A Field Study of Radionuclide Migration - American Chemical Society

9 A Field Study of Radionuclide Migration

1

DARLEANE C. HOFFMAN

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 16, 2018 | https://pubs.acs.org Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

Los Alamos Scientific Laboratory, Los Alamos, ΝM 87545

In the first phase of the field studies which have been described in detail in another report (1), the site of the 0.75-kt nuclear test, Cambric, detonated on May 14, 1965, was investigated by re-entry drilling, and sampling of both solid and water. The Cambric test was fired beneath the water table in tuffaceous alluvium in Frenchman Flat (See Figure 1). It was chosen for study for the following reasons. Sufficient time had elapsed so that the ground water had refilled the cavity and chimney regions to the preshot level of 73 m above the detonation point. Thus, water which had been in contact with the radio active debris for some time could be obtained for analysis of radionuclide content. The Cambric detonation point was only 294 m below the ground surface which made re-entry drilling and sampling less difficult and expensive than for some of the deeper tests. The tritium (T) present from the test was sufficient to provide a readily measurable tracer for water from the region of the test. The postshot debris also contained enough plutonium, uranium, and fission products so that measurements of their relative concentrations in rubble and ground water from various regions could be made. A summary of the intensity of the radio nuclide source term at the time of re-entry is given in Table I. The ratios of the concentrations of the radionuclides relative to Τ are given in Table II. It was believed that this relatively low yield test would have had little effect on the local hydro logy. The alluvium was judged to be a good medium for hydrolo gic studies because of its permeability and the absence of large cracks or fissures, and the very small natural hydraulic gradi ent in the region. Finally, the Cambric site was far enough removed from the areas of active nuclear testing so that damage or interruption of drilling and sampling operations was unlikely.

1

Work conducted under the auspices of the U.S. Department of Energy. 0-8412-0498-5/79/47-100-149$05.00/0 ©1979 A m e r i c a n C h e m i c a l S o c i e t y

Fried; Radioactive Waste in Geologic Storage ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

150

WASTE

IN GEOLOGIC


RADIOACTIVE

Figure 1.

Geologic section at Cambric site (1)


STORAGE

9.

Radionuclide

HOFFMAN

151

Migration

TABLE I CAMBRIC SOURCE TERM AT 10 YEARS

Half-Life (Years)

Activity (Curies)

12.3

3.4 χ 10"

85. Kr

10.7

4.4

90 Sr

29


Nuclide

106 125 137 144

Ru

1.0

2.8

Sb

2.8

3.2

Cs Ce

147. Pm 155

34

Eu

30 0.78 2.6 5.0

99 0.4 33 6.4

Cambric Re-entry Well RNM-1 F i e l d Operations. Safety c o n s i d e r a t i o n s d i c t a t e d that r e entry would be by means of s l a n t d r i l l i n g r a t h e r than v e r t i c a l d r i l l i n g from the ground surface d i r e c t l y above the detonation p o i n t . The Cambric r e - e n t r y hole, designated RNM-1, was d r i l l e d i n May, 1974, nine years a f t e r Cambric had been f i r e d . A s a t e l l i t e w e l l , RNM-2S, was constructed i n A p r i l , 1974. I t was t o be pumped l a t e r i n order to induce an a r t i f i c i a l gradient so that water could be drawn from RNM-1 and provide an opportunity f o r the study o f r a d i o n u c l i d e migration under f i e l d c o n d i t i o n s . RNM2S was d r i l l e d p r i o r to RNM-1 to avoid the p o s s i b i l i t y of cross contamination from Cambric. A schematic diagram o f the placement of RNM-1 and RNM-2S i s shown i n Figure 2. A t o t a l of 67 s i d e w a l l core samples was taken i n RNM-1 as d r i l l i n g progressed from the s u r f a c e to about 50 m below the o r i g i n a l detonation p o i n t . These sampling p o i n t s a r e shown i n F i g u r e 3. One core from each depth was placed immediately i n a n i t r o g e n - f l u s h e d , g a s - t i g h t , s t a i n l e s s - s t e e l container f o r subsequent analyses of K r , HT, HTO, and f o r γ-spectral analyses. Other core samples were sealed i n w a t e r - t i g h t p l a s t i c bags f o r l a t e r γ-spectral and radiochemical analyses of the cores and contained f l u i d s , and f o r l i t h o l o g i e examination of the alluvium. 8 5



RADIOACTIVE W A S T E IN GEOLOGIC

Figure 2.

Schematic of RNM-1 and RNM-2S.


STORAGE

Radionuclide

Migration


H O F F M A N

Figure 3.

Sampling points at RNM-1: (A), core samples (67).


RADIOACTIVE W A S T E

IN GEOLOGIC

STORAGE

TABLE I I


RATIOS FOR RNM-1

SOURCE AT t

(5-14-65)

Nuclide

Half-Life (Years)

(Ν /Ν )

Τ

12.26

1.00

Kr

10.74

1.22 χ Ι Ο "

4

1.38 χ 1 θ "

4

28.9

1.66 χ Ι Ο "

3

7.05 χ Ι Ο "

4

90 Sr o

χ

b

u which are of i n t e r e s t o n a l o n g t i m e s c a l e . 9 5

9 9

9 9

1 0 3

1

3

1

l l f 7

2 3 7

5

5

9 9

7

1

2

9

2 3 5

9 3

2 3 8

Acknowledgments I wish t o acknowledge the many people from the Los Alamos S c i e n t i f i c Laboratory, the Lawrence Livermore Laboratory, the U. S. G e o l o g i c a l Survey, and the Desert Research I n s t i t u t e who have contributed to the studies which have been b r i e f l y reviewed here. R. W. Newman, NV, i s P r o j e c t Manager, and J . E. S a t t i z a h n (LASL), R. H. Ide (LLL), L. D. Ramspott (LLL), and D. C. Hoffman (LASL) have served as T e c h n i c a l D i r e c t o r s . Abstract The radionuclide distribution i n both the water and aggregate around a 0.75-kt nuclear test which was detonated below the water table at the Nevada Test Site has been investigated. An extensive suite of sidewall core samples was obtained from near the surface to below the o r i g i n a l cavity region. Representative water samples were pumped from five different zones i n the cavity and rubble r e gions. Most of the radioactivity was found i n solid material con tained i n the lower cavity region. Water pumped from the region of highest radioactivity showed only tritium and strontium-90 at


166

RADIOACTIVE WASTE IN GEOLOGIC STORAGE

levels higher than the recommended concentration guides for drinking water. Water is being pumped from a s a t e l l i t e well some 90 m away to induce an artificial gradient and draw water from the test zone.


Literature Cited 1.

2.

3.

Hoffman, Darleane C., Stone, Randolph, and Dudley, Jr., William W., Los Alamos Scientific Laboratory Report LA-6877MS (1977), "Radioactivity in the Underground Environment of the Cambric Nuclear Explosion at the Nevada Test Site". ERDA-0524, Standards for Radiation Protection, April 8, 1975, Appendix A, Table II, p. 13; Code 10 Federal Regulations, January 1, 1975, Appendix B, Table II, p. 177. Wolfsberg, Kurt, Los Alamos Scientific Laboratory Report LA7216-MS (1978), "Sorption-Desorption Studies of Nevada Test Site Alluvium and Leaching Studies of Nuclear Test Debris".

RECEIVED January 16, 1979.


A Field Study of Radionuclide Migration - American Chemical Society

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