Speaking at the Asia Future Energy Forum in Singapore Tuesday, Nobuo Tanaka -- now a global associate for energy security and sustainability at the Institute of Energy Economics in Japan -- said he was "very skeptical about the feasibility of this plan," Eco-Business news reports.
Prior to the March 2011 Fukushima crisis, nuclear power generated 30 percent of Japan's electricity, making it the world's third-biggest nuclear generator. The government had aimed to increase that percentage to 50 by 2030.
Now only two of Japan's 50 nuclear plants are operating.
Tanaka said that a low-nuclear scenario for Japan would come at "a huge cost and loss of energy security."
As the world's largest buyer of liquefied natural gas, Japan has seen its LNG import double, to $72 billion, since Fukushima.
Under Japan's new energy strategy announced last month, the government said it wouldn't allow utilities to build new nuclear reactors and will limit the runs of existing reactors to 40 years.
But a day after the government endorsed the new strategy Japanese Industry Minister Yukio Edano said construction of new nuclear plants would be allowed if the projects had already been approved by the government.
The government's new strategy also calls for renewable energy to account for about 30 percent of Japan's future energy. That's an eightfold increase from 2010 levels.
"It is good to develop renewable energy for energy security but it's costly," Tanaka said.
In an interview with Recharge in Singapore, Tanaka said nuclear power is likely to account for 15-25 percent of Japan's future energy supply, while renewables, including hydropower, will reach 20 percent by the 2030s.
Japan is in a weak position because it has only regional grids and isn't connected to surrounding countries, Tanaka said, noting Germany's decision to phase out nuclear power is more easily achieved because it is connected to other grids in Europe.
Japan's nine utilities, each which have a regional monopoly, have resisted plans for an interconnecting grid because they would then be forced to compete, said Tanaka.
"The utilities are now trying to accommodate renewables into their system and there is a discussion by the government about what is necessary for market reform," Tanaka said.
"The government is pushing very hard and may try to help build more connections from north to south. But who is going to pay for that?"