scholarly journals DOSIMETRY MODELING FOR PREDICTING RADIOLYTIC PRODUCTION AT THE SPENT FUEL-WATER INTERFACE

2006 ◽  
Author(s):  
W.H. Miller
Keyword(s):  
Water Interface ◽  
Spent Fuel ◽  
Radiolytic Production

Experimental determination and chemical modelling of radiolytic processes at the spent fuel/water interface

2000 ◽  
Vol 88 (9-11) ◽  
Author(s):  
J. Bruno ◽  
E. Cera ◽  
U.-B. Eklund ◽  
T. Eriksen ◽  
M. Grivé ◽  
...  
Keyword(s):  
Redox Potential ◽  
Redox System ◽  
Water Interface ◽  
Spent Fuel ◽  
Gamma Radiolysis ◽  
Chemical Modelling ◽  
Bulk System ◽  
The Stability ◽  
Radionuclide Release ◽  
Radiolytic Production

The spent fuel matrix constitutes a dynamic redox system, due to the time-dependent generation of oxidants and reductants at the spent fuel/water interface by alpha, beta and gamma radiolysis. In this context it is critical to understand the main processes and mechanisms that control the radiolytic production of redox components at this interface and their impact on the stability of the UOIn order to achieve this, a series of carefully controlled experiments have been carried out in order to determine the time dependence of the radiolytic HThe results of these experiments indicate quite a consistent and reproducible behaviour of the radiolytically generated reductants and oxidants. The results indicate that it is possible to define an equilibrium redox potential for the main redox pairs in the bulk system and that the experimentally determined radionuclide release can be rationalised in terms of the system redox potential.

On the Role of H2 as an Inhibitor of UO2 Matrix Dissolution

2007 ◽  
Author(s):  
Juan Merino ◽  
Xavier Gaona ◽  
Lara Duro ◽  
Jordi Bruno ◽  
Aurora Marti´nez-Esparza
Keyword(s):  
Chemical Composition ◽  
Partial Pressure ◽  
Water Radiolysis ◽  
Water Interface ◽  
Spent Fuel ◽  
Dissolution Rates ◽  
Term Stability ◽  
Long Term Stability

The study of spent fuel behaviour under disposal conditions is usually based on conservative approaches assuming oxidising conditions produced by water radiolysis at the fuel/water interface. However, the presence of H2 from container corrosion can inhibit the dissolution of the UO2 matrix and enhance its long-term stability. Several studies have confirmed the decrease in dissolution rates when H2 is present in the system, although the exact mechanisms of interaction have not been fully established. This paper deals with a radiolytic modelling exercise to explore the consequences of the interaction of H2 with radicals generated by radiolysis in the homogeneous phase. The main conclusion is that in all the modelled cases the presence of H2 in the system leads to a decrease in matrix dissolution. The extent of the inhibition, and the threshold partial pressure for the inhibition to take place, both depend in a complex way on the chemical composition of the water and the type of radiation present in the system.

Modelling Experimental Results on Radiolytic Processes at the Spent Fuel Water Interface. I. Radiolysis Products and U Release

2003 ◽  
Vol 807 ◽  
Author(s):  
J. Bruno ◽  
E. Cera ◽  
T. E. Eriksen ◽  
M. Grivé ◽  
S. Ripoll
Keyword(s):  
Aqueous Phase ◽  
Initial Increase ◽  
Water Interface ◽  
Spent Fuel ◽  
Constant Concentration ◽  
Radiolysis Products ◽  
Reducing Conditions ◽  
Anoxic Environment ◽  
Bicarbonate Solutions

ABSTRACTExperimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2 surfaces in poising the redox state of solid/water systems. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions.The collected data so far, indicate that production and fate of radiolysis products follow the same trends independently on the solution composition used in the tests. Hydrogen and oxygen concentrations show an initial increase with time until reaching a constant concentration. The trend observed for hydrogen peroxide is a decrease at short contact times to reach again a constant concentration with time. These steady-states indicate an overall balance of the generated radiolytic species.Modelling work indicates that uranium dissolution is controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase is governed by the precipitation of schoepite.These results are determinant to highlight that reducing conditions are restored in the aqueous phase in relatively short periods of time and at short distances away from the dynamic redox spent fuel/water interface.

