Japan on Monday shut its second-to-last operating nuclear power station, further straining energy supplies in the reactor-reliant country.

Tokyo Electric Power Co. (TYO: 9501), which also operates the tsunami-crippled Fukushima Daiichi power plant, shut down the No.6 reactor at its Kashiwazaki-Kariwa plant in northern Japan for maintenance.

The country's last remaining operational reactor, Hokkaido Electric Power Co.'s (TYO: 9509) Tomari No.3, will be switched off for maintenance May 5, that company announced Monday.

The announcements add to fears that Japan's already-stretched electricity supplies won't be enough to handle demand in hot summer months.

As for the electricity supply and demand in the foreseeable future, we expect to maintain stable supply, Tepco President Toshio Nishizawa said Sunday in a company statement.

In addition, while we have been carefully reviewing this summer's electricity supply and demand, the shutdown of Unit 6 will result in a significant reduction in our electricity supply capacity. We ask that you continue to make a reasonable effort to save electricity, he added.

Japan has 54 reactors, 53 of which are now either undergoing maintenance, were wrecked during the March 2011 earthquake and tsunami or were closed down after an earlier earthquake.

Since last year's disaster at the Fukushima plant, ongoing public safety concerns and strict testing have kept all but one reactor offline.

To avoid blackouts, authorities have turned to fossil-fuel-powered electrical stations and asked Japanese consumers to conserve as much energy as possible.

But while many fear the prospect of a blackout-filled summer, others, such as Greenpeace Japan's executive director Junichi Sato, said the country could survive without rushing to restart its nuclear plants.

Japan is practically nuclear-free, and the impact on daily life is invisible, Sato was quoted by Reuters as saying.

With proper demand management, energy-efficiency measures and more than sufficient backup generation in place, there is no excuse for shortages in the coming months, and absolutely no need to rush restarts of nuclear plants.

It isn't clear when Japan might restart its network of mothballed reactors, which are now undergoing disaster stress tests by the country's nuclear regulator. Only after approval is given can Prime Minister Yoshihiko Noda approve any restarts, which may face further hurdles in the form of opposition by national and local protest groups.