| 1. |
- Holcombe, Scott, et al.
(författare)
-
A Novel gamma emission tomography instrument for enhanced fuel characterization capabilities within the OECD Halden Reactor Project
- 2015
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 85, s. 837-845
-
Tidskriftsartikel (refereegranskat)abstract
- Gamma emission tomography is a method based on gamma-ray spectroscopy and tomographic reconstruction techniques, which can be used for rod-wise characterization of nuclear fuel assemblies without dismantling the fuel. By performing a large number of measurements of the gamma-ray flux intensity around a fuel assembly using a well-collimated gamma-ray detector, the internal source distribution in the assembly may be reconstructed using tomographic algorithms. If a spectroscopic detection system is used, different gamma-ray emitting isotopes can be selected for analysis, enabling nondestructive fuel characterization with respect to a variety of fuel parameters. In this paper, we describe a novel gamma emission tomography instrument, which has been designed, constructed and tested at the Halden Boiling Water Reactor (HBWR). The device will be used to characterize fuel assemblies irradiated in the HBWR as part of ongoing nuclear fuel research conducted within the OECD Halden Reactor Project (HRP). As compared to single-rod gamma scanning, where the fuel is dismantled and the gamma radiation from each rod is measured separately, handling time associated with characterizing the fuel can be significantly reduced when using the gamma emission tomography device. Furthermore, because gamma emission tomography enables rod-wise fuel characterization without dismantling, even instrumented experimental fuel assemblies may be characterized repeatedly throughout the fuel's lifetime, with limited risk of damaging the fuel or its instrumentation. Accordingly, the capabilities of fuel characterization within the OECD HRP are expected to be strongly enhanced by the deployment of this device. Here, the gamma-tomographic method and the experimental setup are demonstrated through experimental measurements of the fuel stack and gas plenum regions of a nine-rod HBWR fuel assembly configuration, where four rods had a burnup of approximately 26 MWd/kgUO(2) and five rods had a burnup of approximately 50 MWd/kgUO(2). Tomographic images are presented, which show the applicability for assessment of fission gas contents in the gas plena and of fission products in the fuel stack. Furthermore, neutron activation products are analyzed, which give additional information on construction material properties.
|
|
| 2. |
|
|
| 3. |
- Lindgren, Mikaela, 1987, et al.
(författare)
-
Toward a Comprehensive Mechanistic Understanding of Hydrogen Uptake in Zirconium Alloys by Combining Atom Probe Analysis With Electronic Structure Calculations
- 2015
-
Ingår i: ASTM Special Technical Publication. - 0066-0558. - 9780803175297 ; STP 1543, s. 515-539
-
Konferensbidrag (refereegranskat)abstract
- The ability of a zirconium alloy to resist corrosion relies on a compromise between two opposing strategies. Minimizing the hydrogen pickup fraction (HPUF) by invoking metallic electron conduction in the barrier oxide results in rapid parabolic oxide growth. On the other hand, slow sub-parabolic barrieroxide growth, as reflected in rate limiting electron transport, may result in a high HPUF. The objective of the present study is to offer mechanistic insights as to how low concentrations of different alloying elements become decisive for the overall corrosion behavior. Combining atomistic microanalysis with first principles modeling by means of density functional theory, the speciation and redox properties of Fe and Ni towards hydrogen evolution are firstly explored.Complementary atom probe microanalysis at the metal–oxide interface provides evidence for Fe and Ni segregation to grain boundaries in Zircaloy-2 that propagates into the ZrO2 scale. Descriptors for how alloying elements in ZrO2 control electron transport as well as catalytic electron-proton recombination ingrain boundaries to form H2 are determined by means of theory. The findings are generalized by further atomistic modeling, and are thus put in the context of early reports from autoclave experiments on HPUFs of zirconium with the alloying elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Nb. A shunting mechanism which combines inner and outer hydrogen evolution mechanisms is proposed. Properties of the transient zirconium sub-oxide are discussed. A plausible atomistic overall understanding emerges.
