Radiop o ec ion - Colloques, olume 37, Cl (2002) Cl-81
Expe imen al and modelling s udy o a i icial adionuclides
(239Pu,241 Am and 99Tc) up ake by suspended ma e in en i onmen al wa e s
loca ed in he sou h o Spain
R. El-M abe , J.M. Ab il1 and G. Manjon2
Depa amen o de Física A ómica, Molecula y
Nuclea ,
Facul ad de Física,
Uni e si y o Se ille, Apdo., 41060 Se illa, Spain
1 Depa amen o de Física Aplicada 1, Uni e si y o Se ille, EUITA,
Ca e e a de U e a km 1, 41013 Se illa, Spain
2 Depa amen o de Física Aplicada 2, Uni e si y o Se ille, ETSA,
A da. Reina Me cedes s/n, 41012 Se illa, Spain
Abs ac . The in e es on ans e coe icien s s udies ha e inc eased ecen ly, since hey a e impo an pa ame e s
equi ed unde s anding and eliably modelling he dispe sion o conse a i e and non-conse a i e adionuclides in
aqua ic en i onmen s. The app oaches, based in he implemen a ion o he up ake kine ics o dissol ed
adionuclides by solid pa icles, a e mo e app op ia e han hose based in he use o he dis ibu ion coe icien s, k^.
In his wo k, we p esen a se ies o acing expe imen s o s udy he up ake o Pu, Am and Tc in na u al aqueous
suspensions om h ee aqua ic sys ems (Ge gal ese oi , Guadalqui i i e , and he es ua y o Tin o i e ) loca ed
in he Sou h o Spain. The kine ic ans e coe icien o di ec so p ion depends on he o al a ailable su ace o
pa icles and on he concen a ion o ac i e si es in he su ace laye (wha depends on he mine al composi ion, ee
edges,
po es, coa ings, e c.). In o de o compa e esul s om di e en en i onmen s and o ix he condi ions o
applicabili y o he de i ed coe icien s, i is necessa y o handle he pa icle size spec a and he mine al
composi ion o na u al occu ing suspended loads. The ime dependen up ake cu es, co e ing up o a la ge pe iod,
a e i ed o he nume ical solu ions calcula ed wi h di e en models o he up ake kine ics.
1.
INTRODUCTION
In e es in Pu, Am and Tc up ake kine ics in na u al aqueous suspensions has ecen ly inc eased in
o de o unde s and and eliably model he dispe sion o adioac i e was es in aqua ic en i onmen s,
especially when kine ic eac i e anspo models o idal wa e s a e used [1]. The app oaches based on
he implemen a ion o he up ake kine ics a e mo e app op ia e han hose based on he use o dis ibu ion
coe icien s, kd. Mo eo e , [2] ha e discussed he cons ain s o he applicabili y o "in-si u dis ibu ion
coe icien " alues in he quan i ica ion o solu e anspo in na u al wa e s.
In he scien i ic li e a u e we can ind many examples o expe imen al s udies on he up ake kine ics
o dissol ed adionuclides by suspended loads. Thus, [3] ob ained kine ic ans e coe icien s o se e al
elemen s om seawa e on o pa icula e ma e and su ace sedimen s by using a model o wo
consecu i e and e e sible eac ions and con ac imes o se e al weeks. [4] s udied he e ec s o changes
in suspended ma e concen a ions and empe a u e on he kine ic ans e coe icien s o Co and S and
discussed he use o models o wo pa allel and wo consecu i e eac ions. [5] published he expe imen al
de e mina ion o kine ic ans e coe icien s o 133-Ba in es ua ine wa e s and s udied he e ec s o
salini y and suspended load concen a ions. Al hough o he au ho s ha e no ob ained ans e
coe icien s, hei s udies ha e included he e ec o sedimen ype, empe a u e, colloids, pa icle size
and pa icle concen a ion on he up ake o adionuclides by sedimen s.
The p esen s udy epo s he esul s o ace expe imen s wi h 2WPu, 241 Am and MTc in un il e ed
wa e s om h ee aqua ic sys ems in sou he n Spain. The expe imen al p ocedu e e ains he na u al
condi ions, and Pu ac i i y is measu ed by liquid scin illa ion.
