Department of Nuclear PhysicsAMS and Radiation Physics GroupUniversity of Lund

RADIONUCLIDE CONCENTRATION INFUELS AND ASH PRODUCTS FROM

BIOFUEL HEATING PLANTS

Bengt Erlandsson Robert Hedvall Sren Mattsson

Department of Nuclear PhysicsSlvegatan 14S-223 62 LundSweden

Repoit 02/95LUNFD6/(NFFR-3067)/4-38/tt995)Lund"! 995

O 7

SSI P397.91

RADIONUCLIDE CONCENTRATION IN FUELS AND ASHPRODUCTS FROM BIOFUEL HEATING PLANTS

Redogrelse fr projekt SSI P 397.91"Mtning av koncentrationen av radioaktiva mnen i biobrnslen

och dessas restprodukter"

Bengt Erlandsson, Dept. of Nuclear Physics, University of Lund, S-223 62 Lund,Sweden.

Robert Hedvall^, Dept. of Radiation Physics, Lund, University of Lund, S-221 85Lund, Sweden.

Sren Mattsson, Dept. of Radiation Physics, Malm, University of Lund, S-214 01Malm, Sweden.

# ) Present address: Studsvik Nuclear AB, S-611 82 Nykping, Sweden.

Lund December 1994

Contents

1.2.3.4.5.6.7.8.9.

1011.12.

AbstractIntroductionInvestigation sitesTime scheme for samplingInstrumentationResultsEnrichment factorsActivity concentration and generated energyRelation between deposition and activity concentrationin fuelThe release of radioactive substances to the surroundingsConcluding remarksReferences

3456778910

111214

1. Abstract

The activity concentration of the radionuclides K-40, Ac-228, Pa-234, Mn-54, Co-60,Zr-95, Ru-106, Ag-110m, Sb-125, Cs-134, Cs-137 and Ce-144 have been investigatedin peat, wood chips and ash products from 13 Swedish district heating plants duringthe winter seasons of 1986/87,1988/89,1989/90 and 1990/91. There is a significantdecrease in the activity concentration of Cs-137 in the fuel which is especiallypronounced between the first two seasons, 86/87 and 88/89 after the Chernobylaccident. In spite of the varying deposition of Cs-137 over the country it has beenpossible to give a relation between the activity concentration in the peat and woodchips as a function of the deposition. The Swedish biofuel heating plants of which 35-40 are burning peat and 70-75 wood chips have been divided in three groups accordingto the activity concentration in the ash products. The mean Cs-137 concentration inash and the total activity "produced" per year in Sweden have been calculated. Themaximum concentration in air at ground level and the corresponding effective doserate of inhaled Cs-137 as a function of the emission rates of flue gases from stackswith varying heights and during different weather conditions has been calculated.

2. Introduction

The use of biomass fuel has increased rapidly in Sweden during the last decade. Afteroil and coal, peat and wood chips are the most common fuels used in district heatingplants. The energy production from peat burning was 1.1 TWh in 1986 and 3.2 TWhin 1992 and the energy production from wood chips was 3.1 TWh in 1986 and 5.1TWh in 1992. The total energy production from the district heating plants was 46.9TWh in 1986 and 47.7 TWh in 1992. Peat and wood chips have thus increased theirpart in the energy production from 9% to 17%. A total of 3500 kirr of peat landcould easily be used in Sweden which equals 2000 TWh.

K-40 and radionuclides belonging to the uranium and thorium series are the mostprominent natural radionuclides in both peat, wood chips and straw. Fission productsfrom nuclear weapons tests since the I950's are also found. After the Chernobylaccident in April 1986 the deposition of the caesium isotopes Cs-134 and Cs-137 hasreached several hundreds of kBq/m^ in some areas of Sweden (SGAB, 1986). It istherefore of importance to decide if peat from contaminated bogs can be used as fuelwithout exposing workers handling the fuels or ash products or people living near tothe plants to too high levels of external and internal radiation.

In most cases the emission of radioactive material is a minor environmental problemcompared with the emission of sulphur oxides, nitrogen oxides, metals and organicmatter. Emissions of such compounds have been studied more thoroughly (Nilsson &Timm, 1983; Rudling & Lofroth, 1980; Pohjola et ai, 1985) than radionuclideemissions.

The aim of this investigation is to measure the activity concentration of variousradionuclides in the biofuels peat and wood and their enrichment in the combustionprocess. The activity balance of the radionuclides in the heating plants will also beanalysed. The amount of Cs-134 and Cs-137 in ash products produced in powerplants per year in Sweden will be calculated. Finally, a simple model will be appliedfor the calculation of the effective dose from inhalation of stack effluents to a group ofpersons living in the surroundings of the plant. There is also a component of externalexposure. Other ways of increasing the body burden are for example ingestion of foodproducts in areas effected by fall-out from stack emission or by leaching elements fromdeposits of fly-ash.

3. Investigation sites

Samples of biofuel and ash products in the form of grab samples have been taken oncea year from 13 heating plants in Sweden. The location of the heating plants is shownin Fig. 1. Their exact locations together with information whether the plant is burningpeat or wood-chips are given in Table 1. Several of the heating plants are using fuelfrom places located up to 100 km from the plant, where the deposition of radionuclides may be different from that of the plant site and may vary considerably.Therefore a more thorough description of each plant and the area from which the fuelis taken is necessary and will be given below. All deposition values given in the tablerefer to the total deposition as estimated from an airborne gamma ray survey (SGAB,1986). It has also to be observed that the true deposition may be a factor of two largeror smaller than the estimated (Edvarson , 1991).

1. ngelholm The plant has two 15 MW boilers and burns both peat and wood.The peat comes from bogs 110 km NE of ngelholm where the deposition of Cs-137was 0-2 kBq/m^ and the wood chips from forests 17 km N of ngelholm where thedeposition of Cs-137 was 2-3 kBq/m2-

2. Vstervik The plant has one 20 MW boiler and burns wood chips from thenorth-eastern parts of Smland and the south-eastern parts of stergtland. Thedeposition in these areas varied between 3-5 kBq/rrr for Cs-137.

