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Metallic inert matrix fuel concept for minor actinides incineration to achieve ultra-high burn-up
Accepted Manuscript Metallic inert matrix fuel concept for minor actinides incineration to achieve ultra-high burn-up K. Lipkina, A. Savchenko, M. Skupov, A. Vatulin, G. Kulakov, S. Ershov, S. Maranchak PII: DOI: Reference:
S0022-3115(14)00245-1 http://dx.doi.org/10.1016/j.jnucmat.2014.04.030 NUMA 48105
To appear in:
Journal of Nuclear Materials
Received Date: Accepted Date:
3 October 2013 22 April 2014
Please cite this article as: K. Lipkina, A. Savchenko, M. Skupov, A. Vatulin, G. Kulakov, S. Ershov, S. Maranchak, Metallic inert matrix fuel concept for minor actinides incineration to achieve ultra-high burn-up, Journal of Nuclear Materials (2014), doi: http://dx.doi.org/10.1016/j.jnucmat.2014.04.030
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Metallic inert matrix fuel concept for minor actinides incineration to achieve ultra-high burn-up.
K. Lipkina*, A. Savchenko, M. Skupov, A. Vatulin, G. Kulakov, S. Ershov, S. Maranchak A.A. Bochvar All-Russia Research Institute of Inorganic Materials (VNIINM) 123060, P.O.B. 369, Rogova St., 5A, Moscow, Russia Corresponding author: tel.: +7-916-9713175; fax: +7-499- 1964075; e-mail: [email protected]
Key words: Inert matrix fuel; Actinides; Burn-up; Composites; Pu incineration
Abstract
The advantages of using inert matrix fuel (IMF) in a design of an isolated arrangement of fuel are considered, with emphasis on, low temperatures in the fuel center, achievement of high burn-ups, and an environment friendly process for the fuel element fabrication. Changes in the currently existing concept of IMF usage are suggested, involving novel IMF design in the nuclear fuel cycle.
PACS: 28.41.Bm; 81.05.Zx; 81.05.Rm; 81.30.Bx
1.
Introduction
Inert Matrix Fuel (IMF) is considered as one of the options for the incineration of excess Pu and minor actinides (MA) in fast or thermal reactors [1, 2]. IMF can be an advanced nuclear fuel form. It can potentially provide higher burn-up than current fuel form, making it a promising alterative for future generation of nuclear power reactors [3-7]. IMF is capable of reducing plutonium stockpiles (also of reactor-grade plutonium) more efficiently than MOX fuel [7, 8]. The use of IMF has economical benefits especially by obtaining ultra-high burn-ups. Currently, the existing versions of IMF based on pelletized fuel elements, particularly made of various ceramic 1
materials- spinel, Yttria-stabilized zirconia (YSZ), Mg2O, do not fully satisfy this requirement. They have no metallurgical bond between cladding and fuel form, which aside from raising the temperature in the center of a fuel element, degrades its serviceability, especially, in transients [2-5]. This investigation is to propose an IMF concept for achieving high burn-ups. [8-13]. Previous application of IMF or in other words – fuel on the basis of an inert matrix was considered as one of the options of recycling plutonium amount, particularly weapons grade, mostly in thermal reactors and utilization of its energy potential (Fig. 1 (a)) [1, 9]. What has been changed in last years? . The long term development of nuclear power as a part of the world's future energy mix will require fast reactor technology with closed fuel cycle. Fast reactors are a versatile and flexible technology that promises to create or "breed" more fuel by converting nuclear "waste" into "fissile" material. Therefore, it does not make any sense now to incinerate fissile Pu in IMF designs. On the other hand increasing burnup in thermal reactors and using MOX result in poor Pu composition in spent fuel as well as increase in the stockpile of MA needs incineration in FR (Fig. 1 (b)).
