- Email: [email protected]
Triboengineering problems of lead coolant in innovative fast reactors
Nuclear Engineering and Design 265 (2013) 675–681
Contents lists available at ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
Triboengineering problems of lead coolant in innovative fast reactors A.V. Beznosov, O.O. Novozhilova ∗ , A.I. Shumilkov, A.V. Lvov, T.A. Bokova, K.A. Makhov Chair “Atomic, Thermal Power Plants and ME”, Institute of Nuclear Power Engineering and Applied Physics, Nizhny Novgorod State Technical University n.a. R.E. Alekseev, Nizhny Novgorod 603950, Russia
h i g h l i g h t s
g r a p h i c a l
a b s t r a c t
• The contact a pair of heavy liquid
Models of experimental sites for research of processes tribology in heavy liquid metal coolant.
metal coolant for reactors on fast neutrons. • The hydrostatic bearings main circulation pumps. • Oxide coating and degree of wear of friction surfaces in heavy liquid metal coolant.
a r t i c l e
i n f o
Article history: Received 5 March 2013 Received in revised form 30 June 2013 Accepted 1 July 2013
a b s t r a c t So far, there are plenty of works dedicated to studying the phenomenon of friction. However, there are none dedicated to functioning of contact pairs in heavy liquid-metal coolants for fast neutron, reactor installations (Kogaev and Drozdov, 1991; Modern Tribology, 2008; Drozdov et al., 1986). At the Nizhny Novgorod State Technical University, such research is conducted in respect to friction, bearings of main circulating pumps, interaction of sheaths of neutron absorber rods with their covers, of the reactor control and safety system, refueling systems, and interaction of coolant flows with, channel borders. As a result of experimental studies, the characteristic of friction pairs in the heavy, liquid metal coolant shows the presence dependences of oxide film on structural materials of the wear. The inapplicability of existing calculation methods for assessing the performance of the bearing nodes, in the heavy liquid metal coolant is shown. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The working peculiarities of contact pairs in a lead and leadbismuth coolants medium include high efficiency in removal of heat released in the contact area and impossibility of using conventional lubricating materials (oils, cupriferous alloys, etc.). At operating temperatures (400–550 ◦ C), heavy liquid-metal coolants cannot be regarded as lubricating materials having conventional
∗ Corresponding author. Tel.: +7 831 436 80 23; fax: +7 831 436 80 23. E-mail addresses: [email protected] (A.V. Beznosov), [email protected] (O.O. Novozhilova), shumilkov [email protected] (A.I. Shumilkov), knyaz [email protected] (A.V. Lvov), [email protected] (T.A. Bokova), max [email protected] (K.A. Makhov). 0029-5493/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nucengdes.2013.07.033
properties due to non-wettability of oxidized surfaces of steels and cast irons as well as due to low viscosity of coolants. The working efficiency of construction materials in touch with lead and lead-bismuth coolants in reactor loops is provided by oxide films formed and additionally formed on the surface. On metal surfaces in touch with heavy liquid-metal coolants, oxide films are formed due to interaction with oxygen contained in coolants in diluted form or in the form of its oxides. Generally, the wall boundary layer in a heavy liquid-metal coolant medium is enriched in impurities: coolant compounds, construction material components and others. The formed oxide films and the wall boundary layer protect contact surfaces against solidification and related tearing in depth, and other negative effects. They are of major importance in operating contact surfaces. The coolant oxide particles (lead, bismuth) in steel component compounds, bubbles
676
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
Fig. 1. Diagram of TR-2010 high-temperature test bench (a) and model (b). 1 – contact friction pair under test; 2 – free surface level of heavy liquid-metal coolant (lead); 3 – oxygen thermodynamic activity sensor; 4 – gas inlet and outlet tubes; 5 – loading system; 6 – gas system manifold; 7 – motor; 8 – DOU-3I dynamometer tension gage and 9 – temperature sensor.
of vapors, gases, etc. in wall boundary layers of friction surfaces impregnated with the coolant produce an effect similar to that of a lubricating material. The process of oxide film formation on steels and cast irons in a heavy liquid-metal coolant medium exercises a significant influence on their characteristics (Beznosov, 2006; Drozdov et al., 2010). Using the equipment and research facilities mounted on the basis of the Faculty of Nuclear Thermal Plants and Medicinal Engineering of the Nizhny Novgorod State Technical University n.a. R.E. Alekseyev, experimental research is carried out in respect to contact interaction of solid bodies during their relative movement, which research covers a set of issues relating to friction, wear and lubrication of pieces of mechanisms. In addition, calculation and theoretical research is under way in parallel.
first research test bench designed for such studies. Obtained from this bench results are preliminary. Diagram of TR-2010 high-temperature test bench are shown in Fig. 1. The tank is filled up with a heavy liquid-metal coolant. It is heated by electric current using nickel–chromium electric spirals. From outside, the casing is covered with thermal insulation. Inside the bench casing, in the test area on a scaffold, there is a contact friction pair consisting of two samples. Upper sample No.1 is fixed in position. Sample No. 2 is beneath it and is retained against it owing to the action of the Archimedean force and a device providing the required loading force of the test area. Sample No. 2 is moved
2. Determining frictional coefficient at reciprocative movement of a contact pair 2.1. Test objective The main purpose of these experimental researches is to determine the frictional coefficient between wear surfaces of construction materials of different mechanisms operating in a lead coolant. The essence of the experimental researches consists in analyzing a degree of impact of the formed oxide film and the wall boundary layer on the rate of wear of friction surfaces at variable parameters of the lead coolant. Studies were carried out on two experimental test benches TR2010 and TR2012 (Figs. 1–3). 2.2. Description of the test bed So far, the experimental test benches for the study of tribology issues in heavy liquid metal coolant did not exist. TR-2010 was the
Fig. 2. Model of experimental site of the high temperature test bench TR-2012.