3. Skvde The plant has one 18 MW boiler and burns wood chips from thesurroundings of Skvde, where the deposition was low, 0-2 kBq/irr for Cs-137. Thisplant is connected to the Regional hospital and is not giving information to theSwedish district heating association.

4. Eskilstuna The plant has one 50 MW boiler and bums wood ships fromforests within a radius of about 100 km to the north of Eskilstuna. In these parts thedeposition varied between 10 and 60 kBq/m2 for Cs-137.

5. Enkping The plant has two 5.8 MW boilers and burns wood chips fromforests within 100 km from Enkping. The deposition of Cs-137 varied from 10 to 60kBq/m2 in these areas.

6. Sandviken This plant has two 15 MW boilers and burns both peat and woodchips. The peat comes from bogs about 30 km south of Sandviken, where thedeposition of Cs-137 was between 40 and 80 kBq/m2 (Hedvall & Erlandsson, 1992).

7. Hudiksvall The plant has one 35 MW boiler and bums peat from two bogs atLjusdal. The deposition of Cs-137 was 3-10 kBq/m2.

8. Hrnsand The plant has one 16 MW boiler and bums peat from bogs about100 km NW of Hrnsand where the deposition was about 30 2

9. stersund The plant has two 25 MW boilers and bums peat from Strmsund100 km north-east of stersund, from Brcke 60 km south of stersund and fromHammarstrand 85 km east of stersund. In the first area the deposition of Cs-137 was10 to 20 kBq/m2, in the second area 3 to 5 kBq/m2 and in the third 30-40 kBq/m2.

10. Ume The plant has one 30 MW boiler and burns peat from Trskmyranabout 35 km north of Ume, where the deposition of Cs-137 was 10 to 20 kBq/m2.

11. Skellefte The plant has one 25 MW boiler and burns peat and wood chips.The peat comes from bogs at Rjnoret 50 km to the north of Skellefte, where thedeposition of Cs-137 was 2 to 5 kBq/m2

12. Boden The plant has two boilers, one 25 MW boiler for wood chips andanother 20 MW boiler for peat. Both wood chips and peat come from thesurroundings of Boden where the deposition of Cs-137 was 0 to2 kBq/m2.

13. Gllivare The plant has one 20 MW boiler for peat. The peat comes frombogs round Gllivare, where the deposition was 0 to 2 kBq/m .

4. Time scheme for sampling

Samples in the form of grab samples have been taken during the winter seasons of1986/87,1988/89,1989/90 and 1990/91. In Table 1 is given the month and year ofthe sampling.

5. Instrumentation

The activity concentration of the various radionuciides in the samples was determinedwith a HPGe, or a Ge(Li) detector. The HPGe detector had a relative efficiency of35.2% and a resolution of 1.78 keV (1.33 MeV). The Ge(Li) detector had anefficiency of 18% and a resolution of 1.88 keV (1.33 MeV). The detectors wereplaced in lead caves with wall thicknesses of 120-200 mm and the inside of the leadcaves were also lined with 10 mm of copper. For the efficiency calibration an ion-exchange resin method was used (Bjurman et al., 1987). The samples were first driedand homogenised and then packed into either 60,123, or 180 ml tubs which wereplaced close to the front of the detector. With this close geometry, summation effectsfrom cascading gamma rays must be taken into consideration. Other difficulties inanalysing the gamma ray spectra with interfering peaks were also taken intoconsideration. For further details see Hedvall & Erlandsson, (1992).

6. Results

The activity concentration for the following radionuciides has been measured: K-40,Ac-228, Pa-234, Mn-54, Co-60, Zr-95, Ru-106, Ag-110m, Sb-125, Cs-134, Cs-137and Ce-144. The first three are naturally occurring and the others are well knownfrom the Chernobyl fallout. Cs-137 does not entirely come from the Chernobylaccident but also from various atmospheric nuclear weapons tests mainly carried out in1956-58 and 1961-62. Only those radionuciides which have the highest activityconcentration throughout the measuring period are given in Tables 2-14.

At those places where both fly ash and bottom ash have been measured, the activityconcentration of all radionuciides, except K-40 is higher in the fly ash than in thebottom ash. This is probably due to that the enrichment depends on the furnancetemperature. The enrichment decreases when the temperature increases. AtSandviken (Table 7) the activity concentration of Cs-134 and Cs-137 is higher in thebottom ash than in the fly ash for the 1988/89 and 1989/90 seasons. A furtherinvestigation showed that the bottom ash had a higher content of sand from thefurnance, which caused an enrichment of about 4 compared with what it ought to be.The errors given in the tables are only statistical errors originating from the gammaspectrometric measurements and they are small compared with the variations of theactivity concentrations both of the fuel and the ash-products. Notice that the time axesin Fig. 2 just marks the different winter seasons. It can be seen in the figure that thereis a reduction in the activity concentration with time but with some exceptions. For

wood chips both Eskilstuna and Enkping (Tables 5 and 6) show large variationswhich cannot be explained by the single sample technique, but most probably reflectvariations in the contamination of those areas where the wood chips are coming from.In this case the deposition can vary between 3 and 40 kBq/m . Also for peat there aregreat variations. For stersund the activity concentrations are 359,502,129 and 241Bq/kg (Table 10 and Fig. 2). These variations are much larger than those found whena number of samples were taken during the same season. Ravila & Holm, (1994) havefound standard deviations of the activity concentrations for wood chips collected from16 different plants during the 1990/91 season of about 8-12%. For peat Hedvall &Erlandsson, (1992) found variations of 8% for summer samples and 14% for wintersamples at Sandviken. Peat is coming from peat bogs within a rather small area. Thevariations in the activity concentration may therefore not necessarily reflect variationsin the deposition but primarily variations in the activity concentration due to changes inthe harvesting technique. Surface layers used one year may be followed by deeperlayers the next year and then by new surface layers, etc. Variations in depth with 20-50 cm may result in variations in the activity concentration of 10-20 times (Hedvall &Erlandsson, 1992)

