“…Those of the apparent and effective relative densities versus the initial pressure are reported in Table . For all operating conditions considered, the sintering appeared good as it was also reported for lanthanide orthophosphates. − On the basis of the results obtained, the open and close porosities were evaluated to 3−6 vol % each, which seems to be enough to ensure significantly the decrease of the apparent leaching rate during the leaching tests (due to the low specific area of the sample) as well as the elimination of helium produced in situ by the disintegration of α emitter radionuclides, mainly actinide isotopes in the case of the actinide immobilization. 5 Variation of the apparent (open symbols) and effective (solid symbols) relative densities of sintered TPD obtained after heating at 1250 (○) or 1150 °C (□) as a function of holding time (initial pressing at 500 MPa).…”
Section: Resultsmentioning
confidence: 55%
“…The apparent and effective relative densities reach 93 and 97%, respectively, irrespective of the initial pressure considered. For both kinds of solids, the good properties of sintering observed eliminate the need for any sintering aid or organic binder in the compaction process as already observed for lanthanide orthophosphates (monazite structure). ,, …”
Taking into account some attractive properties of the thorium phosphate−diphosphate
(Th4(PO4)4P2O7), called TPD, we focused our research on its potential use as a ceramic for
the long term storage of some radionuclides including trivalent and tetravalent actinides.
In this objective, we already investigated with success several ways of preparation of the
pure TPD and solid solutions with tetravalent actinides either by wet or dry chemical
methods. In the field of nuclear applications and considering handling operations on the
radioactive materials, the preparation of this compound in the ceramic form was developed.
Therefore, a precursor of TPD was especially synthesized in order to get sintered samples
after performing an uniaxial pressing at room temperature followed by a heat treatment at
high temperature. The synthesis, the characterization, and the sintering procedure of the
precursor are described in this paper. The influence of the heating temperature on the specific
area of the powder is examined and then correlated with the granulometry and the
densification of the solid. For all of the samples, the apparent and effective relative densities
obtained are in the range of 87−99% of the value calculated from XRD data. Moreover, some
physical properties such as thermal diffusivity, thermal conductivity, and specific heat were
measured from room temperature up to 1000 °C. The main results are given in this paper.
Finally, the durability of the sintered TPD samples during leaching tests was studied. The
apparent dissolution rates remain low even in very corrosive media (1.25(2) × 10-3 g d-1 in
5 M HNO3 at 25 °C) which shows that the TPD can be considered as a promising candidate
for the immobilization of actinides and some fission products for a long-term storage.
“…Those of the apparent and effective relative densities versus the initial pressure are reported in Table . For all operating conditions considered, the sintering appeared good as it was also reported for lanthanide orthophosphates. − On the basis of the results obtained, the open and close porosities were evaluated to 3−6 vol % each, which seems to be enough to ensure significantly the decrease of the apparent leaching rate during the leaching tests (due to the low specific area of the sample) as well as the elimination of helium produced in situ by the disintegration of α emitter radionuclides, mainly actinide isotopes in the case of the actinide immobilization. 5 Variation of the apparent (open symbols) and effective (solid symbols) relative densities of sintered TPD obtained after heating at 1250 (○) or 1150 °C (□) as a function of holding time (initial pressing at 500 MPa).…”
Section: Resultsmentioning
confidence: 55%
“…The apparent and effective relative densities reach 93 and 97%, respectively, irrespective of the initial pressure considered. For both kinds of solids, the good properties of sintering observed eliminate the need for any sintering aid or organic binder in the compaction process as already observed for lanthanide orthophosphates (monazite structure). ,, …”
Taking into account some attractive properties of the thorium phosphate−diphosphate
(Th4(PO4)4P2O7), called TPD, we focused our research on its potential use as a ceramic for
the long term storage of some radionuclides including trivalent and tetravalent actinides.
In this objective, we already investigated with success several ways of preparation of the
pure TPD and solid solutions with tetravalent actinides either by wet or dry chemical
methods. In the field of nuclear applications and considering handling operations on the
radioactive materials, the preparation of this compound in the ceramic form was developed.
