The safest way to build a nuclear reactor is to float it. If the reactor and containment weigh 40 000 metric tonnes and the raft weighs another 40 000 tonnes, the total of 80 000 tonnes could be supported on a displacement of 100 meters diameter (for an area of about 7 800 square meters) with a depth of 10 meters (one tonne = 1cubic meter of water).
An excavation, somewhat over 100 meters diameter, would be emptied to a depth of 100 meters, some of the excess space would be used for the placement of a concrete lining to retain water. A 120 meter total diameter would have an area of 11 000 square meters, to 110 meters depth would have an excavated volume of 1 200 000 cubic meters. At $100/ cubic meter excavation cost, the total price would be $120 000 000.
The area of the walls would be 120 X pi X 110 = 41 000 square meters. The area of the floor would be 11 000 square meters fora total of 52 000 square meters. If the walls and floor are 3 meters thick, the total concrete would be 160 000 cubic meters. Concrete would cost about $200/ cubic meter and, with labor and placement costs, maybe $2000/ cubic meter, for a total cost of $320 000 000. Added to excavation cost the total would be $440 000 000.
A raft of 40 000 tonnes would represent 20 000 cubic meters of concrete. Again, at $2 000 per cubic meter total cost, it would be $80 000 000, added to the other total, the total cost would be $520 000 000.
The cost of a nuclear reactor is $8 billion to $10 billion, so the cost would not be out of line with other expenses. In fact, the floating of the reactor isolates it from ground motion and obviates the need for earthquake reinforcement, saving an enormous amount in construction costs; the flotation might, in fact, save money from the total cost.
The raft and reactor would be assembled on the floor of the tank and then floated into position as the tank is filled.
The main purpose of the design is in any event in which there is a danger of core melting. The sea-cocks of the platform would be opened and the entire unit sun and submerged. With passive cooling from the surrounding water, there is no danger of melting.
In order for this to work, there needs to be a separation of the feed and exit pipes. In b ^, an outlet pipe is shown fitted into a sleeve pipe. The sleeve can be an active pipe for circulation or a dead-end seal, depending on need. In the illustration the pipe continues. Heavy support and reinforcement would be needed for high-pressure pipes for them to function properly.
In d^, the outlet pipe, o, is shown at a higher elevation than the inlet pipe, o. This is so that the pressure in the inlet pipe is higher form deeper submergence than the outlet driving the liquid from the inlet, through the core of the reactor and then out the outlet to maintain cooling circulation. The heat form the reactor core will warm and expand the water further increasing circulation, as the warmed water will further drive itself through the exit pipe.
Depicted in d, is a pressurized water reactor, the water in the reactor core is under high pressure and circulates to where it exchanges heat with a second pipe, the secondary pipe having water then flashes into steam and drives a turbine to produce power. The outlet pipe is connected to the top of the reactor vessel where a bubble of steam, b, is maintained. This bubble normally prevents the reactor from going solid, being completely filled with water. Water does not compress easily and if the vessel filled with water, the heat produced by the reactions would heat and expand the water potentially causing the water pressure to rupture welds and pipes, leading to a lack of cooling and potential melt-down. The bubble can compress so it can absorb changes form the heating of water or water-hammer, the sudden stopping of a flow of water. When disconnecting the pipes, it is important to disconnect the steam outlet first, if the inlet pipe is disconnected the first, the steam bubble will expand, driving water out the inlet, and potentially uncovering the fuel rods. By the steam pipe being disconnected first, the steam will blow out the pipe relieving the pressure and allowing the entering water to successfully cool the core. In order to ensure the outlet opening first, it would have a shorter sleeve so the raft will sink a shorter distance before it opens. For the pressurized water reactor, the outlet pipe would be connected to a dead-end sleeve.
For the inlet pipe, c, shows deep serrations in the pipe edge periphery, admitting water in a controlled manner as it descends, the systematic filling of the pipe precluding the trapping of an air bubble which could interfere with flow, the water entering in a controlled manner will systematically displace the air. The pipe also has a longer sleeve to delay water entry until the steam has escaped.
In a boiling water reactor, the steam pipe would be the outlet pipe.
In a, e, shows an exhaust pipe connected to the top of he dome, there would also be an inlet pipe for the volume of the dome for additional cooling and to prevent the dome volume from acting as a flotation device. Both pipes, inlet and outlet, would be dead-end connections.
A ring shield, rs in a, would cover the opening between raft and water tank edge. It would be a semi-circular metal enclosure which would ensure that the water remains clean. In cold climates the ring shield and some residual heat from the reactor fed into the water should easily prevent any freezing.
There will be radioactive steam and water released, but the isotopes tend to decay quickly. Additionally, blocks of floating plastic covered by plastic tarping could be placed over the tank after the raft has submerged to further reduce any radioactive releases.
A decision would have to be made on how much additional equipment, such as turbines and alternators, should be placed on the raft. Once the raft sinks, the reactor would be useless. That leaves open the danger that operators may delay submerging and consequently allowing the core to melt.
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