7. Enrichment factors

There is an enrichment of most radioactive nuclides in the ash products because of theloss of organic matter in the combustion process (Table 15). This factor varies withthe type of fuel and year, but is on the average 40 times for wood chips and 14 timesfor peat with a variation of about 50%. These factors are also in agreement with thedifference in the ash content which is 2-5% and 5-10% respectively. For Finnish peat,Mustonen et ai, (1989) have found an enrichment factor of 21 for the heating season1986/87 which is in rather good agreement with 14 found in this investigation ifuncertainties are taken into consideration. The statistics from the Swedish DistrictHeating Association contain no information about fuel consumption or asn production.It only gives the produced thermal energy in GWh per year. To estimate the amountof produced ash it is therefore necessary to calculate a factor that converts GWh ofthermal energy to kg ash. Ash stands here for the total amount of ash products, bothflying- and bottom ash. From some of the plants we have obtained detailedinformation concerning the amount of used fuel, the amount of produced ash products(kg dry weight) and produced energy (GWh) for the four combustion seasons dealtwith in this investigation. The calculated conversion factor is 6 kg ash per MWh forwood chips from Vstervik and 9 kg ash per MWh for wood chips both fromEnkping and Boden. The calculated conversion factor is 13 kg ash per MWh and 12

kg ash per MWh for peat from Sandviken and Boden respectively (Table 16).Adopted factors for the other plants are also given in Table 16. The uncertainties forthese figures are about 25% depending on the quality of the fuel and the condition ofthe burner. Based on these factors and the stated energy production, the measuredactivity concentration (mean value based on the information that the ash is composedof 75% fly ash and 25% bottom ash) the total outgoing activity and the activity perproduced thermal energy unit can be calculated (Table 16).

The 13 investigated power plants are burning fuel from parts of Sweden with greatlyvarying deposition of Cs-137 from the Chernobyl accident. It is not possible tocalculate individually the activity per produced energy unit for each of all the about 75power plants. Both peat and wood burning plants have therefore been arranged inthree "activity groups". For peat, Sandviken and Hrnsand have been arranged ingroup I with 250, 200,150 and 150 kBq/MWh for the four heating seasonsrespectively, stersund and Ume in group II with 150,40,50 and 20 kBq/MWhrespectively and Hudiksvall, Skellefte, Boden and Gllivare in group HI with 10,5, 8and 5 kBq/MWh respectively. For wood chips Enkping and Eskilstuna have beenarranged in group I with 50,40, 30 and 35 kBq/MWh respectively, Vstervik andBoden in group II with 15,10,10, and 5 kBq/MWh respectively and ngelholm andBoden in group III with 10, 5,4 and 3 kBq/MWh respectively. The grouping of theother about 60 power plants is based on the total deposition of Cs-137 in theneighbourhood of the plant or on the deposition on areas from where the plant isobtaining its fuel. Wood chips are mostly coming from areas within a radius of about80 km whereas peat can be transported from bogs far away.

8. Activity concentration and generated thermal energy

In Table 17 the total generated thermal energy (GWh per year), the total yearlyamount of ash products (kg), the total Cs-137 activity (GBq per year) and the activityconcentration (kBq/kg) are given for the different categories of more than 100 plants.For peat ash the calculated mean values for the activity concentration are 5.3,3.5,3.0and 2.1 kBq/kg for the four sampling seasons and for wood chips the values are 2.2,1.5, 1.2 and 1.0 kBq/kg respectively. Although these values are adopted and havegreat uncertainties they reflect the trend of decreasing activity concentration of Cs-137in the ash products produced in Sweden. Very few power plants are taking their fuelfrom the same area year after year. For plants burning wood chips a collecting radiusof 80-100 km can include areas where the deposition can vary from 1 to 100 kBq/m .For plants burning peat not only the geographical distance to the bogs may very but

also the manner in which the bogs have been harvested are causing great variations inthe activity concentration of Cs-137 in the fuel. Nevertheless the mean value of theactivity concentration of Cs-137 in the ash products show a reduction of about 50%both for peat and wood chips in the first 5 years after the Chernobyl accident. Afterthat the reduction expressed as the "practical or effective" half life would approach thephysical half life of 30 years.

9. Relation between deposition and activity concentration in the fuel

As already mentioned the great variations in deposition within the collecting distancefrom the plant makes it very difficult to find a relation between the activityconcentration of Cs-137 in the fuel and a deposition. The "old", pre-Chemobyl Cs-137 from the atmospheric nuclear weapons tests was to about 85% deposited duringthe period 1961-1968. It was also more evenly deposited than the fallout fromChernobyl. The deposition reflects the precipitation and the concentration in the air,which for Cs-137 from weapons fallout as a mean only varied with a factor of twofrom southern (highest) to northern (lowest) Sweden (DeGeer et a!., 1978). Thereforethe variations for "old" Cs-137 within a normal collection radius of 80-100 km oughtto be restricted to about 25%. In Table 18 is given the deposition of "old" Cs-137.Based on an activity ratio of O.580.01 for Cs-134/Cs-137 for the Chernobyldeposition (Arntsing et al., 1991) the amount of "old" (DeGeer et al., 1978) and"new" Cs-137 in both fuel and ash products have been calculated. In Table 18 aregiven the activity concentration of Cs-137 in fuel from the first season 1986/87 and thecalculated total deposition of Cs-137. The smaller the old deposition is compared tothe new deposition the more uncertain the calculated total deposition is. As the samplevalues are from one sole grab sample, the uncertainties are also fairly large. Repeatedsampling of wood chips gives an uncertainty of 12% (Ravila & Holm, 1994) and forpeat the uncertainty is 12-15% (Hedvall & Erlandsson, 1992). Based on these figureswe have attached an uncertainty of 25% to the total deposition. The activityconcentration of Cs-137 in peat and wood chips as a function of the deposition of Cs-137 is shown in Fig. 3. To facilitate the presentation, both axis are exponential and toguide the eye a curve has been drawn. For wood chips the relation between depositionand activity concentration is rather well represented by the curve, whereas for peat nosimple relation seems to exist which may be explained by differences in location of thepeat bogs but also by differences in the harvesting technique. In the table is also giventhe deposition from the aerial survey (SGAB, 86). These values are based on reportsfrom the different power plants concerning the area from which the fuel has come.The agreement between the calculated deposition and the measured deposition is quite

