* Martek Biosciences of Columbia said an explosion last month at one of its plants in Kentucky was caused by the release of a flammable liquid into the local sewer system. The explosion, at a wastewater-treatment site used by the company's Winchester, Ky., plant, destroyed one building and released raw sewage into a waterway. There were no injuries, and the company said the explosion will not affect operations at the company or have a "material" negative financial effect.

* Primus Telecommunications Group of McLean said it bought back nearly $12 million in debt. Approximately $10.2 million worth of its high-yield debt was retired in exchange for about $6.3 million in cash, excluding some additional interest accrued. The purchased debt had annual interest payments of about $1.1 million, and the deal should save the company $6.1 million in future interest payments. Primus also said it had made a final payment of $1.5 million on an $18 million loan from an equipment vendor. The company will keep reducing its vendor debt over the next few years, said K. Paul Singh, chairman and chief executive. Since January 2001, Primus has reduced its debt from $1.4 billion to about $550 million, said Neil L. Hazard, chief operating and financial officer.

* Orbital Sciences of Dulles said it will work with Northrop Grumman Integrated Systems to refine requirements for NASA's proposed Orbital Space Plane. The firms won separate 16-month contracts for the studies totaling about $45 million from NASA's Marshall Space Flight Center. Orbital Sciences makes space systems.

* NCI Information Systems of McLean said its vice president of business development, Thomas T. Reinhardt, is leaving the information technology firm to join the Department of Homeland Security. The former Justice Department and White House staffer will serve as chief of staff to the department's undersecretary of management.

Compiled from reports by Washington Post staff writers, washingtonpost.com and Dow Jones News Service