the low strength? (3) I f accura te, is the strength adequate to withstand all design loads? (4) I f not accurate, what is the true in-situ strength? (5) If not accurate, what caused the inaccurate test results? r (1) Accuracy of Original 90-Day Test: Because the determination of compressive strength involves i destructively testing samples, it is impossible to repeat th a original test. Acceptance criteria for the concrete in que, tion is set out in ACI Standard 318, paragraph 4.3.3, which is 1ased on cylinder strengths. Because no additional cylinders were available, other methods had to be used to evaluate the accuracy of the original tests Guidance in ACI-318 suggests taking cores from concrete which failed. This method was not selected for the following reasons (1) The exact location of " failed" concrete could not be determined; (2) Only a limited amount of the total volume of concrete was accessible for coring; (3) The tremendous amounts of reinforcing steel in the placement would make it almost impossible to obtain cores without cutting some reinforcing steel and thus reducing the strength of the base mat. The Windsor probe method was selected as one method of checking strength. This method was used for the following reasons: (1) The testing in performed on the actual in-situ concrete; (2) The method

Prooram to Investigate Peactor Buildino Base ftat Concrete 2. r has negligible affect on the concrete being tested in that only minor surface damage results; ( 3) The method has demonstrated accuracy, especially when correlation with known strength concrete in made. The Windsor probe method does have the disadvantage of measuring only concrete strength at and near the surface. To partially evercome this difficulty, numerous tests were made around the periphery of the mat so as to maximize the possibility of testing any low strength areas which might be present. Petrographic / chemical (P/C) analysis was selected for the following reasons: (1) These t ests have proven ability to identify many of the causes of low strength; (2) P/C analysin can be made on the same concrete (cylinder fragments) which indicated low strength. P/C analysis has the disadvantage of not directl'/ measuring concrete strength. P/C analysis does, however, measure / identify the factors which directly relate to strength and can identify concreten with substantially dif fcrent strengths. To supplement the P/C analysis 2" cuben were cut from cylinder fragments and destructively tested to determine compressive trength. This test has the advantage of directly neasuring the strength of the concrete which was previously tested as a 6"x12" cylinder. 2" cuben were selected instead of another size and nhape because 2" cubes could be obtained from many of the cylinder remnants Using a larger size or dif ferent shape of test sample would have greatly reduced the number of available test samples and thus limited test data. The strength as measured by 2" cubes does not produce the sane values as 6"x12" cylinders. Previous investigators have at rived at dif ferent values with.8 appearing to be the appropriate factor to apply to 2" cube strength to relate it to 6"x12 cylinder strength. A portion of the on-going test i program is devoted to providing ecpirical data to better determine I the correction factor for the base mat concrete. Plots of the strength e'.ata and sufistical analysis were performed to determine if the data was consinter.' and followed expected distribution. (2) Caune of Low Strenoth Concrete: All of the normal causes of low strength concrete were investigated as part of the program. This included a check on the quantities and quality of materials used in the base mat. s

