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26-04-17 Sodium Chemistry T.Gnanasekaran.ppt

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radhakrishnan unni
radhakrishnan unni

The document discusses sodium and its use as a coolant in fast breeder reactors. Sodium is chosen as the coolant due to its high heat transfer properties, low neutron moderation, and compatibility with steel. It describes the production of reactor-grade sodium through electrolysis and its transportation and storage. Sodium must be kept free of oxygen and other impurities to minimize corrosion. The document outlines the chemistry of sodium interactions with oxygen, nitrogen, and structural materials used in fast reactors like stainless steel and discusses measures to control corrosion like cold traps and maintaining low oxygen levels. Phase diagrams of sodium with various metals and oxygen are also presented.

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Chemical Properties of Sodium An Overview T. Gnanasekaran Raja Ramanna Fellow, IGCAR, Kalpakkam
Choice of sodium as fast reactor coolant Reactivity of sodium with ambient gases Manufacturing of sodium and its uses in other industries Handling and quality control of sodium Purification of sodium in coolant circuits Chemistry of sodium-steel system Chemistry of carbon in sodium Regeneration of cold traps Chemical interaction of sodium with nuclear fuels Sodium fires Topics to be covered
Na IHX Steam Generator Na pump Na pump H2O pump Schematics of a Fast Breeder Reactor
Fast Breeder Reactor and its coolant When neutron induced fission of 235U and 239Pu occurs, 2 to 3 neutrons of high energy generated. In thermal reactor, energy of fission neutrons are thermalised. Thermal neutrons propagate the controlled chain reaction. In a fast reactor, high energy neutrons are used in fission process. No moderation of neutron energy is allowed Hence no hydrogen bearing materials (eg H2O) allowed. Coolant of a FBR should be poor moderator. Fast reactor fuel contains large quantities of either 235U and/or 239Pu Expensive fuel. Hence power rating (i.e. extraction of power) should be high. So a coolant of extraordinary heat transfer characteristics needed.
Heat transfer at the interface with water as coolant Thermal conductivity Water: 0.0067 J/cm/s/oC at 50oC Sodium: 0.84 J/cm/s/oC at 200oC Fuel pellets Cladding
Choice of Sodium as Fast Breeder Reactor Coolant Sodium has excellent heat transfer properties (two orders higher than water) Comparatively higher mass and hence low moderation Neutron activation product, 24Na is short lived (half life = 15h) Though chemically reactive, pure sodium is compatible with steels. Sodium is inexpensive (Several tonnes of coolant are required) Amount of Sodium Used in FBTR : ~ 150 Tons Amount of Sodium for PFBR : ~ 1200 Tons 23Na - Fast neutron absorption cross section ~0.003 barn Thermal neutron cross section ~0.5 barn ~ 150 Rs/kg
Most abundant alkali group metal Present 2.3 % in the earths crust. Very reactive and never found free in nature. Sodium metal Downs Cell Production of sodium Metallic sodium finds extensive technical and industrial applications including manufacture of drugs & pharmaceuticals and nuclear reactors . Sodium for PFBR is imported from France
M. Pt of NaCl is very high (801oC) . Binary eutectic of NaCl-CaCl2 with 58 mass % of CaCl2 or Ternary electrolyte with 46 to 53 mass % BaCl2 23 to 26 % mass % CaCl2 24 to 28 mass % NaCl used Electrolysis temperature 580 to 610oC Production of sodium Ca (and Ba) impurity in the product
26-04-17 Sodium Chemistry T.Gnanasekaran.ppt
MSSA M辿taux Sp辿ciaux Sodium for PFBR is imported from France
Sodium Bricks Sodium bricks, packed in polythene bags and sealed in steel drums, are transported.
Molten sodium loaded in tankers (provided with heaters), cooled and transported in solid form. At the user site, sodium would be melted and transferred.
