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Chemistry Change Of CRUD With Various Metal Ion Concentration Conditions In PWR Fuel Cladding

Since 1960s, CRUD induced problems become an issue in PWR power plant. To enhance economic efficiency of PWR, the burn-ups of nuclear fuel have been increased. In the reactor core, some unexpected power shifts, which shows negative axial offset from prediction, have been observed. This phenomenon is called by AOA (Axial offset Anomaly) and it seems to be caused by deposits on the upper side of fuel cladding surface which is called CRUD.

Product Number: ED22-17313-SG
Author: Yunju Lee, Seung Chang Yoo, Junhyuk Ham, Daehyeon Park, Ji Hyun Kim
Publication Date: 2022
$20.00
$20.00
$20.00

To investigate CRUD deposition on fuel cladding under various water chemistry condition in simulated PWR primary water, the experimental facility has been set up. In previous study, effect of heat flux on CRUD structure and chemistry was examined for high metal ion concentration condition. In this study, to investigate effect of metal ion concentration condition on CRUD formation, CRUD deposition experiment was conducted for three different metal ion concentration. The specimens were observed by optical microscopy and scanning electron microscopy with focused ion beam instrument. The chemistry and microstructure of CRUD specimens are examined by scanning electron microscopy and energy dispersive X-ray spectroscopy.
Thickness of CRUD increased depend on metal ion concentration. In lower metal ion concentration condition primitive structure of CRUD chimneys were found while developed chimney structure were formed in higher metal ion concentration condition. From chemical analysis, it is found that more Ni oxide species deposited in the surface of cladding in lower metal ion concentration condition. CRUD layer formed in high metal ion concentration condition shows low Ni/Fe ratio near cladding surface while Ni/Fe ratio increased in outer layer. Although higher metal ion concentration specimen has thicker CRUD layer, thermal conductivity of CRUD was higher. This can be explained by growth rate of chimney structure, which can promote heat transfer in CRUD layer by enhancing Wick boiling behavior.


To investigate CRUD deposition on fuel cladding under various water chemistry condition in simulated PWR primary water, the experimental facility has been set up. In previous study, effect of heat flux on CRUD structure and chemistry was examined for high metal ion concentration condition. In this study, to investigate effect of metal ion concentration condition on CRUD formation, CRUD deposition experiment was conducted for three different metal ion concentration. The specimens were observed by optical microscopy and scanning electron microscopy with focused ion beam instrument. The chemistry and microstructure of CRUD specimens are examined by scanning electron microscopy and energy dispersive X-ray spectroscopy.
Thickness of CRUD increased depend on metal ion concentration. In lower metal ion concentration condition primitive structure of CRUD chimneys were found while developed chimney structure were formed in higher metal ion concentration condition. From chemical analysis, it is found that more Ni oxide species deposited in the surface of cladding in lower metal ion concentration condition. CRUD layer formed in high metal ion concentration condition shows low Ni/Fe ratio near cladding surface while Ni/Fe ratio increased in outer layer. Although higher metal ion concentration specimen has thicker CRUD layer, thermal conductivity of CRUD was higher. This can be explained by growth rate of chimney structure, which can promote heat transfer in CRUD layer by enhancing Wick boiling behavior.