Document Sample

         Dr. Carolyn D. Heising
            Iowa State University
      Professor of Industrial, Mechanical and
                Nuclear Engineering
               On Leave to GA, ‘08-’09
                   What if we could build a nuclear reactor that
                   offered no possibility of a meltdown, generated its
                   power inexpensively, created no weapons-grade
                   by-products, and burnt up existing high-level
                   waste as well as old nuclear weapon stockpiles?
                   And what if the waste produced by such a reactor
                   was radioactive for a mere few hundred years
                   rather than tens of thousands? It may sound too
                   good to be true, but such a reactor is indeed
                   possible, and a number of teams around the world
                   are now working to make it a reality. What makes
                   this incredible reactor so different is its fuel source:
                   Named after Thor, the warlike Norse god of
                   thunder, Thorium could ironically prove a potent
                   instrument of peace as well as a tool to soothe the
                   world's changing climate. With the demand for
                   energy on the increase around the world, and the
                   implications of climate change beginning to strike
                   home, governments are increasingly considering
                   nuclear power as a possible alternative to burning
                   fossil fuels.
                   (from: April
Spring 2009 Colloquium, UC Berkeley, Dept of
Nuclear Engineering, April 6, 2009

“Safeguards Considerations
of Thorium Utilization in
Nuclear Reactor Fuel Cycles”
Presenter: Dr. Carolyn D. Heising
Professor of Industrial, Mechanical and Nuclear
Iowa State University, Ames, Iowa
(On sabbatical leave to General Atomics, San Diego,
2008-09 academic year)

 • This paper examines Thorium utilization in
    nuclear reactor fuel cycles for once through
    in LWRs and High Temperature Gas Reactors
   (NGNP: Next Generation Nuclear Plant)
 • Focuses primarily on safeguards
    considerations for renewed interest in Thorium
    as a nuclear fuel:
   – Better proliferation resistance
   – Longer fuel cycles/higher burnup/improved
     waste forms

 • Recent proposed legislation in Congress:
 • “Thorium Energy Independence and Security Act of 2008”
     introduced in the U.S. Senate on October 2, 2008
 •    Requests an amendment to the Atomic Energy Act of 1954
     to provide for Thorium fuel cycle nuclear power generation
 • Senators Harry Reid and Orrin Hatch are cosponsors
 • Request $250 million for 2009-13 to DOE
  Introduction, contd.

 Several corporate entities are promoting
 the use of Thorium based fuel cycles
 particularly for countries such as India
 with large Thorium reserves
 Also for the use of reduction of plutonium
 stock piles
• //
Basis for Legislation

  • U.S. and foreign countries will require increasing amounts of
    energy over the next 20 years
  • Nuclear power provides energy without generating greenhouse
  • Nuclear power has been discouraged by concerns regarding
    proliferation of nuclear weapons and the disposal of nuclear

Basis for Legislation, contd
 • Nuclear power operating on an advanced Thorium fuel cycle
   could potentially produce less weapons useable materials than
   Uranium based fueled plants and would produce less waste
 • Thorium is more abundant than Uranium and there is Thorium
   based research in the U.S.
 • Thorium fuel cycle technology was originally developed in the U.S.
   and continues to be carried out in the U.S.

Basis for Legislation, cont’d.

  • It is in the national security interest of the U.S. that foreign countries
    seeking to establish or expand generation and use of nuclear
    power should be provided access to advanced Thorium fuel
    cycle technology and incentives to reduce the risk of nuclear

GNEP Programmatic Environmental Impact
Statement (PEIS)

• The Global Nuclear Energy Partnership
  (GNEP) Programmatic Environmental Impact
  Statement (PEIS) also includes Thorium based
  fuel cycles as options focusing primarily on
  the Thorium open fuel cycle.

 The purpose of this study is to assess, compare and
 evaluate various Thorium based options relative to
 Uranium and mixed oxide options based on recent
 research in this field.
Historical Background

 During the early years of nuclear energy, from 1950s to mid
 1970s, there was considerable interest worldwide to develop
 Thorium fuels and cycles in order to supplement Uranium
 In mid 1960s and 80s, several experimental and prototype
 power reactors were successfully operated using Thorium fuels.
 Indian Point 2 commercial PWR successfully used Thorium
 based fuel as well as Ft St Vrain HTGR built by General Atomics

  Renewed interest in Thorium as a
  nuclear fuel has developed based on
  the need for reactors with better
  proliferation resistance, longer fuel
  cycles, higher burnup and improved
  waste form characteristics, and
  reduction of Plutonium inventories
  Proponents say Thorium has multiple
  advantages over Uranium fuel
  because it is consumed more slowly
  in nuclear reactions than is Uranium
  This has the potential to
  cut the volume of nuclear
  waste in half
What is Thorium?