Electronic configuration of sodium atom Silvery shining metal Na sealed in glass ampoule 1s2, 2s2 2p6, 3s1 In lab. always stored under kerosene
Reactivity of sodium metal Instantaneously reacts with moisture in air. Forms NaOH and hydrogen gas. NaOH absorbs CO2 in air and forms NaHCO3 and Na2CO3. Reaction is highly exothermic. Unattended exposure to humid air can lead to fire. NaOH(s) + CO2(g) NaHCO3(s) Na(s) + H2O(g) NaOH(s) + 1/2 H2(g)
Instantaneously reacts with moisture in air. Forms NaOH and hydrogen gas. NaOH absorbs CO2 in air and forms NaHCO3 and Na2CO3. If left in air with low humidity, a thick layer of NaHCO3, NaOH and Na2CO3 is formed
Reaction with oxygen Highly exothermic Reaction with oxygen in air 4Na(l) + O2(g) 2Na2O(s) H = - 9459 kJ per kg of Na 2Na(l) + O2(g) Na2O2(s) H = -11279 kJ per kg of Na Subsequently products react with water vapour and CO2 in air Na2O(s) + H2O(g) 2NaOH(s/l) 2Na2O2(s) + 2H2O(g) 4NaOH(s/l) + O2(g) Na2O(s) + CO2(g) Na2CO3(s)
Nitrogen does not readily react with sodium and its solubility in sodium is extremely low (ppb levels) solubility similar to that of argon in sodium and is pressure dependent (directly proportional). (Though sodium azide Na3N is known, it decomposes on its contact with liquid sodium) Why nitrogen is not preferred as cover gas ? Chromium, manganese and molybdenum can form very stable nitrides. Though nitrogen is almost insoluble in sodium, nitridation of steel can occur at the sodium-nitrogen interfaces. (Sodium removes the passive Cr2O3 layer and exposes active metal surface) Interaction of nitrogen with sodium SS Passive Cr2O3 layer Cover Gas Na 2Cr2O3 + 3 Na 3NaCrO2 + Cr
For preparation of tetra ethyl lead and tetra methyl lead (antiknocking agents for gasoline) and many other organo-metallic compounds. In manufacture of refractory metal such as titanium, zirconium, hafnium and tantalum by reaction of their halides with sodium. Also used for manufacture silicon and potassium-sodium alloys. Calcium metal and calcium hydride, sodium hydride. As reducing agents in many preparation, manufacture of dyes, herbicides, pharmaceuticals etc. The reaction products of sodium metal with a suitable alcohol are the starting material for the production of large number of drugs and pharmaceuticals. Descaling of metals such as stainless steel and titanium. Uses of metallic sodium: MXn + nNa M + n NaX
Sodium box Liquid Sodium
Specifications of reactor grade sodium (partial list) Element Level (ppm) O < 2 C < 20 Ca 2 B < 5 Cl + Br 5 Ba, Pb, Li < 1 Quality control of sodium
Chemical analysis of sodium for metallic and non-metallic impurities VACUUM DISTILLATION Carbon: Residue burnt in oxygen and CO2 produced is measured manometrically. Oxygen: Residue (Na2O) dissolved in dil HCl and. analysed for Na and back calculated for oxygen Trace metals: Residue dissolved in dil. HCl and analysed for the elements by AAS / ICPMS / ICPOES Vacuum distillation of matrix sodium at 350o C (vapour pressure of sodium at 350oC ~ 0.1 mm Hg) Residue free from sodium taken for analysis Quality control of entire sodium supply for PFBR was carried out at RCL
26-04-17 Sodium Chemistry T.Gnanasekaran.ppt
Purification of sodium in coolant circuits Impurities have temperature dependent solubility By cooling and providing sites for nucleation, these impurities can be removed. Cold traps: Generally SS mesh packed. Sodium cooled and made to pass through. Would need several passes to achieve levels dictated by solubility (even if there is no steady leak into the system) Kinetics of precipitation Carbon cannot be removed by this method. 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 0.1 1 10 100 1000 10000 12001000 800 600 400 C H O Solubility / wppm 1000 K / T T / K
Choice of Structural Materials in Fast Reactors Sodium, when pure, highly compatible with steels Austenitic Stainless Steels (304 / 316) grades with 17-18% Cr, 8-12% Ni) used in the primary circuit Austenitic Stainless Steels prone to chloride stress corrosion and caustic cracking Ferritic Steels (2.25 Cr- 1Mo or 9 Cr 1Mo steels) used in steam generator section Coolant circuit characterised by large temperature gradients (T ~ 150 - 200oC) Use of different materials Corrosion and Mass Transfer Data on solubilities of alloying elements of steels in sodium required
Measured at IGCAR Solubilities of Fe, Cr, Ni, Mn and Mo in liquid sodium Iron solubility strongly dependent on oxygen concentration in sodium Austenite bulk Ferritic layer (NaFexOy)* complex dissolved in sodium are involved Ferrite layer formation in Na-Austenitic steel interface
Corrosion and Mass transfer in Sodium Circuits At low oxygen levels [O]Na < 5ppm Metal dissolution and transfer due to temperature gradient At higher oxygen levels, [O]Na > 5ppm Enhanced corrosion and rate dependent on oxygen conc Control of oxygen level by cold trapping & its continuous monitoring desired ~ 540oC 400oC 355oC 215oC 2o Na loop 165 bar ~ 620oC ~ 580oC 1o Na loop Turbine generator Condenser Reactor core Thermodynamic data on Na-M-O systems required. Sources of oxygen Argon cover gas circuit (Trace level oxygen impurity) Steam leak into sodium Log R = 2.85 + 1.5 log [O] 3.9 x 103 T-1 where R is in m/year.