2
Development and design
2.1 Methods and approaches
The main goal of investigations is to develop IMF design with a metallic matrix that makes it possible to achieve high burn-ups in FR. It should be produced by simple technology and comply with requirement for “Rock-fuel” (making direct geologic disposal of fuel feasible). This can be achieved by replacing ceramics inert matrix of pelletized design by dispersion-type fuel element. A direct metallurgical bond between fuel and cladding provides conductivity while serving to protect against fuel-cladding interactions. Dispersion-type metallic IMF is an ideal separable system, allowing each component to be studied separately (i.e., actinide fuel, inert metallic matrix and cladding) (Fig. 2) [13-15]. Dispersion-type fuel elements with metal matrices that are distinct from the traditional pelletized fuel elements have a number of advantages. They exhibit a low temperature of a fuel center, high irradiation resistance and extended burn-ups [16].
2.2 IMF design and technology
One of the versions of dispersion- type IMF, which we are developing, is a fuel element having a heat conducting metal matrix and an isolated arrangement of PuO2 in a fuel mini-element [16]. The main distinction and advantage of such a fuel element consist in the fact that PuO2 or MA oxide powder is separately arranged in fuel mini-elements that in turn are placed inside a fuel element (Fig. 3 (a)). The space between fuel mini-elements and fuel cladding is filled with Zr matrix alloy using impregnation or capillary impregnation methods (Fig. 3 (b)) [17, 18]. Iron- based matrix alloys can also be implemented for FRs in this design (Fig. 3 (c)). The fuel mini-element is a thin-walled stainless steel or Zr alloy tube, 1.4-2.5 mm in diameter. It is filled with PuO2 powder or granules (60-70 % vol.), sealed and placed within a fuel element (Fig. 4). Aside from PuO2, also oxides of other actinides may be loaded into a fuel mini-element. Actinide oxides can be produced by
pyrochemical method, and (Er,Y,Pu,Zr)O2-x microspheres, prepared by 3
internal gelation process (such as at Institute for Transuranium Elements (ITU) and Paul Scherrer Institute (PSI)) can also be implemented [2, 9, 19-21]. A fuel mini-element has the following functions: 1. Prevent the fuel from interacting with the matrix and the cladding. 2. Provide protection against corrosion. 3. Use as a barrier against fission products release. 4. Accommodate fuel swelling. The fuel mini-elements (from 1 to 6 of them) are inserted in the fuel cladding. The metallurgical contact between the fuel mini-elements and the cladding is provided by liquid-solid sintering (capillary impregnation technology). In this method of fabrication zirconium matrix granules are loaded into a fuel cladding, and fuel element is heated to the temperature 50oC higher than the melting temperature of the matrix alloy. Matrix alloy melts down and under the action of capillary forces moves into the gaps between mini-elements and the cladding to form so –called bridges that provide the fuel form with high thermal conductivity. [11, 18]. Instead of a Zr-matrix an iron-based matrix can be implemented for FRs. Table 1 shows the experimental results of fuel quantity in IMF element depending on a fuel- element design, quantity of fuel mini-elements (4 or 6) and their sizes. The purpose of experiments is to evaluate the maximum quantity of fuel to be inserted into novel IMF design for thermal and fast reactors. For thermal reactors with zirconium cladding, 9.1×0.7 mm, we implemented four zirconium minielements, 2.5×0.15 mm, or six zirconium mini-elements, 2.2×0.15 mm. For fast reactors with steel cladding, 6.9×0.4 mm, we implemented four steel mini-elements, 2.1×0.12 mm, or six steel minielements, 1.8×0.12 mm (Fig. 5). For the fuel kernel itself we used UO2 powder instead of PuO2 40-70 µm sized produced by UO2 pellets grinding. The average volume fraction of UO2powder inside fuel minielement was 65%.
Table 1 Volume fraction of fuel (UO2) under the cladding in various designs of fuel elements. Reactor type
Volume fraction of fuel (UO2), (%) 4
4 mini-elements
6 mini-elements
21
23
24
26
Thermal reactors with zirconium cladding, 9.1×0.7 (mm) Fast reactors with steel cladding, 6.9×0.4 (mm)
We can see from our experiments that the total volume fraction of PuO2 in a fuel element may be varied in average from 5 to 25 %, which is enough for thermal and fast reactor cores. Variations (diminishing volume fraction) can be made by changing the fuel-element diameter, implementation of mixture of PuO2 and inert material as well as
implementation of (Er,Y,Pu,Zr)O2-x microspheres.
