ML20055C301
| ML20055C301 | |
| Person / Time | |
|---|---|
| Site: | 07000925 |
| Issue date: | 02/28/1990 |
| From: | Hurt R NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Haughney C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| NUDOCS 9003020017 | |
| Download: ML20055C301 (3) | |
Text
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FEB 2'8 1990 -
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Docket:No.70-925 y
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- / MEMORANDUM FOR:- Charles 11..Haughney, Chief d
- Fuel Cycle Safety Branch i
O Division of Industrial and t
. Medical Nuclear Safety FROM:
R. Davis Hurt 4
Advanced Fuel.and Special 3'
Facilicite Section Fuel. Cycle Safety Branch
. Division of Industrial and Medical Nuclear Safety SUBi1ECT:
REVISED URANIUM SURVEY PROGRAM FOR THE ?, ERR-MCGEE-CIMARR0N SITE i
In a letter dated February 1, 1990, Kerr-McGee Corporation submitted information t on:a revised method-for surveying the Cimarron, Oklahoma site for uranium
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contamination. We-requested'in our meeting of December 1,1989 that Kerr-McGee revise ~ their: survey program, and the February 3 submittal shows that Kerr-McGee Lhas -taken significant steps 1toward doing so..
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'Kerr-McGee had previously used a borehole gamma logging method to determine
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thelextent.of-uranium contamination in'the soil around their Cimarron Uranium
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Facility. '. Data obtained by this method had led to a' estimate that'3 400,000 "a.
cubicfeetLofLsoilmaybecontaminatedinexcessoftheBranchTechnlcal o.
Position Option One ceiling (30 pCi of t'otal uranium per gram'of soil).
Kerr-NcGee has' agreed in the February 1 submittal that.the borehole logging
' data submitted earlier were invalid.
Specifically, they have agreed that the egamma 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 gamma 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.
- gamma rays emitted by uranium' isotopes in-a small sample of soil placed in-front of the instrument. To establish the validity.of the gamma-spectrometry -
system, Kerr-ficGee has carried out a cross-check program where uranium concentrations measured by gamma-spectrometry were compared with uranium concentrations measured by alpha pulse height analysis in the Kerr-McGee o,
Technical Center. Alpha pulse height analysis is normally considered one of iN' the most accurate, ways to measure uranium. concentrations in soilsor rock. The l h~
y Kerr-McGee alpha system has been cross-checked by our contractors' from 0ak y,
Ri_dge Associated Universities and judged to be fairly accurate (letter of.
,F m ' August 31', 1989 from J. D. Berger to R. D. Hurt).
Furthermore,.the measured p
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FEB t 81990 Charles Haughney U-?34/U-08 activity ratios reported in the February 1 submittal are mostly consistrnt with normal ratios for natural or low-enriched uranium, indicating-that th t 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 4
problem would not affect the system's usefulness as a benchmark for cross-checks against the gamma-spectrometry system in the PO-100 pC1/g range.
Forty-two soil samples were measured with both the gamma-spectrometry system and the alpha pulse height system. The alpha system measured 30 below 30 pCi/g and 12 above 30 pC1/9 Of the 12 "high" samples, the gamma-spectrometry system also measured all 12 above 30 pCi/g, a very good result. Of the 30
" low" samples, the gamma-spectrometry system measured 22 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 27 percent).
For all of the false alarm results, the alpha system measured uranium concentrations at or slightly above backgNund, while the gamma-spectrometry system measured values between 30 pCi/g and 90 pC1/9 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,_1989) 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 gamma energy discrimination is probably necessary.
Kerr-McGee has not submitted any information on their gamma detector desigri or counting software, 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-234 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 gamma 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.
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,a FEB 8 1990 i
Charles Haughney 3
a In conclusion, the submittal shows that the Kerr-McGee gamma-spectrometry system is adequate for measuring uranium concentrations in soil at the Cimarron site for fairly high concentrations, above approximately 50 pCi/9 The system needs to be improved before it can reliably measure uranium concentrations in the 30 50 pC1/g range, If the existing system is used without improvement, it is likely that the volume of soil contaminated with uranium in the Option Two range (30-100 pCi/g) will be overestimated by 25-50 percent.
o OriglulSiped by s
R. Davis Hurt Advanced Fuel and Special Facilities Section Fuel Cycle Safety Branch Division'of Industrial and Medical Nuclear Safety Distribution:
-Docket No.70-925 NRC File Center PDR IMilS Central File IMAF R/F
.NMSS R/F IMSR R/F JSwift DHurt FBrown GComfort GSjoblom JParrott, LLWM (DH/LTR TO HAUGHNEY) a m
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