Nuclear Fuel Origins [UPSC Notes]

In March 2023, Chinese scientists developed a technique to identify whether nuclear fuel originated in one of six types of nuclear reactors. In this article, you can read about identifying the origins of nuclear fuel, and the difficulties thereof, for the IAS exam science and technology segment.

Identifying Nuclear Fuel Origins

Nuclear fuel is highly regulated due to its destructive potential, and various entities, including governments, regulators, and militaries, maintain detailed inventories to safeguard it. 

• Nuclear forensics utilizes analytical methods to identify the source of nuclear materials. 
• The spent nuclear fuel can be uniquely identified based on the reactor type, the fuel’s exposure time inside the reactor, and the degree of enrichment. Enrichment pertains to the quantity of fissile isotopes, such as uranium-235, present in the fuel compound, such as uranium dioxide.

Chinese scientists have developed a technique to identify whether the fuel originated in one of the six types of nuclear reactors.

• Their method can distinguish between spent fuel from two common types of reactors that have historically presented a challenge to scientists. 
• The team used experimental data and machine learning (ML) to identify the origins of nuclear materials and whether they were used for military applications. The work was published in Physical Review Applied in March 2021.

Difficulty in Identifying Fuel from Different Reactors:

• Differentiating spent fuel from boiling water reactors (BWRs) from that of pressurized water reactors (PWRs) is difficult since both types use water as a moderator and have comparable thermal neutron spectra. Consequently, they are similar in terms of neutron reaction mechanisms. 
• Additionally, both reactors produce thermal neutrons with similar energies, further complicating the identification of the reactor type from which the fuel came.

Experimental Data and Machine Learning:

• The scientists used experimental data instead of simulations to develop a technique that can reliably distinguish between spent fuel from BWRs and PWRs. 
• The researchers used a database that contains the composition of different isotopes in spent fuel from reactors over 50 years. They developed equations that related these quantities to each other and applied the equation to different isotope ratios in the database. 
• The team then used machine learning models to distinguish fuel from BWRs from that from PWRs. Their best models correctly identified 91% of fuel from BWRs and 95% of fuel from PWRs.

Conclusion:

• This development has significant implications for nuclear forensics and nuclear security. The ability to identify the origins of nuclear materials can help prevent nuclear terrorism and reduce the risk of nuclear proliferation. 
• The scientists’ technique can identify the reactor type that the spent fuel came from, which will aid in determining whether the fuel was used for military purposes. 
• Using experimental data and machine learning, the team has developed a method that is more reliable than previous simulations-based methods.

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