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
677
Fig. 3. Diagram of TR-2012 high-temperature test bench. 1 – motor; 2 – DOU-3I dynamometer tension gage and 3 – contact friction pair.
relative to Sample No. 1 by means of rotation of the flywheel driven by the motor and a blocking system with cables. The contact friction pair is completely submerged into a lead coolant. Test bench TR-2012 is the optimization and upgrading of the test bench TR-2010. Test bench TR-2012 is designed to determine the frictional coefficient of the contact friction pairs of samples of steel in heavy liquid metal coolant at the temperature 450–550 ◦ C. Diagram of TR-2012 high-temperature test bench are shown in Figs. 2 and 3. The test bench consists of the following main elements: - working capacity with the test area; - melting tank with lead coolant; - the system of the control and regulation of the parameters of the test bench; - system of power supply of consumers of the test bench; - gas system. The melting tank is filled up with a heavy liquid-metal coolant. It is heated by electric current using nickel–chromium electric spirals. At the bottom of the working capacity at the site posted a Sample No. 1. It is designed as the plate of steel 12Cr18N10T. The surface of a contact to condition as supplied. Sample No. 2 was made in a metal cylinder, above a Sample No. 1 and is retained against it owing a device providing the required loading force of the test area. Back-and-forth motion of the Sample No. 2 relative on the Sample No. 1 by working two motors. It provides the necessary tractive effort in the system of metal rods and DOU-3I dynamometer tension gage. The contact friction pair is completely submerged into a lead coolant. 2.3. Research methods and results On the TR-2010 experimental research were carried out under the following conditions and for two types of contact surfaces without oxide film formation and with oxide film formed: -
The test program includes the following stages: - Determination of frictional force introduced by the structural elements of the test bench. Mode is “idling”. The studies were carried out without the sample at a constant speed of the rope 0.01 m/s. In this mode was determined tractive effort equivalent to the frictional force introduced by the structural elements of the test bench. - Determination the frictional coefficient of samples of steel 12Cr18N10T in the condition as supplied in the lead coolant at the temperatures 500 ◦ C, oxygen impurity content in liquid metal 100 , specific load on the contact friction pair ranged 6, 12 and 23 kg/cm2 and speed of moving samples on the contact friction pair is 0.01 m/s. - Determination the frictional coefficient of passivated samples in the lead coolant of steel 12Cr18N10T in the lead coolant at the temperatures 500 ◦ C, speed of moving samples on the contact friction pair is 0.01 m/s, oxygen impurity content in liquid metal 100 and specific load on the contact friction pair ranged 6, 12 and 23 kg/cm2 . Time passivation samples 24 h. Passivation conditions – the temperature of the lead coolant 480 ◦ C, thermodynamic activity of oxygen 100 . - Generalization and analysis of the received results. Have been carried out calculations and material science researches of the samples. Dependence of the frictional coefficient of on the movement of the contact pair at various loads and different states of sample surfaces were constructed. Research results obtained when the specific load on the friction contact pair are plotted in Fig. 4. Example profilogram of surfaces of the contact pair are shown in Fig. 5 and photo thin section are shown in Fig. 6. The vertical axis on the Fig. 5 corresponds to the height profile of the surface in microns. The horizontal axis – the length of the test area in mm.
contact surface treatment – condition as supplied (Ra = 3.2); friction pair material – steel of austenite class 12Cr18N10T; operating fluid – lead; working temperatures 500–550 ◦ C; controlled and regulated oxygen impurity content in liquid metal 100 .
Based on the preliminary results of this experimental research, there was detected a material impact of oxide film presence on the contact pair surfaces on the value of frictional coefficient. The frictional coefficient decreased from = 0.2–0.6 to = 0.2–0.3. Experimental researches were carried out on TR 2012 under similar conditions (on the TR-2010).
Fig. 4. Example of dependence the frictional coefficient from travel of contact pair moving sample (specific load 23 kg/sm2 ).
678
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
Fig. 5. The profilogram surface contact pair with oxide film formed after an experimental research (the temperature of lead coolant 500 ◦ C, oxygen impurity content in liquid metal 100 , specific load 12 kg/sm2 , surface roughness Ra = 1.8).
