ML18215A223

FC-18-003, Rev 1, Cs-137 Global Fallout in Soils at Fort Calhoun Station (Reference 10)

ML18215A223
Person / Time
Site:	Fort Calhoun
Issue date:	06/26/2018
From:	James Smith Omaha Public Power District
To:	Office of Nuclear Material Safety and Safeguards
References
LIC-18-0023 FC-18-003, Rev 1
Download: ML18215A223 (15)

Text

UHHU OtnAi ft iMc AwarAMritf Page 1 of 15 FC-18-003 Revision 1 Evaluation of Cs-137 Global Fallout in Soils at Fort Calhoun Station Approved By: uaicuomim iC ^ /]Date David Brehm!^LoLc^i9(Date Date ffffffff Evaluation of Cs-137 Global Fallout In Soils FC-18-003 at Fort Calhoun Station Revision 1 Page 2 of 15

1.0 INTRODUCTION

This technical document provides a review of information from published global fallout studies and Fort Calhoun Station soil sample data. The technical basis for anticipated soil concentrations attributable to fallout and establishes criteria for investigating soil Cs-137 concentrations that are higher than those anticipated due to world-wide fallout. The end result Is the determination of a site-specific background value for Cs-137 that will be used as the release criteria.2.0 DEFINITIONS 2.1 Data Qualitv Obiectives (DQO): Seven Step DQO process is a component of the planning phase of the data life cycle for site release.2.2 Multi-Aoencv Radiation Survevand Site Investigation (MARSSIM):

Standardized approach to demonstrating compliance with a dose or risk based regulation.

NUREG/CR-1575.

2.3

Background:

means radiation from cosmic sources; naturally occurring radioactive material, including radon (except as a decay product of source or special nuclear material);

and global fallout as It exists in the environment from the testing of nuclear explosive devices or from past nuclear accidents such as Chernobyl that contribute to background radiation and are not under the control of the licensee. "Background radiation" does not include radiation from source, byproduct, or special nuclear materials regulated by the NRG.2.4 Residual Radioactive Material:

Radioactive contamination that may be present at NRG licensed facilities that may be present In structures or impacted areas.2.5 NORM: Naturally Occurring Radioactive Material, radioactive elements found in the environment, such as uranium, thorium and potassium and any of their decay products, such as radium and radon.2.6 Fallout: Radioactive particles that are carried into the atmosphere after a nuclear explosion or accident and gradually fall back as dust or in precipitation.

3.0 BACKGROUND RADIATION SOURCES Different sources of alpha, beta and gamma emitting radionuclides comes from naturally occurring radioactive material (NORM), nuclear weapons testing and previous nuclear accidents.

Most of the testing and all of the accidents have occurred in the northern hemisphere and the highest concentrations of fallout have been found in the 40 - 50 degrees north latitude range. Fort Galhoun Station lies in this range of latitudes.

Since there are various sources of radioactive material pre-existing in the soil, these radionuclides must be taken into account when analyzing soil samples to determine the activity that should be UHHiM Omaha PuUk Pom District Evaluation of Cs-137 Global Fallout In Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 3 of 15 attributed to Uranium fuel cycle activities and whether or not remediation of areas is required.3.1 Nuclear Weapons Testing The estimated total activity of Sr-90 admitted to the atmosphere from nuclear weapons testing has been calculated to be approximately 600 PBq (Ref. 7, UNSCEAR, 1982). The ratio of Cs-137 to Sr-90 from weapons testing has been shown to be fairly consistently 1.6:1 and thus the Cs-137 release could be calculated to be 960 PBq from weapons testing fallout.Weapons testing peaked in the mid-1960's and though there have been several nuclear accidents since this time, the Cs-137 present from fallout is predominantly from weapons testing. Cs-137 has a half life of 30.17 years, where Sr-90 has a half-life of 28.8 years. The distribution of Cs-137 and Sr-90 in soil will vary slightly after deposition as Cs-137 is a group I metal. Group I metals are soluble and will dissociate to ions in water, thus will penetrate deeper into the soil.The deposition of fallout from nuclear weapons testing is generally reported in activity per unit surface area (nCi/m^) as the deposition is not affected by the density of the soils. However for our purposes in site release, the density plays a factor, as more dense soil will indicate a lower activity per unit mass (pCi/g).Thus for 2 different soil areas having a different density, the more dense soil will indicate a lower activity per unit mass than the less dense soil, even though both had the same deposition rate per unit area.. :ti' 30'40-50'- - 60^7^Norfhe>y:}94?1-1-1 395: 39tO I I t i I i I I I I I I I I I I i I I < I I I I I . r t "1 19'0 I9S(1 m"- 199(1 1W5 :00D Figure 1 - Cs-137 deposition density In the northern and southern hemispheres (ref 7) ffPFH Omaha PablkPowtrDisMel Evaluation of Cs-137 Global Fallout in Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 4 of 15 Sr-80 Deposition 65 75 6$ 55 45 35 25 15 5 6 16 26 36 45 66 56 75 85<-N- Degrees Latitude S->Figure 2 - Variation of total Sr-90 deposition with latitude, (ref 11)As Fort Calhoun lies in the latitude range of the highest deposition from fallout testing, the activity present in the soil must be statistically accounted for such that weapons testing fallout is not attributed to licensed operation of Fort Calhoun Station. The following figure presents an estimate of the Cs-137 deposition in Washington County in which Fort Calhoun Station is located.