|
|
| 4. |
- Maimaitiyili, Tuerdi
(författare)
-
Phase transformation and stability studies of the Zr-H system
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zirconium alloys are widely used in the nuclear industry because of their high strength, good corrosion resistance and low neutron absorption cross-section. Zirconium has a strong affinity for hydrogen, however, and if hydrogen concentration builds up, the material will gradually degrade. In one class of such hydrogen caused degradation, called hydride induced embrittlement, hydrogen chemically reacts with zirconium forming one, or several, crystal phases of zirconium hydride. These hydrides play a primary, but sometime not fully understood, role in crack initiation and propagation within these materials. Despite the fact that hydride induced embrittlement in zirconium have been studied for several decades, there are still some unresolved issues. It has been the aim of the research presented in this thesis to provide the research community with new and updated data of the hydrides themselves in order to aid further studies within the field of hydride induced embrittlement in general, and the mechanism of delayed hydride cracking in particular. To that end, the research presented here proceeded, in short, as follows: First, zirconium hydride powder, of well defined hydrogen concentration, was produced from commercial grade zirconium. This powder was subjected to heat treatment and the hydride phases were characterized both in situ and ex situ using neutron, synchrotron X-ray, and conventional laboratory X-ray based diffraction techniques. Next, most of the low-pressure zirconium hydride phases were produced under hydrogen/argon atmosphere from commercial grade zirconium powder. This process was simultaneously monitored and recorded in real time using synchrotron X-ray diffraction. These experiments have produced new data of the behavior of different hydride phases during thermal treatment and in situ hydrogenation. For the first time all commonly reported zirconium hydride phases and the complete transformation between two different hydride phases were recorded with a single experimental arrangement. The phase transformation between δ and ε zirconium hydride was recorded in detail and presented. Finally, the controversial γ zirconium hydride was observed both in situ and ex situ and the preparation route, its crystal structure, and formation mechanisms were analyzed and presented.
|
|
| 5. |
- Persson, Bertil R, et al.
(författare)
-
Radioactivity Exploration from the Arctic to the Antarctic. Part 2. Ymer-80 Expedition
- 2015
-
Ingår i: Acta Scientiarum Lundensia. - 1651-5013. ; 2015:003, s. 1-20
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract Levels of natural radioactivity such as 222Rn (radon) and its long-lived daughters 210Pb and 210Po were measured. The radon gas was trapped on cooled charcoal filters and the long-lived daughter products sampled on fibre filters on a daily basis. In addition, short-lived progenies were followed continuously on the filters in order to achieve a time resolution of about one hour. The average 222Rn concentration in air measured during the Ymer-80 expedition in samples north of latitude 78.8 °N, was 33 ± 4 (one standard error) mBq.m-3 during Leg 1 (July-Aug.) , and 105.3 ± 8.3 mBq.m-3 during leg 2 (Aug-Sept.). During a two-week period of persistent polar winds, the mean radon concentration decreased to 19± 5 mBq.m-3. During July, August and September, the monthly average concentrations of 210Pb in air at positions north of 75 °N latitude were 31 ± 15, 89 ± 61 and 105± 57 μBq.m-3 respectively with a the grand average for all 3 months of 75 ± 28 μBq.m-3. An extensive radiochemistry program was also established to measure 134+137Cs and the trans- uranium elements 238+239+240Pu and 241Am in water, sediment and biota. The concentration of 137Cs in surface seawater along the Norwegian coast was quite constant about 157±7 Bq.m-3. At a latitude about 72 oN it stat do decrease exponentially at a rate of 0.43 deg.-1 to about 20 ± 10 Bq.m-3 above 78 oN. The results of 137Cs in sediments indicate that the total integrated area-content of 137Cs in a 1000 m water-column and sediment is about 12 kBq.m-2. In biota, the highest activity concentration of 137Cs about 1000 Bq/kgdwt was found in lichens. The activity concentration of 137Cs in polar bears was about 10 Bq/kgdwt, in seals about 1 Bq/kgdwt, and in birds about 1-7 Bq/kgdwt. The activity-concentration of 137Cs in Fucus and Laminaria was about 1-2 Bq/kgdwt, and the algae/sea-water activity-concentration ratio was about 75. The distribution of the trans-uranium element 239+240Pu in sea water decrease from 14 to 10 mBq.m-3 up to 73°N but increase again to 17 mBq.m-3 at high latitudes while 137Cs decrease. The average 241Am/ 239+240Pu activity ratio was found to be 0.13 ±0.04 (2 S.E), of 31 samples with the range 0.04 - 0.32 in surface water, Deep-water samples have been sampled at latitudes around 80.4 ±1.4 °N and along longitudes 2° W – 45.5 °E. The results of the salinity and activity concentration of 137Cs and 239+240Pu with depth of water are indicate an exponential decrease with depth of both 137Cs and 239+240Pu. In conclusion, about 25% of 137Cs present in the Arctic water and sediments originates from fall- out specific to the area. Another 25% originates from mixing with Atlantic-water from latitudes with higher fall-out. The remaining 50% might originate from European reprocessing facilities. The levels of 241Am in the Svalbard area originate from in situ build-up due to the decay of 241Pu.
