The gas components analysis apparatus

The gas components analysis apparatus consists of a gas extraction unit, a gas collection and a volumetric measurement unit, the GSU, the gas chromatograph and a computerized integrator. Except for the GSU and the gas chromatograph, this apparatus has been widely used for the volumetric analysis of total gas in nuclear fuel pellets by the high temperature vacuum extraction method [5]. The schematic diagram of the apparatus is shown in Fig.3. The GSU consists of special three-way and four-way valves, a buffer vessel for pressure change and a reference gas injection port, as shown in Fig. 4. Both valves were connected to glass capillary tube of i.d.2mm. The GSU could be connected with the gas collection and volumetric measurement units at vacuum condition (10"2Pa) and the gas chromatograph at carrier gas pressure (2 ~ SKg/cm2) without pressure change of the system and chromatogram fluctuation. The gas chromatograph (Hitachi, GC-3000, Tokyo, Japan) and a computerized integrator (Hitachi, D-2500) were used in our experiments. For gas separation, 4.0m x 3mm i.d. stainless steel columns packed with Porapak Q (50 ~ 80 mesh), 2.0m x 3mm i.d. stainless steel columns packed with Molecular sieve 5A(60 - 80 mesh) and 2.0m x 3mm i.d. stainless steel columns packed with Chromosorb W(60 - 80 mesh) were used. In order to regulate the retention time, an empty stainless steel column of 2.0m x 3mm i.d. was used.

Chromosorb

Fig.3. Schematic diagram of gas extraction and analysis apparatus.

(ij.Hign trequency induction equipment;(2),Glove box; @,Pellets loading part;0,Induction coil; (?) .Molybdenum crucible;©,Quartz furnace tube;©,Pellets unloading part; (f),Mercury diffusion pump : (9).Mercury trap:(jjXDu«t niter; (Tp.Mercury diffusion pump : Mechanical pump;(jj!.McLeod gauge: (Q).Toepler pump.iTjToepler pump controller; @ ,Oil diffusion pump; (}J),GSLi; @,Gas chromatograph; Integrator; @,Open port box;©.Helium cylinder;©,Helium carrier gas.

Fig.3. Schematic diagram of gas extraction and analysis apparatus.

(ij.Hign trequency induction equipment;(2),Glove box; @,Pellets loading part;0,Induction coil; (?) .Molybdenum crucible;©,Quartz furnace tube;©,Pellets unloading part; (f),Mercury diffusion pump : (9).Mercury trap:(jjXDu«t niter; (Tp.Mercury diffusion pump : Mechanical pump;(jj!.McLeod gauge: (Q).Toepler pump.iTjToepler pump controller; @ ,Oil diffusion pump; (}J),GSLi; @,Gas chromatograph; Integrator; @,Open port box;©.Helium cylinder;©,Helium carrier gas.

Fig.4. Gas sampling unit.

A, Spherical buffer vessel; B, Improved four-way valve;C, Reference gas injection port; D,Improved three-way valve;E, MacLeod gauge; F, Glass capillary tube of 2mm i.d.

3.1.2 Procedure of gas analysis by the gas chromatograph

The gases extracted could be simultaneously analyzed by the combination of several stainless steel columns of Porapak Q, Molecular Sieve 5A and Chromosorb W. When the objective gases were injected into flie column packed with Porapak Q using the GSU, these gases were separated into two groups. The gases of both groups were injected into twin separation columns in a computer controlled flow through a changing valve. The gases of the first group (H2, 02, N2 and CO) were separated by the column packed with Molecular Sieve 5A, and those of the other group (CH4, C02 and C2H6) by the column packed with Chromosorb W. Each of the separated gases was detected by the PID. A schematic diagram of the gas chromatography is shown in Fig. 5.

3.2.3 Measurement procedure

The weighed sample (about lg) was transferred into the pellets loading part of the apparatus, which was evacuated to approximately ltt2 Pa using the mercury diffusion pump and the mechanical pump. The molybdenum crucible without the sample was outgassed beforehand until less than 10/i 1 at the S.T.P. condition. Then the sample was dropped into the molybdenum crucible and heated at 1700°C for 30 min. The released gas from the sample was corrected to the McLeod gauge using the mercury diffusion pump and the toepler pump, where the temperature and pressure were measured. The total gas volume of the sample was calculated from the temperature, pressure and volume of the collected gas at the S.T.P. condition. Volumetrically measured gas by the McLeod gauge was transferred into the GSU. The extracted gas was injected into the gas chromatograph at the same pressure as the carrier gas, and analysed by the PID. The total volume of the gas occluded per unit mass in the sample at the S.T.P. was obtained as the sum of all components of the gas analysed.