E l'rouram t o Invest iqat e heactor building I,ase ?1.10 Concreto 3. s ( 1) A.b. _i_l i_t y t o Wi t hn t aml Des ion I.oadn s i Tho A/l: wan direct.ed to perform an analynin to determine if the e f:Nul% onvelopo dm;ign loads, includim; a.2q ea r t. hquake loadinq fo r the nafo shut down eart hquake and a.120 loading for the operatimi banin earthquake, can be supported with a connervative concrete st rengt h of 4460 pni. t (4) A.c. t ua l I n-n i t.u. S t t.rnq t h : Tho Windsor probe t e ; t.i nq iind the te:;t.ing of 2" cuben cut from the oriqinal cylinder fraqmonts were cartled out to determine f actual strenqth valuon. Because the Windnor probe data only relate, to ' ur face concrete, while t. h e ?" cubos relate directly to the concrete n an.p l e s which t.ented low at 90 clays, the 2" cuben are ju<! qed to be the be r; t al t ernate met had of measuring s t.reng t h. I t. won recoquimd that more accurat e det erminat ion of the conversion i factor from 2" cubes to 6"xl?" cylindern was donirable When thin part of the program i n compl e t eil, the st rengt h values of -iny of the oriqinal 6"x12" 90-day cylindern will be er; ta bl i s hed, and t he r;o strengths can be corpared to the ACI-318 acceptance criteria. (5) Pau,o(n) of I naccu ra t e Test Pesults The progran included a review of the tentinq process from the time the cylindors wete molded until they were destructively tested in the compre:,q ion tratinq machine. Act.ivities unch an moulding, storinq (durinq fi rn t 24 hourn), curing, capinq and testing were reviewed. q)nc_1onionn and gummary of Pesul t ? To Date-(1) The program ha' ':hown that the renults of the original 90-day toutn are inaccurate. The concrete in uniform in quality and in utronger than t.he original 90-day tents indicated. (2) The prooram han failed to identify any i. c t. in materialn, batching or mixinq that would produce low-ntrenath concrete. i ( 3) A na l y';i r by the A/I: r e <q.o nn i b l e for the bane mat denign shown i t ha t: even it a conservative concrete atrength of 4460 uni in an ;umod, all deaign loadr can be carried by the Wol f Creek roac t o r base ru t, includinq the SNUPpS envelope ceinmic loads o f. 2q(SSE) and.12q (OBI:). l A

.? Program to investigate Reactor Buildiner Base Mat Concrete 4. (4) The most accurate method of establishing in-situ strength by an alternate means for the reactor base mat appears to be destructively testing 2" cubes cut from cylinder fragments. All cubes from 90-day remnants tested to date have strengths al>ove 5000 psi when reduced by a correction factor of .8. This dita, if compared to ACI-318 acceptance criteria for 5000 psi concret e, will yield no " failures". Iloweve r, the program to more accurately determine a correction factor is still in process and final strength determinations should be made after a conversion factor derived from e.mpirical data is available. (5) tb single cause for the testing error has been fo und. It appears several factors may have combined to produce the erroneous results. Founded cylinder ends, capping comnound strength, and testing machine factors, while all individually withir. specification tolerances, may have combined effects which are sianificant. The testing machine is suspected of being a major factor. A new high-quality machine of greater capacity will replace the existing m.' chine and thus clininate or reduce machine-induced errors. f I p i b i

(hh8 h( hg 5420 OU Orchard Road, Skokse, Illinois 60077

• Area Code 312/966-6200 Rachac[etqas 0@b@GG3@2MO r.a

. ri.,.- c. r., ec muno a.n,a azocaron April 10, 1979 Mr. Glenn L. Koester Vice President - Operations Kansas Gas and Electric Company Wi ch ita, Kansas 67201 EE: Wolf Creek Generating Station Reaccor Basemat Concrete Second Testing Program

Dear Mr. Koester:

Attached are my responses to the several questions posed in your letter of March 26, 1979. If any of them need further clar if ication please call. Also attached are individual strengths of C-109 cubes for cement samples C-UT 15, 16, 17, 18, 20, and 21 as requested by NRC. Sincerely, ) ( J./J. Shideler, Director Administrative and Technical Services JJS/md i CT-0407 RECEIVED on ra, C >y to-hl WuW 3 W. F. K un z e $ gs; 11 1979 ? E. .fognestad I __^%"iF*iI T. I _---. -.. y. j --- -~ l HL,_ f..'N . v_ s c a_ .. L .~ __. &.5. %.'.s.: __ _O '_'g._[ ~ .-_ u m ..t = 9-- - y m,-- 91E 3

_lU;SPO!JSES TO QUESTIO!;S I!I MIt!UTES FOR MI:ETItJG WITil liRC, MA RCl! 15, 1979 [Jues t ion : What is the significance of the ratio of coarse to fine aggreoate as detemined by petrographic analysis. Renponne. The petroqraphic report stated " coarse-to-fine aggregate ratio is approximately 55/45 to 50/50." Such an estinate is made by visual inspection of polished surfaces, includinq inspection with a stereo-microscope, to estimate paste content. TV ; close agreenent to specified ratio of 50/50 is considered to be very good. As Mr. Waugh stated, the most reliable determination of this ratio in the batch tickets. $2ues tion : Can original photographs be furnished. Rosponse Photographs of all remnants received at PCA are attached. Qtestion: What e f fects can capping comnound have on cylinder strength. Responce-It is known that " soft" caps contribute to low strength of cylinders, low strenqth of sulfur - fire-clay caps may be due to temperatures above and below the recommended 280 to 300 F and its contamination by oil in reused capping material, see attached Data Sheet " Atlas Vitrobond Capping Compound. " Question: Were cubes tested on their sides. If so, which. If not, how was this determined. Response: Cubes were tested in the direction of the longitudinal axis of the cylinder. The petrographic reoort (Appendix A) states that the tops

