Políticas Energéticas para a Sustentabilidade 25 a 27 de agosto de 2014
Florianópolis – SC
Thorium as a New Primary Source of Nuclear Energy
José Rubens Maiorino1
João Manoel Losada Moreira
Giovanni Laranjo de Stefani.
Alexander Lucas Busse
Thiago Augusto dos Santos
ABSTRACT
The current nuclear power plants uses Uranium as a primary source of energy in an
once through fuel cycle which, keeping the present uranium consumption, will be
exhausted in the end of this century. To extend the utilization of uranium as source of
energy, new concepts of evolutionary reactors and recycling of uranium and plutonium
in thermal reactors are already in use. The introduction of fast breeder reactors in
closed fuel cycles could extend the Uranium utilization for centuries. Another
alternative for primary source of nuclear energy is Thorium, which is being considered
in several types of reactors and fuel cycles. Thorium reactors present the advantage
of reducing the production of high level waste, and extending the burnup with a
significant gain of natural resources. In addition, a synergy between the utilization of
Uranium and Thorium in closed fuel cycles and transmutation of nuclear waste in
advanced reactors move nuclear power in the direction of a sustainable source of
energy.
Keywords: Primary Energy Sources, Thorium, Nuclear Reactors, Sustainability.
2 1. INTRODUCTION
The present time nuclear power plants (NPP) use Uranium as a primary source
of energy mainly in Light Water Reactors (LWR), which are reactors of Generation II
utilizing the once trough fuel cycle (OTC). These reactors, also called thermal reactors
because they generate energy through fission reactions with thermal neutrons, utilize
Uranium oxide fuels (UOX). Some countries including France, Belgium, Japan and
others use similar reactors but also recycle the spent fuel and utilize mixed oxide fuels
with Uranium and Plutonium (MOX). The new reactors under construction, Generation
III types (WNA, 2014), such as the AP1000 and the EPR are also based on similar fuel
cycles. Nuclear reactors for naval propulsion are based pm Uranium fuels
Most of the Uranium required by the nuclear industry comes from reserves,
which are sized based on their cost of extraction from Uranium mines (NEA/IAEA,
2010). The current Uranium reserves are estimated in ~ 7000 kt including reasonably
assured reserves and inferred reserves (NEA/IAEA, 2010). The current production of
U from mines is estimated to be around 60 kt, whereas the consumption is estimated
to be 70 ktU (WNA, 2010). The deficit is provided by stockpiles accumulated from
previous production or disassembled weapons. The expected reserve duration is
around 40 years for Uranium price less than USD 80.00/kgU and current consumption
rate. It is around 60 years for prices less than USD 130.00/kgU, and around 100 years
for prices less than USD 260/kgU. Therefore Uranium as a primary source of energy
is limited to this century if only thermal reactors and OTC fuel cycle technology are
utilized. New concepts of revolutionary reactors (Generation IV) and advanced fuel
cycles, such as fast reactors and accelerator driven systems, could extend the Uranium
reserves duration for centuries, and provide an answer for the problem of management
of spent fuels (US NERAC& GIF, 2002; NEA, 2002).
In this article, we discuss the use of Thorium as a primary source of energy in
nuclear power plants. We consider the possible utilization of Thorium in current nuclear
power plants such as thermal reactors and in advanced reactors, as well as the
reduction in the radiological toxicity of spent fuels. Finally, we review the past Brazilian
experience in R&D on Thorium utilization.
2. THORIUM AS A PRIMARY SOURCE OF ENERGY
Thorium (Th) is an actinide metallic element with abundance in the earth crust
which has a half-life of 4x1010 years. Thorium oxide (ThO
2) is relatively inert and does
not oxidize further, unlike UO2. It has higher thermal conductivity and lower thermal
expansion coefficients compared to UO2, as well as a much higher melting point
(3300°C).The fission gas release in irradiated Th nuclear fuels is much lower than in
UO2. These properties tend to improve the nuclear and thermal hydraulic
characteristics of Uranium and Thorium mixed oxide fuels compared to current
Uranium oxide fuels(WNA, 2014).
Although the cross section for fission at thermal energy is zero (non-fissile
material), and only fast fission would be possible by using thorium, given the high
capture thermal cross section for the reaction, 232Th(n,γ)233Th→233Pa→233U (fissile),
makes that Th could be used to produce 233U, and used as fuel, mixed with uranium or
plutonium in thermal reactors or in the core or blankets of fast reactors.
