Merja Tanhua-Tyrkkö

Bio: Merja Tanhua-Tyrkkö is an academic researcher from VTT Technical Research Centre of Finland. The author has contributed to research in topics: Dissolution & Nuclear decommissioning. The author has an hindex of 4, co-authored 10 publications receiving 39 citations.

Determination of 14C, 55Fe, 63Ni and gamma emitters in activated RPV steel samples: a comparison between calculations and experimental analysis

Abstract: Determination of 14C, 55Fe, 63Ni and gamma emitters in two different types of activated reactor pressure vessel (RPV) steel samples were carried out. The gamma emitters were analysed using HPGe detectors with ISOCS and standard geometry calibrations. Two radioanalytical procedures for the 14C, 55Fe, 63Ni analysis were developed using inactive samples and activated samples were analysed using modified procedures. A Monte Carlo code was used for the modelling of the activation results. The obtained measured and calculated results were comparable.

Dissolution experiments of Na- and Ca-montmorillonite in groundwater simulants under anaerobic conditions

Abstract: The effects of simulant groundwater composition, pH and temperature on the dissolution and alteration of Na- and Ca-montmorillonite have been studied. Prior to the experiments, Wyoming type Na-montmorillonite, Swy-2, was purified to decrease the amount of accessory minerals. For Ca-montmorillonite experiments, the interlayer cation Na + of purified Swy-2 was exchanged with Ca 2+ . The batch experiments were conducted with the purified montmorillonites in simulated fresh and saline waters at 25°C and 60°C under anaerobic conditions in an Ar atmosphere. The concentrations of Si, Al, Fe and Mg were analysed from ultra-filtered solution samples with High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICP-MS) as a function of dissolution time. The pH evolution was also measured. The solid smectite phases were analysed with X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD analyses indicated that the nature of the smectite mineral did not change over 140 days. However, the experimental conditions, more or less, modified the structure (e.g. the layer stacking of montmorilllonite; the partial dissolution of the smectite), which cannot be detected by XRD but was evidenced by chemical data, and can be considered as a possible contributor to the stacking faults of the montmorillonite. The log rates (mol g -1 s -1 ), based on the dissolved amount of Si, varied between –10.64 and –12.13 depending on the experimental conditions.

Intercomparison exercise on difficult to measure radionuclides in activated steel: statistical analysis of radioanalytical results and activation calculations

Abstract: This paper reports the results obtained during an intercomparison exercise for the determination of difficult to measure radionuclides in activated reactor pressure vessel (RPV) steel samples. In total, eight laboratories participated analysing 14C, 55Fe and 63Ni activity concentrations in RPV steel. In addition, some laboratories also analysed 60Co activity concentrations. Corresponding activity concentrations were also determined using activation calculations. Robust statistical techniques were utilised for the analysis of the results according to ISO 13528 standard. The results showed good agreement for 55Fe and 63Ni results whereas 14C results had significant differences. 60Co results were in quite good agreement.

Preliminary Waste Characterization Measurements in FiR 1 TRIGA Research Reactor Decommissioning Project

Abstract: The objective of the study has been to verify the calculated residual activity in the decommissioning waste of the TRIGA Mark II–type research reactor FiR 1 in Finland. Knowledge of the radioactive...

Kinetics of Water-Rock Interaction

Abstract: Analysis of Rates of Geochemical Reactions.- Transition State Theory and Molecular Orbital Calculations Applied to Rates and Reaction Mechanisms in Geochemical Kinetics.- The Mineral-Water Interface.- Kinetics of Sorption-Desorption.- Kinetics of Mineral Dissolution.- Data Fitting Techniques with Applications to Mineral Dissolution Kinetics.- Nucleation, Growth, and Aggregation of Mineral Phases: Mechanisms and Kinetic Controls.- Microbiological Controls on Geochemical Kinetics 1: Fundamentals and Case Study on Microbial Fe(III) Oxide Reduction.- Microbiological Controls on Geochemical Kinetics 2: Case Study on Microbial Oxidation of Metal Sulfide Minerals and Future Prospects.- Quantitative Approaches to Characterizing Natural Chemical Weathering Rates.- Geochemical Kinetics and Transport.- Isotope Geochemistry as a Tool for Deciphering Kinetics of Water-Rock Interaction.- Kinetics of Global Geochemical Cycles.

Ab Initio Atomistic Thermodynamics of Water Reacting with Uranium Dioxide Surfaces

Abstract: Using first-principles simulations, we study the temperature- and pressure-dependent adsorption reaction of water on the flat (111) and (211) and (221) stepped surfaces of uranium dioxide. Our calc ...

Effects of α-radiation on a direct disposal system for spent nuclear fuel – (1) review of research into the effects of α-radiation on the spent nuclear fuel, canisters and outside canisters

Abstract: The Japanese geological disposal programme has started researching disposal of spent nuclear fuel (SF) in deep geological strata (hereafter “direct disposal of SF”) as an alternative management option other reprocessing followed by vitrification and geological disposal of high-level radioactive waste. In the case of direct disposal of SF, the radioactivity of the waste is higher and the potential effects of the radiation are greater. Specific examples of the possible effects of radiation include increased amounts of canister corrosion; generation of oxidizing chemical species in conjunction with decomposition of groundwater and accompanying oxidation of reducing groundwater; and increase in the dissolution rate of SF and the solubility of radionuclides. Focusing especially on the effects of α-radiation in safety assessment, this study has reviewed research into the effects of α-radiation on the SF, canisters and environment outside the canisters.