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Fallout and radiation doses in Norway after the Chernobyl accident
Environment International, Vol. 14, pp. 157-163, 1988 Printed in the USA. All rights reserved.
0160-4120/88 $3.00 + .00 Copyright © 1988 Pergamon Press plc
FALLOUT AND RADIATION DOSES IN NORWAY AFTER THE CHERNOBYL ACCIDENT Thormod Henriksen Institute of Physics, University of Oslo, N-0316 Oslo 3, Norway
Gunnar Saxeb¢l National Institute of Radiation Hygiene, 1345 Osterhs, Norway (Received 18 August 1987; Accepted I0 May 1988) Due to southeasterly wind and rainfall during the critical days after the Chernobyl accident, Norway received a substantial part of the cesium isotopes released. The radioactive fallout closely followed the rainfall and was mainly concentrated to some thinly populated areas in the central parts of the country. The total fallout of the cesium isotopes was approximately 2300 TBq (137Cs) and 1200 TBq (la4Cs). The average for the country was 11 kBq/m 2 with a variation from 1.5 to 40 kBq/m z for the 19 different counties of the country. The fallout resulted in contamination of food products from some areas, mainly meat from reindeer and sheep, as well as "wild" freshwater fish. A small fraction of the food production in 1986 was not sold due to the regulations enforced. The average radiation dose to Norwegians during the first year after the accident was approximately 0.3 mSv (0.1 mSv from external radiation and about 0.2 mSv from the foodstuffs). This first year extra dose is approximately 5% of the average normal background dose in Norway (estimated to about 6 mSv/year, including medical and industrial use of radiation sources).
Introduction
easterly wind (which brought the contaminated air masses in northwesterly direction towards Scandinavia) and rainfall concentrated to the 28 and the 29 of April (in certain areas we received from 2 to more than 10 mm of rain) N o r w a y received a substantial fallout from the accident. The fallout closely followed the rainfall and was therefore inhomogenously distributed throughout the country.
The Chernobyl accident demonstrated that nuclear accidents also affect countries with no nuclear p o w e r plants. The easy access to hydroelectric p o w e r in N o r w a y implies no immediate need for nuclear power reactors and as a consequence of this no detailed national plans or organization dealing with large scale nuclear accidents exist. The control and certification of radiation sources, including x-ray equipment and radioactive isotopes used for medical and industrial purposes, are c a r d e d out by The National Institute of Radiation Hygiene. After the Chernobyl accident this institution measured and analyzed the fallout situation. The Institute made the first registrations of increased background activity on April the 28th. The following day the highest 131I activity was observed at 10 a.m. A few hours later a project group, called K I E V , was organized with the purpose to collect fallout information, to organize a measuring strategy, and to make dose calculations and estimates. All available personnel and instruments at the Institute were engaged for several weeks to deal with the situation. Due to the particular weather conditions with south-
Radioisotopes in the Air In the first period the activity measurements in the air were given the highest priority. Radioisotopes in the air were measured at six different places (Halden, Oslo, Kjeller, Bergen, Trondheim and Troms¢). Two bursts of activity were recorded with the main part during the last three days of April. An example o f the measurements, as obtained by The National Institute of Radiation Hygiene in Ba~rum (near Oslo) is given in Fig. 1. The highest aerosol c o m p o n e n t iodine activity was measured to 6.3 Bq/m 3 (between 8:20 and 9:47 a.m. on the 29th of April). The measurements were performed on a filter system. A few comparative measurements 157
158
T. Henriksen and G. Saxeb¢l
10000
Table 1. Radioisotopes in air after the Chernobyl accident.
1000 100 tO
E
10
O" m
1,0
\
E
°:'J'2 6
I 30
I 5
I 10
APRIL
I is
I 2o
I 25
!
30
MAY
~0000 1000 -
\
E 17"
f13
ppM
asZr ~Mo l°3Ru l°6Ru L3ZTe 1311 133I 134Cs 136Cs 137Cs 14°Ba 141Ce 144Ce 23aNp
0.49 0.03 0.60 4.00 l 1.30 93.00 0.43 5.30 0.33 6.70 0.21 0.25 5.80 0.33
0.4 0.02 0.5 3.1 8.8 72.2 0.3 4.1 0.3 5.2 0.2 0.2 4.5 0.3
128.77
100.1
All
100
tO
The measurements are made in Baerum, close to Oslo. The activities are given as integrated activites during the first two weeks after the accident and expressed as parts per million (ppM) relative to the ICRP threshold value for workers. The third column yield the relative contribution to the inhaled dose.
10 1,0 0,1 26 3 0 APRIL
5
10
15 20 MAY
25
30
Fig. 1. Level of 13~Csand 131Iactivities in the air at Oslo (given in milliBq/m3) the first month after the ChernobYl accident. The measurements are carried out by The National Institute of Radiation Hygiene.
