PRODUCTION OF ANNULAR AND COMPACT TYPE BURNABLE ABSORBER NUCLEAR FUEL PELLETS BY POWDER METALLURGY AND SOL GEL ROUTE

Öz

One of the major challenges of the nuclear industry is to improve the performance, safety and lifetime of reactors. In this area there are many efforts focused on the research and development of new materials in order to extend the fuel lifetime, increase the burn-up and optimize the power density distribution. With this aim a neutron absorber material is usually incorporated into the UO2 nuclear fuel. Gadolinium is an excellent burnable poison because it presents a large cross section for neutron absorption and allows the compensation of the excess reactivity of the fuel in the beginning of its life. The need to improve reactor performance through longer cycle lengths or improved fuel utilization has been apparent since the beginning of commercial nuclear power generation. Among several modifications introduced as a consequence, the fuel initial enrichment has been increased, which means that the additional amount of fissile material (235U) in the reactor core has to be compensated by the introduction of additional neutron absorber material in the reactor core. This compensation was initially achieved only by using neutron absorber materials assembled in control rods or/and by addition of soluble absorber (boric acid) in the reactor coolant. In Boiling Water Reactors (BWR), the use of soluble absorber in the coolant/moderator was prohibited for technological reasons. In Pressurized Water Reactors (PWR), boric acid as a soluble absorber added to the coolant/moderator has been routinely used, but the increase in initial fuel enrichment cannot be indefinitely compensated by increasing the boric acid concentration. Beyond a certain concentration, thermal expansion of water at start-up reduces the quantity of boron in the core, resulting ultimately in a positive moderator reactivity coefficient, which is an unacceptable situation regarding to the safe reactor operation. This is the reason why the introduction of solid burnable absorbers (or burnable poison) within the fuel rods was considered. The use of a burnable poison in nuclear reactors provides the necessary negative moderator reactivity coefficient at the beginning of core life and help to shape the core power distributions (Yayli,1995, Böhm, 1987 ) The poison material should have a high neutron absorption cross section and form daughter products with low absorption cross sections. Then, as soon as the irradiation proceeds, the burnable poison burns up and the macroscopic absorption cross section decreases. From a nuclear viewpoint, gadolinia is an excellent burnable poison, having a high neutron absorption cross section coupled to a burn up rate that, if properly designed, can match approximately the 235U depletion, minimizing the reactivity penalty at the end-of-cycle (EOC) (Stogen, 1982, Brandberg 1973)

Anahtar Kelimeler

• Burnable Absorber,nuclear fuel,gadolinia,annular type pellets,,solgel

Kaynakça

1. 1) IAEA-TECDOC-844, Characteristics and use of urania-gadolinia fuels, 1995.
2. 2) Yaylı, A., (1995). UO2-Gd2O3 Nükleer yakıt peletlerinde gadolinyum miktarıyla mikroyapı ve yoğunluk değişiminin düşük sıcaklık sinterlemesinde incelenmesi, Yüksek Lisans Tezi (MSc),YTÜ FBE-Yıldız-İstanbul.
3. 3) Böhm W. Kiehlmann H. D., Neufert A.& Peehs M., (1987). Kerntechnik. 50, 234-240.
4. 4) Stogen F. B., Nielsen L. A. & Grummer R. G., (1982). Transactions of the American Nuclear Society.40, 194-198.
5. 5) Brandberg S. G., (1973). Nuclear Technology. 18, 177-184.
6. 6) Zinkle S.J. & Was G.S., (2013). Materials challenges in nuclear energy, Acta Materialia. 61, 3, 735-758.
7. 7) D.Tobia, E.L. Winkler, J. Milano, A.Butera, R.Kempf, L. Bianchi & F. Kaufmann, (2014) Determination of Gd Concentration Profile in UO2-Gd2O3 Fuel Pellets, CNEA and CONICET, (8400) S.C. de Bariloche, Argentina.
8. 8) Durazzo, M., Saliba-Silva, A.M., Urano de Carvalho, E.F. & Riella, H.G. (2013). Sintering behavior of UO2–Gd2O3 fuel: Pore formation mechanism. Journal of Nuclear Materials. 433, 334.

9. 9) Durazzo, M. & Riela, H.G., (2008 September). Studies on the Sintering Behaviour of UO2-Gd2O3 Nuclear Fuel Interlaken, Switzerland, Paper No. 114 IYNC 2008.
10. 10) Song, K.W., Kim K.S., Yang J.H., Kang K.W. & Jung Y.H., (2001). A Mechanism for the Sintered Density Decrease of UO2-Gd2O3 Pellets under an Oxidizing Atmosphere. Journal of Nuclear Materials. 288, 92.
11. 11) Leyva, A.G., Vega, D., Trimarco, V. & Marchi, D., (2002). Homogeneity characterisation of sintered (U,Gd)O2 pellets by X-ray diffraction, Journal of Nuclear Materials. 303, 29-33.
12. 12) Renier J.-P. A. & Grossbeck, M. Development of Improved Burnable Poisons For Commercial Nuclear Power Reactors, ORNL/TM-2001/238.
13. 13) Hoai-Nam Tran, Hung, T.P. Hoang & Peng Hong Liem. (2017). Using Gd2O3 Particles in WWER1000 Fuel Assembly for Controlling Excess Reactivity Energy Procedia 131, 29-36.
14. 14) Grossbeck, M. L., Renier J.P.A. & Bigelow, T. (2003). Development of Improved Burnable Poisons for Commercial Nuclear Power Reactors, Prepared by the University of Tennessee for the Oak Ridge National Laboratory.
15. 15) Study of the Effect of Integral Burnable Absorbers for PWR Burnup Credit NUREG/CR- 6760 ORNL/TM--321 Oak Ridge National Laboratory, 2000.
16. 16) Wang, Y, Fan C., Wang H, Wang F., Xu J., Duan P. & Zhang Y., (2015). Effects of TiO2 on the sintering densification of UO2-Gd2O3 burnable poison fuel, Ceramics International. 41, 10185–10191.
17. 17) Venneri P. F., Michael E. & Yonghee K., (2017). Passive Reactivity Control of Nuclear Thermal Propulsion Reactors. Journal Nuclear Technology.197.
18. 18) Nishida T. & Yuda R., (1998 November). Effect of Particle Size and Oxygen Potential on UO2/Gd2O3 Pellet Sintering”, Proceedings of a Technical Committee Meeting, Vienna, Austria. pp. 73-84. IAEA-TECDOC--1036.
19. 19) Agueda H. C., Heredia A. D., Amaya D. C., Sterba M. E. & Russo D., (1994, September). “Efectos del Oxido del Gadolinio en la Sinterizacion de Dioxido de Uranio”, Proceedings of the 5 General Congress on Nuclear Energy, Rio de Janeiro,2, 567-571, Brazil
20. 20) Song K. Woo, Kim K.S., Yang, J.H., Kang Y.H. & Jung K.W., (2001). A mechanism for the sintered of UO2 –Gd2O3 pellets under an oxidizing atmosphere, Journal of Nuclear Materials. 288 92-99.
21. 21) Loose A., Ilic R., Marinkovic V. & Trkov A., (1987, September) “Diffusion Measurements in UO2-Gd2O3”, Proceedings of The International Symposium on Improvements in Water Reactor Fuel, V. Technology and Utilization, Vienna, Austria. pp. 578-584. IAEA-SM-288/36P.
22. 22) Jeongmook L., Jandee K., Young-Sun Y. & Nazhen L., (2017). Raman Sudy on Structure of U1-y GdyO2. Journal of Nuclear Materials, 486,216-221.