OPPU OmtlaPiOlitPowarDisbkt Evaluation of Cs-137 Global Fallout in Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 5 of 15 C5-137 drposiiioii densit>-(Bq'ni2) n 0 to 2000 nn 2000 to 4000 4000IO 6000 6000to 8000 SOOOtoUOOO nFigure 3- Cs-137 deposition from fallout and Nuclear Weapons Testing (Ref. 1, CDC-NCI, 2013)3.2 Chernobyl In 1986, the accident at the former Soviet Union's Chernobyl Nuclear Power Plant was the world's worst nuclear accident and released significant amounts of radionuclides into the local and global environment.

Chernobyl was a light water cooled, graphite moderated reactor. Sr-90 release into the atmosphere is estimated to have been 10 PBq and Cs-137 released is estimated to be 85 PBq (Ref. 8, UNSCEAR, 2008).3.3 Fukushima Daiichi In March of 2011 the Great East-Japan Tohoku earthquake and tsunami struck the six nuclear power plants in Fukushima prefecture in Japan causing nuclear accidents and subsequent radioactive releases at three of the six boiling water reactors at Fukushima Daiichi. The estimated atmospheric release of Cs-137 was on the order of 20 PBq (Ref. 9, UNSCEAR, 2013).

Ifffi'fff Evaluation of Cs-137 Global Fallout In Soils FC-18-003 OntaheMHePowwDistriet at Fort Calhoun Station Revision 1 Page 6 of 15 3.4 NORM Continuous production of radiation from cosmic rays interacting with the upper atmosphere of earth produces a constant source of radiation that falls to the earth's surface such as Be-7. This radiation varies based on solar effects and thus the levels vary depending on atmospheric and solar conditions.

Additionally, Carbon 14 is continually being produced in the atmosphere and then being absorbed by plant matter which then deposits the C-14 back into the soil after the vegetation dies. Primordial radionuclides also exist in the soil such as Uranium, Radium, Thorium, and Potassium (e.g., K-40) isotopes.4.0 CESIUM-137 TYPICAL SOIL CONCENTRATIONS There have been numerous investigations and studies done to determine typical Cesium 137 concentrations in soil. The concentrations have been found to vary by orders of magnitude within a given area and peak concentrations are expected to be 10 times the concentration predicted from deposition studies.4.1 Surface samples of undisturbed soil produce the greatest variability.

Areas that collect rain water have significantly higher concentrations of Cs-137 in soil than open areas and can vary by as much as three times non-drainage areas.4.2 The concentration in soil decreases significantly with depth. In undisturbed soil, most of the Cs-137 is contained in the top 15 cm. Surface samples from within the top 5 cm in undisturbed soil had significantly higher concentrations than those taken at the same depth in disturbed soil. Samples taken from surface to 10 cm or surface to 15 cm were less sensitive to soil disturbance.

4.3 Soil density from national studies is typically assumed to be 1.6 g/cm^ and a greater or lesser density will affect the average background Cs-137 concentration.

The soil densities in the sampled areas under active cultivation were approximately 1.3 g/cm^.5.0 FORT CALHOUN STATION SPECIFIC 08-137 BACKGROUND CONCENTRATIONS 5.1 Given the potential variability in Cs-137 concentrations between the local site soil properties and the national average, empirical data was taken to determine the background levels of radionuclides in soil at the site that is a result of fallout and global nuclear accidents.