Corrosion in aqueous systems unwanted electrochemical cells In neutral solution:
Corrosion Protection Enhanced corrosion of iron Reduced corrosion of iron
26-04-17 Sodium Chemistry T.Gnanasekaran.ppt
1/2(O ) 3 Na Ni O Na NiO Na O Na O Na NaNiO 2 2 2 2 2 2 Ni 2 NiO Na NiO 2 2 3 5 PHASE DIAGRAM OF Na-Ni-O SYSTEM PHASE DIAGRAM OF Na-Ni-O SYSTEM (623 < T < 923K) PHASE DIAGRAM OF Na-Fe-O SYSTEM Na FeO Na 4 3 Na FeO3 3 Na O 2 Na O 2 2 NaFeO NaO2 2 Fe Fe O Fe O FeO 3 1/2(O )2 3 4 2 PHASE DIAGRAM OF Na-Fe-O SYSTEM Phase Diagrams of Na-M-O systems established at IGCAR Na4FeO3 stable in Sodium Oxygen dependent corrosion of steels in sodium systems R. Sridharan, T. Gnanasekaran and C.K.Mathews, J. Alloys and Compounds, 191 (1993) 9-13. V.Ganesan, Ph.D. Thesis, University of Madras (1989) No ternary compound of nickel is stable in sodium Oxygen independent corrosion of nickel and nickel based alloys in sodium
PHASE DIAGRAM OF Na-Mo-O SYSTEM 1/2(O )2 Mo Na NaO2 Na MoO 2 4 Na O 2 2 Na O 2 MoO 3 2 Na Mo O 2 7 MoO 2 2 Na Mo O 3 6 Na MoO 4 5 at Temp > 681.1K Phase Diagrams of Na-M-O systems established at IGCAR PHASE DIAGRAM OF Na-Mo-O SYSTEM Na Na O 2 1/2(O )2 Na Mo O 2 7 2 MoO3 MoO2 Na Mo O 2 3 6 Na MoO 4 5 Mo NaO2 Na MoO4 2 Na O 2 2 at Temp < 681.1K T. Gnanasekaran, K. H. Mahendran, K. V. G. Kutty and C. K. Mathews, J.Nucl.Mater. 165 (1989) p.210.. T.Gnanasekaran, K.H.Mahendran, G.Periaswami, C.K.Mathews and H.U.Borgstedt, J.Nucl.Mater. 150 (1987) p.113. At high temperatures, Na4MoO5 is stable in liquid sodium
PHASE DIAGRAM OF Na-Mo-O SYSTEM 1/2(O )2 Mo Na NaO2 Na MoO 2 4 Na O 2 2 Na O 2 MoO 3 2 Na Mo O 2 7 MoO 2 2 Na Mo O 3 6 Na MoO 4 5 at Temp > 681.1K fGo m(Na4MoO5, s, T) determined by measuring equilibrium oxygen potentials using a high temperature emf cell T.Gnanasekaran et al, JNM 150 (1987)113 Measurement of Thermochemical Properties Pt,Ar + CO2 + O2, Na2CO3 // NASICON // Na2Mo2O7 + Na2MoO4, O2+CO2 + Ar, Pt Na(l),Ma4MoO5(s), Mo(s) // YDT// In(l),In2O3(s)
400 600 800 1000 1200 1400 -750 -700 -650 -600 -550 -500 Na - [Fe]SS - Na4 FeO3 Na - [Mo]SS - Na4 MoO5 Na - [Mn] SS - NaMnO 2 N a - N a 2 O Na - [Cr] SS - NaCrO 2 100 wppm 10 wppm 1 wppm 0.1 wppm RT lnpO 2 / (kJ.mol -1 ) Temperature / K Note: (NaFexOy)* complex dissolved in sodium are involved in corrosion process Influence of carbon in sodium in formation of NaCrO2 in low temperature section of sodium systems: [Cr]Na + [C]Na CrCx CrCx + [Na2O]Na NaCrO2(s) + x [C]Na + Na(l) 10 to 25 ppm [O]Na needed for NaCrO2 precipitation
Chemistry of carbon in sodium Carbon is an unavoidable impurity in sodium (Electrodes of carbon are used as anode in Downs cell) Carbon is an interstitial alloying element in structural steels. 300 series SS have a carbon content range of 0.03 to 0.08 wt%. Change in this conc. Would severely affect the mechanical properties. NON REVERSE RATCHET CONNECTION OD1850 3279 FLEXIBLE COUPLING BEARING & MECH. IMPELLER DIFFUSER MOTOR PUMP - PIPE ID 900 OD 2350 630/590 10960 1850 SHAFT 14239 5955 SEALS ASSEMBLY NON REVERSE RATCHET 3279 FLEXIBLE COUPLING BEARING & MECH. SEALS ASSEMBLY Shaft cooling by hydrocarbon oils Oil leak can lead to cracking and increase of carbon activity in sodium. Hence carburisation of steels. Centrifugal pump for sodium systems