Observation of Studtite and Metastudtite on Spent Fuel

2002 ◽  
Vol 757 ◽  
Author(s):  
Bruce McNamara ◽  
Edgar Buck ◽  
Brady Hanson
Keyword(s):  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Water Interface ◽  
Spent Fuel ◽  
Surface Corrosion ◽  
Air Water Interface ◽  
Extensive Surface ◽  
Two Phases ◽  
Fuel Particles ◽  
Short Times

ABSTRACTWe have characterized uranyl peroxide phases on commercial spent nuclear fuel (SNF) samples formed under immersion conditions. At short times, crystallites of metaschoepite were observed on the hydrated fuel particles. Over a two-year period, all evidences of metaschoepite disappeared and in many samples, the fuel particles appeared to be coated by a new alteration phase. Additionally, milligrams of corroded fuel aggregates were observed at the sample air-water interface in each sample. The corrosion phases on bulk fuel and on the suspended materials were examined by SEM, EDX, and XRD and were identified as studtite (UO4·4H20) and metastudtite (UO4·2H20), respectively. The reason for the partitioning of the two phases is unclear at this time. SEM micrographs of the bulk powders indicated extensive surface corrosion and fragmentation of particles.

Enhancement of Zirconolite Dissolution Due to Water Radiolysis

2006 ◽  
Vol 985 ◽  
Author(s):  
Nelly Toulhoat ◽  
Nelly Toulhoat ◽  
Nathalie Moncoffre ◽  
Pierre Toulhoat ◽  
Christophe Jegou ◽  
...  
Keyword(s):  
Charged Particle ◽  
Surface Water ◽  
Pure Water ◽  
Water Radiolysis ◽  
Water Interface ◽  
Spent Fuel ◽  
Enhanced Dissolution ◽  
Order Of Magnitude ◽  
Spent Fuel Reprocessing ◽  
Fuel Reprocessing

AbstractZirconolite is a candidate host material for conditioning minor tri- and tetra-valent actinides arising from enhanced nuclear spent fuel reprocessing and partitioning, in the case of disposal of the nuclear waste. Its chemical durability has been studied here under charged particle-induced radiolysis (He2+ and proton external beams) to identify the possible effects of water radiolysis on the dissolution rates in pure water and to describe the alteration mechanisms. Two experimental geometries have been used in order to evaluate the influence of the following parameters: solid irradiation, water radiolysis. In the first geometry the beam gets through the sample before stopping at the surface/water interface. In the second one the beam stops before the surface/water interface. Results on the elemental releases due to the enhanced dissolution of the zirconolite surface during charged particle-induced irradiation of water are presented. Under radiolysis, an increase of one order of magnitude is observed in the Ti, Zr and Nd elemental releases. No difference in the total elemental releases can be noticed when the solid is also irradiated.

Long Term Modelling of Spent Fuel Oxidation/Dissolution Under Repository Conditions

2001 ◽  
Author(s):  
Juan Merino ◽  
Esther Cera ◽  
Jordi Bruno ◽  
Trygve Eriksen ◽  
Javier Quiñones ◽  
...  
Keyword(s):  
Source Term ◽  
Redox System ◽  
Water Interface ◽  
Spent Fuel ◽  
Fuel Oxidation ◽  
The Subject ◽  
The Stability ◽  
Thermodynamic Processes

Abstract A model to study the stability of the spent fuel under repository conditions has been developed. The fuel-water interface is a dynamic redox system, where oxidising conditions due to the radiolysis of water can lead to the release of the uranium and the radionuclides embedded in the fuel matrix. Both kinetic and thermodynamic processes have been taken into account. Special attention is given to the unit rate of matrix oxidation/dissolution, which has been the subject of a specific radiolytic model. The findings of this work have important implications for the applicability of solubility limits in establishing source term models.