The tables in Attachment 1 list the sample locations and activity concentrations found in soils around Fort Calhoun Station. The samples were taken in areas similar in soil composition but in locations distant enough that they would not be impacted by releases of licensed material.

Figure 4 shows the locations of soil samples obtained for this background assessment relative to the site. The table in Attachment 1 shows the data from soil samples and direct scans using a Nal detector at various background locations, along with their GPS coordinates.

UFFff OmtbaPubUe Power Disbiti Evaluation of Cs-137 Global Falloutin Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 7 of 15 Siou* City FC-BKG-OOOI FC-BKG-0002 FC-BKG-OOOr-^

• Q-iLV>>'i ' 'iL \ *FC-BKG-0004

<<FC-BKG-0005

\ .FC-BKG^toosr-^jy.-

• -'^*J^'flrc.BkG-ooia Dei M<mo<<FOBKG^OO?Lincoln FC^BKGWOS FC^BKG-OOIS FC-BKG<K)11 FC-BKG^10 fc-bkg-ooiTP Legend Site 0 Background Sampfe Locations BacKTound Samprie Locauyts FoTiCaircun Biar. NE FC-SKG-0005!

T*?>>><1 F..MJ<<jVAlaiI'7KKS craning 160625% 3 Figure 4 - Background Sample Locations 5.2 After global fallout has settled on top of the soil, rains tend to cause the activity to migrate to a deeper level within the first 10-15 cm of soil. Disturbing the soli such as farming activities tends to bring the activity up from these lower layers and more uniformly distribute the activity within this depth. Areas of the site around Fort Calhoun Station, along with background sample locations have been disturbed by farming activity from the same type of crops that have been grown on site at Fort Calhoun Station (corn and soybean) thus the distribution of fallout within the top layer of soil on site should be similar to background soil locations.

6.0 DATA ANALYSIS Fifteen background samples were taken In areas around Fort Calhoun at locations listed In Attachment

1. Of these background samples, eight showed positive Cs-137 activity levels detectable by gamma spectroscopy.

For the three samples that did not have an Identifiable Cs-137 peak, the Cs-137 activity was calculated by the spectroscopy software (Apex Gamma) was conservatively used. Two of the gamma spectroscopy results had an Identified Cs-137 peak and were less than the minimum detectable activity (MDA). These five values were Included as part of the statistical analysis.

The three samples analyzed off-site which had no identified Cs-137 were not used In the statistical analysis.

ofPo Oaaha Public PomrDlslrkt Evaluation of Cs-137 Global Fallout in Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 8 of 15 0.3 0.25'Background Data[Survey Unit Survey Data 0.2 rv CO oo u a.0.1 .0.05 n n 0 '0 10 15 Sample^^umber 30 35 40 45 50 Figure 5 - Cs-137 Activity Scatter Plot 6.1 Interpretation of the data; The mean of the data used is 0.104 pCi/g and the standard deviation (a) is 0.105 pCi/g. At the 95% confidence interval or two standard deviations (2a), the activity of Cs-137 is 0.314 pCi/g.

7.0 CONCLUSION

The soil sample data obtained from empirical samples falls within the range of expected values from 40 - 50 N Latitude within which Fort Calhoun Station lies.The expected range of Cs-137 is 0.3 to 3.0 pCi/g from historic averages.

Fort Calhoun Station, from empirical data from samples is at 0.314 pCi/g with 95%confidence interval.

8.0 REFERENCES

8.1 CDC-NCI, 2003, A Feasibility Study of the Health Consequences to the American Population from Nuclear Weapons Tests Conducted by the United States and Other Nations Volume 1 Technical Report. Prepared for the U.S. Congress by the Department of Health and Human Services Centers ofr Disease Control &Prevention and the National Cancer Institute.

8.2 NUREG -1757, 2006, Consolidated Decommissioning guidance -Characterization, Survey, and Determination of Radiological Criteria Vol.2 Rev.1, U.S. NRC 8.3 NUREG-1505,1998, A Nonparametric Statistical Methodology for the Design and Analysis of Final Status Decommissioning Surveys. Rev. 1. U.S. NRC.

Iffjrjl/ff Evaluation of Cs-137 Global Fallout in Soils FC-18-003 ft StoftlWftlwrS at Fort Calhoun Station Revision 1 Page 9 of 15 8.4 NUREG 1575, 2000, Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM), U.S. NRG.8.5 10GFR 20.1402, Radiological Griteria for Unrestricted Use, U.S. NRG 8.6 10GFR 20.1403, Griteria for License Termination Under Restricted Gonditlons.

