Direct maintenance

Perform, as directed, maintenance and repair on nuclear weapons, radar, and inertial fuzes, Permissive Action link Devices, ADM Firing Systems, and Adaptation Kits... 

Equipment within the high-radiation area that may experience mechanical or electrical failure or is subject to severe corrosion can be replaced remotely the rest of this equipment is designed for direct maintenance after cleanout and decontamination. 

The alternative to the direct-maintenance philosophy is the canyon using remotely removable equipment as used in the early U.S. plants at Hanford and SRP. This has proved successful but requires more space and is of a more complex design. 

The adoption of the direct-maintenance philosophy sets criteria for the design engineer that affect not only the plant design but that of the process as well. 

In the event of failure of equipment within a radioactive area, three courses of action may be taken (i) switching to duplicate equipment, (ii) replacing or repairing equipment by remote methods remote maintenance, or (iii) repairing by direct maintenance after decontamination. 

Radiochemical plants differ from the conventional type of chemical plant since no direct maintenance or process control by operating personnel can be performed within the immediate site because of the inten.se radioactivity when the plant is in operation. It is only possible to enter the area when the active material has been removed from the equipment... 

Two basically different types of maintenance can be incorporated in the plant design. Direct maintenance involves personal contact service on the equipment in place and requires thorough decontamination, usually a very slow procedure, before entry into the process area. Where possible,... 

Offices Storage Clothing change room Fig. 10-13. Plan of a direct-maintenance fuel reprocessing plant. Division of equip-... 

Materials in contact with radioactive solids, liquids, or gases will pick up activity as the result of physical or chemical adsorption. In some cases it may be impossible to do repair work, even though the radioactive contents are removed. This is true in the case of direct-maintenance plants, and materials should be selected for rapid decontamination to increase the plant on-stream time. 

Factors are for direct-maintenance plants processing enriched spent reactor fuels. 

Remote-maintenance plants will have a capitalized cost about 50 per cent higher than that shown for the direct-maintenance plant. Pyro-metallurgical or fractional-distillation types of plants are in the low range of the costs estimated for direct-maintenance plants. 

The most important isotope of plutonium is Pu = 24,200 years). It has a short half-life so only ultra traces of plutonium occur naturally in uranium ores, and most plutonium is artificial, being an abundant byproduct of uranium fission in nuclear power reactors. The nuclear reactions involved include the radiative capture of a thermal neutron by uranium, U( , y) U the uranium-239 produced is a beta-emitter that yields the radionuclide Np, also a beta-emitter that yields Pu. To date, 15 isotopes of plutonium are known, taking into account nuclear isomers. The plutonium isotope Pu is an alpha-emitter with a half-life of 87 years. Therefore, it is well suited for electrical power generation for devices that must function without direct maintenance for time scales approximating a human lifetime. It is therefore used in radioisotope thermoelectric generators such as those powering the Galileo and Cassini space probes. 

The programmer is typically networked with a process control computer. Both system and data alarms are also transmitted. Another pathway is provided to direct maintenance data to an analyzer management station. This allows for statistical... 

S. E. Beall and R. W. Jurgensen, Direct Maintenance Practices for the Homogeneous Reactor Test, Fourth Nyclear Engineering and Science Conference, iMarch 1958 (Paper 82) and USAEC Report CF-58-4-101, Oak Ridge National Laboratory, April 1958. 

From a maintenance standpoint, a top-maintenance pump appears to be advantageous. Direct-maintenance practices can be used to bolt and unbolt the main flange. The pump casing is a permanent part of the piping system. A top-maintenance pump being developed for the HRE-3 is illustrated in Fig. 8-4. 

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