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 Table of Contents 
ARTICLE
Year : 2010  |  Volume : 33  |  Issue : 4  |  Page : 183-184  

Simulation study of (Th-U)O 2 fuel pin clad defect


Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, India

Date of Web Publication1-Dec-2011

Correspondence Address:
R K Gopalakrishnan
Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai
India
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Source of Support: None, Conflict of Interest: None


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  Abstract 

Advanced Heavy Water Reactor (AHWR) is being developed in India with the aim of utilizing the vast reserve of thorium as fertile fuel and power production. The AHWR is based on (Th-U)O 2 and (Th-Pu)O 2 fuel and hence studies related to various aspects of reactor operation using thorium is required as a part of development and generation of data on thorium fuel cycle. In this experimental study, an attempt is made to simulate a fuel Clad failure with (Th- 233 U)O 2 fuel pellets. The pellets of 91% T.D. with 0.1w% 233 UO 2 were prepared by conventional dry powder metallurgy of cold compaction and were contained in a 0.3mm thick Al capsule. A pin hole 1.76 mm 2 dia. was drilled on clad to simulate small size clad defect. The pellets immersed in demineralised water were irradiated in a reactor for a known period. The isotopic activity analysis of radionuclides released in the water was done by γ-ray spectrometry. The release of Ac 228 in the water indicates the presence of thorium decay products such as Bi 212 , Tl 208 during fuel failures. This would warrant adequate shielding on the primary heat transport system piping in case of MOX fuelled reactors using thorium.

Keywords: Clad defect, gamma spectrometry, thorium decay products


How to cite this article:
Mishra S G, Singh A K, Rath D P, Gopalakrishnan R K. Simulation study of (Th-U)O 2 fuel pin clad defect. Radiat Prot Environ 2010;33:183-4

How to cite this URL:
Mishra S G, Singh A K, Rath D P, Gopalakrishnan R K. Simulation study of (Th-U)O 2 fuel pin clad defect. Radiat Prot Environ [serial online] 2010 [cited 2021 Aug 3];33:183-4. Available from: https://www.rpe.org.in/text.asp?2010/33/4/183/90459


  1. Introduction Top


Advanced Heavy Water Reactor (AHWR) based on (Th-U)O 2 and (Th-Pu)O 2 fuel and hence studies related to various aspects of reactor operation using thorium as fertile fuel is required as a part of development and generation of data on Thorium Fuel Cycle. One of the problems faced during reactor operation is detection and identification of failed fuel. Analysis of primary heat transport system activity has proved to be a good method for detection, identification and estimation of failed fuel in PWR and CANDU type reactors and is widely being used in operating reactors worldwide.

Good amount of research work has been done on determining the isotopic ratio of fission products noble gases and iodines released in primary coolant from defective fuel element and the data so obtained has been very useful as benchmark for quick identification and removal of defective fuel elements in PWR and CANDU type reactors. (Technical Report Series No. 388, "IAEA (1988). In this experimental study, the pellets with ThO 2 -0.1w% 233 UO 2 were prepared by conventional dry powder metallurgy of cold compaction and were contained in a aluminum capsule. The pellets with a pin hole were immersed in demineralised water and irradiated in a reactor for a known time. The isotopic activity analysis of radionuclides released in the water was carried out by γ-ray spectrometry. Suitable pair of fission products which could indicate fuel failure was studied.


