Various kinds of radioactivity are produced via spallation reactions by injecting high energy intense proton beam (3 GeV, 1 MW) on a mercury target in the Materials and Life science experimental Facility of J-PARC. Radioactivity handling strategy was designed based on estimations by using particle transport calculation codes NMTC/JAM, MCNP/4C and an induced radioactivity calculation code DCHAIN-SP 2001. The radiation around a mercury circulation system was estimated to be reduced by draining

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... cury into a shielded tank. The volatile radioactivity produced in mercury was designed to be processed by an off-gas process system. Practical experiences through facility operations were quite different from these strategies. The radiation around the mercury circulation system increased after draining mercury. Mercury radioactivity has not been detected so far in a mercury absorber of the off-gas process system while xenon-127 trapped in the absorber increased radiation dose around the absorber. The amount of tritium release was much higher at a target chamber replacement than that expected from the preceding flushing process. This paper describes how the unexpected issues have been tackled and what was understood for the differences.