Remote Maintenance of Molten Salt Reactors

you in the competition to achieve economic power from nuclear reactors studies are being conducted on the use of high-performance fuel elements in which some fission products escaped into the coolant stream a large part of the reactor development program at Oak Ridge National Laboratory is directed toward systems in which all fission products are permitted in the circulating fuel stream these are known as fluid fuel reactors the molten salt reactor which is one of these employs a mixture of molten fluoride salts circulated between reactor and heat exchanger at temperatures in excess of 1,200 degrees Fahrenheit all reactor systems either the solid or liquid fuel variety with radioactivity in the coolant cannot be approached for contact maintenance consequently repairs must be made indirectly the approach in the molten-salt reactor system is to have components with long serviceability so that when they do fail they can be economically discarded without repairs and replaced in their entirety the laboratory as a result initiated a program to develop an arrangement of reactive components which would permit component maintenance and replacement through remotely controlled operations this facility is a mock-up of a small reactor system approximately 20 thermal megawatts in size a simulated fuel mixture of sodium fluoride zirconium fluoride and uranium fluoride was circulated through the loop at 1,200 degrees Fahrenheit and at 5 pounds per square inch helium blanket pressure components include a reactor core vessel which supports a centrifugal sub pump and a 30 horsepower DC motor the pump impeller circulates 460 gallons of molten salt per minute at 28 feet of head the motor operates at 1,300 revolutions per minute the reactor is connected to the primary piping circuit by 2 6-inch mechanical joints of the freeze flange type 2 heat exchangers of the tube and shell type are arranged in semicircular shape each is suspended from a dolly that is free to move laterally during expansion of loop piping and during replacement both heat exchangers are connected to the primary and secondary systems by four three and a half inch freeze flange mechanical joints piping for the primary circuits consists of three and a half and six inch standard weight in canal pipe secondary circuits are constructed a three and a half inch in Canal in this section there are special electric heaters which can be maintained remotely for preheating the pipes specially designed adjustable spring supports permit all piping to expand or contract freely during operation without over stressing the pipe the piping and supports were designed to permit removal of the piping and major components from overhead to remove and replace a component it must be possible to break and remake pipe connections to extremely leak type specifications considerable attention therefore was given to the design and development of a suitable mechanical joint which would lend itself to remote assembly the freeze flange developed at the laboratory is used at 20 locations in this system such a joint takes advantage of fused salt properties to form a frozen seal of the process material between flange faces this seal is backed up by a conventional metal ring which seals in the fish and gases and also serves as a leak monitor flanges are held together by two sectioned wedge clamps fastened by bolts 1/16 inch gap exists between the faces it is in this volume that the salt seal is formed pen and funnel guides align the flanges during remote assembly the mock-up reactor system is operated from panel boards containing instruments which control pipe pre heaters the cooling air two flanges pump and motor operation and temperature recorders the control room also contains controls for the manipulator overhead crane and the closed-circuit television all of which are used during remote maintenance the television system includes two fixed cameras with automatic zoom lens mounted in separate locations in the reactor cell two other cameras with three lens turrets are mounted as a stereo pair atop the control room roof these cameras located on a dolly which can travel the length of the cell feed their pictures into a pair of monitors mounted in a stereo viewer the stereo system is in use more often than the fixed cameras signals from all four cameras are fed into the monitors through video switches to test the maintenance concept salt was circulated through the system and then dumped before the various reactor components were removed and replaced in removing the motor pump and reactor the motor is first disconnected electrically by the remote manipulator then three bolts holding the motor and pump spool units together are loosened with a pneumatically operated impact wrench with the aid of the overhead crane the motor is lifted from the pump and removed from the cell [Music] the disassembly proceeds with the removal of six oil and helium lines connected to the pump in addition a speed indicator and two thermocouples are disengaged once again the impact wrench is used to free 12 hold down bolts the bolts loosened in sequence remain in the pump four Jack bolts are actuated to break loose the seals between the pump rotary and stationary elements the bolts are turned one revolution during each sequence to free and raise the pump evenly an eyebolt is inserted in the pump shaft to facilitate