In-toto non-destructive assay methodology for the elimination of metallic waste from particle accelerators after melting.

Melting of metallic waste reduces the waste volume, allows more accurate radiological characterization, and minimizes handling at the waste production site. This paper proposes a new non-destructive assay methodology to radiologically characterize low- and intermediate-level (LILW) waste before melting. A non-destructive assay technique is developed and qualified using geometry optimization technique and sample analysis after melting. Additionally, we present an operational methodology to predict the activity values of the major gamma emitters based on the average dose rate measurements.

Radiological characterisation for the clearance of burnable waste produced at CERN.

Burnable waste produced at CERN during upgrading, maintenance and dismantling campaigns may be contaminated with radioactive nuclides produced through activation of accelerator components. Here, we present a methodology for the radiological characterisation of burnable waste, which takes into account the wide range of potential activation conditions (beam energy, material composition, location, irradiation and waiting time). Waste packages are measured using a total gamma counter, with the sum of clearance limit fractions estimated using the fingerprint method. Gamma spectroscopy was found to be unsuitable for classifying this waste due to the long counting times required to identify many expected nuclides, but was retained for quality control purposes. Using this methodology, a pilot campaign was performed in which we were able to clear 13 m3 of burnable waste as conventional non-radioactive waste.

Skin dose contamination conversion coefficients. Benchmark with three simulation codes.

Handling of radioactive material by operators can lead to contamination at the surface of the skin in case of an accident. The quantification of the dose received by the skin due to a contamination scenario is performed by means of dedicated dose coefficients as it is the case for other radiation protection dose quantities described in the literature. However, most available coefficients do not match realistic scenarios according to state-of-the-art of science and technology. Therefore, this work deals with dedicated dose conversion factors for skin contamination. Since there is an increasing demand on dose coefficients in general, these specific coefficients can be used for various calculations in radiation protection. In this work a method to evaluate such coefficients for the skin contamination dose related to photons, electrons, positrons, alpha and neutron particles is proposed. The coefficients are generated using Monte-Carlo simulations with three well established calculation codes (FLUKA, MCNP, and GEANT4). The results of the various codes are compared against each other for benchmarking purposes. The new dose coefficients allow the computation of the skin received dose, in the case of skin contamination scenario of an individual, taking into account the decay radiation of the radionuclides of interest. To benchmark the quantity derived here, comparisons of radionuclide contamination doses to the skin using the VARSKIN code available in the literature are performed with the results of this work.

CERN-MEDICIS: A Review Since Commissioning in 2017.

The CERN-MEDICIS (MEDical Isotopes Collected from ISolde) facility has delivered its first radioactive ion beam at CERN (Switzerland) in December 2017 to support the research and development in nuclear medicine using non-conventional radionuclides. Since then, fourteen institutes, including CERN, have joined the collaboration to drive the scientific program of this unique installation and evaluate the needs of the community to improve the research in imaging, diagnostics, radiation therapy and personalized medicine. The facility has been built as an extension of the ISOLDE (Isotope Separator On Line DEvice) facility at CERN. Handling of open radioisotope sources is made possible thanks to its Radiological Controlled Area and laboratory. Targets are being irradiated by the 1.4 GeV proton beam delivered by the CERN Proton Synchrotron Booster (PSB) on a station placed between the High Resolution Separator (HRS) ISOLDE target station and its beam dump. Irradiated target materials are also received from external institutes to undergo mass separation at CERN-MEDICIS. All targets are handled via a remote handling system and exploited on a dedicated isotope separator beamline. To allow for the release and collection of a specific radionuclide of medical interest, each target is heated to temperatures of up to 2,300°C. The created ions are extracted and accelerated to an energy up to 60 kV, and the beam steered through an off-line sector field magnet mass separator. This is followed by the extraction of the radionuclide of interest through mass separation and its subsequent implantation into a collection foil. In addition, the MELISSA (MEDICIS Laser Ion Source Setup At CERN) laser laboratory, in service since April 2019, helps to increase the separation efficiency and the selectivity. After collection, the implanted radionuclides are dispatched to the biomedical research centers, participating in the CERN-MEDICIS collaboration, for Research & Development in imaging or treatment. Since its commissioning, the CERN-MEDICIS facility has provided its partner institutes with non-conventional medical radionuclides such as Tb-149, Tb-152, Tb-155, Sm-153, Tm-165, Tm-167, Er-169, Yb-175, and Ac-225 with a high specific activity. This article provides a review of the achievements and milestones of CERN-MEDICIS since it has produced its first radioactive isotope in December 2017, with a special focus on its most recent operation in 2020.

Photons fluence to local skin Dose coefficients and benchmark with three Monte-Carlo codes. Application to the computation of radioactive material transport limits.

Fluence to Local Skin Dose Conversion Coefficients (LSD-CC) are radiological protection quantities used for external radiation exposures which allow the conversion of particle fluences into local skin equivalent dose. The International Commission on Radiological Protection published LSD-CC for electrons with an energy range from 10 keV to 10 MeV. However, the literature does not address these radiation protection quantities for all particle types, in particular for photons. In this article, computed LSD-CC values for photons are presented which enrich the literature and are of interest for the radiation protection community. As an example for an application of the use of the computed LSD-CC values, the IAEA A1/A2 working group, which supports the review of the international regulation related to the transport of radioactive material, has decided to estimate the dose to the skin using such coefficients. In this publication, LSD-CC for photons are computed and benchmarked using GEANT4, FLUKA and MCNP. In addition, the FLUKA Monte-Carlo calculation code is used to compute the LSD-CC values for electrons and positrons to compare with existing data in the literature and validate the presented models. As one application of these LSD-CC values, the transfer functions for calculating the IAEA A-values are determined using the LSD-CC and are compared to a one-step direct calculation method.