Microspheres in comparison to PuO2 to a greater extent meet the requirements for non-proliferation and, hence, the “Rock-fuel” criterion.
2.
Results and discussion
The advantage of this design lies in the fact that the number of main dust-forming operations with Pu in the fuel element fabrication is reduced to a single one i.e., filling the mini-elements with powder or granules. The other operations are carried on in clean zones. Aside from this, the fuel-free space of a mini-element is used to accommodate fuel swelling. The fuel is protected against the interaction with matrix and coolant. Fuel element simulators of similar designs with inert zirconium matrix alloy clad in stainless steel, in which UO2 was used in place of PuO2 were successfully in-pile tested. IMF reached burn-ups of 200 MW·d·kg-1U with steam temperature up to 600°C, which makes their use promising in both fast and thermal reactors. Figure 6 presents the scheme illustrating the peculiarities of involving novel IMF design in the nuclear fuel cycle.
5
Pu of poor quality with MA from spent pressurized water reactor (PWR) fuel, particularly spent MOX fuel, after pyrochemical reprocessing can be used as a fissile material. Then it would be delivered to fast or thermal reactors with the achievement of very high burn–up, followed by direct geological disposal as “Rock- fuel”. There is the other option of using fertile Pu+MA from FR.. The fissile components may be taken from the spent innovative composite U-PuO2 fuel after mechanical separation [14, 15]. It should be mentioned that the proposed IMF design fully comply with the requirements for “Rockfuel” as it has three protection barriers: fuel cladding, corrosion resistant metallic matrix and minielement cladding.
3.
Conclusion
In summary, we proposed a novel concept design of IMF based on dispersion-type fuel element. The main distinction and advantage of such a fuel element consist in the fact that PuO2 or MA powder is separately arranged in fuel mini-elements that in their turn are placed inside a fuel element. The space between the fuel mini-elements and the fuel cladding is filled with Zr-matrix alloy using impregnation or capillary impregnation methods. The advantages of using an IMF in a design of an isolated arrangement of fuel are considered, with emphasis on, low temperatures in the fuel center, achievement of high burn-ups, and an environment friendly process for the fuel element fabrication. Changes in currently existing concept of IMF usage and their insertion in nuclear fuel cycle were suggested.
Acknowledgments
6
The authors gratefully acknowledge the IAEA for financial support, Dr. Claude Degueldre (PSI) for his help and assistance in our developments, colleagues from CEA, ITU and the Imperial College for fruitful discussions.
7
Figure Captions Fig. 1. Past (a), and present (b) conception of IMF usage.
Fig. 2. Approach to fuel development and IMF process fabrication stages.
Fig. 3. (a) Six fuel mini-elements inserted into a fuel cladding, (b) microstructure of fuel element with Zr-matrix alloy, and (c) cross section of fuel element – plutonium burner containing four fuel minielements
Fig. 4. (a) PuO2 powder (pyrochemical method), 20-70 mm, and scheme for loading (b) of PuO2 or MA oxides powder, and (c) f ull mini-elements loading in fuel cladding.
Fig. 5. Schematic cross-section of IMF with four and six mini-elements.
Fig. 6. Peculiarities of the insertion of the novel IMF design in the nuclear fuel cycle.
