The heart of North Korea's nuclear program may have been damaged by recent significant flooding from heavy rain, a U.S. based think-tank said on Wednesday.

38 North, a U.S.-based North Korea analysis website, claimed "the flooding exposed how vulnerable the nuclear reactors' cooling systems are to extreme weather events," by showing a view of the Yongbyon Nuclear Scientific Research Center through satellite images.

The North Korea-monitoring website assumed that their pumps and power systems could potentially have been damaged, and piping systems that draw water from the river also could have been clogged due to the flooding, "perhaps the worst in the past several years".

The nuclear center, a facility about 100km north of North Korea's capital Pyongyang has been called the crown jewel of North Korea's nuclear program. The center reportedly comprised nearly 400 nuclear-related buildings. At the heart of its nuclear program, there's the 5 MWe reactor, presumably for the production of weapons grade plutonium and a facility to produce highly enriched uranium (HEU) used to make atomic bombs.

"The August 6 imagery, when compared to imagery from July 22, shows a dramatic rise in the water level of the Kuryong River that flows alongside the Yongbyon complex," the think-tank reported. "The water had reached the two pump houses that service the reactors and completely submerged their respective bases. The overfall dam was also fully underwater.”

The key facility such as the Uranium Enrichment Plant (UEP) seems not to be affected. 38 North said that "partial coverage from August 8 and 11 shows the waters have retreated, suggesting that the major facilities within the complex, such as the UEP, have been spared."

South Korea's Ministry of National Defense hasn't commented on the report, but said it is always monitoring actions about nuclear missiles and maintaining close cooperation with the U.S. government.

In the first week of August, North Korea got nearly more than 33 inches of rain, almost as much as the typical annual amount of 37 inches.

North Korean leader Kim Jong Un visited some parts of North Hwanghae Province where rains flooded hundreds of houses and rice fields last week, according to the state-run Korean Central News Agency (KCNA).

This marks the second time that Kim has visited flood-stricken areas since he became the leader of the country in 2011, following the inspection of North Hamgyong Province hit by a flood in 2015.

The Korean peninsula has been struck by one of the longest rainy spells in recent history. Heavy rains have killed more than 35 people in the South. The rainy season has continued for 51 days as of today, which is the longest in history according to the Korea Forest Service.

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This article originally appeared on VICE US.