Post on 20-Apr-2020
Xiaolin Hou
Center for Nuclear Technologies,
Technical University of Denmark
Determination of pure beta emitters using
LSC for characterization of waste from
nuclear decommissioning
• Closed nuclear facilities:
100 mines;
90 commerical power reactor;
250 research reactors
a number of fuel cycle facilities
A few of them was decommissioned, and
most of them is on the way to be
decommissioned.
Steps of decommissioning of nuclear facility
• Preparation (investigating the background radioactivity around NPP)
• Plant Cleanout • Removal of most radioactive component such as spend fuel elements,
reactor internals, reactor vessel, etc. which is transferred for storage and disposal. (high level waste). (Evaluation of radioactivity before transferring)
• Decontamination • Removal of contamination from surfaces of facilities or equipment by
chemical or mechanical methods, which can reduce the waste volume and active level in the waste. (Measurement of radioactivity to evaluation the decontamination, and estimation of radioactivity in the waste)
• Dismantling • Equipments within the facility are dismantled and classified by estimation of
the radioactivity)
• Demolition and site clearance • Buildings demolished and radioactive wastes removed to storage or disposal
facilities after estimation of the radioactivity in the waste.
• Release of the site to alternative use (measure the radioactivity level in the released area)
Main radionuclides in the nuclear reactor
• Long-lived fission products 137, 135Cs,106Ru, 90Sr, 99Tc, 129I, etc.
• Neutron activation products 58,60Co, 133Ba, 134Cs, 152,154, 155 Eu, 3H,
14C, 36Cl, 41Ca, 63, 59Ni, 94Nb, 55,59Fe, 93Zr, 93Mo,54Mn, 110mAg, etc.
238-241Pu, 241Am, 243,244Cm, 237Np
Main Radionuclides in the nuclear waste and
used materials in the view of measurement
• Gamma radionuclides 60Co, 133Ba, 137Cs, 134Cs, 106Ru, 152,154, 155 Eu,
58Co, 54Mn,59Fe, 110mAg, 94Nb.
• Beta Emitter 3H, 14C, 36Cl, 41Ca, 55Fe, 63, 59Ni, 93Zr, 93Mo, 90Sr,
99Tc, 129I.
• Alpha emitter (actinides) 238-241Pu, 241Am, 243,244Cm, 237Np
Waste samples and the relevant critical
radionuclides for decommissioning
• Graphite (reactor)
• 3H, 14C, 55Fe, 63, 59Ni, 60Co, 152Eu
• Concrete (normal or heavy)
• 41Ca, 60Co, 55Fe, 63, 59Ni, 133Ba, 152Eu
• Steel/stainless steel
• 55Fe, 63, 59Ni, 36Cl, 93Zr, 93Mo, 94Nb, 60Co, 152Eu, transuranics
• Aluminium
• 60Co, 36Cl, 63Ni, 55Fe,
• Lead,
• , 60Co, 63Ni, 55Fe
• Water
• 3H, 14C, 63Ni, 99Tc, 36Cl, 129I, 90Sr, 60Co, 137Cs, transuranics
• Ion exchange resin
• 55Fe, 63,59Ni, 14C, 99Tc, 36Cl, 93Zr, 93Mo, 94Nb 90Sr, 129I, 137Cs, 60Co, 135Cs, transuranics
Determination using chemical separation and LSC
55Fe
63Ni
41Ca, 90Sr
36Cl, 129I
Production of 63Ni and 55Fe in
Nuclear Reactor (neutron activation)
• 63Ni:
• 62Ni(n, g)63Ni (s=14.5 b; h62Ni=3.63%)
• 63Cu(n, p)63Ni, ( h63Cu=69.17%)
• 55Fe:
• 54Fe(n, g)55Fe (s=2.3 b; h54Fe=5.85%)
• 56Fe(n, 2n)55Fe, (h56Fe=91.75%)
Decay of 63Ni and 55Fe
Fe-55 decays by electron
capture emitting X-rays,
conversion electrons and
Auger electrons (5 - 6 keV)
X ray (5.89 keV, 25.4%)
55Fe (2.73 y)
55Mn (stable)
EC (232 keV, 100%)
No gamma ray
b- (66.95 keV, 100%)
No gamma ray
63Ni (100.1y)
63Cu (stable)
Analytical method for 63Ni and 55Fe
• Analytical procedure:
• Decomposition of sample
• Separation of Ni or Fe from matrix elements and all other
radionuclides
• Preparation of a suitable solution for LSC measurement.
Mearement methods
55Fe: X-ray spectrometry ( <1%);
LSC (30-45%)
63Ni: gass flow counting(anti-coincidence, <10-50%)
Ion implanted silicon detector (1-6%)
LSC (60-80%)
Separation of Ni and Fe by
anion exchange chromatography
• Ni can be completely separated from Fe, Co, Cu, Zn, U, Pu, etc.
• Fe can be separated from Ni, Cr, Mn, Th, etc.
Element Content, %
Ni fraction Fe fraction
Fe3+ <0.001 >98.5
Ni2+ >99.5 <0.001
Co2+ <0.01 <0.1
Ba2+ <7.5 <0.001
Eu3+ >99.8 <0.001
Cs+ >99.5 <0.001
Sr2+ >99.5 <0.001
0
20
40
60
80
0 10 20 30 40 50eluate, ml
perc
enta
ge %
Ni
Co
Fig. Separation of Ni from Co by ion exchange, eluted by 9 N HCl (3-20ml) for
Ni and 2 N HCl (21-44 ml) for Co. Bio-Rad AG1x4, 1x15 cm column
0
10000
20000
30000
40000
0 20 40 60 80 100
Volum, ml
co
un
ts
Eu-152
Ba-133Co-60
Separation of Eu, Ba, Co by anion exchange chromatography, Bio-Rad
AG1x4, 1x15 cm, 0-40ml:9M HCl, 40-70ml:4M HCl, 70-90ml, 0.05M HCl
Separation of Ni using Ni-DMG complex
• Ni can form a stable specific
complex with dimethylglyoxime.
By Ni-DMG precipitation or
organic solvent extraction of Ni-
DMG complex at low
concentration, Ni can be
separated from many other
elements.
• While, some other metals, such
as Co, Cu can also form a
complex with DMG and
interferring the separation of Ni.
Purification of Ni using Ni-Resin
The Nickel Resin contains the DMG inside the pores of a polymethacrylate
resin. The nickel-DMG precipitate occurs on the resin , where it is held and
readily separated from other elements in the supernatant.
1. Loading of
solution
2. Washing with 0.2
M ammonium
citrate to remove
other elements
3. Eluting Ni
using HNO3
4. Evaporte eluted
Ni-DMG solution to
0.1-0.2 ml for LSC
Purification of Ni by specific
Ni-extraction chromatography
Element Recovery or
decontamination factor
Ni2+ > 98.5%
Fe3+ 104
Co2+ 103
Ba2+ 104
Eu3+ 104
Cs+ 104
Sr2+ 104
Ni specific extraction
chromatography has a
higher decontamination to
most of elements, such as
Fe, Co, Cu, Cr. Mn, Ba, Eu,
transuranics, etc.
•A higher recovery of Ni can
be obtained in the
procedure.
Hou et al., Anal. Chim. Acta, 2005
Preparation of separated 55Fe for LSC
0
10
20
30
40
0 10 20 30 40 50 60 70
Content of Fe (mg)
Eff
icie
ncy,
%FeCl3 solutionFe3+ +H3PO3(2M)FeSO4
Quench correction for Fe-55
...T0\Q111101N.001 12
...T0\Q030301N.001 12
...T0\Q040401N.001 12
...T0\Q080801N.001 12
...T0\Q101001N.001 12
...T0\Q121201N.001 12
Sample Spectrum
1,000950900850800750700650600550500450400350300250200150100500
7
6
5
4
3
2
1
0
10
20
30
40
50
650 700 750 800 850
SQP(E)
Eff
icie
ncy,
%
Quench curve of Fe-55
Graphite sample
with 2 mg Fe carrie
...T0\Q080801N.001 12
...T0\Q111101N.001 12
...T0\Q121201N.001 12
...T0\Q151501N.001 12
...T0\Q161601N.001 12
...T0\Q171701N.001 12
Sample Spectrum
1.000950900850800750700650600550500450400350300250200150100500
10
8
6
4
2
0
Quench curve of Ni-63
y = -9E-07x3 + 0.0015x2 - 0.6991x + 95.98
20
30
40
50
60
70
80
500 530 560 590 620 650 680 710 740 770 800 830 860 890
SQP(E)E
ffie
ncy, %
Quench correction for Ni-63
Graphite sample
with 2 mg Ni carrie
Recovery of Fe and Ni and decomtamination factors
for main interferring radionuclides and elements
Interference Recovery/decontamination factor Interference Recovery/decontamination factor
Fe fraction Ni fraction Fe fraction Ni fraction
55Fe 85-95% >105 133Ba >106 >105
63Ni >105 80-95% 134,137Cs >106 >106
58,60Co >105 >105 89,90Sr >106 >106
152,154Eu >106 >105 41,45Ca >106 >106
151Sm >106 >105 36Cl >106 >106
54Mn >105 >106 3H >106 >106
51Cr >106 >105 14C >106 >106
For all interferring radionuclides, the decontamination factors higher
than 105.
EC (421.4 keV, 100%)
41Ca (21.03x105y)
41K (stable)
Nuclide Target isotope
Aboundance % Reaction Cross
section, bar Half life Decay
41Ca 96.94 40Ca(n, g)41Ca 0.41 1.03105 y EC
45Ca 2.086 44Ca(n, g)45Ca 0.84 162.7 d b-
47Ca 0.004 46Ca(n, g)47Ca 0.7 4.54 d b, g
49Ca 0.187 48Ca(n, g)49Ca 1.0 8.72 min. b, g
41Ca in the concrete Activation products of calcium isotopes
Energy of X-rays and Auger electrons : 0.3-3.6 keV
Determination: X-ray spectrometry (<0.08%)
LSC (10-20%)
Sr & Ca: Alkline earth element
Determination 41Ca in concrete
• Separation fro matrix
• Decomposition of heavy concrete by alkali fussion
• Leaching Ca by acids
• Separation from active metals such as 60Co, 152Eu, 55Fe, 63Ni, 65Zn, 54Mn, 51Cr,etc.
• Precipitation with Fe(OH)3 by hydroxides at pH9
• Separation from other alkaline metals, such as 133Ba, 226Ra and 90Sr.
• BaCrO4 and SrCrO4 precipitation
• BaCl2 and SrCl2 precipitation in HCl solution
• Ca(OH)2 precipitation in NaOH solution
Concrete in the
reactor
• Ordinary concrete
• Heavy concrete (50-
70% BaSO4 was
added)
Decomposition of concrete for 41Ca
and other radionuclides
• For ordinary concrete,
silicates of calcium does
not easily be
decomposed by acids
• For heavy concrete,
some calcium exists as
CaSO4, which does not
dissolved by acid.
• Alkaline fusion have to
be used for the
decomposition of
concrete for the
determination of calcium
isotopes.
Concetre
Add Na2CO3/NaOH, fuse
at 700 oC for 2-3 hours
Fused sample
Precipitate,
CaCO3, BaCO3
Fitrate, Na, K,
Mg, Al, SO42-
etc.
Leaching with water, filter
through a filter paper and
wash with water
Solution, CaCl2
Dissolve with HCl
Separation
procedure
Element Recovery, % Element Decontamination
factor
Ca 97.73.9 137Cs (4.50.3)105
85Sr 97.92.1 60Co (1.20.4)105
133Ba 97.32.8 152Eu (8.50.5)105
59Fe (2.50.1)105
63Ni (2.50.2)105
Separation of Ca and Sr from other metals by
hydroxides precipitation
• Separation of Sr from Ca by Ca(OH)2 precipitation
• Ca(OH)2: insoluble, Ksp = 5.2 10-6
• Sr(OH)2 and Ba(OH)2: Soluble in alkine solution
The new method for the separation of Ca from Sr and Ba
0
20
40
60
80
100
0.00 0.50 1.00 1.50 2.00
Re
co
ve
ry o
f C
a,
%
Concentration of NaOH, mol/l
1 Ca(OH)2 precipitation
2 times precipitation
3 time precipitation
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
0.00 0.40 0.80 1.20 1.60 2.00
Deconta
min
atio
n facto
r of S
r
Concentration of NaOH, mol/l
1 precipitation 2 precipitations 3 precipitations
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
0.00 0.40 0.80 1.20 1.60 2.00
Deco
nta
min
atio
n fa
cto
r o
f B
a
Concentration of NaOH, mol/l
1st precipitation 2nd precipitation 3rd precipitation
Precipitate Ca as Ca(OH)2 at 0.5 –
0.8 mol/l NaOH, repeat 3 times, 85%
Ca can be recovered, and the
decontamination factor for Sr and Ba
are higer than 5x104
Spectra of 41Ca in heavy concrete from DR-2
...A6\Q024201N.002 12
...A6\Q044401N.002 12
...A6\Q054501N.001 12
Sample Spectrum
1,000800600400200
0.287
0.266
0.246
0.225
0.205
0.184
0.164
0.143
0.123
0.102
0.082
0.061
0.041
0.02
0
Features of Method for 41Ca
• A separation of 41Ca from concrete is easy to
operate
• Good decontamination from interferring
radionuclides (>104)
• The chemical yields of the separation procedures
for 41Ca is 80-90%.
• The detection limits for 41Ca is 0.020 Bq.
Hou X.L., Radiochim Acta, 2005
36Cl is long-lived radionuclides (3x105 yrs)
36Cl decays mainly by pure beta emission of
Emax=708.6 keV.
36Cl measurement is normally carried out by
LSC and AMS
Determination
of 36Cl
Determination of 36Cl and 129I in graphite
--- Sample decomposition
Ashing at 900°C: ---iodine and part of Cl are lost.
Decomposition at 900°C with O2 and trapping iodine in NaOH
solution: ---good recovery for iodine, but not good for chlorine
Leaching with acid (HNO3) at heating: --- not complete remove
iodine and Cl from graphite, and loss of the leached iodine.
Digestion with HNO3 and trapping iodine and chlorine with
NaOH: ---- Not complete removal of iodine and chlorine
• How to Do?
Determination of 36Cl and 129I in graphite
--- Sample decomposition
• Graphite can be completely dissolved in a mixture of
acids: HNO3+H2SO4 +HClO4
• The optima ratio of mixture is:
H2SO4:HNO3:HClO4 =15:4.1
• A closed dissolution system is used for dissolve
graphite in heating, Cl on the condenser tube and trap
solution, while iodine mainly in the trap solution.
1-Heating mantle; 2-three-necked flask; 3-sample in acid mixture; 4-
bubbling tube; 5-separating funnel for adding acids; 6,7-reflux condenser; 8-
receiver; 9-wash bottle containing water; 10, 11-absorption bottles
containing 0.4 mol/l NaOH
Schematic diagram of dissolution system
of graphite for determination of 36Cl and 129I
Determination of 36Cl and 129I in concrete
--- Sample decomposition
Leaching with acid (HNO3) at heating: --- not complete
remove iodine and Cl from graphite, and loss of the
leached iodine.
Digestion with HNO3 and trapping iodine and chlorine with
NaOH: ---- Not complete removal of iodine and chlorine
Alklinal fussion using NaOH and Na2CO3, dissolution of
fused cake in water, the supernatant is used for 129I and 36Cl: ---- sample is completely decomposed and iodine and
Cl are released. Iodine and Cl are not lost in alkaline
medium
Determination of 36Cl and 129I in stainless steel
--- Sample decomposition
Stainless steel is normally dissolved with HCl or
HCl+HNO3: --- could not be used for 36Cl because of too
much Cl in HCl is introduced.
Single acid, HNO3, could not dissolve stainless steel.
10M H2SO4 with H3PO4 is sucessfully used for dissolve
stainless steel for129I and 36Cl: ---- sample is completely
decomposed and iodine and Cl are released.
Separation of Cl from matrices and other radionuclides
Specific precipitation of Cl- with Ag+ (AgCl) can be used to
selectively separation of Cl from matrix and other radionuclides (except
iodine and bromine).
Iodine (129I) should be first separated from the solution before AgCl
precipitation.
No need to separate Br, since no long-lived radioisotopes of Br in the
waste and environmental samples.
The separated AgCl can be dissolved in NH4OH and mixed with
scintillation cocktail for LSC: But less AgCl can be used and high
quench effect. How to improve?
0.0
1.0
2.0
3.0
4.0
0 20 40 60 80 100 120 140 160
volume, ml
Cl-
36
, B
q o
r A
g, x
10
0 m
g
100mg Cl, 0.2 M NH4NO3-0.6 M NH4OH eluting
200mg Cl 0.2 M NH4NO3-0.6 M NH4OH eluting
50 mg Cl, 0.1 M NH4NO3-0.6 M NH4OH eluting
100 mg Cl, 0.1 M NH4NO3-0.6 M NH4OH eluting
b)
c)
d)
a)
Ag+
Cl-
Separation of Ag+ and Cl– in anion
exchange chromatography
Combined Analytical procedure for 36Cl and 129I
Add stable Cl and I carriers, dissolve with acids, combine the absorption solutions and dissolved solution
AG 14 column
Effluent, 36Cl
Wash with NH3
Eluting with 0.1 M
NH4NO3-0.6 M NH4OH
Washes,
Ag+ etc.
discard
Evaporate, dissolved with
H2O ICP-MS for Cl
LSC for 36Cl
Aqueous phase, 129I
ICP-MS for I
LSC for 129I
Graphite, steel Heavy Concrete
Add stable Cl and I carriers and NaOH and Na2CO3, fuse at 500 C, leaching with H2O, cenrifuge to separate the supernatant
Add NaHSO3, transfer to a separation funnels, add CCl4, HNO3, and NaNO2 to extract, repeat the extraction
Organic phase, Aqueous phase,
Back-extract with NaHSO3 solution, repeat extraction and back-extraction
Add Ag+, centrifuge, dissolve AgCl with NH3, separate solution, add HNO3 to re-precipite AgCl, re-dissolve AgCl with NH3, load to the column
Hou et al., Anal. Chem., 2007
Performance of the procedure for 36Cl
Recovery of Cl: >70%
Decontamination factors for most of radionculides: >106
Detection limit using LSC : 14 mBq
Decommissioing samples, concrete, graphite, stainless steel,
aluminum, lead, have been sucessfully analysed for 36Cl
Combined analytical procedure for 36Cl, 129I, 41Ca, 63Ni and 55Fe
Sampling of concrete and graphite from danish reactor, DR-2
Core
A
Core
B
Results of 55Fe, 63Ni, 36Cl
and 41Ca in concrete from
Aanish reactor, DR-2
0
0
1
10
100 150 200 250 300
Distance to core, cm
Ac
tiv
ity
of
41C
a,
Bq
/g Core A
Core B
41Ca in concrete core
Sample
No
55Fe 63Ni
Recovery
,%
Bq/g Recovery
,%
Bq/g
DR-3-
T
92.2 545000 94.63 5552
Iy7.5 90.4 0.53 93.89 92.5
Iy5.5 90.6 1.05 93.74 22.3
Yi7.5 92.5 1.92 93.35 7.71
Yi5.5 91.3 9.21 91.56 43.1
55Fe and 63Ni in graphite of DR-2
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
100 150 200 250 300
Distance to core, cm
Acti
vit
y c
on
cen
trati
on
, B
q/g
55Fe
63Ni
36Cl
Free release criteria:
63Ni<10 Bq/g; 55Fe<1000 Bq/g
• More then 65% of concrete
shield was treated as non-
radioactive waste