|Year : 2010 | Volume
| Issue : 4 | Page : 216-218
Gamma dose mapping at D 2 O heat exchanger room, valve room-dhruva reactor using EPR dosimetry
Jyotsna A Sapkal1, DP Rath1, S Thanamani1, B Rajeshwari2, T Krishna Mohanan1, Pankaj Sorate1, Sajjin Prasad1, S Murali1, RM Kadam2
1 Radiation Safety Systems Division, BARC, Mumbai, India
2 Radiochemistry Division, BARC, Mumbai, India
|Date of Web Publication||1-Dec-2011|
Radiation Safety Systems Division, BARC, Mumbai
Source of Support: None, Conflict of Interest: None
EPR dosimetry finds application in gamma dose measurements whenever the dose range is above Gy level. Suitable matrices are used as cumulative dosimeters. The present study describes the dose mapping of D 2 O heat exchanger room and Valve room of Dhruva reactor, while the EPR dosimetry was used with Alanine and Lithium Carbonate as the dosimeters for cumulative gamma dose measurements. The samples in duplicate, were irradiated for two different irradiation time intervals. Results of the two sets of irradiations for 600 hours (~25 days) and 1200 hours (~50 days) of gamma irradiation and their dosimetric signal readings, found to agree within ±5%, are presented.
Keywords: EPR dosimetry, alanine, Dhruva reactor
|How to cite this article:|
Sapkal JA, Rath D P, Thanamani S, Rajeshwari B, Mohanan T K, Sorate P, Prasad S, Murali S, Kadam R M. Gamma dose mapping at D 2 O heat exchanger room, valve room-dhruva reactor using EPR dosimetry. Radiat Prot Environ 2010;33:216-8
|How to cite this URL:|
Sapkal JA, Rath D P, Thanamani S, Rajeshwari B, Mohanan T K, Sorate P, Prasad S, Murali S, Kadam R M. Gamma dose mapping at D 2 O heat exchanger room, valve room-dhruva reactor using EPR dosimetry. Radiat Prot Environ [serial online] 2010 [cited 2021 Aug 3];33:216-8. Available from: https://www.rpe.org.in/text.asp?2010/33/4/216/90478
| 1. Introduction|| |
Electron Paramagnetic Resonance (EPR) technique is useful in quantifying the radiation induced paramagnetic radicals, as a measure of irradiation dose delivered, thereby has application in the field of dosimetry (Regulla et al., 1982; Murali et al., 1999, 2000, 2005). The EPR dosimetry has a few well known EPR dosimeters. Alanine, Lithium Carbonate to name a few, are among the dosimetric substances, that are commonly used to elucidate dosimetric response in the form of radiation induced (paramagnetic) radicals, in turn quantified by the EPR spectrometer (Murali et al., 1999, 2000, 2005). The D 2 O Heat Exchanger room and Valve room areas exhibit high radiation field during reactor operations, thereby restricting the usage of conventional dosimetric systems. Since EPR dosimetry has viability for high dose ranges, it was decided to carry out gamma dose mapping of select areas of the reactor using EPR dosimetry.
| 2. Dhruva Reactor|| |
2.1 Gamma dose mapping
Dhruva is 100 MW research reactor using U (nat) as fuel with and D 2 O as coolant, moderator and reflector. Maximum thermal neutron flux is of the order of 1.8×10 14 n/cm 2 /sec. There are three Main Coolant Pumps (MCP) for circulating D 2 O coolant coming out from the core through three different loops, where the heavy water is cooled by the process water. In secondary heat exchangers process water is cooled by sea water. Due to the presence of activation products like 16 N and 19 O, the radiation field inside the heavy water loop rooms is very high during reactor operation and become no entry areas during normal reactor operation. Since the high energy gamma emitting activation products are short-lived, the radiation field comes down drastically after 30 minutes of reactor shut down and subsequently, the entry into these rooms are permitted. On account of this, the measurement of radiation field inside the loop rooms is not possible, during reactor operation by conventional radiation survey techniques. To have certain security systems installed at designated places, gamma dose mapping of these areas was desired using certain non-invasive technique.
