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ORIGINAL ARTICLE
Year : 2014  |  Volume : 37  |  Issue : 2  |  Page : 68-70  

Radiological emergencies due to postulated events of melted radioactive material mixed in steel reaching public domain


Department of Atomic Energy, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, India

Date of Web Publication18-Dec-2014

Correspondence Address:
T R Meena
Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.147275

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  Abstract 

Radioactive materials are used widely in various applications, which in turn have resulted in its large scale availability to the various end users. Though in India, there is strict regulatory control on obtaining radioactive material and their use, there have been reported cases of radioactive material detected as steel contaminant in the public domain elsewhere. This led to the analysis on estimation of the radiation field during the postulated event of radionuclides 60 Co and 137 Cs getting into the alloys of steel. The postulated cases of radioactive material getting mixed during the alloy making are studied for two case studies to ascertain the detection and capability of identifying the radioactive material even in trace levels, are presented in this paper. For 60 Co and 137 Cs nuclides - either by design or unintentionally, as low as 10 mg gaining entry into the matrix of 100 kg of the alloy during its making, it is estimated and shown that the radioactive materials can easily be detected. It is feasible due to the use of sensitive radiation monitors available at the Emergency Response Centers-Department of Atomic Energy, which are capable of detecting radiation field above the natural radiation background, the event can be detected, and the consequences can be minimized.

Keywords: 137 Cs, 60 Co, recycling, dose rate, radioactivity, radiological emergency


How to cite this article:
Meena T R, Anojkumar, Patra R P, Vikas, Patil S S, Chatterjee M K, Sharma R, Murali S. Radiological emergencies due to postulated events of melted radioactive material mixed in steel reaching public domain. Radiat Prot Environ 2014;37:68-70

How to cite this URL:
Meena T R, Anojkumar, Patra R P, Vikas, Patil S S, Chatterjee M K, Sharma R, Murali S. Radiological emergencies due to postulated events of melted radioactive material mixed in steel reaching public domain. Radiat Prot Environ [serial online] 2014 [cited 2022 Nov 29];37:68-70. Available from: https://www.rpe.org.in/text.asp?2014/37/2/68/147275


  Introduction Top


Radioactive sources are used in a variety of applications in medicine, industry, and research for the benefit of society. The applications may involve the use of both sealed and unsealed sources. Radioactivity in such sources varies from few kBq (μCi) to hundreds of TBq (thousands of Curies). The regulatory bodies in various countries control the usage of radiation sources. In spite of regulatory controls for assuring safety and security of radioactive sources there have been incidents of theft, loss, or abandoned radioactive sources worldwide. These orphan sources routed through metal scrap used in steel recycling industry will end up as a consumer product with radioactive contamination. Radioactive material in unsealed form may also be present in scrap metal as a consequence of inadequate control during the decommissioning of a nuclear installation or other facilities. It may also arise as a consequence of the presence of radionuclides of natural origin (naturally occurring radioactive materials), which occur in industries that process large amounts of raw material; examples are the mining and processing of various ores and the production of oil and gas.

In the past, export of few contaminated products detected at various countries had been reported to regulatory agencies. [2] Since then, there has been a growing appreciation that such incident which can have significant impacts. The hazard to human health from such low levels of contamination is generally low when compared with that from orphan sources. Hence, the main problem is likely to be a financial loss to metal industries and export. This paper discusses two such postulated cases of melted radioactive material in steel which may give rise to radiological emergencies. The source originating from India is highly unlikely due to robust administrative control on radioactive material. However, in view of its potential threat to cause radiation emergency, the radiological aspects have been estimated on the postulated condition. The response mechanism available at our country is emphasized to mitigate such a scenario.


