Kim, S.; Park, K., and Yang, B.-M., 2017. Validating the applicability of MACCS2 on the assessment of radionuclide deposition over the ocean in Fukushima Daiichi nuclear power plant accident case. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 55–59. Coconut Creek (Florida), ISSN 0749-0208.On 11 March 2011, an enormous earthquake and tsunami occurred and caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan. Following the FDNPP accident, a significant amount of radionuclides were released into the environment. The radionuclides were released into the ocean by direct emission in liquid form or by atmospheric deposition onto the sea surface. According to the 2013 UNSCEAR report, atmospheric deposition of radionuclides significantly contributed to the contamination of the ocean, as did direct emission. The MELCOR Accident Consequence Code System 2 (MACCS2) is a code for estimating the off-site accident consequences of atmospheric radiological releases; the code utilizes the straight-line Gaussian plume model. In this study, to judge the code's applicability for estimating the radionuclide deposition over the sea surface in the Fukushima accident case, we conducted a comparative analysis of the MACCS2 results against previously published data. The long-range dispersion patterns from the MACCS2 calculation have a tendency simply to broaden from those of the short distance from the FDNPP. From the analysis detailed in this paper, we concluded that MACCS2 is applicable only for short-range dispersion (a few tens of kilometers) from an accident site, not for long-range dispersion as in the case of the Fukushima accident. The atmospheric deposition of radionuclides is a major cause of oceanic contamination; a large percentage of released radionuclides are deposited at long range from the accident site. Therefore, we suggest that any simulation code for atmospheric dispersion and deposition over the ocean should be based on another model, such as a Lagrangian or puff model, instead of on the Gaussian plume model, especially for long-range dispersion assessment.