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3.11 Site characterisation: Reporting results

The process of reporting investigation results is an important consideration in planning the site characterization and should be developed during this planning phase. The process of reporting should also be clearly documented in the project plan and communicated with stakeholders. The documentation should provide a complete and unambiguous record of all actions, designs and radiological survey(s). In addition, sufficient data and information should be provided to enable an independent evaluation of the results of the survey including advises for repeating measurements at some time in the future and should comply at least with all applicable regulatory requirements.

Much of the information in the final status report will be available from other decommissioning documents. However, to the extent practicable, this report should be a stand-alone document with minimum information incorporated by reference.
This document should describe briefly:

  • The instrumentation or analytical methods used.
  • How the data were converted to DCGL units.
  • The process of comparing the results to the DCGLs.
  • The process of determining that the data quality objectives were met.
  • The results of actions taken as a consequence of individual measurements or sample concentrations in excess of the investigation levels.
  • Any additional data, remediation, or re-surveys performed to demonstrate that issues concerning potential areas of elevated activity were resolved.
  • The results of the data evaluation using statistical methods to determine if release criteria were satisfied should be described.
  • Criteria that were not met or if results indicate a need for additional data.

Appropriate further actions should be determined by the site management in consultation with the stakeholders, e.g., responsible regulatory agency.

Again, the level of effort for reporting should be based on the complexity of the survey and depends on the specific objectives of the survey. A simple survey with relatively few results may specify a single report, while a more complicated survey may specify several reports to meet the objectives of the survey. Reporting requirements for individual surveys should be developed during planning and clearly documented in the project plan. These requirements should be developed with cooperation from the stakeholders. (e.g., regulators, the analytical laboratory should be consulted on reporting results for samples). The health physics society has developed several suggestions for reporting survey results and these are extended with other solutions from other sources. These suggestions include:

  • The report should provide general information on the radiological status of the site. Survey results should include identification of the potential contaminants (including the methods used for radionuclide identification), general extent of contamination (e.g., activity levels, area of contamination, and depth of contamination), and possibly even relative ratios of radio-nuclides to facilitate DCGL application.
  • The report should also provide information about radioactive contaminants/materials that have never been present or no evidence about the presence could be established from analyses.
  • Report the actual result of the analysis. Do not report data as ‘less than the detection limit’. Even negative results and results with large uncertainties can be used in the statistical tests to demonstrate compliance. Results reported only as ‘< MDC’ cannot be fully used and, for example, complicate even such simple analyses as calculating an average. While the non-parametric tests described in Sections 3.10.3 and 3.10.4, and in Appendix E can accommodate as much as 40% of the results as non-detects, it is better to report the actual results and avoid the possibility of exceeding this limit.
  • Report results using the correct units and the correct number of significant digits. The choice of reporting results using SI units (e.g., Bq/kg, Bq/m2) or conventional units (e.g., pCi/g, dpm/100 cm2) is made on a site-specific basis. Generally, EURSSEM recommends that all results be reported in the same units as the DCGLs. Sometimes the results may be more convenient to work with as counts directly from the detector. In these cases the user should decide what the appropriate units are for a specific survey based on the survey objectives. The user should check the correct number of significant digits to report with the regulator.
  • Report the measurement uncertainty for every analytical result or series of results, such as for a measurement system. This uncertainty, while not directly used for demonstrating compliance with the release criterion, is used for survey planning and data assessment throughout the radiation survey and site investigation process. In addition, the uncertainty is used for evaluating the performance of measurement systems using quality control measurement results (as described in Section 3.3.9 for scans, direct measurements, and for laboratory analysis of samples). The uncertainty is also used for comparing individual measurements to the action level, which is especially important in the early stages of decommissioning (scoping, characterization, and remedial action support surveys described in Section 3.3.10.2) when decisions are made based on a limited number of measurements. Section 3.9.2.9 discusses methods for calculating the measurement uncertainty.
  • Report the minimum detectable concentration (MDC) for the measurement system as well as the method used to calculate the minimum detectable concentration. The minimum detectable concentration is an a priori estimate of the capability for detecting an activity concentration with a specific measurement system. As such, this estimate is valuable for planning and designing radiation surveys. Optimistic estimates of the minimum detectable concentration (calculated using ideal conditions that may not apply to actual measurements) overestimate the ability of a technique to detect residual radioactivity, especially when scanning for alpha or low-energy beta radiations. This can invalidate survey results, especially for scanning surveys. Using a more realistic minimum detectable concentration, as described in Section 3.3.7, during scoping and characterization surveys helps in the proper classification of survey units for final status surveys and minimizes the possibility of designing and performing subsequent surveys because of errors in classification. Estimates of the minimum detectable concentration that minimize potential decision errors should be used for planning surveys.
    If the DCGL is less than or equal to the minimum detectable concentration of the applied instrument, and the radio-nuclide is not detected, report the actual result of the analysis. Do not report data as ‘less than the detection limit’. Even negative results and results with large uncertainties can be used in the statistical tests described in Section 3.3.2.7 and 3.3.2.8 and Appendix E. Results reported as “< MDC” cannot be fully used and, for example, complicate even such simple analyses as calculating an average. When the minimum detectable concentration reported for a radionuclide is near the DCGL, the confidence in both identification and quantisation may be low. Information concerning non-detects or detections at or near minimum detectable concentration should be qualified according to the degree of acceptable uncertainty.
If the DCGL<MDC this measurement equipment or method can not be used to any demostration of compliance. However it can be used if MDC<DCGLemc to look for Elevated Cncentration areas.
– by Rafael Garcia-Bermejo Fernandez about 6 years ago