The two-day Nuclear Security Summit is scheduled to open on Monday in Washington to discuss securing vulnerable nuclear materials and preventing acts of nuclear terrorism.

In recent years, nuclear security has been facing increasing risks that could endanger the future of human race. The issue has drawn wide attention from the international community.

The International Atomic Energy Agency (IAEA), the UN nuclear watchdog, defines nuclear security as "the means and ways of preventing, detecting, and responding to sabotage, theft, and unauthorized access to or illegal transfer of nuclear material and other radioactive substance, as well as their associated facilities."

Many countries have stepped up efforts to develop the peaceful use of nuclear power to diversify energy sources. As hundreds of nuclear power plants are in operation globally, security has been a major concern in nuclear power use ever since the world's first nuclear plant was built in the Soviet Union in 1954.

The world's worst nuclear disaster happened on April 26, 1986, when one of the four reactors at Ukraine's Chernobyl nuclear power plant exploded, killing 30 people on the spot.

The explosion released more than eight tons of radioactive materials, contaminated 60,000 square km of land and exposed more than 3.2 million people to radiation.

The disposal of nuclear waste is another headache in nuclear security. The radioactive waste produced by nuclear power plants remains toxic for even thousands of years. If not properly managed, it is extremely dangerous for humans and the environment.

With the wide use of nuclear power in recent years, the international community also faces the potential threat of nuclear terrorism and the urgent task of nuclear non-proliferation.

According to the IAEA, the cases of nuclear materials lost or stolen have reached 1,500 between 1993 and 2008, with an increase in the smuggling of nuclear materials.

"The greatest threat to U.S. and global security is no longer a nuclear exchange between nations, but nuclear terrorism by violent extremists and nuclear proliferation to an increasing number of states," U.S. President Barack Obama said recently.

Concrete efforts have been made by the international community to ensure nuclear security, including the approval of legal documents such as the Convention on the Physical Protection of Nuclear Material and its amendment, and the International Convention for the Suppression of Acts of Nuclear Terrorism.

The UN Security Council also adopted resolutions, including Resolution 1540 and Resolution 1887, which require all countries to adopt laws to prevent "non-state actors" from manufacturing, acquiring or trafficking in nuclear, biological and chemical weapons, as well as the materials to make them.