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OCR for page 34

CHAPTER 3
DISPOSAL OF RADIOACTIVE WASTES IN THE OCEAN: THE FISSION
PRODUCT SPECTRUM IN THE SEA AS A FUNCTION OF TIME
AND MIXING CHARACTERISTICSl
HARMON CRAIG, Scripps Institution of Oceanography, University of California,
La Jolla, California
I. Introduction: Estimated output of nuclear
heat and fission products at "steady state"
nuclear power production
IN TWO other papers in this report, Wooster
and Ketchum discuss mixing rates in the oceans
on the basis of oceanographic data, and the
present writer reviews the natural isotopic stud-
ies which bear on the problem. In this paper
we attempt to construct a detailed quantitative
picture of the fission product spectrum in the
ocean, in steady state with a given fission rate.
Such an attempt may well be termed premature,
in view of our sketchy knowledge of the in-
ternal mixing rate in the sea. Nevertheless, we
know a good deal more today than was known
five years ago, enough at least to make some
simple model calculations which may well yield
correct results to an order of magnitude. More-
over, the construction of a model and the cal-
culation of its characteristics are often highly
informative, and, at the very least, provide a
basis for the orientation of future studies.
The following figures, available in various
sources, are pertinent to the estimation of fu-
ture consumption rates of nuclear power.
Present U. S. electrical energy:
6x 105mwh/yr.
Present world electrical energy:
10° mwh/yr.
Present world energy consumption (all
sources) is about 4.5 x1010 mwh/yr, doubling
every 30 years.
For the present calculations, we shall assume
a stationary world fission rate of U225 equal to
1000 metric tons/yr, supplying all the fission
products to be disposed of in the sea. We
shall then attempt to construct as reasonable a
1 Contribution from the Scripps Institution of
Oceanography, New Series, No. 902a.
picture as possible of the fission product ac-
tivity in the sea, when this activity reaches
steady state with the rate of fission, i.e., when
the decay rate of each fission product in the sea
is equal to the rate at which it is being dumped
into the sea, so that its concentration remains
constant. We shall also make some calculations
for a linear build up to such a fission rate in
50 years.
Since 1 gram of U2,5 is equivalent to 24
mwh, our assumed fission rate of 1000 tons of
U255 per year is equivalent to 2.4 x 1010 mwh/
yr of nuclear heat. At 50 per cent efficiency,
this is equivalent to a world nuclear power
consumption of 1.2x1010 mwh/yr. If this
latter figure represents 10 per cent of the total
world energy utilization, we are then assuming
a world consumption of 1.2x1011 mwh/yr,
which seems not unreasonable as an estimate
for the year 2000 A. D.
Thus a fission rate of 1000 tons of U25B/yr
represents a 2.7 fold increase in the present
world energy consumption, 10 per cent being
derived from nuclear heat with 50 per cent
efficiency, which should be reached in about
the year 2000 based on the present trend in
energy consumption (see above). Our calcu-
lations will all be linear with the fission rate,
so that data for other fission rates are easily
derived from the present calculations.
The build up of fission products in a reaactor
is given by:
dN ,
where /= fission yield (per cent of fissions
yielding an individual fission product, the sum
equalling 200 per cent) , R is the rate of fission
(atoms U225/yr) here assumed constant and
equivalent to 1000 tons of U2"/yr, and N=the