good. Therefore it ought to be possible to get a rather good value at least for woodchips of the activity concentration of the fuel from an aerial survey and the curve inFig. 3 for both peat and wood chips.

10. The release of radioactive substances to the surroundings

The escape of radioactive products from the biofuel plant may occur in two ways,either as a deposition of the ashes in certain places or as flue-gases from the stacks.The deposits of the ashes can have varying thicknesses and even if it is several metersthick it hardly constitutes any radiation problem (Ravila & Holm, 1994).

It is not possible to calculate how much Cs-137 that is released to the air from what ismissing of Cs-137 in the balance between fuel and ash products based on single grabsamples. Hedvall & Erlandsson, (1992) have however shown that about (122)% ofthe Cs-137 activity from a peat-fired heating plant escapes through the stack in theform of flue gases and is discharged into the environment. Mustonen et al, (1989)mention that the long-term average of the collection efficiency for ash products ofsome Finnish peat-fired power plants has been about 94%. For Sandviken we havealso calculated an emission rate of 1 kg/h. We therefore suggest that for Swedish bio-fuel fired power plants between 1.4% (case 1) and 10% (case 2) of the activity of theash products is leaving the stacks in the form of flue gases and is then deposited in thesurroundings. In Table 19 is shown the emission rates which have been calculated forcase 1 and case 2 based on the total Cs-137 activity in the ash products given in Table17 and the number of plants in the different categories. Using a simple gaussian plumemodel (Slade, 1968) of the atmospheric dispersion of radio nuclides, the maximumground level air concentration has been calculated. The calculations have beenperformed for a wind speed of 4 m/s, for effective stack heights of 20,60 and 100 mand for either Pasquill B- or E-weather conditions. The results are presented in Fig. 4which can be used to translate a given emission rate into a certain air concentration.As an example an emission rate of 33 Bq/s gives a maximum ground concentration of2600 }iBq/m . An effective dose at this distance from the stack has a'so beencalculated using ICRP 56 (ICRP, 1990) and ICRP 61 (ICRP, 1991) with theassumption that the normal inhalation is 201/min for 24 h (Fig.4). If we assume thatthe total stack emission is 1 kg/h all year round from a 90 m tall stack, the effectivedose would be a few (iSv/a (both internal and external) for a person standing 24h/day

at a spot where the ground concentration is at a maximum. The effective dose wouldbe greater for smaller stacks. Although this is a maximum value from Swedish bio-fuelpower plants the dose is very small compared to the dose from natural radiation,mainly from members of the uranium and thorium series (Hedvall & Erlandsson,1992).

Earlier assumptions have suggested an emission rate of about 40 kg/h from smallerstacks from the Uppsala and Skellefte plants during a 7 month period (Gyllander,1986), leading to a somewhat smaller maximum dose. Even if we use the inhalationdose factor (in Sv/Bq emitted) for a distance of 1 km from a 20 m tall stack togetherwith our own estimates of the emission rate, Cs-137 has a negligible effect on theeffective dose. The absolute maximum from bio-fuel power plants is a few \iSv peryear (except for fuels with an extreme uranium and radium content (Hedvall &Erlandsson, 1992)). The dose is negligible compared to the average effective dosecontribution in Sweden from natural sources including radon daughters in indoor-airwhich is about 4mSv per year from all sorts of sources.

11. Concluding remarks

Big differences may occur from one year to another in the activity concentration of thefuel and the ash products. This is due to that both wood chips and peat in many casesare transported from places with great variations in the deposition of Cs-137, i.e.Uddevalla was this summer, 1994 importing peat from Scotland and Nykping wasimporting wood chips from Latvia. It is therefore very difficult to predict the futuredecrease in the activity concentration of both fuel and ash products or when a certainactivity level will be reached.

Based on the results presented in this report it would be possible to calculate theactivity concentration in ash products from an aerial survey of the deposition via Fig.3to the activity concentration in wood chips and peat. From these via an enrichmentfactor found in Table 15 to the activity concentration in various ash products and fromthere via a calculation of the emission rate and Fig. 4 to a maximum groundconcentration and effective dose of Cs-137 for various stack heights and weatherconditions.

During the 1990/91 season the total air emission through the stacks of Cs-137 from allthe heating plants was 1.6 GBq/ year for case 1 and 11.6 GBq/year for case 2 (Table

19) which gives 200 Bq/ MWh and 1550 Bq/MWh respectively. This may becompared with the emission from the stacks of the Swedish nuclear power plantswhich for 1992 was reported to be 0.4 Bq per produced MWh.

References

Amtsing, R., Bjurman, B., De Geer, L-E., Edvardson, L., Finck, R., Jakobsson, S. &Vintersved, I. (1991). Field Gamma Ray Spectrometry and Soil SampleMeasurements in Sweden Following the Chernobyl Accident. A Data Report. FOAReport D-20177-4.3 December 1991.

Bjurman, B., Erlandsson, B. & Mattsson, S. (1987). Efficiency calibration of Gespectrometers for measurements on environmental samples. Nucl. Instrum. Meth.Phys. Res., A262,548-50.

