NRC FINALIZES WHITE FINDING FOR THREE MILE ISLAND 1 

NUCLEAR POWER PLANT OVER FLOODING PROTECTION ISSUE

The Three Mile Island 1 nuclear power plant will receive additional oversight from the 

Nuclear Regulatory Commission based on an inspection finding involving the protection of 

safety equipment from flooding. The finding, which has now been finalized, was identified by 

NRC inspectors during one of the agency’s numerous post-Fukushima reviews of U.S. reactors.

Three Mile Island 1 is located in Middletown, Pa., and operated by Exelon Generation 

Co. LLC.

 The NRC uses a color-coded system to classify inspection findings, which range from 

green, for a safety issue of very low significance, to red, for a safety issue of high significance. In 

this case, the NRC has determined the inspection finding should be categorized as white, or a 

safety issue of low to moderate safety significance. The finding will result in the plant moving 

from the Licensee Response Column of the agency’s Action Matrix to the Regulatory Response 

Column. This will result in additional scrutiny until the agency is satisfied the relevant issues 

have been properly evaluated and satisfactory corrective actions have been developed and 

implemented. While the NRC’s annual assessment of 2012 performance indicated the agency 

would carry out the normal level of inspection at the facility, today’s letter adjusts the agency’s 

regulatory oversight of the unit. 

During a walkdown, or visual inspection, of Three Mile Island 1’s protections against 

flooding last fall, NRC inspectors identified an external flood barrier deficiency. Specifically, the 

inspectors determined that the company had failed to identify and correct, during external flood 

barrier assessments, a problem involving electrical cable conduits – that is, pipes holding such 

cables. The conduits, located in the plant’s air intake tunnel, were not adequately sealed to 

maintain the integrity of the flood barrier. In the event of severe flooding, the problem had the 

potential to pose a threat to plant safety equipment.

Subsequent to the identification of the issue, Exelon took action to seal the conduits and 

restore the integrity of the external flood barrier.

NRC NEWS

U.S. NUCLEAR REGULATORY COMMISSION

Office of Public Affairs, Region I 

2100 Renaissance Blvd., King of Prussia, Pa. 19406-2713

E-mail: opa1@nrc.gov 

Site: www.nrc.gov

Blog: http://public-blog.nrc-gateway.gov

No. I-13-019

Contact: Diane Screnci (610) 337-5330

 Neil Sheehan (610) 337-5331

April 30, 2013

Email: opa1.resource@nrc.gov
Exelon was given an opportunity to attend a regulatory enforcement conference to further 

discuss the NRC’s finding or to respond to the finding in writing. The company declined to do 

so.

“The NRC has made clear that ensuring U.S. nuclear power plants are adequately 

protected against flooding issues remains a priority. This is especially important in light of the 

March 2011 events at the Fukushima Daiichi facility in Japan,” NRC Region I Administrator Bill 

Dean said. “Based on our inspectors’ finding of a deficiency in this area at Three Mile Island 1, 

we will perform additional reviews at the plant to make certain the company’s response is both 

thorough and comprehensive.”

The NRC will conduct a supplemental inspection at a future date to evaluate the 

company’s root cause analysis and corrective actions with respect to the problem.

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