o n a n a c t i v e coal filter i n d i c a t e d that the a e r o s o l c o m p o n e n t o f the i o d i n e a c t i v i t y w a s o f the o r d e r 10% to 20% o f the total i o d i n e a c t i v i t y . T h u s , the total i o d i n e a c t i v i t y f r o m b o t h a e r o s o l a n d gas c o m p o n e n t s might h a v e b e e n in the r a n g e 30 to 60 B q / m 3. D u r i n g the first p e r i o d the K I E V g r o u p m a d e freq u e n t e s t i m a t e s o f the d o s e to the t h y r o i d a n d disc u s s e d w h e t h e r r e c o m m e n d a t i o n s s h o u l d b e g i v e n to k e e p c h i l d r e n i n d o o r s . D u e to the d r o p in a c t i v i t y after the first few d a y s , n o s u c h r e c o m m e n d a t i o n s w e r e given. I n T a b l e 1 p r e s e n t e d are the 14 m o s t i m p o r t a n t
r a d i o i s o t o p e s w h i c h w e r e o b s e r v e d in the air after the C h e r n o b y l a c c i d e n t a n d w h i c h c o n t r i b u t e d to the inhal a t i o n d o s e (Berteig, 1986, R u d j o r d a n d U g l e t v e i t , in press). B a s e d o n I C R P 30 (1979-1982) a n d N R P B - R 1 6 2 (1985) p u b l i c a t i o n s for the r e l a t i o n s h i p b e t w e e n inh a l e d a c t i v i t y a n d effective d o s e e q u i v a l e n t the individual and collective dose equivalents were calculated a n d p r e s e n t e d in T a b l e 2. T h e p o p u l a t i o n is d i v i d e d in t h r e e age g r o u p s ; a d u l t s , 4-15 y e a r s old, a n d 0 - 3 y e a r s old. ~31I is the m o s t i m p o r t a n t i s o t o p e w h i c h g i v e s app r o x i m a t e l y 70% o f the i n h a l a t i o n dose. T h e total col-
Table 2. Individual and collective doses from inhalation of airborne isotopes in Norway after the Chernobyl accident.
Number of Persons
Adults 4-15 years 0-3 years
3.2 million 0.6 million 0.2 million
All
4.0 million
Dose Equivalent Per Person 6.5 microSv 16.0 microSv 59.0 microSv
Dose Equivalent For The Group 21 manSv 10 manSv 12 manSv 43 manSv
1: 132Te 2:131 I 3:140 La 4:130 RU 5:134 Cs 6:137 Cs 7:132 I
80O
(/1 I.Z
Group
Relative Dose (Percent)
Isotope
0
6O0
4
400
o 200
o
3
5 6
5
........
~o ~o ~'oo ENERGY (keV)
!
~oo
Fig. 2. The gamma-spectrum obtained from a grass sample collected outside the University building in Oslo on May 9, 1986. The observation is made with a Ge-counter at The Institute of Physics, University of Oslo.
Radiation doses in Norway
159
2.
.
J
~."~.j~ .c ~
kBq/m2 O~15-
~
~50i
5 30
30 -
50 IO0
~-100
Fig. 3. The fallout of the two cesium isotopes as determined by the end of October, 1986 (National Institute of Radiation Hygiene).
lective dose equivalent due to inhalation was o f the order 50 m a n S v . The individual dose equivalent was f r o m 0.005 to 0.1 millisievert.
Ground Deposition A n u m b e r of different radioactive isotopes were recorded during the first d a y s after the accident. In Fig. 2 is p r e s e n t e d an example showing the g a m m a - s p e c t r u m obtained f r o m grass outside the University buildings in Oslo (May 9th). It was recognized early that the fallout contained v e r y little 9°St. Analysis of the strontium activity f r o m air filters, lichen, cheese and milk have s h o w n the p r e s e n c e of both soSr and 9°Sr. The activity of 9°Sr
c o m p a r e d to '37Cs was less than 2% in m o s t samples. In milk samples the 9°Sr content was s o m e w h a t larger of the o r d e r 4% to 7% of the '37Cs activity (T. Berthelsen and B. Lind; private communications). In order to get information about the fallout pattern the K I E V group organized a collection of samples of snow, soil, and rainwater. The first samples were taken f r o m places located a p p r o x i m a t e l y 100-200 km apart in the north-south direction throughout the country. The results showed large differences. It was evident that an area in the central part of N o r w a y had 5 to 10 times m o r e ground deposition than the Oslo area. The next step was to organize a large scale soil sampling with the p u r p o s e to attain information a b o u t the total, as well as the distribution of the cesium fallout
160
T. Henriksen and G. Saxeb01
Table 3. Radioactive fallout in Norway from the Chernobyl accident, a
Isotope 134Cs ~3rCs l°~Ru lzsSb 144Ce
Half-life
Activity kBq/m 2
Total Fallout in Tbq
2.06 year 30.1 year 369 days 2.77 year 284 days
3.7 7.1 3.2 0.4 1.1
1200 2300 1000 100 400
250-350 ~1150-250 [~ 50-I 50 < 50 . ~
nGy/h nGY/h nGY/h nGy/h
NOT MEASURED
~In addition to the 137Cs from the Chernobyl accident we still have approximately 100--200 TBq from the nuclear tests in the 1960-ties. The specific activity given as kBq/m z in the table is the average one for Norway whereas the data in Fig. 3 yield the variations throughout the country.
