Investigation of Polonium Removal Systems for LBE-Cooled Fast Reactors

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1 Investigation of Polonium Removal Systems for LBE-Cooled Fast Reactors 1 st COE-INES International Symposium Eric Loewen, Ph.D Tokyo, Japan November 2004 Research supported by JNC

2 Presentation Outline The INEEL The polonium issue in lead-bismuth reactors Experiments at the INEEL Initial modeling effort Summary 2

3 The Polonium Issue in LBE-Cooled Reactors Po Release - PbPo evaporation - PbPo+H 2 O H 2 Po+PbO Po Extraction Po Deposition CORE Accidental Pb-Bi spill Po Production Bi + n Bi Po t1 / 2 = 5 days t1 / 2 = 138 Po chemical form in LBE: 99.8% PbPo, 0.2% elementary Po β α days 206 3

4 Why Polonium Removal Processing as low as 0.01% of the coolant mass flow rate can reduce the Po source during accidents by two orders of magnitude Fast Flux=1e15 n/cm 2 s LBE Radioactivity (Ci/kg) Fast Flux=1e14 n/cm 2 s Fast Flux=1e13 n/cm 2 s LBE Mass: 10 6 kg LBE Flow Rate: 80,000 kg/s Efficiency of the Po removal system: 90% f=fraction of the LBE mass flowrate processed by the Po removal system f 4

5 Radiological Risk of Po-210 U.S. Nuclear Regulatory Commission Specific activities 137 Cs - 87 Ci/gram 60 Co - 1,130 Ci/gram 210 Po - 4,500 Ci gram Derived Air Concentrations (DAC s) 60 Co Bq/m Cs Bq/m Po - 10 Bq/m Pu Bq/m 3 5

6 Tellurium as a Surrogate of Polonium Po has no stable isotopes Tellurium and polonium are both Group VI elements. They are both solid and metallic at room temperature and pressure. Their most stable oxidation state is +4. Their atomic radii are comparable. There are similarities in their electrochemical behavior as indicated by their ph-potential diagrams. The Russians used Te as a Po surrogate for their alkaline extraction experiments. 6

7 Experimental Use of Tellurium Like Po, Te forms a stable intermetallic compound with Pb in lead-bismuth. PbTe grains LBE matrix 7

8 Alkaline Extraction This technique was first proposed by IPPE, Russia. - The reaction is: PbPo+4NaOH Na 2 Po+Na 2 PbO 2 +2H 2 O - LBE does not participate in the reaction. - The reaction was found to be impaired by the presence of oxides in the melt. So our experiments will be carried out in a reducing environment. 8

9 The INEEL Apparatus for Investigation of the Alkaline Extraction Mechanism 9

10 Experimental Run Main Steps - Load the LBE and tellurium into the crucible. - Energize the heaters to melt the metals and reach the desired temperature. - Add the NaOH. - Hold conditions for a selected time. - Turn off gas injection to allow for gravity separation of the NaOH from the metals. - Extract samples from the NaOH and metal regions. - Cooldown the apparatus. - Analyze the samples with the ICP and SEM, as needed. 10

11 Alkaline Experimental Steps 11

12 Two different NaOH sampling methods 12

13 A crucible removed from the reaction cell after cooldown 13

14 Post Experiment LBE and NaOH residual removed from crucible 14

15 Alkaline Extraction Experimental Results 15

16 Mass Spec data Exp. 25A 1.00E E-07 H 2 injection started 13: E-08 H 2 increase from heatup 494min 959min Ion Current 1.00E E-10 NaOH, 1&10min 100min 300min Argon Helium Hydrogen Nitrogen Oxygen Water 1.00E E E-13 Exp 25A Time (hours) 25A 16

17 Measured Te concentration in Experiments PPM Run 11 Run [Te] (ppm) The loaded amount Crucible Exp 11 &12 17

18 The solubility of Te in NaOH 1000 Loaded to [Te] = 1,200ppm [Te] (ppm) Exp.14, 550C Exp.15, 550C Exp.16, 450C Loaded to [Te] = 120ppm Exp.17, 450C Time (hrs) 18

19 Experiment 24 Te concentration plotted as a function of time [Te] ppm ,000 Time (min) 19

20 First Order Modeling dc =-kc 1 dt [Te] [Te] t 0 dc c =-k 1 t o dt -(ln[te] t - ln[te] 0) = k1t ln [Te] [Te] t o = -k t 1 20

21 Second Order Modeling -d[te] =k [Te] dt =k t 2 [Te] [Te] t o 21

22 A Idaho linear National Engineering plot and for Environmental a first Laboratory and second order fit of Te extraction data All time step data from Experiment 24 was used in the fit st order fit y = x R 2 = st Order Values nd order fit y = x R 2 = nd Oder Values Time (min) 22

23 A linear plot for a first- and second-order fit of Te extraction data st Order Values 2 First order fit y = x R 2 = y = x R 2 = Second order fit nd Order Values Time (min) 23

24 Second order rate constants compared to loaded Te concentration 1.0E E-03 2nd rate constant (sec-1) 1.0E E E ,000 10, ,000 Te concentrations (ppm) 24

25 Second order rate constants compared to LBE oxygen potential k (sec-1) E E E E E E E E-19 LBE Oxygen Potential (atm) 25

26 Arrhenius rate law k=se -E a/rt log k = -E 1 a + log s 2.3R T 26

27 Log k versus 1/T to determine E a 27

28 Back Reaction kc PbTe + 4NaOH Na2Te + Na2PbO + H 2O k r dc ( PbTe) dt = k ( c ) + k ( Na Te) f PbTe r 2 ( Na2Te) eq ( cpbte) 0 ( cpbte) eq k f = = = ( PbTe) ( c ) k eq PbTe eq r K 28

29 Gibbs-Helmholtz equation δ ( G / T) H = 2 δt Τ δ ( G / T) δ (1/ T ) δ (ln K ) δt p G = RT K = H ln p H = 2 RT ln H K = 2.303log K = + C p p RT -55 kj/mole 29

30 Log K versus 1/T to determine heat of reaction 30

31 Research products Fruitful collaboration between JNC and INEEL. Validation of the alkaline extraction process; NaOH delivery and sampling techniques for future experiments with Po; Rate constants for extraction of Te from LBE as for temperature, Te concentration, and oxygen potential; Validation of the Arrhenius empirical equation for Na 2 Te; Activation energy for the formation determined; Electro-deposition appears that Te will migrate. Three ICONE, one Nuclear Technology and one future (submittal planned in two months) publications 31

32 Thank You. We sincerely wish to acknowledge JNC for providing the funding to perform this fruitful research. 32

33 Electro-Deposition Experiments 33

34 ELECTRODEPOSITION EXPERIMENTS 34

35 Electrodes and thermocouple after cooldown 35

36 Electrodes used in the electrodeposition experiments 36

37 SEM Analysis of Mo Screen A B C D GA a

38 SEM Analysis of LBE Experiment 34 A B C D GA b

39 SEM Analysis of Cathode, No LBE Deposition A B C D GA c

40 SEM Analysis of Anode Showing LBE Deposition A B C 40

Estimation of 210 Po Losses from the Solid 209 Bi Target Irradiated in a Thermal Neutron Flux

Estimation of 210 Po Losses from the Solid 209 Bi Target Irradiated in a Thermal Neutron Flux Estimation of 210 Losses from the Solid 209 Bi Target Irradiated in a Thermal Neutron Flux Dmitri PANKRATOV, Sviatoslav IGNATIEV Institute of Physics and wer Engineering (IPPE), Obninsk 249033, RUSSIA