Most of thorium resources is found in the form of ThO2 (Thorianite), ThSiO4
(Thorite) or in monazite sand (mixture of Calcium, Cerium, Thorium, and other
rare-earth elements). It is important to note that there is probably more energy available for use from thorium in the minerals of the earth’s crust than from combined uranium and fossil fuel sources. There is no standard classification for Thorium resources as one
finds for Uranium resources because it is not a primary exploration target of the mineral
industry. The resources are usually estimated in relation to uranium and rare earth
resources. Table 1 displays the estimated current reserves for reasonably assured and
inferred resources recoverable at a cost of $80/kg Th or less (IThEO, 2014). Table 1
presents upper figures and place Brazil as the owner of the largest Thorium reserves
in the world (IThEO, 2014). Details about the Th reserves in Brazil are presented in
Table 2 (GENTILE, 1996). The IAEA estimates in 606 kt the Brazilian indicated
reserves and 700 kt, the inferred reserves. The last information from International
4
Table 1 - Estimated thorium reserves in the word (higher estimation)
Country
Th reserves
(kt) Country
Th reserves (kt)
Brazil 1300 Canada 172
Turkey 880 Russia 155
India 846 South Africa 148
Australia 521 China 100
US 434 Greenland 93
Europe 430 Kazakhstan 50
Egypt 380 Rest of the world 1781
Venezuela 300 World 7590
.
Table 2 – Potential Thorium resources in Brazil
Occurrence Associated
Mineral
Content (%)
Measured
(kt ThO2)
Estimated
(kt ThO2)
Coastaldeposits (ES) Monazite 5 2.25 -
INB deposits Monazite sand 3.5
Morro do Ferro(MG) Thorite and
others
1 to 2 35 -
Barreiro, Araxá (MG) Pyrochlore 0.09 - 1200
Area Zero, Araxá (MG) Pyrochlore 0.09 30 -
Aluvial andPegmatite Monazite 5 3 2.5
Total 73.75 1202.5
Total (estimated +
measured) reserves 1276.25
3. THORIUM UTILIZATION IN POWER REACTORS
Since the beginning of nuclear energy development, Thorium was considered
as a potential fuel, mainly due to the potential to produce fissile 233U. Several Th/U fuel
cycles using thermal and fast reactors have been proposed, such as the Radkowsky
OTC for PWR and VVER, the thorium fuel cycles for CANDU reactors. Th has been
proposed as fuel for the molten salt reactor, the advanced heavy water reactor, fast
breeder reactors, and more recently, for the innovative accelerator driven system in a
double strata fuel cycle (MAIORINO, 2003). All these concepts besides the increase
constrain) and the waste radiological toxicity reduction. In this section, we review the
thorium utilization in power reactors.
3.1 Light Water Reactors
Given that the majority of the nuclear power plants are PWRs running mainly in
OTC, many R&D programs had focused in this problem. In the sixties in the USA, the
PWR Indian Point Reactor 1 (270 MWe) was the first to utilize mixed oxide fuels with
Thorium,(Th-U)O2. Also the last core of the Shippingport PWR which was shutdown in
1982, was ThO2 and (Th-U)O2, operating as a Light Water Breeder Reactor in the
seed-blanket concept during 1200 effective full power days of operation. The fuel
reached a burnup of 60 MWd/kg HM. The seed-blanket concept proposed by
Radkowsky offers an option for thorium fuel utilization in LWR, and a nonproliferation
fuel cycle. It is basically a typical fuel element of a Westinghouse PWR divided into two
regions: a seed with LEU enriched U, and a blanket with mixed U-ThO2
.(IAEA-TECDOC 2003)
The Radkowsky concept is currently being considered for utilization in Russia’s
VVER with hexagonal assemblies, with studies conducted by the Kurchatov Institute
in Moscow, Brookhaven National Laboratory, and MIT in the USA. The Institute of
Physics and Engineering in Obninsk, Russia, is conducting research in the utilization
of Thorium in a VVER-1000. France performed neutronic studies of thorium utilization
for a 900 MWe PWR. Thorium-plutonium oxide (Th-MOX) fuels for LWRs are being
developed by Norwegian proponents with aview that these are the most readily
achievable option for tapping energy from thorium. A thorium-MOX fuel irradiation
experiment is underway in the Halden research reactor in Norway since 2013.
