Total Gas Analysis-csyfinal
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Stepwise procedure Starting the instrument 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
Switch on the main power supply Switch on the water pump for water supply Switch on the power of the instrument Start the rotary pumps Switch on the power of diffusion/ejector pumps Turn the instrument knob on vacuum Open the both valves in side the glove box Measure the presser by Mc-leod gauge (wait till 1x10-5 mbar) Switch on the power of the QMS Switch on the power of the turbo molecular and rotary pump of the QMS Open the two valves of QMS Switch on the power of filament Switch on the power of pyrometer
Blank analysis 1. 2. 3.
4. 5. 6. 7.
Measure the presser by Mc-leod gauge (must get 1x10-5 mbar) Turn the instrument knob on analysis ( make system static ) Switch on the power of the induction furnace Turn the potentiometer on required temperature Heat crucible for 30 mnt Stop heating and measure the pressure with Mc-leod gauge ( blank rdg ) Feed the gases to QMS for spectra (gas composition )
The sample Loading 1. Lower the crucibl 2. Close the both valves in side the glove box 3. Open the central gate valve 4. Bring the crucible to loading side by horizontal and angular manipulators 5. Close the central gate valve to isolate furnace part 6. Bring the crucible in loading position 7. Open the gas cylinder and then valve of Ar gas 8. Open the loading flange 9. Load the sample in the crucible 10. Change the copper gasket 11. Close the loading flange 12. Close the valves of Ar gas 13. Visually check the sample through viewing window 14. Bring the crucible to furnace side by horizontal and angular manipulators 15. Take the crucible holder to loading side
1
16. Close the central gate valve 17. Open the both valves in side the glove box
Sample analysis 1. 2. 3.
4. 5.
6. 7. 8.
Measure the presser by Mc-leod gauge (must get 1x10-5 mbar) Turn the instrument knob on analysis ( make system static ) Switch on the power of the induction furnace Turn the potentiometer on required temperature Heat crucible for required temperature and temperature (30 mnt ,10000C) Stop heating and measure the pressure with Mc-leod gauge ( blank rdg ) Feed the gases to QMS for taking spectra (gas composition ) Feed the reading to calculate TG content in cc/gm and gas composition
Total or occluded or residual gas content of sintered nuclear fuel pellets is an important specification. The total gas content and its composition were determined employing hot vacuum extraction followed by quadrupole mass spectrometry. The specification of the gas content depends on the nature of the fuel and type of the reactor. In case of nuclear fuels, the total gas content is defined as the amount of non-condensible gases released when the pellet is heated under vacuum at required temperature and time and converting the gas content to STP. . The fuel has to meet stringent specifications, for both major and minor constituents. The trace constituents, if exceed the specified limits, affect the fuel properties and hence its performance under conditions prevailing in an operating reactor. These fuel pellets are enclosed in appropriate cladding material and the gap between the pellets and the clad is filled by suitable cover gas.
The total gas analyser is essentially a static ultra high vacuum system. The system should be free from any contamination from hydrogenous materials. Hence mercury diffusion pumps are incorporated in the system. Since the amount of total gas content is very small, the equipment should hold the vacuum under static conditions for several hours. The equipment can be divided
2
in to two parts, sample loading and gas extraction one. A gate valve separates these two parts. To load the sample, the sample port is opened in flowing inert gas atmosphere and the sample is loaded in to sample dropping manipulator which can be rotated fully by means of vacuum rotational manipulator. This part is closed and evacuated to 10-7mbar by turbomolecular pumping station. Tungsten crucible located in the gas extraction part of the system is brought to the sample loading side employing vertical, horizontal and angular vacuum manipulators after opening the gate valve. The sample is dropped into the tungsten crucible and taken back to the gas extraction part employing manipulators. The gate valve is closed. The crucible is taken into the induction coil zone employing the manipulator. The system is evacuated to 10-5 mbar by means of mercury diffusion pumps and a mercury ejector pump supported by a backing pump. The gas extraction part is made static by isolating it. The sample is then heated to the required temperature and time by induction heating. The temperature is measured by Optical Pyrometer. The gases released are extracted into a pre-calibrated volume by the mercury ejector pump, through a refrigerated cold trap, which condenses all condensible gases. The pressure is measured employing McLeod gauge. Small amount of this gas is then fed to the on-line quadrupole mass spectrometer through a micro leak valve. The quadrupole mass analyser has 90 mm long quadrupole having a resolution of M/∆M ≥ M at 10% valley height. From the volume of the system and the pressure exerted by the occluded gases, after making the correction for the blank, the total gas content is calculated employing gas laws, P1 × V1 / TI = P2 × V2 / T2 The gas composition is calculated from the peak intensities (ion current) at various m/e ratios after correcting for blank spectra. Necessary corrections are incorporated for the ion fractions arising due to the fragmentation of gas molecules. Since the ion current depends on the type of gas, they are normalised with respect to nitrogen whose sensitivity factor is taken as unity.
