ANL-76-127

-. F1TNL-76-127

MAIMANNUAL REPORT FOR FY 1976

ON PROJECT AN0115A:

THE MIGRATION OF PLUTONIUM AND

AMERICIUM IN THE LITHOSPHERE

by

S. FrIed, A. M.-Friedman, J. J. Hines,R. W. Atcher, L. A. Quartorman,

-

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and A. Volfty

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andi A \olesky

Chemistry Division

December 1176

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TABLE OF CONT''N'rS

Pa .tte

ABSTRACT ............................

I. INTRODUCTION. . . . . . . . . . . . . . . . . .

LI. RADIOASSAY PROCEDURE AND 'TRACER

III.

IV.

INSTRUMENT ArION. . . . . . . . . . . . . . .

EXPERIMENT L PROCEDURES . . . . . .

A. Migration of Plutoniimi in Los Alamos

B. Study of the Effect of Rainfall . . . . . .

C. Effect of Deposition Rates and Volume

D. Migration of Plutonium into Dense Ston

PREPARATION

Tuff .

e Samples

E. Movement of Actinides through Fissures . . . . . . . . . . . . . . .

F. Surface Absorption Coefficients: Variation % ith Concentrationof Dissolved Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

G. Attempts to Determine Relative Migration Rates. . . . . . . . . .

H. Electrochromatographic Behavior of Tracer Pu-Am in Water .

V. CONC LUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

RE FERE NC ES ... .... .... ................ ..........

7

()

10

l1

11

1414

1 7

it

4

LIST OF FIGURES

No. Tit!e Page

1. Block Diaj.ram of Scintillation Spectrometer. . . . . . . . . . . . . . . .11

2. High-pressure Chromatographic Apparatus . . . . . . . . . . . . . . . 11

3. Experimental Arrangement for Coring Experiment . . . . . . . . . . 1

4. Schematic Diagram of Coring Apparatus . . . . . . . . . . . . . . . . . 12

5. Results for Cores Taken at Various Radial Distances fromCentral Core (0-0)......................................... i

6. Vertical Distribution of Plutonium in Tuff as a Function ofR a in fa ll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7. Comparative Migration of Plutonium and Americium in Tuff . . . . 15

8. Vertical Distribution of Plutonium as a Function of Deposition

R a te . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. l

9. Radial Distribution of Plutonium as a Function of DepositionR a te . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

10. Comparative Vertical Distribution of Actinides on Tuff. . . . . . . . 17

11. High-pressure Chromatographic Results on Limestone . . . . . . . 18

12. Fabricated Fissure Apparatus . . . . . . . . . . . . . . . . . . . . . . . 18

13. Distribution of Plutor.ium on Basalt Fissure . . . . . . . . . . . . . . . 19

14. Effect of Flow Velocity on Plutonium Distribution on Surface ofB a sa lt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0

15. Variation in k for Plutonium Solutions in Limestone as aFunction of Other Ionic Concentrations . . . . . . . . . . . . . . . . . . 21

16. Variation of k for Plutonium Solutions in Basalts . . . . . . . . . . 22

17. Variation of k for Americium Solutions in Basalts . . . . . . . . . . 22

18. Absorption of Plutonium on Lime-stone as a Function ot NaClC oncentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

19. Schematic Diagram of Elution Column Made with Tuff Plug. . . . . 25

20. Comparison of Relative Migration Rates in Tuff . . . . . . . . . . . . 26

21. Elution of Plutonium and Americium in Column of Tuff. . . . . . . . 26

22. Electromigration Behavior of Activity. . . . . . . . . . . . . . . . . . 27

23. Migration of Plutonium for Hypothetical Depository. . . . . . . . . . 29

24. Migration of Plutonium through an Aquifer . . . . . . . . . . . . . . . . .29

5

LIST OF TABLES

Title Page

I. Absorption of '1u on Niagara Limestone (Chicago Dolomite);IData for Samples ir. a 0.5M Solution of NaCi at Equilibrium . . . .

II. Electronigration of Plutonium and Americium Ions . . . . . . . . .

No

7

ANNUAL REPORT FOR FY 1976

ON PROJECT ANO1 1A:THE MIGRATION OF PIA'TONIUM ANI)

AMERICIUM IN TIlE LITIlOSPIlERE

by

S. Fried, A. M. Friedman, J. .1. Nines,R. W. Atcher. L. A. Quarterman,

and A. Volesky

ABSTRACT

Studies have been carried out on the migration of plu-toniuim and americium in solutions flowing through porous andcrushed rock and through fissures. The migration process canbe described in terms of the surface absorption of these ele-ments. In addition, chemical effects on the absorption have beenobserved. One of these effects is possibly due to the presenceof a plutonium polymer that migrates at a more rapid rate thannormal plutonium.

I. INTRODUCTION

When radionuclides are stor:-d as wastes, either in permanent reposi-tories or in waste-storage areas, the possibility of escape into the environmentmust be considered. This escape may result in airborne contamination or incontamination of environmental surfaces. This report does not concern itselfwith airborne contamination, but rather with the surface contamination and thetransport and migration of radionuclides into the lithosphere through the agencyof water.

