Microreactors can be used to provide electrical power up to 10 MWe for emergency situations, remote areas, or military applications. Combined cycles comprised of an air Brayton topping cycle and an Organic Rankine bottoming cycle were evaluated in HYSYS using different working fluids in the bottoming cycle and in different ambient environments. The results indicate that a bottoming ORC can increase the thermal efficiency of the air Brayton cycle from 35.8 % up to 40.2 %. Exergy analysis was also performed on the combined cycle along with a simple validation of HYSYS on the bottoming cycle. The exergy analysis shows that of available work, most is lost at the reactor or turned into work at the topping cycle. A rudimentary capital cost estimate shows that the addition of a bottoming cycle is not prohibitively expensive.