The use of fine distributed moderating material to enhance the feedback effects and to reduce the sodium void effect in sodium-cooled fast reactor cores is described. The influence of the moderating material on the fuel assembly geometry, the neutron spectrum, the feedback effects, the power and burnup distribution, and the transmutation performance is given. An overview on possible materials is provided and the relationship between hydrogen content and thermal stability is described. A solution for the problem of the limited thermal stability of primarily proposed hydrogen-bearing moderating material ZrH1.6 is developed by the use of yttrium-mono-hydride. The similarity in the effects reached by ZrH and YH is demonstrated by comparison calculations. The topic is closed by an overview on material properties, manufacturing issues, experience in fast reactors, and a comparison of raw material costs. 1. Introduction The positive coolant density feedback coefficient is inherent to the system in sodium-cooled fast reactors (SFRs), and the fuel temperature feedback is comparably low. Both facts are important boundary conditions for the design of future sodium-cooled fast reactors. The relevance of the topic has been highlighted in the last year in the IAEA TM on Innovative Fast Reactor Designs with Enhanced Negative Reactivity Feedback Features in Vienna [1]. The positive coolant density effect is additionally the basis for the sodium void effect, which is the maximal reduction of the sodium density. The reduction of the sodium void effect as well as the enhancement of the negative feedback effects is an important point in the design of sodium-cooled fast reactors. The feedback effects in fast reactors as well as the sodium void effect itself and the different contributions to the effect are well known since the 1960s. Detailed descriptions have already been given in “Reactivity Coefficients in Large Fast Power Reactors” in 1970 [1]. Already in the 1970s numerical studies were conducted with the aim to reduce the sodium void effect [2]. These studies were mostly based on full core calculations for the optimization of the core geometry to reduce the sodium void effect by increasing the leakage component. One important outcome of these full core studies is the development of high leakage cores with their big core diameter (~5 meters) in combination with a very small core height (≤1 meter). Current publications mostly concentrate on the design of sodium-cooled fast reactor cores [3] and basic or detailed discussions on the different influencing parameters on the
References
[1]
“IAEA TM on Innovative Fast Reactor Designs with Enhanced Negative Reactivity Feedback Features,” IAEA Headquarters, Vienna, Austria, 2012, http://www.iaea.org/NuclearPower/Meetings/2012/2012-02-27-02-29-TM-NPTD.html.
[2]
R. N. Hill and H. Khalil, “Evaluation of LMR design options for reduction of sodium void worth,” in Proceedings of the International Conference on Physics of Reactors, vol. 1, pp. 11–19, Marseille, France, 1990.
[3]
G. Rimpault, L. Buiron, P. Sciora, and F. Varaine, “Towards GEN IV SFR design: promising ideas for large advanced SFR core designs,” in Proceedings of the International Conference on the Physics of Reactors (PHYSOR '08), pp. 2394–2400, Bern, Switzerland, September 2008.
[4]
L. Buiron, P. Dufour, G. Rimpault et al., “Innovative core design for generation IV sodium-cooled fast reactors,” in Proceedings of the International Conference on Advances in Nuclear Power Plants (ICAPP '07), Nice, France, May 2007.
[5]
K. Sun, J. Krepel, K. Mikityuk, and R. Chawla, “A neutronics study for improving the safety and performance parameters of a 3600？MWth sodium-cooled fast reactor,” Annals of Nuclear Energy, vol. 53, pp. 464–475, 2013.
[6]
A. Rineiski, B. Vezzoni, D. Zhang, X.-N. Chen, F. Gabrielli, and M. Marchetti, “Sodium void effect reduction and minor actinide incineration in ESFR,” Transactions of the American Nuclear Society, vol. 104, pp. 720–721, 2011.
[7]
M. S. Chenaud, N. Devictor, G. Mignot, et al., “Status of the astrid core at the end of the pre-conceptual design,” in Proceedings of the International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13), Paris, France, March 2013.
[8]
B. Merk, S. Kliem, E. Fridman, and F. P. Wei？, “On the use of zirconium based moderators to enhance the feedback coefficients in a MOX fuelled sodium cooled fast reactor,” Nuclear Science and Engineering, vol. 171, no. 2, pp. 136–149, 2012.
[9]
B. Merk, E. Fridman, and F. P. Wei？, “On the use of a moderation layer to improve the safety behavior in sodium cooled fast reactors,” Annals of Nuclear Energy, vol. 38, no. 5, pp. 921–929, 2011.
[10]
B. Merk and F.-P. Wei？, “Analysis of the influence of different arrangements for ZrH moderator material on the performance of a SFR core,” Annals of Nuclear Energy, vol. 38, no. 11, pp. 2374–2385, 2011.
[11]
B. Merk and F. P. Wei？, “On the effect of different placing ZrH moderator material on the performance of a SFR core,” in Proceedings of the Advances in Reactor, Physics—Linking Research, Industry, and Education, Knoxville, Tenn, USA, April 2012.