Regardless of the original manner of escape of radionuclides from theircontainers and the character of the material with which they come in contact,they must perforce ultimately be found in the rocks that form the conduits andaquifers. Water in the form of rain will inevitably wash contaminants into soilsand thence into conducting rocks. The migration of radionuclides must followwidely varying paths. In the porous rocks, for example, water percolateseasily under a slight pressure gradient, and rapid movement of large volumesof water can result--with possible concomitant transport of large amounts ofcontaminating materials.

In relatively nonporous rocks such as Niagara limestones the transportmeets much more resistance and the volumes of water conducted are corre-spondingly reduced. In such situations, much of the migration of water and its

8

solutes may be through cra, ks and fissures in the ro k ( .rttin i -tre t :rock or rock products may be almost imipt'rvious to flOn watr tntd by thistoken may be _ c,-sidered to be an espec ially suitable , )rtainIer' or lent- risafe storage of nuclear wastes, particularly if these strata art

9

l.xpcriicnt, wcr.. al,,, , arristd ou- i dcttcrriiine thu effect s of salts ontH thso rption ~t .t, tinidc cn ru, k slrtat e" - ifcc.ts of the formal cationic

I.arge 'c thi tddii ftlt d. xc '.ll as tLe rc --t.on of the sal's, were11., t , t I g;at2 t c .

Sc;,rc t Matirial

i1AIaiici 'it: a naturally .0tinpat t'd vc1h ank ash, already hashadl a, t ;iit- wa st t chplo~it ed in Selot tnd lh ation . and it was naturally ofintirc t to, ~1part a t ntrlled laboratory xptriient with the actual situa-tion at .t t(ltsp) al ,.tt :,s Alai.o. tiff is also a parti(ularly desirablt m ate-rial t~ w rk w h in tht labi)rattry sin, u it, physic al Lharat tteristn.s permitca Iy Andlit and , ~ring Constqutintly, txperiun tns wtrtc arried out using1.ccs Alarnicc,'i t ,, 'c Icas rt th- imiigraticn of plutonium into, massive blocksunc lr onit i(ns iiwilat img the "natural" anes o. urring at the Los Alamossit-.

} .lt %,.,is al, t st. (I be. au..t it has be n .sied at the 1-:3R-II sitetor dipcal pcrp

10

arrang-ment. Consequently, laborious plutonium separations from largequantities of rock were avoided, and the sample cores were counted directly.

The 14 'Am was likewise determined by observation of its gamma ray. Thespectrometer used permitted the simultaneous determination of americium

and plutonium in the sample and canceled out any corrections due to geometry.

Similarly, an X-ray spectrometer was used to detect the attenuation of 2 3 8Pu LX rays as the plutonium migrated into the body of a piece of rock. Measuringthe changes in the La/ L9 or Ly/ L ratios permitted the penetration of plutoniuminto the solid to be calculated after calibration with stone absorbers.

Tracer solutions were prepared by using aliquots of stock solutions of

the tracer and evaporating them to dryness with HNO3 in a small volumetric

flask. The evaporation was carried out at a comparatively low temperatureto avoid decomposing the solid nitrates obtained as a residue. The americium

and plutonium were brought into "solution" with distilled water, and this

aqueous solution was used in the rock-migration experiments.

The isotope 2 3 7Pu was obtained by bombardment of 40 Np as the driednitrate with 21-MeV deuterons in the Argonne cyclotron according to the

reaction 2 3 7Np(d,2n)2 3 7Pu. The 2 3 7Pu and the 2 3 7N? nitrate matrix was dissolvedwith 9M HCl Five percent HNO 3 was added to the HCl solution to ensure that

the actinides would be retained on an ion-exchange column (Dowex A- 1) asPu(IV) and Np(VI). Subsequently, however, addition of iodide ion (as Ill or

NH4 1) reduced the plutonium to the III state which was no longer bound by theanion resin and was collected in a receiver as the acid solution passed throughthe column.

Generally, more than one cycle was required to free the 2 37Pu com-pletely from the neptunium.

Americium was obtained by allowing plutonium containing 1Pu to decayThis isotope beta decays to 2 Am. The americium was separated from theplutonium by ion-exchange or solvent-extraction procedures.

III. INSTRUMENTATION

The gamma- ray scintillation spectrometer (Fig. 1) c onsisted of two

single-channel analyzers coupled to a common sodium iodide well detector.preamplifier, amplifier, and scalers. Setting each analyzer for the appro-

priate energy enabled the two isotopes to be determined.

The X-ray spect rometer was a SiLi detector made by KIV EX capableof resolving differences in X-ray energies of 180 eV.

The scanning alpha detector SAISAC was constructed at ArgonneNational Laboratory and consisted of a proportional counter whose aperture

11

was a slit U.005 in. (0.127 mm) wide. The samp was placed on a movabletable and advanced under the slit in a regular manner 0.010 in. (0.254 mm) ata time by a microroeter arrangement. A rcaler and timing device completedthe system. Counts were made at appropriate intervals and the total recorded

as a function of position on the sample.

