Patent Application
20080145170
1. Field of the Invention
The invention relates to an apparatus for safely transporting spent nuclear fuel and other hazardous materials and, more particularly, to a rail transportation system for safely transporting spent nuclear fuel and other hazardous waste materials to interim storage facilities, transfer points, or to a final federal disposal site, the rail transportation system including a railcar and cask cradle.
2. Description of the Related Art
Nuclear reactors and storage sites for radioactive materials have been in operation for many years. In a nuclear reactor, the fissionable material gradually becomes spent and must be removed along with other radioactive byproducts. Since the spent fuel contains fission by products which are highly radioactive and which generate large amounts of heat, the spent fuel is usually temporarily stored in the reactor's spent fuel pool. The spent fuel pool is a pool of water of sufficient volume to prevent the escape of harmful radiation and to absorb and dissipate the heat generated by the decaying fissionable material. Alternatively, the spent fuel may be temporarily stored in a hot cell. A hot cell refers to a heavily shielded structure having the capability to prevent the escape of harmful radiation, while absorbing and dissipating the heat generated by the spent fuel.
Generally, there is limited storage space in a nuclear reactor's spent fuel pool or in its hot cell. Thus, the spent fuel must be moved to a storage site to make room for additional spent fuel. In some cases, there is a desire to shut the nuclear reactor down and remove all fissionable material, in which case, all of the fissionable material must be removed to a storage site. Conventionally, spent nuclear fuel has been stored at various locations across the country. Spent nuclear fuel has been transported by storing it in small groups using multiple fuel storage drums. The spent fuel may be transported in the form of spent fuel rods or in the form of rubble. Conventionally, spent fuel rod assemblies have been transported in fuel transportation containers designed for undamaged fuel rod assemblies. The foregoing attempted solution, however, has required that substantially fewer failed fuel rod assemblies be transported per container, compared to the number of undamaged fuel rod assemblies that can be transported in the same container. By transporting fewer failed fuel rod assemblies, even if some fissionable material escapes from the failed fuel rods and accumulates near other fissionable material in the container, there is not enough fissionable material in the entire container to pose a significant risk of criticality. The problem with the foregoing solution, though, is it wasteful of resources, because significantly fewer failed fuel rod assemblies can be transported per container relative to the number of undamaged fuel rod assemblies that can be transported in the same container.
Another, attempted solution has been to transport failed fuel rod assemblies in fuel transportation containers designed for transporting fissionable material in the form of rubble. That is, the fissionable material is not in the form of rods, but is in the form of small particles. Thus, the failed fuel rods are broken up into rubble, and placed in the container. The problem with this solution, however, is that the method is inefficient for three principle reasons. First, the failed fuel rod assemblies be broken up. Second, such containers are capable only of transporting comparatively few failed fuel rod assemblies. Finally, the transportation container is only designed for transportation, not storage. Thus, once the fissionable material has been transported to another location, the container must be unloaded in a fuel pool or in a hot cell, and other arrangements made to store the fissionable material.
The other major problem with transporting spent nuclear fuel is that United States law imposes stringent safety requirements even on containers used to transport undamaged fuel rod assemblies. The relevant law imposes significantly more restrictive requirements with respect to the transportation of spent nuclear fuel across areas accessible to the public, as opposed to areas inaccessible to the public.
State of the art spent fuel transportation containers for areas accessible to the public are casks with individual compartments. The fuel rod assemblies are loaded into individual compartments in the casks in a spent fuel pool or a hot cell. The purpose of the individual compartments within each cask is to ensure sufficient spacing between adjacent fuel rod assemblies to avoid any danger of criticality. The fuel rod assemblies are loaded into the cask in a spent fuel pool or hot cell. Upon reaching the storage location, the fuel rod assemblies must be removed from the cask in a spent fuel pool or hot cell, and then stored.
In contrast, state of the art spent fuel transportation containers for areas inaccessible to the public are typically a sealed canister placed within a cask. The fuel rod assemblies are loaded into individual compartments in a canister in a spent fuel pool or a hot cell. The canister is then sealed and placed in a cask. When the cask/canister assembly reaches the storage site, the canister is removed from the cask, stored, and the cask may be reused, which is a much more efficient process.
Nonetheless, the cask/canister method cannot be used for transportation in areas accessible to the public because they fail to meet the requirements imposed by U.S. law. Whether the spent fuel is transported by cask or a sealed canister within a cask, there is a significant need for the casks to be transported in a safe and efficient manner so as to eliminated the possibility of hazardous materials leaking into the environment. Accordingly, there is a need for an invention that provides for the transportation and storage of spent fuel rod assemblies, and for a cask/canister device for the transportation and storage of spent fuel across areas accessible to the public. The present invention provides a solution, wherein a existing casks can be used and can be safely transported resulting in much greater efficiency in the transportation over public thoroughfares and storage of spent nuclear fuel.
The invention provides an apparatus for safely transporting spent nuclear fuel and other hazardous materials via rail transport. The system in accordance with the invention includes a transportation cradle that is mountable onto a railcar. The cradle in accordance with the invention is configured so as to securely receive and hold a cask containing spent nuclear fuel or other hazardous materials. The railcar is specifically designed and tested to meet AAR requirements for the transportation of spent nuclear fuel.
