[en] When a gamma-ray spectrometer is used to measure a radioactive sample, the radioactivity distribution in samples may affect the detection efficiency. In order to obtain more accurate content of a radioactive nuclide, the influence of the radioactivity distribution in sample should be estimated. The effect of inhomogeneous radioactivity distribution in I-129 transmutation targets on the detection efficiency was examined employing the MCNP5 code. The ratios of the efficiencies in several extreme situations and various assumed distribution to the efficiency in ideal homogenous distribution were calculated at different sample-detector distances. The calculation results shows that the radioactivity inhomogeneity in samples could not be neglected when the abundance of I-129 was measured by a low energy gamma ray spectrometer, even at a large detection distance, and that the effect of axial inhomogeneity on detection efficiency is much more significant than that of radial inhomogeneity. (authors)

[en] Highlights: • A new type of space nuclear power called NBDEx is investigated. • NBDEx with ²⁵²Cf has better performance than RTG with similar structure. • Its thermal power gets great improvement with increment of fuel enrichment. • The service life of NBDEx is about 2.96 year. • The launch abortion accident analysis fully demonstrates the advantage of NBDEx. - Abstract: Based on the theory of ADS (Accelerator Driven Subcritical reactor), a new type of nuclear battery was investigated, which was composed of a subcritical fission module and an isotope neutron source, called NBDEx (Nuclear Battery Driven by External neutron source). According to the structure of GPHS-RTG (General Purpose Heat Source Radioisotope Thermoelectric Generator), the fuel cell model and fuel assembly model of NBDEx were set up, and then their performances were analyzed with MCNP code. From these results, it was found that the power and power density of NBDEx were almost six times higher than the RTG’s. For fully demonstrating the advantage of NBDEx, the analysis of its impact factors was performed with MCNP code, and its lifetime was also calculated using the Origen code. These results verified that NBDEx was more suitable for the space missions than RTG

[en] To meet the requirement of future missions of deep space exploration, a new nuclear battery system, nuclear battery driven by external neutron source, was introduced in this paper. The ratio of power over weight and power output of the nuclear battery calculated with MCNP in a simple model were 4.45 W/g and 9.88 kW, respectively. Compared with radioactive thermal-electric generator (RTG), this nuclear battery could supply 8 times ratio-power and 3.54 times power output than GPHS-RTG, respectively. Also, the ratio-power and power output of the nuclear battery were calculated in the detail model of GPHS-RTG, and each module could generate 4.3293 W/g of ratio-power and 698.253 W of power output, which are 9.55 times and 10.2 times more than GPHS-RTG, respectively. For a multi-module system, this nuclear battery could generate 6.83 W/g of ratio-power and 22.04 kW of power supply. The advantage of the nuclear battery driven by external neutron source is obvious. (authors)

[en] High temperature nuclear reactor in the field of MHD power generation and nuclear rockets have good application prospects. High temperature reactor has a pile of high core temperature, complex structures, whose physical performance parameters are rather difficult to compute. This paper studies the high temperature nuclear reactor prompt neutron generation time calculation method, introduces the calculation principle of a variety of methods and a new high temperature nuclear reactor's calculation results. The results show that for the same reactor model, calculation results of several methods are in good agreement and the calculated results are credible. (authors)

[en] This paper describes the design and analysis of advanced space nuclear reactor (ASNR) whose design combines the advantages of radioisotope thermoelectric generator (RTG) and space nuclear reactor (SNR). As opposed to current SNRs designs, ASNR is a subcritical system driven by "2"3"2U–Be neutron source to generate thermal power continuously. Most movable control systems in the SNR design are removed. The detailed neutronic calculations by MCNPX (Monte Carlo N-Particle eXtended), including k_e_f_f, flux, burn-up, loss-ratio of neutron source and immersion reactivity, show that ASNR has higher criticality safety and more compact structure to bear the risk of immersion accident compared with the past SNRs, and the new system can provide more thermal power than RTG. Furthermore, the neutron source efficiency is optimized to improve the utilization of "2"3"2U–Be neutron source with the improvement of criticality safety. Compared with the past designs of space nuclear power, ASNR could provide enough thermal power and avoid the occurrence of serious immersion accident in the case of total control system failure. ASNR has potential for future deep space missions. (author)

[en] The feasibility of transmutation of long-lived fission product (LLFP) ⁹⁹Tc and 1291 in pressurized water reactor (PWR), based on Daya Bay PWR, was analyzed. The calculation results show that the maximum transmutation rate is 15.69% for ⁹⁹Te during one refueling cycle of 18 months, and 9.18% for ¹²⁹I. By analyzing the safety related items of different reactor cores. it is shown that, after introducing LLFPs into PWR, the k_eff gets lower and the range of variation with burnup becomes small, and obvious change of the radial neutron flux density of reactor core is not found, but the radial power peaking factor is declined. And also, there is no safety problems for reactivity coefficient and control after considering fuel temperature coefficient, moderator temperature coefficient, differential soluble boron worth and control rod worth. On the contrary, the above parameters get better. In summary, transmutation of ⁹⁹Te and ¹²⁹I in PWR is feasible. (authors)

[en] SNR (Space Nuclear Reactor) with 1 kW level electric power has great potential in the application of deep space mission. Inspired by the theory of ADS (Accelerator Driven Subcritical system) and based on the design of SAFE400, ASNR (Advanced Space Nuclear Reactor) is proposed, which is driven by "2"3"2U-Be neutron source. Through calculation by MCNPX, ASNR can supply 5 kW electric power with 1.13 pin peak factor for 10 years, and keeps -4.29$ reactivity even in the most serious immersion accident. In order to optimize its volume and mass, the performance of ASNR is analyzed with different reflector thickness from 4.3 cm to 12.3 cm. When the reflector is 8.3 cm, the volume and mass of ASNR are optimal under condition of meeting the requirement of -1$ reactivity at least in the most serious immersion accident. Compared with the primary design, its neutron source efficiency φ* increases by 3.8%, and the total mass decreases by 9.86%. For improving the critical safety of ASNR, different contents of Gd_2O_3 are doped into the reflector. The calculations show when the content of Gd_2O_3 is up to 6.0wt%, the reactivity of ASNR is -2.35$ for the wet-sand immersion accident with all the 6 control drums failure, and its critical safety improves 7.46$. But during the same accident, the reactivity of SAFE400 is as high as 11.4$. Therefore, ASNR has simpler structure and safer design, and it is suitable for future deep space missions. (author)