De Geer, L-E., Arntsing, R., Vintersved, I., Sisefsky, J., Jakobsson, S. & Engstrm, J-. (1978). Paniculate radioactivity, mainly from nuclear explosions, in air andprecipitation in Sweden mid-year 1975 to mid-year 1977. Appendix II. FOA Repon C4OO89-T2(A1) November 1978.

Edvarson, K. (1991). Fallout over Sweden from the Chernobyl accident, in TheChernobyl fallout in Sweden, ed. L. Moberg. Swedish Radiation Protection Institute,1991.

Erlandsson, B., Hedvall, R. & Mattsson, S. (1994). Radionuclide concentration infuels and ash products from biofuel power plants. Report LUTFD2/(TFKF-3OA)/1-34/(1994). Department of Nuclear Physics, Univ. of Lund, Lund, Sweden.

Gyllander, C. (1986). Private communication.

Hedvall, R. & Erlandsson, B. (1992). Radioactivity in peat fuel and ash from a peat-fired power plant. J. Environ. Radioactivity, 16, 205-28.

International Commission on Radiological Protection (1990). Age-dependent doses tomembers of the public from intake of radionuclides. ICRP Publication 56 Annals ofthe ICRP. Pergumon Press, Oxford.

International Commission on Radiological Protection (1991). Annual limits on intakeof radionuclides by workers. ICRP Publication 61 Annals of the ICRP. PergamonPress, Oxford.

Mustonen, R., Reponen, A. & Jantunen, M. (1989). Artificial radioactivity in fuel peatand peat ash in Finland after the Chernobyl accident. Health Phys., 56,451-58.

Nilsson, T & Timm, B. (1983). Environmental effects of wood and peat combustion.National Swedish Environmental Protection Board, SNV-1708. (In Swedish)

Pohjola; V., Hahkala, M. & Hsnen, E. (1985). Emission inventory of coal, peat andoil-fired power plants. Technical Research Centre of Finland, Research Reports 231.(in Swedish).

Ravila, A. & Holm, E. (1994). Radioactive Elements in Forest Industry. Sci. of TotalEnviron., 157, 339-356.

Rudling, L. & Lfroth, G. (1980). Chemicai and biological characterization ofemissions from comustion of peat and wood-chips. National Swedish EnvironmentalProtection Board, SNV-1449. (in Swedish).

SGAB (1986). Map of Sweden showing the fallout Levels of Cs-137 after theChernobyl accident, 1:200 000. Swedish Geological Company, Box 1424, S-75144Uppsala, Sweden.

Siade, D.H. (1968). Meteorology and Atomic Energy. US Atomic EnergyCommission Report, TID-24190, Washington DC, USA.

Figure captions

Fig. 1 Heating plants in Sweden studied in this investigation and the deposition of Cs-137 after the Chernobyl accident.

Fig. 2 Variations of the activity concentration of Cs-137 in the fuel and in the fly ash.

Fig. 3 The measured activity concentration of Cs-137 in peat and wood chips as afunction of the estimated deposition.

Fig. 4 The calculated maximum ground concentration and maximum effective dose ofCs-137 as a function of the emission rate for effective stack heights of 20, 60 and 100m for either Pasquill B- or D-weather conditions.

Table 1. Localization of the biofuel heating plants, type of fuel and sampling time.

ngelholmVstervikSkvdeEskilstunaEnkpingSandvikenHudiksvallHrnsandstersundUmeSkellefteBodenGllivare

Location

5615'N; 1253'E5715'N; 1653'E5824'N; 1351'E5922'N; 1630'E5939'N; 1705'E6036'N; 1645'E6144'N; 1706'F6238'N; 1755'E63H'N; 1439'E6350'N; 2015'E6445'N; 2100'E6548'N; 2142'E67O8'N; 2039'E

Fuel

p.wwwww

PPpPPP

p,wp

Mar 87Apr 87May 87Apr 87Mar 87Apr 87Apr 87Mar 87Apr 87Apr 87Mar 87Apr 87Apr 87

Sampling time

Dec 88Dec88Dec 88Dec 88Dec 88Dec 88Jan 89

Jan 89Jan 89Dec 88Jan 89Nov88

Jan 90Jan 90Feb90Jan 90Jan 90Mar 90Jan 90

Feb90Feb90Feb90Jan 90Jan 90

Feb91Feb91Jan 91Feb91Jan 91Feb91Jan 91

Feb91Feb91Feb91Jan 91Jan 91

p: peatw: wood chips

Table 2. Activity concentration of radionuclides (Bq/kg) found in peat, wood chipsand various ash products from the local heating plant at ngelholm.

1986/87

1988/89

1989/90

1990/91

woodpeat

fly ashbottom ash

woodpeat

fly ashbottom ash

woodpeat

fly ashbottom ash

woodpeat

fly ashbottom ash

K-40

n.m.

843392616410

60+651

139+2645020

n.m.

752272045020

428...

2184+25131220

Ac-228

n.m.n.m.

n.m.

n.m.

n.d.21

722251

n.m.n.d.141181

41...

101340l

Ru-106

n.m.n.d.

711492

63n.d.

256n.d.

n.m.n.d.n.d.n.d.

n.d....

84n.d.

Sb-125

n.m.n.d.17531

n.d.n.d.72n,d.

n.m.n.d.n.d.n.d.

n.d....

n.d.n.d.

Cs-134

n.m.

2152310l

31n.d.

38181

n.m.n.d.2+131

Table 3. Activity concentration of radionuclides (Bq/kg) found in wood chips andvarious ash products from the local heating plant at Vstervik.

1986/87

1988/89

1989/90

1990/91

woodfly ash

woodfly ash

bottom ash

woodfly ash

bottom ash

woodfly ash

bottom ash

K-40

66102262+123

118102083123102710

981016711332829150

301517771162489120

Ac-228

3+280+13

3+152+216+1

41275+369+2

n.d.42+248+1

Rul06

30+69001105

n.d.201+8n.d.

