Contents lists available at ScienceDirect Progress in Nuclear Energy journal homepage: www.elsevier.com/locate/pnucene Conceptual core design study for Indonesian Space Reactor (ISR) Muhammad Farid Khandaq, Andang Widi Harto, Alexander Agung * Department of Nuclear Engineering and Engineering Physics, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia ARTICLE INFO Keywords: Indonesian Space Reactor (ISR) Fast neutron spectrum Core design Uranium nitrate Control drum worth ABSTRACT Space exploration is very important for the future of the earth and human beings as it may eliminate earth overpopulation and overcome diminishing of earth resources. One of the obstacles of the space exploration mission is the energy source for the spacecraft. One alternative is using a nuclear reactor as an energy source in spacecraft. A conceptual design of Indonesian Space Reactor (ISR) has been carried out to explore such a pos- sibility. ISR is a liquid metal Na-78 K cooled space reactor with a fast neutron spectrum. It is designed to provide at least 500 kW th power for operating time more than 10 years at full power. The reactor uses 55% high-enriched uranium nitrate as fuel. The ISR hexagonal core is comprised of 61 fuel pins and is designed in the form of a hollow cylinder with an individual cooling channel in each fuel pin. The reactor is also equipped with spectral shift absorbers (SSA) made of Re and Mo-30Re alloy to control the reactivity. Neutronic calculations have been performed to obtain optimum design parameters without compromising safety requirements. These design parameters include variation in uranium enrichment, reactor dimension, reflector thickness and control drum (absorber) design and dimension. The accepted reactor design has an excess reactivity of 4023 ± 9 pcm and shutdown margin of 4852 ± 9 pcm and the reactor is estimated to have a lifetime of 28 years. The temperature and void reactivity coefficients are all negative, implying inherent safety. Several accident scenarios were also considered in this work, both during launch failure and normal operation. It is found that to keep the reactor subcritical for a submerged reactor following a launch failure, the reflector segment should be discarded. Meanwhile, some portions of fuel pins should be removed from the core during operational accidents. 1. Introduction The development of space science is essential for the future. NASA plans to return 5 to 10 astronauts to the moon in 2020 (Hatton and El- Genk, 2009). Space exploration is not limited to experimental missions, where mineral mining is an interesting issue to do. This activity cer- tainly requires large electrical or thermal energy. One of the obstacles of the space exploration mission is the energy source for spacecraft needs. Space reactors have unique characteristics such as high unit mass power, low cost, and strong environment adaptability; so that the space reactor is crucial for aerospace industry (Yuan et al., 2016). The use of space reactors as a source of energy in space can be justified when there is no choice of other energy sources (El-Genk, 2009). Such usage is in- line with the United Nation principle 3 to reduce the amount of radioactive material in space, the use of nuclear energy in space is only permitted if there are no other alternative energy sources for space missions for acceptable reasons” (United Nations General Assembly, 1992). In the mission of deep space exploration that keeps away from the sun, the intensity of sunlight decreases, so that solar panels cannot be used as energy generators. This condition makes no alternative energy generation other than space reactors. In general, there are no big dif- ferences between a space reactor and a typical reactor. It only needs some design adjustments such as mass, dimensions, power, and the operating time of the reactor. By considering the long space reactor operation, compactness, low mass and independent on sunlight, the space reactor becomes very promising to be used as a power plant in space missions, especially for spacecraft on the deep space exploration mission. BUK, TOPAZ, and SNAP-10 were space reactors that used Highly Enriched Uranium (HEU) as fuel, and used 90%–96% enriched U-235 (El-Genk, 2009). In its development, some space reactors such as HOMER, SAIR, S4, and KRUSTY also used HEU as fuel (El-Genk and Tournier, 2004; King and El-Genk, 2006; Mencarini and King, 2018; Poston, 2000). The use of HEU as fuel aims to eliminate the use of moderators so that the reactor is compact and lightweight. The absence of the moderator made the reactor have a fast spectrum of neutrons. It is not an absolute requirement that space reactors cannot use moderators, like SNAP-10 which used uranium-zirconium hydride https://doi.org/10.1016/j.pnucene.2019.103109 Received 10 December 2018; Received in revised form 21 July 2019; Accepted 22 July 2019 * Corresponding author. E-mail address: a_agung@ugm.ac.id (A. Agung). Progress in Nuclear Energy 118 (2020) 103109 0149-1970/ © 2019 Elsevier Ltd. All rights reserved. T