As extended by your invitation of March 24, it is a pleasure to have the opportunity of presenting a resume of our activities in application of radiation protection standards to our nuclear merchant ship program, Construction of the first nuclear powered merchant ship, the N.S. SAVANNAH, is the joint responsibility of the Maritime Administration and the Atomic Energy Commission. The vessel, now nearing completion at Camden, N. J., is expected to start-up and begin initial operation within the next few months. Existing radiation standards, and the considered decisions of responsible bodies, have been applied as the design basis for radiation protection in construction of the SAVANNAH. Design criteria for radiation protection was established to meet the requirements of Title 10, Code of Federal Regulations, Part 20, and the recommendations of the National Committee on Radiation Protection for extemal and internal exposure of occupational workers and the public in the vicinity of reactor operation. In the absence of an international agreement for the disposal of reactor wastes in the open ocean, such as the recommendations of the National Academy of Sciences, Report Number 658, the SAVANNAH has been designed to retain all liquid and solid wastes aboard ship for subsequent removal, processing and disposal by means of a special servicing barge and shore facilities. Details of our specific interests, in the current review of radiation criteria and standards, are given in the enclosed summary report prepared by our Office of Research and Development. SUMMARY REPORT APPLICATION OF RADIATION CRITERIA AND STANDARDS Office of Research and Development Maritime Administration Introduction The conceptual planning of the world's first nuclear merchant ship, the N. S. SAVANNAH, included the application of the 5 rem per year exposure standard for design purposes. In the engineering and construction phase of the project, this basic value has been applied in the design of the reactor system, shielding, waste handling, and all other supporting facilities and operational factors. This report briefly summarizes the radiation protection philoso phies applied in the SAVANNAH program, Personnel Protection Criteria Primary and secondary shielding for the reactor system will limit the maximum exposure of crew members to 5 rem per year, and 1/10 of this value for passengers and dock workers. Because the shielding effect of machinery, tanks, or contents may be variable, these materials and components have not been included in shielding calculations. However, certain practical assumptions are used to determine "design values", such as; average occupancy for an area, average reactor power level, accumulated fission, corrosion, and activation products based on predicted operation of the reactor system. The total amount of primary and secondary shielding materials, required to meet these exposure limits, consists of 2,040 long tons of lead, concrete, water and polyethylene, including weight of the containment shell. To determine the effectiveness of shield design and construction, shield survey for gamma-neutron attenuation will be independently conducted during the test program. Dose rates in normally occupied crew areas during routine operation are actually expected to be 1/10 of the "crew area" design dose of 5 rem per year. Average dose rates in passenger areas are expected to be 3/10 of the design value of 0.5 rem per year. The major portion of exposure to the crew is expected during maintenance operations. This agrees substantially with the experience of other reactor facilities. Radiation surveillance and control of various areas through the use of a fixed radiation monitoring system, portable survey instruments, and personnel dosimetry devices will be an integral part of the shipboard health physics program for personnel protection. Additionally, protective clothing and respiratory equipment will further insure personnel protection under all conceivable working conditions. Surrounding the reactor system and associated primary system is a containment vessel weighing 223 long tons. The containment vessel on the SAVANNAH was designed for an internal overpressure of 173 pounds per square inch, which corresponds to the instantaneous flashing to steam of the coolant in the entire primary system. Radioactive Waste Management By design, all solid and liquid wastes will be retained aboard the SAVANNAH until they are transferred to a servicing barge for proper processing and disposal. This servicing facility will be capable of reducing the activity content of the liquid wastes to an acceptable concentration for overboard discharge by repeated circulation of the liquid stream through ion exchange 58454 0-6049 beds. All solid wastes, including spent ion exchange resins, will be packaged for subsequent land or ocean disposal. Gaseous wastes, principally from the primary coolant system, will be retained within the containment vessel when the ship is operating in confined waters or under adverse weather conditions. Subsequently, the contaiment vessel will be purged at sea under favorable weather conditions. Discharge of airborne radioactivity will be controlled by filtration and monitoring instrumentation. The principal volatile activities, due to the presence of fission products in the primary coolant, are radioactive xenon and krypton. This activity is expected to be discharged at an average concentration from the stack at 1/10 of the present tolerance concentration for unrestricted areas. Monitoring instrumentation in the ventilation exhaust system will detect and record the presence of fission product activity. Filter absorption units for radioiodine and high efficiency particulate filters will remove essentially all airborne activity. In the presence of fission gases, charcoal absorption units may be put into service, thus providing additional protection for personnel and the environment. Supporting Research Several studies are underway to determine dispersion characteristics in estuaries and in the open ocean, with the expectation that this work will lead to establishment of permissible discharge practices for low level radioactive wastes to the ocean, without hazard or adverse effects upon marine life or man. A broad environmental program has been undertaken with the aim of demonstrating that no deleterious release has taken place on land or at sea. The Coast and Geodetic Survey, Weather Bureau and the Corps of Engineers have undertaken, with the Maritime Administration, an integrated environmental analysis as an aid in voyage programming, harbor routing, and berth selection procedures. Effect of Change in Radiation Exposure Standards In providing conservative radiation protection on the SAVANNAH, the weight and capital costs of shielding, containment, and instrumentation have, in effect, penalized the ship severely by "losing" this increment of cargo carrying potential. Further lowering of the permissible levels of radiation and radioactivity would pose additional problems by requiring heavier shielding on ships, by restricting the performance of maintenance on reactor plants, by increasing the difficulty of controlling trace quantities of radioactivity in air and liquid waste and by complicating the problem of measuring and monitoring of radiation and radioactivity. Any additional shielding sufficient to effect a significant decrease in radiation levels throughout the ship would result in substantial weight increases, and a concomitant loss of potential cargo revenue. Increased requirements for containment around the reactor system will add to the cost of the vessel through the increased degree of leaktightness, resistance to missile penetration and increased shielding. Since the current trend in design for cargo ships, and including the SAVANNAH, is for a large cubic volume per deadweight ton, ship revenue is thereby limited to the weight of cargo that can be transported. Thus, any reduction in plant weight yields increased cargo deadweight capacity. The design of economically competitive nuclear merchant ships of the future must necessarily be predicated on larger cargo tonnage capacity per plant deadweight and capital cost. |