History of Materials Research: Six decades of operation of the IEA-R1 nuclear research reactor.


The IEA-R1, the first nuclear reactor in Brazil and the first research reactor in Latin America, completed 60 years of uninterrupted operation. This was commemorated with an international workshop on the use of research reactors. The event was held from November 28 to December 1 2017 in the city of São Paulo, in the auditorium of the Nuclear and Energy Research Institute (IPEN), located on the main campus of the University of São Paulo (USP). According to the organizers, about 300 people from different countries participated in the event.

IEA-R1 is well known in Brazil for producing radioactive isotopes that are used in medicine, industry and agriculture, partially meeting the national needs. Examples are Iodine-131, produced in IEA-R1 since 1959 and used in the diagnosis and treatment of thyroid cancer, and Samarium-153, used as a palliative tool to treat pain in bone metastases.

In addition to providing these elements to hospitals, industries and other entities, the IEA-R1 has been used, since the beginning, in research in several areas, including the Materials area. This research filed uses beams of free neutron (neutrons that were separated from the nuclei of the atoms), generated in the nucleus of the reactor through the nuclear fission process. The interaction of the neutrons with the samples provides unique information on the structure and composition of the materials.

According to Frederico Genezini and Rajendra Narain Saxena, IPEN researchers and current and former manager of the Research Reactor Center (CRPq), respectively, neutrons have a very specific feature of interacting with matter. It is possible, through scattering, to carry out studies of crystalline structures, and since the neutron has a magnetic moment, it is also used to study the magnetic properties of materials.

IEA-R1.
IEA-R1.

Located at IPEN, the reactor is formed by a 9-meter deep pool of deep blue waters. This color is originated by the so-called Cherenkov effect, in which charged particles (in this case, ions generated by nuclear fission) cross the medium (in this case, water) at a higher speed than light in that medium, emitting the flashy blue radiation. The pool water is contained by 1 to 3 meter thick walls constructed of very hard concrete. The bottom of the pool houses the reactor core, in which uranium is bombarded with neutrons, generating nuclear fission reactions. As a result, the nuclei of the uranium atoms are divided into two, while two or three neutrons and a large amount of energy are released (that very strong energy that holds the protons and neutrons together in the nucleus of the atom). While in the nuclear plants the released energy is harnessed, in the research reactors the most important product is the neutrons, the reason why the reactor components aim at preserving the free neutrons.

Water and concrete around the core perform important safety functions that prevent harmful levels of radiation from passing into the vicinity of the pool, where researchers, the team responsible for the reactor and the visitors circulate (about 2,000 people visit the IEA-R1 every year).

The process of producing uranium for IEA-R1 is completely carried out in Brazil. The ore is extracted and processed in the state of Bahia, enriched to a little less than 20% at the Navy Technological Center in Iperó (São Paulo state), and finally packed inside the “fuel elements”, which are then placed in the core of the reactor. Brazil belongs to the group of only 12 countries that can enrich uranium.

Neutrons to investigate matter

Around the pool – at the bottom, the IEA-R1 reactor has 12 experimental stations, in which neutron beams extracted from the reactor are available to be used in conjunction with several experimental techniques.

According to Genezini and Saxena, at present only three of the stations have equipment installed: the high-resolution neutron diffractometer, real-time neutron imaging systems, and the experimental system for boron neutron capture therapy (BNCT). However, other stations are available – on demand – for the installation of instruments. The first two facilities are very useful for studying materials, and have advantages over equivalent equipment that uses X-rays instead of neutrons. According to Genezini and Saxena, the diffractometer allows studying crystallographic structures of materials that an X-ray diffractometer cannot always observe, besides the study of magnetic structures.

“While X-rays interact with matter through electromagnetic forces, neutrons basically interact via nuclear forces,” explains Reynaldo Pugliesi, an IPEN researcher responsible for neutron imaging equipment, designed and built at IPEN and installed in one of the IEA-R1 stations. For example, a sample of 1 cm2 analyzed at this experimental station can receive about 8 million neutrons per second.

Neutron imaging provides, without destroying or damaging the samples, two or three dimension images (the latter called neutron tomography) of details that would otherwise be imperceptible to the human eye. In particular, hydrogen-rich materials (such as oil, water, adhesives and rubbers) are particularly well captured in neutron imaging, even when encapsulated in metals such as steel, aluminum and lead. In fact, the neutrons can penetrate several inches into the metals and reveal what’s inside them. Also in this regard, neutron imaging is complementary to X-ray imaging: while neutrons reveal light materials that are behind heavy materials (such as a crepe tape inside an aluminum frame), X-rays reveal heavy materials behind lightweight materials (such as the bones in the hand).

Neutron tomography: inspection of a restoration made in a ceramic vessel to check the degree of perfection of the work.
Neutron tomography: inspection of a restoration made in a ceramic vessel to check the degree of perfection of the work.

The IEA-R1 is open to the scientific and business community through collaborations with CRPq researchers. “In this model we have many examples of institutions and companies that have used the IEA-R1 neutron beams and other instruments in the CRPq laboratories for measurements,” says Genezini. According to him, other models are not possible because there are no technicians dedicated to each instrument. “However, this model has proven to be inefficient and we are investing in instrumentation and regulations to make neutron beam equipment more accessible to people outside the organization,” concludes the CRPq manager.

History

The origins of the IEA-R1 nuclear reactor date back to the mid-1950s, when the United States, under President Dwight Eisenhower, launched the “Atoms for Peace” program, which disseminated and encouraged worldwide the peaceful use of nuclear technology. In this context, Brazil and the United States signed agreements aimed at the discovery and research of uranium in Brazil and the development and use in Brazil of radioactive isotopes for agriculture and industry. For this, it was necessary to have a nuclear reactor in the national territory.

Thus, in August 1956, the Brazilian government decreed the creation of the Institute of Atomic Energy (IEA), which would later be called IPEN, to supervise the construction and operation of the IEA-R1. The construction was carried out by the US company The Babcock & Wilcox Company, accompanied by a Brazilian team led by the first director of the IEA-R1, the Brazilian nuclear physicist Marcelo Damy de Souza Santos, also the founder of the IEA. In August 1957, the construction of the reactor was completed and, on September 16 of that same year, the reactor reached the necessary conditions to start operating. The inauguration ceremony of the IEA-R1 was held on January 25, 1958, with the presence of President Juscelino Kubitschek and the State Governor of São Paulo Jânio Quadros.

With the IEA-R1, Brazil was able to develop national knowledge to produce nuclear fuel, neutron research instruments and radioisotopes that have been used in health, agriculture and in various industries. The reactor was also used to produce, through the neutron-induced transmutation technique, semiconductors for electronic components that were exported. In addition, it was used to train reactor operators and to conduct academic work. According to Genezini and Saxena, more than 250 doctoral theses and master’s dissertations were defended during this period in the areas of Nuclear Physics and Condensed Matter, and more than a thousand scientific articles were published in indexed journals.

In the near future…

Another chapter in the history of research reactors in Brazil is being written. The Brazilian Multipurpose Reactor (RMB), a more modern nuclear reactor with 30 MW of power (versus 5 MW of IEA-R1) is underway. In conjunction with its experimental stations, the RMB will be a national laboratory open to the community for research and for production of radioisotopes, installed on a 2 million m2 site in Iperó (SP).

According to José Augusto Perrotta, technical coordinator of RMB, the reactor is still in the design phase. The conceptual and basic projects have already been completed, and the detailed project is being executed. In addition, the IBAMA (Brazilian Institute of Environment and Renewable Natural Resources) license has been issued, as well as the site license of CNEN. However, the initial timeline was affected by problems related to financial resources. “The Ministry of Science, Technology, Innovations and Communications did not release the resources in 2017,” says Perrota. “The project continued with only the resources designated in 2014. Every year without resources is a year behind schedule!” he laments.

 

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Featured article: Probing electrons of actinide compounds.


box englishA team led by researchers from Brazil was able to unveil details of the distribution of electrons in materials based on actinide elements (the 15 chemical radioactive elements, with atomic numbers ranging from 89 to 103).

The group of scientists developed an experimental method that allowed a unique probing of the 5f and 6d orbitals and their hybridization in materials based on uranium (one of the most abundant actinide elements in the earth’s crust). This allowed the team to demonstrate, for example, that 5f-6d hybridization determines the magnetic properties of the studied materials. The work left as a legacy an experimental system for research on various magnetic materials (3d metals, rare earths, actinides and others), available to be used by the international scientific community at the Brazilian Synchrotron Light Laboratory (LNLS).