, and bottoms of the cuben were lapped to annure snooth surfaces. After the first longitudinal slice was cut from the cylinder remnant, the area from which the cuben were to be cut was marked with an arrow indicating the axial direction. Question: Were the cubes which were tented, previously an well as recently, noaked for at least 40 hoarn and tested wat. Fesponne-All cuber were se ed at least 48 hours prior to testing, and were covered with a wr towel until placed in the ten t inc; machine. Question: What teuts nhow that the smaller ratio of minimum dimensions to naxinun size aqqregate will produce lower strengths. Iesponne: My statement " Tent namples with a smaller ratio than 3 to 4 of minimum dimensions to naximum size aggreqate will produce lower compressive strength" cannot be completely substant.iated by known tent data. It should be nodified to read, "...agarenate may (or may not be expected to) produce lower compressive strength." Such a statement is inferred by the fact that many standards require a ratio of 3 to 4 for specimen diameter to maximum size aggregate. According to one author (Reference 2, p. 33) cores of 2 and 4-in. diameter drilled from concrete with 3/4-in. aggregate yielded about the name mean strengths, but more variable results were obtained with the smaller core:,. Also "Another investigation involved the testino of coren of 35, 50, 70 and 100-mm diameter with mixen having maximum aqqregate sizen of 4, 8, and 16-mm. It was found that it was difficult to obtain reliable resultn from the cores of 35-mm diameter" (Ibid). I

. puestion: Does field performance of concrete rmde with sand gravels such as those from the Kaw River correlate well with cement alkali content to support the ASTM C-342 mortar bar tests. Fesponse: One nonnible cause of strength retroaression is the alkali-agoregate reaction. Obviously, NRC personnel are aware of the co nplexity of the Kansas-ilebraska " sand-gravel" aggregate cement reaction, and are aware of the work by Conrow, Scholer, Gibson, Lerch, Hadley, et al. The work b'/ Scholer, Gibson, and Smith seemed to indicate such a relationship, but the McPherson Testroad tests uave some contradictory results. If adley found that "The sand-gravel from the rivers along which concrete distress was prevalent were found to be alkali-reactive in the mortar bar test (ASTM C227), while samples from other streams investicated were nonreactive." The general alkali-aggregate reaction in the Kansas area seems to be triggered, or at least aggravated, by an extreme temperature and moisture-drying cycle. These conditions do not pertain either to the basemat or to the control cylinder under consiocration. Limestone "r.weetening" has been found to be consistently ef fective in inhibiting this reaction. " Sweetening" is a minerable term to indicate th a t. the aqqregate gradation was corrected to meet normal requirements by adding a proper anount of crushed limentano as coarse aggregate, Of course, thir, is the case in the subject basemat concrete.

. Q2ention: What in the significance of the typen of breaks observed. Responne: Th r-report staten "Mont broken surfacen of the cylinders expone cross-fractured aggregate" (Appendix A, p. 4). Mont of the coarse aooregate in the fracture plane are broken; there is only a minor amount of "nocketing," indicating a strong pante, and strong paste / aggregate bond. Quention: Are the average and standard deviation values shown in Table 4 accurate. Rennonne. The valuen for average comprennive ':trength and standard deviation of 90-day cylinder strength (Daniel data) in Appendix A, Table 4 are corrected to read, 4813 psi and 488 pni, respectively. nuention: What is the relationship between relative abundance of UFC's and adequacy of mixing. He n po n::e - In Dr. Campbell'n report dated April 19, 1978, he suquented the ponsibility of inadequate mixing based on the ohnervation of relative abundance of UPC'n adjacent to one coarse aqqregate in a thin section of a plug drilled from Cylinder 6444. Examination of another thin section cut from a different plug, also taken from Cylinder 6444, shown no evidence of UPC concent. ration, agreeing with observations on thin sectionn from all other exar..ined cylinders. The range and amount of UPC's estimated in microscopic examination of thin nectionn in considered to be normal for concrcte of this age and quality. The numbers are only subjective estimates an observed in very small arean of each nample.

