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3.2 Definition of key terms adopted in site characterization

An important step in understanding the Radiation Survey and Site Investigation (RSSI) Process is accomplished by understanding the scope of this guideline, the applied terminology and concepts.
As the guidance set out in EURSSEM is based on important documents that have been produced by:

the same terminology has been adopted. In the case of different terms for the same object/purpose, preference is given to terms defined by the IAEA.

In Appendix F a glossary is given with (all) specific terms applied in site characterization, remediation and restoration processes. This section explains some of the terms in the order of their appearance in the guidance.

The process described in EURSSEM begins with the premise that a release criterion has already been provided in terms of a measurement quantity. The methods presented in EURSSEM are generally applicable and are not dependent on the value of the release criterion.

A release criterion is a regulatory limit that can be expressed in terms of dose (mSv/y) or risk (cancer incidence or cancer mortality). A release criterion is typically based on:

  • The total effective dose equivalent (TEDE), or
  • The committed effective dose equivalent (CEDE), or
  • Risk of cancer incidence (morbidity), or
  • Risk of cancer death (mortality)

and generally cannot be measured directly. Exposure pathway modelling has to be used to calculate a radionuclide-specific predicted concentration or surface area concentration of specific nuclides that could result in a dose (total effective dose equivalent or committed effective dose equivalent) or specific risk equal to the release criterion. As an example, a specific approach for the implementation of remediation criteria may be summarized as indicated in the form of the reference levels indicated in Table 3.1 (see also Section 2.2.2.3).

In this manual, such a concentration is termed the derived concentration guideline level (DCGL). Exposure pathway modelling is an analysis of various exposure pathways and scenarios used to convert dose or risk into concentration. In many cases DCGL’s can be obtained from responsible regulatory agency guidance based on default modelling input parameters, while other users may elect to take into account site-specific parameters to determine DCGL’s.

In general, the DCGL can be general (e.g., dose, surface contamination level) or nuclide specific.

The units for the DCGL will be the same as the units for measurements performed to demonstrate compliance (e.g., Bq/kg, Bq/m2, Sv/h, cps/m2).

Band No. Range of annual doses
(to average member of the critical group)

Is remediation needed?
With constraint – Without constraint
Band 6

> 100 mSv/a Always Always
Band 5

10 – 100 mSv/a Always Almost always
Band 4

1 – 10 mSv/a Almost always Usually
Band 3

0.1 – 1 mSv/a Usually Sometimes
Band 2

10 – 100 µSv/a Sometimes Rarely
Band 1

< 10 µSv/a Almost never Almost never

Table 3.1 Examples of reference levels[IAEA-1997].

This allows direct comparisons between the survey results and the DCGL. A discussion of the uncertainty associated with using DCGL’s to demonstrate compliance is included in Appendix B.

An investigation level is a specific level based on the release criterion that, if exceeded, triggers some response such as further investigation or remediation. An investigation level may be used early in decommissioning to identify areas requiring further investigation, and may also be used as a screening tool during compliance demonstration to identify potential problem areas. A DCGL is an example of a specific investigation level. If the DCGL is not superseded, in principle no further investigations or remediation has to be performed. The derivation of DCGL’s from a reference level is given in Section 3.10. Important by the derivation is to understand the assumptions that underlie this derivation. The derivation assumptions must be consistent with those used for planning a compliance demonstration survey. One of the most important assumptions used for converting a dose or risk limit into a specific concentration is the modelled area of contamination. Other considerations include sample depth, composition, modelling parameters, and exposure scenarios. EURSSEM defines two potential DCGL’s based on the area of contamination:

  • If the residual radioactivity (after remediation) is evenly distributed over a large area, EURSSEM looks at the average activity over the entire area. The term DCGLW1 (the DCGLW applies the Wilcoxon Rank Sum statistical test, as indicated in Section 3.10.5) is derived based on an average concentration over a large area, e.g., large number of measurements.
  • If the residual radioactivity (after remediation) appears as small areas of elevated activity2 within a larger area, typically smaller than the area between measurement locations, EURSSEM considers the results of individual measurements. The DCGLEMC is used for the Elevated Measurement Comparison (EMC) (see Section 3.3.2.1 and Section 3.3.2.6) and is derived separately for these small areas and generally from different exposure assumptions than those used for larger areas.

