High-level Radioactive Materials Research Articles

Identification of Distorted Gamma-Ray Signature Patterns Using Digital Filtering and Auto-Associative Memory Implemented with a Hopfield Neural Network

The detection and identification of radioactive sources in search applications involve analyzing passive gamma-ray emissions from high-level radioactive materials. This process uses a mobile detector-spectrometer in a complex field test environment. Recently, the use of artificial intelligence for gamma-ray spectrum analysis has shown promising results. However, challenges persist in identifying isotopic signatures from spectral measurements that may be distorted due to source shielding, random variations in natural radioactive background, or insufficient measurement time to obtain clear spectral lines. This paper presents a novel intelligent signature recognition method that combines digital filtering techniques with an artificial Hopfield Neural Network (HNN). The HNN leverages auto-associative memory to store training sample patterns and match them with incoming gamma spectra from distorted sources. It restores the testing sources’ measurements by finding the closest matching signature patterns in the spectral library. Before HNN recognition, the measured spectrum undergoes preprocessing with a digital image filter to reduce fluctuations. Performance of the proposed method is evaluated using a set of gamma-ray spectra measured with a sodium iodide detector. The data collected include measurements from six pure samples: 241Am, 60Co, 137Cs, 192Ir, 239Pu, and 235U, which are used for training and validation (i.e. six cases). Additionally, the data set contains 24 distorted synthesized sources with various fluctuating backgrounds. Test results demonstrate the potential of the proposed method to accurately recognize the correct isotope with high precision, achieving an accuracy rate exceeding 85%. Furthermore, the proposed method exhibits superior performance compared to the conventional multiple regression fitting and simple feedforward neural network methods.

Investigations of aged metal seals for transport package safety assessment

Abstract. Acceptable limits for activity release from transport casks for high-level radioactive material specified in the IAEA regulations must be kept by the integrity of cask body and the cask sealing system. BAM – the German competent authority for mechanical, thermal and containment assessment of packages liable for approval – verifies the activity release compliance with the regulatory limits. One of the fundamental aspects in assessment is the specification of conservative package design leakage rates. To ensure the required package tightness for both storage and transport of the cask before and after storage, usually metal seals of the HELICOFLEX® type are used. Due to long-term use, the seal behaviour is influenced by temperature and time. The mechanical and thermal loadings associated with the routine, normal and accident conditions of transport specified in the regulations can have a significant effect on the leak tightness of the sealing system. Whereas the safety for application of new, non-aged HELICOFLEX® seals is verified sufficiently, there are still technical data gaps concerning the efficiency of aged HELICOFLEX® seals. BAM performed experiments to learn more about the sealing efficiency of aged HELICOFLEX® seals with aluminium and silver outer jackets. The seals were compressed in test flanges, and for artificial ageing the complete flange systems were stored in an oven for several months at a high temperature. During the compression and decompression tests after the ageing, load-deformation characteristics of the seals and leakage rates were measured. With these tests a load situation was simulated, which can occur in the regulatory drop test of the cask: under high-impact loads the bolted lid can lift a little for a short moment, allowing a little movement of the seal so that the contact area can change before compressing again. The poster presentation will show details about test conditions and first results.

First-principles prediction of universal relation between exchange current density and adsorption energy of rare-earth elements in a molten salt

Using first-principles calculations we developed, for the first time, atomistic-level kinetics model to identify a key descriptor controlling electrochemical behaviors of various rare-earth ions solvated in molten salt electrolyte depositing on a solid electrode. We identified that the thermodynamic adsorption energies of rare-earth elements in the metallic electrode have a universal relation with exchange current densities. Our studies can be very useful guide to separate high-level radioactive nuclear materials and industrially valuable rare-earth materials, which can substantially relieve the environmental protection issues in nuclear waste disposal.

Kinetics of oxidation of 30% TBP solutions in С13 diluent with nitric acid: Effect of temperature and γ-irradiation

The behavior of the two-phase system consisting of a 30% solution of tri-n-butyl phosphate (TBP) in a paraffin diluent (C13) and a 12 M aqueous HNO3 solution was studied in the temperature interval from 70 to 110°С. The parameters of thermolysis of TBP solutions in C13 in the reaction with HNO3 in open vessels were determined with the aim of evaluating the explosion hazard of the system in the course of extraction reprocessing of high-level radioactive materials. Solutions of TBP in C13 in the two-phase systems are characterized in the examined temperature interval by more intense gas evolution compared to that from the singlephase systems.

