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