2.
MATERIAL AND METHODS
De ails conce ning he sampling, he physic-chemical cha ac e isa ion o samples and he
expe imen al and analy ical p ocedu es we e p esen ed in a p e ious wo k [6], Consequen ly, we will
b ie ly desc ibe he e only he mos ele an aspec s.
Wa e samples we e collec ed om h ee di e en aqua ic scena ios om he Sou h o Spain. The
i s s a ion was loca ed he Ge gal ese oi (NW om Se ille). The second sample was collec ed in he
Guadalqui i i e , nea he own o Se ille. Finally a hi d sample was collec ed in he Tin o es ua y,
close o he A lan ic Ocean, du ing he low ide.
A each sample si e, we illed ou 25
1
plas ic bo les. Tempe a u e, pH and elec ical conduc i i y we e
measu ed jus a e collec ion. Samples we e hen ca ied o ou labo a o y and s o ed in da k du ing ew
hou s.
The acing expe imen s gene ally begun a he ollowing mo ning. We used a nephelome e o
measu e he suspended ma e con en .
Cl-82 RADIOPROTECTION - COLLOQUES
In each expe ience, a ypical olume o 1.0
1
o wa e was ans e ed in o a glass beake . The e, he
sample was spiked wi h 239Pu, 241Am o "Tc and con inuously s i ed in o a oid any décan a ion o he
suspended ma e . We ollowed he ime e olu ion o he ac i i y concen a ion in he dissol ed phase by
aking aliquo s a di e en imes a e spiking. A ypical olume o 45 ml was selec ed o e e y aliquo .
Suspended ma e was emo ed by cen i uga ion (20 minu es a 4000 pm). Then, 35 ml o supe na an
we e ans e ed in o a plas ic con aine and acidula ed wi h 1ml o HN03 o a oid loses o plu onium by
adso p ion on o he con aine walls. Finally, 5 ml o acidula ed sample was ans e ed in o a plas ic ial
and mixed wi h 15 ml o liquid scin illa ion cock ail Pha macia Op iphase 3.
A g anulome ic analysis o all he samples was ca ied ou by using a Mas e Size ins umen wi h
100 size bands, om 0.01 o 1000 um. A Scanning elec on mic oscope (SEM) wa^^se^ o s udy he
mo phology o na u al pa icles om all he samples.
Resul s om expe imen s wi h 239Pu a e depic ed in Fig. 1, which shows he ime cou se o he o al
239Pu ac i i y (gi en in cpm) in 5 ml in he supe na an wa e s.
•5
Ri e (1) ~—i
><—
Ge gal (1)
Es ua y <
Ge gal (2)
Ri e (2)
M»-.
h }
(d) *}
1
0.01 0.1 1 10 100
Time (hou s)
Fig. 1: Time e olu ion o I59Pu ac i i ies (in cpm) in he dissol ed phase co esponding o he i e expe imen s (poin s wi h
e o
ba s).
Con inuous lines indica e he di e en sequences o (he up ake kine ics.
3.
MODELLING APPROACHES
In wha ollows we will apply o ou da a a model o wo pa allel, e e sible and concen a ion-
independen eac ions ollowed by a consecu i e, non- e e sible and concen a ion-independen eac ion
o de i e he co esponding alues o he kine ic coe icien s (see discussion in sec ion 4). The equa ions
o he sys em a e:
=
-(*!.!