after the reactor accident. Details o f the sampling procedure, isotope identification, etc. are published by Backe et al. (1987). The results of the soil sampling program showed that the fallout of 1arCs and la4Cs was 2300 + 200 and 1200 _+ 100 TBq, respectively. This implies that approximately 6% of the reported total cesium activity released within the borders of E u r o p e a n USSR in the accident was deposited in N o r w a y which, to the present authors, seems unreasonably high (IAEA, 1986). The mean total deposit for the country was 11.3 kBq/m 2. The distribution o f the cesium fallout is given in Fig. 3. The cesium activity in the 19 different counties varied from 1.5 to 41.5 kBq/m 2. The fallout pattern is closely connected to the rain in the same period and localized mainly to the counties of central N o r w a y (Oppland, Tr0ndelag and Nordland). The total fallout o f the most important 3/- and r-emitting isotopes with half-life of more than 200 days is given in Table 3. The fallout resulted in a slight increased level of radiation inside the houses in some areas of Norway• This was casually measured by Strand and Stranden (1987) due to a research project with the purpose to find a correlation between the normal background radiation and the incidence of cancer. Dosimeters were distributed to 900 houses in the central part of N o r w a y approximately a week before the Chernobyl accident. The dosimeters recorded the average dose rate (given as nGy per hour) the first four weeks after the reactor accident. The results are given in Fig. 4. As can be seen, the extra dose from external radioactivity was in the most decontaminated areas approximately 0.2 mGy the first month (300 nGy per hour in 30 days)• It has been estimated that the average first year dose to the Norwegian public due to external radiation from the fallout products was approximately 0.1 mSv. The observations mentioned above seem to support this estimate. The dose in certain areas may have reached a value approximately 10 times the average•
,- ..-.:; :,
:):.._ .:.::: .2:""" ...':.'........( -?, •
.
- •
•
.
•
.
•
•
.
. %
.
1(; "::"
if?
~'..).......:.
(I \
Fig. 4. The radiation level, as measured in nanoGy pr hour, inside Norwegian homes during the first four weeks after the Chernobyl accident. The values given are due to the fallout only, since the normal background level in the different districts have been deducted. The map, which is based on measurements in 900 homes, is made by Strand and Stranden (1987).
Cesium Activity in the Food Products
In mountain areas of Norway there is reindeer moss (Cladonia rangiferina) which is a gray much-branched lichen (somewhat like a sponge) which is the main food resource in the winter season for the reindeer. The lichen is very efficient in absorbing all kinds of airborne particles including radioactive isotopes from the nuclear bomb tests 25 years ago as well as the fallout from the Chernobyl accident. The reindeer moss in N o r w a y has been contaminated since the nuclear tests
Radiation doses in Norway
161
_I • •
I
_
I
• • • •
I
.=..,,,~~1 _
REI N DEER ' vvv,.
~.0 3
:A &
&
°°°
A
°
•
,
°
•
o
-m •
CY
m
•
• •
MAN
• •
•
a
• i
WO MAN ]
1965
I 970
I 1975
I 980
A
&
&
m
m m
A
I-
I
1985
YEAR Fig. 5. Specific activity of laTCs in reindeer meat from Kautokeino in Finnmark in the period 1965 to 1986. The activity in the Lapplanders which eat these reindeer have been measured with a whole-body counter and the results (average of about 15 persons in each group) are given as Bq/kg. We assume that cesium is evenly distributed throughout the body. The activity is higher in men, probably due to the fact that they have a higher muscle/total body ratio than the women. The figure is based on measurements carried out by Westerlund et al. (1987).
in the 1960-ties. Just before the Chernobyl accident the specific activity of 137Cs was down to about 300 to 400 Bq/kg in the important areas for reindeer production in northern N o r w a y (Finnmark and Troms). After the accident the reindeer moss in the central parts of the country was contaminated, reaching values for '34Cs and 13rCs o f from 4 to 30 kBq/kg. More than 100 kBq/kg was observed in several samples and the maximum was found to be 190 kBq/kg. For the areas o f Finnmark and T r o m s the cesium activity in the reindeer moss increased slightly to 600 to 1500 Bq/kg. The content of radioactive cesium in the grass during the summer of 1986 was found to be approximately a factor 10 lower than that found for the reindeer moss in the same area. All food products from the contaminated areas contain some activity due to the fallout. A large n u m b e r of different products have been studied after the Chernobyl accident (all together more than 30,000 samples from all districts have been measured). The content is generally low (less than 100 Bq/kg), and in the following we shall concentrate on problems which are of particular importance for Norway. The most contaminated food product is reindeer meat in the central part of N o r w a y (including most of the districts south of Rana). Approximately 15% of the production o f reindeer meat originates from these dis-
tricts. Values for individual animals in the 1986 season reached 40 kBq/kg with an average of about 4 to 5 kBq/kg. No increase in the specific activity was found for the animals from northern N o r w a y during the fall season 1986. Also, meat from sheep, fed on grass from the fallout areas, contained radioactive cesium. The specific activity however, was much lower than that for the reindeer, but in several districts activities of the order 2 to 6 kBq/kg were found (a maximum value o f 18 kBq/kg was observed). In June 1986 the health authorities introduced restrictions with regard to the sale of food products contaminated with the cesium isotopes. The limit was 370 Bq/kg for milk and childrens products and 600 Bq/kg for other products. In an early period it was also reco m m e n d e d not to drink rainwater from cisterns (used for a number o f summer houses). The result of these restrictions was that all reindeer meat in central N o r w a y (south of Rana) could not be sold. Since the ecologic halftime of cesium in reindeer (feeding on contaminated reindeer moss) is approximately five years (see below) it was reasonable to assume that these restrictions would have abolished the sale of reindeer meat for 15 to 20 years. Consequently, the restrictions with a limit of only 600 Bq/kg, which from a health physics point o f view is meaningless and
162
T. Henriksen and G. Saxeb~l
U) E
4
Radon 4 --i
Z m
UJ U') 0
¢2
3
,.I
,<
Z
.<
0
m
-Q lad :E
uJ ~X uJ
nI,Ll I-Z
~;
Z
(/) 0
uJ
0,6 ~--~
0~ m
~ 0,37
O,
0.3
Fig. 6. The annual effective dose equivalent to the average Norwegian (in mSv). The main radiation problem appears to be the large radon dose. The first year dose from the Chernobyl accident is included.