OCR for page 34

Chapter 3
35
Effects of Time and Mixing Characteristics
number of atoms of an individual fission prod-
uct present in the reactor at any time.2
Integration with appropriate limits gives the
number of atoms of a given fission product in
the reactor as a function of time:
N=f(1-,-) (1)
where the build up factor (1 — e~^) varies
from 0 to 1 as / varies from 0 to infinity, and
gives the fraction of the equilibrium amount
attained at any time. At secular equilibrium in
the reactor, dN/dt = 0, and \N = fR; we then
have:
N , -1— (t\
JV««!6 — ^~ \*l
from which one sees that at any time in the
reactor, N=N,aII)(1-*-*').
The assumed fission rate of 1000 tons U22S/yr
is equivalent to 2.2x10" megacuries of fission
(1 curie=3.7x1010 disintegrations/sec), and
since the sum of the fission yields is 200 per
cent, at equilibrium the total activity of all
fission products present in the world, in mega-
curies, could be roughly estimated by multi-
plying 4.4 x 10" by the average number of
radioactive members per fission chain. The
amount of an individual fission product would
be fR/\, using the appropriate decay constant,
and its activity would simply be fR, using the
appropriate fission yield.
The lengths of the fission chains are diffi-
cult to estimate because of the extremely short
half-lives of the first members. However, Dr.
E. C. Anderson (personal communication) has
2 The above equation actually applies only to the
first member of a fission chain; for the build up of
the second member (y) of a chain with initial mem-
ber (x), the correct expression is:
where /. and /, are the individual direct fission yields,
and so forth for the succeeding members of each mass
number chain. However the decay constants are very
large for the first members of a chain, and thus one
can neglect the exponential terms and assume a fission
yield which is the total yield of the isotope under
consideration plus all preceding members of the chain,
for all irradiation times with which we shall be
concerned. The experimental fission yield figures gen-
erally refer to the total chain yield, but because of the
very low production of the later members of a chain
by direct fission, there is no error involved in apply-
ing them to the first significantly long-lived chain
member.
studied the experimental data on the activity
of fission product mixtures directly after fission,
and concludes that for times beyond one day
after cessation of fission, on the average only
£ of the chains are still active (i.e. from this
time on there are left only about 0.3 radioactive
members per pair of fission chains initiated).
Thus he points out that assuming a fission rate
of 1000 tons U225/yr as used above, and taking
one day as an assumed minimum delay between
accumulation and disposal, the steady activity
in the sea for continuous stripping and disposal
after one day would be roughly 7 x 105 mega-
curies. This is about the same total activity as
that found below for an average irradiation
time of one year with a 100-day cooling period
before disposal, namely 7.7x105 megacuries
(see calculations in Section IV and Table 1).
The rough agreement of these numbers merely
emphasizes the great predominance of the few
long-lived isotopes of high fission yield in the
fission product activity after very short times.
II. Rate of introduction of fission products into
the sea
A more realistic picture is obtained by con-
sidering the irradiation time, or reactor holding
time for uranium slugs, which is limited by
structural weakening from irradiation, poison-
ing by fission products, etc., and the cooling
period necessary for safe handling and for the
growing in of plutonium in breeder piles. We
assume the fission products of the world are
distributed between (1) reactors, (2) cooling
pits, and (3) the oceans (or any gross disposal
site for that matter). The distribution among
these reservoirs and the fission product spec-
trum in each depends on the irradiation and
cooling times.
We shall assume an irradiation time of tr
years, equivalent to any of the following physi-
cal interpretations:
1. The reactors of the world are operated, on
the average, /r years, then stripped down and
rebuilt.
2. The reactor slugs are continuously pushed
through the reactors, each spending, on the
average, tr years in the reactor.
3. Continuous stripping into a holding tank
which is opened every tr years for removal of
fission products.