8
Fig. 1
a
b
9
Fig. 2
10
Fig. 3
a
b
c
11
Fig. 4
a
b
c
12
Fig. 5
13
Fig.6
14
References [1] C. Degueldre, J.M. Paratte Concepts for an inert matrix fuel, an overview J. Nucl. Mater. 274 (1999) 1-6. [2] C. Degueldre “Inert Matrix Fuel has the potential to produce electricity while burning up more plutonium” Actinide Research Quarterly. Nuclear Materials Technology/ Los Alamos National Laboratory, 1st/2nd quarter 2003, P. 23-30. [3] V.M. Oversby, C.C. McPheeters, C. Degueldre, J.M. Paratte, J. Nucl. Mater. 245 (1997), 17. [4] J. Porta, J.-Y. Doriath, J. Nucl. Mater. 274 (1999), 153. [5] R.P.C. Schram, R.R. van der Laan, F.C. Klaassen, K. Bakker, T. Yamashita, F. Ingold, J. Nucl.Mater. 319 (2003), 118. [6] M.A. Pouchon, M. Nakamura, C. Hellwig, F. Ingold, C. Degueldre, J. Nucl.Mater. 319 (2003) 37. [7] H. Matzke, AIP Conf. Proc. 532 (2000), 20. [8] V.Y. Shishin, V.A. Ovchinnikov, A.E. Novoselov, Behaviour of CERMET fuel compositions in inert matrices (review of experiments), in review, F.C. Klaasen, A.V. Chibinyaev, “Disposition of weapons-grade plutonium with inert matrix fuels”, NRG, Petten, 28 September 2004, 72-80. [9] D. Warin, Future nuclear fuel cycles: prospect and challenges for actinide recycling. In: L. Rao, J.G. Tobin, D.K. Shuh, (Eds.), Actinides 2009, Volume 9 of IOP Conference SeriesMaterial Science and Engineering. Iop Publishing Ltd. [10] A.M. Savchenko, A.V. Vatulin, A.V. Morozov, V.L. Sirotin, I.V. Dobrikova, G.V. Kulakov, S.A. Ershov, V.P. Kostomarov, Y.I. Stelyuk, IMF in dispersion type fuel elements, J. Nucl. Mater. 352 (2006), 372-377. [11] A.M. Savchenko, A.V. Vatulin, A.V. Morozov, I.V. Dobrikova, S.A. Ershov, S.V. Maranchak, Z.N. Petrova, Y.V. Konovalov, IMF with low melting point zirconium brazing alloys, J. Nucl. Mater. 352 (2006), 334-340. [12] A.M. Savchenko, A.V. Vatulin, I.I. Konovalov, A.V. Morozov, V.K. Orlov, O.I. Uferov et al., Dispersion type zirconium matrix fuels fabricated by capillary impregnation method, J. Nucl. Mater. 362 (2007), 356-363. [13] J.T. McKeown, S. Irukuvarghula, S. Ahn, M.A. Wall, L.L. Hsiung, S. McDeavitt, P.E.A. Turchi , J. Nucl. Mater. 436 (2013), 100-104.
15
[14] А.М. Savchenko, I.I. Konovalov, E.М. Glagovsky, A.V. Vatulin, О.I. Uferov, A.V. Morozov, New Concept of Designing Pu and MA Containing Fuel for Fast Reactors, J. Nucl. Mater. 385 (2009), 148-152. [15] Savchenko, A.V. Vatulin, I.I. Konovalov, A.V. Morozov, V.I. Sorokin, S.V. Maranchak, Fuel of Novel Generation for PWR and as Alternative to MOX Fuel, J. Energy Conversion & Management, 51 (2010), 1826-1833. [16] A.M. Savchenko, A.V. Vatulin, A.V. Morozov, O.I. Uferov, S.A. Ershov, A.V. Laushkin, S.V. Maranchak, Y.V. Konovalov, Z.N. Petrova, E.K. Malamanova, Main results of the development of dispersion type IMF at A.A. Bochvar institute, J. Nucl. Mater. 396 (2010), 26-31. [17] A.M. Savchenko, A.V. Vatulin, A.V. Morozov, O.I. Uferov, S.A. Ershov, A.V. Laushkin, S.V. Maranchak, Y.V. Konovalov, Z.N. Petrova, E.K. Malamanova, Zirconium Matrix Alloys for Dispersion Type High Uranium Content Fuel, J. Phys. Chem. Materials Treatment, Issue 3, (2009), 42-49. [18] A.M. Savchenko, A.V. Vatulin, A.V. Morozov, G.V. Kulakov, S.A. Ershov, A.V. Laushkin, S.V. Maranchak, Y.V. Konovalov, E.K. Malamanova, Zirconium alloys matrix as innovative material for composite fuel, Prog. Nucl. Energy, 57 (2012), 138-144. [19] R.J.M. Konings, K. Bakker, J.G. Boshoven, H. Hein, M.E. Huntelaar, R. R. van der Laan, Trasmutation of actinides in inert –matrix fuels: fabrication studies and modeling of fuel behavior, J. Nucl. Mater. 274 (1999), 84-90. [20] M.A. Pouchon, G. Ledergerber, F. Ingold, and K. Bakker (2012) Sphere-Pac and VIPAC Fuel. In: R.J.M. Konings, (ed.) Comprehensive Nuclear Materials, Volume 3, pp. 275-312. [21] M. Cabanes-Sempere, C. Cozzo, S. Vaucher, J.M. Catala-Civera, M.A. Pouchon, Innovative production of nuclear fuel by microwave internal gelation: Heat transfer model of falling droplets, Prog. Nucl. Energy, 57, (2012), 111-116.
