1. CArbon-14 Source Term CAST
14C in TRIGA Irradiated Graphite and its Release under Alkaline Conditions
Name: C. Bucur, C.Ichim, I. Florea, L. Bujoreanu, D.Diaconu
Organisation: RATEN ICN Pitesti
Date:
The project has received funding from the European Union’s European Atomic Energy Community’s (Euratom) Seventh Framework Programme FP7/ under grant agreement no , the CAST project.

2. Outlines RATEN ICN involvement in CAST WP5
i-graphite samples available for experimental activities
total 14C measurement
leaching test
14C release rate
Inorganic/organic 14C released in alkaline conditions 2 2

3. RATEN ICN involvement in WP5
Task RATEN ICN reviewed:
the outcome of CARBOWASTE project in the Romanian context
the 14C content and speciation and their correlation with impurity content and irradiation history in the MTR i-graphite.
Results included in D5.5 “Review of current understanding of inventory and release of 14C from irradiated graphite”
Task RATEN ICN carried out leaching tests under aerobe and anaerobe conditions to assess the 14C release under alkaline conditions
Results are reported in D5.10 “Final report on C-14 release and inorganic/ organic ratio in leachates from TRIGA irradiated graphite” 3

4. Geometry of a graphite brick
i-graphite samples (1/2)
i-graphite from TRIGA thermal column
Block of 96 rectangular bricks of graphite encased in Aluminum
Each brick is composed by graphite pieces with different geometries
The graphite was imported in the ‘50s from a UK producer - documents of its origin were lost
Irradiation power: ~ 10MW
Strong neutron energy and flux variations
CARBOWASTE project: experimental and modeling activities regarding the radionuclide inventory in TRIGA i-graphite
No leaching tests were performed before CAST on i-graphite from TRIGA research reactor, ICN
Geometry of a graphite brick 4

5. i-graphite samples (2/2)
Few bricks from TRIGA thermal column was dismantled in and the i-graphite was stored in air since then
2 i-graphite cylindrical bars were used to cut:
intact samples for leaching tests
powder samples to measure the initial 14C content
Sample code
Diameter mm
Length mm
B1 (1B1 & 2B1) used in aerobe leaching tests 50
200
B2 (1B2 & 2B2)
used in anaerobe leaching tests 60
250 5

6. Total 14C measurement 6

7. Methodology for total 14C measurement (1/2)
Non-catalytic combustion by flame oxidation method
i-graphite samples are combusted in an oxygen-enriched atmosphere with a continuous flow of oxygen using Sample Oxidizer, Model 307 PerkinElmer®
Any hydrogen present is oxidized to H2O
Any carbon present is oxidized to CO2 7 7

8. Methodology for total 14C measurement (2/2)
3H2O - condensed in a cooled coil, washed into a counting vial where it is mixed with LSC cocktail (Monophase®S)
14CO2 - trapped by vapour-phase reaction with an amine (Carbo-Sorb® E ) and the resulting product (carbamate) is mixed with the LSC cocktail (Perma-fluor® E+) directly in the counting vial.
At the end of the combustion cycle, two separate samples - a 3H sample and a 14C sample - are trapped at ambient temperature, minimizing the cross contamination
14C and 3H activity is measured by LSC using Tri-Carb® 3110TR - allow in ULL counting mode a count rate between 1‑20 CPM above the Bkg 8 8

9. Tests on labeled graphite
Tests carried out using virgin graphite labeled with 14C as well as other gamma emitters
to optimize the mineralization process with total recovery of 14C
to assess the presence of potential interfering radionuclides in the 14C vials
The protocol for complete graphite oxidation was selected:
~ 0.15 g of graphite powder
10 ml CarbosorbE
10 ml PermafluorE+
~ 2 min combustion time
14C recovery - 97%
MEM < 0.04%
no gamma emitters identified in the 14C vials 9 9

10. Total 14C measurement in TRIGA i-graphite
4 powder samples from B1 i-graphite bar
12 powder samples from B2 i-graphite bar
14C uniform distributed in the two cylindrical bars
14C content:
B1: Bq/g
B2: Bq/g 10 10

11. Leaching experiments 11

12. Leaching tests conditions
Aerobe conditions
2 samples from B1 bar
surface area: cm2
volume: cm3
mass: / g
leachate volume: 1118 cm3 (Vleachant/Sspecimen = 0.1m)
room temperature: 25±50C
0.1 M NaOH (pH=13)
semi-dynamic: 30 ml of leachate removed for 14C measurement and 30 ml of fresh NaOH solution added at each sampling time
14C measurement in leachate solution by LSC using Tri-Carb® 3110TR 12 12

13. Leaching tests conditions
Anaerobe conditions
2 samples from B2 bar
surface area: cm2
volume: cm3
mass: / g
leachate volume: 1500 cm3 (Vleachant/Sspecimen = 0.1m)
room temperature: 25±50C
0.1 M NaOH (pH=13)
stirring before each sampling step
N2 flushing at the beginning of test and after each leachate renewal step;
semi-dynamic: 50 ml of leachate removed for 14C measurement and 50 ml of fresh NaOH solution added at each sampling time
14C measurement in leachate solution by LSC using Tri-Carb® 3110TR 13 13