The practical importance of this research consists in the fact that on its basis, it is significantly easier to develop calculation methods for predicting parts wear limiting the reliability of equipment units; the research contributes to reasoned selection of materials of rapidly wearing parts and increase of their service life. 3. Research works of hydrostatic plain bearings 3.1. Test objective In main circulating pumps of fast neutron reactors with liquidmetal coolants, it is not possible to use conventional lubricants due to high temperatures and infeasibility of any contact with organic compounds. The only medium in which operation of such bearing is possible includes the coolant itself. A lead coolant does not wet the working surfaces of plain bearings, adhesion operation has a small value, and the coolant is not capable of being held on contact surfaces in the presence of tangential forces. A lead coolant has a low viscosity and may not be regarded as a lubricant in traditional terms (Chernavsky, 1963). This coolant can effectively remove heat released during friction, which has a favorable effect on the operation of contact pairs (Beznosov et al., 2012b).
Within the reactor loop, protective oxide films are formed on all and including contact surfaces, which films under certain conditions have anti-frictional properties, which exclude or minimize any wear-out during start-up, stop and emergency operation of the hydrostatic bearing. 3.2. Research methods and results The currently existing methods for calculating hydrostatic bearings are not applicable for calculation of such bearings operating in a lead and lead-bismuth coolant. In order to develop such methods, a complex of calculation-and-theoretical and experimental works is carried out at the Nizhny Novgorod State Technical University n.a. R.E. Alekseyev. These works include as follows: - Analysis of the lead high-temperature (450–550 ◦ C) coolant properties affecting the serviceability of plain bearings of submerged pumps of reactor loops. - Experimental and calculation-and-theoretical comparative examination of hydrodynamic and other characteristics of the same throttles in a hydrostatic bearing in water and lead melt, and comparison of the results obtained with the calculation results according to the existing methods. - Experimental and calculation-and-theoretical comparative examination in water and lead melt of the following hydrostatic bearing area: throttle – annular clearance and comparison of the results obtained with the calculation results according to the existing methods. The experimental comparative examination, successively in water and in lead, of the characteristics of the same throttles having a bore diameter from 2.0 to 6.0 mm with their thickness from 3.0 to 7.0 mm was carried out on a water-type (t = 20 ◦ C) and a hightemperature lead-type (t = 450–500 ◦ C) benches specially prepared at the NNSTU at an average water and lead flow rate through the throttle opening from 1.0 to 30.0 m/s. The experimentally obtained resistance factor dependences on the flow rate may be divided into two groups: a) Dependences during testing in water and in lead at the minimum reverse pressure of ∼100·103 Pa and the maximum reverse pressure of 220·103 Pa; b) Dependences during testing in water and in lead at the throttle outlet reverse pressure of 110·103 and 120·103 Pa (Fig. 7).
Fig. 6. Photo: thin section of the sample (with oxide film formed, the temperature lead coolant 500 ◦ C, oxygen impurity content in liquid metal 100 , specific load 23 kg/sm2 at 400× magnification).
The data concerning the “theory” is generated from (Idelchik, 1992). A possible reason for differences based on the traditional method and the results of the experiment is that in the
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
679
Fig. 7. Comparative dependence P = f(Re) for a throttle having the following parameters: d0 = 3 mm. l0 = 5 mm. (a) Lead (reverse pressure ≈ 100·103 Pa); (b) lead (reverse pressure 110·103 Pa); (c) lead (reverse pressure 120·103 Pa); (d) lead (reverse pressure 220·103 Pa) and (e) water.
calculation formulas do not take into account the condition of non-wetting the oxidized liquid metal walls of the channel. The difference in values of hydraulic resistance between the results of testing with water and with lead was up to semiorder. The obtained presented and other testing data conclusively showed that the use of the existing methods for calculating throttles in lead was incorrect. The results of calculating throttle characteristics are the same as the results of testing in water and are different from the results of testing in lead (Beznosov et al., 2011).
A comparative experimental and calculation-and-theoretical examination also was conducted using water and a lead coolant in respect to one of the basic hydrostatic bearing areas: throttle – annular clearance between the bushing and the rotating or stopped shaft also. The existing theories do not cover any conditions of a fluid non-wetting the wall and flowing in the clearance between the shaft and the fixed bushing that are typical for operating conditions of a plain bearing in a lead coolant. No frictional coefficients of oxidized metal surfaces in a lead coolant, nor a number of other required characteristics are known, as well as no frictional constraints in the boundaries of contact between liquid
680
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
Fig. 8. Dependence = f(Re) for radial clearance of 1 mm at oxygen impurity in lead a = 10−1 –100 .
and hard metals are discovered, which makes it impossible to build an appropriate correct model and solve it. Experimental examinations were successively performed using water and lead melt to discover hydraulic characteristics of a test section that represented a tank in which a bushing having inner diameter of 114.0 mm was installed. Change shafts having outer diameters of 112.0, 110.0 and 108.0 mm were successively installed inside the bushing. The radial clearance was selected based on the following considerations: - the value of 1.0 mm is close to the clearances of conventional hydrostatic bearings of such diameter; - the value of 3.0 mm is close to the depth of the bearing work chamber; - the value of 2.0 mm is accepted as an intermediate value between the previous options. The bushing contained four throttles of 4.0 mm in diameter. Near one of the throttles, an opening of 4.0 mm in diameter was made to connect a device to monitor pressure in the slot clearance; the second pressure take-off was in a union before the throttle. The examinations were conducted on specially created circulating benches 2010-KZD-VT and 2010-KZD-ST with water and lead coolants respectively. The tests were carried out at 20 ◦ C for water and 400–450 ◦ C for lead during 24 h (per change shaft) at the fluid flow rate in the annular clearance from 0.06 to 0.15 m3 /h (V = 0.04–0.1 m/s), which corresponded to Re = 450–1300 on non-rotating shaft with oxygen content in lead in the
Fig. 9. Dependence = f(Re) for radial clearance of 2 mm at oxygen impurity in lead a = 10−1 –100 .
