ML20002E000
| ML20002E000 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 12/01/1970 |
| From: | Haueter R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Morris P, Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8101260039 | |
| Download: ML20002E000 (4) | |
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~ l m pl/; L: y / Lu Dr. P. A. Morris, Director /- '1 a , ; \\,7 e : Docket 50-155 R Division of Reactor Licensing,h.p 7p('[ l' License No DM-6 United States Atomic Energy Commission Washington, DC 205h5
Dear Dr. Morris:
Attention: Mr. D. J. Skovholt In accordance with Operating License DPR-6, Paragraph 3.D (1) b, this letter is written to report the release of noble gases to the discharge canal at the Big Rock Point Nuclear Plant. The plant has been plagued with a slight condenser tube lenk not large enough to hamper operations nor detectable through normal testing means. The outlet of the main condenser operates at slight negative pressure on the cooling water side. This is caused by an un-avoidable tailgate cetion due to the physical location of the rain con-denser above lake level. After breaking vacuum on the steam side of the main condenser, the tailgate action (coupled with a slight tube leak) provides the mechanism for a release by drawing a portion of the noncondensible gases still in the condenser into the cooling water. On November 13, 1970, icmediately following the plant shutdown with both condenser circulating water pumps in operation, an increase in count rate was observed on the canal discharge monitor. This count rate rose initially to 950 cpm and gradually declined to the background rate of 350 cpm over a 13-hour period. Analysis of a sample of canal water obtained during this period indicated a mixture of noble gases comprised of two Krypton and two Xenon radioisotopes. An estimated total of 1.0h curies of radioactive noble gases was discharged to the canal. The avera'e concentration in the water during the 13-hour period was 6.8 x 10-pCi/cc and the maximum concen-tration was 2.5 x 10-5 pCi/cc. Since the average maximum permissible concentration for these noble gases based upon submersion dose in the air, not water, is 41 x 10-7 uCi/ce, it is felt that effectively no MFC was exceeded. No release to the atmosphere occurred by dissolution of these gases from the water to the ambient air. A search of previous shutdowns v3 th potential tube leaks in the condenser indicated similar conditions existed but to a lesser extent on two occasions. These outages and resulting releases were as follows: Q\\' b u,, a $ WAhh8bf
r-h' Dr. P. A.' Morrio ' 2 Decembsr 1, 1970 Duration of Increased Count Rate on Canal Monitor uCi/cc Calculated Release Outage Date Average Maximum Curies 9/26/70 5 Hr 1.6 x 10 k.2 x 10- .095 -6 11/ T/70 9 Hr 2.6 x 10 h.3 x 10 ,gg5 These releases and release rates were calculated using the following known values and assumptions: I. Canal Discharge Monitor Calibration The sodium iodide crystal canal discharge monitor was cali-brated on September 22, 1970 utilizing solutions of three dif-ferent concentrations of Cs-137. The calibration of this monitor showed the expected linear relationship between net count rate and radioactivity concentration. The decay energy and gamma abundance of the Isotope Cs-137 is 0.662 MeV 86 percent of the time. The isotopes noted in the discharge canal water by. multi-channel analysis of a 1000 m1 sample of discharge canal water were as follows: Isotope Gamma Energy and Abundance Percent of Total Kr-85m 0.15 MeV - 77% 7 Kr-87 0.41 MeV - 87% 7 Xe-133 0.08 MeV - 36% 52-0.25 MeV - 97% Xe-135 0.61 MeV - 3% 34 Two uncertainty factors are present because gamma decay energy of the noble gases involved in the release is somewhat different and genera 31y lower than the calibrating energy of Cs-137 The first uncertainty is introduced by the fact that as ga=ma decay energy decreases, crystal counting efficiency increases. This is due to the greater absorption probability within the crystal. Secondly, as gamma decay energy decreases, the shielding effectiveness of the water solution increases, thereby decreasing the counting efficiency of the system. These two uncertainty factors tend in the direction of cancel-lation. However, the increase in attenuation by water over an energy range of 0.7 MeV to 0.08 MeV is much less than the increase in attenuation by sodium iodide over the same energy + range. Data on sodium iodide crystal attenuation over the stated range from G. R. White, National Bureau of Standards, US Cire 583, 1957; and water attenuation from The Atomic Nucleus J
