An Ohio middle school that was closed this month after highly carcinogenic radioactive chemicals were detected inside and near the building will be closed for all of the next school year, according to a statement from the district.

Enriched uranium was detected inside Zahn’s Corner Middle School in Piketon, according to a May 3 statement from the Pike County General Health District, citing findings from Northern Arizona University researchers.

The statement said the radioactive contamination was from the federally owned Portsmouth Gaseous Diffusion Plant, which the U.S. Department of Energy has been in the process of decommissioning since 2011. The plant is about 2 miles from the school.

On May 13, Scioto Valley Local School District announced that Zahn’s Corner Middle School would be closed for the remainder of the year due to the contamination. Last week, a letter from the district said that, amid additional testing, the school would be closed for the 2019-20 school year.

The Portsmouth Gaseous Diffusion Plant, which once enriched uranium for weapons and nuclear fuel, and closed in 2001, in Piketon, Ohio, on Sept. 26, 2006. Chris Stewart / The Dayton Daily News via AP file

More than 350 fourth, fifth and sixth grade students will have to attend other schools throughout the district, the letter said.

When the enriched uranium was discovered, the Pike County General Health District called for more independent sampling to determine the "extent of contamination" and asked the DOE to cease operations that could be causing any off-site contamination.

The DOE agreed to "sponsor a third-party, independent survey of all of the contamination issues," according to a May 11 statement from the Pike County General Health District. But the DOE has repeatedly refused to stop operations that might cause contamination.

The Pike County General Health District had previously called on the DOE to stop activities at the plant in April after the carcinogen Neptunium was detected by a U.S. Department of Energy air monitor adjacent to the school.

Separately, in 2017, the health district had already passed a resolution opposing some construction on the site.

The Portsmouth Gaseous Diffusion Plant enriched uranium from 1954 until 2001, at first to support the country's nuclear weapons program and later for commercial nuclear reactors.

In 2001, enrichment operations were discontinued at the site. The DOE began a cleanup program at the site in 1989 and began the decontamination and decommissioning process at the plant in 2011.

From 2010 to 2014, the cancer incidence rate in Pike County was almost 488 per 100,000 — 10 percent higher than the national average, according to the Ohio Department of Health.

"Any activity that cannot be performed safely and without leading to off-site contamination or risk to our community must not take place," Pike County General Health District spokesman Matt Brewster told NBC News.

"Any process or activity that leads to off-site contamination must stop. Stop what you are doing, figure out where it is coming from, implement a corrective measure to prevent future releases, and then resume activities with adequate monitoring in place to ensure that the corrective measures are working," he said.

The DOE did not immediately respond to NBC News' request for comment Friday. Earlier this month, DOE spokeswoman Kelly Love had said in a statement that routine air samples revealed trace amounts of Neptunium-237 and Americium-241.

"No enriched uranium was identified in any of the air samples taken by the Department of Energy at this school,” she said.

The department is “working together with state, local officials and the Piketon community to select an independent third party to perform additional sampling and analysis in a scientifically sound, and disciplined manner to properly assess the situation,” and “we are confident those findings will dispel any cause for further concern,” Love said in the statement.

Over Memorial Day Weekend, the DOE conducted sampling at the school, according to the Pike County General Health District, which is awaiting results.

Plans for the independent third-party assessment that will be funded by the DOE are still being finalized, Brewster said.

On May 16, the Pike County General Health District called on local leaders, including Gov. Mike DeWine, to support a pause in some construction at the plant in "the interest of public health and children’s safety until the independent/third-party contractor completes the sampling and analysis to determine source, levels extent, and health risk."

In a May 21 statement, DeWine didn't address that request, but thanked DOE Secretary Rick Perry "for his prompt response and his pledge for the third party study to be completed as quickly as possible."

A spokeswoman for DeWine's office also did not respond Friday to a question about whether the governor planned to support the pause in operations at the site, telling NBC News: "Governor DeWine has been focused on making sure testing occurs so that local officials have the most up-to-date data in making decisions."

Scioto Valley Local School District board president Brandon Wooldridge on Thursday addressed questions about closing the middle school.

"As soon as we found out about the results from Northern Arizona University, we had to make decisions quick and as a board member and a father, I could not keep it from the public if I thought there was something in the school building that could harm our students or staff," he wrote on Facebook.

"The Scioto Valley Local Board of Education is working hard to get answers as fast and efficiently as we can," Wooldridge wrote. "I can also assure you there are no hidden agendas or secrets being kept from the public. I’ll leave the secrets to the Department of Energy."