41339+5513

n.d.1113n.d.

Sb-125

n.d.103+8

n.d.27+3n.d.

n.d.1212n.d.

n.d.712n.d.

Cs-134

24+21141159

12+1364+5911

41197+25511

2+140+134+1

Cs-137

78143514+180

61+117601542+1

28+16971442412

231143+237012

Ce-144

n.m.

n.m.

5111461314+1

1+159+2411

n.d.4+1n.d

n.m.:n.d.:

not measurednot detected

Table 4. Activity concentration of radionuclides (Bq/kg) found in wood chips andvarious ash products from the local heating plant at Skvde.

1986/87

1988/89

1989/90

1990/91

woodfly ash

bottom ash

woodash

woodfly ash

bottom ash

woodfly ash

bottom ash

K40

59+1016501931063193

88+9147I2I

52717511501799150

52+71216171431123

Ac-228

4245+831+5

n.d.1311

4+1521351+3

41133+260+3

Ru-106

n.d.309+39131117

n.d.36+6

n.d.n.d.n.d.

n.d.n.d.n.d.

Sb-125

n.d.14+1

49+11

n.d.n.d.

n.d.1813612

n.d.n.d.n.d.

Cs-134

10+1340118209111

51177+2

1.3+0.3124+37612

1.6+0.329+121+1

Cs-137

24+21261+65794141

261143313

211110371765814

14+141514295+3

Ce-144

n.m.

n.m.

n.m.

n.d.73

n.d.n.d.

1.3+0.2

n.d.n.d.n.d.

n.m.: not measuredn.d.: not detected

Table 5. Activity concentration of radionuclides (Bq/kg) in wood chips and variousash products from the local heating plant at Eskilstuna.

1986/87

1988/89

1989/90

1990/91

woodfly ash

bottom ash

woodfly ash

bottom ash

woodfly ash

bottom ash

woodfly ash

bottom ash

K-40

8814I4278197753

7671784181837118

878210921168020

2110135820136520

Ac-228

n.m.

n.m.

n.m.

2.610.372133211

Table 6. Activity concentration of radion uclides found in wood and a mixture of fly-and bottom ash from the local heating plant at Enkping.

1986/87

1988/89

1989/90

1990/91

woodash

woodash

woodash

woodash

K-40

44101180166

8381471121

66163610+32

64131780+29

Ac-228 Ru-106 Sb-125 Cs-134 Cs-137 Ce-144

n.d.n.d.

n.d.813

n.d.154+4

11165+3

30918471215

1915197+11

n.d.n.d.

n.d.39114

814205116

n.d.10515

n.d.21+3

2124215

219+127372+381

78+2122415

13+1545+3

2311687+30

555129179101919

325+104978+30

73+23314+7

184125649111

n.m.

n.m.

n.d.151+5

n.d.51+4

n.d.13+6

n.m.: not measuredn.d.: not detected

Table 7. Activity concentration of radionuclides (Bq/kg) found in peat and variousash products from the local heating plant at Sandviken.

1986/87

1988/89

1989/90

1990/91

peatfly ash

bottom ash

peatfly ash

bottom ash

peatfly ash

bottom ash

peatfly ash

bottom ash

K-40

1314350597061101

9242610123615

3155661101202120

Table 8. Activity concentration of radionuclides (Bq/kg) found in peat and variousash products from the local heating plant at Hudiksvall.

1986/87

1988/89

1989/90

1990/91

peatfly ash

bottom ash

peatfly ash

bottom ash

peatfly ash

bottom ash

peatfly ash

bottom ash

K-40

26+92942323216

30+2440110351+10

4425411163110

32121261612616

Ac-228

I0377+1281+12

n.d.45114612

4111131410113

13111361413814

Ru-106

n.d.43+1320+6

n.d.9+310+3

813n.d.n.d.

n.d.1016n.d.

Sb-125

3+24+1n.d.

n.d.4+1311

n.d.19+3n.d.

n.d.n.d.n.d.

Cs-134

16121421810516

41144+136+1

811771238+1

21121112411

Cs-137

49+3551+30348118

2611290+2231+2

55+1620+428012

28+128213298+3

Ce-144

n.m.

n.m.

n.m.

n.d.n.d.n.d.

n.d.n.d.n.d.

n.d.n.d.n.d.

n.m.: not measuredn.d.: not delected

Table 9. Activity concentrations of radionuclides (Bq/kg) found in peat and in variousash products from the local heating plant at Hrnsand.

K-40 Ac-228 RulO6 Sb-125 Cs-134 Cs-137 Cc-144

1986/87 peatfly ash

bottom ash

n.m. n.m.

33636 n.m.3824 n.m.

14028 531O 1183+62 29211150 n.m.18311237 857+68 13950+722 34480+1769 n.m.

175144 100+18 2019+105 50051258 n.m.

nun.: not measured

Table 10. Activity concentration of radionuclides (Bq/kg) found in peat and variousash products from the local heating plant at stersund.

1986/87

1988/89

1989/90

1990/91

peatfly ash

bottom ash

peatfly ash

bortoir ash

peat 1)peat 2)fly ash

bottom ash

peat 3)fly ash

bottom ash

K-40

39+15n.d.

91795

441445210121010

345233

43920121450

66529111207ll

Ac-228

S+4.i..193

n.d.312231

91515522610

21332251

Ru-106

n.d.6511

n.d.

n.d.428104

105n.d.

217n.d.

53146n.d.

Sb-125

n.d.194n.d.

4238321

n.d.n.d.163n.d.

41173n.d.

Cs-134

12316n.m.

23310

1101255311027915

20118+1

283158611

2911207+57111

Cs-137

3595n.m.

