EXPERIMENTAL RESEARCH AND OPTIMIZATION OF BREST-OD-300 MCP MODEL PERFORMANCE IN A LEAD COOLANT

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1 EXPERIMENTAL RESEARCH AND OPTIMIZATION OF BREST-OD-300 MCP MODEL PERFORMANCE IN A LEAD COOLANT A.V. Beznosov, P.A. Bokov, O.I. Buzina, A.D. Zudin, A.V. Lvov, T.M. Semayeva, N.D. Trushkov (NNSTU n.a. R.E. Alekseyev, Nizhny Novgorod, Russia) The NNSTU has carried out investigation tests and developments of the main circulation pump flow part of the BREST-OD-300 reactor plant with axial impellers on benches FT-4A NNSTU and FT-4 NNSTU. Heavy liquid-metal coolants (Pb, Pb-Bi eutectics) greatly differ from conventional coolants (H 2 O, Na) by their physical properties. Calculation-theoretical and experimental investigations as well as experience in creating main circulation pumps of reactor plants in nuclear-powered submarines of 705 and 705K projects running on lead-bismuth coolants show that the existing conventional methods for designing pumps are not suited for designing pumps pumping heavy liquid-metal coolants [1]. Testing on FT-4A Bench The purpose of the investigation tests on the FT-4A bench was to preliminarily measure performance of the flow part of the axial pump having a bearing unit. Test conditions: Impeller ø220 mm in diameter, lead coolant temperature Т= о С; pump capacity approx. 100 t/h (design), head approx. 2.0 m of Pb column; shaft speed up to 1,200 rpm; peripheral speed up to 12 m/s, impeller inlet pressure approx MPa (approx. 0.5 kgf/cm 2 (atm)). There was no experience in creating and operating axial pumps pumping hightemperature heavy liquid-metal coolants in the world, so the tests were considered as preliminary. Therefore, the impeller was made of steel 3 having low-strength characteristics under the testing conditions. Figure 1 shows a coolant circulation diagram in the test bench at the axial impeller rotation. Figure 2 contains a picture of the FT-4A bench experimental section.

2 To pressure measuring system Coolant level Working chamber pressure tapping line 1 upper bearing unit; 2 gas seal assembly; 3 axial impeller; 4 outlet straightener; 5 MCP shaft simulator; 6 bearing housing; 7 shaft; 8 pull-out part housing; 9 HLMC tank Fig. 1. Coolant Circulation Diagram in Experimental Section

3 Fig. 2. Photo of FT-4A Bench Experimental Section (Pull-Out Part) The lead coolant circulates through the bench channels as follows. During the shaft rotation, the axial impeller supplies the lead coolant from the bottom upwards to the outlet straightener. Coming out of the outlet straightener, the main flow of the coolant goes upwards to the tank cover, then it turns round 180 С and goes down to the impeller inlet. The rated parameters of the circulating high-temperature ( С) flow of the lead coolant at n=1,200 rpm feed 1,000 1,200 t/h, head approx. 1.5 m of lead column, impeller inlet pressure MPa ( kgf/cm 2 (atm)). A portion of the flow with relatively small feed (approx t/h) is supplied to the hydrostatic bearing. Results of tests on the FT-4A bench

4 In the first series of investigations, the capacity (Figure 1) was filled up with water at о С under atmospheric pressure. The axial impeller rotation speed was 300, 500, 750, 1,000, 1,200 and 1,500 rpm. Time of tests in each mode for performing necessary measurements about 1 hour. In the second series of investigations (5 cycles), the capacity (Figure 1) was heated up to о С, filled up with lead, and there were created conditions for forming oxide coatings on steels in the capacity, and tests were carried out at the axial impeller rotation speed of 300, 500, 750, 1,000 and 1,200 rpm. Time of tests in each mode about 1 hour at O 2 activity а= In the third series (25 cycles), due to unavailability of any system for removing heat from lead, the investigations were conducted in cycles. The cycle composition included: - the pump operation during minutes with an increase in temperature from 420 to 550 о С due to adiabatic heat supply; - the pump shutdown and natural cool-down of the coolant to 420 о С; - the pump start-up and operation during minutes with an increase in temperature from 420 to 550 о С. In the fourth series, the investigations were carried out under conditions similar to the second stage but at О2 thermodynamic activity in lead а= In the fifth series, the investigations were carried out under conditions similar to the second stage but at О2 thermodynamic activity in lead а= The total number of cycles for the investigation time was 60, and the overall length of testing was approximately 80 hours. Following the third testing stage, the bench inspection was carried out, which showed as follows: the axial impeller vanes made of low-quality steel 3 (for inviting wear during testing) were covered with black protective oxide coatings; there was no sign of erosive surface wear; there was a 2-4 mm deformation of the peripheral vane edges (Figure 3) along the flow. A possible reason for that vane deformation included the fact that the vane thickness in this section was 1 mm and less, and low-strength characteristics of steel 3 at 550 ос; there was no sign of erosive wear of the outlet straightener vanes made of steel 08Х18Н10Т (Figure 4). After the inspection, the bent peripheral areas were removed. Following the fourth and fifth series of investigations, the state of the pump flow part surfaces remained unchanged. No sign of cavitation wear was present after completion of all tests. There was no change in acoustic performance similar to cavitation performance.