8.7 UNSGEAR, 1982, Ionizing Radiation:

Sources and Biological Effects, United Nations Scientific Gommlttee on the Effects of Atomic Radiation 1982 Report to the General Assembly, with Annexes. Annex E, Exposures Resulting from Nuclear Explosions.

8.8 UNSGEAR, 2008, Sources and Effects of Ionizing Radiation, United Nations Scientific Gommlttee on the Effects of Atomic Radiation 2008 Report to the General Assembly, with Scientific Annexes. Volume II, Scientific Annexes G,D and E.8.9 UNSGEAR, 2013, Sources, Effects and Risks of Ionizing Radiation, United Nations Scientific Gommlttee on the Effects of Atomic Radiation Volume I, 2013 Report to the General Assembly Scientific Annex A: Levels and Effects of Radiation Exposure Due to the Nuclear Accident After the 2011 Great East-Japan Earthquake and Tsunami.8.10 Wallo III, Moscovitch, M., Rodgers, J., Duffery, D., Scares, G., 1994, Investigations of Natural Variations of Gesium-137 Goncentrations in Residential Soils.8.11 Beck, H., Bennett, B., (2002), "Historical Overview of Atmospheric Nuclear Weapons Testing and Estimates of Fallout in the Gontinental United States", Health Physics, Vol. 82(5), 2002.9.0 ATTACHMENTS 9.1 FGS Background Soil Sample Analysis Data BPPU Omaha Public Power District Evaluation of Cs-137 Global Fallout in Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 10 of 15 Attachment 1 - FCS Background Soil Sample Analysis Data PCS Background Soil Sample Analysis Sample ID Descriptive Location GPS coordinates Type Isotope Activity Uncertainty MDA Mean Nal Std. Dev Nal (cpm)Lab ID Lat. (N)Long. (W)conc.(pCi/g)2a (pCi/g)(cpm)FC-BKG-0001 L76343-1 Boat Ramp (riverview) 41.5852680 96.0916373 dist.Cs-137 4.24E-02 K-40 1.64E+01 1.21 Ra-226 2.12E+00 1.09 Th-232 1.03E+00 0.166 U-233/234 7.23E-01 0.244 U-238 8.54E-01 0.263 FC-BKG-0002 L76343-2 Sorensen East Drainage 41.5689314 96.1142161 dist.Cs-137 2.76E-01 8.34E-02 K-40 2.23E+01 2.08E+00 Ra-226 3.25E+00 1.59E+00 Th-232 1.34E+00 2.83E-01 U-233/234 1.04E+00 4.18E-01 U-238 7.23E-01 3.40E-01 UffU Evaluation of Cs-137 Global Fallout in Soils oUSa^^Disbici at Fort Calhoun Station FC-18-003 Revision 1 Page 11 of 15 Attachment 1 - PCS Background Soil Sample Analysis Data PCS Background Soil Sample Analysis Sample ID Lab ID Descriptive Location GPS coordinates Type Isotope Activity Uncertainty 2a MDA Mean Nal (cpm)Std. Dev Lat. (N)Long. (W)conc.(pCi/g)(pCi/g)Nal (cpm)FC-BKG-0003 L76343-3 Sorensen Cultivated Field 41.5671474 96.1170117 dist.Cs-137 8.28E-02 K-40 1.91E+01 1.54E+00 Ra-226 3.17E+00 1.49E+00 Th-232 1.07E+00 2.28E-01 U-233/234 1.02E+00 3.59E-01 U-238 1.08E+00 3.74E-01 8.77E+03 9.11E+02 FC-BKG-0004 L76343-4 Row Loess Hills 41.5160900 96.1266056 dist.Cs-137 1.84E-01 6.97E-02 K-40 1.62E+01 1.63E+00 Ra-226 2.86E+00 1.17E+00 Th-232 9.36E-01 2.37E-01 U-233/234 1.33E+00 3.93E-01 U-238 1.18E+00 3.62E-01 NfiS^uPPu OmahtPatBePmnr District Evaluation of Cs-137 Global Fallout In Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 12 of 15 Attachment 1 - FCS Background Soil Sample Analysis Data FCS Background Soil Sample Analysis Sample ID Descriptive Location GPS coordinates Type Isotope Activity Uncertainty MDA Mean Nal Std. Dev Nal (cpm)Lab ID Lat. (N)Long. (W)conc.