690+29

502152468+51323+10

129+265+1

185411056616

241121766+561012

Ce-144

n.d.n.m.n.d.

n.d.2.3+0.3

n.d.

n.d.n.d.n.d.n.d.

n.d.n.d.n.d.

n.m.: not measuredn.d.: not detected

Table 11. Activity concentration of radionuclides (Bq/kg) found in peat and woodchips and a mixture of these with 70% peat and 30% wood and ash from the localheating plant at Ume.

1986/87

1988/89

1989/90

1990/91

peatwoodash

pcat+woodash

pcat+woodash

pcal+woodash

K-40

6510107

39230

58674515

2831129140

n.m.41010

Ac-228

n.d.n.d.n.d.

51983

n.d.424

n.m.464

Ru-106

n.d.n.d.

294+51

n.d.2310

n.d.2822

n.m.

n.d.

Sb-125

6293

19626

n.d.424

1+1232

n.m.

16830

Cs-134

975226119

4779+247

29183910

1911164110

n.m.

253+4

Cs-137

271+30573114

122601629

131123788+8

132127375122

n.m.

2185+7

Ce-144

n.d.n.d.n.d.

n.d.3+1

n.d.2+1

n.m.n.d.

n.m.:n.d.:

not measurednot delected

Table 12. Activity concentration of radionuclides (Bq/kg) found in peat and variousash products from the local heating plant at Skellefte.

1986/87

1988/89

1989/90

1990/91

peatfly ash

bottom ash

pcaifly ash

bottom ash

peatfly ash

bottom ash

peatfly ash

bottom ash

K-40

992592

82248

21239719

1087111

36464012

n.m.

3023177

105320

Ac-228

n.d.n.d.n.d.

112ll191

61181n.m.

41221161

Ru-106

n.d.104123

188

n.d.n.d.n.d.

n.d.n.d.n.m.

n.d.n.d.n.d.

Sb-125

n.d.419n.d.

n.d.102n.d.

n.d.92n.m.

n.d.82n.d.

Cs-134

71+4920148533128

22111811265+1

81114212n.m.

8118611611

Cs-137

1871102374+221366170

114129461334011

58111016+10

n.m.

6912837136312

Ce-144

n.d.n.d.n.d.

n.d.n.d.n.d.

n.d.n.d.n.m.

n.d.n.d.n.d.

n.m.:n.d.:

not measurednot detected

Table 13. Activity concentration of radionuclides (Bq/kg) found in peat, wood chipsand various ash products from the local heating plant at Boden.

1986/87

1988/89

1989/90

1990/91

peatfly ash

bottom ash

woodfly ash

bottom ash

peatfly ash

bottom ash

woodfly ash

bottom ash

peatfly ash

bottom ash

woodfly ash

bottom ash

peatfly ash

bottom ash

woodfly ash

bottom ash

K-40

121948112919213

24111942107

1351+81

4755491093717

761018011271019110

4014600125953+10

42+1018411501615120

1813714110960110

40132230+41720122

Ac-228

6+335168+2

3+378+12

93116

n.d.25111611

n.d.48131214

21121122111

111501253+2

n.d.271118+1

21158+348+2

Ru-106

n.d.190+2592121

n.d.109+16

12+4

n.d.1313n.d.

n.d.50+820+8

n.d.1015n.d.

n.d.n.d.n.d.

n.d.n.d.n.d.

n.d.n.d.n.d.

Sb-125

n.d.16+3n.d.

n.d.21+4

n.d.

n.d.711n.d.

n.d.15+2211

n.d.612n.d.

n.d.812n.d.

n.d.n.d.n.d.

n.d.n.d.n.d.

Cs-134

711199+1138+2

16+1345+18

113+7

31173+132+1

3+11841315+1

5+160+13511

2+190+22811

1+117+15+1

11188+24011

Cs-137

3712887+46141+7

46+31268+

65389121

221147812200+22

19111100+610811

51115861333813

131182213257+3

711293+279+2

8111106+649513

Ce-144

n.m.

n.m.

n.m.

n.m.

n.m.

n.m.

n.d.n.d.n.d.

n.d.n.d.n.d.

n.d.n.d.n.d.

n.d.n.d.n.d.

n.d.n.d.n.d.

n.d.n.d.n.d.

n.m.: not measuredn.d.: not detected

Table 14. Activity concentration of radionuclides (Bq/kg) found in peat and variousash products from the local heating plant at Gallivaie.

1986/87

188/89

1989/90

1990/91

peatfly ash

peatfly ash

peatfly ash

peatfly ash

K-40

2211288119

16465610

30l38410

n.d.5591S

Ac-228

n.d.n.d.

n.d.20l

n.d.211

2130l

Ru-106

n.d.72111

n.d.613

n.d.n.d.

n.d.n.d.

Sb-125

n.d.1012

n.d.3+1

n.d.n.d.

n.d.n.d.

Cs-134

111195+5

3126+1

2+18+1

1+11+1

Cs-137

53+3469+20

251128312

241126811

41170+1

Ce-144

n.d.n.d.

n.d.n.d.

n.d.n.d.

n.d.n.d.

n.d.: not detected

Table 15. Enrichment factors of fuel to fly- and bottom ash. Figures within bracketsare not reliable.

Vstervik

Skvde

Eskilstuna

Enkping

Sandviken

Hudiksvall

Hrnsand

stersund

Ume

Skellefte

Boden

Gllivare

woodwood

woodwood

woodwood

woodwood

peatpeat

peatpeat

peatpeat

peatpeat

peatpeatwoodwood

pejit+woodpeal+wood

peatpeat

peatpeat

woodwood

peatpeat

K-40Cs

K-40Cs

K-40Cs

K-40Cs

K-40Cs

K-40Cs

K-40Cs

K-40Cs

K-40Cs

K40Cs

K-40Cs

K-40Cs

K-40Cs

K-40Cs

K-40Cs

86/87

fly-ash

3447

2843

1629

...

2715

1110

1212

nmnm

nmnm

2913

4026

8125

139

bot.ash

. . . .