 • Thorium exists in nature in various mineral forms, e.g.
   Monazite, a rare-earth-and-Thorium phosphate mineral, is
   the primary source of the world's Thorium
 • Thorium was discovered by J.J. Berzelius in 1828
 • Named for Thor the Scandinavian god of war
 • The only Thorium isotope in nature is Th-232
 • Th-232 decays somewhat slower than the Uranium isotopes,
   therefore the abundance in the Earth’s crust is 3-4 times higher
 • Powdered Thorium metal will often ignite spontaneously in
   air (it is pyrophoric) and should be handled carefully.
Decay Chain of Thorium
Isotopes of Thorium

  Isotopes of Thorium occurring within the radioactive disintegration
  chains of Actinium, Thorium and Uranium :
  Radio-Actinium: Th 227
  Radio-Thorium: Th 228
  Ionium: Th 230
  Uranium Y: Th 231
  Uranium X1: Th 234
  Twenty-seven radioisotopes have been characterized, with the most abundant
  and/or stable being Th 232 with a half life of 14.05 billion years, Th 230 with a
  half-life of 75,380 years Th 229 with a half-life of 7340 years, and Th 228 with a half-
  life of 1.92 years.
  All of the remaining radioactive isotopes have half-lives that are less than thirty
  days and the majority of these have half-lives that are less than ten minutes. One
  isotope, Th 229, has a nuclear isomer(or metastable state) with a remarkably low
  excitation energy, recently measured to be 7.6 ± 0.5 eV.
  The known isotopes of Thorium range in atomic weight from 209 to 238.
Thorium is a FERTILE Material

 • Thorium (Th-232) is a fertile material that converts
   into fissile U-233 upon neutron irradiation
 • This is in contrast to natural Uranium (U-238) that
   also is a fertile material that must either be
   enriched with fissile Uranium (U-235) for use in
   LWRs or be utilized directly in Heavy Water
Neutronic Parameters of Fertile Nuclides

The thermal neutron capture cross
section for Th-232 (7.4 barns) is almost
three times higher than for U-238 (2.7
barns) : Quicker buildup of fissile U-233

The fast fission cross section of Th-232
is almost five times smaller than that
of U-238: Smaller contribution from
fast fission
Material Properties of Thorium Based Oxide
Fuels (vs UO2)
Material properties of ThO2 vsUO2:
•Heat conductivity higher
•Melting point > 300 deg C higher
•Heat capacity lower
•Gas diffusion rate lower
•Density 10% lower
•Thermal expansion coefficient lower
•Oxidation rate much lower

•Th02 is chemically more stable and has higher radiation
resistance than UO2. The fission product release rate for
ThO2-based fuels are one order of magnitude lower than
that of UO2.
•ThO2 is relatively inert and does not oxidize (unlike UO2
which oxidizes easily to U3O8 and UO3.) Hence, long term
interim storage and permanent disposal in a repository of
spent ThO2 based fuel are simpler without the problem of
oxidation (Source: IAEA ‘05)
 Thorium oxide fuels have performed
excellently in power reactors

 Large and easily accessible
 resources of thorium exist
 throughout the world
 India has the second largest
 (290,000 tons)
 Norway has 170,000 tons, U.S. has
 160,000 tons, followed by Canada
 with 100,000 tons
 Total World Deposits: 1,200,000
 SOURCE: U.S. Geological Survey (USGS) 2007

   Thorium utilization requires a
   seed of enriched Uranium or
   Plutonium since it is fertile, not
   fissile, which means it is NOT a
   “stand alone” fuel