  Materials and methods Top


The specific activity of radioactive sources such as 60 Co, 137 Cs, 192 Ir, 90 Sr, and 241 Am is high due to their usage for respective applications. Hence, use of a small amount (in few gram amounts) of such radioactive material can cause higher levels of contamination in consumer products. The higher levels of radioactivity in GBq (Ci) may lead to radiation hazard component at recycling phase resulting in higher radiation exposure of industry workers. The radiological impact could be higher and also result in higher levels of contamination in steel products.

Case 1

In general, a pencil of 60 Co containing many pellets (~50 numbers) each of size 1 mm × 6 mm × 8 mm, approximately weight 10 g and the activity content in the pencil is about 100 Ci/g. Thus, the activity content in the pencil of 10 g is 37 TBq (1000 Ci). The radiation dose rate due to such pencils is in tens of Gy/h, could be masked in suitable lead shields. However, exposure due to unshielded pencils can cause lethal dose to the person.

Estimation of the radiation field was effected on the postulated condition of 60 Co pellet of 10 mg with activity content of 37 GBq as smelted and mixed in the material of mass 100 Kg in steel alloy. The radiation field on a sample with attenuation and self-shielding is estimated approximately to be 130 μGy/h. For the estimation of dose rate, a small sample of steel product of roughly 5 mm thickness with activity content 10 μCi as point source is considered. Dose rate is estimated at 2 cm distance by using following formula. [3]



Where

S = Photon fluence rate (photon/s)

E = Energy of photon (Mev)

μen /ρ = Mass energy absorption coefficient (g/cm 2 )

μ = Linear attenuation coefficient (cm − 1 )

t = Thickness of attenuating material (cm)

K = Collective constant to convert energy fluence rate to dose rate; if the dose rate is in Gray/h, k will have a value of 5.76 × 10−7 .

B = Buildup factor (here buildup factor assume one).

Case 2

In general, a pencil of 137 Cs containing many ceramic pellets (~50 numbers) each of size 1 mm × 5 mm × 5 mm, approximately weight 10 g, and the activity content in the pencil is about 6 Ci/g. Thus, the activity content in the pencil of 10 g is 2.2 TBq (60 Ci). The radiation dose rate due to such material is of Gy/h, could be masked in suitable lead shields. Exposure from unshielded ceramic pellets can cause lethal dose to the person.

Estimation of the radiation field is effected on the postulated condition of 137 Cs pellet of 10 mg with activity content of 2.2 GBq as smelted and mixed in the material of mass 100 Kg in steel alloy. The radiation field on a sample with attenuation and self-shielding is estimated approximately to be 20 μGy/h. For the estimation of dose rate, a small sample of steel product of roughly 5 mm thickness with activity content 3 μCi as point source is considered. Dose rate is estimated at 2 cm distance by above formula.


  Results and discussion Top


The process of removal of radioactive material from the housing which will be made up of lead or damaged shielded containers may result in direct exposure of industry workers. However, after sources in melted form may not result in higher exposures, but continue to result in contaminated consumer product over a longer duration. However, the detection probability of finished products due to the presence of contamination always remains because radiation above background level can be detected.

In addition to consequences for human health and the environment, the spectrum of potential consequences of such events is wide after detection of spread of radioactivity. It includes anxiety among workers and the general public about health consequences. The events may also result in large number of people seeking radiation monitoring for reassurance and continuing health surveillance of some people. The events may put substantial demands on the resources of the regulatory body and other authorities (such as police, customs, civil defense, and emergency planners). The demand may exceed the available resources and so necessitate the assistance of other states and other organizations. Spread of metal contamination will also result in severe commercial impact due to interruption of operations. The costs of recovery and clean-up of contamination may well exceed the assets of the affected company, causing bankruptcy and loss of jobs. The further impact includes loss of confidence in the metal recycling and production industries and excessive demand on the national radioactive waste management facilities owing to unplanned waste streams of a quantity that are difficult to manage. There may be adverse effects on international relations if the consequences extend beyond national boundaries. These may occur even if the radiological consequences are very low.

