BILLERICA, MASS. — KBS Real Estate Investment Trust has acquired Rivertech Park in Billerica for $45.2 million. The 285,772-square-foot park, which is located along the Route 3 corridor, contains two twin office buildings that are 100 percent leased. Nuvera Fuel Cells leases Rivertech I, a 110,684-square-foot office facility, and Entegris leases Rivertech II, a 175,088-square-foot building. The seller was undisclosed.