UPDATE 1-Russia signs fourth U.S. uranium deal with Exelon

* Exelon Corp to buy Russian uranium directly in 2014-2020

* 4th such deal since "wall" to U.S. market broken last week

* Rosatom subsidiary plans $3 bln bond to fund expansion

By Simon Shuster

MOSCOW, June 3 (Reuters) - Russia's state nuclear firm Rosatom sealed a uranium supply deal with U.S. utility Exelon Corp (EXC.N) on Wednesday and voiced plans to issue a 100 billion rouble bond as it intensifies its global expansion.

Last week, the company said it had "broken down the wall" into the U.S. uranium market by striking three landmark deals to supply nuclear fuel worth more than $1 billion to U.S. power firms PG&E (PCG.N), Ameren Corp (AEE.N) and Luminant.

U.S. anti-dumping laws, which were relaxed last year, had previously only allowed Russia to sell the United States uranium recovered from dismantled Soviet nuclear weapons.

These sales are carried out through U.S. uranium trader USEC Inc (USU.N), which had an effective monopoly on Russian uranium imports under the so-called "megatons to megawatts" scheme established.

But Exelon will now become the fourth U.S. firm to buy the fuel directly from Rosatom's uranium exporter Tenex, also known as Techsnabexport.

Tenex is expected to gain control of 20-25 percent of the U.S. uranium market over the next decade as the chance to strike direct supply deals opens up. Analysts expect U.S. uranium prices to fall as Russian fuel pours into the market.

Under all four of the contracts already signed, state-owned Tenex will provide uranium to between 2014 and 2020.

But Rosatom has not revealed the volume or price of the fuel it will supply, saying only that it will be in line with market prices.

BOND TO FUND GLOBAL EXPANSION

Russia, one of the world's biggest nuclear players, has long been seeking to expand its clout in the sector by moving into developed markets such as the United States, European Union and Japan.