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 Table of Contents 
ARTICLE
Year : 2010  |  Volume : 33  |  Issue : 3  |  Page : 104-105  

Monitoring of tritium In CORAL reprocessing facility


Radiation Safety Section, Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, India

Date of Web Publication22-Oct-2011

Correspondence Address:
S Bala Sundar
Radiation Safety Section, Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam
India
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Source of Support: None, Conflict of Interest: None


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  Abstract 

Gaseous effluent that is discharged through the stack of CORAL reprocessing facility is continuously monitored and the activity release estimated to comply with the regulatory requirements. Krypton-85, Iodine-131 and particulates are monitored and the activity release quantified in this facility. Release of Tritium in the gaseous effluent also needs to be monitored considering it's long half-life and the consequent environmental impact. Moreover, it has also become a regulatory requirement to monitor and quantify Tritium discharge from a reprocessing facility. In view of this, a prototype setup, adopting bubbler method, has been designed, installed and commissioned at CORAL to monitor and quantify the Tritium release during the recently concluded campaign. It was observed that Tritium was released during the chopping and dissolution processes, in measurable quantities.

Keywords: Tritium, bubbler, stack, off-gas, fuel reprocessing


How to cite this article:
Sundar S B, Chandrasekaran S, Ajoy K C, Yuvaraj N, Akila R, Santhanam R, Rajagopal V. Monitoring of tritium In CORAL reprocessing facility. Radiat Prot Environ 2010;33:104-5

How to cite this URL:
Sundar S B, Chandrasekaran S, Ajoy K C, Yuvaraj N, Akila R, Santhanam R, Rajagopal V. Monitoring of tritium In CORAL reprocessing facility. Radiat Prot Environ [serial online] 2010 [cited 2022 Aug 13];33:104-5. Available from: https://www.rpe.org.in/text.asp?2010/33/3/104/86271


  1. Introduction Top


Reprocessing of spent fuel from Fast Breeder Test Reactor (FBTR) is being carried out in CORAL (COmpact Reprocessing of Advanced fuels in Lead cells) facility, situated at Indira Gandhi Centre for Atomic Research (IGCAR). The major operations involved in the process are chopping, dissolution, three cycles of extraction and reconversion. Description of the facility and details of the process operations are given elsewhere (Rajamani Natarajan, 2007). Irradiated FBTR fuel pins of burn-ups ranging from 25 to 155 GWd/t have been successfully reprocessed at CORAL. The gaseous effluents generated during various operations are released to the environment through a 75 m-tall stack. The stack monitoring system continuously monitors the release of Krypton-85, Iodine-131 and other particulates.

Tritium, a product of ternary fission, is one of the fission products present in the fuel in measurable quantities, in the range of MBq/kg (1665 MBq/kg for 75 GWd/t burn-up and 120 days cooled fuel). As part of R&D activity and also in line with the recommendation of the regulatory authorities that radionuclides such as Carbon-14, Ruthenium-106 and Tritium also need to be monitored in reprocessing facilities, a prototype setup consisting of glass bubblers was made to study the feasibility of monitoring and quantifying Tritium. This setup was connected to an existing off-gas duct sampling system and put into operation during the recently-concluded campaign for the whole reprocessing of 155 MWd/t burn-up fuel pins. Samples were collected during chopping and dissolution processes and Tritium was identified in the samples collected. The details of the design, experimental setup and other associated works carried out are presented in this paper.


  2. Experimental Set Up Top


The off-gases from the dissolver, process vessels, and glove boxes are passed through the deep bed filter (DBF), consisting of glass wool filters with four different packing densities, the HEPA filter and are finally discharged through stack after passing through another HEPA filter bank. A sampling system is connected to the duct carrying off-gas in the downstream of DBF and HEPA filter to monitor the release of Krypton-85, Iodine-131 and other particulates. This location was chosen because of it's proximity to the source of generation and less dilution factor by about 400 times, as compared to stack, which would enable definite identification and quantification of radionuclides. The prototype Tritium monitoring setup was added to this system by making suitable modifications. The schematic of the system is given in [Figure 1]. The off-gas first passes through the filter cone containing a glass fiber filter paper for sampling particulates, followed by iodine filter cartridge and a 2-litre Krypton chamber made of SS. Provision has also been made in the system for the collection of spot gas samples for gamma spectral analysis, which is indicated by the dotted lines in the schematic. The vent from the Krypton chamber was bifurcated into two ie., one channel connected to the suction end of a pump through a rotameter with 100 lpm flow rate and the other channel connected to the suction of the same pump through a rotameter of 1lpm flow rate connected to a tritium sampling system comprising of a pair of glass bubblers. The entire arrangement was kept inside a fume hood arrangement so that any inadvertent leakages from the sampling system are not released into the open environment.
Figure 1: Schematic of the duct sampling system

