LIC-18-0023, FC-18-006, Rev 0, Nai Soil Survey MDC (Reference 11)

FC-18-006, Rev 0, Nai Soil Survey MDC (Reference 11)

ML18215A224
Person / Time
Site:	Fort Calhoun
Issue date:	03/27/2018
From:	Brehm D M Omaha Public Power District
To:	Office of Nuclear Material Safety and Safeguards
References
LIC-18-0023 FC-18-006, Rev 0
Download: ML18215A224 (6)

Text

UFFEM OmlaPatBePowerDisiriet P3Q0 1 Of 6 FC-18-006 Revision 0 Soil Minimum Detectable Concentrations for 2x2 Nal Probes Prepared By: DM Brehm Date Reviewed By; (V.fcojQiUy Date Approved By:

Soil Minimum Detectable Concentrations for 2x2 Nal Probes FC-18-006 OnahiPiMe Power District ReVlsiOD 0 Page 2 of 6 1.0 PURPOSE The purpose of this document is to establish a standard methodology for determining the minimum detectable concentration of radioactive contaminants in soil using a standard 2-inch by 2-inch Nal scintillation detector.2.0 METHODOLOGY The general methodology is described in detail in Section 6.8.2 of NUREG-1507,"Minimum Detectable Concentrations With Typical Radiation Survey Instruments for Various Contaminants and Field Conditions." The Derived Concentration Guideline Levels (DGCLs) used as target values were obtained from FC 18 004, "Soil DCGLs for Fort Calhoun Station Outside the Protected Area Identified for Partial Site Release." MicroShield 11.21 was used to model the soil dose rates that would result from contamination at the DGCLs. See Attachment

1.3.0 ASSUMPTIONS

3.1 The calculations are based on the Cs-137 DGCL determined in FC-18-004.

The other radionuclides are accounted for by scaling them into consideration based on their relative concentrations listed in FC-18-002, "Potential Radionuclides of Concern During the Decommissioning of Fort Calhoun Station." 3.2 The calculations in this document are based on a Ludlum 44-10 (2-in x 2-in Nal) probe connected to a Ludlum 4404-4 data logger. The count rate to dose rate conversion used is the vendor-recommended 900 cpm/liR/hr for Cs-137.3.3 The sample time is assumed to be 1 second for the scanning Minimum Detectable Count Rate calculations.

For field measurement purposes, this will require the probe be over any given 28cm area for one second - an approximate scan speed of 11 inch/sec.3.4 The background count time is assumed to be 1-minute for the scanning Minimum Detectable Count Rate calculations.

3.5 The instrument MDCR is calculated based on the Stapleton Approximation (see NUREG-1575, Figure 20.54).3.6 The probability of Type I and II errors is assumed to be 0.05% (95% confidence) for the scanning Minimum Detectable Count Rate calculations.

Soil Minimum Detectable Concentrations for 2x2 Nal Probes FC-18-006^rSttPttblkPrnftrlSsbkl Revision 0 Page 3 of 6 4.0 CALCULATIONS 4.1 Instrument Minimum Detectable Count Rate (MDCR)Equation 1 - MDCR MDCR=Rbtsli+lts Where: MDCR = minimum detectable count rate (cpm)a = probability of a Type 1 (false positive) error P = probability of a Type II (false negative) error Zi-a = (1 ~ a) quantile of the standard normal distribution (1)Zi-p = (1 - p) quantile of the standard normal distribution (1)ts = sample count time (min)tb = background count time (min)Rb = background count rate (cpm).(1) The "quantile of the standard normal distribution" Is calculated using the Excel NORMSINVO function.Substituting the values into Equation 1 the listed in the assumptions and the measured background count rate of 6,000 CPM: MDCR=(1-64485+1.64485)

^ OO^j .64485+1.64485)

JC6,000)(0.0166)

^1 +0.0166= 2,155 CPM Converting the result into a dose rate:* R, MDCR 2155 cpm ^ uR/MDCR in ^ /f hr nnn 'hi mR/ ljR/900 900 ^cpm cpm 4.2 Soil Activity Model The MicroShield model is included as Attachment

1. The model uses Cs-137 (and the known equilibrium energies & radionuclides) as the primary radionuclide.

The model assumed 5 pCi/g of Cs-137.The assumed dimensions of the soil area surveyed were a 28cm in diameter and 15cm thick disc of soil with a density of 1.6 g/cm^.The calculated dose rate for 5 pCi/g Cs-137 in soil is 1.25 pR/hr.

umu Soil Minimum Detectable Concentrations for 2x2 Nal Probes FC-18-006 OnataMBc^irnDbirict ReVlslOn 0 Page 4 of 6 4.3 Soil Activity that Corresponds to the Instrument MDOR This value is calculated by scaling the dose rate from soil calculated at 5 pCi/g to the dose rate calculated to correspond to the MDOR: Scan MDC (^^'/g) =5/ \MDCR in hr dose rate% I=Mli)=4.B.P0V,

