| 1. |
- Jolkkonen, Mikael, et al.
(author)
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Uranium nitride fuels in superheated steam
- 2017
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In: Journal of Nuclear Science and Technology. - : Informa UK Limited. - 0022-3131 .- 1881-1248.
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Journal article (peer-reviewed)abstract
- Uranium mononitride (UN) pellets of different densities were subjected to a superheatedsteam/argon mixture at atmospheric pressure to evaluate their resistance to hydrolysis. Completedegradation of pure UN pellets was obtained within 1 hour in 0.50 bar steam at 500 °C. Theidentified reaction products were uranium dioxide, ammonia and hydrogen gas, with no detectableamounts of nitrogen oxides formed. However, the reaction could not be carried to completion, andthe presence of uranium sesquinitride and higher uranium oxides or uranium oxynitrides in the solidresidue is indicated. Evolution of elemental nitrogen was seen in connection with very high reactionrates. The porosity of the pellets was identified as the most important factor determining reactionrates at 400 – 425 °C, and it is suggested that in dense pellets, cracking due to internal volumeincrease initiates a transition from slow surface corrosion to pellet disintegration. The implicationsfor the use of nitride fuels in light water reactors are discussed, with some observations concerninghydrolysis as a method for 15N recovery from isotopically enriched spent nitride fuel.
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| 2. |
- Malkki, Pertti, et al.
(author)
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Manufacture of fully dense uranium nitride pellets using hydride derived powders with spark plasma sintering
- 2014
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 452:1-3, s. 548-551
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Journal article (peer-reviewed)abstract
- Applying a combination of hydriding/nitriding of metallic uranium with the spark plasma sintering technique, we show that uranium nitride pellets with an average porosity of 0.2% may be manufactured. This is considerably smaller than the lowest porosity previously reported in the literature. The high density is attained by sintering at 1650 °C for only three minutes.
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| 3. |
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| 4. |
- Malkki, Pertti, et al.
(author)
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Visualization of chromatic correction of fish lenses by multiple focal lengths
- 2005
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In: Journal of Optics. A, Pure and Applied Optics. - : IOP Publishing. - 1741-3567 .- 1464-4258. ; 7:11, s. 691-700
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Journal article (peer-reviewed)abstract
- Many fish and some terrestrial animals have multifocal lenses that compensate for chromatic aberration by a mechanism unique to biological optical systems. We describe four optical methods for the study of such lenses. Significantly improved methods (focal-area imaging, schlieren photography, and laser scanning) are explained in full detail. One method (photorefractometry) was only slightly modified over earlier versions and is illustrated in brief. Portable equipment is available for photorefractometry, schlieren photography, and laser scanning. With our methods we could for the first time directly illustrate chromatic correction by multifocal lenses and detect a number of previously unknown optical features of fish lenses.
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