IAEA-TECDOC-1450 Thorium fuel cycle — Potential benefits and challenges May 2005 IAEA-TECDOC-1450 Thorium fuel cycle — Potential benefits and challenges May 2005 The originating Section of this publication in the IAEA was: Nuclear Fuel Cycle and Materials Section International Atomic Energy Agency Wagramer Strasse 5 P.O. Box 100 A-1400 Vienna, Austria THORIUM FUEL CYCLE — POTENTIAL BENEFITS AND CHALLENGES IAEA, VIENNA, 2005 IAEA-TECDOC-1450 ISBN 92–0–103405–9 ISSN 1011–4289 © IAEA, 2005 Printed by the IAEA in Austria May 2005 FOREWORD Thorium is three times more abundant in nature compared to uranium and occurs mainly as ‘fertile’ 232Th isotope. From the inception of nuclear power programme, the immense potential of 232Th for breeding human-made ‘fissile’ isotope 233U efficiently in a thermal neutron reactor has been recognized. Several experimental and prototype power reactors were successfully operated during the mid 1950s to the mid 1970s using (Th, U)O2 and (Th, U)C2 fuels in high temperature gas cooled reactors (HTGR), (Th, U)O2 fuel in light water reactors 7 232 233 (LWR) and Li F/BeF2/ThF4/UF4 fuel in molten salt breeder reactor (MSBR). Th and U are the best ‘fertile’ and ‘fissile’ materials respectively for thermal neutron reactors and ‘thermal breeding’ has been demonstrated for (Th, U)O2 fuel in the Shippingport light water breeder reactor (LWBR). ThO2 has also been successfully used as blanket material in liquid metal cooled fast breeder reactor (LMFBR) and for neutron flux flattening of the initial core of pressurized heavy water reactor (PHWR) during startup. So far, thorium fuels have not been introduced commercially because the estimated uranium resources turned out to be sufficient. In recent years, there has been renewed and additional interest in thorium because of: (i) the intrinsic proliferation resistance of thorium fuel cycle due to the presence of 232U and its strong gamma emitting daughter products, (ii) better thermo-physical properties and chemical stability of ThO2, as compared to UO2, which ensures better in-pile performance and a more stable waste form, (iii) lesser long lived minor actinides than the traditional uranium fuel cycle, (iv) superior plutonium incineration in (Th, Pu)O2 fuel as compared to (U, Pu)O2 and (v) attractive features of thorium related to accelerated driven system (ADS) and energy amplifier (EA). However, there are several challenges in the front and back end of the thorium fuel cycles. Irradiated ThO2 and spent ThO2-based fuels are difficult to dissolve in HNO3 because of the inertness of ThO2. The high gamma radiation associated with the short lived daughter products of 232U, which is always associated with 233U, necessitates remote reprocessing and refabrication of fuel. The protactinium formed in thorium fuel cycle also cause some problems, which need to be suitably resolved. The information on thorium and thorium fuel cycles has been well covered in the IAEA- TECDOC-1155 (May 2000) and IAEA-TECDOC-1319 (November 2002). The objective of the present TECDOC is to make a critical review of recent knowledge on thorium fuel cycle and its potential benefits and challenges, in particular, front end, applying thorium fuel cycle options and back end of thorium fuel cycles. The review has been prepared based on three consultancy meetings held at IAEA, Vienna 1–3 July 2002, 14–16 April 2003 and 15–16 September 2003, where experts from Canada, France, India, Israel, Japan, the Russian Federation, USA and IAEA had participated and supported by information and published papers from specialists on thorium fuels and fuel cycles. The IAEA wishes to express its gratitude to C. Ganguly (India) for chairing this working group and shaping this publication. The IAEA officers responsible for this publication were F. Sokolov, K. Fukuda and H.P. Nawada of the Division of Nuclear Fuel Cycle and Waste Technology. EDITORIAL NOTE The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA. CONTENTS 1. SUMMARY......................................................................................................................1 2. RATIONALE FOR THORIUM–BASED FUEL CYCLES............................................. 6 3. IMPLEMENTATION SCENARIOS AND OPTIONS.................................................. 10 3.1. Open and closed thorium fuel cycles................................................................ 10 3.1.1. Open fuel cycle ..................................................................................... 10 3.1.2. Closed fuel cycle................................................................................... 11 3.2. Nuclear systems and projects ........................................................................... 14 3.2.1. Light water reactors .............................................................................. 14 3.2.2. Heavy water reactors ............................................................................ 17 3.2.3. High temperature gas cooled reactor .................................................... 28 3.2.4. Molten salt breeder reactor ................................................................... 29 3.2.5. Fast reactors .......................................................................................... 31 3.2.6. Accelerator driven system .................................................................... 32 3.3. Innovative fuel.................................................................................................. 33 4. CURRENT INFORMATION BASE.............................................................................. 34 4.1. Nuclear data and methods................................................................................. 34 4.2. Fuel properties and irradiation behaviour......................................................... 38 4.3. Spent fuel isotopics, radiotoxicity and decay heat ........................................... 42 5. FRONT END ISSUES AND CHALLENGES............................................................... 44 5.1. Resources, mining and milling ......................................................................... 44 5.2. Types of fuels and fuel elements ...................................................................... 48 5.3. Fuel fabrication................................................................................................. 49 5.3.1. Powder-pellet route............................................................................... 51 5.3.2. Sol-gel processes................................................................................... 53 5.3.3. Vibratory compaction ........................................................................... 58 5.3.4. Impregnation technique ........................................................................ 58 5.3.5. Sol-gel microsphere pelletisation.......................................................... 59 5.3.6. Coated fuel particles ............................................................................. 61 6. BACK END ISSUES AND CHALLENGES................................................................. 65 6.1. Back end issues................................................................................................. 65 6.2. Reprocessing..................................................................................................... 69 6.2.1. Head end processes............................................................................... 70 6.2.2. Dissolution and solvent extraction........................................................ 72 6.3. Waste management........................................................................................... 76 6.4. Disposal of thoria fuels..................................................................................... 76 6.4.1. Introduction........................................................................................... 76 6.4.2. Chemistry of thoria ............................................................................... 76 6.4.3. Fission-product segregation.................................................................. 77 6.4.4. Reactor operation.................................................................................. 78 6.4.5. Conclusions........................................................................................... 78 7. PROLIFERATION RESISTANCE................................................................................ 79 7.1. Background....................................................................................................... 79 7.2. An assessment of proliferation resistance–general approach ........................... 79 7.3. Thorium fuel cycle............................................................................................ 81 7.4. Proliferation resistance effect of introducing Th–based fuel............................ 81 8. ECONOMIC ASPECTS OF TH–BASED FUEL CYCLES .......................................... 85 8.1. Background....................................................................................................... 85 8.2. Fuel cycle cost