   The U-233 produced by
   irradiation of Thorium has a
   uniformly good ratio of fission to
   capture probability for all
   neutron energies (both thermal
   and fast) that is larger than U-
   235 at all energies and even
   larger than Pu-239 for all but the
   most energetic fast neutrons
REACTORS: The Light Water Breeder Reactor
In contrast to the U238/Pu239 cycle in which breeding
can be obtained with only fast neutrons, the Th-232/U-
233 fuel cycle can also achieve high conversion ratios
and breeding in epithermal or thermal spectrum reactors
Light Water Breeder Reactor:
Adapting A Proven System
(source: ATOMIC INSIGHTS, 1995)
At 12:30 am, on August 26, 1977, the operators at the Shippingport Atomic Power Station began
lifting the central modules of the experimental breeder reactor core into the blanket section. At
04:38 am, the reactor reached criticality. During the next five years, the core produced more
than 10 billion kilowatt-hours of thermal power - equivalent to about 2.5 billion kilowatt hours of
electrical power - with a current retail value of approximately $200 million.
It showed no signs of approaching the end of its useful life. It was obvious from the core
performance that the reactor was at least a very efficient converter with a long life core.
However, in October, 1982, the reactor was shut down for the final time under budgetary
pressures and a desire to conduct the detailed fuel examination needed to determine if breeding
had actually occurred. A report on the experiment was quietly issued in 1987. The core contained
approximately 1.3% more fissile material after producing heat for five years than it did before
initial operation. Breeding had occurred in a light water reactor system using most of the same
equipment as used for conventional reactor plants.
New Fuel Source
Instead of using uranium-plutonium fuel like a liquid metal fast breeder reactor, the light water
breeder reactor used uranium-thorium. In a process very similar to the one that produces fissile
plutonium from U-238, it is possible to produce a fissile isotope of uranium, U-233, from thorium
The advantage of this combination from a technical point of view is that U-233 produces more
neutrons if fissioned by a low energy (thermal) neutron than does U-235. This characteristic means
that more excess neutrons are available to convert fertile material. In a carefully designed and
constructed reactor, uranium-thorium reactors have enough excess fission neutrons to overcome
the parasitic neutron absorptions inherent in a water cooled and moderated reactor.

Congress Directs The Navy To Look At
Thorium Fueled Reactors For Naval
Propulsion Power Needs
March 24, 2009
“The US House of Representatives had placed before it
on March 16 of this year, last week, a bill sponsored
by Mr Joe Sestak (D-Pa) directing the US Navy to study
all aspects of utilizing thorium in reactor fuel for
shipboard propulsion. Rear Admiral Sestak (Ret) is the
highest ranking former military officer currently serving
in the House of Representatives. Last month Senators
Hatch and Reid introduced into the Senate a
bipartisan bill to amend the Atomic Energy Act of 1954
to authorize the Nuclear Regulatory Commission to
study thorium fuel configurations and to fund such
studies. There is certainly a lot of activity in this session
of Congress with regard to a metal (THORIUM), which
..the US has in abundance, …..”

• Russia, France, the United Arab
  Emirates and many other countries
  have expressed interest
• The Atomic Energy of Canada
  (AECL) is also designing systems for
  retrofitting existing stations to
  convert from Uranium to Thorium
• AECL has signed a memorandum
  of understanding with China to
  cooperate on the design and
  engineering of a Thorium fueled
  CANDU reactor
• India has a full scale Thorium
  fueled reactor design of 300 MWe
  (constructed in next 5 year plan)
GNEP Thorium Alternative

• GNEP studied once through
• Found Thorium fuel cycle
  would require Uranium
  enrichments of 12.2 and 19.9
  percent (versus the 3-5 % for Uranium
  fuel cycle)
• No enrichment capacity yet exists in the
  U.S. to support higher enrichment
  percentages – an existing enrichment
  facility would need to be retrofitted with
  additional centrifuges or gaseous diffusion
  stages , or a new facility constructed
• Also, special fuel fabrication facilities
  would need to be constructed
 Thorium in HTGRs

Since U-233 is an excellent fuel
for reactors, neutronically the
best of all fissile materials, the
Thorium to U-233 conversion is
actually most favored in not-
quite-thermal reactors of low flux
such as the Helium cooled
graphite moderated HTGR, or the
Modular Helium Reactor (MHR) of
General Atomics
 TRISO Fuel Most Experienced with Thorium

Though Thorium fuel has been
  tested on all types of
  reactors with good results,
  the most significant
  experience with Thorium
  based fuels has been with
  ceramic coated TRISO fuel
  in the HTGR (Source: General
The HTGR has considerable
  adaptability to different fuel
  cycles and offers attractive
  opportunities for Thorium
  utilization in combination
  with enriched Uranium and
                     reactor core;
   LEU                intrinsically
                      safe design