No!

PHOTO- SMULT SEALER

- AMP TIMER-r

HV-L S.C.A. SCALER]

Fig. 1

lock Diagram of Scintilla-tion Spectromcter. ANLNeg. No. 122-76-720.

The high-pressure chromatographic apparatus used for forcing waterthrough the relatively impervious Chicago dolomite is shown in Fig. 2; itaoperation is described in Ref. 2.

"0" RINGS

Fig. 2

lIigh-presure C(hromato-graphic Apparatus. ANLNcg. No. 122-903.

PE RFOR ATESUPPORT PLATEFOR ROCK---- -

STO HIGH PRESSUREI N2 TANK

-- PISTON

-- WATER

-- ROCK SAMPLE- ASSEMBLY

SUPPORT PLATE

IV. EXPERIMENTAL PROCEDURES

A. Migration of Plutonium in Los Alamos Tuff

These experiments were laboratory simulations of the movement ofplutonium and americium in Los Alamos tuff.

4-

-- 1

14

In a ty ical experiment , a block of Los Alamos tuff about 30 cm onedge was used. The coring-location apparatus described in Ref. 3 was in-stalled and used to determine the dieposition site of the sample of plutonium.The apparatus is shc)%\"n in Figs. 3 and 4.

+ _#

I fl2. I

eg~.12-T -I

4

K

1

a

-__

Fi . A

I \perimH ntjl Arrang.incnt for t ring

- Gloss Sample Viol

- Foam Filter

-- Rubber Tubing Seal---- Perforated End Cop

- Brass Collar--- To Vacuum Pump

Rubber Stopper Sea'

6mm Gloss Tubeinserted in Drill Coaing

At a chosen dtpositior. sit,, a small depression was drilled and anaqueous solution of 71'11 vi'ry slowly deposited at that point by means of ametering pump.

After the ploton utn track er solution was allowed to dry, the surface waswet with a water shower of known volume and then allowed to dry. This cyclewas repeated several times until the total amount of "rainfall" was the equiva-lent on a laboratory sc ale of "30 in. " of rain. The block of tuff was neversaturated with wat er during any particular application of "rain."

13

After a final sequence of "raining" and "drought," the tuff was coredthe site of introduction of the plutonium. Each core increment was 0.5 cm.

The results are shown in Fig. 5.Scote ft for 30" rainfal o(U~l~ t911 nun atii r

r 25 O 's 100 125 150 :75 200 225 250 Two zones Of plulonium activity are80 3d ' distributed in the rock as a function70 -3 I 2 5

Ic -Cor of depth The n.ajor quantity of50 20 plutonium is found very close to the

original site of deposition and has30 14 only migratc-r to a maximum depth

1of about 2 .,. The secondary zone

125 Co2e5contains about 1% of the plutonium oe3an1"asmgtddwwrdoa83- and 1 as migrant ed downward to a

I depth of about 10 cm.6L5 24 _

3 -

85 -

, -5,

7

6

4

3 -

aa

44~O

'0- F2

o - - --- ---

Fig. 5. Resulrs for C0rc5 Taken at Various RadialI ltance~s from (Cenlrjl (:Or (0-0). ANi.Ncg. No. 122-75-104.

These observations suggest

that the plutonium exists in two

forms in aqueous solution. These

"species" may be different oxidationstates or differing degrees of poly-merization of the Pu(IV) ion. One

of the zones may also contain plu-tonium on colloidal particles asopposed to the ionic condition of itsmore tightly bound couterpart. Atthe extreme dilution of these tracer

solutions (10-11M ), it is difficult tocome to definite provable conclusionsas to which of the aforementioned

possibilities is correct. This"double-zone" observation seems

to be more or less general in re-

gard to the migration of aqueoussolutions of plutonium in rocks. Inaddition. thure were also important

effects due to flow velocity, and insome cases, as much as 35% of theplutonium was observed in the fast-moving zone.

B. Study of the Effect of Rainfall

To determine the migration as a function of the total "rainfall" experi-enced, the experiment described above was modified in that six separate sitesfor the application of tracer were located by the coring apparatus. Americiumand plutonium tracers ( 4 'Am and 2'7Pu) were used simultaneously. This per-mitted migration rates of these nuclides to be simultaneously determined bydetecting the characteristic radiation by means of the gamma-ray spec rom-eter. The 60-keV gamma ray of ?4'Am and the 100-keV X ray of 2 17Pu i.re

00

e

14

readily resolved. Not only is this important as a labor-saving measure, butit enables the direct comparison of the behavior of americium and plutoniumunder the same conditions. The ambiguities of sequential-type experimentsdue to possible inhomogeneity of the rock matrix are e'',inated. Aliquots of

the tracers were applied by means of a metering pump . a rate of 0.05 mil/hrto each site. The size of the aliquot varied from site to site, those sites to be

cored last having the largest aliquots delivered to them. This compensated forthe anticipated deeper penetration of the plutonium.