Vane edge deformation a) b) a) axial impeller; b) axial impeller vane with a deformed edge Fig. 3.

Outlet Straightener In all the series of tests, with water and with lead, fixing the load (current) on the electric motor was

There was no change in the load on the pump electric drive corresponding to the signs of fully-developed cavitation

The conducted investigations proved the possibility in principle of creating an axial pump including a hydrostatic bearing.

5 Vane edge deformation a) b) a) axial impeller; b) axial impeller vane with a deformed edge Fig. 3. Axial Impeller After Stage 3 Before tests After tests with lead after Stage 3 Fig. 4. Outlet Straightener In all the series of tests, with water and with lead, fixing the load (current) on the electric motor was carried out: - with water (N = 7.8 kw, n nom = 1,455 rpm) with lead (N = 45 kw, n nom = 2,960 rpm). There was no change in the load on the pump electric drive corresponding to the signs of fully-developed cavitation appearance in the lead coolant medium. The conducted investigations proved the possibility in principle of creating an axial pump including a hydrostatic bearing. Further research of cavitation performance of axial pump flow parts designed by the NNSTU and the Central Mechanical Engineering Design Bureau was carried out on the FT-4 NNSTU bench. Main Performance Data of FT-4 NNSTU Bench (Figure 5) 1. Coolant lead melt of grade S0 GOST Coolant weight 1х10 4 kg.

6 3. Lead coolant temperature ºС, momentarily 550ºС. 4. Coolant flow rate, maximum up to kg/hour (up to 200 m 3 /hour). 5. Oxygen thermodynamic activity in lead coolant up to 100 plus solid phase of lead oxides. 6. Electric pump drive asynchronous motor, 2 pcs., n nom = 1,500 rpm and 3,000 rpm, N nom up to 50 kw, with frequency speed control. 7. Power of bench electric-heating coils, total up to 100 kw, voltage 380/220 V. 8. Friction-type bearing of electric pump of lead coolant circuit at the first stage hydrostatic slot-type bearing. 9. Impeller and outlet straightener replaceable, 2 components designed by the Central Mechanical Engineering Design Bureau and 2 components designed by the NNSTU. 10. Gas in the gas system: argon, hydrogen, argon-hydrogen and argon-oxygen mixtures. 11. Equipment and pipeline heating system of lead coolant circuit electrical, nickelchromium coils with cordierite beads.

7 1. Melting tank 2. Electric pump 3. Electric motor 4. Pressure tank at pump impeller inlet 5. Pressure tank at pump outlet 6. Pressure tanks on orifice meter 7. Main control valve 8. Filter 9. Water filter of water-air mixture injection system 10. Steam generator 11. Compressor 12. Vacuum pump 13. Gas cylinders 14. Expansion bellows 15. Flow straightener 16. Orifice meter 17. Pump element water cooling filter 18. Pump element water cooling pump 19. Water head tank 20. Water cooling buffer tank 21. Condenser 22. Drain tank 23. Gas flow meter 24. Damper 25. Expansion tank Pump pressure take-off system Pump element water cooling system

Subsequent activities were carried out on the specially created FT-4 NNSTU bench in two directions: Develop the BREST-OD-300 MCP flow part models designed by the Central Mechanical Engineering Design

flow part of axial pumps pumping hightemperature heavy liquid-metal coolants and refining these structural models as applied to the BREST-OD-300 reactor plant MCP.