                      TRISO fuel
                    in fuel blocks
   Thorium            or spheres

             - Key is TRISO coated fuel, secure to 2000oC
  Thorium Fuel Cycle Studied for 30 Years

• The use of Thorium based fuel cycles
  has been studied for 30 years (but on a
  much smaller scale than Uranium cycles)
• Basic R&D has been conducted in
  Germany, India, Japan, Russia, the UK,
  Canada and U.S.
• Test reactor irradiation of Thorium fuel to
  high burnups has been conducted
• AVR experimental pebble bed reactor in
  Julich,Germany operated 1967-88 at 15
  MW with Thorium based fuel
• Burnups as high as 150,000 MWd/t were
  obtained (compare to 40,000 MWd/t in LWRs)
Industrial Experience of Thorium

   •   Country      Name            Type       Power      Operation                Fuel
   •   Germany      AVR             HTGR       15 MWe     1967 – 1988             Th+U235 Driver,coated fuel particles

   •   Germany      THTR            HTGR       300 Mwe    1985 – 1989             Th+U235 Driver,coated fuel particles

   •   UK, OECD
   •   EURATOM      Dragon          HTGR       20 MWth    1966 -1973              Th+U235 Driver,coated fuel particles

   •   USA          Peach Bottom    HTGR        40 Mwe    1967 – 1974             Th+U235 Driver,coated fuel particles
   •                Fort St Vrain   HTGR       330 MWe    1976 – 1989             Th+U235 Driver,coated fuel particles
   •   USA (ORNL)   MSRE            MSBR       7.5 MWth   1964 – 1969             U233 Molten Fluorides

   •   USA          Shippingport    LWBR PWR    100 MWe     1977- 1982               Th+U233 Driver, oxide pellets
   •                Indian Pt 1     LWBR PWR    285 MWe     1962-1980                Th+U233 Driver, oxide pellets
   •   India        KAMINI           MTR        30 kWth     In operation          Al+U233 Driver,’J’ Rod of Th&ThO2
   •                CIRUS           MTR         40 MWth     In operation           same as KAMINI
   •                DHRUVA           MTR       100 MWth     In operation           same as KAMINI
   •                KAPS 1&2        PHWR       220 MWe      Continuing in all      ThO2 pellets
   •                KGS 1&2         PHWR       220 MWe       new PHWRs              same as KAPS
   •                RAPS 2,3,&4     PHWR       220 MWe                              same as KAPS
   •                FBTR             LMFBR      40 MWt        In operation         ThO2 blanket
   •   Canada       NRU &NRX        MTR                     Irradiation-testing     Th+U235, Test fuel
  Molten Salt Reactor (MSR)

One of the earliest efforts to use a Thorium fuel
cycle took place at ORNL in the 1960s. An
experimental reactor was built based on MSR
technology to study the feasibility of such an
approach, using Thorium-fluoride salt kept hot
enough to be liquid, thus eliminating the need for
fabricating fuel elements. This effort culminated in
the MSR experiment that used 232Th as the fertile
material and 233U as the fissile fuel. This reactor has
been operated successfully for about five years.
However due to a lack of funding, the MSR
program was discontinued in 1976. Nowadays this
design is considered a Generation IV reactor.
Generations of Nuclear Energy (DOE-NE)

• Quantity of total Plutonium produced is
  significantly lower (by a factor of 3 to
  4) due to the higher enrichment in the
  seed compared to conventional
  Uranium based fuel
• Distribution of Plutonium isotopes within
  the spent fuel is less attractive for
  potential weapons use
• Proliferation resistance is enhanced
  due to the presence of U-232 and its
  strong gamma emitting daughter
 Safeguards Aspects, contd.
• Thorium can be mixed with Uranium
  initially to “denature” the bred U-233
  to keep its concentration below
  acceptable non proliferation limits
• Weapons useable Pu-239 is a factor
  of 4.2 less in Thorium fuel than in
  Uranium fuel
• The seed is high in Pu-238 leading to
  a decay heat rate of 3.7 times
  greater than that from Plutonium
  derived from Uranium fuel and 29
  times greater than that from
  weapons grade Plutonium
Thorium/Plutonium Fuel

