Safety Analysis of Gas Pressure in a Subcritical Assembly for Molybdenum-99 Production System

Abstract

The Subcritical Assembly for Molybdenum-99 Production system is a subcritical system fueled by uranium nitrate, which utilizes the Kartini reactor’s beam port as the neutron source. One of the problems in using uranium nitrate fuel involves the radiolysis reactions and gaseous fission products that form in the cavity above the Subcritical Assembly for Molybdenum-99 Production fuel tube, resulting in a buildup of pressure. To address this issue, this study examined the total accumulated gas pressure in each Subcritical Assembly for Molybdenum-99 Production tube contributed by gaseous fission products and water radiolysis by neutron and gamma radiation during 7 days of operation. Examinations were performed by combining the Subcritical Assembly for Molybdenum-99 Production and Kartini reactor geometry to obtain the burnup power using a tally within the Monte Carlo N-Particle eXtended code. Subcritical Assembly for Molybdenum-99 Production system was then simulated for 7 days with the obtained burnup power with the same code. Outputs from the code were then calculated and analyzed to determine the total accumulated pressure on each fuel tube from each of the pressure contributors. This research showed that the maximum accumulated pressures were 0.45 atm and 0.5 atm for Kartini reactor’s power of 100 kW and 110 kW, respectively. These pressures are lower than the atmospheric pressure; hence, the current Subcritical Assembly for Molybdenum-99 Production system can be operated safely for 7 days.