  1. 2 RESULTS
  2. 2.1 Determination of occluded gases in MOX fuel pellets

Occluded gases in the MOX fuel pellets were quantitatively and qualitatively analysed. As a results of the standard gas analysis and verification of the retention time, the peaks were qualitatively

Molecular Sieve
Fig.?. Principle of gas separation using gas chromatograph.
  1. gas sampling unit; MS-5A, Separation column with Molecular Sieve 5A
  2. Flo« through changing valve: Ch-W, Separation column with Chromosorb W. P-0- Sepjrjhon column with Porapak Q: HID, Photoionizalion detector.

analysed as H2, O2, N2, CH*, CO, and CO. Further, concentrations of the objective gases in the MOX fuel pellets were quantitatively determined. The obtained results are shown in Table 3. From these experiments, as to die sintered pellets in hydrogen-nitrogen (5% -95%) atmosphere, H2, N2 and CO were found to be main component gases. On the other hand, for the sintered pellets in hydrogen-argon (5% -95%) atmosphere, H2 and CO were the main component gases. Q H was not detected . A typical gas chromatogram of occluded gases in the MOX fuel pellets is shown in Fig. 6.

TABLE 3 Analytical results of occluded gases in MOX fuel pellets

TABLE 3 Analytical results of occluded gases in MOX fuel pellets

No.

Atmosphere

H,

o,

N,

CH,

CO,

CO

QH,

1.

H2-N2 (5% -95%)

46

_b

20

_b

__b

9.4

NDC

2.

H2-Ar (5% - 95%)

14

_b

__b

__b

__b

1.9

NDC

(5% -95%)

14

_b

__b

__b

__b

12

NDC

4.

H2-N2 (5% -95%)

93

0.5

38

__b

_b

15

NDC

(5% -95%)

21

1.3

30

__b

__b

11

NDC

a At S.T.P. condition b Less than the minimum limit of determination c Not detected

0 1 00 200 30 0 400 Gas volume by High Temperature Vaccum Extraction Method (n I)

Retention Time (min)

Fig.6. Typical gas chromatogram of occluded gases in MOX fuel pellets.

0 1 00 200 30 0 400 Gas volume by High Temperature Vaccum Extraction Method (n I)

Retention Time (min)

  1. 6. Typical gas chromatogram of occluded gases in MOX fuel pellets.
  2. 7. Correlation diagram'of High temperature vaccum extraction method and extracted gas analysis by gas chromatography.
  3. 2.2 Comparison of the high temperature vacuum extraction method and the gas chromatography

The total volume of the occluded gases was determined for a large number of samples by the high temperature vacuum extraction method and by the present extracted gas analysis using the gas chromatography. The pellets used in this study were those fabricated for the purpose of production test of the MOX fiiels. The correlation diagram of both methods is shown in Fig. 7. The correlation coefficient value was 0.998 (n = 36). The results of the present analysis of extracted gas using the gas chromatography were in good agreement with those of the high temperature vacuum extraction method in the range of less than 300//1. Therefore, this method is applicable not only to MOX pellets but also to UOz pellets for the analysis of occluded gas below 300/zl.

4. DETERMINATION OF NITROGEN IN MOX BY GAS CHROMATOGRAPHY AFTER

INERT GAS FUSION

This technique is based on chromatographic determination of nitrogen in released gases from fused sample. The sample and iron metal flux in a graphite crucible were heated to 2700°C by an impulse furnace under a helium atmosphere. From the fused sample, which was gases evolved such as H2, N2 and a large amount of CO . Hie CO produced was interfered with the measurement of N2. Consequently, for N2 separation from other gases and CO removed, a gas chromatograph equipped with a pre-cut system was originally developed. Nitrogen separated was determined using a thermal conductivity detector (TCD). The RSD was less than 5%, and the time required for one determination was about 10 min.

  1. 1 EXPERIMENTAL
  2. 1.1 Apparatus

The schematic diagram of the apparatus is shown in Fig. 8. An impulse furnace and a gas chromatograph equipped with the pre-cut system and the TCD were enclosed in the glove-box. The gas chromatograph was installed in the thermostat at 65.5°C. The pre-cut system consisted of 500mm x 4mm i.d. stainless steel columns packed with Porapak N of 60 ~ 80 mesh (C-l) and 600mm x 4mm i.d.

Glove box

Glove box

Simple Schematic Diagram Nitrogen
Fig.8. Schematic diagram of nitrogen analysis apparatus.
  • A) Normal state H e
  • Furnace

(B) Nitrogen analysis state He CO

Pre-cut

Fig.9. Schematic principle diagram of pre-cut system. C-1, Porapak N column; C-2, Silica Gel column; TCD,Thermal conductivity detector.

Fig.9. Schematic principle diagram of pre-cut system. C-1, Porapak N column; C-2, Silica Gel column; TCD,Thermal conductivity detector.

stainless steel columns packed with Silica gel of 60 ~ 80 mesh (C-2) and a carbon monoxide purge valve. The schematic diagram of die precut system is shown in Fig. 9. A computerized peak-area integrator from Shimazu Co., Ltd. CR-3A (Kyoto, Japan) was used.

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