A site is any installation, facility, or discrete, physically separate parcel of land, or any building or structure or portion thereof, which is being considered for survey and investigation.

Area is a very general term that refers to any portion of a site, up to and including the entire site.

Decommissioning is the process of safely removing a site from service, reducing residual radioactivity through remediation to a level that permits release of the property, and termination of the license or other authorization for site operation. Although only part of the process, the term decommissioning is used in this sense for the Radiation Survey and Site Investigation (RSSI) Process.

A survey unit is a physical area consisting of structure or land areas of specified size and shape for which a separate decision will be made as to whether or not that area exceeds the release criterion. This decision is made as a result of the final status survey – the survey in the RSSI Process used to demonstrate compliance with the regulation or standard -. The size and shape of the survey unit are based on factors, such as the potential for contamination, the expected distribution of contamination, and any physical boundaries (e.g., buildings, fences, soil type, surface water body) at the site.

Measurement is used interchangeably to mean:

  • The act of using a detector to determine the level or quantity of radioactivity on a surface or in a sample of material removed from a media being evaluated, or
  • The quantity obtained by the act of measuring.

Direct measurements are obtained by placing a detector near the media being surveyed and inferring the radioactivity level directly from the detector response.

Scanning is a measurement technique performed by moving a portable radiation detector at a constant speed above a surface to semi-quantitatively detect areas of elevated activity.

Sampling is the process of collecting a portion of an (environmental) medium as being representative of the locally remaining medium. The collected portion, or aliquot, of the medium is then analyzed to identify the contaminant and determine the concentration. The word sample may also refer to a set of individual measurements drawn from a population whose properties are studied to gain information about the entire population. This second definition of sample is primarily used for statistical discussions.

Graded approach is the term adopted for the method that makes the best use of resources for decommissioning. EURSSEM places greater survey efforts on areas that have, or had, the highest potential for a radiological contamination. The final status survey uses statistical tests to support decision making. These statistical tests are performed using survey data from areas with common characteristics, such as contamination potential, which are distinguishable from other areas with different characteristics.

Classification is the process by which an area or survey unit is described according to radiological characteristics. The significance of survey unit classification is that this process determines the final status survey design and the procedures used to develop this design. Preliminary area classifications, made earlier in the process, are useful for planning subsequent surveys.

Non-impacted areas are areas that have no reasonable potential for residual radioactive contamination. These areas have no radiological impact from site operations and are typically identified early in the Radiation Survey and Site Investigation (RSSI) Process.

Impacted areas are areas with a reasonable potential for residual radioactive contamination and will have an impact from site operations. Impacted areas are further divided into one of three classifications:

Class 1 Areas: Areas that have, or had prior to remediation, a potential for radioactive contamination (based on site operating history) or known contamination (based on previous radiation surveys) above the DCGLW. Meaning, that at this site radioactive contaminations are of were present above the release criterion. Examples of Class 1 areas include:

  • Site areas previously subjected to remedial actions3.
  • Locations where leaks or spills are known to have occurred of radioactive materials.
  • Former burial or radioactive waste disposal sites.
  • Radioactive waste storage sites
  • Areas with radioactive contaminants in discrete solid pieces of material and high specific radioactivity.

Class 2 Areas: Areas that have, or had prior to remediation, a potential for radioactive contamination or known contamination, but are not expected to exceed the DCGLW. Meaning, that at this site radioactive contaminations are of were present that is not expected to exceed the release criterion. To justify changing the classification from a Class 1 area to a Class 2 area, there should be measurement data that provides a high degree of confidence that no individual measurement would exceed the DCGLW. Other justifications for reclassifying an area as Class 2 may be appropriate based on site-specific considerations. Examples of areas that might be classified as Class 2 for the final status survey include:

  • Locations where radioactive materials were present in an unsealed form.
  • Potentially contaminated transport routes.
  • Areas downwind from stack release points.
  • Upper walls and ceilings of buildings or rooms subjected to airborne radioactivity.
  • Areas handling low concentrations of radioactive materials.
  • Areas on the perimeter of former radioactive contaminated controlled areas.

Class 3 Areas: Any impacted areas that are not expected to contain any residual radioactivity, or are expected to contain levels of residual radioactivity at a small fraction of the DCGLW, based on site operating history and previous radiation surveys. Examples of areas that might be classified as Class 3 include:

  • Buffer zones around Class 1 or Class 2 areas.
  • Areas with very low potential for residual radioactive contamination but insufficient information to justify a non-impacted classification.