|
|
| 6. |
- Tejland, Pia, 1978, et al.
(författare)
-
Oxidation Mechanism in Zircaloy- 2—The Effect of SPP Size Distribution
- 2015
-
Ingår i: ASTM Special Technical Publication. - 0066-0558. - 9780803175297 ; 1543, s. 373-403
-
Konferensbidrag (refereegranskat)abstract
- The metal/oxide interface region in Zircaloy-2 oxidized in autoclave was studied with transmission electron microscopy (TEM) and atom probe tomography. In addition to waviness on the micrometer scale the metal/oxide interface was found to have irregularities on a finer scale, and metal islands were found especially at metal hills (delayed parts of the oxidation front). The thickness of the sub-oxide layer varies considerably along the interface in the same sample, from 100 to virtually 0 nm. The sub-oxide composition may vary on a very fine scale (down to 5nm), and it can sometimes be a mixture of sub-oxides with different oxygen content. The metal matrix in contact with the sub-oxide is saturated with up to 32 at. % oxygen, and the oxygen diffusion profile in the metal is in approximate agreement with literature data for pure Zr. However, the diffusion length appears to be somewhat larger at interface metal hills than under valleys, probably for both geometrical and stress state reasons. Hydride precipitates, hardly visible in conventional TEM, give a good image contrast when employing high angle annular dark field imaging. A model for the oxidation process is presented, where the creep deformation of the metal close to the interface and the formation of lateral cracks in the oxide are of highest importance. The effect of second phase particle (SPP) size is suggested to be twofold: Small and numerous SPPs give a stronger metal and therefore higher stress in the oxide. Small SPPs also nucleate many more lateral cracks in the oxide, which gives a weaker oxide. Together this leads to formation of large cracks associated with transition in the oxidation rate at an earlier time than for a material with larger and fewer SPPs, and thereby a higher oxidation rate.
|
|
| 7. |
- Topping, Matthew, et al.
(författare)
-
The effect of iron on dislocation evolution in model and commercial zirconium alloys
- 2018
-
Ingår i: ASTM Special Technical Publication. - 0066-0558. ; STP 1597, s. 796-822
-
Konferensbidrag (refereegranskat)abstract
- Although the evolution of irradiation-induced dislocation loops has been well correlated with irradiation-induced growth phenomena, the effect of alloying elements on this evolution remains elusive, especially at low fluences. To develop a more mechanistic understanding of the role iron has on loop formation, we used state-of-the-art techniques to study a proton-irradiated Zr-0.1Fe alloy and proton- and neutron-irradiated Zircaloy-2. The two alloys were irradiated with 2-MeV protons up to 7 dpa at 350°C and Zircaloy-2 up to 14.7 × 1025n • m-2, approximately 24 dpa, in a boiling water reactor at approximately 300°C. Baseline transmission electron microscopy showed that the Zr3Fe secondary-phase particles in the binary system were larger and fewer in number than the Zr (Fe, Cr)2and Zr2(Fe, Ni) particles in Zircaloy-2. An analysis of the irradiated binary alloy revealed only limited dissolution of Ze3Fe, suggesting little dispersion of iron into the matrix, while at the same time a higher 〈a〉-loop density was observed compared with Zircaloy-2 at equivalent proton dose levels. We also found that the redistribution of iron during irradiation led to the formation of iron nanoclusters. A delay in the onset of 〈c〉-loop nucleation in proton-irradiated Zircaloy-2 compared with the binary alloy was observed. The effect of iron redistributed from secondary-phase particles because of dissolution on the density and morphology of 〈a〉 and 〈c〉 loops is described. The implication this may have on irradiation-induced growth of zirconium fuel cladding is also discussed.
|
|