Simulated rainfall was intermittently applied between intervals of

drying and covered the entire upper surface of the tuff. As before, the tuffwas never saturated with water during any particular application of "rain."

Since the sites were cored successively, those cored later experienced

more cycles of "rain" and "drought"; thus the migration of plutonium wasmeasured as a function of the quantity of "rainfall." The cycles of artificialrainfall-drying were initiated, and after a predetermined number of these

cycles, the first site was cored. When the coring of each site was complete,the hole resulting from this operation was filled with melted paraffin and the"rain"-"drought" cycle continued with occasional coring. Since the "rainfall"

covered the entire upper surface of the rock, each succeeding site experienced

more "rain" and more "drought."

The results of these experiments are shown in the following figures.

Figure 6 shows the vertical distribution of plutonium after sue cessive rainsand droughts. The curves in Fig. 7 show the comparativ. migration of pluto-nium and americium in tuff.

C. Effect of Deposition Rates and Volumes

The logical extension of the previous experiment was to deposit the

plutonium in successively increasing volumes and deposition rates. Three

large blocks of tuff were used and two sites chosen on each such that mutualinterference was avoided. Two sets of three samples of mixed 24 'A11-1 7 1'1i1were used. In each set, the volumes were 0.3, 30, and 150 ml. In the firstset, the combined solution was deposited at each sample site in 15 min. The

other set received its so t -ition over a period of 15 hr per site.

Figures 8-10 show the results obtained for the radial and vertc al

distributions of plutonium as well as a comparison of americium and plutonium.

D. Migration of Plutonium into Dense Stone Samples

Thin wafers or disks of dense Illinois Niagara limestone and basalt

from the EBR-II site were fabricated. The dimensions were approximately

25 mm in diameter and 1.5 mm in thickness. The wafers were waxed into the

high pressure chromatographic apparatus as shown in Fig. 2.

100 T T I

----- O 150 ml Rainfall

10 ----- x 500 ml Rainfall

-- O 000 ml Rainfall

r1

0.1 k-

Q x, ~x -\\

0.01

\- k .\_ x

I

.1Fig. 6

Vertical Distribution of Plutonium inTuff as a Function of Rainfall. ANLNeg. No. 122-76-724.

3 4 5

DEPTH, cm

Fig; 7

t omtparatIvc Migration of 'lu-tonium and A meric um in Tuff.ANL. Neg. No. 122-76-718.

a.

100 - [ -- --

O 23 Pv -

10 x 2 4 1Am

x 10 Ise Remfll

1-

10 -

O4x r

%x 0

0 01

1 ~ x I[ Q

A'*

3DEPIt, CM

5 6

15

a

0 0010 I 2 6

0 0010 1 2

-

100 ' 1 1 T ' T

Site A- Pu Applied Of Role of 2 ml/mmSite 6- -- Pu Applied at Rate of ; 02 ml/min

- Site 6-.002 ml Pu Applied /min Plus10 IS cm Ran

Total Deposit: Approz 2 x 106 dim

s

W 1- .s

-IJ. 1

\ Ca \

ccsii%

r '." -'

o g...

0.01 :- 0 N

r 0l

0.001-0 I 2 3 4 5 6

DEPmH. cm

Fig.J

Radial M)stribution ol Piutonium asa Function of IXcrsition Ratc. ANLNc-g. No. -C-2.

a

ii.

0

I-Wu-ac

vertical l I)itributionr of iIT'I oniufn a,a 'unction (i D-leps- tion Rate. \','.Neg. No. 122-76-728

100 T--T -- T-- TSite A - Pu Applied of Rote of I ml/minSite B --- Pu Applied of Role of 0 01 ml/min

V * Total Deposit. Appro 2 x 106 d/m10-

- a-

mi-a I

a

S01:

001

-;

0 t 2 %

DIST ANCE FROM SITE Of DEPOSITION. cm

1t

-U4,

v3

*0v

a"44

0

aW

100 --- P I

---Pu

- Am

Applied a Role of II 5 ml/minr0 No Roan1Op xTotal Depoal Appros I x 106 d/m

Ii I

Ir

. ci

01 tl t...q

n 0

0

M

p W.

4 I

P LI

00Li

I-

aWi

Fig. 1

(Aoniparatis e Vertical Iaistribu-tion of Actinides on Tuff. ANLNeb. No. 122-"7C-725.

n)G

0001 1 " 1 - - * . jI 3 S 7

DEPTHcm9 II

A small amount of 135 Pu tracer was deposited in the center of the diskand allowed to dry. The ratio of the intensities of the various L X rays fromthe plutonium deposit was measured, after which the entire apparatus wasassembled. The cylinder of the apparatus was filled with water and pressureapplied (about 1000 psi). About one liter of water was forced through thestone wafer over a period of one week.

At the cone lusion of this operation, the disk was removed from theapparatus and allowed to dry. The ratio of intensities of the various 1. X rd'swas remeasured and compared with the original determinations. The changein the ratio of the intensities is a measure of the depth of puentration of the

plutonium. The results, which are shown in Fig. 1 1. indicate a migrationcoefficient i : 30 * 10 micrometers'meter (um m) of waterflow for the lime-stone and 61 ! 8 um/m for the basalt, where ni is the average distance traveledby the actinide through the disk for every meter traveled by the water.