Class 1 areas have the greatest potential for contamination and therefore receive the highest degree of survey effort for the final status survey using a graded approach, followed by Class 2, and then by Class 3. Non-impacted areas do not receive any level of survey coverage because they have no potential for residual contamination. Non-impacted areas are determined on a site-specific basis. Examples of areas that would be non-impacted rather than impacted usually include residential or other buildings that have or had nothing more than smoke detectors or exit signs with sealed radioactive sources.

Background reference area: If the radionuclide of potential concern is present in background, or if the measurement system used to determine concentration in the survey unit is not radionuclide-specific, background measurements are compared to the survey unit measurements to determine the level of residual radioactivity. The background reference area is a geographical area from which representative reference measurements are performed for comparison with measurements performed in specific survey units. The background reference area is defined as an area that has similar physical, chemical, radiological, and biological characteristics as the survey unit(s) being investigated but has not been contaminated by site activities (i.e., non-impacted). It is evident, that in highly populated or industrial areas no background reference areas can be found. In EURSSEM guidance is given how to adopt the area to investigate with radioactive contaminants also as background reference area.

Data Life Cycle is the term for the process of planning the survey, implementing the survey plan, and assessing the survey results prior to making a decision.

The Data Quality Objectives (DQO) Process is used in the survey planning to ensure that the survey results are of sufficient quality and quantity to support the final decision.

Quality Assurance and Quality Control (QA/QC) procedures are performed during implementation of the survey plan to collect information necessary to evaluate the survey results.

Data Quality Assessment (DQA) is the process of assessing the survey results, determining that the quality of the data satisfies the objectives of the survey, and interpreting the survey results as they apply to the decision being made.
A systematic process and structure for quality should be established to provide confidence in the quality and quantity of data collected to support decision making. The data used in decision making should be supported by a planning document that records how quality assurance and quality control are applied to obtain type and quality of results that are needed and expected. There are several terms used to describe a variety of planning documents, some of which document only a small part of the survey design process. EURSSEM uses the term Quality Assurance Project Plan (QAPP) to describe a single document that incorporates all of the elements of the survey design.

1 The “W” in DCGLW stands for Wilcoxon Rank Sum test, which is the statistical test recommended in MARSSIM and EURSSEM for demonstrating compliance when the contaminant is present in background. The Sign test recommended for demonstrating compliance when the contaminant is not present in background also uses the DCGLW.

2 A small area of elevated activity, or maximum point estimate of contamination, might also be referred to as a “hot spot.” This term has been purposefully omitted from EURSSEM because the term often has different meanings based on operational or local program concerns. As a result, there may be problems associated with defining the term and reeducating EURSSEM users in the proper use of the term. Because these implications are inconsistent with EURSSEM concepts, the term is not used.

3 Remediated areas are identified as Class 1 areas because the remediation process often results in less than 100% removal of the determined radioactive contamination, even though the goal of remediation is to comply with regulatory standards and protect human health and the environment. The radioactive contamination that remains on the site after remediation is often associated with relatively small areas with elevated levels of residual radioactivity. This results in a non-uniform distribution of the radionuclide and a Class 1 classification. If an area is expected to have no potential to exceed the DCGLW and was remediated to demonstrate the residual radioactivity is as low as reasonably achievable (ALARA), the remediated area might be classified as Class 2 for the final status survey.

To include in Sampling definition: " In situ gamma spectrometry in soils and structures is also considered sampling (see EURACHEM guides)"
– by Rafael Garcia-Bermejo Fernandez about 6 years ago
To include "heterogeneity" and "homogeneity" definitions as intrinsec property of the sampled environmental media from EURACHEM UfS:2007 : Homogeneity, heterogeneity The degree to which a property or constituent is uniformly distributed throughout a quantity of material. Notes: 1. A material may be homogeneous with respect to one analyte or property but heterogeneous with respect to another. 2. The degree of heterogeneity (the opposite of homogeneity) is the determining factor of sampling error. IUPAC (1990) [46]; ISO 11074-2: 1.6 (1998) [45]
– by Rafael Garcia-Bermejo Fernandez about 6 years ago