Amato, I.

Colombo, R.

Protti, A

Archive of European Integration

EUROPEAN ATOMIC ENERGY COMMUNITY - EURATOM I 
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m ON A CASE OF SOLARIZATION DURING 
S TEAM SINTERING OF U02 PELLETS ιβ»||1 
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■ S M « . 
LEGAL NOTICE 
This document was prepared under the sponsorship of the Commission of the European 
Atomic Energy Community (EURATOM). 
Neither the EURATOM Commission, its contractors nor any person acting on their behalf : 
I o — Make any warranty or representation, express or implied, with respect to the accuracy, 
completeness, or usefulness of the information contained in this document, or that the use 
of any information, apparatus, method, or process disclosed in this document may not 
infringe privately owned rights; or 
2° — Assume any liability with respect to the use of, or for damages resulting from the use of 
any information, apparatus, method or process disclosed in this document. 
The authors' names are Usted in alphabetical order. 
This reprint is intended for restricted distribution only. It reproduces, 
by kind permission of the publisher, an article from "JOURNAL 
OF NUCLEAR MATERIALS", Vol. 8, No. 2 ­1963, 271­272. For 
further copies please apply to North­Holland Publishing Co., P.O. 
Box 103 — Amsterdam (Netherlands). 
Dieser Sonderdruck ist für eine beschränkte Verteilung bestimmt. Die 
Wiedergabe des vorliegenden in ,,JOURNAL OF NUCLEAR 
M ATERÍ ALS",Vol. 8, Nr. 2­1963, 271­272 erschienenen Aufsatzes 
erfolgt mit freundlicher Genehmigung des Herausgebers. Bestellungen 
weiterer Exemplare sind an North­Holland Publishing Co., P.O. 
Box 103 — Amsterdam (Netherlands) zu richten. 
Ce tiré­à­part est exclusivement destiné à une diffusion restreinte. Il 
reprend, avec l'aimable autorisation de l'éditeur, un article publié dans 
le «JOURNAL OF NUCLEAR MATERIALS», Vol. 8, N° 2 ­1963, 
271­272. Tout autre exemplaire de cet article doit être demandé à 
North­Holland Publishing Co., P.O. Box 103 — Amsterdam (Nether­
lands). 
■ 
Questo estratto e destinato esclusivamente ad una diffusione limitata. 
Esso è stato riprodotto, per gentile concessione dell'Editore, da «JOUR­
NAL OF NUCLEAR MATERIALS», Vol. 8, No 2 ­1963, 271­272. 
Ulteriori copie dell'articolo essere richieste a North­Holland Publishing 
Co., P.O. Box 103 — Amsterdam (Netherlands). 
Âfùitâ 
Deze overdruk is slechts voor beperkte versprediing bestemd. Het artikel 
is met welwillende toestemming van de uitgever overgenomen uit 
„JOURNAL OF NUCLEAR MATERIALS", Vol. 8, no. 2­1963, 
271­272. Meer exemplaren kunnen besteld worden bij North­Holland 
Publishing Co., P.O. Box 103 — Amsterdam (Netherlands). If «Pill 
(■■•lv".'i·'. •.·6η· 
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E U R 3 8 8 . e 
R E P R I N T 
ON A CASE OF SOLARIZATION D U R I N G STEAM S I N T E R I N G OF UO, 
P E L L E T S by I. AMATO. R.L. COLOMBO and A.M. P R O T T I (FIAT, 
Sezione Energia Nucleare). 
European Atomic Energy Community - EURATOM. 
Eura tom - United States Agreement for Cooperation. 
Work performed by FIAT S.p.A. under the Euratom contract No 016-60-9 
RDI - (Part of the EURAEC Report No 321). 
Reprinted from " J O U R N A L OF NUCLEAR MATERIALS" , λ'οΐ. 8, No 2 
- 1963, pages 271-272. 
Summary not available. 
E U R 3 8 8 .e 
R E P R I N T 
ON A CASE OF SOLARIZATION DURING STEAM S I N T E R I N G OF U 0 2 
P E L L E T S by I. AMATO, R.L. COLOMBO and A.M. PROTTI (FIAT, 
Sezione Energia Nucleare). 
European Atomic Energy Community - EURATOM. 
Eura tom - United States Agreement for Cooperation. 
Work performed by FIAT S.p.A. under the Euratom contract No 016-60-9 
RDI - (Part of the EURAEC Report No 321). 
Reprinted from " J O U R N A L OF NUCLEAR MATERIALS" , Vol. 8, No 2 
- 1963, pages 271-272. 
Summary not available. 
E U R 3 8 8 . e 
R E P R I N T 
ON A CASE OF SOLARIZATION DURING STEAM S I N T E R I N G O F U 0 2 
P E L L E T S by I. AMATO, R.L. COLOMBO and A.M. PROTTI (FIAT, 
Sezione Energia Nucleare). 
European Atomic Energy Community - EURATOM. 
Eura tom - United States Agreement for Cooperation. 
Work performed by FIAT S.p.A. under the Eura tom contract No 016-60-9 
RDI - (Part of the EURAEC Report No 321). 
Reprinted from " J O U R N A L O F NUCLEAR MATERIALS" , Vol. 8, No 2 
- 1963, pages 271-272. 
Summary not available. 

