Correlation of Radionuclide Fractionation in Debris from a Transient

18 Correlation of Radionuclide Fractionation in Debris from a Transient Nuclear Test J. R. LAI and E. C. FREILING

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Downloaded by UNIV OF CINCINNATI on May 30, 2016 | http://pubs.acs.org Publication Date: January 1, 1970 | doi: 10.1021/ba-1970-0093.ch018

U. S. Naval Radiological Defense Laboratory, San Francisco, Calif. 94135

Fractionation correlation techniques have been applied to cloud, fallout, and ground-filter samples from the Transient Nuclear Test of January 1965. Although safety analysts do not consider fractionation effects to be of operational im portance for this type of event, analysis of such data pro vides insight into the mechanisms of debris formation. The results show many similarities to the correlations observed for fallout. Those dissimilarities found indicate the impor tance of escape processes to the formation mechanisms for this type of debris.

'Tphis paper describes the physical and radiochemical characteristics of selected debris from the K i w i Transient Nuclear Test ( T N T ) (6, 7). This transient test was conducted in Nevada by the Los Alamos Scientific Laboratory ( L A S L ) , and produced approximately 3 Χ 10 fissions ( J ) . Zero time was 1059 PST on 12 January 1965. About 5 % of the reactor core was vaporized, and some 68% was converted to a cloud of particulate. The measured maximum temperature was 4250°K. (7). Large pieces of fuel rods were recovered near ground zero. The purpose of this test was to ascertain the hazard that would result from a rapid reactivity insertion into a K i w i reactor. The test provided an occasion to study radionuclide fractionation in debris from a reactor excursion. Because fractionation processes distribute hazardous radio nuchdes among debris particles in different manners, their effects require documentation and study. Chapter 17 by Crocker and Freiling in this volume w i l l provide background for the reader who is unfamiliar with fractionation phenomena. A

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Present address: FCA, U.S. Naval Weapons Laboratory, Dahlgren, Va. 22448. 337

Freiling; Radionuclides in the Environment Advances in Chemistry; American Chemical Society: Washington, DC, 1970.

338

RADIONUCLIDES IN

Methodology

and Gross Properties of the

THE

ENVIRONMENT

Debris


Three types of test samples were studied at N R D L : (1) cloud-filter samples ( K C ) obtained by aircraft flying at heights of 5000-8000 ft., (2) a ground-filter sample ( K G ) obtained by ground-level filtration of air at a point 4000 ft. from ground zero, and (3) a ground-fallout sample ( K H ) , aliquotted by weight from a plastic-strip collector located 4000 ft. from ground zero. The cloud and ground-filter samples consisted mainly of small, irregular particles, most of which were less than 50/x i n diameter (see Figure 1). B y contrast, the size of the particles i n the

Figure 1.

Particles from the cloud sample KC-1, showing both spherical and irregular particles

ground-fallout sample ranged from a few microns to several millimeters (see Figures 2, 3, and 4). Prior to radiochemical analysis, the groundfallout sample was sieved into eight fractions. Table I summarizes the


18.

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associated data on mass and activity. The radioactive assay was obtained with a 4-π gamma-ionization chamber.

Figure 2. A forge particle from sample fraction KH-3. The particle is spherical with many spheres stuck to its surface Figures 2 through 4 show photomicrographs of selected spheroidal and irregularly shaped particles from fallout sample fraction K H - 3 . Figure 2 also shows the effect of agglomeration, which was evidenced by only a small portion of the debris. In fraction K H - 3 , about one-fifth of the total weight consisted of spheroids, and these ranged i n density from 1.1 to 2.3 grams/cm. . The spheroids, shown i n Figure 3, ranged from translucent green to black. Gross samples and separated fractions were analyzed further by γ-spectrometry and radiochemistry. 3

Fractionation

Information

from y-Ray

Spectra

γ-ray spectra were taken of all debris samples with a 400-channel, Technical Measurement Corp. ( T M C ) pulse-height analyzer equipped



340

R A D I O N U C L I D E S IN

Figure 3.