CnH2n+2 CH4 + C2H6 + + C + H2(g) Oil leaks can be detected carbon meter and/or by monitoring for CH4 in argon cover gas Carbon in sodium Carbon in sodium has active form (dissolved) and inactive form (suspended carbonaceous material) Sodium from Indian sources have around 15 to 20 ppm of total carbon (solubility at around 500oC ~ 1ppm) Inactive form Active (dissolved) form Kinetics of the process unknown
Carbon in steels
Influence of carbon in sodium in formation of NaCrO2 in low temperature section of sodium systems: [Cr]Na + [C]Na CrCx CrCx + [Na2O]Na NaCrO2(s) + x [C]Na + Na(l)
Steam leak into sodium releases hydrogen 2Na + H2O 2 NaOH + H2 H2 + 2 Na 2NaH NaOH + 2 Na Na2O + NaH Steam Leak and need for Hydrogen Sensors Leak self- propagating in nature Detection of leak at its inception essential 2Na + H2O 2 NaOH + H2 Exothermic rx & highly corrosive product Dissolution kinetics of products into sodium: TNa > 450oC : Fast Instantaneous increase of H level in sodium Leak detection by In-sodium Hydrogen Sensor TNa < 250oC : Slow Gaseous H2 escapes into cover gas Leak detection by Cover Gas Hydrogen Sensor
Na IHX Steam Generator Na pump Na pump H2O pump Schematics of a Fast Breeder Reactor
Regeneration of cold traps: Oxygen impurity (Constant source: Impurities in argon cover gas) Hydrogen impurity ( steam side corrosion, steam leak and oil leak) Purification of cold trap should remove oxygen and hydrogen impurities. Saturation of the cold trap, reduces its efficiency. Can lead to flow blockage also. Contains Na2O, NaH and Na. Why not NaOH ? Na2O(s) + NaH(s) NaOH(s/l) + Na(l) NaOH unstable in sodium at low temperatures by calculation and experimentally studied. 3Fe + 4H2O Fe3O4 + 4H2
GO2 = RT lnPO2 G H2 = RT lnP H2
G H2 = RT lnP H2 GO2 = RT lnPO2
683 K G H2 = RT lnP H2 GO2 = RT lnPO2 Similarly Na2CO3 is also unstable in liquid sodium up to about 600oC. Na2CO3(s)+ 4 Na(l) 3 Na2O(s) + C
Na(l) - Na2O(s) NaOH(l)
NaH(s) Na(l) + H2(g) Hydride loaded cold trap regeneration: Heat under vacuum Temperature to be chosen so that sodium vapour does not interfere the process
Regeneration of cold trap loaded with mainly sodium oxide and less of hydride After draining the residual sodium, heat to a chosen temperature (above 723K) under pH2 above that in phase field 16 Temperature to be chosen so that sodium vapour does not interfere the process Continuously drain the liquid
Fuel-coolant chemical interaction In case of a breach of the clad, sodium would come into contact with fuel. Carbide and metallic fuels are quite compatible with sodium. In fact sodium bonded carbide fuels have been tested in Germany. Oxide fuel, (U,PuO2) with O/M ratio < 2 (~ 1.97 1.98) is used. In the reactor, O/M redistributes. O/M at the clad boundary is 2 and is lower at the centre. Sodium reacts with the fuel to yield Na3MO4(s) [ M= U,Pu] Low density material. In case of a pin hole, this product can block the pin hole. In case of a large breach of clad, this can escalate the extent of reaction.
Na-U-O Phase diagram
Sodium Fire Ignition Temperature of Na Varies as a function of oxygen and moisture content 205oC in dry air 320oC in damp air Ignition temp. reduction under stirred condition Reaction is highly exothermic. Unattended exposure to humid air can lead to fire.
