| 1. |
- Kolbas, Daria, et al.
(författare)
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Role of various influencing parameters on high temperature fretting behaviour of different tribopairs in liquid lead
- 2024
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Ingår i: Nuclear Materials and Energy. - : Elsevier Ltd. - 2352-1791. ; 40
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Tidskriftsartikel (refereegranskat)abstract
- The increasing interest in liquid metal cooled nuclear reactors provides technical and scientific challenges such as the understanding, prevention, and prediction of the degradation of materials in liquid lead. Critical components include the fuel rods, heat exchanger tubes, and pump impellers. These functional elements are exposed to mechanical loading (up to 40 MPa), high temperatures (450–550 °C), and fluid-induced vibrations (up to 25 Hz). Under such conditions, fretting wear occurs between e.g., the spacer wire and the outer surface of the fuel or heat exchanger tubes. This work is aimed to establish a laboratory-scale fretting wear test setup and develop test methodology to enable systematic material characterisation in liquid metal environments. The results obtained by using the described methodology indicate that adhesive wear is the dominant degradation mechanism, and 316L stainless steel shows a higher coefficient of friction but a lower wear volume/tribolayer volume compared to 100Cr6 bearing steel. These results are in agreement with those reported in open literature and demonstrates the suitability of the presented method for conducting fretting tests and analysis for various materials and contact configurations in liquid lead environment.
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| 2. |
- Tokitani, Masayuki, et al.
(författare)
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Co-deposited layers on gap surfaces of bulk tungsten divertor tiles in JET ITER-like wall: Directional effects and nanostructures
- 2024
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- Co-deposited layers on surfaces of bulk tungsten divertor tiles (W lamellae) from the first campaign of JET with the ITER-Like Wall (JET-ILW, 2011–2012) were examined by means of a cross-sectional transmission electron microscope observation. The focus was on geometrical effects in impurity deposition, mainly beryllium (Be), on surfaces located in the poloidal gap separating adjacent lamellae. The study was carried out on the sides (gap surfaces) of two W lamellae from Stack C (located on the outboard part of the horizontal section of the lower divertor), from the region most exposed to the plasma (lamella C23) and in the magnetic shadow of the upstream divertor module (lamella C3). The tile manufacturing process (cold rolling) left shallow grooves, i.e. structures classified as convex (hill) and concave (valley) regions. These regions are decisive for the deposition structure. The main results were: (i) two kinds of impurity deposition features, “homogeneous” and “directional”, have been distinguished; (ii) the directional ones were characterized by nanoscale inclined vertical stripes in the deposition layer; (iii) homogeneous deposition without directional features were in the valley region. The results clearly indicate the impact of the surface finish, even in the tile gaps, on the qualitative and quantitative aspects of deposition.
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| 3. |
- Vesti, Anders, et al.
(författare)
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First-principles study on thermal expansion of W-Re sigma and chi phases
- 2024
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- We investigate how the Re content affects the coefficient of thermal expansion (CTE) of the non-stoichiometric W-based sigma and chi phases, forming upon neutron irradiation of W, to explore and quantify its mismatch between precipitates (W-Re) and matrix (W). To this end, we have conducted first-principles calculations using two approaches: the Debye-Grüneisen (DG) model and the quasi-harmonic approximation (QHA). The two approaches yield different results: the QHA, which is deemed to be the most accurate of the two, predicts substantial changes with Re content, while the acoustic-modes based DG model does not. The CTE of the sigma and chi at stable Re contents is compared to experimental values for bcc-W and bcc-W-Re containing 25 at.% Re. Taking bcc-W as a reference, we find a significant mismatch in CTE of up to 37% and 62% for sigma and chi, respectively, which may contribute to thermal stress buildup in the material at elevated temperatures. The mismatch is shown to increase with the temperature and Re content for both phases. The produced data are used to fit a temperature and Re concentration-dependent analytical function of the CTE for both phases, which can be employed as input for continuum mechanical modeling.
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