Embed Size (px)
Citation preview
Experience after 10 years of monitoring 14C in the
vicinity of the Nuclear Power Plant Krško, Slovenia
Ines Krajcar Bronić1, B. Obelić1, J. Barešić1, D. Borković1,
N. Horvatinčić1, A. Sironić1, A. Volčanšek2, B. Breznik2
1Ruđer Bošković Institute, Zagreb, Croatia 2Nuklearna elektrarna Krško, Krško, Slovenia
INTRODUCTION • Systematic monitoring 14C activity in atmospheric CO2 and in
biological samples (fruits – mostly apples; vegetables, cereals, corn) in the vicinity of the Nuclear Power Plant Krško (NEK) has been performed since 2006
• Aim: estimation of the influence of NEK on the environmental 14C level and on the effective dose of the local population due to ingestion (through food chain)
• Special attention paid to the estimation of the influence of the refuelling (performed in 18-month periods) on environmental 14C level.
• Here: show some characteristics of the 14C in the environment of NEK and some conclusions based on a 10-year monitoring
2
3
Sampling sites Krško and
Dobova.
We are here….
SAMPLING
4
• Atmospheric CO2 sampled on locations A and B within the NEK, in 2-month periods, more often during refuelling
• Biological material integrates 14C from the atmosphere during (relatively short) vegetation period; collected twice per year, usually in June or early July and in autumn, in September or early October, at the end of the vegetation period, just before harvesting, locations C – Q, in two circles around the NEK
• Biological samples also collected at the control site Dobova, 11.2 km SE from NEK, where no effect of air effluents is observed.
Sampling locations A, B – atmospheric CO2, C – O - plants
5
MEASUREMENT METHODS
• Atmospheric CO2 absorbed as Na2CO3 conversion to benzene
• Biological samples dried carbonized combusted to CO2 absorption in Carbosorb®E + Permafluor®E cocktails.
• Measurement of 14C activity by liquid scintillation counter (LSC) Quantulus 1220
6
Methods described in: • Horvatinčić, Nada; Barešić, Jadranka; Krajcar Bronić, Ines; Obelić, Bogomil.
Measurement of Low 14C Activities in Liquid Scintillation Counter in the Zagreb Radiocarbon Laboratory. Radiocarbon 46 (2004) 105-116.
• Krajcar Bronić, Ines; Horvatinčić, Nada; Barešić, Jadranka; Obelić, Bogomil. Measurement of 14C activity by liquid scintillation counting. Applied radiation and isotopes 67 (2009) 800-804.
40
60
80
100
120
1.1.2006
1.1.2007
1.1.2008
1.1.2009
1.1.2010
1.1.2011
1.1.2012
1.1.2013
1.1.2014
1.1.2015
1.1.2016
1.1.2017
0
2x1010
4x1010
6x1010
8x1010
a14C
atm (
mB
q/m
3)
NEK-A
NEK-B
Zagreb
A 1
4C
(B
q)
air-born effluent
atmospheric CO2
7
RESULTS
* Measured at the Jožef Stefan Institute, Ljubljana, Slovenia
Highest monthly 14C activity in the atmospheric CO2, a14Catm, at locations A and B within NEK-a vs. total annual 14C activity in air-born effluents (A14C).
Deviations from the correlation line at higher annual activities A14C may be explained by mismatch of periods of collection of the atmospheric CO2 and periods of the highest effluent activities
The highest measured a14Catm of atm. CO2 in the refuelling period gives a rough estimation of the 14C activity released in gaseous effluents
8
The higher the 14C activity of gaseous effluent, the higher the atmospheric 14C activity
Distribution of 14C activities in plants can best be observed by so-called polar diagrams.
Biological material
100
105
110
115
1200
30
60
90
120
150
180
210
240
270
300
330
100
105
110
115
120
7/2014 inner
outer
Dobova
a14C
(pM
C)
Summer sampling if there was no spring refuelling in the same year
Spatial distribution of a14C is determined by the prevailing winds (SW-NE).