JOURNAL OF NUCLEAR MATERIALS 8, No. 2 (1963) 271-272, NORTH-HOLLAND PUBLISHING CO., AMSTERDAM 
ON A CASE OF SOLARIZATION DURING STEAM SINTERING OF U 0 2 P E L L E T S 1 
I. AMATO, R. L. COLOMBO and A. M. PROTTI 
FIAT, Sezione Energia Nucleare, Torino, Italy 
Manuscript received October 1Θ62 
Solarization is the decrease of density in 
sintered bodies, which takes place with the 
increase of the t reatment time or temperature. 
Occurrence of solarization in uranium dioxide 
is reported occasionally in the literature during 
hydrogen sintering of certain powders 1·2). We 
have observed it during sintering in steam 
atmosphere on material, which did not show 
evidence of it during hydrogen sintering. 
The powder was purchased from the CNEN 
(National Committee for Nuclear Energy) and 
was jjroduced through the "wet process',' (oven-
drying of hydrated oxyde precipitated from 
tetravalent Uranium solution) 3). The 0 /U ratio 
was 2.02 and the surface area 3.6 m2/g. Pellets 
were pressed to about 7 g/cm3 with the addition 
of 1 % in weight of PVA and 1 % of stearic acid. 
Some were sintered in a hydrogen atmosphere 
and had a final density only slightly inferior to 
tha t of joellets made with other kinds of powder. 
The steam sintering cycle was the following: 
1) Heating up in nitrogen to S00° C. 
2) Heating up in hydrogen to 1398° C. 
3) Soaking in steam at 1398° C for various 
periods of time. 
4) Cooling down in hydrogen from 1398° C to 
800° C. 
5) Cooling down in nitrogen to RT. 
Fig. 1 gives the plot of the fired density versus 
the soaking t ime: one may see tha t beyond 
2 h the fired density starts to decrease even 
though it is still below tha t expected for such 
powder. 
Micrographie examination of the sintered 
bodies gives some explanations of this pheno­
menon. Steam sintering of the CNEN powder 
is characterized by discontinuous grain growth 
from its early stages (fig. 2). This, according 
to Coble and Burke's theory 4>5), would result 
in poor densification, since very soon the 
majority of the closed pores would become 
isolated from grain boundaries and cease to 
shrink. 
At this point one would expect little further 
sintering; the decrease in the fired density is 
possibly due to the pressure of the gases trapped 
in the isolated pores, which causes some of them 
95 
90 
o 
80 
75 
70 
POWDER CNEN CER GRADE 
SREEN DENSITY ~7 g / cc 
SOAKING TEMPER 1398° C 
SINTERING ATMOSPH SUM 
2 < 6 8 
SOAKING TIME (h) 
Fig. 1. Fired density versus soaking time during 
steam sintering at 1398° C. 
H e a t i n g a n d cooling r a t e s were k e p t as low P o w d e r : CNEN Cer grade Soaking temp.: 1398° C. 
as 5° C/min. 
t Work performed under Euratom/TJSA contract n° 011-60-9-RDI. 
271 
Green density : sw 7 g/cc Sintering atm. : steam 
272 I . AMATO, K !.. COLOMBO AND A. M. 1'liOTTI 
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l ) i s ( 
s i n i 
Τ 
ontinuous grain growth at the beginning .,· „ ,, .. c ,· , ■ , . ,. ,, , ■ big. ,i. Cavity tormation during solarization. Soaking ering at 1398 C. Soaking time: 30 mm. _ , r„ .-. .,-, . „. , , . .««« time: ;> h, Τ.Π. 82.0 "„ etched. χ 1000 D.: SLS % etched. · 1(100 '° 
EQUIVALENT PORE DIAMETER ι MICRONSi 
0016 
Q0I5 
O.Oli 
0.013 
0.012. 
0.011 . 
0,010 I 
0009 . 
0008 . 
0 0 0 7 . 
0 006. 
0 005. 
O.OOi. 
0003. 
0002 
0.001 
0.000 
S S S 3 S S o r ^ - , r , c — ö ö o o σ 
POWDER: CNEN CERAMIC GRADE 
GREEN DENSITY ~7gr tcc 
SINTERING ATMOSPHERE STEAM 
SOAKING TEMPERATURE: 1396*C 
■ α SV 'I. T O I V2 hr I 
» 83.17. TO. C 1 hr ) 
• 84.1 V. T. D. ( 2 
TO ( 3 
TD I 5 
r.o.( β 
2 P Q OO OOO _ OQOOOO r-, 
" " " ~ S s s s s s s å § 
■■ f i 
ABSOLUTE PRESSURE ι PSI · 
§ ο ο σ ° ο p o o 
r*1 -4 UJ ADO 
Kig. 4. Open pore distribution (Aminen Winslow] 
for isothcnnally sintered pellets. 
to merge owing t o p l a s t i c i t y effects: fig. 3 
shows one of t h e big cavi t ies fo rmed in a 
solarized spec imen . 
T h a t so lar iza t ion is no t due t o some r e v e r t i n g 
of s in te r ing is shown in fig. 4, w h i c h i nd i ca t e s 
t h a t t h e open poros i ty is less for a so la r ized 
specimen t h a n for a non-so lar ized one h a v i n g 
h igher dens i ty . 
References 
') R. Winchell, Atomic Energy, Report YAEC (1960) 
159 
-) A. Bel, R. Delmas e1 B. François. Frittage do 
l'oxyde d'uranium dans l'hydrogène à 1350° C, 
Stockholm Conference (1959) 
:') M. Gabaglio cl al., Euratom/USA Contract 
n ' . 028-60-10-RDI, Final Report 
') R. L. Coble and J . E. Burke, In : Reactivity of 
Solids 38 (Amsterdam, Elsevier, 1901) 
"') R. L. Coble, J. Appi. Phys. 32 (1901) 787 