Various groups are evaluating the option of using thorium fuels in in an
advanced reduced-moderation BWR(RBWR). This reactor platform, designed by
Hitachi Ltd and JAEA, should be well suited for achieving high U-233 conversion
factors from thorium due to its epithermal neutron spectrum. High levels of actinide
destruction may also be achieved in carefully designed thorium fuels in these
6 3.2 Heavy Water Reactors
Thorium in heavy water reactor is of strategically interest in heavy water reactors
in countries like Canada and India, since the natural resources in these countries are
significant. For the Canadian Deuterium Reactor (CANDU), AECL is conducting
programs on thorium fuel cycles, including fuel-cycle studies, reactor physics
measurement, and development of reactor physics methods, fabrication of thorium
fuels, and fuel irradiation.
Chinese R&D groups associated with Canadians study the possible Thorium
fuel use in the China's Qinshan Phase III PHWR units (pressurized heavy water
reactor). Closed Thorium fuel cycles have been designed in which PHWRs play a key
role due to their fuelling flexibility. Thorium based HWR fuels can incorporate recycled
U-233, residual plutonium and uranium from used LWR fuel, and also minor actinide
components in waste-reduction strategies. In the closed cycle, the driver fuel required
for starting is progressively replaced with recycled U-233, so that an increasing energy
share in the fuel comes from the Thorium component. AECL has a Thorium Roadmap
R&D project (WNA, 2014). In July 2009 a second phase, agreement was signed among
AECL, the Third Qinshan Nuclear Power Company (TQNPC), China North Nuclear
Fuel Corporation and the Nuclear Power Institute of China to jointly develop and
demonstrate the use of Thorium fuel in heavy water reactors ( WNA, 2014)
In India, the utilization of Thorium is a priority since it has relatively modest U
resources but very large Th resources. BARC (Brabha Atomic Research Center), is
actively involved in R&D, fabrication, characterization and irradiation testing of ThO2,
(Th-Pu)O2, (Th-U)O2 fuels in power and test reactors. Some steps towards utilization
of Thorium in India include use of ThO2 for flux flattening in PHWR, use of (Th-Pu)O2
fuels, and use of ThO2-233UO2 fuels in the Advanced Heavy Water Reactor. In addition,
the KAMINI Test Reactor was the first to utilize 233U-Al alloy fuels. Fuel cycles studies
in PHWR (SSET- Self Sustaining Equilibrium Thorium), had been also conducted by
India.
India’s nuclear developers have designed an Advanced Heavy Water Reactor (AHWR) specifically as a means for ‘burning’ thorium – this will be the final phase of their three-phase nuclear energy infrastructure plan. The reactor will operate with a
form. It is a heavy water moderated and light water cooled reactor expected to maintain
a self-sustaining 233U production. In each assembly, 30 of the fuel pins will be Th-233U
oxide, arranged in concentric rings. About 75% of the power will come from the
Thorium. Construction of the pilot AHWR is envisaged in the 12th plan period to 2017,
for operation about 2022.
For export, India has also designed an AHWR300-LEU which uses low-enriched
Uranium, Thorium and no Plutonium input. About 39% of the power will come from
Thorium via in situ conversion to 233U. This fuel, with about 8 % fissile isotopes, can be
used in light water reactors (WNA, 2014)
3.3 Generation IV and Accelerator Driven Systems
The Generation IV proposed reactors and Accelerator Driven Systems (ADS)
include technical features aiming at improving safety and sustainability issues. Some
of these proposals consider Th fuels for energy generation. The High Temperature
Gas Cooled Reactor (HTGR) considered in its design coated micro spheres of Thorium
and high enriched uranium. The only US commercial Th/U fuelled HTGR in operation
was the Fort St. Vrain (330 MWe). The Gas Cooled Fast Breeder Reactor, also
propose to utilize Th as blanket. Since HTR is one of the Generation IV proposed
reactors, it is expected they adopt Th fuels.
In the 1960s the Oak Ridge National Laboratory (USA) designed and built a
demonstration molten salt reactor (MSR) using 233U as the main fissile driver in its
second campaign. From 1954 to 1969 the reactor ran at power as high as 7.4 MWt.
The lithium-beryllium salt worked at 600-700ºC and ambient pressure. The R&D
program demonstrated the feasibility of this system and identified corrosion and safety
issues that would require further studies.
There is a renewed interest in developing thorium-fuelled MSRs. Projects is
underway in China, Japan, Russia, France and the USA (MAIORINO& CARLUCCIO,
2004). The MSR is one of the six Generation IV reactor designs selected as worthy of
further development( US NERAC&GIF, 2002).
