pdf WGDECOM_0417 Correa

Surface & Subsurface Soil Characterization for the Release Process at José Cabrera NPP
Cristina CORREA SAINZ, Jose Luis LEGANES NIETO, ENRESA, Spain

The presentation begins by outlining the technical and regulatory documents that govern the decommissioning and characterization activities at José Cabrera. These documents include remediation plans (060-PL-JC-0033), definitions of Source Term (060-ET-EN-0001 - the type and quantity of radioactivity potentially released), Scaling Factors (060-IF-IN-0039 - coefficients used to estimate the activity of hard-to-measure radionuclides from easier-to-measure ones), Release Levels (RL's) (PRE 060-RE-EN-0001), Reference Residual Levels (RRL's) (060-IF-JC-1721), and the classification of Release Units (RU's) (060-PC-JC-0430).

RL's are the contamination thresholds above which the site cannot be released. RRL's are even lower levels, based on dose assessments for future populations, and serve as targets for decontamination. RU's are defined portions or volumes of material that are managed and characterized as distinct entities for the release process.

The site is divided into RU’s for systematic management of the characterization. These RU's are classified according to the probability of contamination. This classification helps optimize sampling and measurement efforts. The use of EIC codes (Installation Body Identifier) for each RU is mentioned, ensuring traceability.

Geostatistics: A key aspect of the presentation is the application of geostatistics. This is a statistical method used to model the spatial distribution of contamination in soils. It is employed to: estimate the average activity within the RU’s, quantify the uncertainty coming from these estimations, define a proper sampling plan which consists in determining where and how much samples we need to collect, check if the average activity in the RU’s is below the RRL and use Kriging which is a geostatistical technique process used for spatial interpolation of data and the estimation of radionucleid concentrations in unsampled areas.

Remediation: If characterization reveals contamination levels above the thresholds, remediation actions are undertaken. This typically involves excavation and removal of contaminated soils to radioactive waste management facilities, or on-site treatment if feasible. The goal is to achieve the RRL's. Uncontaminated materials can be used after for backfill.

Final Characterization with MARSSIM: Following remediation, a final characterization is conducted. The presentation highlights the use of the MARSSIM (Multi-Agency Radiation Survey and Site Investigation Manual). This is a standardized and robust approach, based on statistical principles, for demonstrating that residual radioactivity levels on a decommissioned site comply with release criteria. MARSSIM outlines clear steps for survey planning, sampling, measurement, and evaluation of results.

On site, multiple types of measurement devices are used in order to analyze the samples that have been collected. For surface characterization, scintillation detectors are used, sometimes mounted on vehicles for surveys. Count rates are measured and compared to background count rates to identify contaminated areas. For boreholes, specific detectors are inserted into boreholes to measure contamination at depth. Techniques like in situ gamma spectrometry are employed to identify present radionuclides and measure their concentration. GPS systems are integrated to precisely map measurement points.