There are seven 27-kW Miniature Neutron Source Reactors (MNSR) in the world, which were all made by China. They are research reactors that use 1 kilogram of 90% (or greater) enriched uranium as the core, according to IAEA (see below).
The Russian Foreign Ministry warns that "the region [the Middle East and North Africa] could be at risk of “contamination by highly enriched uranium". The ministry spokesman urged IAEA to conduct risk assessment.
About Miniature Neutron Source Reactors, from IAEA (emphasis is mine):
The Chinese-built Miniature Neutron Source Reactors (MNSR, 27 kW) reactors (two in China, five abroad) are low-power, neutron source RRs [Research Reactors] used primarily for neutron activation analysis, education, and training. These reactors have cores consisting of about 1 kilogram of HEU [Highly Enriched Uranium], enriched to 90% or greater. The IAEA initiated a Coordinated Research Project (CRP) in June 2006 to assist in the conversion of these reactors to LEU [Low Enriched Uranium].
Institutions in China, Ghana, Iran, Nigeria, Pakistan, and Syria are participating as contract holders in this CRP. The U.S. (Argonne National Laboratory) is an agreement holder. All contract holders have acquired an understanding of the technical and other steps necessary as well as the documentation that will be required to satisfy regulatory requirements. Information acquired through the CRP will be published by the Agency in the form of a technical publication. This will serve as an addendum to the IAEA’s existing core conversion handbook.
Russia's warning, from CBS News (6/5/2013):
A Russian Foreign Ministry spokesman warned any military intervention in Syria would create a nuclear disaster.
“If a warhead, by design or by chance, were to hit the Miniature Neutron Source Reactor (MSNR) near Damascus, the consequences could be catastrophic,” Russian Foreign Ministry spokesman Aleksandr Lukashevich stated, according to Russia Today.
Lukashevich said if a military strike were launched without seeking approval from the United Nations Security Council that new suffering for other countries of the Middle East and North Africa would occur. He added that the region could be at risk of “contamination by highly enriched uranium and it would no longer be possible to account for nuclear material, its safety and control.”
He urged the United Nations International Atomic Energy Agency (IAEA) to complete a risk evaluation carrying out “an analysis of the risks linked to possible American strikes on the MNSR and other facilities in Syria.”
Rueters quoted an IAEA spokesperson stating the agency was aware of the statement, but is waiting for a formal request asking the agency to complete risk evaluation and that the group would consider the questions raised if a request is received.
(Full article at the link)
The atomic bomb that was detonated over Hiroshima on August 6, 1945, Little Boy, contained 65 kilograms of uranium enriched to 80%. Less than 1 kilogram underwent nuclear fission, and 0.6 gram was transformed into initially kinetic energy, then heat and light, according to Wiki.
A typical light-water reactor has the core with Low Enriched Uranium (LEU) enriched to 3 to 5%.