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Geostatistics perspectives for sampling optimization during radiological characterization
On Tuesday 23rd October 2018 at 3:30 pm
by Yvon Desnoyers, GEOVARIANCES
Dismantling and decommissioning of nuclear facilities or remediation of contaminated sites are industrial projects with huge challenges. Precise knowledge of the contamination state is required . Radiological evaluations have multiple objectives to be considered: determination of average activity levels, to allow the categorization of surfaces or volumes (sorted into different radioactive waste categories); location of hot spots (small areas with significant activity levels); and estimation of the source term (total activity) contained in soils or building structures. In addition, there are radiation protection and other logistics considerations.
This paper deals with feedback experience over years in the use of geostatistics and sampling optimization for the radiological characterization of various media (soils, concrete structures, process equipment, groundwater…), various activity levels (clearance, low and intermediate, high), and various sizes from very small areas (a few m2 or a few m3) to very large sites (at a country scale in post-accidental context).
Prediction reliability of chemically contaminated volumes of soils. Feedback on 23 former industrial sites (RECORD study) and lessons learnt for radioactively contaminated sites
On tuesday 23rd october 2018 at 4:50 pm
By Hélène Demougeot-Renard, eOde; Yvon Desnoyers, GEOVARIANCES; Bénédicte Couffignal, RECORD
A feedback on remediation of chemically contaminated sites was carried out for the French cooperative research network on waste and environment (RECORD). For 23 former industrial sites that were already cleaned up, volumes of contaminated soils predicted at the characterization stage were compared to those really extracted at the remediation stage. Reasons explaining the discrepancy between predictions and real remediated volumes were systematically studied, computing statistics on a list of criteria. The study shows that sampling plans and interpolation methods are two key factors for reducing the difference between estimation and real volumes. Major benefits are gained with geostatistical interpolation methods, provided that they are rigorously applied. General advice for characterization could be provided at the end of the study to increase the reliability of predictions.
The opportunity of transferring these results to the assessment of volumes of soils in radioactively contaminated sites was studied based on the experience of the authors on these kinds of sites. Due to large similarities, most of recommendations for characterizing chemical contaminations are found to be relevant for radioactive contaminations. Adaptations are nevertheless required to account for the specificities of radiological characterization, with the use of non-intrusive sub-surface measurements for a 2D mapping as a first step before soil sampling in boreholes to investigate depth migration.
In this paper, the methodology and the results of the feedback study on chemically contaminated sites are presented and followed by a discussion of the lessons learnt for radioactively contaminated sites, to increase reliability of the contaminated volumes predictions.
Geostatistics cost-benefit analyses for classification of waste during initial radiological characterization
On Wednesday 24th October 2018 at 10:10 am
By Yvon Desnoyers, GEOVARIANCES
The objective of radiological characterization  is to find a suitable balance between gathering data (constrained by cost, deadlines, accessibility or radiation) and managing the issues (waste volumes, levels of activity or exposure). It is necessary to have enough information to have confidence in the results without multiplying useless data.
Geostatistics processing of data considers all available pieces of information: historical data, non-destructive measurements and laboratory analyses of samples. The spatial structure modelling is then used to produce maps and to estimate the extent of radioactive contamination (surface and depth). Quantifications of local and global uncertainties are powerful decision-making tools for better management of remediation projects at contaminated sites, and for decontamination and dismantling projects at nuclear facilities. They can be used to identify hot spots, estimate contamination of surfaces and volumes, classify radioactive waste according to various radiological thresholds, estimate source terms, and so on.
This paper deals with feedback experience over years in the use of geostatistics for cost-benefit analyses about material segregation integrating estimation uncertainty and decision support impact. This approach puts the emphasis on one interesting geostatistics output: probability of exceeding a threshold.
Cetama working group n°10 contributions on sampling and radiological characterization
Poster – Topic 04 – Initial Radiological State Characterization
by Anne Courtadon, CEA Marcoule ; Yvon Desnoyers, GEOVARIANCES; Didier Dubot, CEA Marcoule; Guy Granier, INSTN Marcoule ; Catherine Ollivier-Dehaye, EDF ; Danièle Roudil, INSTN Marcoule
CETAMA is a major contributor in France for the validation and promotion of laboratory techniques (reference samples, inter-laboratory comparison…) through dedicated working groups. On a regular basis the half of the 30 groups are active and slowly rotated.
Working group n°10 (WG10) is one of the transversal groups (not dedicated to a specific laboratory technique) and deals with sampling and characterisation issues. After several years of official dormancy, but not technical one as background work was still done in other groups (WG27 in particular), it has been re-activated in 2012 with a lot of projects around three main themes:
– Characterisation of contaminated soils and building structures
– Sampling in laboratory
– Process and in-line sampling
Indeed, the French regulatory framework focuses more on final radiological state (Guides 14 and 24 from ASN) while operators needs are concentrated on the proper determination of the initial radiological state as it has huge consequences on dismantling and remediation scenarios, planning, budget and waste management.
CETAMA WG10 benefits from a permanent secretariat and a presidency. It is then structured in 3 sub-groups to tackle more efficiently the 3 identified themes. Thematic and plenary meetings are organized two or three times a year. Generally, between 15 and 20 persons attend these meetings in Paris, Lyon and Marcoule. More than 100 persons have participated at least once and belongs to the diffusion list. The audience is interestingly constituted representatives from all major nuclear organizations in France, as well as industrial companies, consultants and experts.