35 3.7 MSBRPUMPS,
A. G. Grindell
H. C. Savage
H. C. Young
3.7.1 Salt Pumps for MSRP Technology Facilities
The coolant pump tank and volute that were removed recently from the MSRE and the spare rotary element from storage will be used in the coolant-salt technology facility. When used with a 10.33-in.-diam impeller, this combination will provide the required 90-ft head and 800-gpm flow at 1765 rpm by operating slightly toward the shutoff side of its approximate MSRE operating point of 85-ft head and 900-gpm flow rate. This operation is not expected to impose excessive radial hydraulic forces on the pump shaft. The available 75-hp motor will be loaded to approximately 45 hp for this service. The rotary element will be reconditioned with new bearings, and the shaft seals will be relapped. It will then be operated in a cold shakedown stand to check shaft seal leakage rates prior to installation in the coolant-salt technology facility. The head and flow requirements for the gas system test facility will be provided by installing an available 11'4-in.-diam impeller of MSRE coolant-salt pump design in the MSRE Mark 2 fuel-salt pump. This impeller will provide 1000 gpm and approximately 100-fthead with 100-bhp input at near 1800-rpm pump speed. Since the inlet and discharge openings in the coolant-salt pump impeller are smaller than those in the fuel-salt pump impeller, a stationary filler piece will be installed in the volute inlet. A spare MSRE coolant pump drive motor, nominally rated for 75 hp at 1200
rpm, but wound for 1800-rpm operation, will be used. This oversize motor can sustain continuous operation to 113 hp at 1800 rpm. The oversize frame was selected early during MSRE design to standardize the motor-tobearing housing mounting dimensions for both the 1200-rpm fuel pump and 1800-rpm coolant pump. The rotary element from the Mark 2 pump will be reconditioned. New bearings will be installed, the shaft seals will be relapped, and the rotary assembly will be balanced dynamically. The element then will be operated in the cold shakedown stand to check shaft seal leakage rates prior to installation in the gas system technology facility. During the assembly, measurements will be made of radial load vs shaft deflection and shaft critical frequency of the Mark 2 pump shaft with the 11'&-in.-diam impeller.
Spare parts for the two pump assemblies have been inventoried, and spare hollow metal O-rings made from Hastelloy N tubing have been ordered. The '/,-in.-OD by 0.035-in.-wall tubing for the O-rings will be formed by drawing '4 -in.-OD by 0.072-in.-wall Hastelloy N tubing that is on hand.
3.7.2 ALPHA Pump Initial operation of the ALPHA pumpI4 with hightemperature salt in the MSR-FCL2 test facility demonstrated the need for several modifications to improve reliability; the design of these modifications is in progress. In the meantime, the pump is being operated in the MSR-FCL2 at the specified design conditions. Prior to installation in the salt facility, the pump was subjected to a cold shakedown test to ensure that bearings and rotating and static seals function properly. The results of several tests indicate steady-state oil leakage rates past the rotating shaft seals ranging from 0.3 to 3.5 cc/day for a pump speed of approximately 4000 rpm and a seal differential pressure of 7 psi. Considerable difficulty was experienced with the hollow metal O-ring gaskets which seal the removable pump rotary element to the pump bowl. In the present design the space between two concentric gaskets is buffered with helium. The gaskets are of hollow stainless steel tube construction, have a toroidal diameter of '4 in., an overall diameter of 6 in., and are plated with silver or gold. In an initial test with silver-plated gaskets, after carefully hand polishing the sealing surfaces in the matching flanges, a total leak rate of approximately 6 cc/hr past both rings was attained with the buffer zone pressurized to 6.5 psig. The plating flaked from gold-plated gaskets during installation, and so gold plating is not receiving current attention. The total leak rate was reduced in a later installation by carefully hand polishing the silver-plated gaskets: the total leak rate of approximately 1 cc/hr was attained with the buffer zone pressurized to 8 psig. This leak rate was considered satisfactory because it is unlikely that either air or moisture can enter the pump in a significant quantity past the buffer gas barrier. However, because of the difficulty in attaining and maintaining the polished surfaces needed to achieve a satisfactory seal with the hollow metal O-rings, we plan to replace them with a buffered ring joint seal utilizing a solid metal gasket.
14. MSR Program Semiannu. Rogr. Rep. Feb. 28, 1971, ORNL-4676, p. 59.