Sodium fire is different from oil fire Burns only on the surface Produces dense white smoke (Na2O, Na2O2, NaOH and Na2CO3)
Spray fires Sodium leaks out as jet & hits the ceiling/walls of the containment cell Shower of sodium droplets falling downwards Small droplets and hence the burning area high Burning rate higher than in pool fires Types of Sodium Fires Pool fires Leaked sodium collects as a pool and leads to burning Burning rate in pool fires is low Burning area is confined to the pool surface
Spray Fire Sodium leaks out as jet & hits the ceiling of the containment cell Shower of sodium droplets falling downwards Small droplets and hence the burning area high Burning rate higher than in pool fires
Sodium Conduction O2 Na Oxide Na(g) Convection Combustion Plane Pool Surface Flame combustion model for sodium pool fire Combustion plane pool distance (l) (l) Sodium temperature Estimated distance (l) at 823 K ~ 50
Spray Fire Sodium leaks out as jet & hits the ceiling of the containment cell Shower of sodium droplets falling downwards Small droplets and hence the burning area high Burning rate higher than in pool fires
combustion model for sodium spray fire Oxygen supply diffusion controlled Na2O formed as major fraction
Thank you

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26-04-17 Sodium Chemistry T.Gnanasekaran.ppt

  • 1. Chemical Properties of Sodium An Overview T. Gnanasekaran Raja Ramanna Fellow, IGCAR, Kalpakkam
  • 2. Choice of sodium as fast reactor coolant Reactivity of sodium with ambient gases Manufacturing of sodium and its uses in other industries Handling and quality control of sodium Purification of sodium in coolant circuits Chemistry of sodium-steel system Chemistry of carbon in sodium Regeneration of cold traps Chemical interaction of sodium with nuclear fuels Sodium fires Topics to be covered
  • 3. Na IHX Steam Generator Na pump Na pump H2O pump Schematics of a Fast Breeder Reactor
  • 4. Fast Breeder Reactor and its coolant When neutron induced fission of 235U and 239Pu occurs, 2 to 3 neutrons of high energy generated. In thermal reactor, energy of fission neutrons are thermalised. Thermal neutrons propagate the controlled chain reaction. In a fast reactor, high energy neutrons are used in fission process. No moderation of neutron energy is allowed Hence no hydrogen bearing materials (eg H2O) allowed. Coolant of a FBR should be poor moderator. Fast reactor fuel contains large quantities of either 235U and/or 239Pu Expensive fuel. Hence power rating (i.e. extraction of power) should be high. So a coolant of extraordinary heat transfer characteristics needed.
  • 5. Heat transfer at the interface with water as coolant Thermal conductivity Water: 0.0067 J/cm/s/oC at 50oC Sodium: 0.84 J/cm/s/oC at 200oC Fuel pellets Cladding
  • 6. Choice of Sodium as Fast Breeder Reactor Coolant Sodium has excellent heat transfer properties (two orders higher than water) Comparatively higher mass and hence low moderation Neutron activation product, 24Na is short lived (half life = 15h) Though chemically reactive, pure sodium is compatible with steels. Sodium is inexpensive (Several tonnes of coolant are required) Amount of Sodium Used in FBTR : ~ 150 Tons Amount of Sodium for PFBR : ~ 1200 Tons 23Na - Fast neutron absorption cross section ~0.003 barn Thermal neutron cross section ~0.5 barn ~ 150 Rs/kg
  • 7. Most abundant alkali group metal Present 2.3 % in the earths crust. Very reactive and never found free in nature. Sodium metal Downs Cell Production of sodium Metallic sodium finds extensive technical and industrial applications including manufacture of drugs & pharmaceuticals and nuclear reactors . Sodium for PFBR is imported from France
  • 8. M. Pt of NaCl is very high (801oC) . Binary eutectic of NaCl-CaCl2 with 58 mass % of CaCl2 or Ternary electrolyte with 46 to 53 mass % BaCl2 23 to 26 % mass % CaCl2 24 to 28 mass % NaCl used Electrolysis temperature 580 to 610oC Production of sodium Ca (and Ba) impurity in the product
  • 10. MSSA M辿taux Sp辿ciaux Sodium for PFBR is imported from France
  • 11. Sodium Bricks Sodium bricks, packed in polythene bags and sealed in steel drums, are transported.
  • 12. Molten sodium loaded in tankers (provided with heaters), cooled and transported in solid form. At the user site, sodium would be melted and transferred.
