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ORIGINAL ARTICLE
Year : 2021  |  Volume : 44  |  Issue : 3  |  Page : 135-140  

Analysis of postoperation radiation hazards in inertial electrostatic confinement fusion neutron source facility at center of plasma physics under institute for plasma research


1 Institute for Plasma Research, Gandhinagar, Gujarat, India
2 Centre of Plasma Physics-Institute for Plasma Research, Nazirakhat, Assam; Homi Bhabha National Institute, Mumbai, Maharashtra, India
3 Institute for Plasma Research, Gandhinagar, Gujarat; Homi Bhabha National Institute, Mumbai, Maharashtra, India

Date of Submission09-Jun-2021
Date of Acceptance13-Oct-2021
Date of Web Publication04-Jan-2022

Correspondence Address:
H L Swami
Institute for Plasma Research, Gandhinagar - 382 428, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rpe.rpe_20_21

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  Abstract 


Center of Plasma Physics-Institute for Plasma Research, Nazirakhat, Assam, has the neutron source based on Inertial Electrostatic Confinement of Fusion. In order to scale up the source, it is planned to build a neutron source facility. The facility needs the construction approval from AERB India for occupational radiation safety during the operation and after the operation. It will also assess the short-term and long-term radiological hazards due to the neutron source. In order to evaluate the post irradiation radiation hazards due the neutron source, the radioactivation analysis of laboratory is carried out and reported here. The radioactivity in the laboratory building and source components after short-term and long-term operation has been assessed. The tritium activity in the soil is also evaluated. The calculation is also done for the contact dose rate estimations after operation to assess the maintenance applicability inside the laboratory. The inhalation dose inside the laboratory after the operation has been also calculated to avoid any hazards after operation maintenance activities. The article provides the complete details of post operation hazards analysis for the Inertial Electrostatic Confinement Fusion neutron source facility.

Keywords: Activation, FISPACT, fusion, Inertial Electrostatic Confinement Fusion, nuclear


How to cite this article:
Swami H L, Mohanty S R, Vala S, Srinivasan R, Kumar R. Analysis of postoperation radiation hazards in inertial electrostatic confinement fusion neutron source facility at center of plasma physics under institute for plasma research. Radiat Prot Environ 2021;44:135-40

How to cite this URL:
Swami H L, Mohanty S R, Vala S, Srinivasan R, Kumar R. Analysis of postoperation radiation hazards in inertial electrostatic confinement fusion neutron source facility at center of plasma physics under institute for plasma research. Radiat Prot Environ [serial online] 2021 [cited 2022 Jan 21];44:135-40. Available from: https://www.rpe.org.in/text.asp?2021/44/3/135/334777




  Introduction Top


Inertial Electrostatic Confinement Fusion (IECF) is a one of the way to generate the nuclear fusion process and produce neutrons. Center of Plasma Physics under Institute for Plasma Research has the IECF neutron source.[1],[2],[3] Deuterium–deuterium nuclear fusion process occurs in the device. It produces the neutron of 2.45 MeV energy. In order to operate the source with the maximum yield of 108 n/s, center is planning to build a laboratory for neutron source. The neutron source facility construction requires the approval from Atomic Energy Regulatory Board India. The construction of the building has been planned as per the radiation shielding assessment made using the radiation transport simulation.[4],[5] Details of the simulation and operational occupational dose rate assessment documented in the reference report.[6] A schematic model used in the neutronic calculation model of the laboratory is given in the [Figure 1]. Moreover, for the AERB approval process, the postirradiation effect on the laboratory components and construction is also required. The calculation of the postoperation impact on the laboratory due to the neutron irradiation has been estimated using the activation assessment code FISPACT.[7] It provides the details of expected hazards after the operation and support in the planning of postirradiation maintenance activities considering the protection of occupational workers.
Figure 1: Schematic model of Inertial Electrostatic Confinement Fusion lab

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  Methodology Top


The neutron spectrum estimation at desired locations is done using the Monte Carlo radiation transport code.[1],[2] It is estimated in the 175 energy group. The energy spectrum of neutrons in the IECF neutron source facility is shown in [Figure 2]. The peak on the 2.45 MeV shows the D-D nuclear fusion neutrons. The source strength of the IECF sour is 1 × 108 n/s. The material composition considered for the estimation of the radioactivation analysis is given in [Table 1]. The operation times considered for the analysis are 5 h, 100 h, and 1000 h which will provide the idea for short-term as well as long-term operation hazards. The radioactivation hazards estimations have been performed using the FISPACT inventory code.[7]
Figure 2: Neutron energy spectra at various locations inside Inertial Electrostatic Confinement Fusion laboratory

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Table 1: Elemental composition of materials

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FISPACT solves the Bateman equation and estimate the radioactive inventory in the material for certain fluence. It is developed for the neutron-induced activation calculations for nuclear fusion devices.[8] The number of atoms and isotopes formed during the irradiation and after the irradiation can be estimated though the code. It uses the EAF nuclear data libraries for the estimation. It can take various energy group spectrum for the activation calculation such as Vitamin-J (175), Vitamin-J+ (211), WIMS (69), GAM-II (100), etc., which makes it useful for other applications also apart from fusion.


