Introduction

Wisconsin Public Health Statues 254.41 mandates the Department of Health Services to conduct environmental radiation monitoring around the nuclear power facilities that impact Wisconsin. This environmental monitoring report is for the Zion nuclear generating plant for the calendar year January - December 2008 and provides a description and results of this environmental monitoring program.

The WI DHS environmental monitoring program consists of the collection of various types of samples from the air, water and terrestrial exposure pathways.  The sampling program included samples of air, ambient gamma radiation (TLD), surface water, soil and vegetation that are collected from selected locations at planned sampling intervals.  

Table 1 is a listing of presently used sampling sites that have been renumbered after eliminating sample sites that have been discontinued.  Sampling sites that have been discontinued were last listed as sampling sites in WI DHS’s environmental monitoring report for the Zion nuclear plant for the calendar year of January - December, 2000.  Table 2 provides a listing of types of samples collected, collection frequency, sites where samples are collected, the number of samples collected, number of samples that were missed or had sample or analysis deviations and a listing of the required analyses.  Table 3 provides an explanation of missing samples or non-routine sample analyses.  Figure 1 is a map showing the location of each environmental sampling site.

In January 1998 ComEd announced that it was permanently closing the Zion nuclear power station and initiated the process of decommissioning the Zion station.  In response to this and due to other funding restrictions, the Zion environmental monitoring program was reviewed and modified in 1998 and 2000.

There were no additional program modifications for 2008.

The analysis of the samples is performed under contract with the State Laboratory of Hygiene (SLH).  SLH maintains a quality assurance program.  Analytical procedures provide for routine replicate analyses to verify methods and instrument operation.  Traceable sources are used to regularly calibrate the counters and daily performance checks are made between calibrations.  In addition, quality control charts are maintained on the counters.

SLH participates in the Environmental Resource Associates’ Proficiency Testing program and has performed satisfactorily over the report period.  Proficiency testing results are available from the State Laboratory of Hygiene.

Detection Limits

Detection limits, required by WI DHS, will be expressed as a lower limit of detection (LLD).   The required WI DHS LLD as indicated in Table 4 under the heading “LLD” is an "a priori" estimate of the capability for detecting an activity concentration by a given measurement system, procedure, and type of sample.  Counting statistics of the appropriate instrument background are used to compute the LLD for each specific analysis.  Using 4.66 times the standard deviation (s_b) of the instrument background, the LLD for each specific analysis is defined at the 95% Confidence Level.

The LLD for each radioisotope listed in Table 4 has been calculated from the following equation:

                       4.66 s_b
LLD = ---------------------------------------------
             E * V * 2.22 * Y * S * exp(-dt)

Where:

Typical values for E, V, Y and dt have been used to calculate the LLD.

Reporting of Sample Analysis Results

Results for specific analyses will be reported as either a “less than” (<) value or an actual activity value. The reporting of results in Table 4 under the heading “Range” and in Tables 5-9 is “a posteriori” calculation based on the actual analysis performed using the actual sample values for E, V, Y and dt. Typically the reported “less than” (<) results are lower than the required WI DHS LLD indicating that the required WI DHS LLD has been met.

An actual activity value will be accompanied by an uncertainty term for that analysis.  The uncertainty term is a plus or minus counting uncertainty term at the 2 sigma (95%) confidence interval and is printed as (+- or ±).  Examples and explanations of data reporting are:

Example      

Nuclide 

1

¹³⁷Cs

2

¹³⁷Cs

In example 1 we can be 95% confident that the sample activity, if any, is less than the LLD of 10 pCi/liter.  In example 2 we can be 95% confident that the actual sample activity is greater than the LLD for that analysis and is between 12 and 18 pCi/liter.

Air Particulate

A summary of reported activities by WI DHS for air particulate samples is included in Table 4.  Results from the individual sample analyses are listed in Tables 5 and 6.