also in conflict with I C R P optimalization principle, could have d e s t r o y e d the living for a n u m b e r of people (the so called South-Lapplanders). In N o v e m b e r 1986 the working limit for cesium in reindeer meat was increased to 6000 Bq/kg. A p p r o x i m a t e l y 30% o f the sheep production in 1986 exhibited a cesium content a b o v e the limit of 600 Bq/kg. A b o u t 3%, which showed a content a b o v e 2000 Bq/kg, was destroyed directly. F o r the 27% with a specific activity in the range 600 to 2000 Bq/kg feeding e x p e r i m e n t s with n o n c o n t a m i n a t e d food were started. Since the biological halftime for cesium in sheep is of the order three weeks it was possible within a few w e e k s to reduce the activity to the set level of 600 Bq/kg. The specific activity in " w i l d " freshwater fish in the c o n t a m i n a t e d areas were high with a m a x i m u m of 55 kBq/kg. Other food products like fruits, vegetables, potatoes, etc. contained only negligible activity.
Doses to the Public Based on an average diet in N o r w a y c o m b i n e d with the specific activity in the different food products Strand et al. (in press) calculated that the average Norwegian, during the first year after the accident, received a p p r o x i m a t e l y 11,000 Bq of the cesium isotopes through the food products. This c o r r e s p o n d s to a radiation dose of less than 0.2 mSv. T o g e t h e r with an external dose of 0.1 m S v the total extra dose during the first y e a r after the Chernobyl accident is of the order 0.3 m S v or smaller. Certain groups which use reindeer m e a t and " w i l d " f r e s h w a t e r fish f r o m the contaminated areas have re-
ceived an extra dose m u c h larger than the average value.
Estimation of Total Doses From the Chernobyl Accident In an attempt to calculate the total dose which will be received from the Chernobyl accident knowledge a b o u t the ecological half-lives of the cesium isotopes in the food products must be known. S o m e information exists already from the nuclear tests in the 1960-ties. The radioactivity in the reindeer m e a t used by the L a p p l a n d e r s has b e e n followed during the last 20 years. F u r t h e r m o r e , a small n u m b e r of L a p p l a n d e r s , which have reindeer as their main source of meat, have been followed with whole b o d y counters. The results, given in Fig. 5 are based on observations by Westerlund et al. (1987). It must be pointed out that the fallout from the nuclear tests was not restricted to a few weeks as was the case for the reactor accident, but continued for years. It a p p e a r s that the results in Fig. 5 can be fitted quite well to a straight line in this plot, yielding a half-life of about six years. I f the data in Fig. 5 are c o m b i n e d with the fallout data an ecologic half-life of about five years appears. It is reasonable to assume that an ecological half-life of about five years should be used for the groups using reindeer as their main source o f meat. This is a small group h o w e v e r , but for those included a total b o d y dose due to fallout from Chernobyl (with no change in their diet) m a y be quite large. T h e y have therefore been r e c o m m e n d e d to change their dietary habits. The average dose to the general public from food products was estimated to be a p p r o x i m a t e l y 0.2 mSv.
Radiation doses in Norway
If the same ecologic half-life of five years is assumed for this group the total dose will be about 1.5 mSv. However, it is evident that the ecologic half-life for an ordinary Norwegian diet, including only 0.6 kg reindeer meat, is shorter than five years. Experiments by Eklund and Falk (1986) on a control group in Stockholm indicate a half-life of less than three years. Based on such an ecologic half-life the total dose from the Chernobyl accident to the average Norwegian will be about 0.9 mSv. Consequently, a fair estimate is that the total dose due to the Chernobyl accident in Norway will be about 1 mSv spread out over more than ten years. From a health physics point of view the extra radiation dose to the general public in Norway must be compared to that attained from natural and medical sources which is approximately 6 mSv every year as shown in Fig. 6. References Backe, S., Bjerke, H., Rudjord, A. L., and Ugletveit, F. (1987) Fallout pattern in Norway after the Chernobyl accident estimated from soil samples, Rad. Prot. Dos. 18, 105-107.
163
Berteig, L. (1986) Virksomhet, prosjekter og beredskap ved Statens institutt for str~tlehygiene i forbindelse med reaktorulykken i Tsjernobyl (In Norwegian) Report 1986:9, SIS. Eklund, G. and Falk, R. (1986) Cesium-137 i strCdskyddsinstitutets kontrollgrupp 1985 (in Swedish). SSl-report 86-06. Statens str~lskyddsinstitut, Box 60204, 104 01 Stockholm. IAEA (1986) USSR State Committee on the utilization of atomic energy. The Accident at the Chernobyl nuclear power plant and its consequences. IAEA Experts Meeting in Vienna, August
1986, Part 1, pp. 41. ICRP 30 (197%1982) International Commission on Radiological Protection. Limits fi)r Intakes o f Radionuelides by Workers. ICRP, Publication 30, Oxford, Pergamon Press. NRPB-R162 (1985) Greenhalgh, J. R., Fell, T. P., and Adams, A. Doses from Intakes o f Radionuclides by Adults and Young People. National Radiological Protection Board, NRPB-RI62
(London:HMSO). Rudjord, A. L. and Ugletveit, F. (in press). Radioactivity in ground level air in Oslo during the first 5 weeks after the Chernobyl accident. Strand, T. and Stranden, E. (1987) Indoor gamma radiation in Norwegian dwellings during the first three months after the Chernobyl accident, Rad. Prot. Dos. 18, 13-17. Strand, T., Strand, P., and Baarli, J. (in press) Radioactivity in foodstuffs and doses to the Norwegian population from the Chernobyl fallout, Rad. Prot. Dos. Westerlund, E. A., Berthelsen, T., and Berteig, L. (1987) Cesium137 body burden in Norwegian Lapps, 1965-1983. Health Phys. 52, 171-177.