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  3. Materials and Methods Top


Several techniques such as (i) silica gel adsorption (ii) collection of tritium in a cryostat at -20°C and (iii) the bubbler method are available for the monitoring of Tritium. Of all the methods listed, the bubbler method is widely used, as it is simple and inexpensive. In the present experiment, bubbler method was used for Tritium monitoring. This method requires a pair of glass bubblers of capacity 250 ml, a vacuum pump and a flow rate meter. The air to be sampled is made to pass through the glass bubblers, containing about 200 ml distilled water, which are connected in series. The flow rate is fixed at one lpm to ensure effective sampling. The tritium present in the air gets dissolved in the water. However, this depends primarily on the flow rate of air through the bubblers and the resonance time of the vapor in the bubbler though the temperature and humidity also contribute to a lesser extent. The sampling system was put into operation during the recent campaign while reprocessing fuel pins of 155 GWd/t burn-up. Off-gas from the duct was allowed to bubble through the bubblers in the setup, continuously, at a flow rate of about one lpm. Water samples were collected after 24-hour period and analyzed in the Liquid Scintillation System (LSS) at RSD [PACKARD make, Tri- Carb 2900 TR, cocktail used: Ultima Gold] and tritium was identified in all the samples.


  4. Results and Discussion Top


To establish the background, ten blank samples were collected from the bubbler setup prior to the chopping and dissolution operations and the tritium activity in all the samples was below the detection level [MDA: 0.5 Bq/ml]. When the samples were subjected to analysis, it was observed that the tritium was released during the chopping and dissolution process. The concentration of Tritium, as estimated from the measurements, during chopping and dissolution operations ranged from 30-40 Bq/ml and 600-1000 Bq/ml respectively, implying higher release of Tritium during dissolution as compared to the release during chopping. This trend is identical to the one exhibited by Krypton-85. The inventory of Tritium present in the fuel was extrapolated from the data available for 25 GWd/t burn-up fuel and estimated to be 2.6x10 9 Bq. The total quantity of the tritium released, as deduced from the sample results, was found to be about 73% of the inventory. Many reprocessing plants operating abroad have reported Tritium release through stack (~7% of the inventory) during operations (Ooyama, et al, 2006).


  5. Conclusions Top


The Tritium sampling setup, designed and commissioned at off-gas duct at CORAL reprocessing facility, attempted for the first time, was helpful in identifying and quantifying the release of Tritium during chopping and dissolution. Based on the experience gained during the present set of experiments and with a few modifications for achieving standardization, it is planned to incorporate a similar setup in the stack monitoring system to monitor the release of Tritium through stack. This will pave way in incorporating Tritium monitoring in upcoming reprocessing facilities in the design stage itself.


  6. Acknowledgements Top


Thanks are due to Shri. M. Venkataraman, Head, RPOD for having permitted to install the sampling system and his valuable suggestions during the design and installation of the system. Thanks are also due to Dr. V. Meenakshisundaram, Head, RSS, RSD for useful discussions. The service rendered by Shri. Vishnukumar, SO/E and Shri. Francis Angelus, FM/B of RPSD, RpG in setting up the sampling system is thankfully acknowledged.


  7. References Top


  1. Ooyama K., Keta S., Kanou M., Moriyama T., Okamura Y., Ogaki. K. and Noda K, (2006), Proceedings of "Monitoring Of Radioactive Gaseous and Liquid Wastes at Rokkasho Reprocessing Plant", 15 th Pacific Basin Nuclear Conference, 2006.
  2. Rajamani Natarajan and Baldev Raj (2007), Fast Reactor Fuel Reprocessing Technology in India, Journal of Nuclear Science and Technology, Vol. 44 (3), 393-397.



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  In this article
Abstract
1. Introduction
2. Experimental ...
3. Materials and...
4. Results and D...
5. Conclusions
6. Acknowledgements
7. References
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