ML20012B768
| ML20012B768 | |
| Person / Time | |
|---|---|
| Site: | 07000295 |
| Issue date: | 03/13/1990 |
| From: | Haughney C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Stauter J CIMARRON CORP. |
| References | |
| NUDOCS 9003160244 | |
| Download: ML20012B768 (1) | |
Text
F g g i 8 1990 Do'cket No. 70 925
'Cimarron Corporation ATTN:
J. C. Stauter, Director Environmental Affairs P.O. Box 25861 Kerr-McGee Center Oklahoma City, OK 73125 f
Dear Dr. Stauter:
Enclosed for your information is our review of the information contained in your submittal of February 1,1990, concerning the gamma. spectrometry system l
you are using to determine the extent of uranium contamination in soil on the Cimarron site. The data in the February 1 submittal show tbt the gamma.
spectrometry system is suitable for purposes of surveying the site, although j
we recomend that you take steps to improve the system's performance in the i
30 50 pCi/g concentration range. Our discussions of March 1, 1990, on the occasion of your visit to our office to discuss the Site Investigation Report,
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indicated that such improvements may already have been made. You also told us that you will submit a new estimate of the total volume of soil on the site conteminated to the Branch Technical Position Option Two level or above.
The description in your submittals bf procedures for excavating and sorting the contaminated soil also needs to be revised. The description in the October 1989 submittal was based on the assumption that the borehole gamma. logging method would provide a meaningful measure of uranium contamination. That assumption l
was apparently invalid, and we understand that you will not be using the borehole gamma. logging method for future surveying or soil sorting work.
Please provide us an updated description of your excavation, soil sampling, and soil sortirg procedures.
Sincerely, 99IIIW W Charles J. Haughney, Chief Fuel Cycle Safety Branch Division of Industrial and Medical Nuclear Safety
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Enclosure:
NPC Staff Review of Revised Cimarron Survey Program n
i M L E8'N cc: Dale McHard Oklahoma State Department
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ex James Berger
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Distribution:
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February 28, 1990 Docket No.70-925 MEMORANDUM FOR:
Charles J. Haughney, Chief fuel Cycle Safety Branch Division of Industrial and Medical Nuclear Safety l
FROM:
R. Davis Hurt Advanced Fuel and Special Facilicite Section Fuel Cycle Safety Branch i
Division of Industrial and Medical Nuclear Safety i
Sl%1ECT:
REVISED URANillM Sl!RVEY PP0 GRAM FOR THE KERR-NCGEE CIMARR0N SITE i
In a letter dated February 1,1990, Kerr-HcGee Corporation submitted information on a revised method f or surveying the Cimarron, Oklahoma site for uranium contamination. We requested in our meeting of December 1,1989 that Kerr-!!cCre rev se their survey program, and the February 1 submittal shows that Kerr-McGee has taken significant steps toward doing so.
Kerr-HcGee had previously used a borehole gamma loggino method to determine the extent of uranium contamination in the coil around their Cimarron tiranium Facility. Data obtained by this methed had led to a estimate that 3,400,000 cubic feet of soil may be contamineted in excess of the Branch Technical Position Option One ceiling (30 pCi of total uranium per gram of soil).
Kerr-McGee has agreed in the February I submittal that the borehole logging data submitted earlier were invalid.
Specifically, they have agreet that the gamma counts measured by the borehole logging instrument do not correlate to any meaningful' extent with the uranium concentration in the soil.
They have confirmed this by comparing pamma counts measured by the borehole logging instrument with uranium concentrations measured by more accurate methods.
Future surveys will be based on a gamma-spectrometry system that measures the gama rays emitted by uranium isotopes in a small sample of soil placed in front of the iristrument. To establish the validity of the gamma-spectrometry system, Kerr-McGee has carried out a cross-check program where uranium concentrations measured by gamma-spectrmetry were compared with uranium concentrations measured by alpha pulse height analysis in the Kerr-McGee Technical Center. Alpha pulse height analysis is normally considered one of the most accurate ways to measure uranium concentrations in soil or rock.
The Kerr-HcGee alpha system has been cross-checked by our contractors from Oak ridge Associated Universities and judged to be feirly accurate (letter of August 31, 1989 from J. D. Berger to R. D. Hurt).
Furthermore, the measured
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FEB t 81990 Charles Haughney L 1
U-?34/U-?38 activity ratios reported in the February ) submittal are mostly
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consistent with normal ratios for natural or low-enriched uranium, indicating that the alpha system produced plausible results. There is some indication in both the February 1 submittal and the ORAU letter that the Kerr-McGee alpha system overestimates the uranium concentration in uncontaminated samples.
That problem would not affect the system's usefulness as a benchmark for cross-checks i
against the gamma-spectrometry system in the 70-100 pCi/g range.
Forty-two soil samples were measured with both the gama-spectrometry system l
and the alpha pulse height system.
The alpha system measured 30 below 30 i
pCi/g and 12 above 30 pCi/9 Of the 12 "high" samples, the gama-spectrometry i
system also measured all 12 above 30 pCi/g, a very good result. Of the 30
" low" samples, the gama-spectrometry system measured 27 below 30 pCi/g and 8 above.
These last 8 should be viewed as false alarms in the context of the cross-check program, which gives the gamma-spectrometry system a fairly high false alarm probability (8 out of 30, or 77 percent).
For all of the false alarm results, the alpha system measured uranium concentrations at or slightly above background, while the gama-spectrometry system measured values between 30 pC1/g and 90 pCi/9 It is likely that the false alarms were caused by the presence of gamma rays from non-uranium isotopes.
Data from the Cimarron Site Investigation Report (submitted October 9, 11,89) indicate that there is enough naturally occurring thorium in some of the rock under the site that thorium daughters may be the problem. Or there may be thorium contamination on some parts of the site from thorium-bearing materials that were once stored at Cimarron.
In any case, better gama energy discrimination is probably necessary.
Kerr-McGee has not 1
submitted any information on their gama detector design or counting sof tware, so it is hard to say more about this.
The footnotes to Tables 1 and 2, and the heading of Table 5, in the February 1 submittal indicate that the Kerr-McGee gamma-spectrometry system counts U-?34 and U-238 gamma rays, but not U-235. This may be a typographical or labeling error since the normal procedure would be to count U-235 gama rays alone if the enrichment is known, or U-235 plus the Pa-234 daughter of U-238 if the enrichment is not known.
Kerr-McGee should clarify what they are counting.
1 FEsaaisso Charles Haughney.
In conclusion, the submittal shows that the Kerr-PcGee gamma-spectrometry
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system is adequate for measuring uranium concentrations in soil at the Cimarron site for fairly high concentrations, above approximately 50 pCi/o.
The system needs to be improved before it can reliably measure uranium l
concentrations in the 30-50 pCi/g range.
If the existing system is used without improvement, it is likely(30-100 pCi/g) will be overestimated by 25-50 that the volume of soil contaminated with uranium in the Option Two range percent.
.D R. Davis Hurt Advanced Fuel and Special Facilities Section Fuel Cycle Safety Branch Division of Industrial and Medical Nuclear Safety
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