ML20099G193
| ML20099G193 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 06/19/1984 |
| From: | Bayer A, Helton J, Muller A ARIZONA STATE UNIV., TEMPE, AZ, KERNFORSCHUNGSZENTRUM, KARLSRUHE, GE, SANDIA NATIONAL LABORATORIES |
| To: | |
| References | |
| OL-A-155, NUDOCS 8411270157 | |
| Download: ML20099G193 (44) | |
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Contamination of Surface-Water Bodies } g' p W .
after Reactor Accidents by the Erosion of V
\, A 7 q2) -p Atmospherically Deposited Radionuclides
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{\d J. C. Helton", A. B. Muller' A. Bayer*
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- This work performed under contract to Sandia National Laboratories for the Office of Nuclear Regulatory Research, U. S. Nuclear Regulatory Commission.
l
' Department of Mathematics l
Arizona State University Tempe, Arizona 85287 USA
'Sandia National Laboratories, on leave of absence to:
Division of Radiation Protection and Waste Management OECD Nuclear Energy Agency 38 Boulevard Suchet 75016 Paris, France "Kernforschungszentrum Karlsruhe 5 7500 Karlsruhe 1. Federal Republic of Germany 0411270157 840619 PDR ADOCK 05000352 N O PDR L
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P 9s Abstract Reactor. safety analyses usually do not consider the popula-tion risk which might result from the contamination of surface-water-bodies after reactor accidents by_the erosion of
' atmospherically deposited radionuclides. This paper is intended to provide perspective on the reasonableness of this omission. Data'are presented which are suggestive of the rates
'at which atmospherically deposited radionuclides might erode into surface-water bodies. These rates are used in the calcu-lation of potential health effects resulting from surface-water contamination due to such erosion. These health effects are a compared'with predicted health effects due to atmospheric and terrestrial pathways after reactor accidents. The presented i results' support the belief that the contamination of surface-water bodies after reactor accidents-by the erosion of
- atmospherically deposited radionuclides is not a major contributor to the' risk associated with such accidents.
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- 1. Introduction. As indicated in several recent reports, reactor safety analyses usually do not consider the population risk which might result from the contamination of surface-water
' bodies after reactor accidents-by the erosion of atmospherically deposited radionuclides (e.g., A182a, US82. US83). The_fol-lowing: presentation is intended to provide perspective on the reasonableness of this omission. To this end, the paper has three primary purposes. The first is to present data which are suggestive of the rates at which atmospherically deposited radionuclides might erode into surface-water bodies. The second is to present calculations which are suggestive of the health effects which might result from such erosion. The third is-to provide a comparison of the health effects associated with the erosion of atmospherically deposited radionuclides into surface-water bodies with the health effects associated with the atmospheric and terrestrial pathways after a reactor
, accident. The presented results support the belief that the contamination of surface-water bodies after reactor accidents l by the erosion of atmospherically deposited radionuclides is l not an important contributor to the risk associated with reactor accidents.
L l
' Section 2 presents models and data which have been i
developed to relate radionuclide concentrations in surface l
water to radionuclide concentrations on land due to fallout from nuclear weapons tests. It is suggested that these models ,
and data can be used to infer the behavior of radionuclides O
- . _ -,__ _ --~..__. ~ -..__ _ _ _ ____._____._ ._ _ ..._._..______ _._.i..____
. - - . _ - = . _ - _ . -. ._ _ - - . . . _ - - - -
released in a reactor accident. Section 3 describes how the
(
models and data presented in Section 2 can be used to predict health effects from tha, contamination of surface-water bodies due to the erosion of atmospherically deposited radionuclides. ,
Then, Section 4 uses the computational procedures described in 1
Section 3 to calculate health effects associated with reactor i
accidents at three different sites. Finally, Section 5 con- ,
tains a comparison of the results calculated in Section 4 with results calculated for atmospheric and terrestrial pathways after reactor accidents.
- 2. Radioactive Fallout Data. Past testing of nuclear wea-pons has injected a large inventory of radionuclides into the atmosphere and thence into the terrestrial environment. The manner in which these fallout radionuclides erode from land to i
surface-water bodies provides a potential source of information l-with respect to the behavior of atmospherically deposited l radionuclides after reactor accidents. A large effort has been h
i devoted to gathering da;.' on radioactive fallout and its rela-tion to radionuclide levels in the environment (e.g., Ru69, Un77, Aa79). In particular, it has been found to be possible to relate fallout rates and accumulated fallout levels to radionuclide concentrations in various environmental components by relatively simple empirical relationships. The simplest of l these relations is l
Cg=aDg + b Ag ,y ,) , (2.1) l where C g is the radionuclide concentration in the environ-mental component of interest in year 1 (units: Ci/1 or Ci/kg, ;
A' as appropriate), D g is the fallout rate of the radionuclide 2
for year i (units: Ci/km /yr), Ag _yg,) is the accumulated fallout from year 1 to year 1-1 with an assumed effective half-2 2 life of n years (units: Ci/km ), and each of a (units: km yr/1 or km yr/kg) and b (units: km /1 or km /kg) is a coef-ficient determined by regression analysis. The effective half-life n is at most the radioactive half-life of the radionuclide but can be less as it may also account for radionuclide loss by mechanisms other than decay (e.g., irreversible binding to soil materials).
