Alekseev P.A., Ekhlakov I.A., Ovcharenko M.K., Pyshko A.P.
A.I. Leypunsky Institute for Physics and Power, Obninsk, Russia
One of the problems related to designing space nuclear power systems consists in ensuring safe reactor start-up in space. The process of the reactor start-up becomes more complicated because it is impossible to keep track of the reactor power variations at its initial stage with the conventional means of control. To solve this problem, an external neutron source is used; it provides the controllable level of reactor power in the course of its start-up.
The use of external neutron source is related to certain problems as well. Firstly, additional structural elements, the source holder, feedthroughs to the core and other components are required, thus increasing the mass and reducing the reliability of the nuclear power system (SNPS). Secondly, before being placed in the launcher the SNPS is subjected to numerous prior operations. The personnel, who perform this work in the immediate vicinity to a powerful neutron source (~106 n/s), will be subject to radiation exposure.
Earlier in publication it was shown that cosmic ray protons cause the ingress of 105-107 n/s to the core of the upgraded thermionic reactor-converter (TRC) of the “TOPAZ” type, i.e. the amount of neutrons capable of inducing the number of fission events sufficient to ensure the controllable power level.
Getting onto the SNPS surface, streams of cosmic ray protons significantly depend on the height and geographic coordinates of the spacecraft position relative to the Earth. Due to non-uniformity of proton streams, we should expect non-uniformity of neutron flux that will be entering the reactor core in the course of spacecraft orbital flight. In this case the reactor start-up should be performed in the time periods when the spacecraft is going through the areas with the highest values of neutron fluxes.
This paper considers the possibility to start-up the modified thermionic reactor-converter without any special neutron source but with consideration of the effect of cosmic ray protons and uncertainty of their streams in the course of changing the spacecraft position relative to the Earth.
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