Fig. 10. Dependence = f(Re) for radial clearance of 3 mm at oxygen impurity in lead a = 10−1 –100 .
saturation line and with lead oxides in the flow. Figs. 8–10 show the analysis of the friction factor-Reynolds number dependence. It’s figures show that the water and lead flow regime is laminar. An analysis of dependence of the local resistance factor on the Reynolds criterion when using a lead coolant shows that with an increase of the radial clearance, the local resistance factor grows, probably, due to an increase in flow turbulence. No material dependence of the run of the curves = f(Re) on the shaft speed in the lead melt is registered, which may be accounted for by the rheological properties of the wall boundary layer. The obtained differences in hydraulic resistances of one and the same test section in water and in lead melt are definitely identified by the difference in the physical properties of these coolants and their interaction with the channel borders. Comparing the design fluid flows (heading) through the bearing and the results of the tests showed a material (from one to five orders) incongruity of these results. The possible reasons for such incongruity may include the fact that the formulas only take into account the geometrical characteristics of the annular clearance and the shaft speed, and do not take into account that the fluid in the clearance has an axial component and moves along the circular helices, and that the test section represents a system of successively installed local resistances: a throttle and an annular clearance. After testing in water, noticeable areas of wear were registered on the contact surfaces of the shaft and the bushing. No sign of wear was detected after testing using a lead coolant; the existing wear areas as well as other sections of contact surfaces made of steel 08X18H10T were coated with a black dense (oxide) film (Beznosov et al., 2012a). The findings of hydraulic tests and calculations of the hydrostatic bearing sections using water and lead melt may differ by one-two orders, and calculations of the hydrostatic bearings using unknown methods may turn out incorrect. Based on the tests and experiments performed, it is possible to assume the following: - the relative energy loss in a bearing submerged in lead will be less than in water; - operating in a lead coolant requires larger differential pressure in the bearing (under other equal conditions) than when operating in water; - to ensure hydrostatic bearing operation, the required volume flow rates of water and lead melt will be of the same magnitude.
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
681
4. Conclusions
References
The existing methods for calculating hydrostatic bearings are good-for-nothing for calculating such bearings of main circulating pumps of fast neutron reactors cooled by lead coolant. Based on the information acquired, analysis and calculationand-theoretical examinations, the following two structural schemes of bearings have been selected for further testing:
Beznosov, A.V., 2006. Heavy Liquid-Metal Coolants in the Nuclear Power Industry, Beznosov, A.V., Dragunov Y.G., Rachkov V.I., М.: IzdAt, p. 370. Beznosov, A.V., Antonenkov, M.A., Bokova, T.A., et al., 2011. Experimental Research of Throttle Hydrodynamics in Lead Coolant and Water Flow, Izvestiya VUZov Nuclear Power Engineering, 2. Beznosov, A.V., Antonenkov, M.A., Bokova, T.A., et al., 2012a. Experimental Research of Hydrodynamics of Lead Coolant and Water Flow Through ThrottleAnnular Clearance Test Section, Izvestiya VUZov Nuclear Power Engineering., pp. 1. Beznosov, A.V., et al., 2012b. Tribology hydrostatic bearings of the main circulation pumps nuclear fast reactor cooled by lead-cooled. Frict. Wear 33 (5), 465–472. Chernavsky, S.A., 1963. Friction Bearings. Mashgiz, Moscow. Drozdov, Y.N., et al., 2010. Applied Tribology (Friction, Wear and Lubrication). Publishing House of the Eco-Press, pp. 604. Drozdov, Y.N., Pavlov, V.G., Beams, V.N., 1986. The Friction and Wear in Extreme Conditions. M. “Engineering”, pp. 224. Idelchik, I.E., 1992. Flow Friction Reference Guide, under the Editorship of M.O. Steinberg, 3rd ed., Revised. Mashinostroyenie, Moscow. Kogaev, V.P., Drozdov, Y.N., 1991. The Strength and Durability of Machine Parts. M. “High School”, pp. 320. Modern Tribology, 2008. In: Frolov, K.V. (Ed.), Results and Prospects. M. Out-of LCI, p. 480.
1) chamber-type with a throttle; 2) chamber-type with slot throttle control. The results of the hydrodynamic successive comparative tests of the bearing in water and in lead generally confirm inapplicability of the existing methods for calculating the bearing operating in a lead coolant. It is suggested to make a final choice between the structural schemes of the hydrostatic bearing for the pump of reactor installations with a heavy liquid-metal coolant after endurance testing of bearing alternatives and examination of their serviceability under emergency increase of disperse particles content in the lead flow.
