Ahead of the announcement, the broadcast showed military parades, missile launches, fireworks over the monument to the founding of the ruling Workers' Party, and other patriotic images.
In front of a backdrop of Mount Paektu, the dormant volcano on the Chinese border that is the fount of Korean nationhood, she trembled with excitement, smiling broadly as she pronounced the test's success.
It "clearly proved" that the North's nuclear weapons had a "highly precise basis", she said, wearing a pink and black traditional dress, known as hanbok in the South and choson chogori in the North, adorned with a badge of Kim Il-Sung and his son and successor Kim Jong-il.
The broadcaster carried images of leader Kim Jong-un, the third generation of the family to rule the Democratic People's Republic of Korea, as the country is officially known, sitting at a circular table with a general and three other officials.
It also showed his handwritten order for the test to be carried out at noon on September 3.
The test "marked a very significant occasion in attaining the final goal of completing the state nuclear force", Ri said.
Last year, Ri made headlines as she enthusiastically announced that North Korea had dropped a new bomb.
"The republic's first hydrogen bomb test has been successfully performed at 10am on January 6, 2016, based on the strategic determination of the Workers' Party," the woman announced brimming with pride.
"With the perfect success of our historic H-bomb, we have joined the rank of advanced nuclear states," the announcer said, adding that the test was of a "miniaturised" device.
According to an article in North Korea's Chosun Monthly magazine interpreted by Reuters in 2009, Ri is known as "the people's broadcaster".
She is an actor turned newsreader who first went to air in 1971 when the North's state TV channel was taking off.
The magazine reports she was guided by state founder Kim Il-sung, who nurtured her "with warm love and faith". Kim pushed her to be a broadcaster with fiery speech, the magazine said, in one of the few North Korean news stories giving details of her life.
"As these days passed, her voice grew to have an appeal so that whenever she would speak on the news, viewers were touched," the magazine claimed. "When Ri announced reports and statements, enemies would tremble in fear."
Ri lives in relative luxury in Pyongyang with her husband, children and grandchildren, the magazine story said.
If North Korea has a shocking announcement to make, Ri will be the one to make it.
According to Michael Madden, who runs the website North Korea Leadership Watch, she also came out of retirement for last year's announcement. "This is the equivalent of Walter Cronkite coming out," Madden told Mashable. "Or, for a younger generation, Tom Brokaw, Peter Jennings, or Dan Rather. This is the top anchor for North Korean news."
Dr Victor Cha, Director of Asian Studies at Georgetown University, said last year that her appearances on TV were significant. "The fact that they brought her back is a sign of the regime's desire to return to the hard line Cold War-era ideology of the leader's grandfather," he told Mashable, adding, "It's no accident that they bring her out."