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ON A CASE OF SOLARIZATION DURING SST EAM SINTERING OF U02 PELLETS. EUR 388.e

EUROPEAN ATOMIC ENERGY COMMUNITY - EURATOM I .»¡AU». ^ ϊ^ί,-ΗΓ;.','..».; ,;piSi£ ¡sm m m ON A CASE OF SOLARIZATION DURING S TEAM SINTERING OF U02 PELLETS ιβ»||1 fei? ■ S M « . LEGAL NOTICE This document was prepared under the sponsorship of the Commission of the European Atomic Energy Community (EURATOM). Neither the EURATOM Commission, its contractors nor any person acting on their behalf : I o — Make any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this document, or that the use of any information, apparatus, method, or process disclosed in this document may not infringe privately owned rights; or 2° — Assume any liability with respect to the use of, or for damages resulting from the use of any information, apparatus, method or process disclosed in this document. The authors' names are Usted in alphabetical order. This reprint is intended for restricted distribution only. It reproduces, by kind permission of the publisher, an article from "JOURNAL OF NUCLEAR MATERIALS", Vol. 8, No. 2 ­1963, 271­272. For further copies please apply to North­Holland Publishing Co., P.O. Box 103 — Amsterdam (Netherlands). Dieser Sonderdruck ist für eine beschränkte Verteilung bestimmt. Die Wiedergabe des vorliegenden in ,,JOURNAL OF NUCLEAR M ATERÍ ALS",Vol. 8, Nr. 2­1963, 271­272 erschienenen Aufsatzes erfolgt mit freundlicher Genehmigung des Herausgebers. Bestellungen weiterer Exemplare sind an North­Holland Publishing Co., P.O. Box 103 — Amsterdam (Netherlands) zu richten. Ce tiré­à­part est exclusivement destiné à une diffusion restreinte. Il reprend, avec l'aimable autorisation de l'éditeur, un article publié dans le «JOURNAL OF NUCLEAR MATERIALS», Vol. 8, N° 2 ­1963, 271­272. Tout autre exemplaire de cet article doit être demandé à North­Holland Publishing Co., P.O. Box 103 — Amsterdam (Nether­lands). ■ Questo estratto e destinato esclusivamente ad una diffusione limitata. Esso è stato riprodotto, per gentile concessione dell'Editore, da «JOUR­NAL OF NUCLEAR MATERIALS», Vol. 8, No 2 ­1963, 271­272. Ulteriori copie dell'articolo essere richieste a North­Holland Publishing Co., P.O. Box 103 — Amsterdam (Netherlands). Âfùitâ Deze overdruk is slechts voor beperkte versprediing bestemd. Het artikel is met welwillende toestemming van de uitgever overgenomen uit „JOURNAL OF NUCLEAR MATERIALS", Vol. 8, no. 2­1963, 271­272. Meer exemplaren kunnen besteld worden bij North­Holland Publishing Co., P.O. Box 103 — Amsterdam (Netherlands). If «Pill (■■•lv".'i·'. •.·6η· ' . - * ■ : > > FSMÉKMJ E«».»