Study on External Environmental Radiation of Nuclear Thermal-propulsion Reactor

Abstract

Nuclear thermalpropulsion reactor has attracted more and more attention because of its long service life, strong mobility and high concealment. However, in order to achieve higher mobility, nuclear thermalpropulsion reactor reduces its weight and does not have perfect radiation shielding measures, which will cause a lot of radiation to the external environment after operation. The radiation has an important impact on the application and development of nuclear thermal propulsion reactor. Therefore, it is necessary to study its radiation characteristics. This paper studies the radiation caused by the radioactive fission products produced after the operation of “Pluto” TORY ⅡC reactor published by the United States in the last century, ignoring the direct radiation of chain fission reaction, the radioactivity of component activation and the leakage of radioactive gas. Firstly in this paper, the burnup products of the reaction after 10 hours of full power operation were calculated by Monte Carlo method and the energy spectra of 106 radionuclides with high radioactivity were calculated, including Xray, gamma ray, bremsstrahlung and spontaneous fission gamma ray. Then the radiation field outside the reactor was calculated by pointkernel integral method. Because the pointkernel integral method has higher accuracy in calculating the simple structure, the reactor geometry was simplified in calculating the radiation field in this paper. The calculation results show that the reactor consumes 056% 235U after operation. The radioactivity increases gradually with time and finally reaches 1298×1021 Bq. Gamma radiation accounts for the main part. The maximum dose rate on the outer surface of TORY ⅡC shielding layer can reach 67185 Sv/h. Because the rear reflection layer is the thinnest and the side reflection layer is the thickest, the dose rate at the tail is the highest and the side dose rate is the lowest. At the same time, the calculated radiation field maintains a high dose rate in a large range. Therefore, this paper concludes that TORY ⅡC will produce a large amount of radiation after operation. Radiation shielding facilities must be installed to reduce the area of high radiation area, protect the environment and ensure personnel safety. At the same time, this paper calculates that the burnup products are regarded as uniform distribution and compares them with the previous accurate calculation results. It is found that there is little difference between the two calculation results in a far position. It can be inferred that when the distance is far enough, the two calculation results will be infinitely close. When the accuracy is not pursued, the burnup products can be regarded as uniform distribution to simplify the calculation and speed up the calculation time.

Keywords

• nuclear thermal-propulsion reactor
• fission product
• radioactive source term
• radiation