Patent Number: 050376012
Section: summary

BACKGROUND OF THE INVENTION The glass-pool, air-cycle nuclear power plant of this invention is designed as an isolated system that requires minimal monitoring and is of a "walk-away" type, that is, one that can be shut down and decommissioned without any external intervention other then the poisoning of the nuclear reaction. In such event, the containment structure that contains the glass matrix pool and reaction core solidifies into a glass solid that can remain in place or be removed to a storage site. Recent disasters and near disasters in the operation of existing nuclear power plants of large size have required a reevaluation of the technology of nuclear power plant design. Far greater attention has been placed on power plants that are considered "passively-safe," that is, which do not require the intervention of an operator during a nuclear crisis in order to return the plant to a safe operating condition. The expense and complexity of current and future designs of light water reactor plants have required the nuclear industry to rethink its nuclear energy goals and have generated renewed interest in smaller, modular type plants that operate without the use of water as a coolant or as a steam generating medium. Renewed interest in more inherently safe designs such as liquid sodium systems, including static designs that do not require sodium pumps, such as that proposed in my prior patent, entitled "Nuclear Power Plant With On-Site Storage Capabilities," U.S. Pat. No. 4,313,795, issued Feb. 2, 1982. In that patent there is disclosed a nuclear reactor power plant having a gas cycle that utilizes superheated steam in its superheated state throughout the cycle. The use of a gas cycle reactor avoids a motive substance that must undergo a phase change. The use of a substance that has a phase change between liquid and gas, can typically result in emergency conditions. For example, when quantities of water contact high temperature core material the explosive reaction releases large volumes of contaminated steam. This is the heart of the traditional disaster scenario. Operating the reactor core in the very material that is to constitute its entombment on decommissioning, provides an attractive safety feature that other plants of advanced design appear to lack. This feature can provide a attractive solution to the problem of decommissioning and disposal of reactor cores. The use of new reactor fuel sources utilizing thorium/uranium.sup.233 in encapsulated fuel pellets with neutron moderation and containment by graphite shells and casings, provides the basis for advanced designs of walk-away nuclear power plants that require little or no monitoring during the life of operation of the plants. By use of smaller modular systems that are standardized with lower power goals which do not include failure prone internal or external liquid circulation pumps, the goal of a passively-safe or a walk-away nuclear power plant can realistically be achieved. One of the crucial problems facing the nuclear power industry in the United States is the fact that, all of the nuclear plants that have been constructed to date are different from one another. In addition to the huge capital cost, large scale, custom power plants cause difficulty in staffing and safe monitoring of plant operation. Furthermore, at the time of decommissioning, each plant must be considered as a separate entity for which a decommissioning plan must be devised that in many cases can result in decommissioning costs that exceed the original cost of construction. With a lower ultimate power goal for each plant, the system design can be standardized. By simply multiplying the number of identical plants, any desired greater power capacity can be obtained. Given a substantial flexibility in power rating and design, small inexpensive plants under one megawatt can be placed in operation to test operating parameters over a larger number of units at minimal financial and safety risk. The glass-pool, aircycle, nuclear power plant described and claimed herein resolves many of the current problems in the design of a safe power plant that utilizes fissionable nuclear materials that will not adversely impact the environment during operation or after shut-down. SUMMARY OF THE INVENTION This invention relates to a nuclear power plant and in particular to a glass-pool, gas-cycle plant having a thorium/uranium.sup.233 reactor in a glass matrix that is designed to constitute the heat dissipating core during operation, and, the inert tomb upon deactivation. The nuclear power plant of this invention couples a safe thermal source with a safe conversion means for converting thermal energy of a nuclear reaction to useful power, for example, electricity. Because the design of the power plant is directed to lower power goals, the thermal energy can also be converted directly to mechanical work useable on-site, for example, in pumping irrigation water. The design concept is such that the plant can be operated in an isolated environment as a self-contained system that requires no external support to either monitor operations or respond to an emergency situation. Key to the isolated system concept is the combination of an energy core that is immersed in a glass matrix that provides a heat sink to allow operation of the core at maximum temperature with the molten pool becoming the entombment matrix on solidification. The glass matrix includes in its composition fertile thorium material that is reduced in proportion to inert silicates as the distance from the central fissile core increases. During nuclear reaction, the glass matrix is in a molten state with a viscosity that increases as the distance from the core increases. The core and glass pool are encapsulated in a containment structure that is of a neutron reflecting substance such as graphite. The containment structure has a thermally conductive casing that provides a heat exchange from the glass-pool, thermal sink to a closed-cycle gas system. The other primary feature that insures the safety of the device is the use of a power extraction system that has a drive medium that does not undergo a phase change from liquid to gas. The use of a liquid to gas drive medium has been a significant contributor to the safety problems of prior art devices. In the preferred embodiment the gas is simply air. A unique divided cycle enables the effective use of air to comprise the motive force in an enclosed system. The unique, dual-path, air-cycle system utilizes a common compressor for each of two paths, with the compressor outlet coupled to a first path that communicates with the nuclear thermal source and a second path that communicates with an intercooler before being supplied to a turbine. Preferably, the compressed air from both sources drives a common turbine with the air from both sources combining in a common collector where the divergent temperatures are effectively moderated for return to the compressor. The nuclear reaction is preferably accomplished by utilizing a thorium/U.sup.233 breeding reaction in a glass matrix that on activation provides both a starting fissile material and a fertile feed material to continue a long term nuclear reaction preferably without the addition of more fuel. The life of the reaction can be determined at the time the plant is commissioned. At the time of decommissioning, when the fuel reaction is diminishing to the point that adversely affects the thermodynamic efficiency of the plant, the reduced-level, nuclear reaction is finally poisoned with a probe of a neutron absorbing material such as boron, allowing the glass matrix and core to cease reaction and gradually cool to a solid glass block. The entire core and encapsulation structure can either be removed for easy transportation as a vitrified solid to a central storage location, or can be entombed on site. If entombed on site, the volume of open space in the heat exchange area, between the pressure vessel and the encapsulation structure can be filled with a solidifying substance such as concrete, doped with a neutron absorber such that the outer containment structure totally entombs the decommissioned reactor capsule and shields any low level residual radiation that may be emitted from the core. These and other features of the preferred embodiment of this invention will be considered in greater detail in the detailed description of the preferred embodiments that follows.