Hafnium and dysprosium titanate based control rods for thermal water-cooled reactors

Abstract

Boron carbide and boron steel are used for control rods in BBER reactors. Investigations have shown that their operation is limited to a burnup of up to 45-50% t~ This is due to the large amount of radiation damage to the absorbing materials as a result of the formation of gaseous products of nuclear reactions, which results in strong swelling of the materials and destruction of the control rods. The maximum burnup l~ hi boron ~arbide Dr the absorbing eleraeats of a BBER-1000 reactor is reached within three years of operation of the automatic tonal rod~..Control rods based on n, ~, absorbers are promising for thermal reactors. Gaseous pmdtm,'~ of-tmc~.m' ,re, actions are not formed in such rods, and the rods are characterized by a higher radiation resistance. Of,a, -~, ,absorbers, ~aly europium oxide and europium oxide in a metallic matrix are used in reactors built in this country. It has'been confu'med erperimentally that the operating time of control rods based on europium oxide absorbers can exceed 20 yr. :But, despite the high radiation resistance and neutron absorption efficiency with prolonged operation, europium based materials cannot be recommended for widespread use in reactor construction because of the high induced "r activity and the slow decrease :in this activity, which creates serious problems during storage and utilization of spent parts and can result in catastrophic con~quences in the ease of an accident. Therefore a search is being made for other radiation resistant n, 7r absorbers. These iinclude dysprosium titanate and hafaium.This paper reports the results of investigations of the radiation resistance of hafnium amd dyslmasium titanate a~ well as the main criteria which the absorbing materials must satisfy in order to ensure that the comical rode.can,operate for :~ long tinle.Choice of Criteria. Allowing for the increasing requirements on :safety ard x, eliabiI'm/,of almxation~ ~ arollo~ing criteria for the working capacity of the control rods were adopted:at least 8-10% reactivity margin; not more than 10% decrease in the efficiency of control rods at the .end of,~ration; shape and integrity preservation during operation; not more than 0.5 % increase in the diameter of the claddings of the control rods; strucatrally stable material for the absorbing core, not subjected to phase transitions with a large change in volume (not more than 10-15%); ultimate strength of carrying structural elements of at least 200 MPa, and relative elongation not exceeding 0.5%; rate of interaction of the absorbing and structural materials of not more than 0.001 mm/yr; and, rate of corrosion of absorbing and structural materials in the coolant medium of not less than 0.01 ram/yr. The first four criteria are the main criteria. If one of these criteria is not satisfied, then in order to show that the control rod is operable, specific features of the construction and characteristics of the reactor, in which it is used, must be specially substantiated. The next four are also extremely important. They make it possible...

Relationship Between the Orthorhombic and Hexagonal Phases in Dy2TiO5

“…[3][4][5] Several materials have been studied in an effort to find a suitable replacement. 1,2 Radiation damage caused by (n, a)-reactions with 10 B isotopes results in helium formation, causing swelling to occur and cracks to nucleate and grow, ensuring decreased operational lifespans.…”

Development of Dysprosium Titanate Based Ceramics

“…B oron carbide (B 4 C) and boron steels, because of large neutron absorption cross section of B 10 isotope, are used in nuclear industry as control rod elements and shielding materials 1 . However, these materials exhibit post‐irradiation swelling caused by (n, α) reaction of B 10 and formation of helium bubbles 2 . In the case of B 4 C, the irradiation swelling can cause clad failure.…”

Microstructural Evolution, Thermodynamics and Kinetics of Mo-Tm₂O₃ Powder Mixtures during Ball Milling

“…The advantages of using gray control rods to control nuclear reactivity are that they greatly reduce the daily dealing with reactor coolant, distinctly simplify the chemical and tolerant control system and its operation, significantly decrease high expense for short time change, and also make the nuclear reactor safer [2][3]. The key to gray control rods controlling and adjusting nuclear reactivity is in their internal neutron absorbers, which can be prepared from bulk with elemental boron, Dy2TiO5 materials, Ag-In-Cd alloys, tungsten and silver and their alloys [4][5][6][7]. Initially, boron carbide and boron steels were used as neutron absorbers in Russian nuclear power water reactors such as VVER-1000, VVER-440 and RBMK-1000 [4].…”

“…However, the nuclear reactivity worth of gray control rod assemblies drops to approximately 80% of its initial value after running five years, which no longer meets the control condition of mechanical shim. Dy2TiO5 pellets are used as neutron absorbers in Russian thermal reactors such as VVER-1000 RCCAs [5,8]. However, the neutron absorption ability decreased with increasing service time [9,10].…”