THORIUM AND ITS UTILIZATION IN MOLTEN SALT REACTORS

1. Daniela Baldová NRI Řež, dept. 2401 THORIUM AND ITS UTILIZATION IN MOLTEN SALT REACTORS

2. OUTLINES Motivation for research of thorium fuel cycle The basic features of Th-U fuel cycle Nuclear system and projects of Th-U fuel cycle Thorium-based fuel cycle of MSBR Fuel salt requirements of MSBR Calculations Experimentation

3. RATIONALE FOR THORIUM FUEL CYCLE It is attractive way to produce long term NE Thorium is 3 to 4 times more abundant than uranium Better nuclear characteristics of Th232 and U233 Higher chemical and radiation stability of ThO2 Excellent past performance of ThO2, (Th,U)O2, ThC2 and (Th,U)C2 fuels in HTGRs Excellent possibility in CANDU-PHWR, ACR and AHWR

4. NUCLEAR SYSTEMAND PROJECTS Thorium-based fuel cycle is reasonable for both fast and thermal reactor systems In 1960s and 70s, the development of thorium-based nuclear fuel was a great interest worldwide The highest activity on Th as a nuclear fuel is found in India. Its nuclear power program is divided in three stages. In the development of Th-U oxide fuel in LWRs, there are two types arrangement: homogeneous and heterogeneous HTGR – KFA Juelich (Germany) has four decades of experience with Th as a nuclear fuel Molten Salt Breeder Reactor – fuel is contained in molten salt

5. DEVELOPMENT OF MSR Definition of MSR: fissile and fertile materials are dissolved in high-temperature, low pressure molten fluoride salt coolant The MSR concept was first studied in the fifties at ORNL The successful operation of the Aircraft Reactor Experiment In 1961 was started MSRE, which operated very successfully until shut down in 1969 Early in 1970 until 1976 ORNL worked on project of MSBR All molten salt projects were stopped in 1976

6. FUEL CYCLE OF MSR MSR fuel cycle scenarios – TRU burner (transmuter, MSTR) Th breeder (MSBR) Closed fuel cycle -Front-end reprocessing technology could be place separately - Back-end process should be directly connected with primary fuel circuit Fuel cycle technologies for MSR - Pyrochemical (dry method) – on-line reprocessing for MSR - Hydrometallurgical (aqueous method) – PUREX, THOREX, the LWR spent fuel reprocessing

7. SCHEME OF MSBR

8. FUEL CYCLE MSBR

9. SINGLE-FLUID versusTWO-FLUID MSBR Reprocessing technology of TWO-FLUID system could be significantly simplified Positive void effect in the case of loss of fertile salt in TWO-FLUID system Major drawback of the design of TWO-FLUID system is very short graphite lifetime

10. ONE-FLUID MSBR REPROCCESSING

11. TWO-FLUID MSBR REPROCESSINGFISSILE SALT

12. TWO-FLUID MSBR REPROCESSINGFERTILE SALT

13. FUEL SALT REQUIREMENTS Melting point of salt should be as low as possible Radiative capture cross section as low as possible Suitable physical properties – high heat conductivity, low vapour pressure, viscosity as low as possible Radiation resistance and thermal resistance Sufficient solubility of U, Th High electrochemical stability Optimal candidate for carriersalt is LiF-BeF2

14. SELECTED FUEL SALTS FOR MSBR

15. CALCULATIONS Calculation of Th-U cycle – what amount of U233 is formed by irradiation ofTh232 Calculation will be done by analytical methods (code MAPLE) Results are for neutron spectrum in core LWR-15: various mass of Th232 various irradiation time various decay time

16. RESOLTS Mass of Th232: 15E-3 g Irradiation time: 4 days Decay time: 270 days Resolution Mass of U233:3.44E-6 g Protactinium decay and formation U233

17. EXPERIMENTATION The main outline of this experimentation is to propose and experimentally verify methods for detection and determine U233 production in thorium. U233 production have been studied in case of two-fluid system (in Th salt) or in case of single-fluid system (in Th-U salt). We have needed samples of Th, U+Th, U for few days irradiation in reactor and the same as referential.

18. MEASURING PROCEDURE Sampleshave been irradiated in LVR-15 (ŘEŽ) for nearly 4 days Gammaspectrometry Decay time for few month (5 month) is requisite Measurement of delayed neutrons U233 amount analysis Comparison of the calculation withexperiment

19. IRRADIATED SAMPLES

20. GAMMA SPECTROMETRY • HPGe detector with relative efficiency of 18% • The detector is placed in a shielding box with 5 cm thickness lead walls. Detector and sample changer in shielding box

21. RESULTS OF GAMMA SPECTROMETRY • The Genie 2000 software is used for the activity evaluation. From the original Genie 2000 reports data are converted for loading to the Excel file. • From known activity U233 mass have been estimated

22. MEASUREMENT OF DELAYED NEUTRONS Pneumatic tube of LVR-15 have been used for irradiation Irradiation time 30 s The proportion detector He3 12NH25/1 have been used for measurement of delayed neutrons He detector was connected to measuring instrumentation EMK Device for measurement was formed from two cylinder made of paraffin Data taking from 25s to approximately 500s

23. DEVICE FOR MEASUREMENT

24. RESOLUTS OF MEASURMENET

25. CONCLUSION The closed Th-cycle offers the best performance with respect to long-lived waste radiotoxicity compared with U/Pu scenarios Ideal is a self-sustaining cycle, i.e. after number of cycles there is no further need for topping fuel In thermal reactors need to be excellent neutron economy, on-line refuelling and possibility of on-line reprocessing The best system in light of these points are MSBRs Study of MSBR confirmed excellent features of this system in particular Two-fluid concept Development of MSR is at the beginning but in future could play important part safety aspects and high breeding ratio of the reactor system

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