  Results Top


IECF source neutrons first interact with the source chamber which is made of stainless steel. The neutron flux at the chamber is around 1.19 × 104 n/cm2.s. The radioactivity in chamber material is estimated after continues irradiations of 5 h, 100 h, and 1000 h, respectively. The simulated results of radioactivity with cooling time are presented in [Figure 3]. The activity level at chamber just after irradiation of 5 h, 100 h and 1000 h are 328 Bq/kg, 701 Bq/kg, and 1030 Bq/kg, respectively. The radioactivity generated in the SS304 is mainly due to the radioisotopes Co58m, Mn56, Co58. The radioactivity level even after 1000 h of irradiation is very low as per the IAEA radioactive waste categorization.[9],[10]
Figure 3: Activity in stainless-steel chamber after operation

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The contact dose rate after operation is shown in [Figure 4]. The dose rate at the surface of the chamber after 100 h of continuous operation is 0.15 μSv/h which is quite low as per occupational exposure control guideline of AERB.[11] Therefore, the maintenance near to the IECF source is quite safe even just after the operation.
Figure 4: Contact dose rate on stainless-steel chamber after operation

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The support structure for the source chamber is also got irradiated during the operation of IECF neutron source. The expected neutron flux at the support structure is around 1.4 × 103 n/cm2.s. The maximum radioactivity generated in the support structure after 1000 h of the operation is 680 Bq/kg which is quite low and falls under low level waste category. The radioactivity data are shown in [Figure 5]. The contact dose rate is also estimated at support structure and it is found below the regulatory guidelines. The short-term maintenance activities near the support are permissible immediate after the operation. The dose rate variation with cooling time after operation is shown in [Figure 6].
Figure 5: Activity in stainless-steel chamber support structure after operation

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Figure 6: Contact dose rate on stainless-steel chamber support structure after operation

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The radioactivation in the nearby concrete wall is also estimated and it is found low. The value after 100 h of the operation is 446 Bq/kg. It is not increase much even for 1000 h of the operation because the neutrons flux level at wall is quite low around 1.45 × 103 n/cm2.s. The radioactivity profile in the concrete wall is shown in [Figure 7]. The activity plot shows the flat profile up to 10 years of cooling. The reason of the flat profile is radioisotope K40. It is mainly leading the radioactivity in concrete during initial cooling years.
Figure 7: Activity in concrete wall after operation

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The contact dose rate at laboratory wall is also estimated after the operation and it is found below the 0.1 μSv/hr. It is quite low and safe for the working personnel. The contact dose rate profile is shown in [Figure 8].
Figure 8: Contact dose rate on concrete wall after operation

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The estimated neutron flux at the concrete floor near to the source is around 9.18 × 102 n/cm2.s. The radioactivity profile of the concrete floor is shown in [Figure 9] and contact dose rate is shown in [Figure 10]. The radioactivity and contact dose rate at the floor surface is quite low even after the 1000 h of the operation. Radioactivity after 100 h of operation is around 439 Bq/kg and contact dose rate around 0.05 μSv/h. It is very low as per the IAEA guideline for the radioactive waste.
Figure 9: Activity in concrete floor after operation

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Figure 10: Contact dose rate on concrete floor after operation

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The radiological hazards in the door of the IECF laboratory due to the neutron operation are also estimated. The door of the lab is made of HDPE material with sports of the SS-304. The neutron flux at the door is around 2 × 102 n/cm2.s. The radioactivity generated in the HDPE is very low. The maximum activity in the HDPE after 1000 h of the operation is 1.0 Bq/kg. The contact dose rate is below the considerable estimation. The radioactivity in the SS-304 structure of the door is higher than the HDPE. The radioactivity profile in the SS structure of the door is shown in [Figure 11]. The activity at the SS structure is around 376 Bq/kg, which is also quite low for the radiological consideration. The contact dose rate profile of the SS structure of the door is shown in [Figure 12]. The dose rate is quite low and safe for handling the door after operation.
Figure 11: Activity in stainless-steel structure of door after operation

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Figure 12: Contact dose rate on stainless-steel structure of door after operation