5.0 REFERENCES

5.1 PC 18 002, "Potential Radionuclides of Concern During the Decommissioning of Fort Calhoun Station," 2018 5.2 FC 18 004, "Soil DCGLs for Fort Calhoun Station Outside the Protected Area Identified for Partial Site Release," 2018 5.3 Fort Calhoun Nuclear Station Limited Site Radiological Characterization Survey Report, January 2017 5.4 Fort Calhoun Nuclear Station Limited Site Non-Radiological Characterization Survey Report, January 2017 5.5 NUREG-1507, "Minimum Detectable Concentrations With Typical Radiation Survey Instruments for Various Contaminants and Field Conditions," NRC, June 1998 5.6 NL)REG-1575, "Multi-Agency Radiation and Site Investigation Manual (MARSSIM)," Rev. 1, August 2000.5.7 NUREG-1576, "Multi-Agency Radiological Laboratory Analytical Protocols Manual (MARLAP)," July 2004 5.8 NUREG-1757, Volume 1, Revision 2, "Consolidated Decommissioning Guidance: Characterization, Survey and Determination of Radiological Criteria," U.S. Nuclear Regulatory Commission, September 2006.5.9 NUREG-1757, Volume 2, Revision 1, "Consolidated Decommissioning Guidance: Characterization, Survey and Determination of Radiological Criteria," U.S. Nuclear Regulatory Commission, September 2006.6.0 ATTACHMENTS 6.1 Attachment 1 - MicroShield Soil Activity Model Soil Minimum Detectable Concentrations for 2x2 Nal Probes FC-18-006 OmlaMacnwtrlMict ReVlslOn 0 Page 5 of 6 Attachment 1 - MicroShield Soil Activity Model MicroShield 11.21 OPPD File Name Run Date Run Time Duration X:\NucOperations\Low\RadProtection\Procedures\Rad Analysis\Rad Analysis 2018\FC-18-006 Nal Soil Scanning MDCXSoii DGCLmsd March 21.2018 12:13:39 PM 00:00:00 Project Info Case Title Soil DGCL Description Soil DGCL Geometry 8 - Cylinder Volume - End Shields Source Dimensions Height Radius 15.0 cm (5.9 in)28.0 cm (11.0 in)Dose Points X#1 0.0 cm (0 in)25.0 cm (9.8 in)0.0 cm (0 in)Shields Shield N Source Air Gap Dimension 3.69e+04 cm^Material Soil Air Density (g/cm^)1.6 0.00122 UWU Soil Minimum Detectable Concentrations for 2x2 Nai Probes FC-18-006 OnalmPatIk Power Dislriel Revision 0 Page 6 of 6 Attachment 1 - MicroShield Soil Activity Modei Source Input: Grouping Method - Actual Photon Energies Library: Grove Nuclide Ci Bq pCI/cm*Bq/cm" Ba-137nn 2.7960e-007 1.03450+004 Cs-137 2.95560-007 1.09360+004 7.56800-006 8.00000-006 2.80020-001 2.96000-001 Buildup Buildup: Th0 mat0rial r0fer0nc0 is Sourc0.Integration Parameters Radial Circumferential Y Direction (axial)20 10 10 Results Energy (MeV)4.470e-03 3.182e-02 3.2198-02 3.6408-02 6.6168-01 Total Activity (Photons/sec) 1.0748^-02 2.1428-^02 3.9526-^02 1.4388-^02 9.3098+03 1.017e-^04 Fiuence Rate MeV/cmVsec No Buildup 2.8108-07 3.3948-05 6.5318-05 3.6438-05 3.5798-01 3.580e-01 Fiuence Rate MeV/cmVsec With Buildup 2.9218-07 4.3778-05 8.4818-05 5.1418-05 6.4408-01 6.4428-01 Exposure Rate mR/hr No Buildup 1.9268-07 2.8278-07 5.2568-07 2.0708-07 6.9388-04 6.950e-04 Exposure Rate mR/hr With Buildup 2.0028-07 3.6468-07 6.8256-07 2.9218-07 1.248e-03 1.250e-03 Absorbed Dose Rate mrad/hr No Buildup 1.681e-07 2.468e-07 4.589e-07 1.8078-07 6.0578-04 6.067e-04 Absorbed Dose Rate mrad/hr With Buildup 1.7488-07 3.1838-07 5.9598-07 2.5508-07 1.0908-03 1.091e-03 Absorbed Dose Rate mGy/hr No Buildup 1.681e-09 2.468e-09 4.589e-09 1.8078-09 6.0578-06 6.067e-06 Absorbed Dose Rate mGy/hr With Buildup 1.7488-09 3.1838-09 5.9596-09 2.5508-09 1.0908-05 1.091e-05