A Radiochemical Analyses of Metastudtite and Leachates from Spent Fuel

2004 ◽  
Vol 824 ◽  
Author(s):  
Bruce McNamara ◽  
Brady Hanson ◽  
Edgar Buck ◽  
Chuck Soderquist
Keyword(s):  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Radiochemical Analysis ◽  
Water Interface ◽  
Spent Fuel ◽  
Air Water Interface ◽  
Two Phases ◽  
Floating Phase ◽  
Static Immersion

AbstractWe have characterized considerable amounts of the two known uranyl peroxide phases that formed under static immersion conditions on commercial spent nuclear fuel (CSNF) samples. Milligrams of corroded fuel aggregates were observed at the air-water interface in each sample. The bulk fuel and the interfacial solids were examined by SEM, EDX, and XRD and were found to contain studtite and metastudtite, respectively. The reason for the partitioning of the two phases is not clear at this time. The unique occurrence of the floating phase prompted a radiochemical analysis of these solids. The analysis indicated that 90Sr, 137Cs, 99Tc, and to a lesser extent of 238,239Pu and 237Np, had partitioned with the air-water interface aggregates. The concentration of 241Am in the interfacial solids was two orders of magnitude lower than the inventory in the fuel prior to contact with water. The radiochemical analyses of two fuel leachate samples are compared to reported leaching data of a similar fuel which did not result in the formation of studtite.

Sampling and analysis of the air-water interface with SEM and EDS of microlayers

1989 ◽  
Vol 47 ◽  
pp. 1004-1005
Author(s):  
Randall W. Smith ◽  
John Dash
Keyword(s):  
Heavy Metals ◽  
Surface Microlayer ◽  
Surface Films ◽  
Water Interface ◽  
Physical Processes ◽  
Infrared Spectroscopic Analysis ◽  
Eds Analysis ◽  
Air Water Interface ◽  
Significant Area ◽  
Bulk Chemical

The structure of the air-water interface forms a boundary layer that involves biological ,chemical geological and physical processes in its formation. Freshwater and sea surface microlayers form at the air-water interface and include a diverse assemblage of organic matter, detritus, microorganisms, plankton and heavy metals. The sampling of microlayers and the examination of components is presently a significant area of study because of the input of anthropogenic materials and their accumulation at the air-water interface. The neustonic organisms present in this environment may be sensitive to the toxic components of these inputs. Hardy reports that over 20 different methods have been developed for sampling of microlayers, primarily for bulk chemical analysis. We report here the examination of microlayer films for the documentation of structure and composition.Baier and Gucinski reported the use of Langmuir-Blogett films obtained on germanium prisms for infrared spectroscopic analysis (IR-ATR) of components. The sampling of microlayers has been done by collecting fi1ms on glass plates and teflon drums, We found that microlayers could be collected on 11 mm glass cover slips by pulling a Langmuir-Blogett film from a surface microlayer. Comparative collections were made on methylcel1ulose filter pads. The films could be air-dried or preserved in Lugol's Iodine Several slicks or surface films were sampled in September, 1987 in Chesapeake Bay, Maryland and in August, 1988 in Sequim Bay, Washington, For glass coverslips the films were air-dried, mounted on SEM pegs, ringed with colloidal silver, and sputter coated with Au-Pd, The Langmuir-Blogett film technique maintained the structure of the microlayer intact for examination, SEM observation and EDS analysis were then used to determine organisms and relative concentrations of heavy metals, using a Link AN 10000 EDS system with an ISI SS40 SEM unit. Typical heavy microlayer films are shown in Figure 3.

Porous materials from cellulose nanocrystal and mxene surfactants at the oil/water interface

2020 ◽  
Author(s):  
Bingqing qian ◽  
Haiqiao Wang ◽  
Dong Wang ◽  
Hao-Bin Zhang ◽  
Jessica Wu ◽  
...  
Keyword(s):  
Porous Materials ◽  
Cellulose Nanocrystal ◽  
Water Interface ◽  
Oil Water
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