0160-4120/88 $3.00 + .00 Copyright © 1988 Pergamon Press plc
FALLOUT AND RADIATION DOSES IN NORWAY AFTER THE CHERNOBYL ACCIDENT Thormod Henriksen Institute of Physics, University of Oslo, N-0316 Oslo 3, Norway
Gunnar Saxeb¢l National Institute of Radiation Hygiene, 1345 Osterhs, Norway (Received 18 August 1987; Accepted I0 May 1988) Due to southeasterly wind and rainfall during the critical days after the Chernobyl accident, Norway received a substantial part of the cesium isotopes released. The radioactive fallout closely followed the rainfall and was mainly concentrated to some thinly populated areas in the central parts of the country. The total fallout of the cesium isotopes was approximately 2300 TBq (137Cs) and 1200 TBq (la4Cs). The average for the country was 11 kBq/m 2 with a variation from 1.5 to 40 kBq/m z for the 19 different counties of the country. The fallout resulted in contamination of food products from some areas, mainly meat from reindeer and sheep, as well as "wild" freshwater fish. A small fraction of the food production in 1986 was not sold due to the regulations enforced. The average radiation dose to Norwegians during the first year after the accident was approximately 0.3 mSv (0.1 mSv from external radiation and about 0.2 mSv from the foodstuffs). This first year extra dose is approximately 5% of the average normal background dose in Norway (estimated to about 6 mSv/year, including medical and industrial use of radiation sources).
Introduction
easterly wind (which brought the contaminated air masses in northwesterly direction towards Scandinavia) and rainfall concentrated to the 28 and the 29 of April (in certain areas we received from 2 to more than 10 mm of rain) N o r w a y received a substantial fallout from the accident. The fallout closely followed the rainfall and was therefore inhomogenously distributed throughout the country.
The Chernobyl accident demonstrated that nuclear accidents also affect countries with no nuclear p o w e r plants. The easy access to hydroelectric p o w e r in N o r w a y implies no immediate need for nuclear power reactors and as a consequence of this no detailed national plans or organization dealing with large scale nuclear accidents exist. The control and certification of radiation sources, including x-ray equipment and radioactive isotopes used for medical and industrial purposes, are c a r d e d out by The National Institute of Radiation Hygiene. After the Chernobyl accident this institution measured and analyzed the fallout situation. The Institute made the first registrations of increased background activity on April the 28th. The following day the highest 131I activity was observed at 10 a.m. A few hours later a project group, called K I E V , was organized with the purpose to collect fallout information, to organize a measuring strategy, and to make dose calculations and estimates. All available personnel and instruments at the Institute were engaged for several weeks to deal with the situation. Due to the particular weather conditions with south-
Radioisotopes in the Air In the first period the activity measurements in the air were given the highest priority. Radioisotopes in the air were measured at six different places (Halden, Oslo, Kjeller, Bergen, Trondheim and Troms¢). Two bursts of activity were recorded with the main part during the last three days of April. An example o f the measurements, as obtained by The National Institute of Radiation Hygiene in Ba~rum (near Oslo) is given in Fig. 1. The highest aerosol c o m p o n e n t iodine activity was measured to 6.3 Bq/m 3 (between 8:20 and 9:47 a.m. on the 29th of April). The measurements were performed on a filter system. A few comparative measurements 157
158
T. Henriksen and G. Saxeb¢l
10000
Table 1. Radioisotopes in air after the Chernobyl accident.
1000 100 tO
E
10
O" m
1,0
\
E
°:'J'2 6
I 30
I 5
I 10
APRIL
I is
I 2o
I 25
!
30
MAY
~0000 1000 -
\
E 17"
f13
ppM
asZr ~Mo l°3Ru l°6Ru L3ZTe 1311 133I 134Cs 136Cs 137Cs 14°Ba 141Ce 144Ce 23aNp
0.49 0.03 0.60 4.00 l 1.30 93.00 0.43 5.30 0.33 6.70 0.21 0.25 5.80 0.33
0.4 0.02 0.5 3.1 8.8 72.2 0.3 4.1 0.3 5.2 0.2 0.2 4.5 0.3
128.77
100.1
All
100
tO
The measurements are made in Baerum, close to Oslo. The activities are given as integrated activites during the first two weeks after the accident and expressed as parts per million (ppM) relative to the ICRP threshold value for workers. The third column yield the relative contribution to the inhaled dose.
10 1,0 0,1 26 3 0 APRIL
5
10
15 20 MAY
25
30
Fig. 1. Level of 13~Csand 131Iactivities in the air at Oslo (given in milliBq/m3) the first month after the ChernobYl accident. The measurements are carried out by The National Institute of Radiation Hygiene.
