Development of structural steel for fuel elements and fuel assemblies of sodium-cooled fast reactors

Abstract

The main results of development work and post-reactor studies of different structural materials for fuelelement cladding and hexahedral fuel-assembly jackets for sodium-cooled fast reactors are examined. Austenitic and ferritic-martensitic steels, including steel obtained by powder metallurgy, are examined as promising materials for fuel-element cladding for staged increase of fuel burnup.Successful work on and development of fast reactors are largely determined by the functional properties of the structural materials at high damaging dose. The most important characteristics are the swelling and creep, which determine the shape change of articles, and the degradation of the mechanical properties.The Bochnar All-Russia Research Institute for Inorganic Materials (VNIINM) is developing fuel elements and structural materials in close cooperation with Afrikantov Experimental Design Bureau of Mechanical Engineering (OKBM), which is the main contractor, and the Leipunskii Institute for Physics and Power Engineering (FEI), which is the scientific direactor for fast reactors. The results of post-reactor studies, which are being conducted at the Beloyarskaya nuclear power plant, at IRM, the Research Institute for Atomic Reactors (NIIAR), and the FEI, are very important for making decisions. The objects of post-reactor studies are materials-engineering, experimental, reference, and standard fuel assemblies.The objective of the first comprehensive program for the development of radiation-resistance materials was to develop steel that would give burnup of at least 10% h.a [1]. In this program, the following steels were tested: austenitic steel in various states of mechanical-heat treatment -08Kh16N11M3, 08Kh16N11M3T, 06Kh16N15M3B (EI-847), 06Kh16N15M3BR (EP-172), 06Kh16N15M2G2TFR (ChS-68); ferritic-martensitic steel Kh13M2BFR (EP-450), 05Kh12N2M, Kh12MSFBR (EP-823); and high-nickel alloys with 30-40% nickel. In 1987, it was decided on the basis of the results of the tests to use in BN-600 ChS-68 c.d. and EP-450 steels, respectively, as the standard materials for the fuel-element cladding and fuel-assem-

Analyzing the causes for the dispersion of the fast reactor spent fuel rod cladding properties

“…The tube conversion for all of the claddings was based on a multi-stage technology (Tselishchev et al 2010;Spitsyn et al 2015) which is currently in the process of adjustment. The experimental cladding fabrication technology differed from the standard technology in a longer (approximately fivefold) hold time during recrystallization annealing at the same temperature.…”

“…Further material studies identify an equally considerable difference in the cladding properties such as magnitude of swelling (Portnykh et al 2007), degree of the inner surface corrosive damage, and strength and ductility at elevated temperatures (Barsanova et al 2018). The dispersion of properties can be supposedly caused by the chemical (segregational) heterogeneity of the metal or by its structural heterogeneity as the result of the tube fabrication process (Bakanov et al 2005;Tselishchev et al 2010). The condition of a test assembly with the fuel cladding manufactured using three different technologies has been studied to check these statements.…”

Electron microscopy and atom probe tomography of nanoindentation deformation in oxide dispersion strengthened steels

“…Furthermore, increasing the primary coolant temperature and increasing the fuel burn up fraction are two methods that could significantly improve the efficiency, optimise resource use, reduce nuclear waste, and increase the economic viability of sodium-cooled fast reactors [4]. Unfortunately these methods would also exclude the use of established ferritic-martensitic steels , such as HT9 [5], T91 [5] or EP-450 [6], due to their limited high temperature creep resistance, and austenitic stainless steels, such as Type 316 [5], [2] or D9 [7], due to their extensive void swelling. New structural materials are therefore required to meet the demands of high temperature coolants, high fuel burn up fraction methods and tolerate the associated increase in neutron flux [8].…”

Neural Network Model of Iron Diffusion in Austenitic Steels

“…Для иллюстрации на рис. 3 представлены результаты расчета D Fe в чистом железе и аустенитных реакторных сталях ЧС68 и ЭК164 [17,18].…”

“…Резонно предположить, что ТВЭЛьные трубки изготовлены по одной технологии, тогда разница в радиационных повреждениях может быть вызвана количественным различием в содержании химических элементов в рамках допустимого варьирования химического состава стали ЭК164. Разрешенный диапазон изменения содержания является весьма существенным, например, допускается содержание кремния от 0,3 до 0,6 % (по массе), а титана в пределах 0,25 - 0,45 % (по массе) [17].…”