Thorium and Its Future Importance for Nuclear Energy Generation

Thorium was discovered in 1828 by the Swedish chemist Jons J. Berzelius. Despite some advantages over uranium for use in nuclear reactors, its main use, in the almost two centuries since its discovery, thorium was restricted to use for gas mantles, especially in the early 20th century. In the beginning of the nuclear era, many countries had interested on thorium, particularly during the 1950-1970 period. There are about 435 nuclear reactors in the world nowadays. They need more than 65,000 tons of uranium yearly. The future world energy needs will increase and, even if we assumed a conservative contribution of nuclear generation, there will be a significant increasing in the uranium prices occur, taking into account that uranium, as used in the present thermal reactors, is a finite resource. Thorium is nearly three times more abundant than uranium in the Earth＇s crust. Despite thorium is not a fissile material, ^232Th can be converted to ^233U （fissile） more efficiently than ^238U to ^239pu. Besides this, since it is possible to convert thorium waste into non-radioactive elements, thorium is an environment-friendly alternative energy source. Thorium fuel cycle is also inherently resistant to proliferation. Some papers evaluate the thorium resources in Brazil over 1,200,000 metric t. Then, the thorium alternative must be seriously considered in Brazil for strategic reasons. In this paper a brief history of thorium is presented, besides a review of the world thorium utilization and a discussion about advantages and restrictions of thorium use.

Conceptual Proposal of a Facility Design for Accommodating Minipigs for Pharmaceutical and Radiopharmaceutical Research

The use of Animal House Facilities of IPEN-CNEN/SP （Nuclear and Energetic Research Institute-National Nuclear Energy Commission/SP, Brazil） has provided rats and mice with controlled sanitary quality for research and quality control in the production of radiopharmaceuticals lots, produced at IPEN, following rules of CONCEA-Brazilian National Council for Animal Experimentation Control and approved in CEUA （Ethics Committee on the Use of Animals）, before they are sent to hospitals and clinics spread out in Brazil, for use in nuclear medicine. The production and the supply of high quality laboratory animals have fundamental importance for the accomplishment of vanguard scientific research, with reproducibility and universality. The quality of those animals depends, largely, on the available facilities for their production and lodging, to assure the demanded sanitary control and animal＇s welfare, in agreement with the ethical principles that control the activity. Therefore, the facilities design is of vital importance so that the mentioned requirements can be reached. Nevertheless, pigs and miniature pigs have gained importance as large animal models in medicine. With their size, organ capacity, and physiology resembling in several aspects that of humans, pigs are well suited for preclinical experiments and long-term safety studies. Minipigs will be used for preclinical testing of radiopharmaceuticals and assays radioactive materials for cardiac tests. This paper describes the premises and preliminary activities that have been performed at IPEN for the design of new Animal House Facilities dedicated to keeping minipigs taking into account fundamental aspects such as： animal＇s welfare, sanitation, genetic, in agreement with the ethical principles that control the activity and environmental concerns.

Cutting Techniques for Facilities Dismantling in Decommissioning Projects

Fuel cycle related activities were accomplished in IPEN-CNEN/SP in laboratory and pilot plant scale and most facilities were built in the 70-80 years. Nevertheless, radical changes of the Brazilian nuclear policy in the beginning of 90＇s determined the interruption of several fuel cycle activities and facilities shutdown. Some laboratory and pilot plant decommissioning activities have been performed in IPEN in the last years. During the operational activities in the decommissioning of old nuclear fuel cycle facilities, the personnel involved in the task had to face several problems. In old facilities, the need of large components dismantling and material removal use to present some difficulties, such as lack of available and near electricity supply. Besides this, the spread out of the superficial contamination in the form of dust or aerosols and the exposure of workers should be as much as possible avoided. Then, the selection and availability of suitable tools for the task, mainly those employed for cutting and segmentation of different materials is of significant importance. Slight hand tools, mainly those powered by rechargeable batteries, facilitate the work, especially in areas where the access is difficult. Based on the experience in the dismantling of some old nuclear facilities of IPEN-CNEN/SP, some tools that would have facilitated the operations were identified and their availability could have improved the quality and efficiency of different individual tasks. In this paper, different cutting problems and techniques, as well as some available commercial hand tools, are presented as suggestion for future activities.

Use of Dopants for Thoria Sintering TemperatureReduction-Characterization of TH02

Thorium is nearly three times more abundant than uranium in the Earth＇s crust. Some papers evaluate the thorium resourcesin Brazil over 1,200,000 metric t. These figures mean that the country is probably the biggest thorium resource in the world, with onlypart of the territory prospected. Nevertheless, Brazil has not a research program for use of thorium in nuclear reactors, even havingdedicated special attention to the subject in the beginning of its nuclear activities, in the fifties and sixties. From 1985 until 2003 IPENoperated a pilot plant for thorium nitrate production and purification, used by Brazilian industry for production of gas mantles. Thisfacility produced over 170 metric t of thorium nitrate. Despite the non-nuclear application, the pilot plant was unique in the southernhemisphere. On the other hand, Brazil has the biggest world niobium resources. The Brazilian thorium and niobium resources added tothe predictable future importance of alternative fissile materials have motivated this research, since uranium is a finite resource if usedin the present thermal nuclear reactors. Besides this, thorium oxide is an important nuclear reactor material. It is a refractory oxide andits ceramic fabrication process involves a very high temperature sintering treatment considering that thoria melting point is very high（3,650 K）. Cations of elements of the group VB （V, Nb and Ta） have a known effect in the reduction of thoria sintering temperature.IPEN has initiated an investigation about the use of niobium as a dopant for thoria sintering temperature reduction. The thoria used inthe research was produced in the IPEN＇s pilot plant and different amounts of niobium oxide （Nb2Os） will be added to thoria by differentroutes. The powders will be compressed and the compacted pellets will be sintered at different temperatures. The influence of thedifferent parameters in the density of sintered pellets is being investigated. This paper presents the chemical and physicalcharacterization for the thoria used in the investigation.

Molten Salts as Stripping Media for Radioactive Superficial Decontamination

The main practical difficulty associated to the task of the dismantling and decommissioning of the IPEN＇s old nuclear fuel cycle facilities has been the big amount of radioactive waste generated in the dismantling operations. The waste is mainly in the form of contaminated carbon steel structures. In the IPEN, the presence of contamination in the equipments, structures and buildings, although restricted to low and medium activity levels, constituted an important concern due, on one hand, to the great volume of radioactive wastes generated during the operations. On the other hand, it should be outstanding that the capacity of radioactive wastes stockpiling in IPEN found been exhausted. In function of the large waste volume generated in the dismantling operations, the main concems and focuses of research and technological development in the IPEN＇s Chemical and Environmental Center--CQMA have been the effluent and waste treatment subjects, besides the development of some special decontamination techniques, since most old nuclear fuel cycle facilities are installed in the CQMA＇s area. The reduction of the radioactive waste volume has a significant impact in the decommissioning costs and in the amount of material to be stored. The mentioned steel structures, during the operations and after ten or twelve years after the facilities shut down, have presented severe corrosion. In the past, to protect them, several layers of paint were applied. Traditional decontamination methods were tried, such as acid pickling, alkaline washing and ultrasonic baths. Nevertheless, these methods have failed to reach effective decontamination. In this paper, we described some aspects and problems in decommissioning of IPEN＇s nuclear fuel cycle facilities and it is presented an innovative method for radioactive superficial decontamination of steel structures using different molten salt compositions and temperatures as stripping media.