THE

ENVIRONMENT

Large spheroidal particles from fraction KH~3s. Scale divisions are 1 mm.

with a 4 χ 4-inch N a l ( T l ) crystal. In general, the spectra of a ma jority of samples agreed qualitatively with the corresponding radio chemical data and were especially valuable i n identifying radionuclides at early times. Some typical gross y-spectra are illustrated in Figure 5. This figure shows the 13-day y-spectra of a typical cloud-filter sample K C - 1 , the ground-filter sample K G , and two fractions, K H - 1 and K H - 8 (largest and smallest sizes, respectively), of the ground-fallout sample. The figure compares these spectra with the unfractionated fission-product spectrum of irradiated U C . Various degrees of fractionation can be seen between samples and between different size fractions of the same sample. For instance, the spectrum of the cloud-filter sample shows, by comparison with the unfractionated U C spectrum, a rela tively small degree of fractionation. B y contrast the spectrum of the ground-filter sample indicates a strong enrichment in the volatile be having nuclides I and T e - I , and a deficiency i n " M o . Subsequent radiochemical results, described below, substantiate these findings. As 2 3 5

2

2 3 5

1 3 1

1 3 2

2

1 3 2


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341

to the fallout sample K H , the largest size fraction ( K H - 1 ) shows a slight depletion of the volatiles ( I , T e , etc.); the small size fraction ( K H - 8 ) , shows a strong depletion of the volatiles, an absence of B a - L a , and a very strong enrichment of Ru. Various degrees of fractionation of X e ( γ = 0.081 M.e.v.) can be seen in Figure 5, after the adjustment for interference arising from Nd (γ = 0.091 M.e.v.; assumed not to fractionate from U ) . The extent of the N d interference is estimated by comparison with the reference spectrum as indicated above. The cloud sample K C - 1 shows a substan tial depletion of X e ; the ground-filter K G shows a slight depletion; and the ground-fallout fraction K H - 1 , no discernible depletion. N o data are available for sample K H - 8 . The wide variation i n X e activity may well be attributed to differences i n the shock and thermal history of the samples and reflects the fission-product release rate from the fuel of the X e precursors—namely, 21-hour I and 2-min. T e (14). Recent calculations by Crocker have shown that, at 13 days after an event, the X e should constitute about 1 3 % of the total fission-product activity. Laboratory investigations (9) with U C microspheres (similar to 1 3 1

1 3 2

1 4 0

1 4 0

1 0 3

133

1 4 7

2 3 5

1 4 7


133

1 3 3

1 3 3

1 3 3

133

133

2 3 5

Figure 4.

2

Large irregularly shaped particles from fraction KH-3f. Scale divisions are 1 mm.


342

RADIONUCLIDES


Table I.

IN

THE

ENVIRONMENT

Weight and Activity Measurements of Ground-Fallout Sample K H After Sieve Size Separation

Designation

Sieve Size Range, mm.

Weight, gram

KH-1 KH-2 KH-3 KH-4 KH-5 KH-6 KH-7 KH-8

>2.794 1.397-2.794 0.701-1.397 0.351-0.701 0.175-0.351 0.088-0.175 0.044-0.088 Ί

' •'ΚΗ-Ια L A S L CLOSE-IN SAMPLES

0

Ο 1

0.01

! 1 1 1 1

00 I

Ο

1 111 11

0.1 r

Figure 7.

1

1.0

1

1

1 1 1 1 1

1

1 1 111 1 1

10

89,95

Fractionation plot for Y (LASL data is from Réf. 1 ) 91


100

344

RADIONUCLIDES

IN

THE

10

ENVIRONMENT

• KG

-

LASL CLOUD SAMPLE \

V mg. 10»i„/g

KH-la KH-2s KH-3s KH-3f KH-6c KH-7 a 6 c

a

98.0 44.2 23.5 52.0 14.8 20.6

s

S

S

M

9i

89

12.5 6.02 8.85 2.81 8.04 14.8

5.98 0.27 0.31 1.40 0.68 0.20

S

7

10.3 7.1

12.1 8.5

2.93

2.35

17.9 41.6

4.0 3.5

— — —

2.40 3.45

— — —

— —

— —

2.98 2.33

Single irregularly shaped particle. Oralloy was 93% 235TJ. At 1415 on Feb. 2, 1965 or D + 21 days or H + 507 hours.

