Complete dissolution of solid matrices using automated borate fusion in support of nuclear decommissioning and production of reference materials

Development of reference material for quality control of uranium analysis in marine sediments

Environmental radioactivity monitoring is strengthening due to public concerns over radioactive contamination since the Fukushima nuclear power plant accident. Therefore, various research laboratories, institutes, and universities have been conducting environmental radioactivity surveys around nuclear power plants (NPPs). However, the reliability of the results continues to trigger controversy in society. This study was conducted to develop reference material (RM) for the quality control of 238U and 234U analyses in marine sediments. The RM was prepared according to ISO Guides 31, 34, and 35. A homogeneity test of the marine sediment RM was implemented by analyzing two batch samples from ten bottles using multiple acid digestion and alkali fusion, respectively. We found that the 238U and 234U reference values of the RM were 43.0 ± 1.7 Bq kg-1(k=1) and 41.5 ± 1.9 Bq kg-1(k=1), respectively. This marine sediment RM will be useful for the quality control of analytical methods for similar samples and proficiency tests.

Capture and electrochemical conversion of CO2 in molten alkali metal borate-carbonate blends

A family of blended compositions of molten mixed lithium and sodium borate (Li_1.5Na_1.5BO₃) and eutectic lithium-potassium carbonate (Li_1.24K_0.76CO₃) salts has been introduced as reversible carbon dioxide absorbents and as media for CO₂ electrolysis for carbon conversion. Material properties, temperature effects and kinetics of CO₂ uptake were examined. Li, Na borate can absorb up to 7.3 mmol g^-1 CO₂ at 600 °C. The blended borate-carbonate compositions are molten in the 550-600 °C temperature range, with viscosity adjustable to within a 10-1000 Pa s window depending on the borate/carbonate ratio. The blends can withstand cyclic temperature and CO₂ pressure swings without significant deterioration of their CO₂ uptake capabilities. Addition of eutectic carbonate into mixed Li, Na borate salts lowers overall CO₂ uptake due to the lower solubility of CO₂ in carbonate. However, addition of the eutectic lowers the temperature of the pressure swing operation and dramatically accelerates the CO₂ uptake during the initial stage of the absorption, potentially enabling a faster cycling. Electroreduction of CO₂ and carbon deposition on a galvanized steel cathode was more effective with increasing carbonate fraction in the molten alkali borate/carbonate blend. Blended borate/carbonate compositions with 50-60% borate content possessed sufficiently high loading capacity for CO₂ and simultaneously enabled maximum carbon product yield and Coulombic efficiency. Most of the recovered carbon product was shown to be in the form of multiwalled carbon nanotube.

Sustainable Decommissioning Strategies for Nuclear Power Plants: A Systematic Literature Review

The decommissioning of nuclear power plants (NPPs) is rapidly increasing because NPPs are not only no longer profitable in many cases but are also being decommissioned due to a lack of public acceptance or political reasons in many countries, particularly in Europe, following the explosion of the Fukushima Daiichi NPP. Accordingly, a significant body of research has focused on achieving safe, environmentally sound, and sustainable decommissioning in many countries where there is demand for NPP decommissioning. In order to achieve sustainable decommissioning that restores the NPP site to its pre-NPP environmental state, it is necessary to understand the safety, technology, and cost aspects as well as having the process and strategy to systematically promote them. Although there are a limited number of countries with experience and knowledge in the management of decommissioning multiple NPPs, researchers in countries just starting NPP decommissioning need diverse research information on how to formulate a sustainable decommissioning strategy as well as related factors. In particular, a systematic review of decommissioning strategies, such as DD, ID, and ET, and the influencing factors associated with each strategy is needed from the researcher’s point of view. In this regard, this study reviews the research literature on decommissioning strategies for nuclear power plants with a sustainable perspective. A systematic method involving a meta-analysis is used. The results of this study confirm that many researchers are most interested in DD and are dealing with ID and ET at the same level, but in reality, DD and ID are being adopted at similar rates. Thus far, only three ETs have been adopted in the United States. Most countries that have adopted ID are deemed to have been influenced by political decisions.

Development of 3H, 14C, 41Ca, 55Fe, 63Ni radiochemical analysis methods in activated concrete samples

Development of 3H, 14C, 41Ca, 55Fe and 63Ni radiochemical analysis methods were carried out independently by two laboratories using both inactivate and activated concrete samples. Two preliminary radioanalytical procedures for the non-volatile radionuclides (41Ca, 55Fe, 63Ni) and one Thermal oxidation method for the volatile radionuclides (3H, 14C) were developed. The difficulties in the method development and analysis of results are discussed.

Agile fusion method for the determination of Pu isotopes in diverse sediments

Atmospheric nuclear testing has occurred worldwide resulting in trace amounts of plutonium (Pu) isotopes in soils and sediments across the globe. Soils and sediments can vary greatly in both physical and chemical properties within close geographic regions presenting a major challenge for sample preparation in the analysis of fallout radionuclides. It is vital to have a rapid, agile method for the complete digestion of samples containing refractory Pu particles to address this challenge. A radioanalytical procedure for the analysis of Pu isotopes in soils/sediments has been developed improving sample preparation using fusion. This is done by eliminating the need for pre-dissolution combustion to remove organic material and providing greater application to a diverse range of samples including those of metal-bearing mineralogy. The integration of borate and peroxide flux materials creates a sample dissolution procedure that is greater than the sum of its parts. This method is applicable to the analysis of ^239/240Pu in soil/sediment samples with a sample mass of 3 g, ranging from 0.05 to 5000 mBq/g achieving ²⁴²Pu tracer recoveries between 50 and 94%, with a trace-level detection limit of 0.04 mBq/g and measurement uncertainties down to 19%; adjustable to measurement priorities with variation in count time, background counts, chemical recovery and total activity of the sample. This sample preparation technique can be utilized with complementary analysis of alpha spectrometry or ICP-MS. Achieving these parameters provides a highly adaptable standard method for ^239/240Pu in soil/sediment analysis applicable to samples from radioecological research at trace environmental levels to emergency response scenarios with 48-h turn-around producing highly repeatable, succinct and high-quality analysis.