Three of the four candidates running to become Japan's next prime minister called Sunday for maintaining a nuclear fuel recycling program, as they geared up for a presidential election of the ruling Liberal Democratic Party.

In a Fuji TV program ahead of Wednesday's election, vaccination minister Taro Kono, the only contender who has pushed for phasing out nuclear power generation, said Japan should change course from fuel recycling "as soon as possible."

However, Seiko Noda, executive acting secretary general of the LDP, said fuel recycling is necessary to ensure a stable power supply.

The process involves recovering plutonium from spent nuclear fuel for recycling back into new fuel.

Fumio Kishida, a former foreign minister, and Sanae Takaichi, a former minister of internal affairs and communications, said power companies cannot run nuclear power plants if Japan stops the fuel recycling program.

Kono was negative about a call by Kishida and Takaichi for the government to introduce small modular reactors, saying they are not economically viable and he does not see any sites in Japan where they can be built.

Besides a call for introducing the reactors, Kishida and Takaichi have advocated restarting currently idled nuclear reactors in Japan and introducing nuclear fusion reactors as part of efforts to achieve the goal of net zero carbon emissions by 2050.

Most of Japan's nuclear reactors have been offline since the 2011 Fukushima nuclear disaster. Small modular reactors are said to be cheaper to produce and safer to run than conventional reactors, while nuclear fusion reactors do not emit high-level radioactive waste.

In the Fuji program, Kono and Takaichi said the government should consider acquiring nuclear-powered submarines.

But Kishida and Noda were cautious about Japan possessing such assets, with Noda citing Japan's three non-nuclear principles of not producing, possessing or allowing the introduction of nuclear weapons.

The LDP vote effectively decides the successor to outgoing Prime Minister Yoshihide Suga as the party currently controls the House of Representatives, the powerful lower chamber of parliament.