The variation i n oralloy content shown i n Column 5 explains some of the variability i n s . Column 5 is calculated on the assumption that the oralloy is 9 3 % U . W h e n one considers that U C has 90 wt. % of uranium, the concentration of uranium i n K H - 7 indicates that about half this fraction arose from primary fuel material. The value of s is normalized in terms of the uranium content i n Column 6 to give the number of equivalent Z r fissions per gram of oralloy. This value for the large fritted particle ( K H - l a ) exceeds the calculated fragmentation threshold of 1 0 / / g (8). The evident negative correlation of this ratio with degree of fragmentation is noteworthy. Evidently, either degree of burn alone is an insufficient criterion of frag mentation, or large fractions of the mass 95 chain escaped as S r . The latter conclusion is supported b y independent, unpublished observations. Finally, the ionization current per gram, s , has been calculated for 21 days after the event and compared with s . Unlike the cloud sample, the K H sample was fractionated. The standardized (i.e., corrected to a reading of 560 χ 10" ma. for a 100-/xgram radium standard) unfrac tionated value of this ratio at 21 days has been determined b y Mackin to be 4.7 χ 10" ma. per fission (10). The value determined here is only half of the theoretical value. Crocker's calculations show that L a con tributes 60% of the ionization rate from an unfractionated sample at this time ( 2 ) . Depletion i n L a therefore undoubtedly contributes to the 95

2 3 5

2

9 5

95

15

95

95

y

95

9

21

1 4 0

1 4 0


18.

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L A I A N D F R E I L I N G

351

in Debris

low value of this parameter. However, the ratio s /s is relatively con stant while the degree of depletion i n the 140 chain varies considerably among the samples, and hence other causes must be contributing. T h e variation of " M o , R u , R u , and U indicates that variability i n the content of other mass chains may be compensating. y

1 0 3

1 0 6

Q5

2 3 7


Conclusions Although the transient test was orders of magnitude below a nuclear weapon in regard to energy release and temperature achieved, the debris showed many similarities to fallout. These included not only the size and appearance of the particles but also the correlation properties of various radionuclides. Dissimilarities in the correlations and the variation of specific activity with particle type confirm expectations of the impor tance of escape processes to the formation mechanisms for this type of debris. This study shows that data-correlation techniques developed for fallout characterization are also useful i n studying reactor debris.

Literature Cited

(1) Bryant, Ε. Α., Sattizahn, J. E., Wagner, G. F., Los Alamos Scientific Lab oratory, LA-3290 (June 23, 1965) (Classified). (2) Crocker, G. R., U. S. Naval Radiological Defense Laboratory, USNRDL -TR-1009(Dec. 28, 1965). (3) Crocker, G. R., Nature 210, 1029 (1966). (4) Crocker, G. R., Kawahara, F. K., Freiling, E. C., "Radioactive Fallout from Nuclear Weapons Tests," A. W. Klement, Ed., p. 72 (Nov. 1965). (5) Freiling, E. C., Science 133, 1991 (1961). (6) Fultyn, R. V., Intern. Symp. Fission Prod. Release, Transport, Accide Conditions, Oak Ridge, Tenn., CONF-650407, 537 (1965). (7) Henderson, R. W., Intern. Symp. Fission Prod. Release, Transport, Ac dent Conditions, Oak Ridge, Tenn., CONF-650407, 557 (1965). (8) King, L. D. P., Mills, C. B., Trans. Am. Nucl. Soc. 8, 565 (1965). (9) Lai, J. R., Pascual, J. N., Wong, D. T., U. S. Naval Radiological Defense Laboratory, USNRDL-TR-68-68 (Nov. 24, 1967). (10) Mackin, J. L., Weisbecker, L. W., Zigman, P. E., U. S. Naval Radiological Defense Laboratory, USNRDL-TR-811 (Jan. 18, 1965). (11) Rymer, G. R., Grandy, G. L., Henninger, W. Α., Roll, J. Α., Westinghouse Astronuclear Laboratory, WANL-TNR-162 (July 1, 1964) (Classified). (12) Strom, P. O. et al., U. S. Naval Radiological Defense Laboratory, USNRDL-935 (Nov. 5, 1965). (13) Weaver, L. E., Strom, P. O., Killeen, P. Α., U. S. Naval Radiological De fense Laboratory, USNRDL-TR-633 (March 5, 1963). (14) Zumwalt, L. R., Gethard, P. E., Anderson, Ε. E., Nucl. Sci. Eng. 21, 1-12 (1965). September 25, 1968. Work sponsored by the Space Nuclear Pro pulsion Office under Contract AT-(49-5)2505 (5). RECEIVED


Correlation of Radionuclide Fractionation in Debris from a Transient

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