E. Movement of Actinides through Fissures

The movement of plutonium in aqueous solution through fissures inbasalt from the EB3R-1l site was modeled by construction of an artificial fissuredesigned to give controlled width of the fissure and rate of percolation. ofwater through it.

The fissure war simulated by the apparatus shown in Fig. 12. Tabletsof basalt were cut with smooth surfaces. Five of the six surfaces of the tablet

17

001

L 3

100,000

10,000

L2

Fig 11

High-pressure Chromatographic Result,on Limestone. ANI. Neg. No. 1'.-904.

...........-- Surfoce- 990 m

------ 1727s m

1000 20 40 60 80 100

CHANNEL

c. POD "'d F&uOM Y C"P i'. 1' ip

Fig. 1:

i'abricatcd Fissure A pp.ir.itu,.ANI. Neg. No. 12.-1 '.

I

i

I.

K

44'A4m 'AuF

ty)

INS) if*

18

* '

' II:ti1

-J

zz

z0V-

1000

) F+ d

7 B.'4 4

4. '4''

.

I'

r .

I 1

were rendered impervious to water by coating them with wax. Th. sixth sur-face was left untreated and was held in the apparatus in such a manner as tobe exposed to ai.d wetted bi a solution containing plutonium. This "active"surface was held in the apparatus in such a way that it face 4 an inert surface

(Teflon) a short distance away (about 0.01 cm), as shown in Fig. 12. The space

between the basalt and Teflon surfaces then constituted the fissure throughwhich the aqueous medium could flow. Since all other surfaces of the basalt

were waxed, they did not participate in the experiment. Consequently, all

results on the distribution of plutonium on the surface of the basalt were un-

perturbed by effects that would otherwise have related to more complex

geometries.

The plutonium, in this case the alpha-emitting 2 3 8 Pu, was introduced

at the top of the fissure in a very small volume (about 50 I1) by means of an

infusion pump. The subsequent elution of the absorbed plutonium from the

surface of the basalt also made use of the infusion pump. Water was the

elution medium, and, since the pump was constructed to deliver predetermined

volumes at a slow, steady rate, it was well suited for this kind of experiment.

After the requisite amount of water had been allowed to flow over the

surface of the basalt, the flow was stopped and the basalt tablet was removed

from its holder and dried. Scanning the surface of the rock for alpha activityby means of the scanning alpha counter (SADSAC) delineated the distributionof the plutonium on the rock.

Here too, the distribution was found to occur in a double peak. This

is clearly shown by the graph in Fig. 13, where there appears to be a more

loosely bound, rapidly migrating component as well as a tightly bound compo-

nent on the surface of the basalt "fissure." Thus the same effect is seen in

two dimensions with basalt that was seen in three dimensions with Los Alamos

tuff.

1000 TOP BOTTOM

I .

100I I IFig. 13Iistribution of Plutoniumn on BasaltS issue. ANI. Neg. No. 1'.'.'-I1C.

; 10

0 02 04 06 08 1C 12 14 '6 0 OiNCHkS FROM TOP

20

A further objective was to study the kinetics of the process. Theabsorption of the monomer and polymer, and their exchange, can be expressedby the three following equations:

K1PU+4 (solution) - Pu+ (surface), R = R1;

KzPu+4 (solut ion) Pun (solution), R = Rz ;

K3Pun (solution) : Pun (surface), R = R .

(1)

(2)

( i)

If the rate Rz is much slower than R1 or R3 and if the equilibrium con-stant K1 is much larger than KZ or K3 , then, at sufficiently slow flow rates, theplutonium will be absorbed as a single peak of Pu-" (surface) calculable fromEq. 1.

As the rate of flow increases, the two forms of plutonium will not havetime to interchange and two peaks will be absorbed due to reactions 1 and 3

At moderate flow rates, the peaks will be overlapping and appear as a broad

peak. At faster flow rates, they will be completely separated. Figure 14 shows

this effect and is a composite plot of the results of experiments on similar

slabs of basalt. The curve marked experiment 6 was taken using a flow veloc-

ity of 17.2 cm/hr; experiment 9 used 51.7 cm/hr. As can be seen, at the slower

velocity the peak is much sharper.

600,- Eaperment #6

500

400

300' E "rimen?#9

200

100.

00 05 10 '5 2C

F~ir. 14

I ffect of Flog, V\ch ity, on Plutoniun:Distribution mi airf.ICL' of B-1.111. .

Nieg. No. '.2.-'75-At', Rte%. 1.

INC HE S FROM TOP

F-

z

a

z0U

0

F. Surface Absorption Coefficients. Variation with Concentra'ion of DissolvedSalts

This 51p ti of the investigation attempted to dhterniine the effect ofdissolved salts, which may be present in natural ground waters, on the surfaceabsorption ( efficient k, defined as

k (act vIt y. ml solution) /(activity! ni stone).