16
S0022-3115(14)00245-1 http://dx.doi.org/10.1016/j.jnucmat.2014.04.030 NUMA 48105
To appear in:
Journal of Nuclear Materials
Received Date: Accepted Date:
3 October 2013 22 April 2014
Please cite this article as: K. Lipkina, A. Savchenko, M. Skupov, A. Vatulin, G. Kulakov, S. Ershov, S. Maranchak, Metallic inert matrix fuel concept for minor actinides incineration to achieve ultra-high burn-up, Journal of Nuclear Materials (2014), doi: http://dx.doi.org/10.1016/j.jnucmat.2014.04.030
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Metallic inert matrix fuel concept for minor actinides incineration to achieve ultra-high burn-up.
K. Lipkina*, A. Savchenko, M. Skupov, A. Vatulin, G. Kulakov, S. Ershov, S. Maranchak A.A. Bochvar All-Russia Research Institute of Inorganic Materials (VNIINM) 123060, P.O.B. 369, Rogova St., 5A, Moscow, Russia Corresponding author: tel.: +7-916-9713175; fax: +7-499- 1964075; e-mail: [email protected]
Key words: Inert matrix fuel; Actinides; Burn-up; Composites; Pu incineration
Abstract
The advantages of using inert matrix fuel (IMF) in a design of an isolated arrangement of fuel are considered, with emphasis on, low temperatures in the fuel center, achievement of high burn-ups, and an environment friendly process for the fuel element fabrication. Changes in the currently existing concept of IMF usage are suggested, involving novel IMF design in the nuclear fuel cycle.
PACS: 28.41.Bm; 81.05.Zx; 81.05.Rm; 81.30.Bx
1.
Introduction
Inert Matrix Fuel (IMF) is considered as one of the options for the incineration of excess Pu and minor actinides (MA) in fast or thermal reactors [1, 2]. IMF can be an advanced nuclear fuel form. It can potentially provide higher burn-up than current fuel form, making it a promising alterative for future generation of nuclear power reactors [3-7]. IMF is capable of reducing plutonium stockpiles (also of reactor-grade plutonium) more efficiently than MOX fuel [7, 8]. The use of IMF has economical benefits especially by obtaining ultra-high burn-ups. Currently, the existing versions of IMF based on pelletized fuel elements, particularly made of various ceramic 1
materials- spinel, Yttria-stabilized zirconia (YSZ), Mg2O, do not fully satisfy this requirement. They have no metallurgical bond between cladding and fuel form, which aside from raising the temperature in the center of a fuel element, degrades its serviceability, especially, in transients [2-5]. This investigation is to propose an IMF concept for achieving high burn-ups. [8-13]. Previous application of IMF or in other words – fuel on the basis of an inert matrix was considered as one of the options of recycling plutonium amount, particularly weapons grade, mostly in thermal reactors and utilization of its energy potential (Fig. 1 (a)) [1, 9]. What has been changed in last years? . The long term development of nuclear power as a part of the world's future energy mix will require fast reactor technology with closed fuel cycle. Fast reactors are a versatile and flexible technology that promises to create or "breed" more fuel by converting nuclear "waste" into "fissile" material. Therefore, it does not make any sense now to incinerate fissile Pu in IMF designs. On the other hand increasing burnup in thermal reactors and using MOX result in poor Pu composition in spent fuel as well as increase in the stockpile of MA needs incineration in FR (Fig. 1 (b)).
2
Development and design
2.1 Methods and approaches
The main goal of investigations is to develop IMF design with a metallic matrix that makes it possible to achieve high burn-ups in FR. It should be produced by simple technology and comply with requirement for “Rock-fuel” (making direct geologic disposal of fuel feasible). This can be achieved by replacing ceramics inert matrix of pelletized design by dispersion-type fuel element. A direct metallurgical bond between fuel and cladding provides conductivity while serving to protect against fuel-cladding interactions. Dispersion-type metallic IMF is an ideal separable system, allowing each component to be studied separately (i.e., actinide fuel, inert metallic matrix and cladding) (Fig. 2) [13-15]. Dispersion-type fuel elements with metal matrices that are distinct from the traditional pelletized fuel elements have a number of advantages. They exhibit a low temperature of a fuel center, high irradiation resistance and extended burn-ups [16].
2.2 IMF design and technology
One of the versions of dispersion- type IMF, which we are developing, is a fuel element having a heat conducting metal matrix and an isolated arrangement of PuO2 in a fuel mini-element [16]. The main distinction and advantage of such a fuel element consist in the fact that PuO2 or MA oxide powder is separately arranged in fuel mini-elements that in turn are placed inside a fuel element (Fig. 3 (a)). The space between fuel mini-elements and fuel cladding is filled with Zr matrix alloy using impregnation or capillary impregnation methods (Fig. 3 (b)) [17, 18]. Iron- based matrix alloys can also be implemented for FRs in this design (Fig. 3 (c)). The fuel mini-element is a thin-walled stainless steel or Zr alloy tube, 1.4-2.5 mm in diameter. It is filled with PuO2 powder or granules (60-70 % vol.), sealed and placed within a fuel element (Fig. 4). Aside from PuO2, also oxides of other actinides may be loaded into a fuel mini-element. Actinide oxides can be produced by
pyrochemical method, and (Er,Y,Pu,Zr)O2-x microspheres, prepared by 3
internal gelation process (such as at Institute for Transuranium Elements (ITU) and Paul Scherrer Institute (PSI)) can also be implemented [2, 9, 19-21]. A fuel mini-element has the following functions: 1. Prevent the fuel from interacting with the matrix and the cladding. 2. Provide protection against corrosion. 3. Use as a barrier against fission products release. 4. Accommodate fuel swelling. The fuel mini-elements (from 1 to 6 of them) are inserted in the fuel cladding. The metallurgical contact between the fuel mini-elements and the cladding is provided by liquid-solid sintering (capillary impregnation technology). In this method of fabrication zirconium matrix granules are loaded into a fuel cladding, and fuel element is heated to the temperature 50oC higher than the melting temperature of the matrix alloy. Matrix alloy melts down and under the action of capillary forces moves into the gaps between mini-elements and the cladding to form so –called bridges that provide the fuel form with high thermal conductivity. [11, 18]. Instead of a Zr-matrix an iron-based matrix can be implemented for FRs. Table 1 shows the experimental results of fuel quantity in IMF element depending on a fuel- element design, quantity of fuel mini-elements (4 or 6) and their sizes. The purpose of experiments is to evaluate the maximum quantity of fuel to be inserted into novel IMF design for thermal and fast reactors. For thermal reactors with zirconium cladding, 9.1×0.7 mm, we implemented four zirconium minielements, 2.5×0.15 mm, or six zirconium mini-elements, 2.2×0.15 mm. For fast reactors with steel cladding, 6.9×0.4 mm, we implemented four steel mini-elements, 2.1×0.12 mm, or six steel minielements, 1.8×0.12 mm (Fig. 5). For the fuel kernel itself we used UO2 powder instead of PuO2 40-70 µm sized produced by UO2 pellets grinding. The average volume fraction of UO2powder inside fuel minielement was 65%.