The bench electric pump NSO-01 NNSTU is designed to carry out tests and refine flow part models of the BREST-OD-300 reactor plant MCP comprising the electric pump in order to ensure circulation

8 Subsequent activities were carried out on the specially created FT-4 NNSTU bench in two directions: Develop the BREST-OD-300 MCP flow part models designed by the Central Mechanical Engineering Design Bureau; Carry out investigation tests of the axial pump flow part models designed by the NNSTU as applied to the BREST-OD-300 MCP with a view to developing representative design procedures for the flow part of axial pumps pumping hightemperature heavy liquid-metal coolants and refining these structural models as applied to the BREST-OD-300 reactor plant MCP. Main performance data of the FT-4 NNSTU bench (Figure 5). The bench electric pump NSO-01 NNSTU is designed to carry out tests and refine flow part models of the BREST-OD-300 reactor plant MCP comprising the electric pump in order to ensure circulation across the main circulation circuit of the bench, and to verify the design solutions and refine the hydrostatic bearing comprising the electric pump. a) b) Figure 6. Electric Pump NSO-01 NNSTU 1 Pump reservoir; 2 Pull-out part; 3 Cage; 4 Gasket; 5 Nut; 6 Washer; 7 Pin; 8 Coupling HRC-150; 9 Torque sensor; 10 Coupling HRC-180; 11 Electric motor a) Impeller version designed by the NNSTU; b) Impeller version designed by the Central Mechanical Engineering Design Bureau The flow part of the NSO-01 electric pump includes replaceable areas of the models (supplied by the Central Mechanical Engineering Design Bureau and the NNSTU): the inlet tube; the impeller and the outlet straightener. The area of the flow part model from the outlet

9 straightener and the lower part of the constant head pipe is a part of the NSO-01 NNSTU and is irreplaceable (fixed). The area of the upper part of the model constant head pipe and the flow turning device is a part of the NSO-01 and could be removed during testing. The tests carried out in 2013 with regard to the flow part designed by the Central Mechanical Engineering Design Bureau included the following stages: cavitation tests; determination of head-and-rate and energy characteristics with the upper part and flow turning device installed; determination of head-and-rate and energy characteristics with the constant head pipe upper part and flow turning device removed; endurance tests. The cavitation tests made it possible to determine conditions of incipient cavitation (gaseous) and their characteristics. The head-and-rate and energy tests of models designed according to the conventional techniques showed, as could be expected, a material inconsistency in characteristics of tests on lead with the design calculations. After the tests at Stages 3 and 4, there was detected a change in geometry (bend) of the trailing edges of all vanes and appearance of erosive wear on them (Figure 7). Fig. 7. Erosive Wear of Vane Trailing Edges Following Endurance Tests In the course of testing for determining impact of the axial clearance between the impeller and the outlet straightener on the NNSTU model design, due to an emergency selfinduced loosening of the nuts in the hold-down bolts of the inlet tube, there occurred a conjoint rotation of the impeller and the inlet tube (n=1,200 rpm) causing shifting from the latter's axis by approx. 3.0 mm. The pump shaft seizure, development and running of the emergency resulted in destruction of the impeller vane trailing areas (Figures 8 and 9).

part of axial pumps pumping heavy liquid-metal coolants.

10 Fig. 8. Destruction of Impeller Vanes Figure 9. Destruction of Impeller Hub Conclusion 1. The initial-stage testing of the impeller model of the BREST-OD-300 reactor plant running on a lead coolant has confirmed inapplicability of the conventional design procedures for the flow part of axial pumps pumping heavy liquid-metal coolants. The experimentally obtained characteristics of the flow part with impellers having seven and four vanes designed according to the conventional techniques have virtually coincided, but they greatly differ from the design characteristics. 2. The experimental findings show no damage or destruction at the inlet areas of the impeller vanes and changes in geometry and specific erosive wear of the impeller vane trailing areas.

ANALYSIS OF BREST-OD-300 SAFETY DURING ANTICIPATED OPERATIONAL OCCURRENCES

ANALYSIS OF BREST-OD-300 SAFETY DURING ANTICIPATED OPERATIONAL OCCURRENCES D.V. Didorin, V.A. Kogut, A.G. Muratov, V.V. Tyukov, A.V. Moiseev (NIKIET, Moscow, Russia) 1. Brief description of the aim and