More complex relations than (2.1) are also used. For example,
+ ( }
Cg=aD g + b Dg ,7 + c Ai-2(m) i-2(n)*
is the radionuclide concentration in the environ-f where C mental omponent of interest in year 1 (units: Ci/1 or Ci/kg, as appropriate), D g and D g _1 are the fallout rates for years i 7
and 1-1 (units: Ci/km /yr), A i-2(m) and A i-2(n) are i
accumulated fallout from year 1 to year 1-2 with assumed effec-tive half-lives of a and n years (units: Ci/km 2), and each of a (units:
2 km2 yr/1 or km yr/kg), b (units: km2 yr/1 or km yr/kg), c (units: km 2 /1 or km /kg), and d (units:
km /1 or km2 /kg) is a coefficient determined by regression analysis. Sometimes months and various other time increments are used in relations of the form of those in (2.1) and (2.2).
Additional developments based on regression analysis (e.g.,
l Ri77, Ly78) and other modeling approaches (e.g., Huf70, Hub 80, He82) are also possible.
!O l
t
w,vr The particular environmental component:of. interest in this
' analysis is: surface water. Thus. for our purposes. Cg is
- concentration in surface water. There are-numerous studies which provide.information.on the coefficients a and b-in (2.'1) for water draining fron-regions varying in size from large watersheds to small experimental plots. For this reason, the following investigation will use the model presented in (2.1) rather than one of the more complicated models indicated in the preceding paragraph for which less data are available. For a given region, the coefficients a and b depend on the size of the region, the amount of runoff from the region, and the fractions of recently deposited and accumulated radio ~nuclide removed in runoff. In particular, a and b are given by a = L X,/R and.b = L Kb/R, (2.3) km 2), R is the where L is the area of the watershed (units:
annual runoff rate (units: 1/yr), X, is the fraction of recently deposited rad'.onuclide removed by runoff (units: dimen-sionless) and.K b is the rate constant for the removal of accumulated radi'onuclide (units: yr-1). Then, 100 K, and 100 l are.the percent of recently deposited radionuclide removed b
in runoff and the annual percentage of accumulated radionuclide removed in runoff, respectively. The time periods for which X,
~ has been calculated vary but are typically less than or equal to a year. Due to the varying conditions under which radionu-clide washoff data have been recorded, it is more-informative
'to present such information in terms of K, and Kb than in terms of the regression coefficients a and b.
Tables .1 and 2 'present -values for A, and Ab that have been determined in field investigations. The values in Table l'are for larger' regions while the values in Table 2 are for experi-mental plots. There is a tendency for higher washoff rates from the smaller experimental plots. The washoff rates from.the larger regions are the ones most relevant.to this analysis. The fact'that initial washoff rates are generally higher than subse-quent washoff rates is probably due to time-dependent processes such as the movement of radionuclides into the soil column and the fixation of radionuclides to soil materials. The higher washoff rates for small plots probably result from factors such as short travel paths to collection points and use of experi-mental plots with little or no plant cover.
() Other substances which have been dispersed in the environ-Two ment can also be used in the estimation of washoff rates.
such substances are pesticides and herbicides. These are often
^
spread on the surfaces of plants and fields, and considerable data exist on their washoff rates (e.g., Pio73, Caro 76, Wau?8, Leo 79, We80). The pattern of data here is similar to that for fallout. The overall washoff rates tend to be small with the initial washoff rates greater than subsequent washoff rates.
As another example Andren et al. (An75) studied a watershed in Tennessee and found that 2-3% of the annual atmospheric lead input is transferred out of the watershed by streamflow.
- 3. Modelina Anoroach. For the prediction of radionuclide washoff from land surfaces to surface-water bodies after reactor
() accidents, it is assumed that radionuclides behave in a manner f
'/
-- consistent with the relationship in (2.1) and the data in Table
-1. There exist various reviews on both the properties of radioactive fallout (e.g., Ad60, Bj63, Cr66. No71, Pa73) and the properties of fission products released in reactor accidents'(e.g., Nu79, Ca81, Mo81 US81). There also exist a number of reviews on the behavior of fallout radionuclides in soils (e.g., Sc65, Po73, Pr73). However, the authors are una-i ware of any reviews which directly compare the properties of t.
radioactive-fallout from weapons tests with the chemical and l
physical properties of fission products potentially released in reactor accidents. This is unfortunate as the behavior of I fallout radionuclides is often used to infer the behavior of radionuclide releases associated with such accidents.
In the present study, the practice of using fallout radio-nuclides as analogues f;r the same radionuclides released in reactor accidents is continued. If a given element is either f soluble in both types of release, forming the same aqueous spe-cies, or is insoluble in both, due to the physical nature of the deposited particles or to rapid sorption after deposition, then the behavior of that element in fallout probably provides a good analogy for the behavior of that element in a reactor accident release. The thermodynamically most stable forms of both Sr and Cs released in a reactor accident will probably be soluble. Such stable oxides and hydroxides are indicated in i
several studies of reactor accident source terms (e.g., Mo81:
US75, Table VI 8-2). Also, thermochemical equilibrium calcula-I tions indicate that the soluble strontium hydroxides reported I
- - ~ . . - - - - -
-,.,.,_-_.,,,._,.__-.,._.,,,,_,n._,nnn___.,,e,,,.a.,,. an__ ,mv __.m-, - e n _ - n., n. m-
.f%
\s-) 'by' Francis'(Fra78) and by Huff and Kruger (Huf67) for weapons
-fallout are the most stable forms of strontium, in preference to'similarly soluble oxides. .The observed behavior of Cs in fallout is consistent with-initially highly soluble solid phases, speciating to Cs* which rapidly undergoes ion exchange and is sorbed onto soil materials. Thus, since the behavior of Sr and Cs appears to be controlled by rapidly .
formed, thermodynamically stable phases and species independent
'of the origin of the material, the use of fallout as an analogue for these elements after reactor accidents seems jus-tified.