There were three sets of experiments. The first set consisted ofneasurements of the surface absorption coefficient of americium and plutonium

on basalts and limestones. In these experiments, disks of the stone wereinmmersed in solutions of 4 x 10- 5M Pu(NO) 4 or 10-7M Ar(NO),. Small ali-quots (0.05%") of the solutions were removed, dried on ;antalum planchets, andthen placed in an internal alpha proportional counter. When the counting rate

of samples taken at 12-hr intervals had become constant, this was regarded

as evidence of the attainment of equilibrium. The value of k for pure solutions

of Pu(NO) 4 at 4 x 10- 5M was found to be 0. 10 ' 0.02 for limestone and 0.070.02 for basalts. The value of k for 10- 7 M solutions of Am(NOi), was 0.0410.02 for basalts. To observe the effect on this absorption constant of otherions, the value of k was measured for solutions containing Na', Ca; }, Sr'+,La+', and Zr 4 ions at various molarities. Figures 15- 17 illustrate the varia-tion in k for americium and plutonium as a function of the concentration of

these salts.

115*

\ .1111il111 kl for I'll.1oll1itl 'alutl 'll11 x.111'. s[t)is J .1 E tlek hi tal i tI c 1 1 11 0 ll 1 fi 01 rlrfltl 6'I15. \1 1.

I~

I,

! to S

0 0408 1 ; ! 0?4?IF

1v

i' k .V

\'JrjJIaionf tl < fur '.ne'c icjlI "ottiinfl

Basalt Cores

NoCI A, B. C

CoCI 2

J iZrtNO3)

-- La(NO3) 3

0 04 0.8 '2 1.6 2.0 2.4k

0 -- -

S,

x-41 I1

10 L -

X1 ' ...

'.4

2 Ci ~ I C I U ~' *' S * 4 4 *, *~ (I *' '~

The concentrations of the ""Pu in the salt solullmins shown rn I-'igs. 15and 16 were determined by alpha counting; the concentrations of amuritc-ilm inthe salt solutions shown in Fig. 17 were determined by gamia counting. Sint cthe alpha-counting techniques are much more susceptible to sample thiLkness.

ig. i

variation n of 1 C .' t" 12-fI

in Basalts. .\":[. \e No+ 1 -' ' 1 l .

10-1

10-2

E-

0

00

10-6

10-

U-n

the abrupt b)nd!- the iurves m Fig. it,

:4

T ABL1: 1. Absorption ut Fl'u on Niaga.r.I Lutnc tuini Cht igo 1)oliittData for Samnple, n . U.. M solution ul N.\ tl ,t 1.uilrlrinut'

Act.vit~y us unt, p.r trlrnut,-

Solution Ab-orbcd

S.-nple and lubi N ETI ml l n to. k

18

1 'r

21

278:b

~t

7070

8 10

8b 14

.74 9

7812

729'0

t 87

12 20

h;71

807t)

8821

4} I. I 4

"1- 19

4208

i7tie8

1 U l

ilc.1

411 i4ii tI

o8 17

7004

7 i48

8 il 1

S07 -

7-'!

7 S8

7704

Ni e.: i24u0

i.'l

I148

1.01

1244

285

1.'70

1! 17

i 1'

1 127

1 r. ent

1. 7 -. '. d

1.12

1. 1

1.17

1.07

1.01

1. -1

1.04

1.20

Average 1.2-1

1 t.u7I 1.02

4'. Id"11.7.'

4* .1

44 ".0 U

-1"}. t

alt ma . duturzmianed that A t'+t tubt L Ontafning 0. M :',*I: %-.ouLi ..,'i ur4.04 - 0.t8u of the 'Pu frui the . mi of +ulution.

bTh9.- value given in t. . 1 nil ulumu is 1. r 4.04 due to Oil. .ad.urp-tion on tliv gls,.

'The values for k fall within thu r.nga- of thu tandard du iatiun.dThu valuc given in thI P. reunt Absurbed Lolunm I. the avvr g for that

sanmpli ot the plutonium, absorbed Irom 1 ml of sulutaon to I cmn' of rue k.

af

30.U

0 0 00 .0NOt AiN 01 Atf I OLU110M

lig. l . Albie ption o f PlIa'df lui1 I' 1.1 (tie.n n'e s A !t lrctl"fn

tot .. I t tllall f At. I. N g.N . -- e- .

gloss tube15 x 1.6cm

Ig2. 1A

'k hvnaic lIiagr., ,.of I I ation (.ulurnn : ?dd:- wash water .ith Iuf Pi . Ai f f1.: Nf. 1 .- 75- .

paratine

tuf' specimen2 5 x I 2cm

At the end of this period, an attempt was made to (lute the deposit of

americium and plutonium through the 7.8-cm length of rock by passing waterthrough the system. This elution was carried out over an eight-week periodusing 2500 ml of water during the process (1000 free-column volumes). Thiscorresponds to a rate of about 52 m a year for the rate of advance of the water

through the stone.

