The end of two-day meeting saw Canada renew commitments to battling nuclear terrorism, including a $367 million renewal of the Global Partnership Program for five years. The initiative has already seen an over $800 million investment by Ottawa.
The federal government will also step up the return of spent highly enriched uranium to the United States and helped switch Mexican reactors to low enriched uranium.
Also, as the collection plate was passed for the International Atomic Energy Agency Nuclear Security Fund, Canada contributed another $5 million. That is on top of the $17 million already given to the organization that co-ordinates global nuclear security efforts.
The threat of nuclear material falling into the wrong hands was cast in dire terms by President Barack Obama's in his remarks to other world leaders.
"The security of the world depends on the actions that we take," said Obama, who initiated the security summit and hosted first one in 2010.
"There are still too many bad actors in search of these dangerous materials and these dangerous materials are still vulnerable in too many places. It would not take much — just a handful of so of these materials — to kill hundreds of thousands of innocent people."
Chinese President Hu Jintao called for leaders to "commit to eliminating nuclear proliferation and the roots of nuclear terrorism."
Harper was more subdued, calling nuclear terrorism "one of the most challenging threats to global security today."
He said Ottawa is proud of its record, but that issue was overshadowed in bilateral meetings with Italy, India, Spain and the European Union, where Harper delved into trade and foreign investment.
"I don't think it's any secret, if you talk to most leaders today, the economic circumstances of the global economy and their own economies are very much centre and very much top of mind," he told reporters at end of the summit.
"We're working hard here to work with others and increase jobs, growth and long-term prosperity. Ultimately our view as a trading nation, in a global economy, all of interests are linked."
He said the economy remains his "No. 1 priority."
Much of Harper's whirlwind swing through Asia, which ended Tuesday, has been focused on trade and investment.
Harper responded to criticism that Canada is slowing the charge to switch away from bomb-grade uranium because of the business interest of Nordion Inc.
The Ottawa-based company has signed a 10-year deal with Russia to purchase its highly enriched uranium for use in the production of medical isotopes — something critics say gives Moscow less of an incentive to do away with its stock.
"We are committed over time to eliminating that practice, to moving away from it," he said. "We've said we would not do it instantly, but we are making new investments, specifically on alternatives to that of isotope production in Canada."
The federal government is funding into non-highly enriched uranium, but the actual commercial application is still years down the road.
Harper said in the hallways there's been a lot of chat among leaders about nuclear proliferation, specifically the threat posed by North Korea and Iran.
"I think there is virtually a universal assessment, that Canada would share, that the recent actions by North Korea by launching a satellite are a contravention of UN resolutions," he said.
"As you known, unfortunately, this regime seems to delight in irritating the international community."
As Harper spoke, Foreign Affairs Minister John Baird was making his way back from a clandestine trip to the Demilitarized Zone between North and South Korea, about an hour from here.
He led a handful of MPs on the excursion.
The unannounced visit came to light in a Tweet from Baird, who used the opportunity to condemn the regime in Pyongyang.
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