100
105
110
115
1200
30
60
90
120
150
180
210
240
270
300
330
100
105
110
115
120
inner
outer
Dobova
a14C
(p
MC
)
7/ 2010
7/2010 Refuelling 4/2009 and 10/2010
7/2014 Refuelling 10/2013
9
RESULTS
0
30
60
90
120
150
180
210
240
270
300
330
100
105
110
115
120
125
130
135
100
105
110
115
120
125
130
135
DL
J
IC
inner
outer
Dobova
a14C
(pM
C)
0
30
60
90
120
150
180
210
240
270
300
330
100
105
110
115
120
125
130
135
100
105
110
115
120
125
130
135
K
N MF
HG
I
J
L
Da14C
(pM
C)
inner
outer
Dobova
C
0
30
60
90
120
150
180
210
240
270
300
330
100
105
110
115
120
125
130
135
100
105
110
115
120
125
130
135
R CE
DL
I
J
inner
outer
Dobova
a14C
(p
MC
)
0
30
60
90
120
150
180
210
240
270
300
330
100
105
110
115
120
125
130
135
100
105
110
115
120
125
130
135
I
R
J
E
DL
C
inner
outer
Dobova
a14C
(pM
C)
Sampling after spring (April) refuelling
2006 2009 2012
100
110
120
130
140
150
0
30
60
90
120
150
180
210
240
270
300
330
100
110
120
130
140
150
6/2012 inner
outer
Dobova
a14C
(pM
C)
0
30
60
90
120
150
180
210
240
270
300
330
100105110115120125130135140145150155
100105110115120125130135140145150155
9/2012 inner
outer
Dobova
a14C
(pM
C)
10
155
135
Spring refuelling - 2015
11
• higher a14C in samples taken in summer than in the autumn samples, because during spring plants use CO2 from the atmosphere immediately after the refuelling
• good correlation between the released A14C and the mean a14C of the inner locations
2015 100
105
110
115
120
1250
30
60
90
120
150
180
210
240
270
300
330
100
105
110
115
120
1257/2015
inner
outer
Dobova
a14C
(p
MC
)
100
105
110
115
120
1250
30
60
90
120
150
180
210
240
270
300
330
100
105
110
115
120
1259/2015
inner
outer
Dobova
a14C
(p
MC
)
115
Spring refuelling – before the vegetation period – significantly affects distribution of 14C activitis in plants in summer sampling, somewhat less in autumn sampling. Autumn refuelling – after the vegetation period – does not influence plant 14C activity in the next year. In years without a refuelling – a14C in the outer circle of NEK similar to the a14C at the control location Dobova, in the inner circle higher a14C values
7/20
0610
/200
67/
2007
9/20
077/
2008
10/2
008
6/20
099/
2009
7/20
109/
2010
7/20
119/
2011
6/20
129/
2012
7/20
139/
2013
7/20
149/
2014
7/20
159/
2015
6/20
169/
2016
100
105
110
115
120
125
130
a14C
(pM
C)
month/year
In
Out
Dobova
12
Comparison of the average plants a14C values in the inner circle (C, D, E, I, J, R), in the outer circle (F, G, H, K, L, M, N, O, P, Q) around NEK, at the control location Dobova, and the atmospheric a14C in Zagreb
Average a14C (pMC) 2006 – 2016
Inner circle 109.7 ± 4.1
Outer circle 106.4 ± 1.9
Control location - Dobova
103.6 ± 1.0
Zagreb (atm. CO2) 102.3 ± 1.2
13
14
to asses the effective dose (by consumption/ingestion):
• activity conc. in foodstaffs, a14C [Bq/kgC]
• relevant consumption rates – daily uptake of C by food:
0.3 kg (ICRP, 1996)
• ICRP ingestion dose coefficients are needed
e = 5.8 10-10 Sv/Bq
however, obtaining the consumption data for particular areas
may not be simple;
luckily – the specific 14C activity in all types of (terrestrial)
foodstaff is the same
Consumption model: 2 months NEK + 10 months Dobova
E = e × a14C × m × t
15
Comparison of annual effective doses due to ingestion of 14C for population in the close environment of NEK and at the control point Dobova. No significant difference is observed.
2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
14.4
14.6
14.8
15.0
15.2
15.4
15.6
refuelling
4/2015
refuelling
4/2012refuelling
4/2009
Eff
ective d
ose,
ingestion (S
v)
year
NEK
Dobovarefuelling
4/2006
16
Increase of 14C activity in atmospheric CO2 and in plants was observed during and immediately after the refuelling of the nuclear power plant
The influence is short-term and spatially limited
Spatial distribution depends on the local wind rose and the distance from the exhaust of the plant ventilation system
Higher activities in plants collected after the spring refuelling outage - intake of 14C from gaseous effluents during the vegetation period
Correlation between the total released A14C in air-born effluents and measured a14C in both atm CO2 and in plants has been observed
CONCLUSIONS
17
The maximum increase of total annual dose to local population due to the release of 14C from NEK (even in the years of spring refuelling) was estimated to be negligible and within the errors of the estimate
CONCLUSIONS