OCR for page 34

Atomic Radiation and Oceanography and Fisheries
From these sources, the fission products are
assumed to enter the cooling pits, from which
they are dumped into the sea.
At the end of the irradiation time /„ the
amount of a fission product is given by (1) as:
Assuming for the moment no cooling time, the
fission products are stripped out every tr years
and dumped into the sea. Thus the introduc-
tion rate into the sea of a given fission product
is equal to its activity A, in the sea at steady
state, and is given by Ntr/tr or:
where tc denotes the cooling time, here assumed
to be 0.
The activity of the fission products in the
world reactors at any time, Ar, may be evaluated
in the following way. The fission products are
stripped out every tr years, and Nr, the amount
in the reactors, varies from 0 to Nir in cycles,
as / varies from 0 to tr. For many reactors
operating independently (the sum of the fission
rates being R) with random distribution on the
tr cycle, we take the average of Nr consistent
with R by integrating equation (1) from 0 to
tr and dividing by tr; i.e., the steady state value
of Nr is:
Performing the integration, and setting Ar =
\Nr, we have for the steady state activity of a
fission product in the reactors of the world:
and from equations (4) and (5) we see that
N, + Nr=fR/*.=N,vlt, the total amount of the
fission product in the world, as of course it
must.
Still neglecting cooling time, the fraction of
the world total of a fission product which is
in the sea is given by N,/N,Qit = A,/A,0lt =F,,
and:
(6)
A/r
Neglecting cooling time, the effect of irradia-
tion time may be demonstrated by considering
the long and short-lived radioisotopes of stron-
tium, calculating the fraction of the world
totals, for the assumed fission rate, which is in
the sea, as a function of tr, as given below.
(%).
tr (years)
Sr90 (28y)
5r* (54<*)
0.1
99.9
79.8
0.5
99.4
38.6
1
98.8
21.2
2
97.5
10.7
10
88.5
2.1
Equation (6) shows the following character-
istics:
For long half -lives (\}r small): F,= 1-^
. . .(approaching 1).
For short half-lives (A/r>5): F,= —
A/r
For tr= 1 year, and for any isotope with a half-
life of less than 60 days:
F, = 0.4/1/2 (where tltl is here in days, /„=
0).
Thus, as shown above, increasing the irradia-
tion time from 0.1 to 1 year cuts the fraction
in the sea of a 60 day isotope by $', neglecting
cooling time effects, but does not affect the
long-lived isotopes.
We next interpose the cooling time between
the reactor stripping and the disposal in the
sea. The amount of an isotope left after the
cooling period is:
and from (4), the steady state activity of a
given fission product in the sea, equal to its
introduction rate, now becomes:
and Ft is reduced to:
A/r
(7)
(8)
III. Fission product concentration in the sea as
a function of linearly increasing fission rate
We can get some idea of the transient char-
acteristics of the fission product spectrum in
the sea by examining the build-up of fission
products with an increasing rate of fission. We

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Chapter 3
37
Effects of Time and Mixing Characteristics
shall take R, the world rate of fission, as 0 at
the present time (/ = 0) and increasing linearly
from the present time until it reaches the 1000
ton rate in 50 years. We shall further assume
continuous stripping of fission products into
the sea, and examine the transient character-
istics of long-lived and a short-lived fission
product.
The rate of increase of a fission product in
the sea is given by:
f =/(?>-'
where (R/t) is a constant by virtue of the
assumed linear increase from R = 0. N is now
the amount of a fission product in the sea at any
time /. We thus have:
JN+ [AN— (fR/t) f]dt — 0
Multiplication by e** makes the equation exact,
and the solution is:
(A/-1)
Activity (megacuries) in the sea
-AN
A2
Evaluating the constant from N = 0 at / = 0, we
have the general solution:
NI = ,§}&-(! -«-*)] (9)
where N( is the amount in the sea at the time /.
Multiplication by A to give the activity is seen
to give an equation of the same form as (5)
for the steady state amount in reactors, except
that in (9) both R and / are variables, with
R/t being constant.
We take R=0 at the present time, increas-
ing linearly to 1000 tons U225/year in 50 years.
As noted previously, this rate is equivalent to
2.2x10° megacuries of fission, and thus R/t=
4.4 x 104 megacuries/year. Thus the activity of
a fission product in the sea at any time / is
given by:
/4, = 4.4x104— [A/— (1 — *~*')] (10)
where At is in megacuries, A=yrs~1, / is in
years, and / is the fission yield. We tabulate
below the increasing activity in the sea for a
long-lived and a short-lived isotope with con-
tinuous stripping into the sea.
Sr9°
JlSl
>i/2 = 28;y
t1/2 = 84
/ (years)
/=0.05
f = 0.028
1
26.4
1200
10
2640
12,300
50
4.8x104
6.2 x 104
100
1.4x105
1.2 x105
200
3.5 x105
2.4x105
1000
2.1x10"
1.2 x 10"
At 50 years, when the fission rate of 1000
tons/year is reached, the Sr90 activity is half
the amount which would be in steady state with
this fission rate with an irradiation time of 1
year (see below and Table 1). If R continues
to increase at the same rate, the steady state Sr90
activity for constant R is reached in about 100
years, and thereafter the activity increases lin-
early at a rate given by: At= 2200(1 — 40), the
mean life of Sr90 being 40 years. The factor
(1— e-*f) grows in to 95 per cent at 3 mean
lives or 4 half-lives.
With a constant fission rate of 1000 tons
U225/year, irradiation time one year, and no
cooling time, the I121 steady state activity in
the sea would be 2000 megacuries (calculated
as in Table 1, but with no cooling time). With
the linear increase of fission rate and continu-
ous stripping as shown above, this level is sur-
passed in two years. These data illustrate rather
strikingly how rapidly the short half-life iso-
topes build up to secular equilibrium with an
increasing fission rate. Sr90 does not equal the
I121 activity until after 100 years of dumping
into the sea, under the above conditions. For
all species which have grown into secular equi-
librium with the increasing fission rate, the ac-
tivity ratios in the sea are simply given by the
fission yield ratios.
IV. Steady state fission product spectrum in a
homogeneous, rapidly mixed sea
The first three columns of Table 1 list all
the fission products of any significance, together
with their half-lives and fission yields. Col-
umns 4 and 5 show the total amounts of each
isotope in the sea, in metric tons and mega-
curies of activity respectively, in secular equi-
librium with a fission rate of 1000 tons U22B

OCR for page 34

38
Atomic Radiation and Oceanography and Fisheries
per year (2.2x10° megacuries of fission), as-
suming an irradiation time ( /, ) of one year, and
a cooling time (tc) of 100 days (0.274 years).
With such conditions, the expression for the
activity of each fission product in the sea, as
given by equation (7), becomes:
x 2.2 x 10' megacuries (11)
where A is in years-1.
For half-lives greater than 1 year there is
essentially no reduction in the oceanic activity
by the cooling time. For all isotopes with half-
lives greater than 5 years, more than 90 per
cent of the isotope will be in the sea at steady
state.
Of the 30 isotopes shown, 22 are independ-
ent and 8 are short-lived daughters which come
quickly into secular equilibrium with their par-
ents, decaying thereafter with the activity of
the parent. Cs127 has a branching decay with
8 per cent going directly to the ground state of
Bat9T; thus the secular activity of Ba127m is only
92 per cent of the parent activity. The activities
listed are beta activities only, for all isotopes
except Ba127m, TeI29m, and Cd11Bnl, which decay
from their excited states by gamma emission.
The Sm and Eu activities depend on the actual
rate of burn-up in the reactors, and may vary
considerably with different reactor conditions.
In the calculations, the first long-lived mem-
ber of each fission chain was taken, and the
fission yield for the entire chain was used for
this isotope. The direct fission yield for the
11-day Nd which lies above the 2.5-year Pm
in the 147 fission chain is not known, and thus
this isotope has been neglected; the Nd comes
quickly into secular equilibrium in the reactor,
so that the total chain fission yield can be used
for the Pm calculation.
The fission products are listed in order of
decreasing total activity in the sea, with radio-
active daughters paired with their parents. The
total amount of all fission products in the sea
is found to be about 3200 metric tons, cor-
responding to almost one million megacuries of
activity. This represents almost twice the pres-
ent activity in the sea, which is mainly due to
the radioactivity of potassium 40. The figures
for K40 and Rb57 are shown for comparison,
the activity of the other radioactive elements
in the sea being negligible relative to these
isotopes.
We shall now discuss the effects of the mix-
ing barrier at the thermocline in the sea on the
distribution of the fission products between the
deep sea and the upper mixed layer of the sea.
V. Distribution of fission products between the
deep sea and the mixed layer
We shall assume a simple model, convenient
for calculation, in which we divide the ocean
into two geophysical reservoirs: a mixed layer
above the thermocline, and the bulk of the
ocean, termed the "deep sea," below the ther-
mocline. The exchange of fission products be-
tween these two reservoirs is assumed to be a
first order process, the rate of removal of a
fission product from a reservoir being simply
proportional to the amount of the isotope in
the reservoir. The thermocline is assumed to
represent the boundary across which the hold-up
in mixing takes place.
Thus, for example, the rate of transfer of
water from the mixed layer to the deep sea is
assumed to be kmNm, where Nm is the mass of
water in the mixed layer and km is the exchange
rate constant for transfer of material from the
mixed layer to the deep sea. In general, we
write kt as the fraction of material in reservoir
/ removed per year.
The residence time of a molecule in a reser-
voir, r, is defined as the average number of
years a molecule spends in the reservoir before
being removed by the physical mixing process.
The meaning of T may be shown by the follow-
ing derivation which gives a rigorous definition.
Assume a reservoir with a steady-state fixed
content of N molecules of a substance, and a
continuous flux into and out of the reservoir
of molecules/year. At a particular time, /=0,
we have N0 particular molecules in the reser-
voir, and at some later time /, we have N' of
these original N0 molecules still present. Then
we define the average life of a molecule in the
reservoir in the usual way, as
/=oo,N'=0
r 2< nt *** N0 J '
where «< is the number of molecules of the
original N0 which remain in the reservoir for
each time /<, and dN' is the number of mole-

OCR for page 34

Chapter 3
39
Effects of Time and Mixing Characteristics
cules removed in the interval / and t+dt, i.e.,
the number of molecules with a reservoir life-
time equal to /.
The number of molecules of the original
particular set of N0 which are removed in any
interval dt is simply given by the concentration
of such molecules in the reservoir, multiplied
by the total flux from the reservoir, i.e.:
which yields on integration N =N0 exp
Substituting for dN' and then for N' in the
integral expression for r, and integrating be-
tween / = 0 and infinity, we obtain:
N
m = average depth of mixed layer of the
sea (taken as 100 meters).
D = average depth of the ocean (taken as
3800 meters).
We assume that the fission products are intro-
duced into the deep sea after the 100 day cool-
ing period, the disposal rate or flux of a given
fission product isotope, termed <£, being equal
to the steady-state total activity in the sea A,
as given by equation (11). is thus in "mega-
curies of flux," = atoms/sec divided by 3.7x
1010. We wish to ask what steady-state activity
per unit volume of water will be in the mixed
layer, as a function of the rate of cross-thermo-
cline exchange of sea water and fission products.
The water balance between the reservoirs is
given by:
and from the expression for N' one sees that
T, the average life, is also the time required
for the original number of N0 particular mole-
cules to be reduced to l/e times the initial
number, r is thus formally equivalent to a
radioactive mean life.
In our particular model we are assuming the
rate of removal to be dependent only on the
total amount of substance, N, in the reservoir,
so that the outgoing flux is given by

40
Atomic Radiation and Oceanography and Fisheries
particular model in the paper by Craig. From
these discussions, we choose for the present
calculations a value T(J = 300 years as perhaps
the best guess. As discussed by the writer in a
separate chapter of this report, radio carbon data
indicate a residence time for water of about
1000 years, as a world-wide average. Mixing
in the Atlantic is probably a good deal faster
than in the Pacific, and 300 years is probably a
safe lower limit estimate for the Atlantic, con-
sidering the material to be deposited on the
bottom. Thus the mixed-layer activities we cal-
culate should be upper limits, which would be
approached more closely in the Atlantic than in
the Pacific.
The average world-wide depth of the mixed
layer, m, is taken as 100 meters, and the average
depth of the sea is taken as 3800 meters. The
volume of the sea is 1.4x1021 liters; thus the
volume of the mixed layer is taken as 1/38 of
this or 3.7 x1019 liters. Putting these nu-
merical values into (16), and noting that —
A,, we have for the activity of any fission prod-
uct per unit volume of sea water in the mixed
layer:
in disintegrations per second per liter, where
A, is in megacuries, as tabulated in column 5
of Table 1, and X is in years-1. From this
equation the values tabulated in column 8 of
Table 1 were calculated, and were converted
to microcuries per liter for column 9.
From the relation ad/am= (AJ/m/A^A) =
(Ad/Am) (m/D-m) we obtain:
a* — \ _i_t
-- ATm+1
am
where Tm the residence time of a water mole-
cule in the mixed layer, is given by (12) as
1/37 of 7,1 = 8.1 years. We thus write:
= 8.1A+1=a
(18)
from which, given the values of am computed
above, the values of ad tabulated in column 7
of Table 1 were computed. We call a the
"oceanographic partition factor." It is a func-
tion of the mixing rate of the sea and the decay
constant of the individual isotope, and is a
measure of the effectiveness of the cross-thermo-
cline exchange rate in buffering the mixed
layer from the fission products introduced into
the deep sea. Values of a are tabulated in
column 6 of the table, and range from about
1 for the longest lived isotopes to about 250
for an isotope with a half-life of 8 days. For
stable isotopes A is 0, a is 1, and (18) reduces
to simple statistical partitioning.
From (17) we see that as A, the decay con-
stant of an isotope, increases, the activity in
the mixed layer decreases; i.e., if more of the
isotope can be removed from the deep sea by
decay, less needs to be transferred to the mixed
layer to preserve the steady state. If the half-
life were so long that the radioactivity did not
affect the distribution between the mixed layer
and the deep sea, we would have simply a sta-
tistical partitioning of the isotope between these
reservoirs, such that the activity per unit volume
in each reservoir would be the same. From the
above equations we can derive the ratio of the
activity in the mixed layer for an isotope to the
activity per unit volume which would be ob-
served if the partitioning were statistical:
am . Tj + Tm 1
—., j <=*—
am(stat) art+rm a
and we see that a~1 is approximately the frac-
tion of the statistical activity per unit volume
attained by a fission product in the mixed layer.
Equation (19) can be written exactly as:
»m '!/»
(20)
where /1/2 is the half-life of the isotope in years.
The ratio am/am(stat) is plotted in Figure 1
as a function of the half-life, and one reads,
for example, that an isotope with a 5 year half-
life attains about 48 per cent of the activity
per unit volume in the mixed layer which it
would have if its half-life were so long, relative
to the mixing rate in the sea, that its radio-
activity had no effect on its distribution.
The values of a^, && and a are tabulated in
Table 1, in which the isotopes are arranged in
order of their activity in the deep sea. For
comparison, the activities of potassium 40 and
rubidium 87, which provide essentially all the
radioactivity in the sea, are also listed. In the
deep sea, the predicted fission product activity
is 19.3 disintegrations per second per liter, as
compared with the natural activity of 12.2 dps/
liter; thus the fission products in steady state
with the 1000 ton fission rate would almost
triple the deep-sea activity.