  • 13. Electronic configuration of sodium atom Silvery shining metal Na sealed in glass ampoule 1s2, 2s2 2p6, 3s1 In lab. always stored under kerosene
  • 14. Reactivity of sodium metal Instantaneously reacts with moisture in air. Forms NaOH and hydrogen gas. NaOH absorbs CO2 in air and forms NaHCO3 and Na2CO3. Reaction is highly exothermic. Unattended exposure to humid air can lead to fire. NaOH(s) + CO2(g) NaHCO3(s) Na(s) + H2O(g) NaOH(s) + 1/2 H2(g)
  • 15. Instantaneously reacts with moisture in air. Forms NaOH and hydrogen gas. NaOH absorbs CO2 in air and forms NaHCO3 and Na2CO3. If left in air with low humidity, a thick layer of NaHCO3, NaOH and Na2CO3 is formed
  • 16. Reaction with oxygen Highly exothermic Reaction with oxygen in air 4Na(l) + O2(g) 2Na2O(s) H = - 9459 kJ per kg of Na 2Na(l) + O2(g) Na2O2(s) H = -11279 kJ per kg of Na Subsequently products react with water vapour and CO2 in air Na2O(s) + H2O(g) 2NaOH(s/l) 2Na2O2(s) + 2H2O(g) 4NaOH(s/l) + O2(g) Na2O(s) + CO2(g) Na2CO3(s)
  • 17. Nitrogen does not readily react with sodium and its solubility in sodium is extremely low (ppb levels) solubility similar to that of argon in sodium and is pressure dependent (directly proportional). (Though sodium azide Na3N is known, it decomposes on its contact with liquid sodium) Why nitrogen is not preferred as cover gas ? Chromium, manganese and molybdenum can form very stable nitrides. Though nitrogen is almost insoluble in sodium, nitridation of steel can occur at the sodium-nitrogen interfaces. (Sodium removes the passive Cr2O3 layer and exposes active metal surface) Interaction of nitrogen with sodium SS Passive Cr2O3 layer Cover Gas Na 2Cr2O3 + 3 Na 3NaCrO2 + Cr
  • 18. For preparation of tetra ethyl lead and tetra methyl lead (antiknocking agents for gasoline) and many other organo-metallic compounds. In manufacture of refractory metal such as titanium, zirconium, hafnium and tantalum by reaction of their halides with sodium. Also used for manufacture silicon and potassium-sodium alloys. Calcium metal and calcium hydride, sodium hydride. As reducing agents in many preparation, manufacture of dyes, herbicides, pharmaceuticals etc. The reaction products of sodium metal with a suitable alcohol are the starting material for the production of large number of drugs and pharmaceuticals. Descaling of metals such as stainless steel and titanium. Uses of metallic sodium: MXn + nNa M + n NaX
  • 20. Specifications of reactor grade sodium (partial list) Element Level (ppm) O < 2 C < 20 Ca 2 B < 5 Cl + Br 5 Ba, Pb, Li < 1 Quality control of sodium
  • 21. Chemical analysis of sodium for metallic and non-metallic impurities VACUUM DISTILLATION Carbon: Residue burnt in oxygen and CO2 produced is measured manometrically. Oxygen: Residue (Na2O) dissolved in dil HCl and. analysed for Na and back calculated for oxygen Trace metals: Residue dissolved in dil. HCl and analysed for the elements by AAS / ICPMS / ICPOES Vacuum distillation of matrix sodium at 350o C (vapour pressure of sodium at 350oC ~ 0.1 mm Hg) Residue free from sodium taken for analysis Quality control of entire sodium supply for PFBR was carried out at RCL
  • 23. Purification of sodium in coolant circuits Impurities have temperature dependent solubility By cooling and providing sites for nucleation, these impurities can be removed. Cold traps: Generally SS mesh packed. Sodium cooled and made to pass through. Would need several passes to achieve levels dictated by solubility (even if there is no steady leak into the system) Kinetics of precipitation Carbon cannot be removed by this method. 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 0.1 1 10 100 1000 10000 12001000 800 600 400 C H O Solubility / wppm 1000 K / T T / K
  • 24. Choice of Structural Materials in Fast Reactors Sodium, when pure, highly compatible with steels Austenitic Stainless Steels (304 / 316) grades with 17-18% Cr, 8-12% Ni) used in the primary circuit Austenitic Stainless Steels prone to chloride stress corrosion and caustic cracking Ferritic Steels (2.25 Cr- 1Mo or 9 Cr 1Mo steels) used in steam generator section Coolant circuit characterised by large temperature gradients (T ~ 150 - 200oC) Use of different materials Corrosion and Mass Transfer Data on solubilities of alloying elements of steels in sodium required
  • 25. Measured at IGCAR Solubilities of Fe, Cr, Ni, Mn and Mo in liquid sodium Iron solubility strongly dependent on oxygen concentration in sodium Austenite bulk Ferritic layer (NaFexOy)* complex dissolved in sodium are involved Ferrite layer formation in Na-Austenitic steel interface
  • 26. Corrosion and Mass transfer in Sodium Circuits At low oxygen levels [O]Na < 5ppm Metal dissolution and transfer due to temperature gradient At higher oxygen levels, [O]Na > 5ppm Enhanced corrosion and rate dependent on oxygen conc Control of oxygen level by cold trapping & its continuous monitoring desired ~ 540oC 400oC 355oC 215oC 2o Na loop 165 bar ~ 620oC ~ 580oC 1o Na loop Turbine generator Condenser Reactor core Thermodynamic data on Na-M-O systems required. Sources of oxygen Argon cover gas circuit (Trace level oxygen impurity) Steam leak into sodium Log R = 2.85 + 1.5 log [O] 3.9 x 103 T-1 where R is in m/year.