Therefore, a precursor of TPD was especially synthesized in order to get sintered samples
after performing an uniaxial pressing at room temperature followed by a heat treatment at
high temperature. The synthesis, the characterization, and the sintering procedure of the
precursor are described in this paper. The influence of the heating temperature on the specific
area of the powder is examined and then correlated with the granulometry and the
densification of the solid. For all of the samples, the apparent and effective relative densities
obtained are in the range of 87−99% of the value calculated from XRD data. Moreover, some
physical properties such as thermal diffusivity, thermal conductivity, and specific heat were
measured from room temperature up to 1000 °C. The main results are given in this paper.
Finally, the durability of the sintered TPD samples during leaching tests was studied. The
apparent dissolution rates remain low even in very corrosive media (1.25(2) × 10-3 g d-1 in
5 M HNO3 at 25 °C) which shows that the TPD can be considered as a promising candidate
for the immobilization of actinides and some fission products for a long-term storage.
“…The apparent "resistance" of monazite to radiation-induced amorphization was an important factor in the initial proposal of monazite ceramics as potential candidates for the immobilization of nuclear waste. Further, the chemical durability of monazite has led to its increasing use in U/Pb dating of minerals in both igneous and metamorphic rocks (Parrish 1990, Harrison et al, this volume) and was an important aspect of the proposal of monazite as a waste form for actinides (Boatner 1980, Floran et al 1981, Poitrasson et al 2000.…”
INTRODUCTIONThe disposal of radioactive "waste" generated by the nuclear fuel cycle is among the most pressing and potentially costly environmental problems of the 21st century, a heritage from the Atomic Age of the 20th century. Proposed disposal strategies are complicated, not only because of the large volumes and activities of waste, but also because of the political and public-policy issues associated with the long times required for containment and disposal (10 4 to 10 6 years). The development and use of highly durable waste forms, materials that have a high chemical durability and resistance to radiation damage effects, can simplify the disposal strategy (Ewing 2001).An interest in phosphate-based waste forms has developed because the high-level waste generated by reprocessing of spent nuclear fuel can contain substantial amounts of phosphates (up to 15 wt % P 2 O 5 ) that result from processing technologies that utilized either a bismuth phosphate or tributylphosphate process (Bunker et al. 1995). In addition to the high phosphate content, other metal oxides may achieve significant proportions (up to 15 wt % Fe 2 O 3 ; up to 30 wt % Bi 2 O 3 ; up to 30 wt % UO 2 ) (Lambert and Kim 1994). These complex compositions have presented special challenges in developing crystalline ceramics that can accommodate the full compositional range of the waste streams.The early work on phosphate glasses led to the idea that crystalline phosphates might make extremely durable waste forms, particularly for actinides. The earliest suggestion was for the use of monazite (Boatner 1978, Boatner et al. 1980, McCarthy et al. 1978, 1980. The attractive qualities of monazite as a nuclear waste form are: (1) a high solubility for actinides and rare earths (10 to 20 wt %); (2) evidence from natural occurrences of good chemical durability; (3) an apparent resistance to radiation damage, as natural monazites are seldom found in the metamict state, despite very high alphadecay event doses (Boatner and Sales 1988). There have been extensive studies of monazite and apatite as potential waste form phases, and a considerable amount of work on a number of synthetic phosphate phases has been completed.The crystal chemistry of monazite, apatite, and related phosphate minerals, has been discussed in detail (see this volume, Chapters 1, 2, and 4 by Hughes and Rakovan, Pan and Fleet, and Boatner, respectively) and will not be repeated here. Rather, we will summarize the work relevant to the consideration of these phosphate phases as nuclear waste forms.
TYPES OF NUCLEAR WASTEThe design and evaluation of nuclear waste forms requires some understanding of the sources, volumes, compositions and activities of the various waste streams generated by the nuclear fuel cycle. There are three primary sources of radioactive waste in the United States (DOE 1997): the high-level waste (HLW) from the reprocessing of spent nuclear fuel, the spent nuclear fuel itself, and plutonium reclaimed by reprocessing or obtained by the dismantlement of nuclear weapons.
67...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
