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Absorption of helium by irradiated samples of austenitic steels
Journal of Nuclear Materials 66 (1977) 215-216 0 North-Holland Publishing Company
ABSORPTION OF HELIUM BY IRRADIATED SAMPLES OF AUSTENITIC STEELS V. KISLIK 10apt. 122, Rusanovsky Boulevard, Kiev-154,
SSSR
Received 22 June 1976
The austenitic steels used in the described experiments are designated as OKhl6N15M3B and OKhl6N15M3BR. They are aging steels and belong to a group of moderately alloyed heat-resistant steels with a stable structure at 700-750°C. The two steels differed from each other only by the presence of 0.005 wt% boron in the latter. The boron was added by a method that made its distribution to be mainly along the grain boundaries [ 11. Their grain size ranged from 20 to 30 ym. Some experiments were also performed with samples of the boronfree steel that had undergone a 90% deformation and had been stress annealed; the grain sizes in these samples were I to 3 pm. The samples were irradiated in the active zone of Reactor VVR-M with an effective neutron flux of 4 X 10”‘n/cm2 1set (E>, 3MeV) and 6 X IOi3n/ cm2 . set (E < 0.03 eV) at a fixed temperature in the range of 600 to 850°C. The temperature fluctuation during the irradiation was +lO”C [2]. The integrated neutron flux was 6 to 8 X 10’9n/cm2. The experimental arr~gements and procedures used in the measurements of the helium release from the irradiated samples have been described in previous papers [3,4]. Fig. I shows typical curves of helium release as a function of annealing temperature of irradiated samples of the boron-bearing steei 0~16NlSM3BR, using a linear heat-up rate of 20”C/min. It was noted that for samples irradiated at temperatures above ‘700°C the curve of helium release fell below the background curve (fig. 1, curve III) in the annealing temperature range of 700 to 12OO”C,with a minimum at 950°C. The effect was best noted during annealing of samples irradiated at 85O’C (fig. 1, curve II). It is significant that the “fall” of the kinetic curve of helium release exceeded by more than a factor of 3 the maximum measurement error.
2&l
400
600
800
Temperature
1000
1200
(‘C)
Fig. 1. Helium release rate in irradiated samples of steel O~hl6Nl5M3BR as a function of temperature during annealing at a constant heat-up rate of 20’C/min. I -irradiation at 6OO”.C,II -irradiation at 85O”C, III-the background curve.
Further study of this phenomenon showed: (1) There is no such effect or the same kinds of steel irradiated at temperatur Ifs of 600 to 650°C. (2) The phenomenon did not occur in the samples of boron-free steel (OKh16N15M3B) with a large grain size (20 to 30 cun>irradiated at temperatures from 600 to 85O’C. (3) The “fall” of the kinetic curve of helium release below the background curve also occurred during the annealing of samples of the fine-grained (1 to 3 m) boron-free steel (OKhl6NlSM3B) that had undergone a significant deformation before irradiation. However, the effect was noted only for samples irradiated at 750 to 850°C. Its magnitude was less than in the boronbearing steel. (4) A study of samples which were subjected to uniaxial tensile stress during irradiation using a constant load showed that the deformation during the irradia215
216
V. Kislik /Absorption
tion process increased the magnitude of the “fall” both for boron-bearing and fine-grained boron-free steels. The observations suggest that there is an absorption of helium from the atmosphere of the annealing chamber, and that it occurs only in steels with grain boundaries enriched by boron or with very fine grains after they had been irradiated at high temperatures (750 to 850°C). As such the phenomenon would merit further study since it may have practical implications in view of the possible development of high-temperature reactors with gaseous coolants, particularly helium.
of helium References [l] S.N. Votinov, V.M. Prohorov et al., Atomic Energy 27 (1969) 506. [2] V.S. Karasev et al., Atomic Energy 22 (1967). (31 V.S. Karasev, V.S. Kislik et al., Atomic Energy 34 (1973) 251. [4] N.I. Emelianov, R.V. Grebennike et al., Atomic Energy 31 (1971) 215.