+ *1J K + *2ja
T.l + K2.2 "V,2
a
da ,
i
ia
= *l.l l. -*!.ia,,.l -*!.ia„,l
= *l,l°» -*2jO».2_*3.2a».2
(1.1)
(1.2)
(1.3)
da sp j
d = k,
,a,„,
+ k* ,am < 4
whe e aw [Bq/1] is he ace concen a ion in he dissol ed phase;
aspj
and
aSpj
[Bq/1] a e he
concen a ions ela ed o si es in solids pa icipa ing in i s and in second pa allel and e e sible
ECORAD 2001 Cl-83
eac ions, espec i ely. Simila ly,
aS >
3 [Bq/1] is he concen a ion in solids ela ed o he non- e e sible
unions. The six kine ics ans e coe icien s ha e uni s in e sely p opo ional o ime (s' o h"1). In he
i s ins ance we assumed a simila alue o £37 and ¿32 coe icien s. The concen a ions in solids a e
ela ed o he co esponding speci ic ac i i ies ( in Bq/kg and deno ed wi h *) by means o suspended load
concen a ion, ms, in uni s o
kg/1:
asp,l = a sp.l ms-> asp,2 = a sp,2 ms, and
asp,3=a*sp,3nis ' ,
We s a ed some ini ial alues o kine ic coe icien s in a compu e code ha nume ically sol es
equa ions 1.1 o 1.4. The pa ame e alues a e hen a ied o ge he bes i (i.e., minimises he
summa ion o he weigh ed squa ed di e ences be ween nume ical solu ion and obse a ional da a
poin s). As each pa hway is dominan o e a egion (o in e al) in he up ake cu e, an o e all pa ame e
i ing is no ad isable. Thus, he i is sequenced egion by egion and hen e ined o e all. The
g aphical ep esen a ion ensu es he quali y o he solu ion. The so de i ed pa ame e alues a e
summa ised in Table 1.
Table
1.- Pa ame e alues a e i ing expe imen al da a ( o case o 239-Pu) o a model o wo pa allel plus a consecu i e
and
non- e e sible
eac ion.
The esul o
he
x- es
o he i ing is shown in he las
column.
Expe imen k„(h-') Kii(h ) ku(h-')
Es ua y, 2 days, /.62 ppm 1.9 8.2 o.iy 0.28 0.0005 1.03
(ie gal, 2 days, 1.5
1
ppm 1.1 2.6 0.05 0.25 0.009 0.95
Ki e , 2 days, 12.6 ppm 12.3
17
o.oy 0.20 0.055 1.55
In Figs. 2 o 6 we show he nume ical solu ion o expe imen s wi h Pu, Am and Tc.
4.
DISCUSSION
F om Fig. 1 (in case o Pu), in loga i hmic scale, h ee di e en egions cha ac e ised by di e en slopes
can be dis inguished: egion (a) co esponds o a as eac ion, las ing o ew minu es, du ing which ime
up o 30% o dissol ed Pu is ans e ed on o suspended solids. This co esponds o a as physical-
adso p ion eac ion (Pu is ixed by coulombian o ces on o he ex e nal ee su ace o pa icles); in
egion (b), a second eac ion go e ns he Pu up ake du ing 10-20 hou s ime, ans e ing up o 30% o
emaining Pu in dissol ed o m. This eac ion co esponds o physical adso p ion on o he inne su ace
o po es and ee-edges, and o he o ma ion o e e sible unions o a di e en na u e and/o s eng h. In
egion (c), he up ake (up o 50% o he emaining Pu in solu ion) con inues du ing se e al days ( he
du a ion o he expe imen s was oo sho o allow a conclusion conce ning he inal cou se o he
eac ion). This eac ion may co espond o a slowe p ocess in which p e iously adso bed Pu is
ans e ed in o he inne ma ix o he pa icles o o ms o he non- e e sible unions. Region (d)
co esponds o a as e up ake o Pu om he dissol ed phase. I is obse ed only in he i s expe imen
wi h i e wa e s and may be ela ed o loccula ion e ec s.
We obse e he same si ua ion in case
o 241
Am. "Tc is conside ed as conse a i e adionuclide and
he beha iou is di e en han o he Pu o Am.