At the end of this period, a total of 1.5 x 103 c m of 3 7Pu and 110 c nof Z 4 1Am had been collected, indicating that the bulk of the activity was still

bound to the tuff.

The column was disassembled and an effort made to locate the activity

in the body of the cylinder of tuff. By successive sectioning of the material,

and measuring the activity in each section (normalized for the weight of tuff),the distribution of the activity could be determined. The results are shown inFig. 20.

It can be seen that the activity had not advanced through the rock morethan 1 or 2 cm. When this is compared with the movement of water, it is seenthat the water advances about 25,000 times more rapidly through the pores inthe tuff, assuming a 10% pore volume.

At this rate, if the apparent advance of the radionuclides represents

an equilibrium condition, it would require about 2 x 10 4 ml of water to removeit from the cylinder of tuff. We therefore decided to reduce the column of tufffor this experiment to more manageable dimensions.

100

237- .. Pu

10-- 0-_o 24 1Am

I0I

'. I- t\

0.01 i

I 2 3 4 5 6 7DEPTH in cm

small column packed with crushed

column volume was of the order of 0.07 ml,

free-column volume was 0.007 ml.

Fig. 20

oniparison of ReIZativC Migration Ratvsin Tuff. ANIL Neg. No. 122-7t-722.

washed tuff was constructed. The

and assuming about 10% void, the

Plutonium-237 was deposited on the top of the column. The first

100 ml, or 1.4 x 104 free-column volumes, contained about 0.5% of the pluto-nium. About 0.75% of the total was contained in 1400 ml or 2 x 105 ColImnvolumes (see Fig. 21). This implies that the boundary of the water progressed

100 - --- Pu

Fig. ':1

I lotion of Plutonium and Aimericiuni in col-umn of Tiff. .\NI. Neg. No. 122-76-727.

E

a.

10

K

- Am

Total Deposit of Approx. 260,000 cpm (Am)and Appro. 140,000 cpm (Pu)

-I

100 500 500 700 900 1100 i100TOTAL ml ELUTED

26

0

--

27

2 x 10" times niorc rapidly thar, the bulk of the plutonium. A typical aquiferwill have a rate of water flow between 0.16 and 1.6 kn per year. The rate ofplutonium advance Iroin a site in such a stratum having the same bindingproperties as tuif would be from 1.6 x 10~' to 1.6 x 10~5 kin/year. Obviously,a tracer experiment such as this is only an approximation to real field condi-tions, but it may be argued that the tracer experiment is essentially conserva-tive and that a real straturn would be a much more effective filter for colloidal

particles that the short column used here.

11. Electrochromatographic Behavior of Tracer Pu-Am in Water

It has generally been assumed 'hat both plutonium and americium inneutral aqueous solutions existed as positive ions with the plutonium in the

plus (IV) state and the americium in the plus (II) state. It was understood that

the ions were not necessarily quadruply or triply charged and that hydrolysis,or polymerization could effectively lower the net positive charge. However,

experiments by Cohen5 cast some doubt on these assumptions, and an experi-ment was therfore carried out to determine the sign of the charge on theseions in water equilibrated with tuff.

A mixture of 17I'u-24 'Am in water was spotted on prewetted filter paper(7.5 x 25 cm). and a 400-V de potential was applied for 110 min. Under these

conditions, a current of about 7 mA flowed. The data shown in Fig. 22 and

I I

CATHODE- - -- ANODE

I 1

3000 -I I

I XII 0

E I-

I IE I

2000: -

I II x

O /

10001I Ix xI IX

4 2 2DISTANCE, cm

2 37pu

-- 24 1Am[ig. 22

I:lectoimligaationi Behaviorof Activity. ANL Neg.No). 122-76-7h).

x

4

x

4 6 8

listed in Table II indicate the activity of anerik iumu and plutuI1i1n ii igr.it 11nto the negative and positive poles. As can be seen, these rt Its 5 ha thatthe americium is essentially neutral or slightly anions (necat iv l %' rg&()while the plutonium is much more anionic. A small anionw pltOltnIi pl-kwas observed at aboutspecies of plutonium.

k..dti Io,;,

\zn.\ttn

3.5 cm. This again indicates the existent e 4.4 a onid

A:., ,

I,..

4I .* t '

I r, ,.ti

21 till

V. CONC 1.USIONS

The objective of these experiments is the i< tern.:nittI. 'ii tl mip) *r-tant parameters concerned in the ',redit tion of the iim ration t at t inele *rIfrom geological storage sites. Several on lusitons .oflt ernin, '1, '. ,may be inferred from these data.

1. The bulk of the plutonium and anerit- timf s % Very tei1at iu4.sly h. lrby the stony materials studied (tuff, basalt, limieit0one). Tlii' 11 eVI(lt n1 ed by

a. The slow rate of migrant mon (10 m n f't wat-r ihm) in themodeling experiments.

b. The fissure experiments and sori o e absorpmt n m11e.sIremlet -whil-h yield similar results when t orret terl for pore s./e.

8

I: . B IB. H!. I ..s t rmu ,i r , - -):.