Contents lists available at ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
Triboengineering problems of lead coolant in innovative fast reactors A.V. Beznosov, O.O. Novozhilova ∗ , A.I. Shumilkov, A.V. Lvov, T.A. Bokova, K.A. Makhov Chair “Atomic, Thermal Power Plants and ME”, Institute of Nuclear Power Engineering and Applied Physics, Nizhny Novgorod State Technical University n.a. R.E. Alekseev, Nizhny Novgorod 603950, Russia
h i g h l i g h t s
g r a p h i c a l
a b s t r a c t
• The contact a pair of heavy liquid
Models of experimental sites for research of processes tribology in heavy liquid metal coolant.
metal coolant for reactors on fast neutrons. • The hydrostatic bearings main circulation pumps. • Oxide coating and degree of wear of friction surfaces in heavy liquid metal coolant.
a r t i c l e
i n f o
Article history: Received 5 March 2013 Received in revised form 30 June 2013 Accepted 1 July 2013
a b s t r a c t So far, there are plenty of works dedicated to studying the phenomenon of friction. However, there are none dedicated to functioning of contact pairs in heavy liquid-metal coolants for fast neutron, reactor installations (Kogaev and Drozdov, 1991; Modern Tribology, 2008; Drozdov et al., 1986). At the Nizhny Novgorod State Technical University, such research is conducted in respect to friction, bearings of main circulating pumps, interaction of sheaths of neutron absorber rods with their covers, of the reactor control and safety system, refueling systems, and interaction of coolant flows with, channel borders. As a result of experimental studies, the characteristic of friction pairs in the heavy, liquid metal coolant shows the presence dependences of oxide film on structural materials of the wear. The inapplicability of existing calculation methods for assessing the performance of the bearing nodes, in the heavy liquid metal coolant is shown. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The working peculiarities of contact pairs in a lead and leadbismuth coolants medium include high efficiency in removal of heat released in the contact area and impossibility of using conventional lubricating materials (oils, cupriferous alloys, etc.). At operating temperatures (400–550 ◦ C), heavy liquid-metal coolants cannot be regarded as lubricating materials having conventional
∗ Corresponding author. Tel.: +7 831 436 80 23; fax: +7 831 436 80 23. E-mail addresses: [email protected] (A.V. Beznosov), [email protected] (O.O. Novozhilova), shumilkov [email protected] (A.I. Shumilkov), knyaz [email protected] (A.V. Lvov), [email protected] (T.A. Bokova), max [email protected] (K.A. Makhov). 0029-5493/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nucengdes.2013.07.033
properties due to non-wettability of oxidized surfaces of steels and cast irons as well as due to low viscosity of coolants. The working efficiency of construction materials in touch with lead and lead-bismuth coolants in reactor loops is provided by oxide films formed and additionally formed on the surface. On metal surfaces in touch with heavy liquid-metal coolants, oxide films are formed due to interaction with oxygen contained in coolants in diluted form or in the form of its oxides. Generally, the wall boundary layer in a heavy liquid-metal coolant medium is enriched in impurities: coolant compounds, construction material components and others. The formed oxide films and the wall boundary layer protect contact surfaces against solidification and related tearing in depth, and other negative effects. They are of major importance in operating contact surfaces. The coolant oxide particles (lead, bismuth) in steel component compounds, bubbles
676
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
Fig. 1. Diagram of TR-2010 high-temperature test bench (a) and model (b). 1 – contact friction pair under test; 2 – free surface level of heavy liquid-metal coolant (lead); 3 – oxygen thermodynamic activity sensor; 4 – gas inlet and outlet tubes; 5 – loading system; 6 – gas system manifold; 7 – motor; 8 – DOU-3I dynamometer tension gage and 9 – temperature sensor.
of vapors, gases, etc. in wall boundary layers of friction surfaces impregnated with the coolant produce an effect similar to that of a lubricating material. The process of oxide film formation on steels and cast irons in a heavy liquid-metal coolant medium exercises a significant influence on their characteristics (Beznosov, 2006; Drozdov et al., 2010). Using the equipment and research facilities mounted on the basis of the Faculty of Nuclear Thermal Plants and Medicinal Engineering of the Nizhny Novgorod State Technical University n.a. R.E. Alekseyev, experimental research is carried out in respect to contact interaction of solid bodies during their relative movement, which research covers a set of issues relating to friction, wear and lubrication of pieces of mechanisms. In addition, calculation and theoretical research is under way in parallel.
first research test bench designed for such studies. Obtained from this bench results are preliminary. Diagram of TR-2010 high-temperature test bench are shown in Fig. 1. The tank is filled up with a heavy liquid-metal coolant. It is heated by electric current using nickel–chromium electric spirals. From outside, the casing is covered with thermal insulation. Inside the bench casing, in the test area on a scaffold, there is a contact friction pair consisting of two samples. Upper sample No.1 is fixed in position. Sample No. 2 is beneath it and is retained against it owing to the action of the Archimedean force and a device providing the required loading force of the test area. Sample No. 2 is moved
2. Determining frictional coefficient at reciprocative movement of a contact pair 2.1. Test objective The main purpose of these experimental researches is to determine the frictional coefficient between wear surfaces of construction materials of different mechanisms operating in a lead coolant. The essence of the experimental researches consists in analyzing a degree of impact of the formed oxide film and the wall boundary layer on the rate of wear of friction surfaces at variable parameters of the lead coolant. Studies were carried out on two experimental test benches TR2010 and TR2012 (Figs. 1–3). 2.2. Description of the test bed So far, the experimental test benches for the study of tribology issues in heavy liquid metal coolant did not exist. TR-2010 was the
Fig. 2. Model of experimental site of the high temperature test bench TR-2012.