3
After the measurement of the pressure of the extracted gases, the gases were fed to online quadrupole mass spectrometer through a micro leak valve. The peak heights at m/e 2, 12, 14, 16, 20, 28, 32, 40 and 44 were monitored both in blank and sample. After correcting for the blank, the composition of gases was computed. It was observed that the main constituent of the released gases was hydrogen (>95%). The rest of the gases were a mixture of carbon monoxide, nitrogen and carbon dioxide. The pellet was subjected to the required temperature by induction heating. The temperature was attained within a fraction of a minute. After the extraction of the gases for the specified time, the integrity of the pellet was physically examined.
Occluded gas is mainly hydrogen. Hence it is more stringent specification in thermal reactors compared to fast reactors due to its reaction with the cladding material. The extraction of occluded gases is diffusion phenomena, which is proportional to the temperature. The oxide pellets are heated at relatively higher temperatures compared to carbides and hence shorter time periods are sufficient for quantitative release of gases. Occluded gas content can be substantially reduced if a vacuum degassing step is incorporated at the fag end of the pellet fabrication.
4
V
Extn. P IC
C
EV
MC
Load. P A M
V
V V LV
V
SP/RM PC D.P
HM TMP
R.S
Q.M.S
E.P
PR
V
G.V V M
G.B
TMP DP
RP RP
RP
TOTAL GAS ANALYSER SYSTEM
Load. P: Sample loading part, Extn. P: Gas extraction part, SP: Sample port, HM/AM/VM/RM: Horizontal/ angular/ vertical/ rotational Vacuum Manipulator; GV: Gate Valve; C: Tungsten Crucible; IC: Induction Coil; DP: Mercury Diffusion Pump; EP: Mercury Ejector Pump; TMP: Turbomolecular Pump; RP: Rotary Pump; V: Valve; LV: Leak Valve; MC: McLeod Gauge; EV: Extra Volume; RS: Refrigeration System; QMS: Quadrupole Mass Spectrometer; PC: Personal Computer; PR: Printer; GB: Glove Box.
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6
Switch on the main power supply Switch on the water pump for water supply Switch on the power of the instrument Start the rotary pumps Switch on the power of diffusion/ejector pumps Turn the instrument knob on vacuum Open the both valves in side the glove box Measure the presser by Mc-leod gauge (wait till 1x10-5 mbar) Switch on the power of the QMS Switch on the power of the turbo molecular and rotary pump of the QMS Open the two valves of QMS Switch on the power of filament Switch on the power of pyrometer
Blank analysis 1. 2. 3.
4. 5. 6. 7.
Measure the presser by Mc-leod gauge (must get 1x10-5 mbar) Turn the instrument knob on analysis ( make system static ) Switch on the power of the induction furnace Turn the potentiometer on required temperature Heat crucible for 30 mnt Stop heating and measure the pressure with Mc-leod gauge ( blank rdg ) Feed the gases to QMS for spectra (gas composition )
The sample Loading 1. Lower the crucibl 2. Close the both valves in side the glove box 3. Open the central gate valve 4. Bring the crucible to loading side by horizontal and angular manipulators 5. Close the central gate valve to isolate furnace part 6. Bring the crucible in loading position 7. Open the gas cylinder and then valve of Ar gas 8. Open the loading flange 9. Load the sample in the crucible 10. Change the copper gasket 11. Close the loading flange 12. Close the valves of Ar gas 13. Visually check the sample through viewing window 14. Bring the crucible to furnace side by horizontal and angular manipulators 15. Take the crucible holder to loading side
1
16. Close the central gate valve 17. Open the both valves in side the glove box
Sample analysis 1. 2. 3.
4. 5.
6. 7. 8.
Measure the presser by Mc-leod gauge (must get 1x10-5 mbar) Turn the instrument knob on analysis ( make system static ) Switch on the power of the induction furnace Turn the potentiometer on required temperature Heat crucible for required temperature and temperature (30 mnt ,10000C) Stop heating and measure the pressure with Mc-leod gauge ( blank rdg ) Feed the gases to QMS for taking spectra (gas composition ) Feed the reading to calculate TG content in cc/gm and gas composition
Total or occluded or residual gas content of sintered nuclear fuel pellets is an important specification. The total gas content and its composition were determined employing hot vacuum extraction followed by quadrupole mass spectrometry. The specification of the gas content depends on the nature of the fuel and type of the reactor. In case of nuclear fuels, the total gas content is defined as the amount of non-condensible gases released when the pellet is heated under vacuum at required temperature and time and converting the gas content to STP. . The fuel has to meet stringent specifications, for both major and minor constituents. The trace constituents, if exceed the specified limits, affect the fuel properties and hence its performance under conditions prevailing in an operating reactor. These fuel pellets are enclosed in appropriate cladding material and the gap between the pellets and the clad is filled by suitable cover gas.