• An alternative for the reuse of
  plutonium in LWRs is
  Thorium/Plutonium fuel
• This is an attractive fuel cycle option
  for an effective reduction of
  Plutonium stockpiles
• The once through fuel cycle with
  Plutonium as initial fissile material
  reveals the potential for significant
  Plutonium reduction rates and for
  proliferation resistant spent fuel

Though some advocates of
Thorium fuel have suggested
that Thorium based fuel
cycles are entirely
proliferation resistant, the
fact remains that it is
possible to use U-233 to
assemble both gun and
implosion type nuclear
It is also true that it is much easier to
do so with U-235 for the gun type and
with Pu-239 for the implosion type
Radkowsky Design
                                           Dr. Alvin Radkowsky
                                            American-Israeli physicist
                                           American-born Israeli nuclear physicist (b. June 30,
                                           1915, Elizabeth, N.J.—d. Feb. 17, 2002, Tel Aviv,
                                           Israel), helped build the world’s first nuclear-
                                           powered submarine, the USS Nautilus, in the early
                                           1950s and, later in his career, worked on
                                           developing a nuclear reactor fuel that would
                                           produce a minimal amount of radioactive waste.
                                           Radkowsky studied electrical engineering at the
                                           City College of New York (B.S., 1935) and physics
                                           at George Washington University, Washington, D.C.
                                           (M.S., 1942), and the Catholic University of
                                           America, Washington, D.C. (Ph.D., 1947). In 1938 he
                                           went to work for the Department of the Navy as a
 Thorium Power has patented a
                                           civilian nuclear physicist. From 1950 to 1972 he was
 proprietary seed and blanket              the department’s chief scientist in charge of
 configuration proposed by Radkowsky       developing nuclear-ship technology, and he
                                           guided the construction of the Nautilus, which was
 Kazimi at MIT studied this design and
                                           launched in 1954. Radkowsky lived in Israel from
 other Thorium fuel cycle alternatives     1972. While teaching at Tel Aviv University, he
 MIT did confirm that the Pu-238 content   proposed using thorium to replace much of the
                                           uranium in nuclear reactors as a way to limit the
 would be 3-4 times higher than with
                                           creation of harmful waste; his thorium theory was
 conventional Uranium fuels                being tested at the time of his death in 2002.
 Radkowsky design does facilitate a
 significant reduction in Plutonium
 production as verified by MIT (60 -70%)
Thorium Power Collaboration with Kurchatov
Institute, Moscow

• For the past 5 years, Thorium Power
  has been testing its fuel design- a
  Thorium-Uranium blend designed to
  be more proliferation resistant-in a
  research reactor at Moscow’s
  Kurchatov Institute.
• Over the next few years plans exist to
  test fuel in a commercial reactor and
  to market the technology with the
  Russian government approval
• (Source: U.S. News & World Report,
The Norwegian Thorium Initiative

 • Technical feasibility study indicated existing reactor
   systems are suitable to operate on a large fraction of
   Thorium fuel
 • Thor Energy of Norway’s Thorium initiative derives from
   Norway’s Thorium energy potential from large reserves
 • Closing the cycle is necessary to achieve the best benefit
   of using Thorium and will require substantial R&D
 • Norwegian company Thor Energy AS plans to set up
   Norway's first Thorium-fuelled nuclear power plant (NPP) in
   the mountains outside Porsgrunn in Grenland, eastern
   Norway, Norwegian business daily Dagens Naeringsliv (DN)
   was quoted as saying on January 28, 2008

 • Further detailed safeguards studies
   need to be performed of the relative
   proliferation resistance of Thorium
   based fuels versus
   Uranium/Plutonium mixed oxide
   fuels with and without reprocessing
 • Because of the high gamma activity
   of Th-U spent fuels, remote and
   automated reprocessing and
   refabrication in heavily shielded hot
   cells will be required for closed
   cycle options with increased costs

 • Data base for Thorium fuels is limited (compared to U and
   U/Pu fuels) and will need to be extended before making
   large commercial investments
 • MIT determined that Thorium based fuels could cost
   anywhere from 10 percent less to 10 percent more than
   conventional nuclear fuels
 • This wide range stems from fundamental uncertainties
   about the cost of seed Uranium which must be four times
   more enriched in U-235 than is the case for typical nuclear

  • Interest in Thorium utilization is continuing in many
    countries, particularly India, where collaborations are
    being established for joint research in the deployment of
    Thorium nuclear fuel designs motivated by non proliferation

                     Nuclear power reactors throughout the world

Shared By: