| 1. |
- Eriksson, Marcus, et al.
(författare)
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Safety Analysis of Na and Pb-Bi Coolants in Response to Beam Instabilities
- 2003
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Ingår i: UTILISATION AND RELIABILITY OF HIGH POWER PROTON ACCELERATORS, WORKSHOP PROCEEDINGS. - 9264102116 ; , s. 227-236
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Konferensbidrag (refereegranskat)abstract
- A comparative safety study has been performed on sodium vs. lead/bismuth as coolant for accelerator-driven systems. Transient studies are performed for a beam overpower event. We examine a fuel type of recent interest in the research on minor actinide burners, i.e. uranium-free oxide fuel. A strong positive void coefficient is calculated for both sodium and lead/bismuth. This is attributed to the high fraction of americium in the fuel. It is shown that the lead/bismuth-cooled reactor features twice the grace time with respect to fuel or cladding damage compared to the sodium-cooled reactor of comparable core size and power rating. This accounts to the difference in void reactivity contribution and to the low boiling point of sodium. For improved safety features the general objective is to reduce the coolant void reactivity effect. An important safety issue is the high void worth that could possibly drive the system to prompt criticality.
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| 2. |
- Seltborg, Per, et al.
(författare)
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Definition and application of proton source efficiency in accelerator driven systems
- 2003
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Ingår i: Nuclear science and engineering. - 0029-5639 .- 1943-748X. ; 145:3, s. 390-399
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Tidskriftsartikel (refereegranskat)abstract
- In order to study the beam power amplification of an accelerator-driven system (ADS), a new parameter, the proton source efficiency psi* is introduced. psi* represents the average importance of the external proton source, relative to the average importance of the eigenmode production, and is closely related to the neutron source efficiency rho*, which is frequently used in the ADS field. rho* is commonly used in the physics of subcritical systems driven by any external source (spallation source, (d,d), (d, t), Cf-252 spontaneous fissions, etc.). On the contrary, psi* has been defined in this paper exclusively for ADS studies where the system is driven by a spallation source. The main advantage with using psi* instead of rho* for ADS is that the way of defining the external source is unique and that it is proportional to the core power divided by the proton beam power, independent of the neutron source distribution. Numerical simulations have been performed with the Monte Carlo code MCNPX in order to study psi* as a function of different design parameters. It was found that, in order to maximize psi* and therefore minimize the proton current needs, a target radius as small as possible should be chosen. For target radii smaller than similar to30 cm, lead-bismuth is a better choice of coolant material than sodium, regarding the proton source efficiency, while for larger target radii the two materials are equally good. The optimal axial proton beam impact was found to be located similar to 20 cm above the core center. Varying the proton energy, psi*/E-p was found to have a maximum for proton energies between 1200 and 1400 MeV Increasing the americium content in the fuel decreases psi* considerably, in particular when the target radius is large.
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| 3. |
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| 4. |
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| 5. |
- Tucek, Kamil, et al.
(författare)
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Coolant void worth in fast breeder reactors and accelerator-driven transuranium and minor-actinide burners
- 2004
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 31:15, s. 1783-1801
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Tidskriftsartikel (refereegranskat)abstract
- Liquid metal coolant void worth have been calculated as a function of fuel composition and core geometry for several model fast breeder reactors and accelerator-driven systems (ADSs). The Monte Carlo transport code MCNP with continuous energy cross-section libraries was used for this study. With respect to the core void worth, lead/bismuth cooled FBR, appear to be inferior to those employing sodium for pitch-to-diameter ratios exceeding 1.4. It is shown that in reactor systems cooled by lead/bismuth eutectic radial steel pin reflector significantly lowers the void worth. The void worth proves to be a strong function of the fuel composition, reactor cores with high content of minor actinides in fuel exhibiting larger void reactivities than systems with plutonium based fuel. Enlarging the lattice pitch in ADS burners operating on Pu rich fuel decreases the void worth while the opposite fact is true for ADSs employing americium based fuels.
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| 6. |
- Tucek, Kamil, 1972-
(författare)
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Neutronic and burnup studies of accelerator-driven systems dedicated to nuclear waste transmutation
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Partitioning and transmutation of plutonium, americium, and curium is inevitable if the radiotoxic inventory of spent nuclear fuel is to be reduced by more than a factor of 100. But, admixing minor actinides into the fuel severely degrades system safety parameters, particularly coolant void reactivity, Doppler effect, and (effective) delayed neutron fractions. The incineration process is therefore envisioned to be carried out in dedicated, accelerator-driven sub-critical reactors (ADS). However, ADS cores operating in concert with light-water reactors (two-component scenario) also exhibit high burnup reactivity swing with penalty on the system performance/economy. In the frame of this design work, we attempted, by choice of coolant and optimisation of fuel concept and core design, to achieve favourable neutronic, burnup and safety characteristics of the transuranium ADS burner. Key thermal hydraulic and material-related constraints were respected. A novel fuel matrix material, hafnium nitride, was identified as an attractive diluent option for highly reactive transuranics. (TRU,Hf)N fuels appeared to have a good combination of neutronic, burnup and thermal characteristics: maintaining hard neutron spectra, yielding acceptable values of coolant void reactivity and source efficiency, and providing small burnup reactivity loss. A conceptual design of a (TRU,Hf)N fuelled, lead/bismuth eutectic cooled ADS was developed. The average discharge burnup of 20% fissions per initial metal atom could be reached even without fuel reshuffling. The fission fraction ratios of even-neutron number americium nuclides are increased by a factor of two in comparison to burners with inert matrix based fuels. Hence, thanks to the reduced production of higher actinides and helium, fuel cycle economy is improved. The coolant void worth proved to be a strong function of the fuel composition - reactor cores with high content of fertile material or minor actinides in fuel exhibit larger void reactivities than systems with plutonium-rich, inert matrix fuels. In reactor systems cooled by lead/bismuth eutectic, a radial steel pin reflector significantly lowered coolant void reactivity. For transuranic fuel, fertile and strongly absorbing matrices exhibited increasing void worth with increasing pitch, while the opposite was valid for the coolant void worth of inert matrix fuels. Large pitches also appeared to be beneficial for limiting the reactivity worth of the cladding material and improving source efficiency. The economy of the source neutrons was investigated as a function of core and target design. An incentive to design the core with as low target radius as allowable by the thermal constraints posed by the ability to dissipate accelerator beam power was identified.
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| 7. |
- Tucek, Kamil, et al.
(författare)
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Studies of an accelerator-driven transuranium burner with hafnium-based inert matrix fuel
- 2007
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 157:3, s. 277-298
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Tidskriftsartikel (refereegranskat)abstract
- Neutronic and burnup characteristics of an accelerator-driven transuranium burner in a startup mode were studied. Different inert and absorbing matrices as well as lattice configurations were assessed in order to identify suitable fuel and core design configurations. Monte Carlo transport and burnup codes were used in the analyses. The lattice pin pitch was varied to optimize the source efficiency and coolant void worth while respecting key thermal and material-related design constraints posed by fuel and cladding. A HfN matrix appeared to provide a good combination of neutronic, burnup, and safety characteristics: maintaining a hard neutron spectrum, yielding acceptable coolant void reactivity and source efficiency, and alleviating the burnup reactivity swing. A conceptual design of a (TRU,Hf)N fueled, lead-bismuth eutectic-cooled accelerator-driven system was developed. Twice higher neutron fission-to absorption probabilities in Am isotopes were achieved compared to reactor designs relying on ZrN or YN inert matrix fuel. The production of higher actinides in the fuel cycle is hence limited, with a Cm fraction in the equilibrium fuel being similar to 40% lower than for cores with ZrN matrix-based fuel. The burnup reactivity swing and associated power peaking in the core are managed by an appropriate choice of cycle length (100 days) and by core enrichment zoning. A safety analysis shows that the system is protected from instant damage during unprotected beam overpower transient.
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