[12]
B. Merk and F. P. Wei？, “On the use of moderating material to enhance the feedback coefficients in SFR cores with high minor actinide content,” in Proceedings of the International Conference of Applied Psychology (ICAPP '12), Paper 12428, Chicago, Ill, USA, June 2012.
[13]
B. Merk, “Moderating material to compensate the drawback of high minor actinide containing transmutation fuel on the feedback effects in SFR cores,” Science and Technology of Nuclear Installations, vol. 2013, Article ID 172518, 10 pages, 2013.
[14]
B. Merk, “On the use of fine distributed moderating material to enhance feedback coefficients in fast reactors,” in Proceedings of the IAEA TM on Innovative Fast Reactor Designs with Enhanced Negative Reactivity Feedback Features, Vienna, Austria, February 2012.
[15]
E. A. Villarino, R. J. J. Stamm'ler, A. A. Ferri, and J. J. Casal, “HELIOS: angularly dependent collision probabilities,” Nuclear Science and Engineering, vol. 112, no. 1, pp. 16–31, 1992.
[16]
R. Sanchez, J. Mondot, Z. Stankovski, A. Cossic, and I. Zmijarevic, “APOLLO II: a user-oriented, portable, modular code for multigroup transport assembly calculations,” Nuclear Science and Engineering, vol. 100, no. 3, pp. 352–362, 1988.
[17]
IAEA Fast Reactor Database—2006 Update, http://www.iaea.org/nuclearenergy/nuclearknowledge/.
[18]
A. E. Waltar and A. B. Reynolds, Fast Breeder Reactors, Pergamon Press, New York, NY, USA, 1981.
[19]
A. Pay, E. Francillon, B. Steinmetz, D. Barnes, and N. Meda, “European Fast Reactor (EFR) fuel element design,” in Proceedings of the 10th International Conference on Structural Mechanics in Reactor Technology, Anaheim, Calif, USA, 1989.
[20]
HELIOS Methods, Studsvik Scandpower, Waltham, Mass, USA, 2003.
[21]
R. Rachamin, C. Wemple, and E. Fridman, “Neutronic analysis of SFR core with HELIOS-2, SERPENT, and DYN3D codes,” Annals of Nuclear Energy, vol. 55, pp. 194–204, 2013.
[22]
W. M. Mueller, J. P. Blackledge, and G. G. Libowitz, Metal Hydrides, Academic Press, New York, NY, USA, 1968.
[23]
K. Tsujimoto, T. Iwasaki, N. Hirakawa, T. Osugi, S. Okajima, and M. Andoh, “Improvement of reactivity coefficients of metallic fuel LMFBR by adding moderating material,” Annals of Nuclear Energy, vol. 28, no. 9, pp. 831–855, 2001.
[24]
D. Olander, E. Greenspan, H. D. Garkisch, and B. Petrovic, “Uranium-zirconium hydride fuel properties,” Nuclear Engineering and Design, vol. 239, no. 8, pp. 1406–1424, 2009.
[25]
J. C. Lefèvre, C. H. Mitchell, and G. Hubert, “European fast reactor design,” Nuclear Engineering and Design, vol. 162, no. 2-3, pp. 133–143, 1996.
[26]
U. Rohde, U. Grundmann, and S. Kliem, “DYN3D—advanced reactor simulations in 3D,” Nuclear Energy Review, vol. 2, pp. 28–30, 2007.
[27]
C. Beckert and U. Grundmann, “A nodal expansion method for solving the multigroup SP3 equations in the reactor code DYN3D,” in Proceedings of the Joint International Topical Meeting on Mathematics and Computations and Supercomputing in Nuclear Applications (M&C+SNA '07), Monterey, Calif, USA, April 2007.
[28]
E. S. Funston, “Physical properties of yttrium hydride,” in Nuclear Metallurgy, A Symposium on Metallic Moderators and Cladding Materials, American Institute of Mining and Metallurgical Engineers, New York, NY, USA, 1960.
[29]
C. V. Owen and T. E. Scott, “Hydrogen embrittlement of yttrium,” Journal of the Less-Common Metals, vol. 90, no. 2, pp. 275–282, 1983.
[30]
J. B. Vetrano, “Hydrides as neutron moderator and reflector materials,” Nuclear Engineering and Design, vol. 14, no. 3, pp. 390–412, 1971.
[31]
R. van Houten, “Selected engineering and fabrication aspects of nuclear metal hydrides (Li, Ti, Zr, and Y),” Nuclear Engineering and Design, vol. 31, no. 3, pp. 434–448, 1974.
[32]
D. W. Wootan, J. A. Caggiano, L. L. Carter, D. P. Jordheim, and A. H. Lu, “Isotope production test in the fast flux test facility,” in Proceedings LMR: A Decade of LMR Progress and Promise, Washington, DC, USA, November 1990, American Nuclear Society, La Grange Park, Ill, USA, 1990.
[33]
D. W. Wootan, J. A. Rawlins, L. L. Carter, H. R. Brager, and R. E. Schenter, “Analysis and results of a hydrogen-moderated isotope production assembly in the fast flux test facility,” Nuclear Science and Engineering, vol. 103, no. 2, pp. 150–156, 1989.