14. Evaluation of results
cumulative leaching fraction in the n-step of the leaching
leaching rate in the n-step of the assay, cm/day,
ao - the initial amount of 14C in the i-graphite specimen, Bq
an - amount of a 14C that has been released from the i-graphite specimen in the n-step of the leaching test, Bq
tn - duration of the n-step of the assay, days
V - volume of the i-graphite specimen, cm3
S - apparent or geometrical surface of the i-graphite specimen, cm2
K - characteristic constant of the leaching test, cm/Bq. 14 14

15. Leaching tests results15 15

16. Aerobe leaching tests A0 = 7.79E+04 Bq
~ 1.3 kBq of 14C was released after 376 days of leaching, as dissolved species
~ 1.7% of the initial 14C content of the i-graphite
very similar results for 2 parallel tests - confirm the reproducibility of the leaching tests 16 16

17. Anaerobe leaching tests
A0 =2.4E+04 Bq
~ 0.45 kBq of 14C was released after 376 days of leaching, as dissolved species
~ 1.87% of the initial 14C content of the i-graphite
very similar results for 2 parallel tests - confirm the reproducibility of the leaching tests 17 17

18. Inorganic and organic 14C measurement18

19. Inorganic/organic 14C
Sequential extraction (combination of acid stripping and wet oxidation) from the same SIERs (A.Magnusson et all., 2008)
1st step: Acid stripping – inorganic fraction of 14C
14CO2 is absorbed in the first set of alkaline washing bottles
2nd step: Wet oxidation – organic fraction of 14C
K2S2O8 and AgNO3 combined with heating (~95C)
organic 14C are decomposed and it is absorbed in a second set of alkaline washing bottles placed after the catalytic furnace
catalytic furnace (holding Pt + CuO catalyst inside a quartz tube) – for complete oxidation of any reduced 14C compounds
vacuum of bar: to avoid any gas release from the system
N2 carrier gas : flow rate ml/hour

20. Preliminary tests for 14C recovery (1/2)
labeled solution with:
inorganic 14C: Na2CO3/ NaHCO3
organic 14C: CH3COONa and CH3-(CH2)10-COOH
3H: HTO
 emitters: 137Cs, 60Co, 241Am and 152Eu
To optimize the experimental conditions and chemicals used
To assess the 14C recovery
To evaluate the reproductibility of the method
Since SIERs could contain beside 14C also tritium, iodine and other beta emitters that interfere with 14C measurement by LSC the gas washing lines consists in iodine traps (both before and after the catalytic furnace) with silver nitrate (AgNO3), slightly acidic trap with sulphuric acid (5% H2SO4) for absorption of the tritium and other potential interfering radionuclides and four alkaline traps (two placed before the catalytic furnace and two after it) with 2M sodium hydroxide (NaOH)

21. Preliminary tests for 14C recovery (2/2)
Acid dissolution: 10 ml HNO3
Wet oxidation: 10 K2S2O8 5% + 4 AgNO3 (3 cycles)
inorganic 14C recovery: 98% (96 – 100%)
organic 14C recovery: 96%
MEM: < 1%
reproductibility: the standard deviation of the results of six identical tests were below 15%
good efficiency for 14C purification
no gamma emitters identified in solution sampled from alkaline gas washing bottles

22. Inorganic & organic 14C released in alkaline conditions
The ratio between inorganic and organic 14C release during the leaching test is almost constant during the test
Both organic and inorganic 14C species are released in alkaline conditions
Aerobe conditions:
more inorganic than organic 14C was released
inorganic 14C: 66% - 70% from the total 14C released as dissolved species, with an average of 67.89%
organic 14C: 30% - 34% from the total 14C released as dissolved species, with an average of 32.11%.
Anaerobe conditions:
more organic than inorganic 14C was released
inorganic 14C: 32% - 38% from the total 14C released as dissolved species, with an average of 35.24%
organic 14C: 61% and 66% from the total 14C released as dissolved species, , with an average of 64.57%

23. Conclusions ~ 35% inorganic 14C and 65% organic 14C
In alkaline conditions, very low amount of 14C is available for release from the i-graphite
aerobic conditions: ~ 1.70 % of the initial 14C content of the i-graphite subject of the leaching test was released as dissolved species
anaerobic conditions: ~ 1.85 % of the initial 14C content of the i-graphite subject of the leaching test was released as dissolved species
the leaching rates are high in the first days of immersion and decrease after that, indicating a two stage process: an initial quick release
less than 0.09 % of inventory/day for the first 40 days
followed by a slower release rate (around % of inventory/day).
more inorganic 14C was released under aerobe conditions
~ 68% inorganic 14C and 32% organic 14C
more organic 14C was released under anaerobe conditions
~ 35% inorganic 14C and 65% organic 14C

24. THANK YOU FOR YOUR ATTENTION!24 24