Environmental Engineering Reference
In-Depth Information
Although not a new phenomenon, observed second phase precipitate
dissolution and re-precipitation have required a new perspective on
alloy development and hydrogen pickup.
BWR channel bow at high burnup has required a new understanding of
the relationships between hydrogen pickup, shadow corrosion and irra-
diation growth.
A broader listing of issues needing resolution includes:
Corrosion related to oxide thickness and H pickup
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BWRs and PWRs:
Mechanism of solid hydrides on corrosion mechanisms.
BWRs:
Effect of Nb.
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Shadow corrosion mechanisms and their relation to channel
bow.
Late increased corrosion and HPU of Zircaloy-2 at high
burnups.
Crud-chemistry-corrosion interaction.
Effect of water chemistry impurities, as well as specifi c effects of
NMCA, with or without Zn-injection.
PWRs:
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Effects of surface contaminations and/or boiling on Zr-Nb alloys.
Welding of the new alloys may need improved processes (Zr-Nb
alloys).
Effect of increased Li together with increased duty (subcooled
boiling) with and without Zn-injection.
Effects of increased hydrogen coolant content (to mitigate
PWSCC).
Axial offset anomaly (AOA) mechanisms.
Mechanical properties related to irradiation and H pickup
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Decreased ductility and fracture toughness as consequence of the
increased HPU and formation of radial hydrides during any situa-
tion (e.g. RIA, PCMI, LOCA and post-LOCA events, seismic event,
transport container drop-accident conditions).
Quantifi cation of the effect of irradiation on hydrogen solubility and
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mechanism(s) by which the phenomenon occurs.
Details of deformation mechanisms in zirconium alloys, including
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being able to predict the dislocation channelling system.
Development of micromechanical models applicable to deformation
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at appropriate component conditions.
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