_ r, _ The uniformit'/ of batching and nixing is further verified by the narrow range of cement contents determined on the individual samples. I f f i i l i i

CCIIFFESSIVE STFEUIli, PSI (ISN C-109 30r125) Ccmnt 3 day 7 day 28 day Sam.le (C-CT) Dat'd. Icce. Spread Dat'd. Te/e. Spread De t ' c'. leco. Spread 15 a) 2425 3550 5425 b) 2425 2460 + 65 3550 3565 + 35 5325 5365 ~+ 60 c) 2525 3600 5350 18 a) 2500 3375 5350 b) 2475 2485 + 15 c) 2475 3375 3390 + 35 5325 5340 + 15 3425 5350 20 a) 2125 2875 5050 b) 2025 2035 + 90 2900 2885 -+ 15 4975 5015 + 40 c) 1950 2875 5025 21 a) 2200 3300 5475 b) 2325 2290 -+ 90 3325 3315 -+ 15 5275 5400 -+ 125 c) 2350 3325 5450

• NorS: All spreads on individual cement sa.ples are w211 within the accepted range of + 10%

of average reported value at each age.

CCRPPESSIVE STFE GTH, FSI (ASm C-109 MCPr76S) Ce n t 7 day 28 day 45 day S,mle (C-UT) D2t'd. Ave. Scread Det'd. Ave. Spread Det'd Ave. Scread 16 a) 3675 5550 5975 b) 3650 3625 + 75 5575 5'.15 + 75 5900 5900 + 75 c) 3550 5450 5825 17 a) 3725 5650 6175 b) 3700 3715 + 15 5575 5600 + 50 5375 6015 + 160 c) 3725 ~ 5575 ~ 6000 ~

• OTE:

Spread of values in each case is mil within the acceptable range of + 102 of average reported value (see Section 10.1, ASr C-109-77).

~~' FC A T A \\ g gag SHEET NOe 8 55su (e-71) Supersedes 8 55SU (9-70) VITROBOND CAPPING COMPOUND De_scriptir n VITHOBOND is a mineral filled sulfur based compound which is well suited for capping concrete test cylinders. It is easily melted, pours smoothly, possesses high compressive strength and gives consistent test results. VITROBOND has been in use many years by independent testing laboratories, pre-stressed concrete structures manufacturers and federal, state and local testing agencies. This compound is even suitable for running compressive strength tests upon high strength concrete. Where a stronger compound is required, CARBO VITROBOND, a 100% carbon filled material, is used. ACvantages_ 1. Ready to use-just melt and pour. No mixing is required; therefore no possibility of low strength or erratic results due to improper measuring or mixing of ingredients. k 2. Does not require controlled room temperature or humidity conditions during pouring of caps. 3. Does not require moist curing or other tedious handling procedures. 4. Not af fected by dry cylinders. 5. Can be tested two hours af ter cooling. 6. Virtually no settling when in the melting pot-thus, uniform results are obtained from cylinder to cyhnder. 7. Molten VITROBOND does not emit unpleasant odor which is characteristic of most other sulfur type compounds. 8. Can be stored for years without any deterioration whatsoever. ( hb S QD ATLAS MINERALS AND CHEMICALS DIVISIDN: ESil INcORPOR ATFn a MERTZIDWN. PENNA. Conman Preat Cemevi. re: : revewidi. Coanap. f sak tmrngs. Plait.s f abraations. Fles.ble C.tung. Porsus Plainti. P,pe Jo.,*g Compound,

