Patent Number: 044937920
Section: summary

DESCRIPTION TECHNICAL FIELD The invention generally relates to nuclear fuels and, more particularly, to methods and apparatus for drawing radioactive samples from vessels containing radioactive materials. BACKGROUND ART There is serious concern throughout the world that with the increasing deployment of reprocessing facilities that there is an increased likelihood of the further proliferation of nuclear weapons. This concern is due to the fact that essentially all reprocessing methods used heretofore are derived from the processes originally developed during or shortly after World War II for producing plutonium for nuclear weapons. These processes are undesirable because they have the potential to make purified fissionable materials available and therefore susceptible to diversion by terrorist groups. In addition, there is international concern because such reprocessing plants could readily be converted over to the extraction of weapons material by a change of intention by a government which had previously pledged by treaty to forego the production of nuclear weapons. In answer to this threat Milton Levenson and Edwin Zebroski conceived of a process for reprocessing spent nuclear reactor fuel which makes plutonium highly resistant to diversion. Their concept, which is called The CIVEX Process, includes a combination of changes in the method of reprocessing spent fuel and changes in the design of a reprocessing plant. The CIVEX concept is disclosed in the U.S. patent application entitled "METHOD AND APPARATUS FOR PROCESSING SPENT NUCLEAR REACTOR FUEL" Ser. No. 878,392 which was filed on Feb. 16, 1978. Within a fuel reprocessing facility a sampling station is a major focus for diversion because it is a point where plutonium containing liquid can be obtained directly without arising suspicion. It is also a point where radiation exposure is minimized and where equipment is readily accessable for transporting radioactive materials. A sampling station is a shielded outlet where radioactive samples are taken by plant personnel in order to monitor the status of the process. These samples are taken at sampling stations located throughout the plant. In a typical plant there are between 40 and 50 such sampling stations. Samples are taken at various rates depending on what is being sampled and which step is occurring in the process. Samples are normally taken either hourly, once per shift, or daily. In the past sampling stations have been designed principally with the objectives of shielding plant personnel from radiation exposure and insuring that representative samples of the process was taken. It is believed that aside from these objectives no attempt has heretofore been made to limit the amount and frequency of the samples taken. It is also believed that no attempt has heretofore been made to control physical access to sampling stations so that the diversion of plutonium containing liquid could be prevented. The present invention is directed to overcoming one or more of the problems as set forth above. DISCLOSURE OF THE INVENTION The present invention contemplates methods and apparatus for minimizing the diversion of radioactive samples from a nuclear fuel sampling system. The apparatus includes a sampler for drawing a sample from a vessel containing nuclear fuel in solution and a enclosure for preventing direct access to the sampler. The apparatus further includes a tray which moves a sample vessel in and out of the shielded enclosure and means for moving the sample vessel within the shielded enclosure. In one aspect of the invention the tray is periodically immobilized and in another aspect the sample vessel moving means is periodically immobilized for periods of time sufficient to minimize the diversion of radioactive samples from the plant. The present invention overcomes the disadvantages of the prior art by limiting the access of personnel to radioactive samplers in nuclear fuel processing plants. The amount and frequency of sampling is regulated by a time controlled escapement and physical access to the apparatus is restricted. Other aspects, objects, the advantages of this invention can be obtained from a study of the drawings, the disclosure, and the appended claims.