The Nikkei index closed down 90.47 points at 9,558.30.
On Sunday it was announced that a meltdown had begun at Fukushima within hours of the devastating 11 March earthquake, earlier than first thought. The share price of plant operator Tokyo Electric Power (Tepco) plunged 7.28 per cent.
The arrest of International Monetary Fund chief Dominique Strauss-Kahn added to uncertainty in the Asian markets. There were concerns that his absence from talks in Brussels on Monday could affect the IMF rescue packages for Portugal and Greece being successfully negotiated.
“The nuclear power plant issue seemed to have momentarily calmed, but investors are once again concerned about the difficulties in achieving a safe shutdown,” Mizuho Securities equity strategist Tsuyoshi Segawa said.
Chubu Electric Power fell 4.51 per cent and Tohuku Electric Power dropped 5.35 per cent.
On Monday Moody’s rating agency downgraded Tepco’s senior secured debt one notch to Baa2. It also downgraded the company's long-term issuer rating two notches to Baa3.
This was the third downgrade of the plant since the March disaster.