8 555U (6-71) Page 2 of 3 PhY1Lcpt Propertjes,_ Typical Standard Color Dark Gray Density (Ibsicu. f t.) ASTM D702 137 Tensile Strength (psi. O 75' F.) ASTM C287 600 Compressive Strength (psi. G 75' F.) ASTM C287 8,000 Modulus of Rupture (psi. 0) 7 5' F.) ASTM C287 1,300 5 Coef ficient of Expansion (in./in./*F.) 8 x 10 Water Absorption, (%) ASTM C413 0.3 Thermal Shock (% retained) ASTM C287 50 Tendency of Aggregate to Settle ASTM C287 0.07 Preparation of VITROBOND 1. Break up ingots and place in a thermostatically controlled electrical melting pot. A home apphancecookcr-fryer or oven unit, such as the Westinghouse Cooker Fryer Model RF-300HDC can be used. Soiltest Inc., 4713 West North Avenue. Chicago, Ilknois 60639, of fers a suitable electric melting pot, Model L 114. Sta-Warm Electric Company of Ravenna, Ohio, produces various types and sizes of melting pots. Melt the VlT ROBOND and stir occasionally with metal rod or ladie. Recommended pouring temperature range is from 280' F. to 300' F. 2. Do not set thermostat above suggested pouring temperature or the VITROBOND may ignite due to overheating. If so, turn of f unit and cover with lid. If flame is extinguished promptly, no harm will be done. Burning for long periods of time consumes the sulfur making the compound unusable. 3. If molten VITROBOND foams due to entrapped air, stir until the liquid becomes smooth. Procedure for Use VITHOBOND caps are applied to the concrete test cyhnder per ASTM Method C617. Suitable capping rigs are avaitable from manufacturers such as the following: Humbolt Mf g. Co., 7302 W. Agatite Avenue, Chicago, Illinois 60656 Model H 2952 Cylinder Capper Soiltest Inc., Subsidiary Cenco Instruments Corp.,2205 Lee Street, Evanston, Illinois 60202 Model CT-53, Vertical Capper Model CT 52, Horizontal Capper Also available-a complete capping set, CT 56 Tinius Olsen Testing Machine Co.,2100 Easton Road, Willow Grove, Penna,19090 Olsen Nardiello ~ Horizontal Capper

8-55SU (6-71) Page 3 of 3 Simple devices for occasional capping can also be made by following procedures given by Frank M. Masters, Jr. and A. C. Loewer, Jr. in their article "The Ef fects of Capping Materials on Apparent Strength of Concrete Specimens" in the November,1952 issue of Concrete and by S. K. Waldorf in his article " Simple Devices for Capping Compression-Test Samples" in the September,1956 issue of ASTM Bulletin. It is suggested that at least two rigs be prepared to avoid loss of time in testing. The base plates of the rig should be very lightly oiled or coated with a silicone compound such z.s a 1% solution in toluene of General Electric Fluid SPFE to facilitate removal of the cap. When silicone release agents are used, the rig should ik let stand about 30 minutes af ter coating before pouring caps. If oil is used, extreme care should be taken to see that there is not an excess of oil which would af fect the VITROBOND. It is recommended that the base plate of the capping rig be preheated to retard the cooling rate of the VI T F.O BON D. For the most consistent test results it is suggested that the caps be applied using a vertical capper. Pour the molten VITROBOND on the base plate of the rig and promptly place the cylinder into the molten compound to a depth so that a cap of approximately 1/8" thick will be obtained it is essential to ascertain that each cylinder is properly aligned so that the caps will be p allel. The cylinder may be removed as soon as the VITROBOND has hardened and the other end may then be capped. The specimen may be tested 2 hours af ter the final pouring but should not be tested prior to this time, it ( is not necessary to carry out any moist curing before the tests are made. Storane VITROBOND can be stored indefinitely without deterioration. I Containen I VITROBOND is supplied in 50 pound cartons containing ten t, cound ingots. The gross weight is 51 l pounds. Technicel Service Atlas maintains a staff of Technical Service Representatives who are available to assist you with the use of Atlas products. In the event of any difficulties with the use of VITROBOND, consult Atlas Technical Service Department for assistance. (.

.a - .t m -U .j e {Ji ~ sums a ' hl? v:N;; " ~ i Remnants of 33 cylinders judged to be suitable for cube tests. Mr. IIitt's letter of December ll 7h 7 ~ i I. .,i /- f ~ l,f ' 2'

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