Although Thorium is a fertile material (233U producer) and quite eligible for fast
reactors it has not been considered as fuel for the liquid metal fast reactors. The only
8
of ThO2 as axial and radial blanket in the Kalpakkam Fast Breeder Test Reactor in
India (IAEA-TECDOC, 2003).
ADS are an innovative reactors in which a subcritical fuel mixture (U,Th,Pu, and
transuranium isotopes) is bombarded with ultra-fast neutrons coming from a spallation
source induced by an accelerator. Given the hard fast spectrum this concept is being
considered as a dedicated burner of high level waste (minor actinides, and long lived
fission products) ( MAIORINO, 2003). The preferable fuel cycle is the double strata
using the concept of partition and transmutation (NEA, 2002). Thorium and Th/U fuel
cycle are considered for the ADS concept.
A group from CERN, led by Carlos Rubbia, presented two concepts of ADS
named Fast Energy Amplifier, a sub critical nuclear system based in the utilization of
233U and Thas fuel and cooled by melted lead ( RUBBIA, 1995). The Rubbia concept
was applied to study the possible incineration of Spain’s nuclear waste. The study concluded that to incinerate the waste from its 9 large PWRs it was necessary a cluster
of 5 Fast Energy Amplifiers would be an effective solution. The present and foreseen
(2029) PWR waste stockpile of Spain would be eliminated in 37 years with a major
improvement over Geological repository solution (RUBBIA, 1997).
3.4 Review of the Thorium fuel cycle (Brazilian experience)
Since the 1960’s it was recognized the possible importance of the Thorium for
Brazil. A research group from Minas Gerais conducted the first studies. This research
group, called “Thorium Group”, in cooperation with the French CEA aimed at the
development of a Thorium fueled pressurized heavy water reactor (PHWR) with a
concept of a pre-stressed concrete reactor vessel. This project was named “Instito/Toruna”, and developed its reactor conceptual design (fuel technology, reactor physics, thermal hydraulics, reactor vessel, materials and component test and fuel
cycle economics). In the early 1970’s the project was discontinued
(MAIORINO&CARLUCCIO, 2004).
In the early 1970’s, in a cooperation between IPEN and USA General Atomic, several research studies regarding Th technology for HTGR were carried out. Many of
these studies resulted in thesis presented at São Paulo University, papers, and internal
reports on thorium utilization in HTGR, Gas Cooled Fast Reactors, and even the
possible utilization of Thorium in PWRs. In 1975 this research program was
During 1979 and 1988 was carried out the largest and comprehensive R&D
program on Thorium utilization in power reactors ( KFA/NUCLEBRAS, 1988). It was
conducted by the Brazilian Center for Development of Nuclear Technology (CDTN) in
Belo Horizonte. The general objectives of the program were: a) to analyze and prove
thorium utilization in PWRs; b) to design PWR fuel elements and the reactor core for
the Th-fuel cycle; c) to manufacture, test and qualify Th-U and Th-Pu fuel elements
under operating conditions; d) to study spent fuel treatment and thorium fuel cycle by
reprocessing spent Th-containing PWR fuel assemblies. The program was interrupted
in 1988 when a complete reformulation of the Brazilian nuclear sector took place and
the CDTN was transferred from NUCLEBRAS to the Comissão Nacional de Energia
Nuclear (CNEN). A final report (KFK/NUCLEBRFAS, 1988) contains detailed technical
results obtained in this research program. A very important one was the U-Th fuel
behavior studies conducted in irradiation experiments at the FRJ-2 reactor at the KFA,
a German nuclear research center in Jülich.
Other research initiatives regarding Thorium took place at IEAv (Institute for
Advanced Studies) in São José dos Campos. More recently, IPEN, Universidade
Federal de Minas Gerais (UFMG) and Universidade Federal do ABC (UFABC) conduct
research studies on Th fuels(FERNANDES&MAIORINO, 2011).
4. FINAL REMARKS
This paper has shown that there is a great interest in the Th utilization in power
reactors and waste burners. Studies show that (Th-U)O2 fueled reactors have an
extended burnup compared to UO2 fueled reactors and reduce significantly the amount
of high level waste (Pu, minor actinides and long lived fission products). Regarding the
utilization of thorium in Brazilian reactors, we notice that current Uranium reserves is
sufficient for no more than 33 new PWRs with 1000 MW electric power. This number
could be significantly increased with Thorium utilization.
Finally, given the Brazilian large Thorium reserves, it appears important to follow
the steps taken by India and other countries and promote R&D programs on Thorium
in the country. In addition, energy planners should consider Thorium as a nuclear
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