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
677
Fig. 3. Diagram of TR-2012 high-temperature test bench. 1 – motor; 2 – DOU-3I dynamometer tension gage and 3 – contact friction pair.
relative to Sample No. 1 by means of rotation of the flywheel driven by the motor and a blocking system with cables. The contact friction pair is completely submerged into a lead coolant. Test bench TR-2012 is the optimization and upgrading of the test bench TR-2010. Test bench TR-2012 is designed to determine the frictional coefficient of the contact friction pairs of samples of steel in heavy liquid metal coolant at the temperature 450–550 ◦ C. Diagram of TR-2012 high-temperature test bench are shown in Figs. 2 and 3. The test bench consists of the following main elements: - working capacity with the test area; - melting tank with lead coolant; - the system of the control and regulation of the parameters of the test bench; - system of power supply of consumers of the test bench; - gas system. The melting tank is filled up with a heavy liquid-metal coolant. It is heated by electric current using nickel–chromium electric spirals. At the bottom of the working capacity at the site posted a Sample No. 1. It is designed as the plate of steel 12Cr18N10T. The surface of a contact to condition as supplied. Sample No. 2 was made in a metal cylinder, above a Sample No. 1 and is retained against it owing a device providing the required loading force of the test area. Back-and-forth motion of the Sample No. 2 relative on the Sample No. 1 by working two motors. It provides the necessary tractive effort in the system of metal rods and DOU-3I dynamometer tension gage. The contact friction pair is completely submerged into a lead coolant. 2.3. Research methods and results On the TR-2010 experimental research were carried out under the following conditions and for two types of contact surfaces without oxide film formation and with oxide film formed: -
The test program includes the following stages: - Determination of frictional force introduced by the structural elements of the test bench. Mode is “idling”. The studies were carried out without the sample at a constant speed of the rope 0.01 m/s. In this mode was determined tractive effort equivalent to the frictional force introduced by the structural elements of the test bench. - Determination the frictional coefficient of samples of steel 12Cr18N10T in the condition as supplied in the lead coolant at the temperatures 500 ◦ C, oxygen impurity content in liquid metal 100 , specific load on the contact friction pair ranged 6, 12 and 23 kg/cm2 and speed of moving samples on the contact friction pair is 0.01 m/s. - Determination the frictional coefficient of passivated samples in the lead coolant of steel 12Cr18N10T in the lead coolant at the temperatures 500 ◦ C, speed of moving samples on the contact friction pair is 0.01 m/s, oxygen impurity content in liquid metal 100 and specific load on the contact friction pair ranged 6, 12 and 23 kg/cm2 . Time passivation samples 24 h. Passivation conditions – the temperature of the lead coolant 480 ◦ C, thermodynamic activity of oxygen 100 . - Generalization and analysis of the received results. Have been carried out calculations and material science researches of the samples. Dependence of the frictional coefficient of on the movement of the contact pair at various loads and different states of sample surfaces were constructed. Research results obtained when the specific load on the friction contact pair are plotted in Fig. 4. Example profilogram of surfaces of the contact pair are shown in Fig. 5 and photo thin section are shown in Fig. 6. The vertical axis on the Fig. 5 corresponds to the height profile of the surface in microns. The horizontal axis – the length of the test area in mm.
contact surface treatment – condition as supplied (Ra = 3.2); friction pair material – steel of austenite class 12Cr18N10T; operating fluid – lead; working temperatures 500–550 ◦ C; controlled and regulated oxygen impurity content in liquid metal 100 .
Based on the preliminary results of this experimental research, there was detected a material impact of oxide film presence on the contact pair surfaces on the value of frictional coefficient. The frictional coefficient decreased from = 0.2–0.6 to = 0.2–0.3. Experimental researches were carried out on TR 2012 under similar conditions (on the TR-2010).
Fig. 4. Example of dependence the frictional coefficient from travel of contact pair moving sample (specific load 23 kg/sm2 ).
678
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
Fig. 5. The profilogram surface contact pair with oxide film formed after an experimental research (the temperature of lead coolant 500 ◦ C, oxygen impurity content in liquid metal 100 , specific load 12 kg/sm2 , surface roughness Ra = 1.8).