Transient thermal analysis for radioactive liquid mixing operations in a large-scaled tank

A transient heat balance model was developed to assess the impact of a Submersible Mixer Pump (SMP) on radioactive liquid temperature during the process of waste mixing and removal for the high-level radioactive materials stored in Savannah River Site (SRS) tanks. The model results will be mainly used to determine the SMP design impacts on the waste tank temperature during operations and to develop a specification for a new SMP design to replace existing long-shaft mixer pumps used during waste removal. The present model was benchmarked against the test data obtained by the tank measurement to examine the quantitative thermal response of the tank and to establish the reference conditions of the operating variables under no SMP operation. The results showed that the model predictions agreed with the test data of the waste temperatures within about 10%.

Investigation of corrosion behaviours of high level waste container materials in simulated groundwater in China

Appropriate high level radioactive waste container materials in China are still under investigation. The corrosion behaviours of four types of materials (carbon steel Q235, aluminium alloy 2024, copper and stainless steel SUS 304) in simulated groundwater at room temperature were investigated. The corrosion rate was measured through the weight loss method. The chemical composition of corrosion product films formed on the surface of materials was investigated by means of X-ray diffraction and energy dispersive X-ray spectroscopy. The results showed that there was no crevice and pitting corrosion for carbon steel after one year of immersion; the corrosion was dominated by general corrosion, the composition of the corrosion product film being mainly γ-FeOOH, as well as Fe3O4. Copper underwent slight crevice corrosion, but aluminium alloy 2024 suffered serious localised corrosion. No corrosion was observed on stainless steel SUS 304. The presence of oxygen promoted crevice corrosion of copper and aluminium alloy 2024.

First-principles calculations of the thermodynamic properties of transuranium elements in a molten salt medium

We utilized first-principles density-functional-theory (DFT) calculations to evaluate the thermodynamic feasibility of a pyroprocessing methodology for reducing the volume of high-level radioactive materials and recycling spent nuclear fuels. The thermodynamic properties of transuranium elements (Pu, Np and Cm) were obtained in electrochemical equilibrium with a LiCl-KCl molten salt as ionic phases and as adsorbates on a W(110) surface. To accomplish the goal, we rigorously calculated the double layer interface structures on an atomic resolution, on the thermodynamically most stable configurations on W(110) surfaces and the chemical activities of the transuranium elements for various coverages of those elements. Our results indicated that the electrodeposition process was very sensitive to the atomic level structures of Cl ions at the double-layer interface. Our studies are easily expandable to general electrochemical applications involving strong redox reactions of transition metals in non-aqueous solutions.

Introduction of “Guideline for Radiation Shielding Evaluation of Transport Casks by Monte Carlo Method” -sample calculation-2: NFT-14P wet type cask-

Introduction of “Guideline for Radiation Shielding Evaluation of Transport Casks by Monte Carlo Method” is planned in Japan by National Maritime Research Institute (NMRI) because so for Monte Carlo codes are not popular to use for these kind of shielding analysis. Target of this Guideline is transport casks loading high level radioactive materials such as spent fuel. With a view to preparing the backup data to support the Guideline, we perform the radiation shielding calculation by using MCNP code for NFT-14P wet type cask which is the representative spent fuel cask of Japan. The measurements of dose rate for this cask were performed in 2009 by NMRI. The measurement results for neutrons and gamma rays for the cask loaded 14 PWR spent fuels were shown. All calculations pass the relative deviation criteria. With regard to 10 statistical checks provided by the MCNP output, some articles are not satisfied with the criteria in this study. However, the calculated dose rate obtained by the point detector and the track length estimator are in good agreement. In addition, in comparison with the measurements, the axial distribution profiles of the dose rate are in good agreement. These trends represent that the calculated dose rate are acceptable as a reasonable analysis result. In many cases, the calculated dose rate is larger than the measured dose rate, and therefore the calculation procedure presented in the Guideline is conservative and useful for the purpose of the safety analysis.

Activity Coefficients of di-(2-ethylhexyl) Phosphoric Acid in Select Diluents

This work characterizes the non-ideal behavior of the solvent extraction agent di-(2-ethylhexyl) phosphoric acid (HDEHP), constituting one piece of an effort to develop increasingly accurate models of advanced fuel separation processes such as TALSPEAK. Robust models are particularly important for processing high-level radioactive material in order to minimize the generation of secondary waste and to ensure reliable process control. Here, vapor pressure osmometry (VPO) data on binary solutions of HDEHP in toluene, dodecane, or cyclooctane yields the activity coefficients for each component after analysis. Initially, diluent activity data is obtained using the VPO results and then modeled using Scatchard-Hildebrand theory to provide the activity coefficients for HDEHP.

THE NUCLEAR ENERGY OUTLOOK—A NEW BOOK FROM THE OECD NUCLEAR ENERGY AGENCY

This paper summarizes the key points of a report titled Nuclear Energy Outlook, published in 2008 by the Nuclear Energy Agency of the Organization for Economic Cooperation and Development, which has 30 member nations. The report discusses the commitment of many nations to increase nuclear power generating capacity and the potential rate of building new electricity-generating nuclear plants by 2030 to 2050. The resulting decrease in carbon dioxide emissions from fossil fuel combustion resulting from an increase in nuclear power sources is described. Other topics that are discussed include the need to develop non-proliferative nuclear fuels, the importance of developing geological disposal facilities or reprocessing capabilities for spent nuclear fuel and high-level radioactive waste materials, and the requirements for a larger nuclear workforce and greater cost competitiveness for nuclear power generation.

Kinetics of thermochemical reaction of TBP solutions in HCBD with nitric acid in single-phase systems

The kinetics of thermochemical reaction of 30% TBP in hexachlorobutadiene (HCBD) saturated with HNO3 (1.35 M HNO3) in two-phase systems with 12 M HNO3 at temperatures from 90 to 115°C was studied. The kinetic parameters of thermolysis of organic solutions of TBP in HCBD, contacting with HNO3 in open and closed vessels, were determined experimentally for the subsequent estimation of the explosion hazard of these systems under conditions of extraction recovery of high-level radioactive materials. It was shown that, in two-phase systems, solutions of TBP in HCBD exhibit increased resistance to thermochemical oxidation with nitric acid in comparison with hydrocarbon solutions of the extractant in the entire temperature range.

Book Reviews: Uncertainty Underground: Yucca Mountain and the Nation's High-Level Nuclear Waste. A. M. Macfarlane and R. C. Ewing, eds. 2006. Island Press, Washington, DC. 416 pp. $72 cloth, $29 paperback.

"Book Reviews: Uncertainty Underground: Yucca Mountain and the Nation's High-Level Nuclear Waste. A. M. Macfarlane and R. C. Ewing, eds. 2006. Island Press, Washington, DC. 416 pp. $72 cloth, $29 paperback.." Environmental Practice, 9(4), pp. 281–282

Digital positron lifetime spectrometer for measurements of radioactive materials

A digital positron lifetime spectrometer for the measurements of high-level radioactive materials has been constructed and successfully tested. The equipment consists of a digital oscilloscope and three movable scintillation detectors operating in triple-coincidence mode. The time resolution of 188 ps full-width at half-maximum (FWHM) is achieved for the positron lifetime measurements of radioactive specimens. The set-up has been calibrated, optimised and tested by comparison of the results of well-known material with and without high background radiation. This paper reports on the radiological shielding, electronic update, stability and the performance of this new spectrometer that has been installed in the controlled area of the Laboratory for High and Medium level Activity (LHMA) at SCK•CEN.

A multiple detector approach to radiological hot cell nuclear and chemical remote measurements

A remote measurement system has been constructed for in-situ gamma and beta isotopic characterization of highly radioactive nuclear material in hostile environments. A small, collimated, planar CdZnTe detector is used for gamma-ray spectroscopy. Spectral resolution of 2% full-width-at-half-maximum at 662 keV has been obtained remotely using risetime compensation and limited pulse shape discrimination (PSD). Isotopic measurement of high-energy beta emitters was accomplished with a ruggedly made, deeply depleted, surface barrier silicon detector. The primary function of the remote nuclear screening system is to provide fast qualitative and quantitative isotopic assessment of high-level radioactive material.

GIS for Radioactive Materials Transportation

Abstract: Stimulated by debate surrounding the potential siting of a national repository, critical issues related to transporting high‐level radioactive material (HLRM) are emerging. Techniques such as route characterization and risk/impact analysis are being developed or refined to facilitate routing decisions. Key inputs to analysis include demographic data, environmental features, and transportation system characteristics—inputs that are spatial in nature and difficult to manage without appropriate technology. This paper demonstrates the application of geographic information systems (GISs) to HLRM transportation analysis and identifies three transportation risk‐analysis methodologies: comparative study, worst‐case assessment, and probabilistic risk assessment. While known for its ability to integrate, manage, process, and effectively present large amounts of complex spatial data, the GIS technology potential for HLRM transportation risk analysis has not been fully exploited. This potential is demonstrated here in applications of GIS technology to develop estimates of resident and visitor population and ecologically sensitive areas along transportation corridors. The applicability of GIS technology is also illustrated through a discussion of linking models for risk assessment and examples of effective display of data and results.

Project salt vault: Design of equipment

Handling, transfer and storage techniques applicable to high-level solid waste disposal operations have been successfully demonstrated with short-cooled ETR fuel assemblies. The design of equipment for the encapsulation of the fuel assemblies, cross-country shipment, transfer from the surface to the mine level, movement within the mine, and transfer into storage are described. The operations are unique in that high-level radioactive materials are transferred from a shipping cask on the surface to the mine level 1000 ft below without the use of hot cells.