(pCi/g)2a (pCi/g)(cpm)FC-BKG-0005 L76343-5 Valley Substation 41.3062700 96.3247820 dist.Cs-137 1.07E-01 K-40 1.92E+01 1.81E+00 Ra-226 1.49E+00 Th-232 9.35E-01 2.27E-01 U-233/234 6.43E-01 2.54E-01 U-238 8.36E-01 2.98E-01 L4-BKG-0006s HPGe ISOCS 41.5091668 96.0673679 Cs-137 2.88E-03 9.81 E-03 K-40 1.23E+01 5.05E-01 Ra-226 2.11E+00 2.21 E-01 9743 1280 L4-BKG-0007s HPGe ISOCS 41.5204040 96.0480132 Cs-137 1.57E-01 1.53E-02 K-40 1.54E+01 6.23E-01 Ra-226 2.52E+00 2.65E-01 fIFFil OaahtMllc/'mmOlsttel Evaluation of Cs-137 Global Fallout in Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 13 of 15 Attachment 1 - FCS Background Soil Sample Analysis Data FCS Background Soil Sample Analysis Sample ID Lab ID Descriptive Location GPS coordinates Type Isotope Activity conc.(pCi/g)Uncertainty 2a MDA (pCi/g)Mean Nal (cpm)Std. Dev Nal (cpm)Lat. (N)Long. (W)U-235 1.53E-01 1.63E-02 L4-BKG-0008s HPGe ISOGS 41.5140565 96.0388763 Cs-137 3.66E-02 1.11 E-02 K-40 1.36E+01 5.58E-01 U-235 9.93E-02 1.29E-02 L4-BKG-0009s HPGe ISOGS 41.4930132 96.0981551 Gs-137 4.88E-03 5.62E-02 K-40 14.3 0.589 U-235 0.138 1.59E-02 L4-BKG-0010s HPGe ISOGS 41.4891150 96.0980097 Gs-137 2.68E-01 2.01 E-02 K-40 1.49E+01 5.99E-01 Mn-54 1.04E-02 7.96E-03 U-235 1.38E-01 1.60E-02 L4-BKG-0011s HPGe ISOGS 41.4537819 95.9522425 Gs-137 4.26E-02 UHHBM OmriuMBs Power DIstrtct Evaluation of Cs-137 Global Fallout in Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 14 of 15 Attachment 1 - FCS Background Soil Sample Analysis Data FCS Background Soil Sample Analysis Sample ID Lab ID Descriptive Location GPS coordinates Type Isotope Activity cone.(pCi/g)Uncertainty 2a MDA (pCI/g)Mean Nal (cpm)Std. Dev Nal (cpm)Lat. (N)Long. (W)K-40 12.5 0.498 Ra-226 1.2 0.163 U-235 7.32E-02 9.96E-03 L4-BKG-0012s HPGe ISOCS 41.4475814 95.9645488 Cs-137 6.43E-03 3.55E-02 K-40 1.15E+01 4.62E-01 U-235 4.45E-02 8.85E-03 L4-BKG-0013s HPGe ISOCS 41.4671317 96.0017925 Cs-137 4.15E-02 K-40 10.8 0.438 Ra-226 1.24 0.159 U-235 7.55E-02 9.73E-03 L4-BKG-0014s HPGe ISOCS 41.5016617 96.0589678 Cs-137 5.67E-02 1.28E-02 K-40 1.56E+01 6.28E-01 UHFU OmaliBMIkPowtrtHsliia Evaluation of Cs-137 Global Fallout in Soils at Fort Calhoun Station FC-18-003 Revision 1 Page 15 of 15 Attachment 1 - FCS Background Soil Sample Analysis Data FCS Background Soil Sample Analysis Sample ID Descriptive Location GPS coordinates Type Isotope Activity Uncertainty MDA Mean Nal Std. Dev Nal (cpm)Lab ID Let. (N)Long. (W)conc.(pCi/g)2a (pCi/g)(cpm)Mn-54 7.97E-03 8.56E-03 U-235 1.96E-01 1.77E-02 L4-BKG-0015s HPGe ISOCS 41.5014825 96.0504468 Cs-137 1.30E-01 1.62E-02 K-40 1.64E+01 6.64E-01 U-235 1.60E-01 1.70E-02 mean Gs-137 1.24E-01 std. dev 1.06E-01