TMI History

Updates on



  • From October 5-9, 2001, “Licensee sirens in Lancaster County were inoperable October 5 through October 9, 2001, due to a radio transmitter being deenergized at the county facility. The transmitter is part of the siren actuation system. This issue is unresolved pending further investigation into the lines of ownership and maintenance of the actuation system.” (IR 50-289/01-07).
  • On January 11, 2002 , Siren testing at TMI encountered numerous problems: all sirens failed in York County and one siren failed in Lancaster County. AmerGen attributed to computer malfunctions.
  • On March 3, 2002, a siren malfunctioned in York County again. During TMI’s annual test on on January 30, 2002, all 34 sirens in York County, located within ten-miles of the plant, failed to activate.
  • On June 25, 2002, “...station emergency preparedness personnel discovered that the emergency planning siren base station at the site, was unable to communicate with the off site sirens, due to external radio frequency noise in the area.” (IR-50-277/02-05; 50-278/02- 05)
  • On December 12, 2002, TMI sirens malfunctioned in Cumberland and York counties. In Dauphin County, 28 sirens malfunctioned due to the “inadvertent” discharge of the “space bar” by a computer operator (Refer to June 22, August 15 and October 5-9, 2001 and January 11, March 3 2002, for related problems.)
  • On July 28, 2010, the NRC issued a report of an inspection at the Three Mile Island plant for the quarterly period ending June 30.
    The NRC said it found no findings of significance. However, it noted that the TMI plant operator identified a violation that was determined to be of very low safety significance. The NRC said it would treat the violation as a non-cited violation.
    The issued stemmed from the TMI Emergency Plan and the plant paging system. The report said that plant operator Exelon began testing its on-site speakers in March 2010. A total of 301 out of 405 speakers were tested, and of those tested, 108 had identified deficiencies, the report said. “Contrary to the TMI Emergency Plan, the 108 speakers would not provide immediate warning and instruction to on-site personnel during an emergency,” the report said. “Upon discovery, Exelon issued a standing order to issue blow horns to operations and security staff to notify people in areas that would need to be evacuated during an emergency.“ The report added, “The finding is of very low safety significance because prompt compensatory measures were taken upon discovery.”
  • June 23, 2011, Three Mile Island's emergency sirens sounded at 12:15 p.m. Thursday as part of an annual test -- but it didn't work everywhere. The 96 sirens, which cover five counties and are within a 10- mile radius of TMI, were set to sound for three minutes. They sounded everywhere except in Lancaster County.
    Officials ran another test, this time just in Lancaster County, at 1:15 p.m. At that time, the sirens did work in Lancaster County. (WGAL)
    A Lancaster County EMA official said Lancaster County and another county pressed the siren test button simultaneously and the system did not register the Lancaster County test.
  • July 14, 2011, A Three Mile Island warning siren sounded accidentally on Thursday afternoon, according to Dauphin County officials.
    The TMI siren at 2nd and Hanover streets in Hummelstown inadvertently sounded at 1:19 p.m. It lasted for fewer than 30 seconds, according to Stephen Libhart, Director of the Dauphin County EMA.
    Libhart says Exelon will repair or replace any components of the siren if necessary. (WGAL)



The following list of terms and acronyms may facilitate your reading of the events that have taken place at nuclear power plants on the Susquehanna River and elsewhere.


 By Russell Dupree


 Three Mile Island and the Vigilant Professor

    Thirty years ago, April 1, 1979, on the rooftop of a building at the University of Southern Maine in Portland, a nuclear radiation recording device went from being relatively quiescent to rapidly recording extremely high levels of beta radiation, 100 times the normal background levels.

    The equipment had been set up by USM physics professor Charles Armentrout a few days earlier as a teaching project for his students to see if any fission products from the Three Mile Island power plant accident could be detected in Maine. It was a rainy Sunday, five days after the partial meltdown at the power plant just southeast of Harrisburg, Pennsylvania.



Re-published by Three Mile Island Alert - February 2009 

Originally published March 2004 


Because the Nuclear Regulatory Commission continues to publicize false 

information about the TMI accident, we correct the record once again. The 

NRC’s erroneous statements are listed in the red text which follows. 

“The main feedwater pumps stopped running, caused by either a mechanical 

or electrical failure, which prevented the steam generators from removing 





 To view a collected history of problems with sirens at nuclear power plants, open pdf. 


This is an excellent article written by Aileen Mioko Smith

for the 10th anniversary of the Three Mile Island Accident in 1989. The author interviewed residents who lived near 

Three Mile Island at the time of the accident and chronicled their stories and experiences, which are stil denied by
and nuclear industry officials. 

Aileen is executive director of Green Action, a Japanese environmental NGO based in Kyoto, Japan.
She was nominated for the
National Book Award (USA) in 1976 for the book "Minamata," co-authored with W. Eugene Smith.
(Holt, Rinehart and Winston, 1975.) 


February 13, 2009 12:47 pm         

The most serious accident in US commercial nuclear power history: people vs. government

By Nicole Back - Staff Writer

After three decades, the debate continues. [img_assist|nid=112|title=A crowd gathers near TMI after the 1979 accident. Many residents were demanding information.|desc=|link=none|align=right|width=72|height=50]


The Nuclear Regulatory Commission stands by its claim that the most serious accident in US commercial nuclear power history did not cause any physical harm to those who were directly affected.


Hundreds of people lived near Three Mile Island when equipment malfunctions, design related problems and worker errors led to the partial meltdown of the TMI-2 reactor core. Residents insist the US government is lying about what really happened to them.



Three Mile Island-1  (TMI-1) came on line in September 1974 at a cost of  $400 million. Legal intervention was conducted by the Environmental Coalition on Nuclear Power (ECNP) based in State College.