"This accident has become a concern not only to Japan but to the whole world," Obuchi said after spending 25 minutes in the Tokaimura nuclear complex. "I wanted to come to the site as soon as I could."
Obuchi visited Tokaimura, 70 miles northeast of Tokyo, as the investigation into the accident intensified with police raids on the uranium-processing plant and the Tokyo headquarters of the plant's operator, JCO Co.
Authorities are searching for evidence of wrongdoing behind the Sept. 30 accident, which sent three workers to the hospital, forced the evacuation of surrounding homes and kept hundreds of thousands locked in their houses for fear of contamination.
Japanese media reported that the Science and Technology Agency was considering revoking JCO's operating license after confirming that the company had ignored government-approved processing procedures. Agency officials, however, said no decision would be taken until the investigation was finished.
Police said late Wednesday that about 260 items were seized in the raid on JCO's Tokyo office and about 700 items were seized from the Tokaimura plant. Among the items were reports on procedures at the plant and other documents. Kyodo News service said they included the illegal manual workers had used at the plant for years to shorten their work, but police would not confirm that.
Obuchi, who also planned to visit with one of the families evacuated in the aftermath of last week's accident, acknowledged that the government response was lacking.
"As this was an accident that we had not imagined, our system was inadequate," he said.
He also said he hoped to review the current laws related to nuclear accidents and, if necessary, to present changes to those laws during the next parliamentary session.
Obuchi vowed to change the system of overseeing the country's nuclear facilities so that "the nation can once again feel secure."
Outrage at the accident has focused on allegations of systematic disregard for security procedures at the plant, where shortcuts taken by workers handling uranium led to an uncontrolled nuclear reaction and release of radiation.
JCO has reportedly acknowledged habitual corner-cutting. More evidence of mismanagement emerged Wednesday, when newspapers reported that monitoring cameras placed around the plant to keep tabs on employees were always turned off.
Some residents in Tokaimura were hoping the prime minister's visit would lead to a more rigorous investigation.
"I think it's good if it means the government is taking this problem seriously," local pharmacist Hiroko Gocho said of Obuchi's visit. "But just his coming won't solv anything."
Life in the town surrounding the plant had apparently returned to normal. A jogger ran around the perimeter of the plant Wednesday, and parents strolled with small children.
Accounts of the accident emerging from official statements and media reports describe a series of missteps, irregularities and oversights that led to disaster.
Workers at the plant reportedly put a large amount of a powdered uranium compound in liquid nitric acid in stainless steel buckets, instead of using the proper equipment, and did the processing by hand, police say.
The workers involved also had little knowledge of the chemical substances they were handling and of what quantities would set off a self-sustained nuclear chain reaction, police sources said.
The accident contaminated 49 people, including local residents. Two of the three JCO workers involved in the process were in critical condition, awaiting transplants of vital blood-stem cells to replenish their bodies' ability to produce white blood cells.
The transplant on the most severely injured of the workers began Wednesday with the removal of blood-stem cells from his brother. Hisahi Ouchi remained in critical condition today. The second worker was awaiting a similar transplant.
Sumitomo Metal Mining Co., which owns JCO, promised to pay damages for the accident.
The accident has badly damaged the already troubled reputation of Japan's nuclear plants, and could complicate plans to expand Japan's reliance on atomic energy. Nuclear facilities now produce about one-third of Japan's electricity needs.