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The estimation of the inhalation dose inside the neutron source hall is also estimated using the FISPACT. The air activation calculation is done with the maximum flux level near to the source (air volume = 1 m × 1 m × 1 m). The flux level is 1.25 × 103 n/cm2.s. The inhalation dose profile is shown in [Figure 13]. It is around the 1 μSv/h after 1000 h of the operation. It is safe for the occupational workers as per the AERB. It also reduces further after few minutes of cooling. The inhalation dose estimation is made for stagnant air inside the hall, it is without ventilation circulation. It will be reduced further if ventilation is considered. The Ar41 derived concentration is also estimated which is 20 Bq/m3. The level of the Ar41 is well below the limit of 0.1 MBq/m3.[12] It is very safe for the human accessibility after the operation.
Figure 13: Inhalation dose due to air activation inside facility after operation

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The activation of the soil is also assessed to evaluate the ground water related radioactive hazards. It is found the activation level in the nearby soil is around 0.042 bq/kg which is very low after 1000 h of the operation. The tritium activity in the generated after 1000 h of the operation is around 7.0 mBq/l. As per the health advisory of the World Health Organization (WHO) and IAEA regarding the tritium in water,[13] the value 7.0 mbq/l produced due to the IECF operation is much smaller than the limit (104 Bq/l).


  Conclusions Top


The radioactivation analysis has been done to evaluate the radioactive hazards in the IECF laboratory after operation and assess the human accessibly to components during maintenance. The calculation has been performed using the inventory estimation code FISPACT. The radioactivity in the source chamber after 1000 h of the irradiation is 1030 Bq/kg that is very low as per the rad-waste classification criteria. The contact dose rate is also below the 1 μSv/h which makes the lab accessible for the maintenance activities. The laboratory door and concrete wall also have very low contact dose rate and activity after irradiation. The tritium generation in the soil is also very lower than the WHO limit for drinking water. The inhalation dose and Ar41 DAC value is also below the regulatory limit. The radioactivation assessment shows that IECF neutron source with 1 × 108 n/s yield is not going to create trouble making radiological hazards. The IECF facility seems safe for the operation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Buzarbaruah N, Dutta NJ, Bhardwaz JK, Mohanty SR. Design of a linear neutron source. Fusion Eng Des 2015;90:97-104.  Back to cited text no. 1
    
2.
Buzarbaruah N, Dutta NJ, Borgohain D, Mohanty SR, Bailung H. Study on discharge plasma in a cylindrical inertial electrostatic confinement fusion device. Phys Lett A 2017;381:2391-6.  Back to cited text no. 2
    
3.
Buzarbaruah N, Mohanty SR, Hotta E. A study on neutron emission from a cylindrical inertial electrostatic confinement device. Nucl Instrum Methods Phys Res A 2018;911:66-73.  Back to cited text no. 3
    
4.
Swami HL, Vala S, Abhangi M, RatneshKumar, Danani C, Kumar R, et al. Occupational radiation exposure control analyses of 14Â MeV neutron generator facility: A neutronic assessment for the biological and local shield design. Nucl Eng Technol 2020;52:1784-91.  Back to cited text no. 4
    
5.
Chadwick MB, Obložinský P, Herman M, Greene NM, McKnight RD, Smith DL, et al. ENDF/B-VII.0: Next generation evaluated nuclear data library for nuclear science and technology. Nucl Data Sheets 2006;107:2931.  Back to cited text no. 5
    
6.
Swami HL, et al. Radiation shielding assessment of proposed lab for IECF neutron source facility at CPP-IPR, IPR RR-1158.  Back to cited text no. 6
    
7.
Forrest RA. FISPACT-2007: User Manual. Culham: Report UKAEA FUS 534; 2007.  Back to cited text no. 7
    
8.
Swami HL, Danani C and Shaw AK. Activation characteristics of candidate structural materials for near term Indian fusion reactor and the impact of their impurities on design considerations. Plasma Sci Technol 2018;20:065602.  Back to cited text no. 8
    
9.
International Atomic Energy Agency. Classification of Radioactive Waste, IAEA Safety Standards Series No. GSG-1. Vienna: IAEA; 2009.  Back to cited text no. 9
    
10.
International Atomic Energy Agency. Application of the Concepts of Exclusion, Exemption and Clearance: Safety Guide. Vienna: IAEA; 2004.  Back to cited text no. 10
    
11.
AERB Directive No. 01/2011, [Under Rule 15 of the Atomic Energy (Radiation Protection) Rules 2004], Ref. No. CH/AERB/ITSD/125/2011/1507. Available from: https://aerb.gov.in/english/acts-regulations/safety-directives. [Last accessed on 2011 Apr 27].  Back to cited text no. 11
    
12.
International Atomic Energy Agency. Health Effects and Medical Surveillance, Practical Radiation Technical Manual No. 3 (Rev. 1). Vienna: IAEA; 2004.  Back to cited text no. 12
    
13.
World Health Organization. Guidelines for Drinking-Water Quality: Fourth Edition Incorporating the First Addendum. Geneva: World Health Organization; 2017.  Back to cited text no. 13
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13]
 
 
    Tables

  [Table 1]



 

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