o n a n a c t i v e coal filter i n d i c a t e d that the a e r o s o l c o m p o n e n t o f the i o d i n e a c t i v i t y w a s o f the o r d e r 10% to 20% o f the total i o d i n e a c t i v i t y . T h u s , the total i o d i n e a c t i v i t y f r o m b o t h a e r o s o l a n d gas c o m p o n e n t s might h a v e b e e n in the r a n g e 30 to 60 B q / m 3. D u r i n g the first p e r i o d the K I E V g r o u p m a d e freq u e n t e s t i m a t e s o f the d o s e to the t h y r o i d a n d disc u s s e d w h e t h e r r e c o m m e n d a t i o n s s h o u l d b e g i v e n to k e e p c h i l d r e n i n d o o r s . D u e to the d r o p in a c t i v i t y after the first few d a y s , n o s u c h r e c o m m e n d a t i o n s w e r e given. I n T a b l e 1 p r e s e n t e d are the 14 m o s t i m p o r t a n t
r a d i o i s o t o p e s w h i c h w e r e o b s e r v e d in the air after the C h e r n o b y l a c c i d e n t a n d w h i c h c o n t r i b u t e d to the inhal a t i o n d o s e (Berteig, 1986, R u d j o r d a n d U g l e t v e i t , in press). B a s e d o n I C R P 30 (1979-1982) a n d N R P B - R 1 6 2 (1985) p u b l i c a t i o n s for the r e l a t i o n s h i p b e t w e e n inh a l e d a c t i v i t y a n d effective d o s e e q u i v a l e n t the individual and collective dose equivalents were calculated a n d p r e s e n t e d in T a b l e 2. T h e p o p u l a t i o n is d i v i d e d in t h r e e age g r o u p s ; a d u l t s , 4-15 y e a r s old, a n d 0 - 3 y e a r s old. ~31I is the m o s t i m p o r t a n t i s o t o p e w h i c h g i v e s app r o x i m a t e l y 70% o f the i n h a l a t i o n dose. T h e total col-
Table 2. Individual and collective doses from inhalation of airborne isotopes in Norway after the Chernobyl accident.
Number of Persons
Adults 4-15 years 0-3 years
3.2 million 0.6 million 0.2 million
All
4.0 million
Dose Equivalent Per Person 6.5 microSv 16.0 microSv 59.0 microSv
Dose Equivalent For The Group 21 manSv 10 manSv 12 manSv 43 manSv
1: 132Te 2:131 I 3:140 La 4:130 RU 5:134 Cs 6:137 Cs 7:132 I
80O
(/1 I.Z
Group
Relative Dose (Percent)
Isotope
0
6O0
4
400
o 200
o
3
5 6
5
........
~o ~o ~'oo ENERGY (keV)
!
~oo
Fig. 2. The gamma-spectrum obtained from a grass sample collected outside the University building in Oslo on May 9, 1986. The observation is made with a Ge-counter at The Institute of Physics, University of Oslo.
Radiation doses in Norway
159
2.
.
J
~."~.j~ .c ~
kBq/m2 O~15-
~
~50i
5 30
30 -
50 IO0
~-100
Fig. 3. The fallout of the two cesium isotopes as determined by the end of October, 1986 (National Institute of Radiation Hygiene).
lective dose equivalent due to inhalation was o f the order 50 m a n S v . The individual dose equivalent was f r o m 0.005 to 0.1 millisievert.
Ground Deposition A n u m b e r of different radioactive isotopes were recorded during the first d a y s after the accident. In Fig. 2 is p r e s e n t e d an example showing the g a m m a - s p e c t r u m obtained f r o m grass outside the University buildings in Oslo (May 9th). It was recognized early that the fallout contained v e r y little 9°St. Analysis of the strontium activity f r o m air filters, lichen, cheese and milk have s h o w n the p r e s e n c e of both soSr and 9°Sr. The activity of 9°Sr
c o m p a r e d to '37Cs was less than 2% in m o s t samples. In milk samples the 9°Sr content was s o m e w h a t larger of the o r d e r 4% to 7% of the '37Cs activity (T. Berthelsen and B. Lind; private communications). In order to get information about the fallout pattern the K I E V group organized a collection of samples of snow, soil, and rainwater. The first samples were taken f r o m places located a p p r o x i m a t e l y 100-200 km apart in the north-south direction throughout the country. The results showed large differences. It was evident that an area in the central part of N o r w a y had 5 to 10 times m o r e ground deposition than the Oslo area. The next step was to organize a large scale soil sampling with the p u r p o s e to attain information a b o u t the total, as well as the distribution of the cesium fallout
160
T. Henriksen and G. Saxeb01
Table 3. Radioactive fallout in Norway from the Chernobyl accident, a
Isotope 134Cs ~3rCs l°~Ru lzsSb 144Ce
Half-life
Activity kBq/m 2
Total Fallout in Tbq
2.06 year 30.1 year 369 days 2.77 year 284 days
3.7 7.1 3.2 0.4 1.1
1200 2300 1000 100 400
250-350 ~1150-250 [~ 50-I 50 < 50 . ~
nGy/h nGY/h nGY/h nGy/h
NOT MEASURED
~In addition to the 137Cs from the Chernobyl accident we still have approximately 100--200 TBq from the nuclear tests in the 1960-ties. The specific activity given as kBq/m z in the table is the average one for Norway whereas the data in Fig. 3 yield the variations throughout the country.
