[en] To evaluate the safety for sea disposal of low-level radioactive wastes, hydraulic pressure-resistance tests were carried out on multi-stage type packages of practical size under the condition simulating 6000m deep sea, i.e., hydraulic pressure 600 kg/cm² and pressure increasing rate 1 kg/cm²/sec. In the course of increasing pressure, ingress of sea water occurred through leak paths incorporated in advance so that the inside pressure was equalized with the outside pressure. As a result, no appreciable damages of the packages that would give rise to controversy in safety were observed. (auth.)