Republic of the Marshall Islands Supplemental Nuclear Compensation Act of 2008

Republic of the Marshall Islands Supplemental Nuclear Compensation Act of 2008 - (Sec. 2) Amends the Compact of Free Association Amendments Act of 2003 to direct the Secretary of Energy, as a part of the Marshall Islands program, to periodically conduct: (1) a visual study of the concrete exterior of the Cactus Crater containment structure on Runit Island; and (2) a radiochemical analysis of the groundwater surrounding, and in, the Cactus Crater containment structure on Runit Island. Makes specified funds available to conduct such radiochemical groundwater analysis.

Directs the Secretary to report to the appropriate congressional committees whether the surveys and analyses indicate any significant change in the health risks to the people of Enewetak from the contaminants within the Cactus Crater containment structure.

(Sec. 3) Amends the Energy Employees Occupational Illness Compensation Program Act of 2000 to include a citizen or national of the Republic of the Marshall Islands or the Federated States of Micronesia within the definitions of "covered employee," "atomic weapons employee," and "Department of Energy contractor employee."

Provides for an offset of benefits under such Act for an individual who has received benefits under such Act and under the Compact of Free Association between the United States and the Republic of the Marshall Islands for the same illness (other than medical benefits and benefits for vocational rehabilitation that the individual received by reason of the illness).

(Sec. 4) Amends the Compact of Free Association Amendments Act of 2003 to direct the Secretary of the Interior to provide to the Republic of the Marshall Islands an annual supplemental health care grant to: (1) provide enhanced primary health care, with an emphasis on providing regular screenings for radiogenic illnesses by upgrading existing services or by providing quarterly medical field team visits in Enewetak, Bikini, Rongelap, Utrik, Ailuk, Mejit, Likiep, Wotho, Wotje, and Ujelang Atolls, which were affected by the U.S. nuclear testing program; (2) enhance the capabilities of the Marshall Islands to provide secondary treatment for radiogenic illness; and (3) operate a whole-body counting facility on Utrik Atoll.

Appropriates FY2009-FY2023 funds.