after the reactor accident. Details o f the sampling procedure, isotope identification, etc. are published by Backe et al. (1987). The results of the soil sampling program showed that the fallout of 1arCs and la4Cs was 2300 + 200 and 1200 _+ 100 TBq, respectively. This implies that approximately 6% of the reported total cesium activity released within the borders of E u r o p e a n USSR in the accident was deposited in N o r w a y which, to the present authors, seems unreasonably high (IAEA, 1986). The mean total deposit for the country was 11.3 kBq/m 2. The distribution o f the cesium fallout is given in Fig. 3. The cesium activity in the 19 different counties varied from 1.5 to 41.5 kBq/m 2. The fallout pattern is closely connected to the rain in the same period and localized mainly to the counties of central N o r w a y (Oppland, Tr0ndelag and Nordland). The total fallout o f the most important 3/- and r-emitting isotopes with half-life of more than 200 days is given in Table 3. The fallout resulted in a slight increased level of radiation inside the houses in some areas of Norway• This was casually measured by Strand and Stranden (1987) due to a research project with the purpose to find a correlation between the normal background radiation and the incidence of cancer. Dosimeters were distributed to 900 houses in the central part of N o r w a y approximately a week before the Chernobyl accident. The dosimeters recorded the average dose rate (given as nGy per hour) the first four weeks after the reactor accident. The results are given in Fig. 4. As can be seen, the extra dose from external radioactivity was in the most decontaminated areas approximately 0.2 mGy the first month (300 nGy per hour in 30 days)• It has been estimated that the average first year dose to the Norwegian public due to external radiation from the fallout products was approximately 0.1 mSv. The observations mentioned above seem to support this estimate. The dose in certain areas may have reached a value approximately 10 times the average•
,- ..-.:; :,
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.
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.
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.
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.
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.
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if?
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Fig. 4. The radiation level, as measured in nanoGy pr hour, inside Norwegian homes during the first four weeks after the Chernobyl accident. The values given are due to the fallout only, since the normal background level in the different districts have been deducted. The map, which is based on measurements in 900 homes, is made by Strand and Stranden (1987).
Cesium Activity in the Food Products
In mountain areas of Norway there is reindeer moss (Cladonia rangiferina) which is a gray much-branched lichen (somewhat like a sponge) which is the main food resource in the winter season for the reindeer. The lichen is very efficient in absorbing all kinds of airborne particles including radioactive isotopes from the nuclear bomb tests 25 years ago as well as the fallout from the Chernobyl accident. The reindeer moss in N o r w a y has been contaminated since the nuclear tests
Radiation doses in Norway
161
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I
_
I
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I
.=..,,,~~1 _
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°
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I 970
I 1975
I 980
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1985
YEAR Fig. 5. Specific activity of laTCs in reindeer meat from Kautokeino in Finnmark in the period 1965 to 1986. The activity in the Lapplanders which eat these reindeer have been measured with a whole-body counter and the results (average of about 15 persons in each group) are given as Bq/kg. We assume that cesium is evenly distributed throughout the body. The activity is higher in men, probably due to the fact that they have a higher muscle/total body ratio than the women. The figure is based on measurements carried out by Westerlund et al. (1987).
in the 1960-ties. Just before the Chernobyl accident the specific activity of 137Cs was down to about 300 to 400 Bq/kg in the important areas for reindeer production in northern N o r w a y (Finnmark and Troms). After the accident the reindeer moss in the central parts of the country was contaminated, reaching values for '34Cs and 13rCs o f from 4 to 30 kBq/kg. More than 100 kBq/kg was observed in several samples and the maximum was found to be 190 kBq/kg. For the areas o f Finnmark and T r o m s the cesium activity in the reindeer moss increased slightly to 600 to 1500 Bq/kg. The content of radioactive cesium in the grass during the summer of 1986 was found to be approximately a factor 10 lower than that found for the reindeer moss in the same area. All food products from the contaminated areas contain some activity due to the fallout. A large n u m b e r of different products have been studied after the Chernobyl accident (all together more than 30,000 samples from all districts have been measured). The content is generally low (less than 100 Bq/kg), and in the following we shall concentrate on problems which are of particular importance for Norway. The most contaminated food product is reindeer meat in the central part of N o r w a y (including most of the districts south of Rana). Approximately 15% of the production o f reindeer meat originates from these dis-
tricts. Values for individual animals in the 1986 season reached 40 kBq/kg with an average of about 4 to 5 kBq/kg. No increase in the specific activity was found for the animals from northern N o r w a y during the fall season 1986. Also, meat from sheep, fed on grass from the fallout areas, contained radioactive cesium. The specific activity however, was much lower than that for the reindeer, but in several districts activities of the order 2 to 6 kBq/kg were found (a maximum value o f 18 kBq/kg was observed). In June 1986 the health authorities introduced restrictions with regard to the sale of food products contaminated with the cesium isotopes. The limit was 370 Bq/kg for milk and childrens products and 600 Bq/kg for other products. In an early period it was also reco m m e n d e d not to drink rainwater from cisterns (used for a number o f summer houses). The result of these restrictions was that all reindeer meat in central N o r w a y (south of Rana) could not be sold. Since the ecologic halftime of cesium in reindeer (feeding on contaminated reindeer moss) is approximately five years (see below) it was reasonable to assume that these restrictions would have abolished the sale of reindeer meat for 15 to 20 years. Consequently, the restrictions with a limit of only 600 Bq/kg, which from a health physics point o f view is meaningless and
162
T. Henriksen and G. Saxeb~l
U) E
4
Radon 4 --i
Z m
UJ U') 0
¢2
3
,.I
,<
Z
.<
0
m
-Q lad :E
uJ ~X uJ
nI,Ll I-Z
~;
Z
(/) 0
uJ
0,6 ~--~
0~ m
~ 0,37
O,
0.3
Fig. 6. The annual effective dose equivalent to the average Norwegian (in mSv). The main radiation problem appears to be the large radon dose. The first year dose from the Chernobyl accident is included.
also in conflict with I C R P optimalization principle, could have d e s t r o y e d the living for a n u m b e r of people (the so called South-Lapplanders). In N o v e m b e r 1986 the working limit for cesium in reindeer meat was increased to 6000 Bq/kg. A p p r o x i m a t e l y 30% o f the sheep production in 1986 exhibited a cesium content a b o v e the limit of 600 Bq/kg. A b o u t 3%, which showed a content a b o v e 2000 Bq/kg, was destroyed directly. F o r the 27% with a specific activity in the range 600 to 2000 Bq/kg feeding e x p e r i m e n t s with n o n c o n t a m i n a t e d food were started. Since the biological halftime for cesium in sheep is of the order three weeks it was possible within a few w e e k s to reduce the activity to the set level of 600 Bq/kg. The specific activity in " w i l d " freshwater fish in the c o n t a m i n a t e d areas were high with a m a x i m u m of 55 kBq/kg. Other food products like fruits, vegetables, potatoes, etc. contained only negligible activity.