  • 27. Corrosion in aqueous systems unwanted electrochemical cells In neutral solution:
  • 28. Corrosion Protection Enhanced corrosion of iron Reduced corrosion of iron
  • 30. 1/2(O ) 3 Na Ni O Na NiO Na O Na O Na NaNiO 2 2 2 2 2 2 Ni 2 NiO Na NiO 2 2 3 5 PHASE DIAGRAM OF Na-Ni-O SYSTEM PHASE DIAGRAM OF Na-Ni-O SYSTEM (623 < T < 923K) PHASE DIAGRAM OF Na-Fe-O SYSTEM Na FeO Na 4 3 Na FeO3 3 Na O 2 Na O 2 2 NaFeO NaO2 2 Fe Fe O Fe O FeO 3 1/2(O )2 3 4 2 PHASE DIAGRAM OF Na-Fe-O SYSTEM Phase Diagrams of Na-M-O systems established at IGCAR Na4FeO3 stable in Sodium Oxygen dependent corrosion of steels in sodium systems R. Sridharan, T. Gnanasekaran and C.K.Mathews, J. Alloys and Compounds, 191 (1993) 9-13. V.Ganesan, Ph.D. Thesis, University of Madras (1989) No ternary compound of nickel is stable in sodium Oxygen independent corrosion of nickel and nickel based alloys in sodium
  • 31. PHASE DIAGRAM OF Na-Mo-O SYSTEM 1/2(O )2 Mo Na NaO2 Na MoO 2 4 Na O 2 2 Na O 2 MoO 3 2 Na Mo O 2 7 MoO 2 2 Na Mo O 3 6 Na MoO 4 5 at Temp > 681.1K Phase Diagrams of Na-M-O systems established at IGCAR PHASE DIAGRAM OF Na-Mo-O SYSTEM Na Na O 2 1/2(O )2 Na Mo O 2 7 2 MoO3 MoO2 Na Mo O 2 3 6 Na MoO 4 5 Mo NaO2 Na MoO4 2 Na O 2 2 at Temp < 681.1K T. Gnanasekaran, K. H. Mahendran, K. V. G. Kutty and C. K. Mathews, J.Nucl.Mater. 165 (1989) p.210.. T.Gnanasekaran, K.H.Mahendran, G.Periaswami, C.K.Mathews and H.U.Borgstedt, J.Nucl.Mater. 150 (1987) p.113. At high temperatures, Na4MoO5 is stable in liquid sodium
  • 32. PHASE DIAGRAM OF Na-Mo-O SYSTEM 1/2(O )2 Mo Na NaO2 Na MoO 2 4 Na O 2 2 Na O 2 MoO 3 2 Na Mo O 2 7 MoO 2 2 Na Mo O 3 6 Na MoO 4 5 at Temp > 681.1K fGo m(Na4MoO5, s, T) determined by measuring equilibrium oxygen potentials using a high temperature emf cell T.Gnanasekaran et al, JNM 150 (1987)113 Measurement of Thermochemical Properties Pt,Ar + CO2 + O2, Na2CO3 // NASICON // Na2Mo2O7 + Na2MoO4, O2+CO2 + Ar, Pt Na(l),Ma4MoO5(s), Mo(s) // YDT// In(l),In2O3(s)
  • 33. 400 600 800 1000 1200 1400 -750 -700 -650 -600 -550 -500 Na - [Fe]SS - Na4 FeO3 Na - [Mo]SS - Na4 MoO5 Na - [Mn] SS - NaMnO 2 N a - N a 2 O Na - [Cr] SS - NaCrO 2 100 wppm 10 wppm 1 wppm 0.1 wppm RT lnpO 2 / (kJ.mol -1 ) Temperature / K Note: (NaFexOy)* complex dissolved in sodium are involved in corrosion process Influence of carbon in sodium in formation of NaCrO2 in low temperature section of sodium systems: [Cr]Na + [C]Na CrCx CrCx + [Na2O]Na NaCrO2(s) + x [C]Na + Na(l) 10 to 25 ppm [O]Na needed for NaCrO2 precipitation
  • 34. Chemistry of carbon in sodium Carbon is an unavoidable impurity in sodium (Electrodes of carbon are used as anode in Downs cell) Carbon is an interstitial alloying element in structural steels. 300 series SS have a carbon content range of 0.03 to 0.08 wt%. Change in this conc. Would severely affect the mechanical properties. NON REVERSE RATCHET CONNECTION OD1850 3279 FLEXIBLE COUPLING BEARING & MECH. IMPELLER DIFFUSER MOTOR PUMP - PIPE ID 900 OD 2350 630/590 10960 1850 SHAFT 14239 5955 SEALS ASSEMBLY NON REVERSE RATCHET 3279 FLEXIBLE COUPLING BEARING & MECH. SEALS ASSEMBLY Shaft cooling by hydrocarbon oils Oil leak can lead to cracking and increase of carbon activity in sodium. Hence carburisation of steels. Centrifugal pump for sodium systems
  • 35. CnH2n+2 CH4 + C2H6 + + C + H2(g) Oil leaks can be detected carbon meter and/or by monitoring for CH4 in argon cover gas Carbon in sodium Carbon in sodium has active form (dissolved) and inactive form (suspended carbonaceous material) Sodium from Indian sources have around 15 to 20 ppm of total carbon (solubility at around 500oC ~ 1ppm) Inactive form Active (dissolved) form Kinetics of the process unknown
  • 37. Influence of carbon in sodium in formation of NaCrO2 in low temperature section of sodium systems: [Cr]Na + [C]Na CrCx CrCx + [Na2O]Na NaCrO2(s) + x [C]Na + Na(l)