OCR for page 34

Chapter 3
41
Effects of Time and Mixing Characteristics
TABLE 1 FISSION PRODUCT SPECTRUM IN THE OCEAN AT STEADY STATE DISPOSAL INTO DEEP SEA. CALCU-
LATED FOR FISSION RATE OF 1000 TONS U*M/YR (2.4 X 101 0 MWH/YR OF NUCLEAR HEAT), IRRADIATION
TIME OF 1 YR AND COOLING TIME OF 100 DAYS. AVERAGE LIFE OF A WATER MOLECULE IN THE DEEP
SEA TAKEN AS 300 YEARS; AVERAGE DEPTH OF THE MIXED LAYER TAKEN AS 100 METERS.
Total amount in ocean
Activity (dps/liter)
Isotope
Half-
life
33 y
Fission Metric
yield % tons
6.3 1750
Activity
megacuries
1.4 X 10*
1.3 X 10*
a =
1.17
Deep sea
3.64
3.35
tm
Mixed layer
Microcuries
per liter
8.4 X 10'*
7.7 X 10-*
MBa1*™
2.6m
3.12
2.87
•Sr*0
28 v
5.0 780
— 0.20
1.1 X 10*
1.1 X 10*
1.20
8.32
2.90
2.90
2.42
2.42
6.5 X 10-*
6.5 X 10-*
•Y"
. 64h
•Ce1" . . .
280 d
5.3 19
6.0 X 10*
6.0 X 10*
1.62
1.62
0.19
0.19
5.2 X 10-*
5.2 X 10-*
.JV"
. 17.5 m
2.5v
2.6 48
0.7 630
4.6 X 10*
1.5 X 10*
3.24
1.06
32.5
1.23
0.40
0.38
0.38
1.0 X 10-*
1.0 X 10'*
1.0 X 10'*
«Smm
. 100 y
tiZ]St
65 d
6.4 0.58
— 0.32
1.2 X 10*
1.2 X 10*
0.33
0.33
2.7 X 10-'
2.7 X 10-'
uNbK
. 36 d
i.o x 10-*
»Y"
60 d
5.9 0.39
0.5 2.0
9.4 X 10*
35.1
6.61
0.25
7.2 X 10-1
1.9 X 10-*
«Ru100
1 v
6.6 X 10*
6.6 X 10*
0.18
0.18
2.7 X 10J
2.7 X 10-*
7.2 X 10-'
7.2 X 10'7
. 35s
«Sr*
54 d
4.6 0.22
3.7 7.2 X 10-*
6.0 X 10*
38.9
52.0
0.16
4.1 X 10-*
1.1 X 10-'
uRuM.
. 40 d
2.3 X 10*
6.1 X 10-*
6.1 X 10'1
1.2 X 10-*
1.2 X 10-*
3.2 X 10-*
3.2 X 10-*
. 55 m
2.3 X 10*
/"—Ml
32 d
5.7 6.3 X 10-*
0.03 0.44
0.3 3.4 X 10-*
1.8 X 10*
5.1 X 10*
65.0
3.8
4.9 X 10-*
1.4 X 10J
7.6 X 10-4
3.6 X 10-*
2.0 X 10-*
9.7 X 10-*
caEu™
2 v
33d
1.0 X 10*
1.0 X 10"
63.4
2.8 X 10-*
2.8 X 10J
4.4 X 10-*
4.4 X 10-*
1.2 X ID-*
1.2 X 10-*
saTe1**
70m
..Pr1"
13 7d
5.4 —
6.1
40
151
161
1.1 X 10-*
7.2 X 10-*
2.0 X 10-"
wBa1"
. 12.8 d
30
30
8.0 X 10-*
8.0 X 10-*
5.0 X 10-*
5.0 X 10J
1.3 X 10-"
1.3 x 10-"
1 7d
soSn1"
130 d
1.2 X 10-* —
8 X 10-* —
2.8 —
0.01 —
0.01 —
0.02 —
0.018 —
6.8
0.64
0.35
0.15
7.5 X 10-*
1.7 X 10-*
1.4 X 10-*
16.8
47.4
256
134
151
206
268
1.8 X 10-*
1.7 X 10-*
9.5 X 10-*
4.0 X 10-*
2.0 X 10-*
4.7 X 10'T
3.9 X 10-*
19-3
1.1 X 10-*
3.6 X 10-'
3.7 X 10J
3.0 X 10J
1.3 X 10-*
2.3 X 10J
1.4 X 10-10
12.1
3.0 X 10-"
9.8 X 10-"
1.0 X 10-u
8.0 X 10'1*
3.6 X 10-"
6.2 X 10-"
3-9 X 10-"
3.2 X 10-*
aCd1"- ....
. 44d
8d
BEu""
. 15.4 d
•.Cs""
. 13.7 d
wSn1"
10 d
nAg"1
7.6 d
Totals:
Natural
K"
Rb"
potassium
3230
and rubidium in the
6.3 X 10"
1.2 X 10"
7.7 X 10*
sea:
4.6 X 10*
1
1
12
0.22
12
3.2 X 10-*
5.9 X 10^
8.4 X 10*
0.22
All activity values are Beta activities only, except where isomeric transitions are indicated.
Conversion: 1 disintegration per second = 2.7 X 10-° microcuries.
1 curie = 3.7 X 1010 disintegrations per second.

OCR for page 34

42
Atomic Radiation and Oceanography and Fisheries
100
90
80
ro
60
50
40
SO
20
10
.2
.3 .4 .5
2345 10
HALF-LIFE (YEARS)
FIGURE 1
20 30 40 50
100
However, the effect of the internal mixing
rate of the sea in the model adopted, is to cut
the activity in the mixed layer down to 12.1
dps/liter which is, by coincidence, just equal
to the natural activity and which would thus
just double the activity in the mixed layer.
It should be noted that the figures given in
the table for the predicted activities in the
mixed layer refer only to cross-thermocline mix-
ing by physical processes, exclusive of biological
transfer through the thermocline. However,
the figures listed provide a basis for speculation
on the hazardous effects of the mixed layer
activity, in that comparison may be made with
biological concentration factors, discussed else-
where in this report, to predict the activity
levels in marine organisms. In this way, rough
predictions may be made of the hazard to man,
not only by direct exposure to the waters of the
mixed layer of the sea, but by the activity con-
centrated in marine organisms used for food.