National level response mechanism is developed at Emergency Response Centers of Department of Atomic Energy (DAE-ERCs) at 22 different locations spread all over the country, and National Disaster Response Forces with National Disaster Management Authority (NDMA). [1] ERCs are equipped with radiation monitors, radionuclide identifiers, personnel radiation dosimeters with monitoring capabilities of the order of tens of nGy/h (μR/h) above the radiation background at any suspected locations. Even if small amounts of radioactive material are smuggled and brought in some other form into the public domain, ERCs are capable to detect, identify, and segregate the radioactive material from any inactive scrap. DAE-ERCs have demonstrated their capability in source search, detection, identification, and recovery during the radiological emergency at Mayapuri, New Delhi.


  Conclusion Top


The operators of a metal recycling and production facility should review the various steps involved in its processing of scrap metal, from receipt of the scrap metal to the dispatch of any metal products or wastes. This method will determine the point at which radiation monitoring would be the most effective. Account should be taken of possible shielding by any overlying scrap metal or a container of a source. In particular, the operator should routinely monitor the consignments of scrap metal on arrival at the facility, preferably close to the point of site entry, samples during the steel melting process, and final products before dispatch. The monitoring equipment should be selected in accordance with the type of facility. Facilities that handle large consignments of scrap metal should use stationary (portal) monitors for monitoring photon (and sometimes also neutron) radiation from consignments on arrival and any products (ingots, metal bars, wastes, etc.,) prior to dispatch. Such equipment should be sufficiently sensitive to be able to detect small increments in the level of radiation above natural background levels. Monitoring of consignments on arrival facilities; the identification of the origin of any radioactive material detected; by-product streams and waste streams, in particular gaseous effluents but also furnace dusts and slag, should be monitored routinely. Stationary detectors/installed radiation monitors rather than laboratory analysis of samples should be used wherever possible, as this will allow an immediate response to be made to any radioactive material detected.

The installation of portal monitors and vehicle monitoring systems at sea ports and airports have been initiated to prevent any illicit trafficking and import of orphan sources/contaminated metal scrap in the country. Periodic radiation monitoring of the major cities in the country, monitoring of vital places of public utility etc., can help in early detection of orphan sources, if any, in the public domain. A robust and much reliable emergency preparedness and response mechanism which is made available in India by DAE-ERCs can prevent such incidents and even if it happens, with technical and monitoring capability, the consequences can be minimized.

A comprehensive program of measures is a need of the hour to prevent, detect, and respond to cases of radioactive material in scrap metal across the globe. The countries without any Nuclear power program should have minimum program and capability for responding to such events. These measures include:

  • Prevention (physical protection; inventory and control, export-import control)
  • Detection (passive and active physical search for radioactive material)
  • Response (emergency response, investigation, law enforcement, information exchange, corrective action).



  Acknowledgment Top


The authors are grateful to Dr. D. N. Sharma, Director, HS and EG, BARC. The authors are also thankful to Dr. Pradeepkumar K.S., Head, RSSD, BARC and Shri Rajvir Singh, Head, ERSMS, RSSD for their continuous encouragement and providing valuable suggestions.

 
  References Top

1.
Emergency Response Centre, AMD. Nuclear/Radiological Emergencies. Challenges and Preparedness for Response: A Guide Book. Bangalore: Emergency Response Centre, AMD; 2006.  Back to cited text no. 1
    
2.
Singh KR, Agarwal SP, Radioactive contamination in steel products - Indian experience. In: Proceeding of International Conference on "Control and Management of Radioactive Material Inadvertently Incorporated into Scrap Metal." Tarragona, Spain: 23-27, Feb 2009. p. 263-271.  Back to cited text no. 2
    
3.
Chabot GE Jr. Shielding of Gamma Radiation, http://www.hps.org/documents/shielding_of_gamma_radiation.pdf  Back to cited text no. 3
    




 

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Abstract
Introduction
Materials and me...
Results and disc...
Conclusion
Acknowledgment
References

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