Since Sr and Cs tend to form soluble phases.in aqueous environments near the earth's surface, any differences in the
) actual solubility of the forms released in a reactar accident will probably have minor effect on the general. appropriateness of the analogy made. Even if some differences occur, the i
removal rates' assumed for the following calculations should be acceptable for use in a preliminary assessment of the effects associated with radionuclide washoff after a reactor accident.
This statement is made because the following pattern of behavior seems to occur for a wide range of materials deposited on surfaces in the environment (e.g., see the data on different radionuclides in Table 1 and the previously cited data on her-bicides and pesticides): a few percent or less of the depos-l I-t ited material washes off over a relatively short time period after deposition and then a smaller percentage of the remaining
) material is removed each year thereafter.
t
1 For the following, it-is assumed that an initial fraction A, (units: dimensionless) of a-deposited radionuclide-washes off in a relatiiely short time period after an accident and that thereafter the radionuclide washes off with a rate constant Ab (units: yr ).
This assumption is that i
described by (2.1) with the effective half-life conservatively taken to be the same as the radioactive half-life. If x 0 (units: Ci) denotes the total amount of a radionuclide with a radioactive decay constant A(units: yr~1) initially i
released to a land surface and x(t) denotes the amount present on the land surface at time t, then the change of x(t) subse-quent to the initial washoff is described by the differential equation
) dx/dt = - (A + Ab) x, x(0) = (1 - Aa) XO e (3 1) i which has the solution x(t) = (1 - Aa) xo exp [-(A + Ab )t] . (3.2)
! Hence, the total amount W (units: Ci) of the radionuclide washing into the surface-water body is given by W = Aa XO + ) Ab x(t) dt f
= ka X0 + (1 - Aa) Ab XO/ (A + Ab)
= (Aak + Ab ) XO /(A + Ab ) - (3 3)
For subsequent calculations to examine the effects of radionu-i clide washoff, the preceding relation will be used to estimate the total amount of a radionuclide washing off of a land i
() surface and into a surface-water body. The assumption that 1
f
-_- - - - _ . - - - = - . . _ - . . -
remains constant'rather'than decreasing with time is probably conservative.
The determination of potential health effects which might result from radionuclide washoff after reactor accidents to Three pathways are surface-water bodies is now considered.
included: drinking water, fish and irrigated food. The models used are similar to those presented in NUREG 1.109 (US77); a more detailed development of the use of these models to determine population exposure and risk from long-term radionu .
clide releases-to the surface environment is available else-where (He83).
Exposure from drinking water is considered first. Suppose Wg (units: C1) represents the amount of a radionuclide wash-() ing off a land surface during the i year after.an accident t
and into a river system with an average annual discharge D 7
(units: 1). Then, the average radionuclide concentration in the river for the ith year can be approximated by Wg/D,
~
and the future population health effects HE y (units: Icf*) from water ingestion during the ith year after the accident are f
given by HEvi = (Wi/D) WT WC POP RF , (3.4)
-where WT is a water treatment factor (units: dimensionless), WC is annual individual water consumption (units: 1/ind**), POP is the f
size of the population receiving drinking water from the l
!. contaminated system (units: ind), and RF is a risk factor (units:
i
- 1atent cancer fatalities j
l O ** individual
L.
1 i~
N/ .lef/Ci). Thus, if total washoff W (units: Ci) and total population
- health effects HE ,(units: Icf) are given by W=E g Wg and HE ,= Eg HE ,g , (3.5) t respectively, then i
HE ,= (W/D) WT WC POP RF . (3.6)
- i. In a similar manner, population health effects HEg (units: Icf) from fish consumption can be approximated by HEg = (W/D) CR FP RF , (3.7) where CR is a concentration ratio from water to fish (units:
1/kg) and FP is the annual production of edible fish products from the water body (units: kg). Also, the population health effects HE 'from the direct contamination of plant material for human consumption by sprinkler irrigation can be approxi-mated by HE = (W/D) IR FR (WHL/LN(2.)) RF, (3.8) p where IR is the annual rate at which water used in the sprink-1er irrigation of plant material for direct
- human consumption (units: 1/yr), tu is the fraction of radionuclide in sprinkler irrigation water which is retained on edible plant material (units: dimensionless), WHL is the weathering half- life for radionuclidea retained on edible plant materials (units: yr),
and LN(2.) is the natural logarithm of 2. The preceding calculation ignores potential exposure due to root. uptake.
However, it is felt that this omission is unlikely to seriously O
'd affect'the overall predicted consequences (Ru67).
For each radionuclide, the. risk factor RF (units: Icf/Ci) is based on the data and methodology used in the WASH-1400 analysis (US75). Each risk factor is actually a sum of the form RF jk DF jk EF) (3.9)
RF = I) Ik where RF jk is the risk factor (units: Icf/ren) for the j th th time period after exposure. DF is the cancer and-k jk ingestion dose factor (units: rem /Ci) for the organ associated th time period after exposure with the j th cancer and the k and EF) is the effectiveness factor (units: dimensionless) associated with the j* cancer. For this analysis, the fol-lowing cancers.are considered: leukemia, lung, gastrointes-4 tinal, pancreatic, breast, bone and "other". The values for
- RF jk and DF jk are derived from Tables VI 9-5 and VI 8-4, l respectively, of WASH-1400 (US75). The central estimate risk model described in WASH-1400 is used. In WASH-1400, whole-body
- dose factors are used for pancreatic, breast and "other" cancers
- this same pairing of factors is employed in-the CRAC2 computer model (Ri83) for the calculation of reactor accident consequences. As exposures are at very low levels, an effec-tiveness factor of .2 (US75, Table VI 9-7) is applied in this
- study for all cancers except breast cancer (US75, p. 9-25).