« flutit·) ' Ili ■ I * ψ. L· • Jj l i*l£ • 'Si ill •oy άκάκώ;- ;Br& E U R 3 8 8 . e R E P R I N T ON A CASE OF SOLARIZATION D U R I N G STEAM S I N T E R I N G OF UO, P E L L E T S by I. AMATO. R.L. COLOMBO and A.M. P R O T T I (FIAT, Sezione Energia Nucleare). European Atomic Energy Community - EURATOM. Eura tom - United States Agreement for Cooperation. Work performed by FIAT S.p.A. under the Euratom contract No 016-60-9 RDI - (Part of the EURAEC Report No 321). Reprinted from " J O U R N A L OF NUCLEAR MATERIALS" , λ'οΐ. 8, No 2 - 1963, pages 271-272. Summary not available. E U R 3 8 8 .e R E P R I N T ON A CASE OF SOLARIZATION DURING STEAM S I N T E R I N G OF U 0 2 P E L L E T S by I. AMATO, R.L. COLOMBO and A.M. PROTTI (FIAT, Sezione Energia Nucleare). European Atomic Energy Community - EURATOM. Eura tom - United States Agreement for Cooperation. Work performed by FIAT S.p.A. under the Euratom contract No 016-60-9 RDI - (Part of the EURAEC Report No 321). Reprinted from " J O U R N A L OF NUCLEAR MATERIALS" , Vol. 8, No 2 - 1963, pages 271-272. Summary not available. E U R 3 8 8 . e R E P R I N T ON A CASE OF SOLARIZATION DURING STEAM S I N T E R I N G O F U 0 2 P E L L E T S by I. AMATO, R.L. COLOMBO and A.M. PROTTI (FIAT, Sezione Energia Nucleare). European Atomic Energy Community - EURATOM. Eura tom - United States Agreement for Cooperation. Work performed by FIAT S.p.A. under the Eura tom contract No 016-60-9 RDI - (Part of the EURAEC Report No 321). Reprinted from " J O U R N A L O F NUCLEAR MATERIALS" , Vol. 8, No 2 - 1963, pages 271-272. Summary not available. JOURNAL OF NUCLEAR MATERIALS 8, No. 2 (1963) 271-272, NORTH-HOLLAND PUBLISHING CO., AMSTERDAM ON A CASE OF SOLARIZATION DURING STEAM SINTERING OF U 0 2 P E L L E T S 1 I. AMATO, R. L. COLOMBO and A. M. PROTTI FIAT, Sezione Energia Nucleare, Torino, Italy Manuscript received October 1Θ62 Solarization is the decrease of density in sintered bodies, which takes place with the increase of the t reatment time or temperature. Occurrence of solarization in uranium dioxide is reported occasionally in the literature during hydrogen sintering of certain powders 1·2). We have observed it during sintering in steam atmosphere on material, which did not show evidence of it during hydrogen sintering. The powder was purchased from the CNEN (National Committee for Nuclear Energy) and was jjroduced through the "wet process',' (oven-drying of hydrated oxyde precipitated from tetravalent Uranium solution) 3). The 0 /U ratio was 2.02 and the surface area 3.6 m2/g. Pellets were pressed to about 7 g/cm3 with the addition of 1 % in weight of PVA and 1 % of stearic acid. Some were sintered in a hydrogen atmosphere and had a final density only slightly inferior to tha t of joellets made with other kinds of powder. The steam sintering cycle was the following: 1) Heating up in nitrogen to S00° C. 2) Heating up in hydrogen to 1398° C. 3) Soaking in steam at 1398° C for various periods of time. 4) Cooling down in hydrogen from 1398° C to 800° C. 5) Cooling down in nitrogen to RT. Fig. 1 gives the plot of the fired density versus the soaking t ime: one may see tha t beyond 2 h the fired density starts to decrease even though it is still below tha t expected for such powder. Micrographie examination of the sintered bodies gives some explanations of this pheno­menon. Steam