In all cases (Pu and Am), he i s pa allel eac ion is he as e . I ans e s an impo an ac ion o
he dissol ed adio ace o he pa icula e phase, kjj is he a e o adso p ion, and depends on he o al
a ailable su ace o pa icles pe uni olume o solu ion (which in u n go e ns he numbe o physical
collisions and hus, kjj should be p opo ional o mSi i he es o physical-chemical p ope ies we e
p ese ed), and on hé concen a ion o ac i e a eas (which go e ns he p obabili y o eac ion). The
physical meaning o kjj and ¿2,2 's na ° a p obabili y o deso p ion, which implies he up u e o
physical-chemical unions in si es associa ed wi h he wo pa allel eac ions. F om ou in e p e a ion, kj 2
does no depend di ec ly on he o al ee su ace o pa icles, bu also on he exis ence and geome y o
po es and ee edges and he accessibili y o he eac ion si es. The hi d eac ion is go e ning he long-
e m beha iou o he pa i ion coe icien , k^. E ec i ely, he ans e o adionuclides o he inne ac i e
a eas ees he si es hey occupied in he su ace laye o pa icles. This enhances he up ake o
adionuclides by he pa icula e ma e .
Cl-84 RADIOPROTECTION - COLLOQUES
.a
Fig.2:
Time e olu ion
o
Pu
ac i i ies
(in
cpm)
in he
dissol ed phase co esponding
o he
sé ie
o
expe imen
o
he case
o
he Ge gal ese oi . Measu ed alues appea s wi h e o
ba s,
while con inuous line co esponds o he bes i o
he
model.
20
30
Time (hou s)
Fig.3:
As in
Figu e
2 bu o
he case
o
he
Guadalqui i i e
3
0
10
F g.4:
As in
Figu e
2
bu
o
he case o he Tin o es ua y
ECORAD 2001
CI-85
20
25 30
40
45 50
FigS:
As in
Figu e
2 bu
wi h 141
Am, o
he case
o
he
Guadl^u'wi n e
16l
. , , . . . , 1
0
5 10 15 20 25 30 35 40
Time (hou s)
Fig.6:
As in
Figu e
2 bu
wi h
**Tc,
o he
case
o
he
Guadalqui i i e
5.
CONCLUSIONS
L- In his wo k we applied a use ul expe imen al p ocedu e o s udy he up ake o Pu, Am and Tc by
na u al aqueous suspensions, based on he use o liquid scin illa ion echnique.
2.-
By using a model o a single and e ec i e oxida ion s a e, wi h wo pa allel e e sible and
concen a ion-independen eac ions, ollowed by a consecu i e non- e e sible eac ion, we ob ained
a easonable unde s anding o he up ake cu es.
3.-
We ha e p o ided a se o kine ic pa ame e s use ul o desc ibe he mos ele an aspec s o he
elec oly ic eac ions o "9Pu,241 Am and "Tc in he aqua ic en i onmen s s udied unde en i onmen al
condi ions p e ailing du ing he sampling.
4.-
The expe imen al esul s show ha each pa hway o eac ion is go e ning he up ake a di e en
s ages, and some possible in e e ing and/o modi ying ac o s a e iden i ied (s o age, loccula ion,
compe i i e ions). This p o ides a good basis o imp o e he expe imen al se up o p oduce mo e
accu a e alues o kine ic pa ame e s

Cl-86 RADIOPROTECTION - COLLOQUES
Acknowledgemen s
This wo k has been pa ially suppo ed by I+D con ac wi h ENRESA, Spain.
Re e ences
1.
Pe iá iez R. Jou nal o Ma ine Sys ems 22 (1999)
37-51.
2.
Mckinkley I.G. and Alexande W.R. Jou nal o En i onmen al Radioac i iy 15 (1992) 19-34.
3.
Ny ele U.P, Yuan-Hui Li and San shi P.H. Geochim. Cosmochim. Ac a 48 (1984) 1513-1522.
4.
Benes P., Cemik M. and Lam Ramos P. Jou nal o Radioanaly ical and Nuclea Chemes y. 159(2)
(1992) 201-218.
5.
Laissaoui A., Ab il J.M., Pe iáñez R., Ga cía León M., Ga cía Mon ano E. Jou nal o Radioanaly ical
and Nuclea Chemes y. 237 (1-2) (1998)
55-61.
6. R. El M abe , J.M Ab il, G. Manjón and R. Ga cía Teno io. Wa e Resea ch (2001) (accep ed o
publica ion).