The practical importance of this research consists in the fact that on its basis, it is significantly easier to develop calculation methods for predicting parts wear limiting the reliability of equipment units; the research contributes to reasoned selection of materials of rapidly wearing parts and increase of their service life. 3. Research works of hydrostatic plain bearings 3.1. Test objective In main circulating pumps of fast neutron reactors with liquidmetal coolants, it is not possible to use conventional lubricants due to high temperatures and infeasibility of any contact with organic compounds. The only medium in which operation of such bearing is possible includes the coolant itself. A lead coolant does not wet the working surfaces of plain bearings, adhesion operation has a small value, and the coolant is not capable of being held on contact surfaces in the presence of tangential forces. A lead coolant has a low viscosity and may not be regarded as a lubricant in traditional terms (Chernavsky, 1963). This coolant can effectively remove heat released during friction, which has a favorable effect on the operation of contact pairs (Beznosov et al., 2012b).
Within the reactor loop, protective oxide films are formed on all and including contact surfaces, which films under certain conditions have anti-frictional properties, which exclude or minimize any wear-out during start-up, stop and emergency operation of the hydrostatic bearing. 3.2. Research methods and results The currently existing methods for calculating hydrostatic bearings are not applicable for calculation of such bearings operating in a lead and lead-bismuth coolant. In order to develop such methods, a complex of calculation-and-theoretical and experimental works is carried out at the Nizhny Novgorod State Technical University n.a. R.E. Alekseyev. These works include as follows: - Analysis of the lead high-temperature (450–550 ◦ C) coolant properties affecting the serviceability of plain bearings of submerged pumps of reactor loops. - Experimental and calculation-and-theoretical comparative examination of hydrodynamic and other characteristics of the same throttles in a hydrostatic bearing in water and lead melt, and comparison of the results obtained with the calculation results according to the existing methods. - Experimental and calculation-and-theoretical comparative examination in water and lead melt of the following hydrostatic bearing area: throttle – annular clearance and comparison of the results obtained with the calculation results according to the existing methods. The experimental comparative examination, successively in water and in lead, of the characteristics of the same throttles having a bore diameter from 2.0 to 6.0 mm with their thickness from 3.0 to 7.0 mm was carried out on a water-type (t = 20 ◦ C) and a hightemperature lead-type (t = 450–500 ◦ C) benches specially prepared at the NNSTU at an average water and lead flow rate through the throttle opening from 1.0 to 30.0 m/s. The experimentally obtained resistance factor dependences on the flow rate may be divided into two groups: a) Dependences during testing in water and in lead at the minimum reverse pressure of ∼100·103 Pa and the maximum reverse pressure of 220·103 Pa; b) Dependences during testing in water and in lead at the throttle outlet reverse pressure of 110·103 and 120·103 Pa (Fig. 7).
Fig. 6. Photo: thin section of the sample (with oxide film formed, the temperature lead coolant 500 ◦ C, oxygen impurity content in liquid metal 100 , specific load 23 kg/sm2 at 400× magnification).
The data concerning the “theory” is generated from (Idelchik, 1992). A possible reason for differences based on the traditional method and the results of the experiment is that in the
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
679
Fig. 7. Comparative dependence P = f(Re) for a throttle having the following parameters: d0 = 3 mm. l0 = 5 mm. (a) Lead (reverse pressure ≈ 100·103 Pa); (b) lead (reverse pressure 110·103 Pa); (c) lead (reverse pressure 120·103 Pa); (d) lead (reverse pressure 220·103 Pa) and (e) water.
calculation formulas do not take into account the condition of non-wetting the oxidized liquid metal walls of the channel. The difference in values of hydraulic resistance between the results of testing with water and with lead was up to semiorder. The obtained presented and other testing data conclusively showed that the use of the existing methods for calculating throttles in lead was incorrect. The results of calculating throttle characteristics are the same as the results of testing in water and are different from the results of testing in lead (Beznosov et al., 2011).
A comparative experimental and calculation-and-theoretical examination also was conducted using water and a lead coolant in respect to one of the basic hydrostatic bearing areas: throttle – annular clearance between the bushing and the rotating or stopped shaft also. The existing theories do not cover any conditions of a fluid non-wetting the wall and flowing in the clearance between the shaft and the fixed bushing that are typical for operating conditions of a plain bearing in a lead coolant. No frictional coefficients of oxidized metal surfaces in a lead coolant, nor a number of other required characteristics are known, as well as no frictional constraints in the boundaries of contact between liquid
680
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
Fig. 8. Dependence = f(Re) for radial clearance of 1 mm at oxygen impurity in lead a = 10−1 –100 .
and hard metals are discovered, which makes it impossible to build an appropriate correct model and solve it. Experimental examinations were successively performed using water and lead melt to discover hydraulic characteristics of a test section that represented a tank in which a bushing having inner diameter of 114.0 mm was installed. Change shafts having outer diameters of 112.0, 110.0 and 108.0 mm were successively installed inside the bushing. The radial clearance was selected based on the following considerations: - the value of 1.0 mm is close to the clearances of conventional hydrostatic bearings of such diameter; - the value of 3.0 mm is close to the depth of the bearing work chamber; - the value of 2.0 mm is accepted as an intermediate value between the previous options. The bushing contained four throttles of 4.0 mm in diameter. Near one of the throttles, an opening of 4.0 mm in diameter was made to connect a device to monitor pressure in the slot clearance; the second pressure take-off was in a union before the throttle. The examinations were conducted on specially created circulating benches 2010-KZD-VT and 2010-KZD-ST with water and lead coolants respectively. The tests were carried out at 20 ◦ C for water and 400–450 ◦ C for lead during 24 h (per change shaft) at the fluid flow rate in the annular clearance from 0.06 to 0.15 m3 /h (V = 0.04–0.1 m/s), which corresponded to Re = 450–1300 on non-rotating shaft with oxygen content in lead in the
Fig. 9. Dependence = f(Re) for radial clearance of 2 mm at oxygen impurity in lead a = 10−1 –100 .