1827

113

27t33t

545

97

22

242

6t47t39t21tnm

nm

918

165

568

nmnm

88/89

fly-ash

1831

...

2318

...

4720

1511

nmnm

105

nmnmnmnm

198

1223

2460

4110

botash

91

17t16t

246

18t16t

15543

129

nm

nm

283

nm

nm

nm

nm

13t29t

523

2010

136

nmnm

S9/90

fly-ash

1725

3572

24(72)

...

nm

nm

6411

nm

nm

1314

nm

nm

nm

nm

1818

1512

4453

138

DOLash

2:15

3685

19(29)

55t44t

nm

nm

415

nmnm

458

nm

nm

nm

nm

40t58l

nm

nm

247

3817

nm

nm

fly-ash

(59)20

2325

6514

...

nm

23

411

nm

nm

(88)7

nm

nm

nm

nm

nm

nm

1112

4029

56113

nm

18

90/91

botash

(83)17

2818

652

28t31t

nm

11

412

nmnm

(201)3

nm

nmnmnmnmnm

351

538

4351

nmnm

mean

31+12

4724

2O8

194

Ill

95

134

237

6337

115

nm: not measured t: total fly- and bottom ash

Table 16. Conversion factor for total produced ash (kg/MWh) which is eithercalculated or adopted, total activity per year (MBq) and activity per produced energyunit (kBq/MWh) of Cs-137.

Wood chips

ngelholmVstervikSkvde

EskilstunaEnkping

Boden

Peat

SandvikenHudiksvallHrnsandstersundSkellefte

BodenGllivare

Mixed

Ume

Con. fac.(kg/MWh)

7 (a)7 (c)7 (a)9 (a)9 (c)9 (a)

13 (c)12 (a)12 (a)12 (a)12 (a)10 (c)12 (a)

12 (a)

86/87

0.083.57

6.4211.00.90

24.70.8210.1

2.450.850.51

26

Total activity(GBq)

88/89

0.221.39

7.612.020.65

22.50.42

3.890.700.500.30

7.0

89/90

0.020.64

8.110.690.86

11.90.78

2.570.730.390.31

12

90/91

0.380.46

5.652.491.33

16.50.43

1.860.660.160.09

2.6

Activity per energy(kBq/MWh)

86/87

3.9258.0311610.4

1976.6325

257.04.7

147

88/89

2.7103.036457.7

1963.6

299.54.12.8

45

89/90

0.44.46.631306.1

1307.1

18105.22.7

89

unit

90/91

3.42.92.719518.6

1303.8

188.12.40.7

26

(a) adopted(c) calculated

information missing

Table 17. Total generated thermal energy, total amount of ash products produced peryear, total Cs-137 activity per year and activity concentration from 13 Swedish powerplants.Peat Category I: Sandviken and Hrnsand, II: stersund and Ume, III: Hudiksvall,Skellefte, Boden and Gllivare.Wood chips Catgory I: Enkping and Eskilstuna, II: Vstervik and Boden, III:ngelholm and Skvde.

Category

peatI

II

III

total

wood chipsI

II

III

total

86/87(GWh)(lO^g)

1992.39

2653.18

112113.5

158519.0

4363.49

12399.91

165813.3

333326.7

88/89(GWh)(lO^g)

2523.02

6457.74

105212.6

194923.4

4003.20

11849.47

150112.0

308524.7

89/90(GWh)U0kg)

2322.78

94411.3

146617.6

264231.7

4303.44

12269.81

180914.5

346527.7

90/91(GWh)(iokg)

2863.43

125715.1

147817.7

302136.3

5794.63

157912.6

226118.1

441935.4

86/87(GBq)(kBq/kg)

5020.9

4012.6

110.8

1015.3

226.3

191.0

171.2

582.2

88/89(GBq)(kBq/kg)

5016.5

263.4

50.4

813.5

165.0

121.3

80.7

361.5

89/90(GBq)(kBq/kg)

3512.6

474.2

120.7

943.0

133.8

121.2

70.5

321.2

90/91(GBq)(kBq/kg)

4312.5

251.7

70.4

752.1

204.3

90.7

70.4

361.0

Table 18. Activity concentration of Cs-137 in the fuel, pre-Chemobyl (old) activity ofCs-137, calculated old deposition, calculated total deposition and estimated depositionof Cs-137 from the aerial survey (SGAB, 1986).

Wood chips

ngelholmVstervikSkvde

EskilstunaEnkping

Boden

Peat

SandvikenHudiksvallHrnsandstersundSkellefte

BodenGllivare

Mixed

Ume

Act. cone.

(Bq/kg)

12802516856747

108950

29213671913954

277

Old

(%)

7581963477542327

21328

410681

4386215

74

Old deposition

(kBq/m2)

1.40.91.151.151.1

0.65

1.050.850.80.80.70.650.8

0.9

Depositionaerial survey

(kBq/m2)

0-22-50-23-105-300-2

20-602-5

30-402-102-100-20-2

10-20

Cs-137(kBq/m2)>10060-10030-603-30

- / Enkping Eskilstuna

Fig. 1 Heating plants in Sweden studied in this investigation and the deposition of Cs-137 after the Chernobyl accident.

KT-

10

ngelholm Vsterviko Skvde

o EnkpingEskilstuna

V

-\ 1 1 h-TH 1

o SandvikenHudiksvall

o Hrnsand stersund

- \

peat wood

fly ash

1 1 1 1 1 1

Skellefte Umefi

\

h

Boden,peat Boden,wood0 Gllivare

iI\-86/87 88/89 90/91 I 88/89 90/91 I 88/89 90/91 I 88/89 90/91 I 88/89 90/91 i 88/89 90/91

86/87 86/87 86/87 86/67 86/87

Fig. 2 Variations of the activity concentration of Cs-137 in the fuel and in the fly ash.

1000

"o"pa

euCo

I 100