Prerequisite requirements for higher graphite temperature limits and/or nitrogen atmosphere at all reactors

摘要

The graphite temperature limits specified in the process standards-are being closely approached or have limited power levels at B, D, DR, and reactors. An increase of approximately 50--100 C in graphite temperature limits at these reactors would permit year-around operation on bulk outlet temperature limits. There has been considerable recent interest in extending to all reactors the use of nitrogen as a reactor gas constituent. With present graphite temperature limits, significant benefit from nitrogen usage will not be obtained during the winter months at reactors which are graphite temperature limited with approximately 100 per cent helium. However, during the summer months when bulk outlet temperature limitations result in graphite temperatures considerably below the maximum permissible graphite temperatures, the substitution of nitrogen for carbon dioxide could be of value. Under these circumstances, both a reduction in helium usage and a reduction in enrichment costs could result. With an increase in permissible graphite temperature limits, year-around benefit from reduced helium usage and reduced enrichment costs would be possible. To meet the Pu-240 specification with higher graphite temperatures however, would require a reduction in current goal discharge exposures with resulting increased fuel and burnout costs. Additionally, the incentives for higher graphite temperatures are very sensitive to both the mode of operation and to the assumed product worth. An economic study by the Process Analysis Unit discussing in detail the factors influencing the incentive for higher graphite temperature will be published in the near future. At a meeting among the staff several weeks ago, the prerequisite requirements for permitting higher graphite temperatures and/or nitrogen usage at all reactors were discussed. It is the purpose of this letter to briefly outline the prerequisite steps considered necessary to achieve these goals.