sintering of the CNEN powder is characterized by discontinuous grain growth from its early stages (fig. 2). This, according to Coble and Burke's theory 4>5), would result in poor densification, since very soon the majority of the closed pores would become isolated from grain boundaries and cease to shrink. At this point one would expect little further sintering; the decrease in the fired density is possibly due to the pressure of the gases trapped in the isolated pores, which causes some of them 95 90 o 80 75 70 POWDER CNEN CER GRADE SREEN DENSITY ~7 g / cc SOAKING TEMPER 1398° C SINTERING ATMOSPH SUM 2 < 6 8 SOAKING TIME (h) Fig. 1. Fired density versus soaking time during steam sintering at 1398° C. H e a t i n g a n d cooling r a t e s were k e p t as low P o w d e r : CNEN Cer grade Soaking temp.: 1398° C. as 5° C/min. t Work performed under Euratom/TJSA contract n° 011-60-9-RDI. 271 Green density : sw 7 g/cc Sintering atm. : steam 272 I . AMATO, K !.. COLOMBO AND A. M. 1'liOTTI ■\*k^*<": • v-Κ>ν^Λ#..& (il s t Cli II l ) i s ( s i n i Τ ontinuous grain growth at the beginning .,· „ ,, .. c ,· , ■ , . ,. ,, , ■ big. ,i. Cavity tormation during solarization. Soaking ering at 1398 C. Soaking time: 30 mm. _ , r„ .-. .,-, . „. , , . .««« time: ;> h, Τ.Π. 82.0 "„ etched. χ 1000 D.: SLS % etched. · 1(100 '° EQUIVALENT PORE DIAMETER ι MICRONSi 0016 Q0I5 O.Oli 0.013 0.012. 0.011 . 0,010 I 0009 . 0008 . 0 0 0 7 . 0 006. 0 005. O.OOi. 0003. 0002 0.001 0.000 S S S 3 S S o r ^ - , r , c — ö ö o o σ POWDER: CNEN CERAMIC GRADE GREEN DENSITY ~7gr tcc SINTERING ATMOSPHERE STEAM SOAKING TEMPERATURE: 1396*C ■ α SV 'I. T O I V2 hr I » 83.17. TO. C 1 hr ) • 84.1 V. T. D. ( 2 TO ( 3 TD I 5 r.o.( β 2 P Q OO OOO _ OQOOOO r-, " " " ~ S s s s s s s å § ■■ f i ABSOLUTE PRESSURE ι PSI · § ο ο σ ° ο p o o r*1 -4 UJ ADO Kig. 4. Open pore distribution (Aminen Winslow] for isothcnnally sintered pellets. to merge owing t o p l a s t i c i t y effects: fig. 3 shows one of t h e big cavi t ies fo rmed in a solarized spec imen . T h a t so lar iza t ion is no t due t o some r e v e r t i n g of s in te r ing is shown in fig. 4, w h i c h i nd i ca t e s t h a t t h e open poros i ty is less for a so la r ized specimen t h a n for a non-so lar ized one h a v i n g h igher dens i ty . References ') R. Winchell, Atomic Energy, Report YAEC (1960) 159 -) A. Bel, R. Delmas e1 B. François. Frittage do l'oxyde d'uranium dans l'hydrogène à 1350° C, Stockholm Conference (1959) :') M. Gabaglio cl al., Euratom/USA Contract n ' . 028-60-10-RDI, Final Report ') R. L. Coble and J . E. Burke, In : Reactivity of Solids 38 (Amsterdam, Elsevier, 1901) "') R. L. Coble, J. Appi. Phys. 32 (1901) 787 iiii teiiiiiliiiiiill J. >u:i'ilnlnHI"f ï mPW ¡flîii ^ W t r ø t ' '$ Siv ■ ilillpp '' t ΒΗΙ ΙΠ ' ! * SSr*"'· l^21nií.'a*í'Ci(tjKKn'i> °ii»e f . 'Mt l ΜΗ ISIISI sil iiii I?Miif:$ 

ON A CASE OF SOLARIZATION DURING SST EAM SINTERING OF U02 PELLETS. EUR 388.e

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