  • 38. Steam leak into sodium releases hydrogen 2Na + H2O 2 NaOH + H2 H2 + 2 Na 2NaH NaOH + 2 Na Na2O + NaH Steam Leak and need for Hydrogen Sensors Leak self- propagating in nature Detection of leak at its inception essential 2Na + H2O 2 NaOH + H2 Exothermic rx & highly corrosive product Dissolution kinetics of products into sodium: TNa > 450oC : Fast Instantaneous increase of H level in sodium Leak detection by In-sodium Hydrogen Sensor TNa < 250oC : Slow Gaseous H2 escapes into cover gas Leak detection by Cover Gas Hydrogen Sensor
  • 39. Na IHX Steam Generator Na pump Na pump H2O pump Schematics of a Fast Breeder Reactor
  • 40. Regeneration of cold traps: Oxygen impurity (Constant source: Impurities in argon cover gas) Hydrogen impurity ( steam side corrosion, steam leak and oil leak) Purification of cold trap should remove oxygen and hydrogen impurities. Saturation of the cold trap, reduces its efficiency. Can lead to flow blockage also. Contains Na2O, NaH and Na. Why not NaOH ? Na2O(s) + NaH(s) NaOH(s/l) + Na(l) NaOH unstable in sodium at low temperatures by calculation and experimentally studied. 3Fe + 4H2O Fe3O4 + 4H2
  • 41. GO2 = RT lnPO2 G H2 = RT lnP H2
  • 43. 683 K G H2 = RT lnP H2 GO2 = RT lnPO2 Similarly Na2CO3 is also unstable in liquid sodium up to about 600oC. Na2CO3(s)+ 4 Na(l) 3 Na2O(s) + C
  • 44. Na(l) - Na2O(s) NaOH(l)
  • 45. NaH(s) Na(l) + H2(g) Hydride loaded cold trap regeneration: Heat under vacuum Temperature to be chosen so that sodium vapour does not interfere the process
  • 46. Regeneration of cold trap loaded with mainly sodium oxide and less of hydride After draining the residual sodium, heat to a chosen temperature (above 723K) under pH2 above that in phase field 16 Temperature to be chosen so that sodium vapour does not interfere the process Continuously drain the liquid
  • 47. Fuel-coolant chemical interaction In case of a breach of the clad, sodium would come into contact with fuel. Carbide and metallic fuels are quite compatible with sodium. In fact sodium bonded carbide fuels have been tested in Germany. Oxide fuel, (U,PuO2) with O/M ratio < 2 (~ 1.97 1.98) is used. In the reactor, O/M redistributes. O/M at the clad boundary is 2 and is lower at the centre. Sodium reacts with the fuel to yield Na3MO4(s) [ M= U,Pu] Low density material. In case of a pin hole, this product can block the pin hole. In case of a large breach of clad, this can escalate the extent of reaction.
  • 49. Sodium Fire Ignition Temperature of Na Varies as a function of oxygen and moisture content 205oC in dry air 320oC in damp air Ignition temp. reduction under stirred condition Reaction is highly exothermic. Unattended exposure to humid air can lead to fire.
  • 50. Sodium fire is different from oil fire Burns only on the surface Produces dense white smoke (Na2O, Na2O2, NaOH and Na2CO3)
  • 51. Spray fires Sodium leaks out as jet & hits the ceiling/walls of the containment cell Shower of sodium droplets falling downwards Small droplets and hence the burning area high Burning rate higher than in pool fires Types of Sodium Fires Pool fires Leaked sodium collects as a pool and leads to burning Burning rate in pool fires is low Burning area is confined to the pool surface
  • 52. Spray Fire Sodium leaks out as jet & hits the ceiling of the containment cell Shower of sodium droplets falling downwards Small droplets and hence the burning area high Burning rate higher than in pool fires
  • 53. Sodium Conduction O2 Na Oxide Na(g) Convection Combustion Plane Pool Surface Flame combustion model for sodium pool fire Combustion plane pool distance (l) (l) Sodium temperature Estimated distance (l) at 823 K ~ 50
  • 54. Spray Fire Sodium leaks out as jet & hits the ceiling of the containment cell Shower of sodium droplets falling downwards Small droplets and hence the burning area high Burning rate higher than in pool fires
  • 55. combustion model for sodium spray fire Oxygen supply diffusion controlled Na2O formed as major fraction