Half-lives and risk factors for selected radionuclides are given in Table 3: these are the radionuclides considered in the WASH-1400 analysis for long-term ingestion exposure (US75, Sections 8.3.1.3 and E3.2). The risk factors are calculated as indicated in this paragraph. The authors are aware of the l l-l
m I
(_/] uncertainties associated with the prediction of health effects due to very low exposures; however, the approach outlined in this paragraph was selected so that health effects would be calculated in the same manner as in the WASH-1400 analysis.
- 4. Potential Consecuences. Consequences are now estimated for the potential contamination of surface-water bodies after reactor accidents by the erosion of atmospherically deposited radionuclides. An example involving direct deposition on a large lake is also given. Accidents involving reactors located near the following areas are considered: the middle and lower Mississippi valley, Lake Michigan, and the Rhine-Meuse valley.
These locations were selected due to the convenience of using data in their analyses which were already compiled for use in
( other studies. Due to their potentially large release quanti-ties, relatively long radiological halflives, and recognized
! radiotoxicity, effects associated with the following radionu-clides are considered: 'Sr. 90Sr. 134 Cs and 3 Cs.
As already indicated, these are the radionuclides considered in the WASH-1400 analysis for long-term ingestion exposure. The '
preceding radionuclides are assumed to be released due to an SST1 accident (i.e., a core melt with loss of all installed safety features followed by a large overpressure failure of the containment building (A182b)). The radionuclide releases assumed to take place in association with such an accident are presented in Table 4. For each example, the entire release is deposited on the watershed or waterbody under consideration.
) As the models used to predict health effects are linear with l
. , - . , , - .,.-,,--....n.-.r.,.-,n.-..,_,.,.s.,._,e , - - - . .,.,---,,--.nw,c, s- ~m,-.~....,,n,,-,.-,,--.r-w~.a.,,m,--r~ - g- n e p.---
t 4;
respect to the size of this deposition, the presented results can be scaled to represent the effects of a fractional deposi-tion.
Mississioni Valley. The release involving the middle and lower Mississippi valley is considered first. This region was
! selected due to the convenience of using the data compiled on the area by Nienczyk et al. (Nie81). Of the studies on radio-nuclide washoff compiled in Table 1, the one by Menzel (Me74) is selected for guidance with respect to the present analysis. ,
This study estimates A, and Ab f r various regions of L the United States, of which the Southern Plains is the region which contains the lower Mississippi valley. For this region, the estimated values of A, and Ab ff ' 8* ***
-1 A, - 1.79E-2 and Ab = 0.51E-2 yr (4.1) l (Me74, Table 2). These values will be used for 8'Sr and
'O Sr. Adjoining regions have values which are both larger and ,
smaller but the overall variation is not large. There is not 90 as much information available on 137 Cs as on Sr. Examination of Tables 1 and 2 suggests that a smaller percentage of deposited 137 Cs than of deposited 90 Sr washes into surface-water j-bodies. Aarkrog (Aa79) indicates that the washoff rate for 3 90 Sr. Further, measurements Cs is perhaps 20% that for l involving New York City tap water (Hea76) indicate that the ratio 137 Cs to 90 Sr is about .1 even though there is about 50%
of 137 90 f more Cs than Sr in fallout and their half-lives are approximately equal. However, for the following calculations, it is conservatively assumed that the wash-off rates for Cs and Sr L -
~ are;the same. Thus, the values for 1, and Xb i" I4'1I *** "I
13 If desired, the results contained in used for Cs Cs.
this' paper can be easily scaled to indicate the effects of other wash-off rates. As indicated in (3.3), the values for 1, and Kb can be used to estimate the fraction of a
.radionuclide release eventually transported-into the river.
The results of this calculation are given in Table 5.
The calculated health effects for an SST1 accident due to radionuclide washoff into the middle and lower Mississippi river are presented in Table 5. The value for D is taken to be 5.7E14 1 (Nie81. Table B7). Further, for the other values in (3.6) for water consumption WT = .87 for Sr and NT = .53 for Cs (Nie81, Table D2.1), NC = 370 L/yr (US77, Table D-1), and POP = 2.9E6 ind (Nie81. Table E7). For the additional values in (3.7) for fish consumption, CR = 30 1/kg for Se and 2000 1/kg for Cs (US77, Table A-8), and FP = 2.0E6 kg/yr from an assumed catch of 6.5E6 kg/yr (Nie81 Table E35) and an edible fraction of .31 (Nie81, p. 229). Finally, for the additional values in (3.8) for the direct contamination of plant material for human consumption by sprinkler irrigation. IR 8.1E8 1/yr (Nie81. Table E42 with the conservative assumption that all plant material raised with sprinkler irrigation is used for human consumption), FR = .2 (Bo81), and NHL = .038 yr (Bo81).
Lake Michiaan. As a second example, radionuclide washoff around Lake Michigan is considered. This situation is approached by first determining the effects of an SST1 accident with release directly to Lake Michigan. Again, the following
.O 1 137 Cs.