  2. Experimental Top


The pellets of ThO 2 -0.1w% 233 UO 2 were prepared by conventional dry powder metallurgy of cold compaction and high temperature sintering in reducing atmosphere. These pellets were contained in a 0.3 mm thick Al capsule and to simulate cladding the fuel-to-sheath gap was minimized by keeping the diametric clearance between pellet and aluminum capsule as small as possible with technical limitations of fabrication. Further, to simulate small clad defect, the pellets with 91% T.D. were drilled to create a pin hole of 1.76 mm 2 size at the of capsule. The details of sample dimensions and material used in the experiments are as given [Table 1]. The pellet with known quantity of de-mineralized water was sealed in quartz ampoule using glass blower technique such that the pellet was not heated. [Figure 1] shows actual photograph of such a sample used in experiments. The samples were irradiated at a constant flux of flux of 1.3x10 12 neutrons/cm 2 /s at ambient temperature (~300 K) in swimming pool type research reactor, for one hour such that maximum achievable burn-up was 5.1x10 13 fissions/cc. The water sample was collected by breaking the ampoule and activity released in water could be analysed by gamma spectrometry after 3 hours delay using high resolution HPGe detector with relative efficiency of 50% and energy resolution of 2 keV at 1332 keV of 60 Co. The spectrum analysis was carried out using 8K MCA coupled with a personal computer.
Figure 1: Actual photograph of sample used in experiments

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Table 1: Details of irradiation experiments

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Two set of experiments were conducted with high density sintered pellet with clad defect in order to confirm and support the viability of data generated so that any erratic data due to experimental error or analysis is eliminated. The experimental set up and irradiation conditions were by and large similar in both the cases.


  3. Results And Discussion Top


The 133 I/ 131 I ratio is found to be good indicator of fuel clad failure due to comparatively different half lives (8.04d for 131 I and 20.8h for 133 I for all size of defects in fuel pin as is observed for various types of fuel failures in PHWR. The value of 133 I/ 131 I ratio in the experiments was observed to be 20.0 and 16.94 indicating release of iodine due to fuel failure. However, this ratio is very close to their independent fission yield ratio i.e. 19.56. As birth rate of an isotope depends on it's independent fission yield apart from release rate, mass of fuel and decay constant, caution must be exercised in this experimental analysis as the activity of iodines could be suspected due to surface release of uranium contamination. Also, it is well established by analysis of primary coolant of power reactors that on a logarithmic plot, if ratio of release rate and yield is independent of decay constant, then the source of release of activity in coolant is due to uranium contamination (Lewis, 1983; 1988). Hence, more experimental work and analysis is required to confirm the source of release and physical mode of release of fission products into water.

228 Ac (half-life: 6.13 h) of thorium series was detected in the water sample. 228 Ac activity in water is indicative of the presence of thorium decay products such as Bi 212 , Tl 208 .


  4. Conclusion Top


The release of Ac 228 into water indicates the presence of thorium decay products such as Bi 212 , Tl 208 (having high gamma energies of 727.2 keV and 2.614 MeV respectively) during fuel failures, warranting adequate shielding on the primary heat transport system piping and fuel handling machine in case of MOX fuelled reactors using thorium. However, more studies are required to understand the mode of release of these radionuclides into PHT systems and to identify specific signatures of thorium decay chain leaching out on a fuel failure.


  5. Acknowledgements Top


Authors are thankful to Dr. D.N. Sharma, Head, RSSD and Dr. P. C. Gupta, Head, RHC, RSSD for their support and encouragement in conducting the experiments. Authors are also thankful to the staff at Glass Ceramic Laboratory specially, Shri Radhakrishnan and Shri Boje for their co-operation extended in manufacturing the quartz ampoule used in experiments. Authors wish to express their sincere thanks to Shri Harimohan Sharma, AFD for manufacturing and providing the aluminium container with thickness simulated close enough to actual clad thickness.


  6. References Top


  1. Lewis B.J., Fission product release to the primary coolant of a reactor, Canadian Nuclear Society 6 th Annual Conference, June, 1983.
  2. Lewis B.J. (1988), Fundamental Aspects of Defective Nuclear Fuel Behavior and Fission Product Release, Journal of Nuclear Materials, 160, 201-217.
  3. Technical Report Series No. 388, IAEA (1988), Review of Fuel Failures in Water Cooled Reactors, IAEA, Vienna.



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  In this article
Abstract
1. Introduction
2. Experimental
3. Results And D...
4. Conclusion
5. Acknowledgements
6. References
Article Figures
Article Tables

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