I I " U"

U

I

f l, .J '1lp r tt .It1++l ,2 IJ tl.t )!r l.1l . :I1 +, 1: l t"- t1)Il . a s l1.t :1 ' r t' l lt,-X-riY abl)4)rption, ywldiin: .a relative iiigratiotn rat4 (Il, at U(Ost. iO ..Iu n eIOwater Iow. ThS Jhi,% I I .bstaintial a.dreen-nwith th.e other types 4 expe~rI-lfitent% +1SIing the avcrdg' v. (l0. 2 . thi rcl.s' ve hIJi rattn o t4:. . wfnt br pl)itl-

n ioni . (1(1 , n Ill 11, : L.Ia tt r :. . ) a.tt.l :1 .'ltl r -i +:Lw ',t It l, ty' +. ( . jt. l1 yli r.1"'Igu rt" .. 1J ,t tat t it a, tiv~tv" /21ttrlb t o : '} 1,,1 r :r ::,; rOn) : I.yp(,-th)1ts 1, :,I -it1)t it()r"

A, t an1 bet wer"I. In t. Vi .:-1. Ilhy bulk w: tht. :'' ~ ld (it' ay Ions,1 r ' it . ul d niitrr te I 1I1. I his . in t}.t ev n +, t atal.tr+p).. : j rk.siton

t: 1Jp Iitlut ll '1m iI n I) .ei . : i I .nI trnsf'

appears to give an ' exponential leading tdge" in a plot of t ont entration ofthese species against distant e migrated. however, once fixed, even thisfraction becomes smu h less mobile. This is evidenced by the observationsthat:

a. Although rapid migration occurs upon addition of the originalsolut ion in the experiments, the at t ivit y (list ributi ions do not appear to change(or move) radically fter arnounts of rainfall itiuch larger than the originalsolution volumes (see rig. tfl are added.

b. Varying the addition rate of plutonium by an order o! magnitudealso hanged the amount of rapidly moving plutonium by an order otf maLnitude

(from 0 ' to 1 0) but did not change the miaximum depth of pcnet rat ion appre' iably.

I'his rapid migrat ion may be due to plutonium solute being t arrit'dthrough the pLres by a high-vclocity. unatiurated flow of solution, which may

no have had suffit lent tinme to absorb on the potre surfaces In addition, thethin solvent film present under unsaturated flow conditions may contain verylarge concentrations of dissolved salts. thus the plutoniuin absorption may beconsiderably din inishied. Therefore it would appear 1o be most important to

minimize this type of unsaturated migration of the wastes ;n a storage site inthe event of a calamitous inc'irs:ui of water. 'Ihis co.ild be accomplislled byplacing the storact site in hiLh-ex hange-t apacity, nonporous strata and bysurrounding the wastes with a stable. ion-ext hanging absorptive material.Both of these m:ea, Tres wouldd have the etifec t of slow:ng tie original outflowof dissolved wastes and thus reducing the irasaturated n ei:rat ion.

4. Ti, , hen' al milieu t an drastically increase the nig r. zon rateof plutonium and aimeri. im Iliis t an be interred from the Ia't 1s that

a. 1 he sirfa abs, rpiion t( etficients are ted by the ty )esand concen rations of other s1Y [-.von optionss as dilute *t- 10"M ( o: highlycharged ions t an e!ft a sbst.-,i ! h- t.rpt ion ef plutt'll .!ind .iineri tum.

1). (on -n rated so! iion- of los se r liarLite'' ,pet it .) , slit ii aNaCl, t ause much ,mialier but stili aippr '. iable dcse)rptien

It i, therofire important ti, t ', oider no' rlny the 'eelogit al q it S-cence of a storage site but also thio '.heii. al and migrat ional behavior in caseof an a' . idental influx ot water.

These t. on( lesion, indR( ate that if appropriate attent ion iS givento the geologic al and e I'enni. il iedia, it is p ssible to c.onst rut-I an actinidiewaste depository. that will maintain isolation from the e.ivironmient, even inthe event of a ma or int rusion of water

31

Rr.rr.RENCES

1. D. R. Rogers, :: !b:-'r .' ' I.4o10izw'I- 3 .'' ut h:d 2. t..E .:oiZ and h?-.r, Vg...'1:n!;u fi: >L r:, Monsanto Research Corp., Mound Laboratory, Miamisburg,

Ohio, presented at the Actinide-Sediment Reactions Working Meeting,Feb. 10-11, 1976, Seattle, Wash.

2. S. M. Fried, A. M. Friedman, and L. A. Quarterman, Ar.;ual Vie.ort or" ' :-2: Yc 21.'-4, ANL-8115 (July 1974).

3. S. M. Fried, A. M. Friedman, J. J. Hines, and L. A. Quarterman, AnnuaL.E; r t , :'.'..' ' . t A1''11.:< F:< s : YL ;r 1 7 , ANL-75-64 (Sept 1975)

4. A. F. Volesky, Argonne .rational Laboratory, private communication (19 76).

5. D. Cohen, Argonne National Laboratory, private communication (1975).