Fig. 10. Dependence = f(Re) for radial clearance of 3 mm at oxygen impurity in lead a = 10−1 –100 .
saturation line and with lead oxides in the flow. Figs. 8–10 show the analysis of the friction factor-Reynolds number dependence. It’s figures show that the water and lead flow regime is laminar. An analysis of dependence of the local resistance factor on the Reynolds criterion when using a lead coolant shows that with an increase of the radial clearance, the local resistance factor grows, probably, due to an increase in flow turbulence. No material dependence of the run of the curves = f(Re) on the shaft speed in the lead melt is registered, which may be accounted for by the rheological properties of the wall boundary layer. The obtained differences in hydraulic resistances of one and the same test section in water and in lead melt are definitely identified by the difference in the physical properties of these coolants and their interaction with the channel borders. Comparing the design fluid flows (heading) through the bearing and the results of the tests showed a material (from one to five orders) incongruity of these results. The possible reasons for such incongruity may include the fact that the formulas only take into account the geometrical characteristics of the annular clearance and the shaft speed, and do not take into account that the fluid in the clearance has an axial component and moves along the circular helices, and that the test section represents a system of successively installed local resistances: a throttle and an annular clearance. After testing in water, noticeable areas of wear were registered on the contact surfaces of the shaft and the bushing. No sign of wear was detected after testing using a lead coolant; the existing wear areas as well as other sections of contact surfaces made of steel 08X18H10T were coated with a black dense (oxide) film (Beznosov et al., 2012a). The findings of hydraulic tests and calculations of the hydrostatic bearing sections using water and lead melt may differ by one-two orders, and calculations of the hydrostatic bearings using unknown methods may turn out incorrect. Based on the tests and experiments performed, it is possible to assume the following: - the relative energy loss in a bearing submerged in lead will be less than in water; - operating in a lead coolant requires larger differential pressure in the bearing (under other equal conditions) than when operating in water; - to ensure hydrostatic bearing operation, the required volume flow rates of water and lead melt will be of the same magnitude.
A.V. Beznosov et al. / Nuclear Engineering and Design 265 (2013) 675–681
681
4. Conclusions
References
The existing methods for calculating hydrostatic bearings are good-for-nothing for calculating such bearings of main circulating pumps of fast neutron reactors cooled by lead coolant. Based on the information acquired, analysis and calculationand-theoretical examinations, the following two structural schemes of bearings have been selected for further testing:
Beznosov, A.V., 2006. Heavy Liquid-Metal Coolants in the Nuclear Power Industry, Beznosov, A.V., Dragunov Y.G., Rachkov V.I., М.: IzdAt, p. 370. Beznosov, A.V., Antonenkov, M.A., Bokova, T.A., et al., 2011. Experimental Research of Throttle Hydrodynamics in Lead Coolant and Water Flow, Izvestiya VUZov Nuclear Power Engineering, 2. Beznosov, A.V., Antonenkov, M.A., Bokova, T.A., et al., 2012a. Experimental Research of Hydrodynamics of Lead Coolant and Water Flow Through ThrottleAnnular Clearance Test Section, Izvestiya VUZov Nuclear Power Engineering., pp. 1. Beznosov, A.V., et al., 2012b. Tribology hydrostatic bearings of the main circulation pumps nuclear fast reactor cooled by lead-cooled. Frict. Wear 33 (5), 465–472. Chernavsky, S.A., 1963. Friction Bearings. Mashgiz, Moscow. Drozdov, Y.N., et al., 2010. Applied Tribology (Friction, Wear and Lubrication). Publishing House of the Eco-Press, pp. 604. Drozdov, Y.N., Pavlov, V.G., Beams, V.N., 1986. The Friction and Wear in Extreme Conditions. M. “Engineering”, pp. 224. Idelchik, I.E., 1992. Flow Friction Reference Guide, under the Editorship of M.O. Steinberg, 3rd ed., Revised. Mashinostroyenie, Moscow. Kogaev, V.P., Drozdov, Y.N., 1991. The Strength and Durability of Machine Parts. M. “High School”, pp. 320. Modern Tribology, 2008. In: Frolov, K.V. (Ed.), Results and Prospects. M. Out-of LCI, p. 480.
1) chamber-type with a throttle; 2) chamber-type with slot throttle control. The results of the hydrodynamic successive comparative tests of the bearing in water and in lead generally confirm inapplicability of the existing methods for calculating the bearing operating in a lead coolant. It is suggested to make a final choice between the structural schemes of the hydrostatic bearing for the pump of reactor installations with a heavy liquid-metal coolant after endurance testing of bearing alternatives and examination of their serviceability under emergency increase of disperse particles content in the lead flow.