( radionuclides are considered: 89Sr. 90Sr. Cs and The rate of radionuclide removal from the lake will be based on empirical rate constants derived from radioactive fallout 90 data. The radionuclide Sr seems to be little removed by incorporation into lake sediments; for example, Lerman and Tanaguichi (Ler72a, Ler72b) estimate that the annual 90 Sr from Lake Michigan by outflow and incorporation loss of into sediments to be near 2%. Klein (Kle75) also estimates a small loss for Sr due to sedimentation. In this analysis, it 89 90 is assumed for both Sr and Sr that the annual loss from Lake Michigan is that due to radioactive decay plus a 2% loss due to outflow and incorporation into sediments. The. physical ~
removal rate for Cs appears to be much higher. Wahlgren et al.(Wah74, Wah75a, Wah75b) estimate the effective half-life of Cs in Lake Michigan to be on the order of 3 to 4 years and suggest that it may be shorter (i.e., 1 year). Similar estimates are also given by Klein (Kle75) and Lerman and Taniguchi (Ler72b). In a study of Lake Huron, Barry (Bar73) estimated an effective half-life of .97 years for Cs. For this study, an effective half-life of 3.5 years is assumed for 137 Cs in Lake Michigan. For Cs, it is assumed that loss from Lake Michigan is due to radioactive decay plus a physical removal with the same effective half-life of 3.5 years that was 13 The resulting effective half-lives for assumed for Cs.
the four radionuclides under consideration are summarized in Table 6.
O n i L f l
For the following, it is assumed that Lake Michigan can be l
' treated.as a single uniformly-mixed cell with the already indi- l 137 cated effective half-lives for "Sr 90Sr. 134Cs and Cs.
- f. Thus, with the assumption that the lake has a volume of 4.87E15 I
I' 1 (Nie81. Table B4). it follows that the resultant concentration c(t)-(units: Ci/1) in the. lake at a time t after an initial release of size x n is c(t) =x 0 e
~
/4.87E15. (4.2) f' where K = LN(2.)/HL and HL is the effective half-life of the l l f particular radionuclide under consideration. In turn, the L integrated concentration (units: ci yr/1) is given by j l_
l I{.c(t)dtandcanbeusedinthecalculationoftotalhealth .
I effects. For an SST1 accident with complete deposition on Lake Michigan, the resultant concentration integrals are given in Table 6. The initial releases (i.e., the x ) *** NY'" "
0 l
Table 4.
l The integrated concentrations can be used in conjunction with (3.6), (3.7) and (3.8) to predict the consequences of an SST1 accident with complete deposition of the released radio- activity j l
onto Lake Michigan. This event might occur if the contents of the plume were washed out over the lake by a rainstorm. In such a calculation, the integrated concentration is used instead of j the ratio W/D. (Note: For the units to come out correctly in this computation, the water consumption represented by WC should !
be treated as a rate with the units of 1/yr.) The results of this calculation are given in Table 6. Except as indicated in O
the following, the parameterivalues used in the generation of Table 6 are the same as those used in the generation of Table 5.
For (3.6), NT = 1. is conservati.ely assumed for all Fo r ( 3 . */ ) ,
radionuclides and POP = 1.1E7 id (Nie81 Tdble E3).
FP = 5.lE6 kg/yr (Nie81, Table d16). For (3.8), IR = 6.8E9 L, which is obtained from a withdrawal of 7.E9 L/yr from Lake Michigan for irrigation (Nie81, Table E45) and an application of 97% of this withdrawal by sprinkler irrigation (Nie81, Table E42).' It is conservatively assumed that all sprinkler-irrigated foodstuffs are used for human consumption (Nie81 Table E42).
The results presented in Table 6 are for Lake Michigan 90 Sr. the possibility exists for signifi-only. For at least cant population exposures in the lower Great Lakes. However, inclusion of these lower lakes would probably not increase the 90 Sr by much more than a factor of 2.
results in Table 6 for This conclusion was arrived at by using the integrated concen-trations for the lower lakes following a release to Lake Michigan (Nie81, Table B17) and appropriate usage parameters for these lakes (Nie81, Tables E3, E16 and E45). For Cs, i
Lake Michigan is almost a closed system (Wah75b) and so expo-I sure in the lower lakes following a release to Lake Michigan
[
l would be small relative to the exposure in Lake Michigan itself. Due to their short half-lives. Lake Michigan is in 89 13 effect a closed system for Sr and Cs.
The effects of washoff into Lake Michigan are now consi-dered. If the data for the north central United States in Menzel's study (Me74. Table 2) are used as a guide, then 2.02%
O 89 Sr and 90 Sr is removed, and there-V of recently. deposited after. .63% per year is removed. As indicated in (3.3), this results in an eventual removal to Lake Michigan of 2.1% of the 89 Sr and 21.9% of the deposiced 90 Sr. As before, the deposited removal rates for Cs and Cs are assumed to be the same as 90 This results in an eventual removal of 2.5% of those for Sr.
34 Cs and 23.1%'of the deposited 13 Cs. Due to the deposited the linearity of the underlying models, the results of such washoff for an SSTl accident can be obtained by multiplying the health 90 37 Cs in Table 6 by .021, effects for 'Et, Sr. *Cs and
.219, .025 and .231, respectively. The results of this calculation are presented in Table 7. The watershed for Lake Michigan is only twice the area of the lake; thus, a release encirely to the lake or entirely to the watershed may be unlikely. However, the values in Tables 6 and 7 provide an indication of the potential magnitude of the effects.
Rhine-Meuse Valley. As a final example, radionuclide washoff in the Rhine-Meuse valley is considered. As in the two previous examples, an SSTl accident is modeled (i.e., an FK1 accident in the terminology of the German Reactor Safety Study).
Data describing the release are taken from the German Reactor Safety Study (Bu?9, Tables F8, 3-1 and F8, 3-2) and are presented in Table 8. The washoff rates are taken from the extensive study by Jacobi et al. (Ja69a) for fallout B-emitters in Germany.
