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Equi-axed and columnar grain growth in UO{sub 2}

Abstract

The grain size of UO{sub 2} is an important parameter in the actual performance and the modelling of the performance of reactor fuel elements. Many processes depend critically on the grain size, for example, the degree of initial densification, the evolution rate of stable fission gases, the release rates of radiologically hazardous fission products, the fission gas bubble swelling rates and the fuel creep. Many of these processes are thermally activated and further impact on the fuel thermal behavior thus creating complex feedback processes. In order to model the fuel performance accurately it is necessary to model the evolution of the fuel grain radius. When UO{sub 2} is irradiated, the fission gases xenon and krypton are created from the fissioning uranium nucleus. At high temperatures these gases diffuse rapidly to the grain boundaries where they nucleate immobile lenticular shaped fission gas bubbles. In this paper the Hillert grain growth model is adapted to account for the inhibiting ``Zener`` effects of grain boundary fission gas porosity on grain boundary mobility and hence grain growth. It is shown that normal grain growth ceases at relatively low levels of irradiation. At high burnups, high temperatures and in regions of high temperature gradients, columnar  More>>
Authors:
White, R J [1] 
  1. Berkely Technology Centre, Nuclear Electric plc, Berkeley (United Kingdom)
Publication Date:
Aug 01, 1997
Product Type:
Conference
Report Number:
IAEA-TECDOC-957; CONF-9409411-
Reference Number:
SCA: 210000; PA: AIX-28:068399; EDB-98:023846; SN: 97001863036
Resource Relation:
Conference: IAEA technical committee meeting on water reactor fuel element modelling at high burnup and its experimental support, Windermere (United Kingdom), 19-23 Sep 1994; Other Information: PBD: Aug 1997; Related Information: Is Part Of Water reactor fuel element modelling at high burnup and its experimental support. Proceedings of a technical committee meeting; PB: 559 p.
Subject:
21 NUCLEAR POWER REACTORS AND ASSOCIATED PLANTS; GRAIN GROWTH; SIMULATION; URANIUM DIOXIDE; FEEDBACK; FUEL ELEMENTS; KRYPTON; WATER COOLED REACTORS; XENON
OSTI ID:
575597
Research Organizations:
International Atomic Energy Agency, Vienna (Austria)
Country of Origin:
IAEA
Language:
English
Other Identifying Numbers:
Journal ID: ISSN 1011-4289; Other: ON: DE98602336; TRN: XA9744815068399
Availability:
INIS; OSTI as DE98602336
Submitting Site:
INIS
Size:
pp. 419-427
Announcement Date:

Citation Formats

White, R J. Equi-axed and columnar grain growth in UO{sub 2}. IAEA: N. p., 1997. Web.
White, R J. Equi-axed and columnar grain growth in UO{sub 2}. IAEA.
White, R J. 1997. "Equi-axed and columnar grain growth in UO{sub 2}." IAEA.
@misc{etde_575597,
title = {Equi-axed and columnar grain growth in UO{sub 2}}
author = {White, R J}
abstractNote = {The grain size of UO{sub 2} is an important parameter in the actual performance and the modelling of the performance of reactor fuel elements. Many processes depend critically on the grain size, for example, the degree of initial densification, the evolution rate of stable fission gases, the release rates of radiologically hazardous fission products, the fission gas bubble swelling rates and the fuel creep. Many of these processes are thermally activated and further impact on the fuel thermal behavior thus creating complex feedback processes. In order to model the fuel performance accurately it is necessary to model the evolution of the fuel grain radius. When UO{sub 2} is irradiated, the fission gases xenon and krypton are created from the fissioning uranium nucleus. At high temperatures these gases diffuse rapidly to the grain boundaries where they nucleate immobile lenticular shaped fission gas bubbles. In this paper the Hillert grain growth model is adapted to account for the inhibiting ``Zener`` effects of grain boundary fission gas porosity on grain boundary mobility and hence grain growth. It is shown that normal grain growth ceases at relatively low levels of irradiation. At high burnups, high temperatures and in regions of high temperature gradients, columnar grain growth is often observed, in some cases extending over more than fifty percent of the fuel radius. The model is further extended to account for the de-pinning of grains in the radial direction by the thermal gradient induced force on a fission gas grain boundary bubble. The observed columnar/equi-axed boundary is in fair agreement with the predictions of an evaporation/condensation model. The grain growth model described in this paper requires information concerning the scale of grain boundary porosity, the local fuel temperature and the local temperature gradient. The model is currently used in the Nuclear Electric version of the ENIGMA fuel modelling code. (author). 14 refs, 3 figs, 1 tab.}
place = {IAEA}
year = {1997}
month = {Aug}
}