ABSORPTION OF HELIUM BY IRRADIATED SAMPLES OF AUSTENITIC STEELS V. KISLIK 10apt. 122, Rusanovsky Boulevard, Kiev-154,
SSSR
Received 22 June 1976
The austenitic steels used in the described experiments are designated as OKhl6N15M3B and OKhl6N15M3BR. They are aging steels and belong to a group of moderately alloyed heat-resistant steels with a stable structure at 700-750°C. The two steels differed from each other only by the presence of 0.005 wt% boron in the latter. The boron was added by a method that made its distribution to be mainly along the grain boundaries [ 11. Their grain size ranged from 20 to 30 ym. Some experiments were also performed with samples of the boronfree steel that had undergone a 90% deformation and had been stress annealed; the grain sizes in these samples were I to 3 pm. The samples were irradiated in the active zone of Reactor VVR-M with an effective neutron flux of 4 X 10”‘n/cm2 1set (E>, 3MeV) and 6 X IOi3n/ cm2 . set (E < 0.03 eV) at a fixed temperature in the range of 600 to 850°C. The temperature fluctuation during the irradiation was +lO”C [2]. The integrated neutron flux was 6 to 8 X 10’9n/cm2. The experimental arr~gements and procedures used in the measurements of the helium release from the irradiated samples have been described in previous papers [3,4]. Fig. I shows typical curves of helium release as a function of annealing temperature of irradiated samples of the boron-bearing steei 0~16NlSM3BR, using a linear heat-up rate of 20”C/min. It was noted that for samples irradiated at temperatures above ‘700°C the curve of helium release fell below the background curve (fig. 1, curve III) in the annealing temperature range of 700 to 12OO”C,with a minimum at 950°C. The effect was best noted during annealing of samples irradiated at 85O’C (fig. 1, curve II). It is significant that the “fall” of the kinetic curve of helium release exceeded by more than a factor of 3 the maximum measurement error.
2&l
400
600
800
Temperature
1000
1200
(‘C)
Fig. 1. Helium release rate in irradiated samples of steel O~hl6Nl5M3BR as a function of temperature during annealing at a constant heat-up rate of 20’C/min. I -irradiation at 6OO”.C,II -irradiation at 85O”C, III-the background curve.
Further study of this phenomenon showed: (1) There is no such effect or the same kinds of steel irradiated at temperatur Ifs of 600 to 650°C. (2) The phenomenon did not occur in the samples of boron-free steel (OKh16N15M3B) with a large grain size (20 to 30 cun>irradiated at temperatures from 600 to 85O’C. (3) The “fall” of the kinetic curve of helium release below the background curve also occurred during the annealing of samples of the fine-grained (1 to 3 m) boron-free steel (OKhl6NlSM3B) that had undergone a significant deformation before irradiation. However, the effect was noted only for samples irradiated at 750 to 850°C. Its magnitude was less than in the boronbearing steel. (4) A study of samples which were subjected to uniaxial tensile stress during irradiation using a constant load showed that the deformation during the irradia215
216
V. Kislik /Absorption
tion process increased the magnitude of the “fall” both for boron-bearing and fine-grained boron-free steels. The observations suggest that there is an absorption of helium from the atmosphere of the annealing chamber, and that it occurs only in steels with grain boundaries enriched by boron or with very fine grains after they had been irradiated at high temperatures (750 to 850°C). As such the phenomenon would merit further study since it may have practical implications in view of the possible development of high-temperature reactors with gaseous coolants, particularly helium.
of helium References [l] S.N. Votinov, V.M. Prohorov et al., Atomic Energy 27 (1969) 506. [2] V.S. Karasev et al., Atomic Energy 22 (1967). (31 V.S. Karasev, V.S. Kislik et al., Atomic Energy 34 (1973) 251. [4] N.I. Emelianov, R.V. Grebennike et al., Atomic Energy 31 (1971) 215.