It follows the leak of a draft paper from the EU's sustainable energy technology plan, which is being steered by the European Commission.
According to the document, leaked to the German media, member states should strengthen cooperation on researching, developing, financing and constructing innovative reactors.
The EU proposal to fund nuclear energy research is expected to be formally tabled by European energy union Commissioner Maroš Šefčovič on Wednesday. The report would then be presented to MEPs.
On Tuesday, Der Spiegel reported that the EU plans to advance the mini-reactors, with the hope that such technology should be in use no later than 2030.
The plans contradict policy in Germany, which currently intends to end the domestic use of nuclear power by 2022.
Following the Der Spiegel article, Greenpeace EU energy policy adviser Bram Claeys said: "The suggestion that public funds should be used to support nuclear research in Europe is a denial of reality: nuclear is a failed technology and represents a dangerous waste of time and money in the fight against climate change."
He went on, "Take the Hinkley project in the UK: despite the promise of massive subsidies for two new reactors at Hinkley Point, it is uncertain whether French-based energy companies EDF and Areva will actually be able to deliver, because of mounting costs and technology failures.
"The EU has also invested massive funds chasing the utopia of nuclear fusion technology, resulting in delays and spiralling costs."
Claeys added, "Europe does not need nuclear energy to back the development of renewables. Just in the past few weeks, Germany and Portugal were able to temporarily meet close to all their electricity demand with renewables. Europe should be investing in more renewables and stop wasting money on the nuclear delusion."
Further reaction came from Greens/EFA group co-Chair Rebecca Harms who said, "This paper again highlights the Commission's tendency to dress up the figures on nuclear power. The supporters of nuclear power want to do all within their means to secure massive financial support to keep the industry alive, despite the fact it is not able to stand on its own two feet. EU competition law and state aid rules should be set aside for nuclear power.
"Following early proposals to extend the lifetime of nuclear power for up to 60 years, this paper from the depths of the Commission's research directorate is proposing the crazy idea of promoting decentralised mini-nuclear reactors. EU nuclear proponents have already backed one wrong horse in pushing for European pressurised reactors since Chernobyl."
The German deputy added, "The cost explosions in the foreseen and underway projects in Olkiluoto, Flamaville and now Hinkley Point have underlined that EPR is unviable and have driven the French nuclear firm Areva to ruin.
"The Commission needs to finally give up on this failed and risky technology and instead put innovation and sustainability at the heart of the nascent European energy union."
She said, "Majorly boosting energy efficiency and renewable energies, supported by urgently-needed research in energy storage, is the only path for tackling climate change and combining this with economic development, creating jobs across Europe."
The Chernobyl disaster in 1986 was a turning point for nuclear power in Europe, with few new plants built since. While nuclear still plays a major role in the EU, aging facilities present financial and security risks.
Earlier this year, an official request was made by Germany's environment minister to the government of Belgium to shut down two nuclear reactors. Germany believes safety risks have not been properly addressed.