(ATTN: ADDS more info in paras 3-4)
SEOUL, March 5 (Yonhap) -- North Korea stopped the operation of its 5-megawatt reactor at its mainstay nuclear complex in Yongbyon, north of Pyongyang, late last year with no signs of reprocessing activities there, South Korea's spy agency said Tuesday.
During a briefing to the National Assembly's intelligence committee, the National Intelligence Service (NIS) also said that the underground tunnels of the North's nuclear test site in Punggye-ri remain shut down and unattended since their destruction in May last year, according to lawmakers of the committee.
On a jarring note, the NIS said that it detected signs of the North restoring part of the Dongchang-ri missile launch site it tore down.
"(The North) appears to be putting back a roof and a door (to a Dongchang-ri facility)," the NIS was quoted as saying.
The NIS also said that the military authorities of South Korea and the United States have run a "thorough" monitoring system to keep track of the North's nuclear and missile facilities, including its uranium enrichment sites that were apparently brought up in nuclear negotiations between Washington and Pyongyang.
"The U.S. information is the same as ours, but we can't comment on what facilities are located where," the NIS was quoted as saying during the briefing.
The 5-megawatt graphite-moderated reactor is one of the key facilities at the Yongbyon nuclear complex. It is capable of producing spent fuel rods, which if reprocessed can yield 5 to 7 kilograms of weapons-grade plutonium annually. About 6 kg of plutonium is required to build a single bomb.
The Yongbyon complex was apparently part of the agenda for the nuclear talks between U.S. President Donald Trump and North Korean leader Kim Jong-un last week in Hanoi.
The talks ended without an agreement as they failed to narrow differences over the scope of Pyongyang's denuclearization and Washington's sanctions relief.
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