Fuel coolant interaction (FCI) phenomena when molten corium falls into water pool on containment floor during a sever accident of LWR were experimentally investigated in COTELS Test A. In the tests, about 60kg of mixture of UO_2,Zr ZrO_2 and SS was poured into water pool. In most tests conducted, measured pressure in the test vessel reached the first peak value in about 0.5 s, then it gradually approached the final quasi-steady state pressure within 10 s. No violent steam explosion was observed in any tests. Most of poured corium was broken up and the first peak pressure was well correlated by the corium particle size. The observed final quasi-state pressure was larger than that evaluated by the initial stored energy in corium due to non-condensible gas generation by oxidation of metallic components in the corium. The non-dimensional first peak pressure was well correlated by one non-dimensional parameter not only for COTELS data but also for FARO data.