ML19242C946
| ML19242C946 | |
| Person / Time | |
|---|---|
| Site: | 07000036 |
| Issue date: | 06/08/1979 |
| From: | Eskridge H ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY |
| To: | Crow W NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| NIS-79-631, NUDOCS 7908140222 | |
| Download: ML19242C946 (4) | |
Text
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C-E Power Systems Tel. 314/937 4631 Combustion Engineering, Inc.
gti,n'/ Z96-5640 314 Route 21-A W
Hematite, Wssouri 63047 NIS/79/631 d %'zz ',,. n; POWER p,,M SYSTEMS
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cc?., ?.W$itC8 9v June 8, 1979 Mr. W. T. Crow Section Leader Uranium Fuel Fabrication Section Division of Fuel Cycle and Material Safety U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Dear Mr. Crew:
Enclosed is an analysis supported by experimental data to justify that release of spent limestone for unrestricted use will have a negligible short or long tenn environmental impact. This is in response to Item 8 of the attachment to your letter dated January 18, 1979.
Very truly yours,
COMBUSTION ENGINEERING, INC.
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H. E. Eskridge Su;:ervisor, Nuclear Licensing, Safety and Accour.tability
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JUSTIFICATION FOR RELEASE OF SPENT LIMESTONE FOR UNkTSTRICTED USE Release of the spent limestone for unrestricted use is to be based on the following proposed conditions:
1 - The spent limestone must have no detecta~ le activity as determined o
by monitoring with an alpha survey instrument.
2 - A composite sample from 3 scrubber loads (one day's maximum generation) will be tumbled, sampled aad counted in a proportional counter. The sample must have an activity level of less than 4 dpm.
This procedure is described and the iinit justified below.
3 - A sample of the spent limestone will be analyzed for parts per million total uranium on a monthly frequency. This analysis will be used as a control check on the tumbling procedure. To allcw for statistical variation, the control limit will be twice the natural uranium content of limestone as received from the quarry.
An experimental program was conducted to determine potential radiological exposures that could result frem inhalation of dust originating from abrasion of the surface of spent limestone rock, and te determine measurable criteria for release of the spent limestone for unrestricted use.
Airborne dust was generated by tumbling two-pound limestone charges in a tumbler resemoling a small concrete mixer.
Cust samples were collected on filter paper by placing a standard air sampler head in the mouth of the tumbler bcwl. The filter papers were "eighed before and after sampling to determine the sample weight.
Dust Icadings in the tumbler bowl were quite high, averaging 23 milligrams per cubic meter (mg/m ).
After 3
is 5nen.
790814oua 13C3
/D weighing, the samples were counted in a gas proportional counter with a g/cm, and a nominal efficiency of 30%.
Counter 2
windcw thickness of 150 background is typically I to 2 dpm.
Samp1'ng_ new ai d spent limestone using the above technique showed no statistically significant difference in radioactivity levels:
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New limestone 3.1 X 10 uCi/mt Spent limestone 2.7 X 10~
Ci/mi However, the minimum detectable activity (M0A) for this sampling, based on sample volume and counter characteristics, was 6 X 10~
uCi/mi. The relatively high MDA is largely due to the small volume of air having a high dust loading that can be sampled before excessive build-up occurs. A " thin" source that will minimize self-absorbtion in alpha counting is necessary, thus limiting sample volume.
Ambient air quality suspended particulate sampling by Union Electric Company shows concentrations ranging from 24.5 to 80.2 micrograms per cubic meter (ug/m ) at three stations in the St. Louis area. The annual average 3
concentration ranged frca 36.1 to 43.7 ug/m.
Using the radioactivity 3
concentrations we observed in the above tests, an assumed dust, loading of 40 pg/m3 equates to 4.4 X 10-rCi/mt.
Since radioacti/ity concentrations in the air for both new and spent limestone are belcw MDA for the counter, it was decided to use contaminated limestene to better characterize the sampling and counting technique. Spent 2
limestone having a contaminaticn level cf 500 dpm/100 cm, as measured with an alpha survey instrument, was selected for tumbling.
Eleven s01ples were collected rar /ng from 72.1 to 340.2 milligrams in weight.
Analysis of the data from counting these samples shcws the folicwing:
1 - Sample activity ranged from 124 to 179 dpm, generally showing good agreement with the alpha survey instrument measurement (when adjusted for relative area).
137.'rd ms n b 4 f f.i "!b...
2 - Above a sample weight of 100 milligrams there is no aporeciable increase in the count rate.
Above this sample thicknes. (11 mg/cm2) only the upper layer of the samole is being counted due to self-absorption.
3 - Above a sample weight of 300 milligrans the count rate begins to decrease. This indicates that the activity is actually present on the spent limestone rock as surfaca contamination. The decrease is due to the sample becoming coated with cleaner under surface rcck as the contaminated surface abrades away.
Experiments with the contaminated limestone show that the tumbling, sampling and analysis techniques are an effective way to measure surface c ntamination level s.
By collecting a sample in the 100 to 300 milligram range a maximum count rate is cbtained.
Then, if an acceptable limit is set on the allowable count rate, it is not necessary to calculate a related air concentration for the actual sampling. Also, the concentration in the mouth of the tumbler is orders of magnitude greater than those projected frcm any conceivable use of the spent limestone rock.
Considering statistical variation in counter background and the count rates cbserved with new limestone, a limit of 4 dpm was set so as to have a better than.99% probability of not receiving a false indication of contamination.
Using an assumed dust leading of 40ag/m3, the 4 dpm limit is equivalent to 7.2 X 10 16 aci/mt.
To determine if the spent limestene generated over the past few years would meet the 4 dpn limit, 20 samples were taken on a grid pattern of the spent limestone pile.
These samples were tumbled and dust collected described above. Activity rangec frcm 0 to 2.7 dpm, with an average of 0 dpm.
The 1.0 dpm average is ecuivalent to 1.8 X 10-uCi/mt.
Continuous exposure to spent limestone dust at the 4 dpm limit, at a concentration of 40 ;g/m3, would result in a maximum annual dose of 3.6 mr.
The observed 1.0 dpm level would result in an annual dose of only 0.9 ar.
As the doses are only a fraction of the proposed 25 mr annual limit, release of the spent limestone for unrestricted use is environmentally acceptable.V % ",3 n w.x :..
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