Doses to the Public Based on an average diet in N o r w a y c o m b i n e d with the specific activity in the different food products Strand et al. (in press) calculated that the average Norwegian, during the first year after the accident, received a p p r o x i m a t e l y 11,000 Bq of the cesium isotopes through the food products. This c o r r e s p o n d s to a radiation dose of less than 0.2 mSv. T o g e t h e r with an external dose of 0.1 m S v the total extra dose during the first y e a r after the Chernobyl accident is of the order 0.3 m S v or smaller. Certain groups which use reindeer m e a t and " w i l d " f r e s h w a t e r fish f r o m the contaminated areas have re-
ceived an extra dose m u c h larger than the average value.
Estimation of Total Doses From the Chernobyl Accident In an attempt to calculate the total dose which will be received from the Chernobyl accident knowledge a b o u t the ecological half-lives of the cesium isotopes in the food products must be known. S o m e information exists already from the nuclear tests in the 1960-ties. The radioactivity in the reindeer m e a t used by the L a p p l a n d e r s has b e e n followed during the last 20 years. F u r t h e r m o r e , a small n u m b e r of L a p p l a n d e r s , which have reindeer as their main source of meat, have been followed with whole b o d y counters. The results, given in Fig. 5 are based on observations by Westerlund et al. (1987). It must be pointed out that the fallout from the nuclear tests was not restricted to a few weeks as was the case for the reactor accident, but continued for years. It a p p e a r s that the results in Fig. 5 can be fitted quite well to a straight line in this plot, yielding a half-life of about six years. I f the data in Fig. 5 are c o m b i n e d with the fallout data an ecologic half-life of about five years appears. It is reasonable to assume that an ecological half-life of about five years should be used for the groups using reindeer as their main source o f meat. This is a small group h o w e v e r , but for those included a total b o d y dose due to fallout from Chernobyl (with no change in their diet) m a y be quite large. T h e y have therefore been r e c o m m e n d e d to change their dietary habits. The average dose to the general public from food products was estimated to be a p p r o x i m a t e l y 0.2 mSv.
Radiation doses in Norway
If the same ecologic half-life of five years is assumed for this group the total dose will be about 1.5 mSv. However, it is evident that the ecologic half-life for an ordinary Norwegian diet, including only 0.6 kg reindeer meat, is shorter than five years. Experiments by Eklund and Falk (1986) on a control group in Stockholm indicate a half-life of less than three years. Based on such an ecologic half-life the total dose from the Chernobyl accident to the average Norwegian will be about 0.9 mSv. Consequently, a fair estimate is that the total dose due to the Chernobyl accident in Norway will be about 1 mSv spread out over more than ten years. From a health physics point of view the extra radiation dose to the general public in Norway must be compared to that attained from natural and medical sources which is approximately 6 mSv every year as shown in Fig. 6. References Backe, S., Bjerke, H., Rudjord, A. L., and Ugletveit, F. (1987) Fallout pattern in Norway after the Chernobyl accident estimated from soil samples, Rad. Prot. Dos. 18, 105-107.
163
Berteig, L. (1986) Virksomhet, prosjekter og beredskap ved Statens institutt for str~tlehygiene i forbindelse med reaktorulykken i Tsjernobyl (In Norwegian) Report 1986:9, SIS. Eklund, G. and Falk, R. (1986) Cesium-137 i strCdskyddsinstitutets kontrollgrupp 1985 (in Swedish). SSl-report 86-06. Statens str~lskyddsinstitut, Box 60204, 104 01 Stockholm. IAEA (1986) USSR State Committee on the utilization of atomic energy. The Accident at the Chernobyl nuclear power plant and its consequences. IAEA Experts Meeting in Vienna, August
1986, Part 1, pp. 41. ICRP 30 (197%1982) International Commission on Radiological Protection. Limits fi)r Intakes o f Radionuelides by Workers. ICRP, Publication 30, Oxford, Pergamon Press. NRPB-R162 (1985) Greenhalgh, J. R., Fell, T. P., and Adams, A. Doses from Intakes o f Radionuclides by Adults and Young People. National Radiological Protection Board, NRPB-RI62
(London:HMSO). Rudjord, A. L. and Ugletveit, F. (in press). Radioactivity in ground level air in Oslo during the first 5 weeks after the Chernobyl accident. Strand, T. and Stranden, E. (1987) Indoor gamma radiation in Norwegian dwellings during the first three months after the Chernobyl accident, Rad. Prot. Dos. 18, 13-17. Strand, T., Strand, P., and Baarli, J. (in press) Radioactivity in foodstuffs and doses to the Norwegian population from the Chernobyl fallout, Rad. Prot. Dos. Westerlund, E. A., Berthelsen, T., and Berteig, L. (1987) Cesium137 body burden in Norwegian Lapps, 1965-1983. Health Phys. 52, 171-177.