From the quarterly gross beta activities listed in Table 5 it may be noted that there are no significant differences due to distance from the Zion nuclear facility.  With no significant differences due to distance from the Zion nuclear facility an increase in gross beta activity attributable to the Zion plant operation is not evident.

The gamma isotopic analysis of the quarterly air particulate filter composites detected only small amounts of the radioisotopes listed in Table 6.  Beryllium-7 (⁷Be), detected in all composites, is constantly produced through nuclear reactions between cosmic rays and nuclei in the atmosphere and is detected in air composites from other areas of the state. 

Influence by the Zion nuclear facility on air quality is not evident from air particulate analysis.

Ambient Gamma Radiation (TLDs)

A summary of reported activities by WI DHS for ambient gamma radiation is included in Table 4.  Results from the individual sample analyses are listed in Table 7.

Ambient gamma radiation (TLD) data for 2008 from the WI DHS network was comparable for all sites. Significant differences in exposure were not noticed at different distances from the Zion nuclear facility. The average quarterly exposure from the three sites located within Wisconsin was 13.2 ± 1.8 milliroentgens. The average yearly exposure is at background levels and is comparable to other areas within Wisconsin.

Surface Water

A summary of reported activities by WI DHS for surface water samples is included in Table 4.  Results from the individual sample analyses are listed in Table 8.

The surface water samples showed no unusual activities and are at background levels comparable to previous years.  From the gamma isotopic analysis, all radioisotopes were below their respective minimum detectable concentration.  All reported activities for gross beta, gross alpha and tritium (³H) are at background levels.  The surface water samples uniformly show activities well below state or federal standards. 

Vegetation

A summary of reported activities by WI DHS for vegetation samples is included in Table 4.  Results from the individual sample analyses are listed in Table 9.

Analysis of the vegetation samples showed no unusual activities.  The gamma isotopic analysis detected only small amounts of the naturally occurring radioisotopes beryllium-7 (⁷Be) and potassium-40 (⁴⁰K) listed in Table 4.  All other radioisotopes were below their respective minimum detectable concentration.

Soil

A summary of reported activities by WI DHS for soil samples is included in Table 4.  Results from the individual sample analyses are listed in Table 9.

Analysis of the soil samples showed no unusual activities.  The gamma isotopic analysis detected only small amounts of the radionuclides listed in Table 4.  Potassium-40 (⁴⁰K) is a naturally occurring radioisotope.  The reported activities for cesium-137 (¹³⁷Cs) were also detected in previous years and are attributable to fallout from previous atmospheric nuclear tests.  Naturally occurring radioisotopes such as radium-226 (²²⁶Ra), bismuth-214 (²¹⁴Bi), lead-214 (²¹⁴Pb), actinium-228 (²²⁸Ac), bismuth-212 (²¹²Bi) and lead-212 (²¹²Pb) from the naturally occurring uranium-238 (²³⁸U) and thorium-232 (²³²Th) decay series are commonly detected but have not been quantified or reported.

Dose to an Average Individual

Federal regulations 10 CFR 20, 10 CFR 50 Appendix I and 40 CFR 190 restrict the annual exposure of the population from all parts of the nuclear fuel cycle, including nuclear power plants. Doses resulting from gaseous and liquid effluent releases from the Zion nuclear generating facilities are less than the limits as stated in these Federal regulations.

The WI DHS limits for permissible levels of radiation exposure from external sources in unrestricted areas is defined in the Wis. Adm. Code section DHS 157.23.  Doses resulting from gaseous and liquid effluent releases from the Zion nuclear generating facilities are less than the limits as stated in Wis. Adm. Code section DHS 157.23.

State of Wisconsin, Wisconsin Administrative Code, DHS 157.23

U.S. Environmental Protection Agency, Environmental Radiation Requirements for Normal Operations of Activities in the Uranium Fuel Cycle, EPA 520/4-76-016, 40 CFR Part 190, November 1976.

U.S. Nuclear Regulatory Commission, Title 10, Part 20.

U.S. Nuclear Regulatory Commission, Title 10, Part 50, Appendix I.