e-y Dr.iP. A. Mora;s 3 DecImber 1, 1970 by R. D. Evans, McGraw-Hill _ Book Co, 1955, shows that the in-crease in sodium iodide attenuation is to be about a factor of thirty over the_ stated energy range; whereas, water attenuation increases only -by a factor of two. Hence, total system counting efficiencies for Ca-137 in calculating the release of noble gases vill be used and are conservative based upon the above analysis. - Finally, due to the fact that gamma' abundance for Xe-133 is only 36 percent, a correction to canal discharge monitor count rate due to Xe-133 will be mede by multiplying that portion of the count rate by 86/36. The average gross count over the 13-hour release period .vas 600 cpm. Background rate was 350 cpm. Net count rate was, therefore, 250 epm. If 52 percent of total release was Xe-133 by multichannel analysis, then 0.52 x 250 = 130 cpm was con-tributed by Xe-133 correcting this for gamma abundance yields: 130 x 86/36 = 310 + remaining counts 120 Total net corrected count rate h30 cpm From the calibration graph, a net c9unt of h30 cpm cor-responds to a concentration of 6.8 x 10-D pCi/cc. For a 13-hour period, the following activity was therefore released: 3 -6 (5.2 x 10 gpm)(3.78 x 10 cc/ gal)(6.8 x 10 Ci/ce) (60 min /hr)(13 hr) = 10ho mil 11 curies The peak count rate observed on the canal discharge monitor was 950 counts per minute gross. Making corrections for the background and Xe-133 gamma abundance, the peak concentration in the discharge canal was 2.5 x 10-5 pCi/ce. Releases for the other periods.when canal monitor count rate increases were noted were calculated on the same basis as above. II. Calculations of Releases to the Atmosphere By Henry's Law at saturation and equilibrium at STP using 1 ppm Kr and 0.05 ppm Xe in normal atmosphere, the following can be calculated: Saturated Water Solution Element cc Gas /cc Water Atoms Gas /cc Water ~0 12 Kr 6.02 x 10 1.61 x 10 ~9 11 Xe 6.16 x 10 1.65 x 10 I 1 1
J l l k Dr. P. A. Morris Dec;mb2r 1, 1970 The release of activity to the circulating water dis-charge canal and the contribution to ' total dissolved stable Kr and Xe is as follows: Concentration Concentration Isotope uCi/cc Atoms /cc ~I Kr-85m h.75 x 10 h00 -I Kr-87 h.75 x 10 110 Total Kr 510 -6 Xe-133 3.5h x 10 8.6 x 10 -6 3 Xe-135 2.32 x 10 h.0 x 10 Total Xe 9 0 x 10 Since the addition of radioactive Kryton and Xenon produced a negligible contribution to the stable concentration of these elements, atmosphere release of these nuclides is considered to be negligible. Steps to be taken to reduce discharge of radioactive gas via the circulating water in the future are as follows: If a condenser tube leak is known or suspected: 1. The mechanical vacuum pump will be operated to maintain a vacuum on the steam side for an appropriate length of time to minimize any such future release. 2. Canal monitor will be checked on each shutdown when con-denser is brought to atmosphere pressure. 3. Tube leaks will be repaired as appropriate to plant operation. Yours very truly, l vw RBS/ deb Robert L. Haueter Electric Production Superintendent - Nuclear
i l I I l t -9 )[ l <. k ' 9 b v,f j <'.y.. .(, F ROM. DATE OF DOCUMENT: DATE RECElvED No.: Ceeg Feuer company 12-1-70 12-7-70 c, Ah, EMp M201 LT R. = E = O. R EPOR r. OT En Robert L. Baneter I TO: O RIG.: CC. OTHER. 1 Signed 4 can'f Dr. F.A. Morris ,,,,,,,c,,,,,, co,cy,,,,c, o,,,,,,,,,, no.cTioR Ricassaar O co==E~T O e v. CLAS $ a F. PO$T OF F aCL F8LE COOL U 50-155 ,, c,,. DLSCRIPTION. (Must Be Unclassified) REFERRED TO DATE RV ElvED Sy DATE Ltr submitted to rept operating difficuni i in the release of noble gasses to the E amann 12-7-70 w 9 cys for ACTION discharge canal at Big Rock Point Nucle ar Plant. DISTRIBUTION: E~CoosuRo$. ,g ygg, AEC PDR compliance (2) occ-ne P-506-A E. Price & sta ff P. Bowe Skovbolt y'*3 morris /s 1 dr ,in..d .. [d.E " ' " ^ " " ' ' ( ifT" g4 N u! y,[,]>
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