|Year : 2011 | Volume
| Issue : 4 | Page : 246-248
Radiological safety study of clad failed fuel handling during fifty years of operation of cirus
TR Meena1, RK Yadav1, SK Prasad1, SS Deolekar1, KS Babu1, N Ramesh2, Rakesh Ranjan2
1 Department of Atomic Energy, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, India
2 Department of Atomic Energy, Reactor Operations Division, Bhabha Atomic Research Centre, Mumbai, India
|Date of Web Publication||17-Jan-2013|
R K Yadav
Department of Atomic Energy, Radiation Safety Systems Division, Mumbai
Source of Support: None, Conflict of Interest: None
CIRUS reactor, the nucleus of nuclear programme of India is a 40MW research reactor commissioned in July 1960. The reactor was operated efficiently for nearly five decades before it was shutdown permanently on 31 st December 2010. During the reactor operation, incidences of Clad Failed Fuel (CFF) were considered as Safety Related Unusual Occurrences (SRUOs). Incidences of CFF could sometimes lead to severe contamination of system resulting in personnel exposure and generation of large amount of liquid and solid radioactive wastes. CFF detection system used earlier was Gaseous Fission Product Radiation Alarm (GFPRA), which was replaced with new gamma based Failed Fuel Detection (FFD) system during refurbishing of Cirus during 1997-2002. CFF rods handling during nearly five decades of CIRUS reactor operation were studied in detail. Important radiological data related to identification and removal of CFF rod were also analyzed. Collective dose consumption and waste generated both solid and liquid for each CFF was also studied in detail. The use of the new gamma-based FFD system resulted in lowering of collective dose from 110 to 12 Person-mSv per incidence and also reduction in spread of contamination.
Keywords: Clad failed fuel, failed fuel detection, person-mSv
|How to cite this article:|
Meena T R, Yadav R K, Prasad S K, Deolekar S S, Babu K S, Ramesh N, Ranjan R. Radiological safety study of clad failed fuel handling during fifty years of operation of cirus. Radiat Prot Environ 2011;34:246-8
|How to cite this URL:|
Meena T R, Yadav R K, Prasad S K, Deolekar S S, Babu K S, Ramesh N, Ranjan R. Radiological safety study of clad failed fuel handling during fifty years of operation of cirus. Radiat Prot Environ [serial online] 2011 [cited 2020 Jun 6];34:246-8. Available from: http://www.rpe.org.in/text.asp?2011/34/4/246/106180
| 1. Introduction|| |
CIRUS reactor is natural Uranium metal fuelled, demineralized light water cooled and heavy water moderated research reactor.  Clad Failed Fuel (CFF) is a safety related unusual occurrence which affects reactor operation and depending on the extent of split or clad failure can lead to significant spread of contamination in the primary coolant system. To prevent significant contamination at various locations and to limit the individual exposure, it is required to identify the split rod position and remove it from the reactor pile as early as possible. Gross beta activity based detection system was being used for detection and identification of CFF during 1960-1990. However due to decrease in the efficiency of detection of CFF with time and high collective dose consumption during its frequent maintenance, a Gamma based CFF detection system was commissioned during refurbishing. Gamma based detection system does not require any maintenance and has helped in detection of all CFF thereafter. CFF rods handling during the 50 years of CIRUS reactor operation were studied in detail. Important radiological data during various CFF operations like detection, identification, removal of CFF rod, exhaustive decontamination and normalization of system were also studied. Collective dose consumption for the various CFF rods, important radionuclides present in air samples and liquid waste samples collected during handling CFF rods are described in this paper.
| 2. Materials and Methods|| |
Gross beta activity based Gaseous Fission Product Radiation Alarm (GFPRA) system was in service earlier for detection and identification of CFF rod in core. The GFPRA system was replaced during refurbishing by an improved Failed Fuel Detection (FFD) system.  Following a CFF rod incidence, the reactor is shutdown. The identification of CFF rod was carried out by radiation field measurements at bottom of individual rods in Lower Header Room (LHR) and also by estimating gross beta activity of cooling water outlet of suspected individual rods. The difference between the radiation field at the bottom of the normal fuel rod and on suspected rod along with the difference in gross beta activity of coolant water samples used to give an indication of presence and location of CFF rod in reactor pile. Installation of new gamma based FFD system led to the reduction in the collective dose for detecting of CFF rod. After confirmation of its position in pile, the CFF rod is removed from the pile and transferred to Rod Cutting Building (RCB) buggy with the help of shielded Vertical Flask (VF). This buggy transfers the CFF rod to RCB for further action. After CFF rod has been successfully transferred to RCB for further action, the primary coolant lines, primary coolant heat exchangers and other equipment's of the primary coolant system are flushed with demineralized water for removal of contamination. After thorough flushing the system in normalized and reactor is restarted. CFF rod is removed with all necessary radiological safety procedures so as to minimize personnel exposure, spread of contamination and radioactive waste generation.