its removal by the crane you the pump flange hole ring gasket is the final piece of equipment removed in this setup total time for removal of the motor and pump was six hours in removing the reactor core vessel 23 thermocouple and heater leads our first disconnected after the four freeze flange cooling lines are detached the pump bowl vent is removed all of these items are left suspended for easy pickup later [Music] both bolts on the upper and lower flange clamps are then loosen the special torque tool consists of two pneumatic air motors gang to give either alternate or simultaneous operation by air pressure and to absorb counter torque the same tool after conversion to a bolt runner unscrews the bolts until the clap have separate far enough to slip over the flanges one of the air motors simultaneously turns both 2 and 5/8 inch socket extensions to a geared drive this unscrews both bolts the same number of terms the loosened flange clamps are moved aside then the jack controlled handles atop heat exchanger dollies are turned to separate the flange faces and permit lifting of the reactor vessel the action is alternated between both jack handles after every two turns the reactor remains stationary while the screw jacks push the reactor piping system including the heat exchangers away from the core vessel this is possible because the entire reactor piping system is floating and free within limits to move in any direction approximately 36 counterclockwise turns are needed to open a two inch gap between flanges for reactor hole down both Tsar next loosened and left in position following attachment of a lifting jig the reactor vessel is carefully raised from its support stand and removed [Music] installation of a new or repaired reactor pump and motor is essentially the reverse of the removal of these components occasionally it is necessary to use the manipulator to assist the crane in positioning the reactor during installation this operation like the others requires experience care and patience total time for removing and installing the reactor less pump is 24 hours the replacement pump is lowered into position after the o-ring gasket is installed [Music] the new motor follows this unit and the pump are connected by a self guiding flexible coupling after the hold-down bolts are tightened the electrical connection is made removal and installation of the motor pump and reactor takes 36 hours another component designed for remote installation is the electric pre heater these units heat luke piping to 1,200 degrees Fahrenheit prior to filling the loop with fuel the for heater and thermocouple leaves are disconnected first as the preheater lifting handle is pulled the hinged sections spread out and the unit is withdrawn the replacement heater is then lowered and locked into position by pushing down on the handle the first step in replacing a heat exchanger is the disengagement of 23 thermocouple and heater leads these connectors are hung nearby for easy pickup and reconnection eight forced air cooling lines servicing the for heat exchanger flanges are also disconnected once again the special tool is used to loosen the flange clamp bolts the port runner unscrews both bolts in each clamp using socket extensions on the lower clamps wedges are installed to hold the pipe in position on the sliding spring supports during the jackscrew loosening operation the hook on the jackscrew is engaged permitting movement of the heat exchanger horizontally [Music] the jackscrew control arm is actuated until the heat exchanger is free from the piping the hook is disengaged to permit removal of the heat exchanger the overhead crane is then hooked to the lifting on [Music] cautiously the operator maneuvers the heat exchanger out of its support stand to complete the removal operation [Music] a replacement heat exchanger is lowered onto the dolly track of the support staff then the unit is pulled into position for engaging the jackscrew hook after the hook is engaged the control arm is actuated to mate the flanges finally the wedges are removed total time required for removal and replacement of the heat exchanger is 24 hours the life expectancy of reactor components is estimated to be years the 36 hours required in replacing the most difficult component in the mock-up therefore constitutes a negligible cost item if such efficiency can be achieved on a real molten salt reactor other advantages of the molten salt cycle include high thermal efficiency the possibility for thermal breeding and low fuel cycle costs the operations photographed at this facility indicate it is feasible to remove and replace remotely components of a molten salt reactor without direct or semi direct manual assistance the maintenance operator can be several hundred feet away from the reactor and still perform the necessary operations since there is increasing interest in many types of reactors in which fission products are not entirely confined to fuel elements the procedures developed at this facility are expected to assist designers of other type reactors [Music]

Channel: Oak Ridge National Laboratory

Views: 23,636

Rating: 4.9412842 out of 5

Keywords: MSR, MSRE, molten salt reactor, Molten Salt Reactor Experiment, nuclear power, nuclear reactor

Id: uHT-w2x6dDg

Length: 19min 40sec (1180 seconds)

Published: Wed Oct 04 2017

Reddit Comments

[u/WaywardPatriot]

WAAAAHHH?? This is so cool!