2.2 EPR measurements
During gamma dose mapping study the dosimetric samples were kept at the identified places for irradiation, for known duration of time interval (~25 days, ~50 days). The dosimetric signal got accumulated as radiation induced paramagnetic radicals. The paramagnetic radical concentration is quantified as a measure of spectral peak intensity, under identical conditions using EPR spectrometer. A calibration plot was obtained for the different dosimetric samples irradiated with a known amount of irradiation dose against the EPR intensity. Using this plot the cumulative irradiation dose received at the reactor site by the samples that were exposed at desired locations could be estimated.
| 3. Experimental|| |
The gamma chamber GC-900, RCD, RLG was calibrated using the secondary standard viz., Fricke Dosimetry. The gamma dose rate was estimated as 1.5 kGy/h. It was proposed to use Alanine and Lithium Carbonate samples for the dose mapping study. Set of Alanine and Lithium Carbonate samples drawn from the same batch, in duplicate, were irradiated in the calibrated gamma chamber. Thereby, the gamma dose delivered to the samples was known. EPR (first derivative) spectra of the irradiated Alanine and Lithium carbonate samples were recorded at room temperature. The peak-peak height of the first derivative signal at g = 2.0038 for alanine samples was used and for Lithium Carbonate samples the signal at g=2.0036 was used for EPR dosimetry. The first derivative EPR signal of the dosimetric systems is given in [Figure 1].
|Figure 1: First derivative EPR spectra, a. Alanine, b. Lithium carbonate|
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Calibration graph was generated for each of the dosimetric systems using the EPR spectral peak intensity (arb. units) Vs Gamma irradiation dose in 25-1000 Gy range. The calibration graph for the Alanine and Lithium Carbonate is as shown below [Figure 2] and [Figure 3].
The set of Alanine and Lithium Carbonate samples (100 mg of 2 sets each) used for calibration and the samples irradiated in DHRUVA reactor at designated places for gamma radiation dose mapping, were analyzed using EPR spectra obtained under identical conditions. Irradiated samples were read at room temperature, using Bruker ESP-300 at X-band frequencies [9.67 GHz, 15 dB (6.3 mW), 6.3×10 4 , 2.5 G, 3300-3550 G]. The average of dosimetric signal readings of either set of samples was used for calibration and dose mapping studies.
| 4. Results and Discussion|| |
The gamma dose mapping results at the places indicated in the reactor site is given in [Table 1]. The radiation field at the respective places can be worked out since the irradiation (Reactor operating) time-for the either set of samples is known (~25 days/600 hrs and ~50 days/1200 hrs).
| 5. Conclusion|| |
Thus, the EPR dosimetry is found useful in the dose mapping of high radiation areas and in specific cases where the conventional dosimetric systems/techniques could not be used. From the results of dose mapping, the radiation field at the desired locations could be estimated. The results of radiation field at the locations of D 2 O Lines are in conformity to the anticipated radiation field at the site.
| 6. Acknowledgements|| |
The authors wish to thank Head, ROD for the facilities during irradiation of samples at Dhruva reactor. The authors thank Dr. D. N. Sharma, Head, RSSD, Dr. V. K. Manchanda, Head, RCD and Dr. P. C. Gupta, Head, RHCS, RSSD for their support and facilities for the gamma dose mapping studies.
| 7. References|| |
- Murali S., Natarajan V., Venkataramani R., Pushparaja, Bora J.S., and M. D. Sastry (1999), Alanine-EPR dosimetic studies under simulated conditions of a reactor containment, Journal of Rad. Prot. and Env.,
- 22 (4), 1999.
- Murali, S., Natarajan V., Sarma K.S.S., Venkataramani R., Pushparaja, and M. D. Sastry (2000), Alanine-EPR dosimeter: Application for dosimetry in Industrial Electron Beam Accelerator, Journal of Rad. Prot. and Env., 23 (3), 164, 2000.
- Murali. S., Thanamani M. and Pushparaja (2005), 'ESR Dosimetric Investigation of Li 2 CO 3 ' , IARPNC -2005.
- Regulla D.F et al., (1982), Dosimetry by EPR spectroscopy of alanine, Int. Jrl. Appl. Rad. Isot. 33, 1982.
[Figure 1], [Figure 2], [Figure 3]