The total gas analyser is essentially a static ultra high vacuum system. The system should be free from any contamination from hydrogenous materials. Hence mercury diffusion pumps are incorporated in the system. Since the amount of total gas content is very small, the equipment should hold the vacuum under static conditions for several hours. The equipment can be divided
2
in to two parts, sample loading and gas extraction one. A gate valve separates these two parts. To load the sample, the sample port is opened in flowing inert gas atmosphere and the sample is loaded in to sample dropping manipulator which can be rotated fully by means of vacuum rotational manipulator. This part is closed and evacuated to 10-7mbar by turbomolecular pumping station. Tungsten crucible located in the gas extraction part of the system is brought to the sample loading side employing vertical, horizontal and angular vacuum manipulators after opening the gate valve. The sample is dropped into the tungsten crucible and taken back to the gas extraction part employing manipulators. The gate valve is closed. The crucible is taken into the induction coil zone employing the manipulator. The system is evacuated to 10-5 mbar by means of mercury diffusion pumps and a mercury ejector pump supported by a backing pump. The gas extraction part is made static by isolating it. The sample is then heated to the required temperature and time by induction heating. The temperature is measured by Optical Pyrometer. The gases released are extracted into a pre-calibrated volume by the mercury ejector pump, through a refrigerated cold trap, which condenses all condensible gases. The pressure is measured employing McLeod gauge. Small amount of this gas is then fed to the on-line quadrupole mass spectrometer through a micro leak valve. The quadrupole mass analyser has 90 mm long quadrupole having a resolution of M/∆M ≥ M at 10% valley height. From the volume of the system and the pressure exerted by the occluded gases, after making the correction for the blank, the total gas content is calculated employing gas laws, P1 × V1 / TI = P2 × V2 / T2 The gas composition is calculated from the peak intensities (ion current) at various m/e ratios after correcting for blank spectra. Necessary corrections are incorporated for the ion fractions arising due to the fragmentation of gas molecules. Since the ion current depends on the type of gas, they are normalised with respect to nitrogen whose sensitivity factor is taken as unity.
3
After the measurement of the pressure of the extracted gases, the gases were fed to online quadrupole mass spectrometer through a micro leak valve. The peak heights at m/e 2, 12, 14, 16, 20, 28, 32, 40 and 44 were monitored both in blank and sample. After correcting for the blank, the composition of gases was computed. It was observed that the main constituent of the released gases was hydrogen (>95%). The rest of the gases were a mixture of carbon monoxide, nitrogen and carbon dioxide. The pellet was subjected to the required temperature by induction heating. The temperature was attained within a fraction of a minute. After the extraction of the gases for the specified time, the integrity of the pellet was physically examined.
Occluded gas is mainly hydrogen. Hence it is more stringent specification in thermal reactors compared to fast reactors due to its reaction with the cladding material. The extraction of occluded gases is diffusion phenomena, which is proportional to the temperature. The oxide pellets are heated at relatively higher temperatures compared to carbides and hence shorter time periods are sufficient for quantitative release of gases. Occluded gas content can be substantially reduced if a vacuum degassing step is incorporated at the fag end of the pellet fabrication.
4
V
Extn. P IC
C
EV
MC
Load. P A M
V
V V LV
V
SP/RM PC D.P
HM TMP
R.S
Q.M.S
E.P
PR
V
G.V V M
G.B
TMP DP
RP RP
RP
TOTAL GAS ANALYSER SYSTEM
Load. P: Sample loading part, Extn. P: Gas extraction part, SP: Sample port, HM/AM/VM/RM: Horizontal/ angular/ vertical/ rotational Vacuum Manipulator; GV: Gate Valve; C: Tungsten Crucible; IC: Induction Coil; DP: Mercury Diffusion Pump; EP: Mercury Ejector Pump; TMP: Turbomolecular Pump; RP: Rotary Pump; V: Valve; LV: Leak Valve; MC: McLeod Gauge; EV: Extra Volume; RS: Refrigeration System; QMS: Quadrupole Mass Spectrometer; PC: Personal Computer; PR: Printer; GB: Glove Box.
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