2.1. Analysis of various radiological parameters during CFF handling
Analysis of various radiological parameters during handling of number of CFF rods in 50 years of reactor operation is done in detail.  It is observed that the maximum doses were received by personnel in LHR during CFF rod detection and removal and during Cuno filter replacement in LHR. Radiological parameters during normal reactor operation and during various stages of CFF handling are given in [Table 1]a-c. 
Gamma spectrometric analysis of the water samples collected from the bottom of the CFF rods were carried out after each incidence of CFF. A typical Gamma spectrometry result of coolant water from CFF rod is given in [Table 2] below. It may be noted that nearly 76% of the activity is contributed by fission product iodine isotopes present in the coolant.
|Table 2: Gamma spectrum results of typical failed fuel rod water sample (Rod Bottom)|
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2.2. Management of contaminated waste
During detection and removal of CFF rod, solid and liquid radioactive wastes get generated. Activity concentration of contaminated primary coolant water which is diverted to dump tank is observed to be in the range of 300-4000 Bq/ml. This active coolant water is sent to Effluent Treatment Plant for treatment and final disposal. Total volume of liquid waste generated per CFF rod incident varies between 300-1140 m 3 . Solid waste generated was found to comprise of Cuno filters from LHR and top of pile (TOP), contaminated PVC suits, cotton mops, cotton boiler suits (used to soak spilled active water on TOP), gum boots, gloves, other clothing's and various other contaminated material. Air activity concentration during various CFF rod handling on TOP was found to have varied between 100 to 2700 Bq/m 3 . Gamma spectrometry of the air samples collected also indicated presence of significant amount of fission product iodine isotopes.
2.3. Liquid waste
Category-III and Category-II liquid waste get generated during CFF rod handling, is transferred to Effluent Treatment Plant (ETP) for treatment and disposal. Details of liquid waste generated during CFF handling is given in [Table 3]. A typical gamma spectrometry of liquid effluent sample showed the presence of radionuclides like 131 I, 141 Ce, 140 La, 239 Np etc.
2.4. Solid waste
Radioactive solid waste gets generated during the CFF rod handling work, is packed in PVC bags, sealed in drums for disposal. Radiation field on these PVC bags was found to vary between 3-100 mGy/h. Radiation field on LHR and TOP cuno filters varied between 0.1-5.0 Gy/h, which got categorized by Solid Waste Management Site as Category-III waste and remaining solid waste got disposed as Category II and Category-III waste. [Table 4] gives details of the solid waste generated during CFF rod removal and post CFF event clean up operations.
| 3. Results and Discussion|| |
From the study of various CFF during last fifty years, it is found that each CFF rod incident generated 300 to 1140m 3 of liquid waste with total activity varying between 150-2615 GBq. Gamma spectrometry analysis of coolant water showed presence of significant amount of 133 I and 131 I, along with other fission products like 137 Cs, 140 La and 140 Ba. The collective dose consumption during CFF handling over the years was reduced significantly by lowering the Lower Header Room (LHR) background after thorough decontamination. Shower was installed inside LHR rubber station. After each flushing of fuel rods personnel were asking to take shower, so as to reduced external contamination on PVC suit, thereby reducing the external exposure. Contamination level at TOP and other areas in reactor hall varied in the range of 5-2000 Bq/cm 2 . Maximum contamination level during handling of CFF rod was always observed at TOP. Contaminated areas were subsequently decontaminated. Maximum air activity sample collected during one of such CFF rod event showed 3150 Bq/m 3 contributed significantly by 131 I. Contaminated clothes, mops, gloves and gumboots are packed in PVC bags and get disposed of as active waste. Radiation field on drums containing above waste varied between 10-100 mGy/h. Personnel involved in the work get thoroughly checked for contaminated and get decontaminated in case of contamination. All personnel involved are sent for whole body counting laboratory for assessment of any intake of radionuclides (if any) during handling of CFF rod. No internal dose was detected during handling of CFF rod.
| 4. Conclusion|| |
Radiological experience gained in handling of CFF rod with time resulted in lowering of collective dose from 110 to 12 Person-mSv per incidence and also reduction in spread of contamination. Radiation exposure to the personnel involved in CFF rod removal activity was kept as low as reasonably achievable (ALARA). During the last few years of Cirus reactor operation, no case of internal or external contamination was noticed during CFF rod handling.
| 5. Acknowledgements|| |
Contributions of all shift health physicists, RHC technician staff and Operational staff of Reactor Operations Division (ROD), Shift engineers, Senior Engineers and Maintenance personnel in the jobs related to above are acknowledged with thanks. Thanks are due to Dr. Anil Kumar Radiation Safety Systems Division (RSSD) and his group members for their whole hearted support in recording gamma spectrometry of samples.
| References|| |
|1.||Chuga RK. An Introduction to Cirus. 1982. |
|2.||Sharma VK, Singh KD, Gopalkrishan RK, Prasad SK. New FFD System at Cirus, Internal Report; 1999. |
|3.||SRUOR, ROD, Cirus (1965-2010). |
|4.||Radiological Surveillance Reports on Split Rod Removal by RHC Unit, Cirus (2004-2010). |
[Table 1], [Table 2], [Table 3], [Table 4]