The signatories say the letter was prompted by the arrest of former Atomic Energy Minister Yevgenii Adamov on 4 May.
Adamov was seized in Switzerland on an extradition warrant from the United States, which accuses him of embezzling funds earmarked for the improvement of Russian nuclear security.
Russian prosecutors have charged Adamov with fraud and abuse of power and are seeking his extradition to Russia.
Aleksei Yablokov, the director of the Moscow-based Center for Russian Environmental Policy, is one of the most prominent signatories of the open letter.
"The nuclear field is in a bad way," Yablokov said. "Adamov is not the only one to have mismanaged funds; there are thefts and the general working discipline in the field is below any acceptable level, and this worries us. Taking advantage of the fact that Adamov has been arrested and attention has been drawn to the situation of the industry, we are declaring that not only Adamov, but the industry as a whole is in a state of crisis."
He said the government's plan to build up to 50 more nuclear reactors in Russia is irresponsible and, considering current conditions, could easily lead to a nuclear disaster like the one in Chornobyl.
"We are saying that in the present conditions of the [nuclear] field -- when discipline is poor, thefts take place, security measures related to nuclear radiation are not sufficient -- it is madness to decide like the government did two years ago to build 50 more nuclear reactors in the long term," Yablokov said. "This decision by the government seems irresponsible to us. If it is implemented, other Chornobyls are unavoidable."
The International Atomic Energy Agency's (IAEA) press service could not be reached for comment yesterday or today.
Russia currently operates 31 nuclear reactors, but environmental rights groups say nuclear plants are poorly run and some of them are in dire need of repair.
They have repeatedly accused the Mayak plant, near the city of Chelyabinsk in the Urals, of releasing massive quantities of radioactive materials in the atmosphere and the water.
Incidences of cancer and birth defects in the Chelyabinsk region have risen more than 20 percent over the past three decade, and half the men and women are estimated to be sterile.
Environmentalists also blame the authorities for extending the working life of aging nuclear plants without carrying out proper environmental-impact studies.
The open letter comes just days after a U.S. report said that, despite recent progress, security at Russian nuclear plants remains inadequate. It cited incidents in which guards left security doors open and patrolled facilities unarmed.
Yablokov also lamented the waste of energy in Russia.
"There are vast possibilities to save energy," he said. "Between 30 and 40 percent of the electric power we produce can be saved. It is used badly, squandered. To be produced, one item here requires three or four times more energy than in Europe, and five to six times more than in Japan."
The United States, China, Iran, and Finland are among the other countries that are either building nuclear plants or have announced plans to do so.
Most European countries are gradually turning to sustainable resources to meet their energy needs.
Russia should follow Europe's example, Yablokov said, and has all it needs to produce energy using alternative methods.
According to him, wind power in the Kolskii Peninsula, in Russia's northwest, could generate more energy than the local nuclear plant. He also noted that two tidal-energy plants located in the Far East of the country are able to provide for the total energy needs of the region.
In Russia's south, he said, attempts to use solar energy have shown promising results.
Environmental groups estimate that alternative power sources, which currently account for less than 10 percent of the energy produced in Russia, could grow to cover at least 20 percent of Russia's needs.
Nuclear plants produce roughly 15 percent of Russia's electricity, which is mainly generated by hydroelectric and natural gas and coal-fired plants.