90 Cs, it is Although the results are not specific for Sr and indicated that the individual washoff rates for these nuclides are
) probably similar to those obtained for B-emitters collectively
t l
(Ja71, p. 1154). The particular washoff rates selected are those for the Rhine watershed above Wesel-Wittlaer/Beckum (Ja69a, Table j 3). Thus,'
K, = 1.05E-2 and Kb = 0.63E-2 yr- . (4.3)_
These values are used for both Sr and Cs: this probably overestimates the washoff rate for Cs. The resulting washoff fractions can be obtained with use of (3.3) and are presented
^
in Table 9.
The calculated health effects for this case are presented in Table 9. The'same calculational procedures are used as for the Mississippi river. The value for D is taken to be 8.5E13 1/yr (Bay 78, p. 80). Further, for the other values in (3.6) for water consumption WT = 1. for Sr and WT = .1 for Cs (A) T-20), WC = 440 L/ind-yr (Bay 82a p. (A) T-30),
(Bay 82a, p.
and' POP = 1.3E7 ind/yr (Bay 82a, p. T-3). For fish consumption, I
the concentration ratios are the same as used earlier, and FP =
7.8E5 kg/yr from an assumed catch of 2.5E6 kg/yr (Bay 82a,
- p. T-14).and an edible fraction of .31. For exposure from
_ sprinkler irrigation, it is possible to derive a value for IR L
from assumptions in Bayer (Bay 82a). It is assumed that (1) 1.E6 i
individuals are supplied with foodstuffs grown on irrigated-land (Bay 82a, p.-32), (2) a population of 60.4E6 individuals is sup-ported on an area of 2.2E5 km (Bay 82a, p. Tl), (3) 20% of all land is_used to grow foed for direct human consumption (Bay 82a, p. Til), and (4) an irrigation rate of .1 m/yr is used
! .(Bay 82a, p. 32). From the preceding, it follows that IR =
-7.4E10 1/yr.
l- . . - ~ __. _ . . _ , . _ _ . _ . _ , _ _ _ _ _ _ _ , , , _
. . . - _ . . . . - ... . -. - . - . .. . =. . _ - - - - -.
- 5. Discussion. The purpose of this paper is to provide perspective with respect to the potential importance of-radio-nuclide washoff from land surfaces into surface-water bodies as a contributor to the risk associated with' reactor accidents.
The preceding section presents estimates of consequences associated with such washoff for three sites: two in the
. United States and one in central Europe. To interpret the significance of these consequences as contributors to risk, it ,
4 is necessary to compare them with the consequences assoca-red with other aspects of reactor accidents. For the two sites in the United States, it is informative to use the con- . .1ces
- calculated in a recent study of reactor accidents in the United
- States which was performed to assist in the development of
() reactor siting criteria (A182b).
informative to use consequences calculated in the German For the German site, it is 4
, Reactor Safety Study (Bu?9, Bay 81, Bay 82b).
i The siting criteria study (A182b) considered four reactor sites in the middle and lower Mississippi valley-and five reactor. sites at Lake Michigan. The study analyzed the conse-l-
i quences associated with accidents involving a standard 1120 MWe i
reactor at each sitc; the results of this analysis are summa-l- rized in Appendix C of the study's documentation (A182b). For the four sites in the middle and lower Mississippi valley, the number of latent cancer fatalities associated with an SST1 accident ranged from a few tens to a few thousands. The mean number of such fatalities ranged from 700 to 950. For the five
() sites at Lake Michigan, the number of latent cancer fatalities I
( ,
- . ....,......w..--...,.,--,-...,,,...,~,.m..-.,,#.w,--evv%+4y,,-,,,,,m,--%,,wm,,,-~meww,_y, we, - , - - - ,
~ \> associated with an SST1 accident ranged from a few tens to a few ten thousands. The mean number of such fatalities ranged from 1400 to 4000.
Tables 5 and 7 present predicted consequences associated with radionuclide washoff into surface-water bodies after SSTl accidents in the two regions in the United States. These acci-dents have the same assumed radionuclide releases as the SST1 accidents considered in the Siti g Study (A182b). As comparison with the results indicated in the preceding paragraph shows, the consequences are much smaller than predicted mean consequences associated with atmospheric and terrestrial exposure pathways after reactor accidents. Indeed, it is only when the entire release-of the radionuclides under consideration is assumed to go into the receiving surface-water body that the predicted consequences from aquatic pathways start to exceed the smaller of the consequences associated with the atmospheric and terrestrial pathways (see distribution of latent cancer fatalities in Appendix C of (A182b)). Such results for a com-plete deposition on Lake Michigan are given in Table 6. Fur-ther, due to the linearity of relations used, the results in
' Table 5 can be scaled to provide an estimate of the effects associated with the entire release of the radionuclides under consideration going into the river. The calculations performed for the present study are conservative in the sense that no mitigating actions are assumed to be taken to reduce the effects l of any radionuclides which may enter a surface-water body. In contrast, various interdiction and decontamination procedures 1
i
f'"-
.k ,)y are assumed in the generation of the results presented in the Siting Study (A182b).
For the 25 reactors considered in the German Reactor Safety-Study, the mean, minimum and maximum numbers of. predicted latent cancer fatalities subsequent to an SSTl accident are 43,100 lef, 160 lcf and 107,800 1cf.respectively (Bu?9, Table F8,8-6). In
'the American Reactor Safety Study (US75), the previously refer-enced siting. study (A182b) and the calculations performed in this paper, a dose effectiveness factor of .2 is assumed in the calculation of cancer induction due to low levels of radiation exposure for all cancers except breast cancer. Such a factor 4
was not used in the German Reactor Safety Study. Thus, for comparison with the number of predicted latent cancer fatalities from the German Reactor Safety Study, it may be best to use five times the estimates presented in Table 9. However, even then the estimates derived from Table 9 are in the lower range of the consequences predicted in the German Reactor Safety Study
~
(- for exposure from atmospheric and terrestrial pathways and are far below the mean estimate of 43,100 latent cancer fatalities.
Indeed, this is even the case if the entire release of the four radionuclides considered is assumed to go into the river. As with the American sites, no mitigating actions are assumed to be taken to reduce the effects of the radionuclide releases to the. Rhine. Also, the calculated results in Table.9 may be high
~
due to conservative assumptions with respect to the size of the exposed population, the individual water consumption rate, and
! () the washoff rate for Cs.
Although the authors' recognize that radiation exposure and resultant cancer induction after a reactor accident are highly sensitive to both site and release characteristics, it is felt that the contamination of surface-water bodies after reactor accidents by the erosion of atmospherically deposited radionu-clides is not a major contributor to the risk associated with such accidents. This conclusion is drawn because of the use of conservative modeling techniques to determine the effects of the erosion of radianuclides into surface-water bodies and the small size of such effects in comparison with the effects predicted for atmospheric and terrestrial pathways. Although this study and the studies to which it is compared contain large uncer-tainties, it is felt that inclusion of these uncertainties
_m
, ) probably would not change the conclusion which has beer reached.
Further, this conclusion is consistent with the results of l various other analyses of widespread radioactive depositions l
(e.g., Gu69, Har69, Ja69b, Aa71. Ng73, Da81, Klu81, Gj82. US82).
In each of the preceding analyses, various ingestion pathways were considered after a radionuclide release (primarily fallout from weapons tests); the water-related pathways were consis-tently found to be among the smallest contributors to exposure.
- 1. For_the water-exposure pathway after a reactor accident to be important, an extensive entry directly into a public water supply would be necessary (e.g., Nic81). However, this seems unlikely and would generally be amenable to interdiction.
I
(T V
2 i
i ..
1 Acknowledgement: 'The authors wish to thank D..C. Aldrich, D. J. Alpert and R. M. Ostmeyer of Sandia National Laboratories for many useful discussions and suggestions l.
during the development of this paper.
J J .
f i
4' i
1 O
l O
i
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l l
l f
l
__.______,-__._._______.,__a...._____..-.____..
. i
,m bh,lidas Ditar=in d en C Regitn21 B.010. (v Tcb13 1. Removal R:tos for F=11 cut RIdi Locatien. Commest Reference Nuclide 100 l a 1E.0 Ab Continental United States Three month period Straub et al. 90S r 1.7*- Nine month perion i
6-emitters 1.6 Continental United States. Three month period (St60) 3.9-12.2 Pive watersheds in Ohio 90S r Valley ,
l
- The values for la may'be overestimated as A a is defined by A =R/D, a where R and D areNothecredit removal in is taken for
- surf ace water and total deposition, respectively, for each time period considered.
l removal of accumulated fallout.
10 watersheds in Japan Mean value for 90S r Miyake and 90S r .7-3.3 is 1.5. Value for i Tsubota (M163) 137Cs 1.7 137C s is estimateo as that due ts direct .
deposition on water bodies. .;
1 month period for Aa
.31 Japan Yamagata et al. 90f r 7.2
.06 (Ya63) 13'Cs 1.3 4
Twenty watersheds in 1 month period for Aa*
Jacobi et al. 8-emitters .20-1.05 .12 .97 West Germany Extensive study.
l (Ja69a) .
l .036 Tropical rain forest, Derives Ab for stable i, Jordan et al. 90S r -Puerto Rico St and uses to predict l
(Jo73, Jo76) behavior of 90Sr.
90S r .2-2.* Three watersheds in Kanada et al. Japan (Ka73)
- The values for Ab may be overestimated as Ab is defined by Ab=R/D, where R and D are the annual radionuclide removal to surface water and total accumulated deposition, respectively.
l i
i l
i i
k i
A '
- Euld)-
W T;ble 1.
ig,Q Ab (Gj Locrti*n
~
Comme *t
{
k/
\
Reference ,Nuclide @Ag Miyake et al. 239Pu .12 Japan (M173) .
90S r .2-2. Four watersheds-Kanada et al. in Japan (Ka74) ,
Eight regions in Two month period Menzel 90S r .59-2.17 .17 .75 for Aa. Extensive United States (Me74) investigation.
Simpson et al. 137Cs .1 Hudson River Watershed (S176)
Small watershed Carlsson 137Cs 1.9 .56 in Sweden (Ca78) 239,24 cpu .05 Ohio Sprugel and Bartelt (Sp?8)
Denmark Extensive Aarkrog 90S r .5 .1 investigation.
(Aa79)
- 1. Upland lake water 90S r model for Linsley et al. 90S r 10.
supplies, England upland lake-water slightly (L182) different from (2.1).
.067 River Thames, England 90S r 1.
.0067 River Thames, England 137Cs .1
(h T blo 2.
( ).
R;movs1 cctos far Falltu(Ladianuclidas Detsreined From. Emperimentti Plat 3.. {'/ ;
Location Comment Reference Nuclide 100 Aa ISE Ab La Crosse, W1. Various experimental plots.
Menzel 90S r and Tifton, Ga. Removal measured for each (Ne60) rainfall event. Considerable variability in amount of 90S r removed in runoft after raintall event.
Amount removed over 25% in one case.
Coshocton, Oh. One-third to two-thirds of Frere and 90S r 90S r deposited by fallout Roberts up to 1960 lost from culti-(Fre63) vated experimental plots.
McCredle, Mo. Three month periods, variety Graham SSS r .009 .98 of experimental plots.
(Gr63)
Oak Ridge, Tn.
Three month periods bare, Rogowski and 137C s 2.6-11.9 clipped meadow and tall Tamura (Ro65) meadow plots.
Wooster, Oh. Five experimental plots.
90S r .23-1.02 Results based on five year Naghire (Hag 69) period for loss by runoff water and runof f sediment.
Oak Ridge, Tn. Bare plot.
137Cs 30.7* 12.3 Clipped meadow plot.
Rogowski and .57 Oak Ridge, Tn.
Tamura (Ro70s, 137C s 18.9 Oak Ridge, Tn.
Tall meadow plot.
137Cs 6.7 .11 Ro70b)
- A a and Ab determined from first and second year, respectively, of two year experiment.
.16 Experimental plots.
Pisarev et al. 90S r .62 (Pis72)
d
+
i i
h t
e i
Table 3. Half-lives and Risk Factors for Selected Radionuclides.
134Cs 137Cs 89S r 90Sr Half-life 2.05 30.2 0.14 28.1 (units: yr) 3.3 2.5 0.30 2.8
- i. Risk Factor .
! (units: Icf/Ci)
I i
l-I l.
. . . _ . .:_.c-._ _._ ..-__ _._ _ __ _ _ _ _ _ _ _ _ _ . _ _ _ . . . _ _ _ _ _ . _ _ _ _ . . , _ _ _ . . . _ _ _ . _
4 4
i 4-Table 4. Radionuclide Release Used in Siting Criteria Development for an SSTl Accident.
Nuclide Initiala Released Inigigi Inventory Fraction Release ,
89S r 9.6E7CCi ~ 0.07 6.7E6 Ci 90S r 5.2E6 Ci 0.07 3.6ES Ci
' O 134Cs 1.3E7 Ci O.67 8.7E6 Ci 137Cs 6.5E6 Ci 3.67 4.4E6 Ci aFrom Table B.1-1 (A182b) bFrom Table 2.3.1-2 (A182b) c9.6E7 = 9.6xlO7 l
l l
O .
f
~ - - - . . . . . . ~ . , _ _ _ _ . , . , _ _ _ . _ _ _ , . _ _
Table 5. -Calculated Latent Cancer Fatalities for i an SST1 Accident Due to Radionuclide Washoff into the Middle and Lower Mississippi River.
4
' Nuclide Washoff Drinking -Fish- Sprinkler.
Fraction Water Irriaation i . 89S r .02 .06 Icf <.01 1cf <.01 lcf.
90S r . 19 .3 lef .02 1cf <.01 1cf 134Cs . 03 .9 1cf 6.4 1cf .01 1cf 137Cs . 20 2.2 1cf 15.0 lcf .03 1cf
- O i'
i ,
i 1
- O
'S-e-,.,+,r----
,, ~ , . ,--ree....,,,w,.-,. ,.,-+ww.w-%---.,.w.ww,,,*,,..'e,...wem.,-e,..wme,we,w...-,.-reww,. ,ww e _ ..m v g w-
D Table 6. Calculated Latent Cancers for an SSTl Accident due to Complete Deposition on Lake Michigan.
Integrated Drinking Fish Sprinkler Nuclide Effective Concentration Water -Irrication Half-life 2.8E-10 Ci yr/1 .34 1cf .01 1cf: .01 Icf-89S r- .14 yr Icf .69 Icf .34 Icf 90S r - 15.4 yr 1.6E-9 Ci yr/1 18.2 Ci yr/l 45.7- Icf 114.4 Icf .86 Icf 134Cs 1.3 yr 3.4E-9 Ci yr/l 45.8 lcf 114.7 Icf .87 1cf 137Cs 3.5 yr 4.5E-9 t
l t
O .
t t
.. __. . _ = . . . . -. -
3.
O .
Table 7. Calculated Latent Cancer Fatalities for
'an SSTl Accident due to Radionuclide Washoff into Lake Michigan.
Nuclide Drinking Fish Sprinkler Water Irrication a 89S r <.01 1cf <.01 Icf <.01 Icf 90St- 4 .' O Icf .15 lcf .07-lef -
1 134Cs 1.1 lcf 2.9 lcf .02 lcf I 137Cs 10.6 Icf 26.5 1cf .20 1cf i
1 O
1 O
O t
1 L
'- Table 8. Radionuclide Release Used in German Reactor Safety Study for an SST1 Accident.
Nuclide Initiala Released Initial.
O Inventory Fraction
.067 Release 7.0E6 Ci 89S r 1.05E8 Ci 5.30E6 Ci .067 3.6E5 Ci 90S r 1.38E7 Ci .5 6.3E6 Ci 134Cs 7.06E6 Ci .5 3.5E6 Ci 137Cs aFrom Table F8. 3-1 (Bu?9) bFrom Table F8, 3-2 (Bu?9)
I O ,
I l
_- .. . . . . . - . _ . .- . ~ . . . . , . . - . . . - . . _ _ . . - . - .
t i
O i
i i i
?
t i.
I c
i.
~
Table 9. Calculated Latent Cancer Fatalities for an SST1 Accident Due to Radionuclide.
Washoff into the Rhine River, a.
l' Nuclide Washoff Drinking Fish Sprinkler
! Irrication Fraction Water
- 89S r .012 1.7 1cf <.01-Icf .24 lcf 90S r .212 14.3 1cf .06 Icf 2.0 lef l
l 134Cs .029 22.2 1cf 12.1 lef 6.3 1cf r
137Cs .223 65.6 lef 35.8 lef 18.6 Icf 4
I l
1
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t-i j
4 '
i e
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