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Title: Leaching of used CANDU fuel: Results from a 19-year leach test under oxidizing conditions

Abstract

A fuel leaching experiment has been in progress since 1977 to study the dissolution behavior of used CANDU fuel in aerated aqueous solution. The experiment involves exposure of 50-mm clad segments of an outer element of a Pickering fuel bundle (burnup 610 GJ/kg U; linear and peak power ratings 53 and 58 kW/m, respectively), to deionized distilled water (DDH{sub 2}O, {approximately}2 mg/L carbonate) and tapwater ({approximately}50 mg/L carbonate). In 1992, it was observed that the fuel in at least one of the leaching solutions showed some signs of deterioration and, therefore, in 1993, parts of the fuel samples were sacrificed for a detailed analysis of the physical state of the fuel, using SEM and optical microscopy. Leaching results to date show that even after >6900 days only 5 to 7.7% of the total calculated inventory of {sup 137}Cs has leached out preferentially and that leach rates suggest a development towards congruent dissolution. Total amounts of {sup 137}Cs and {sup 90}Sr leached are slightly larger in tapwater than in DDH{sub 2}O. SEM examinations of leached fuel surface fragments indicate that the fuel surface exposed to DDH{sub 2}O is covered in a needle-like precipitate. The fuel surface exposed to tapwater shows evidencemore » of leaching but no precipitate, likely because uranium is kept in solution by carbonate. Detailed optical and SEM microscopy examinations on fuel cross sections suggest that grain-boundary dissolution in DDH{sub 2}O is not prevalent, and in tapwater appears to be limited to the outer {approximately}0.5 mm (pellet/cladding) region of the fuel. Grain boundary attack seems to be limited to microcracks at or near the surface of the fuel. It thus appears that grain-boundary attack occurs only near the fuel pellet surface and is prevalent only in the presence of carbonate in solution.« less

Authors:
; ; ; ;  [1]
  1. AECL, Pinawa, Manitoba (Canada). Whiteshell Labs.
Publication Date:
OSTI Identifier:
572116
Report Number(s):
CONF-961202-
Journal ID: ISSN 0275-0012; TRN: 98:003727
Resource Type:
Book
Resource Relation:
Conference: 1996 Fall meeting of the Materials Research Society (MRS), Boston, MA (United States), 2-6 Dec 1996; Other Information: PBD: 1997; Related Information: Is Part Of Scientific basis for nuclear waste management XX; Gray, W.J. [ed.] [Pacific Northwest National Lab., Richland, WA (United States)]; Triay, I.R. [ed.] [Los Alamos National Lab., NM (United States)]; PB: 1389 p.; Materials Research Society symposium proceedings, Volume 465
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 05 NUCLEAR FUELS; 21 NUCLEAR POWER REACTORS AND ASSOCIATED PLANTS; URANIUM DIOXIDE; DISSOLUTION; SPENT FUELS; LEACHING; PICKERING-1 REACTOR; CESIUM 137; STRONTIUM 90; EXPERIMENTAL DATA; SPENT FUEL STORAGE

Citation Formats

Stroes-Gascoyne, S, Johnson, L H, Tait, J C, McConnell, J L, and Porth, R J. Leaching of used CANDU fuel: Results from a 19-year leach test under oxidizing conditions. United States: N. p., 1997. Web.
Stroes-Gascoyne, S, Johnson, L H, Tait, J C, McConnell, J L, & Porth, R J. Leaching of used CANDU fuel: Results from a 19-year leach test under oxidizing conditions. United States.
Stroes-Gascoyne, S, Johnson, L H, Tait, J C, McConnell, J L, and Porth, R J. 1997. "Leaching of used CANDU fuel: Results from a 19-year leach test under oxidizing conditions". United States.
@article{osti_572116,
title = {Leaching of used CANDU fuel: Results from a 19-year leach test under oxidizing conditions},
author = {Stroes-Gascoyne, S and Johnson, L H and Tait, J C and McConnell, J L and Porth, R J},
abstractNote = {A fuel leaching experiment has been in progress since 1977 to study the dissolution behavior of used CANDU fuel in aerated aqueous solution. The experiment involves exposure of 50-mm clad segments of an outer element of a Pickering fuel bundle (burnup 610 GJ/kg U; linear and peak power ratings 53 and 58 kW/m, respectively), to deionized distilled water (DDH{sub 2}O, {approximately}2 mg/L carbonate) and tapwater ({approximately}50 mg/L carbonate). In 1992, it was observed that the fuel in at least one of the leaching solutions showed some signs of deterioration and, therefore, in 1993, parts of the fuel samples were sacrificed for a detailed analysis of the physical state of the fuel, using SEM and optical microscopy. Leaching results to date show that even after >6900 days only 5 to 7.7% of the total calculated inventory of {sup 137}Cs has leached out preferentially and that leach rates suggest a development towards congruent dissolution. Total amounts of {sup 137}Cs and {sup 90}Sr leached are slightly larger in tapwater than in DDH{sub 2}O. SEM examinations of leached fuel surface fragments indicate that the fuel surface exposed to DDH{sub 2}O is covered in a needle-like precipitate. The fuel surface exposed to tapwater shows evidence of leaching but no precipitate, likely because uranium is kept in solution by carbonate. Detailed optical and SEM microscopy examinations on fuel cross sections suggest that grain-boundary dissolution in DDH{sub 2}O is not prevalent, and in tapwater appears to be limited to the outer {approximately}0.5 mm (pellet/cladding) region of the fuel. Grain boundary attack seems to be limited to microcracks at or near the surface of the fuel. It thus appears that grain-boundary attack occurs only near the fuel pellet surface and is prevalent only in the presence of carbonate in solution.},
doi = {},
url = {https://www.osti.gov/biblio/572116}, journal = {},
issn = {0275-0012},
number = ,
volume = ,
place = {United States},
year = {Wed Dec 31 00:00:00 EST 1997},
month = {Wed Dec 31 00:00:00 EST 1997}
}

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