Calculation and benchmark of fluence-to-local skin equivalent dose coefficients for neutrons with FLUKA, MCNP, and GEANT4 Monte-Carlo codes.

Dose equivalent limits for single organs are recommended by the ICRP (International Commission for the Radiological Protection publication 103). These limits do not lend themselves to be measured. They are assessed by convoluting conversion factors with particle fluences. The Fluence-to-Dose conversion factors are tabulated in the ICRP literature. They allow assessing the organ dose of interest using numerical simulations. In particular, the literature lacks the knowledge of local skin equivalent dose (LSD) coefficients for neutrons. In this article, we compute such values for neutron energies ranging from 1 meV to 15 MeV. We use FLUKA, MCNP and GEANT4 Radiation transport Monte-Carlo simulation codes to perform the calculations. A comparison between these three codes is performed. These calculated values are important for radiation protection studies and radiotherapy applications.

Qualification of the activities measured by gamma spectrometry on unitary items of intermediate-level radioactive waste from particle accelerators.

In the frame of maintenance, upgrade and dismantling activities, activated equipment are removed from the accelerator complex and require characterization in view of their disposal as radioactive waste. The characterization process consists of a series of radiation measurements, complemented by analytical studies, which quantify the activity of radionuclides inside an object. A fraction of the radioactive waste produced at CERN presents contact dose-rates higher than 100 µSv/h, and can therefore be classified as LILW Waste ("Low and intermediate level radioactive waste"). These objects, due to the activation mechanisms, are often subject to large activity heterogeneities. The quantification of gamma-emitting radionuclides is typically performed by gamma spectrometry, under the assumption of homogeneous distributions of activity within an object. However, this assumption can lead to underestimating the activity value of such radionuclides. In this article we perform a gamma spectrometry qualification in order to quantify the impact of assuming homogenous distribution.

Qualification of gamma spectrometry measurement for the radiological characterization of mixed VLLW cables in particle accelerators.

In the framework of maintenance activities in particle accelerators, such as upgrades and dismantling, a large number of activated equipment are removed from the accelerator complex and require characterization in view of their disposal as radioactive waste. In particular, cables can be of different types. This feature induces variations of the efficiency calibration curves due to the variation of the material composition, source distribution and density. Hence, quantifying the activities of the gamma-emitting radionuclides can be quite challenging for mixed cables. In this article, we propose a new qualification methodology, based on gamma spectrometry, in order to assess the activity results uncertainties of gamma-emitting radionuclides. This new methodology is developed to define the envelop efficiency calibration curves and allows for the establishment of more accurate activity values with their corresponding uncertainties.

An enhanced characterization process for the elimination of very low level radioactive waste in particle accelerators.

The elimination of very low level waste towards the French national repository requires their radiological characterization to estimate the radionuclide inventory and the associated activities within a waste package. Such characterization is performed by means of activation calculations and measurements. Two elimination projects have been identified at CERN, to dispose of bulk metallic waste and cables activated in the CERN accelerator complex. Based on the experience gained over the last 4 years, we develop a large scale elimination process to dispose of such types of activated equipment. A program for quality controls has therefore been developed through a novel software tool whose purpose is to compute the radiological data required by the repository for the acceptance of the waste as well as performing quality controls.

Classification of radiological objects at the exit of accelerators with a dose-rate constraint.

Maintenance activities and operations of high-energy particle accelerators can lead to the collection of radioactive equipment as well as waste materials. In order to ensure their proper classification as radioactive or non-radioactive, one has to quantify the activities of radionuclides produced. According to the regulatory requirements in Switzerland, these activities need to be compared with nuclide-specific clearance limits. In particular, a new set of clearance limits was introduced by the Swiss authorities in January 2018, leading to more conservative values for a number of relevant radionuclides. We describe in this paper a new methodology based on dose-rate measurements to classify potentially radioactive objects at the exit of the CERN accelerator complex. This methodology concerns the specific material compositions typically found at CERN and takes into account the latest clearance limits introduced by the Swiss authorities.

A new gamma spectroscopy methodology based on probabilistic uncertainty estimation and conservative approach.

The gamma spectroscopy technique is commonly used in many applications to evaluate the activity of gamma emitters in a given sample. This assessment of activity is of particular interest for the disposal of radioactive waste or for clearance purposes. However, for these specific applications, one needs to show that the evaluated activities are reasonably conservative. This paper shows an application of a methodology developed to quantify the efficiency calibration curve uncertainties originating from a test case sample and its associated geometry modelling. Therefore, the effects of enclosing geometries on the activity measurement results are discussed. The purpose is to provide an example of uncertainty analysis for an approach that could be applied to other studies in which a conservative estimation of the activity is required.

A novel technique for the optimization and reduction of gamma spectroscopy geometry uncertainties.

Material activation can sometimes cause large heterogeneities in the distribution of radioactivity (hotspots). Moreover, the sample geometry parameters are not always well known. When performing gamma-spectroscopy to quantify the radionuclide inventory in activated materials, often predefined models are used to represent the sample geometry (dimensions, source-to-detector distance, material type) and their activity distribution, for efficiency calibration. This simplification causes uncertainties of the efficiency curves associated with the model and consequently, to the activity results. In this paper, we develop a new approach, based on ISOCS/LabSOCS to quantify and reduce uncertainties originating from the geometry model. The theory is described in this document and an experimental case is discussed.