The cradle in accordance with the invention includes the main structure of the cradle which supports the dead weight and dynamic loads from the transportation cask, restraining members which restrain the transportation cask from an upward movement as well as horizontal movements, and a rotational support member which allows the transportation cask to be placed in the vertical position onto the cradle and rotated to the horizontal position for final transportation. The main structure of the cradle supports both the weight of the cask as well as the dynamic loads that will be experienced during transportation of the cask. The restraining members are designed to provide adequate support to protect the cask including protection to the cask from the cradle allowing the cask to be exposed to loads in excess of the maximum cask design load (i.e., The restraining members will fail at a lower force than the maximum design force for the cask which will allow the impact absorbers located on the ends of the cask to prevent the cask from receiving a force greater than the design of the cask itself). Thus, the cradle design provides support to protect the spent fuel transportation cask and also to protect the cask should it be exposed to loads that would exceed the design load for the cask. In accordance with the invention, the cradle will be secured to the railcar in four locations to accommodate the camber in the railcar flatbed. This will reduce potential failure of the cradle to railbed connection.
The railcar in accordance with the invention is designed with high structural safety margins in the railcar body and railcar trucks, high precision railcar trucks and brakes to assure performance safety and reliability, and a performance monitoring system to allow for early warning of potential structural or performance problems. The monitoring system in accordance with the invention provides early warning to the train crew of component or performance degradation to assure pro-active actions prior to failure. The railcar monitoring system in accordance with the invention includes the monitoring and recording of the following factors: railcar speed, truck movement, rocking, wheel flats, bearing conditions, braking performance, as well as vertical, lateral and longitudinal acceleration. By monitoring and recording each of these factors, the pro-active actions can be taken to prevent railcar and/or cradle failures that could increase the risk of damage to the spent nuclear fuel cask.
The cradle and railcar in accordance with the invention are designed together so as to provide a high level of assurance against structural failure of the railcar and cradle combination.
Thus, the invention provides transportation cask cradle that includes a front cradle section load bearing brace, the load bearing brace including a first and second opposing end portions, a rear cradle section having a first non-loading bearing brace and a second non-loading brace, the first non-load bearing brace having a first top section and the second non-load bearing brace having a second top section, the first and second top sections opposing each other, first and second horizontal support members connecting the front cradle section to the rear cradle section and a first trunnion disposed on the first top section of the first non-load bearing brace and a second trunnion disposed on the second top section of the second non-load bearing brace.
The invention also provides a nylon bearing surface affixed to load bearing brace as well as a stop bar affixed to the load bearing brace to prevent longitudinal movement of the cask.
The invention further includes a plurality of base members disposed on a bottom surface of the cradle, the base members allowing the transport cradle to be affixed to a vehicle surface.
The invention also provides an uplift prevention device affixed to the first top section of the first non-load bearing brace and the second top section of the second non-load bearing brace which prevents upward (vertical) movement of the cask.
The invention also provides a railcar for transporting hazardous materials that includes a depressed flatbed disposed on a planar surface of the railcar, at least one retaining bracket disposed on the depressed flat bed, the at least one retaining bracket configured so as to facilitate coupling with a transportation cradle, as described above. In accordance with the invention, the railcar may also include braking performance sensors dispose at each end of the railcar which gather data related braking of the railcar. In accordance with the invention, the railcar may also include sensors for truck hunting, rocking and vertical, lateral and longitudinal acceleration, whereby the sensors are disposed at a middle section of the railcar. In accordance with the invention, the railcar may also include a Global Positioning Satellite (GPS) sensor disposed at a front section of the railcar. In accordance with the invention, the railcar may also include a plurality of wheel bearing sensors corresponding to each of the wheel bearing assemblies.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention. Together with the written description, these drawings serve to explain the principles of the invention. In the drawings:
As shown in
As shown in
Thus, the cradle 100 is configured to receive a spent fuel transportation cask that can be lowered into the cradle 100. When placed into the cradle 100, the transportation cask is in contact with the cradle 100 at the bearing surfaces that coat the front load bearing brace 115 located at the front cradle section 110. The transportation cask is also in contact with the trunnions 160 and 165 on the rear section 110 of the cradle 100.
In accordance with the invention, the cradle 100 is configured so as to be placed on the railcar for transport.
Thus, the connection between the cradle 100 and depressed center flatbed railcar 420 utilizes round lug pins. The lug pins at the front and rear of the cradle 100 are fixed in the base members located on the bottom surface of the cradle and the retaining bracket. The retaining brackets, when mated to the base members, allows only rotational movement of the cradle 100 at this connection (i.e. no horizontal or vertical movement). The retaining brackets on the railcar at front section of the cradle 100 also only allow rotational movement with no vertical or horizontal movement. However, the retaining brackets on the rear (trunnion end) of the railcar 400 are slotted allowing both rotational and horizontal movement and no vertical movement. This design allows for deflection in the railcar bed camber without applying additional load or stress onto the cradle.
The cradle 100 shown in
The railcar 400 also provides certain features beyond conventional railcars that enhance its safety which is a significant issue when transporting spent nuclear fuel. These features include electronic braking, superior suspension and sway control systems, and a performance monitoring system to allows early detect of degradation in the railcar performance which will identify railcar component degradation prior to component failure. Electronic braking allows for more even braking of the railcars which reduces dynamic loading that can occur with conventional railcar braking. The superior suspension and sway control provides a smoother and less rocking type ride which will limit the total overall swaying movement of the railcar.
The performance monitoring system incorporated into the railcar will provide real time monitoring when operating in the dedicated-train mode. The performance monitoring system collects and stores various data relating to the operation of the railcar. The data will be retrievable both in the passenger car and remotely. The system will produce exception reports when parameters exceed established setpoints. The exception reports will alarm in the passenger car and then be transmitted to the train crew in the engine.
The monitoring system will store time-history data for the parameters monitored. The storage media will be capable of storing the data for continuous operation of the train for 14 days. The media will be retrievable for review and archiving.
The monitoring system in accordance with the invention will include the following:
The foregoing description of the preferred embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching.
