they were suspended for climatic reasons. Finally, on 25 February after completion of the path all operations were finished. On 20 April, a day on which sea conditions were quiet and moderate, the wrecked bow section was lifted from the water, transferred to the Seto Inland Sea and broken up after conducting an investigation for the causes of the incident.
? Oil spill control near nuclear power plants As many as one-third of the nuclear power plants in Japan (compared by output) are located concentrically in areas embracing Wakasa Bay, so the imminent task was to prevent spilled oil from seeping into the plants. Therefore;
(a) Each plant was instructed to strengthen defences and remove oil around 8 January, when oil drifting in the sea began flowing into Wakasa Bay.
(b) Oil booms near cooling water intakes were subjected to stricter quality requirements, the number of lines was multiplied, and in the meantime, cleaning up oil by local vessels, etc., was started. Then, measures were taken by monitoring drifting oil at night, precisely observing drifting conditions using chartered aircraft and collecting oil slicks inside the oil booms on the shore. These actions fortunately resulted in maintaining power supplies without lowering output in all nuclear power plants. [Fig. 7]
? Resources mobilized to collect oil and oil quantities collected An interim estimate made in early March, when collecting operations in the sea were almost completed is shown below. Vessels and Boats (Maritime Safety Agency, Self-Defense Force) about 4,700 vessels Quantity of oil/water mixtures collected in the sea (related to the nation) about 5,700 kL
(3) Sunken tanker and monitoring spilled oil
? It was not until 12 January, 10 days after the casualty occurred, that oil was confirmed to be drifting near waters where the tanker had sunk. Therefore, in response to the oil spill, oil dispersants were sprayed on one hand; and oil-contaminated waters were agitated by the stern vortex of vessels on the other hand; and the monitoring system in the sea area was tightened.
? During the period from late January to late February, the detailed condition of the tanker, which sank in waters roughly 2,500 m deep, was detected by an unmanned underwater robot of Japan Marine Science & Technology Center, followed by detection of the tanker's position. In addition, in the middle of February, an investigation was conducted by Dr.H.Rye (Norway) to determine the rising of oil from the wreck in cooperation with Ship and Ocean Foundation.
? At the end of March, the Committee of the Ministry of Transport assessed the sunken tanker and leakage of remaining oil as shown below, on the basis of observations of spill conditions by patrol vessels and aircraft and the investigation described above ?.
(a) Remaining quantity of oil is 3,700〜9,900 kL
(b) Quantity of oil expected to leak per day is 3〜14 kL, which is not likely to go ashore.
(c) It cannot be expected that the hull of the tanker would suddenly break up causing a massive oil spill, although oil leaks would continue for some time.
? Although the oil spill rate varies day by day, oil from the spring-head of the remaining hull lying on the sea bottom continued to float on the sea surface in the shape of a circle with a diameter of approximately 5 m within a circular water area with a diameter of approximately 100 m even in early June, 5 months after the incident. The oil then drifts on the sea, dividing into several long slicks measuring 100〜200 m wide and several km long, disappearing at the end of oil slicks due to wind and waves. [Fig. 8]
2. The Japan Sea and Marine Pollution
(1) Firstly, the number of marine pollution incidents caused by vessels in the surrounding waters of Japan has declined sharply in recent years, as shown in Fig. 9. This is considered to be ascribable to strict