Table 1 Volume fraction of fuel (UO2) under the cladding in various designs of fuel elements. Reactor type
Volume fraction of fuel (UO2), (%) 4
4 mini-elements
6 mini-elements
21
23
24
26
Thermal reactors with zirconium cladding, 9.1×0.7 (mm) Fast reactors with steel cladding, 6.9×0.4 (mm)
We can see from our experiments that the total volume fraction of PuO2 in a fuel element may be varied in average from 5 to 25 %, which is enough for thermal and fast reactor cores. Variations (diminishing volume fraction) can be made by changing the fuel-element diameter, implementation of mixture of PuO2 and inert material as well as
implementation of (Er,Y,Pu,Zr)O2-x microspheres.
Microspheres in comparison to PuO2 to a greater extent meet the requirements for non-proliferation and, hence, the “Rock-fuel” criterion.
2.
Results and discussion
The advantage of this design lies in the fact that the number of main dust-forming operations with Pu in the fuel element fabrication is reduced to a single one i.e., filling the mini-elements with powder or granules. The other operations are carried on in clean zones. Aside from this, the fuel-free space of a mini-element is used to accommodate fuel swelling. The fuel is protected against the interaction with matrix and coolant. Fuel element simulators of similar designs with inert zirconium matrix alloy clad in stainless steel, in which UO2 was used in place of PuO2 were successfully in-pile tested. IMF reached burn-ups of 200 MW·d·kg-1U with steam temperature up to 600°C, which makes their use promising in both fast and thermal reactors. Figure 6 presents the scheme illustrating the peculiarities of involving novel IMF design in the nuclear fuel cycle.
5
Pu of poor quality with MA from spent pressurized water reactor (PWR) fuel, particularly spent MOX fuel, after pyrochemical reprocessing can be used as a fissile material. Then it would be delivered to fast or thermal reactors with the achievement of very high burn–up, followed by direct geological disposal as “Rock- fuel”. There is the other option of using fertile Pu+MA from FR.. The fissile components may be taken from the spent innovative composite U-PuO2 fuel after mechanical separation [14, 15]. It should be mentioned that the proposed IMF design fully comply with the requirements for “Rockfuel” as it has three protection barriers: fuel cladding, corrosion resistant metallic matrix and minielement cladding.
3.
Conclusion
In summary, we proposed a novel concept design of IMF based on dispersion-type fuel element. The main distinction and advantage of such a fuel element consist in the fact that PuO2 or MA powder is separately arranged in fuel mini-elements that in their turn are placed inside a fuel element. The space between the fuel mini-elements and the fuel cladding is filled with Zr-matrix alloy using impregnation or capillary impregnation methods. The advantages of using an IMF in a design of an isolated arrangement of fuel are considered, with emphasis on, low temperatures in the fuel center, achievement of high burn-ups, and an environment friendly process for the fuel element fabrication. Changes in currently existing concept of IMF usage and their insertion in nuclear fuel cycle were suggested.
Acknowledgments
6
The authors gratefully acknowledge the IAEA for financial support, Dr. Claude Degueldre (PSI) for his help and assistance in our developments, colleagues from CEA, ITU and the Imperial College for fruitful discussions.
7
Figure Captions Fig. 1. Past (a), and present (b) conception of IMF usage.
Fig. 2. Approach to fuel development and IMF process fabrication stages.
Fig. 3. (a) Six fuel mini-elements inserted into a fuel cladding, (b) microstructure of fuel element with Zr-matrix alloy, and (c) cross section of fuel element – plutonium burner containing four fuel minielements
Fig. 4. (a) PuO2 powder (pyrochemical method), 20-70 mm, and scheme for loading (b) of PuO2 or MA oxides powder, and (c) f ull mini-elements loading in fuel cladding.
Fig. 5. Schematic cross-section of IMF with four and six mini-elements.
Fig. 6. Peculiarities of the insertion of the novel IMF design in the nuclear fuel cycle.
8
Fig. 1
a
b
9
Fig. 2
10
Fig. 3
a
b
c
11
Fig. 4
a
b
c
12
Fig. 5
13
Fig.6
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