The study was reported in a paper that was recently published in Nature Communications (Impact Factor 12,124). “In this paper, we demonstrate the use of magnetic circular dichroism (XMCD) on the L-border of uranium to directly probe the 6d and 5f orbitals and also their degree of hybridization, rather than just probing the 5f orbitals as for instance the actinides M absorption edges,” details the corresponding author of the paper, Narcizo Marques de Souza Neto, professor at UNICAMP and researcher at LNLS.

In order to probe the orbitals of the uranium compounds, especially UCu2Si2 and UMn2Si2, the scientists had to overcome the difficulties of manipulating the materials due to their toxicity. They also had to make a series of adjustments in the high-energy XMCD technique to improve its sensitivity (to extend its detection limits).

These developments were initially performed at the LNLS DXAS line, dedicated to X-ray absorption techniques. Currently, the XMCD instrumentation is part of the XDS line of LNLS which is dedicated to X-ray diffraction and spectroscopy, where it is being used and improved. In the future the technique will be available in Sirius (the latest generation of synchrotron light source which is being built in Campinas), more precisely in the EMA line, which will be dedicated to X-ray techniques under extreme conditions of pressure and temperature. According to Souza-Neto, who coordinates both the XDS line and the EMA project, the conditions for studying actinides and similar materials by XMCD will be unparalleled in Sirius.

In addition to advancing the knowledge on actinides, the research demonstrated the potential of the XMCD technique improved by the Brazilian team to continue unveiling the characteristics of these still experimentally understudied elements. A deeper understanding of actinides, says Souza-Neto, is necessary to propose new uses for these elements, and also to be able to use them more efficiently in existing applications, such as, for example, power generation, diagnosis and treatment of diseases and the production of special glasses.

Ricardo dos Reis (left) and Narcizo Souza-Neto (right), main authors of the paper. Between them, a screen with the representation of EMA beamline where XMCD experiments will be available in Sirius fourth-generation synchrotron source.
Ricardo dos Reis (left) and Narcizo Souza-Neto (right), main authors of the paper. Between them, a screen with the representation of EMA beamline where XMCD experiments will be available in Sirius fourth-generation synchrotron source.

The history behind this work

The origin of this work dates back to 2009, when Souza-Neto was studying rare earth electronic structure and magnetism during his postdoctoral fellowship at the Argonne National Laboratory in the United States. “I had the idea of expanding the study of rare earths to actinide compounds (Souza-Neto et al., Phys. Rev. Lett., 102, 057206 (2009)) using XMCD to probe a charge transfer in the 4f and 5d orbitals”, the researcher reports. Looking for materials with similar characteristics, he came across uranium compounds. “We first tried to start this study in Argonne, but the conditions there to carry this out were not as we had hoped,” he adds. He returned to Brazil in 2010 as a researcher of CNPEM, with the desire to continue this initiative. Thus, in 2011, Souza-Neto began to guide the doctoral research of Ricardo Donizeth dos Reis on this subject together with the co-supervisor Flávio César Guimarães Gandra, a professor at Unicamp, with whom he had previously collaborated.

Samples of uranium compounds were prepared and characterized in the Laboratory of Metals and Alloys of Unicamp, coordinated by Professor Gandra, where there was already research experience on actinide and rare earth materials. The X-ray absorption spectroscopy experiments were performed at Argonne’s Advanced Photon Source and at LNLS. “All experiments on the L edges of uranium, which make up the main innovative contribution of this work, were carried out at LNLS,” Souza-Neto details. “At Argonne the experiments were carried out on the M edge of uranium to probe the contribution of the 5f orbitals separately and corroborate our interpretation of the results,” he adds. Furthermore, the Brazilian group had the participation of a researcher from France in the theoretical simulations performed for interpreting the data.

The research was carried out with financial resources from the São Paulo Research Foundation; from the Brazilian federal agency Capes; from the Ministry of Science, Technology and Innovation of Brazil, and from the Office of Science of the United States Department of Energy.

Scientific paper:

“Unraveling 5f-6dhybridization in uraniumcompounds via spin-resolved L-edge spectroscopy”. R. D. dos Reis, L. S. I. Veiga, C. A. Escanhoela Jr., J. C. Lang, Y. Joly, F. G. Gandra, D. Haskel & N. M. Souza-Neto. Nature Communications 8:1203 (2017). DOI: 10.1038/s41467-017-01524-1. Link: https://www.nature.com/articles/s41467-017-01524-1