Initial risk assessment for a single stage to orbit nuclear thermal rocket

•The risks posed by the surface launch of a nuclear thermal rocket are considered.•Radiation exposure at the public viewing distance is insignificant.•Production of fission products and actinides during launch is limited.•The production of activated argon around the rocket may be a significant concern.

In order to consider the possibility of a nuclear thermal rocket (NTR) ground launch, it is necessary to evaluate the risks from such a launch. This includes analysis of the radiation dose rate around the rocket, determining the rate of activation of the materials near the launch, and considering the radionuclides present in the core after the launch. This paper evaluates the potential risk of the NTR ground launch for a range of payloads from 1 to 15 metric tons (MT) using three NTR reactor cores (40, 80, and 120 cm in length) designed in a previous study, based on data produced by MCNP5 and MCNPX models. At the same power level, the 40 cm core length reactor results in the lowest radiation dose rate of the three reactors. Radiation dose rates decrease to background levels 3.5 km from the launch site. After a 1-year decay time, all of the activated materials produced by an NTR launch would be classified as Class A low-level waste. The activation of air produces significant amounts of argon-41 and nitrogen-16 within 100 m of the launch. The derived air concentration (DAC) ratio of the activation products decays to less than unity within 2 days, with only argon-41 remaining. After 10 min of full power operation, the 120 cm core for a 15 MT payload contains 2.5 × 1013, 1.4 × 1012 and 1.5 × 1012 Bq of 131I, 137Cs, and 90Sr, respectively. The decay heat after shutdown increases with increasing reactor power with a maximum decay heat of 108 kW immediately after shutdown for the 15 MT payload.