Patent Number: 054127009
Section: summary

BACKGROUND OF THE INVENTION The invention relates to a reactor refueling containment system, where refueling is accomplished without removing the reactor vessel primary pressure boundary. More specifically, a barrier plate is used to form a primary coolant boundary and a closure head carries the applied pressure load. The barrier plate has all required penetrations for fuel replacement, instrumentation, and poision injection systems with an elastomer seal for each penetration. These penetrations are for inserting and removing fuel rods, assemblies, control rods, etc. Because of the large number of penetrations required, it was thought that the most efficient closure head would be one that is removed for refueling (Heads-off refueling) as in current light water reactors. Such a closure head would require penetrations only for control rods and instrumentation. The design of heavy water reactors have special requirements that make refueling as currently done in light water reactors inappropriate. Both Heavy and light water reactors require ready access to the reactor cores for fuel installation and refueling. In commercial light water reactors this is accomplished by depressurizing the system and removing the reactor vessel head to a storage area. During refueling, the area located above the reactor is flooded with additional light water to provide added nuclear shielding. This method is more commonly called "Heads-off" method of refueling. This allows the light water surface to be in direct contact with the air in the containment area. While appropriate in light water applications this method is inadequate for refueling heavy water reactors. The tritium ladden heavy water causes two problems with the Heads-off method. First, the tritiated heavy water evaporates very quickly and contaiminates the containment area which is undesirable and hazardous. Secondly, there is a contamination of the heavy water reactor coolant from light water vapor and humidity in the containment environment. This contamination by the light water is an impairment to subsequent operation of the heavy water reactor and should be avoided. Thereby requiring that a barrier be provided between the heavy water coolant and containment environment. The reactor refueling system of the instant invention eliminates the need for a seal plate mechanism and potential long term exposure of the heavy water to the atmosphere. Thereby, eliminating the need for massive environmental cleanups and their associated costs now required with the present Heads-off method. SUMMARY OF THE INVENTION The present invention relates to a reactor head refueling system which allows refueling while limiting the amount of exposure and contamination to a minimum. The only penetrations in the closure head structure are those for the control and shutdown drives. The drive mechanisms are mounted on top of the closure head. The invention uses a barrier plate coupled to the reactor vessel creating a primary coolant boundary. The barrier plate has all the required penetrations, and elastomer seals, seal each penetration opening encasing each fuel cell as it extends beyond the barrier plate. Compression posts located between the barrier plate and the closure head allows for an even transfer of the applied pressure load from the closure head to the barrier plate. In refueling the reactor after depressurization, the control rod drivelines are disengaged and removed by activating a jacking mechanism that raises the closure head. The area between the barrier plate and closure head is exhausted through the closure head penetrations. The closure head, upper control rod, and bellows seal are lifted away and transported to a safe area. The barrier plate acts as the primary boundary and penetrations for the control rod drivelines have covers preventing excessive tritium gases from escaping. The individual instrumentation plugs are disengaged allowing the corresponding fuel to be replaced. However, at any one time, only one plug is removed from the barrier plate allowing that penetration to be temporarily sealed during refueling, maintaining separation between the air environment and heavy water coolant. It is an object of the invention to provide an efficient method to refuel nuclear reactors while minimizing the release of contaminates to the atmosphere. Another object of the invention is to provide a closure structure which allows refueling of a nuclear reactor without complete exposure of the heavy water to the containment environment. Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the invention may comprise a system for contaminate recovery for a nuclear reactor during reactor fuel cell refueling comprising: a closure head connected to said nuclear reactor, said closure head having a predetermined limited number of penetrations; a barrier plate sandwiched between said nuclear reactor and said closure head forming a primary containment boundary; and a means for sealing connected to said closure head and said barrier plate creating a secondary containment boundary.