****MEDIA ADVISORY**** 

30TH ANNIVERSARY OF THREE MILE ISLAND NUCLEAR PLANT 

ACCIDENT – RESOURCES FOR REPORTERS 

 March 28 will mark the 30th anniversary of the accident at the Three Mile Island Unit 2 

(TMI-2) nuclear power plant near Middletown, Pa. The TMI-2 accident had the greatest impact 

on nuclear regulation of any single event in history. Although there were no deaths or injuries, 

the accident is a reminder for the NRC and those who operate plants to remain vigilant in 

watching over the 104 operating reactors in the United States to ensure their safe operation. 

 Since the accident, there have been substantial regulatory changes and other 

improvements that have contributed to making nuclear plants operate safer and better today. 

Some of the major changes that have strengthened NRC’s regulation of public health and safety 

include placement of at least two NRC resident inspectors at each plant site, immediate NRC 

notification by plants of serious events, expanded emergency preparedness including an NRC 

Operations Center staffed 24/7, increased identification, analysis and publication of plant 

performance information, and recognizing human performance as a critical component of plant 

safety. 

Key indicators of plant safety performance have improved dramatically, as indicated in the 

attached charts. They show: 

 The average number of significant reactor events over the past 20 years has dropped to 

nearly zero. 

 Today there are far fewer, much less frequent and lower risk events that could lead to a 

reactor core damage. 

 The average number of times safety systems have had to be activated is about one-tenth 

of what it was 22 years ago. 

 Radiation exposure levels to plant workers has steadily decreased to about one-sixth of 

the 1985 exposure levels and are well below federal limits. 

 The average number of unplanned reactor shutdowns has decreased by nearly ten-fold. 

In 2007 there were about 52 shutdowns compared to about 530 shutdowns in 1985. 

NRC NEWS

U.S. NUCLEAR REGULATORY COMMISSION

Office of Public Affairs Telephone: 301/415-8200 

Washington, D.C. 20555-0001 

E-mail: opa@nrc.gov 

Site: http://www.nrc.gov

No. 09-033 February 18, 2009
 The NRC is offering a limited number of interviews with the following NRC officials 

that need to be coordinated through the Office of Public Affairs by calling 301-415-8200 or 

sending an e-mail to OPA@nrc.gov. 

 For historical perspective of the TMI-2 accident: J. Samuel Walker, NRC Historian, 

author of Three Mile Island – A Nuclear Crisis in Historical Perspective.

 For plant performance improvements: Eric J. Leeds, Director of Nuclear Reactor 

Regulation.

 For views of an actual TMI-2 participant: John White, Region I Branch Chief in the 

Reactor Safety Division.

 Other TMI-related resources for reporters are provided below. 

TMI Fact Sheet: http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/3mile-isle.html. 

Harold Denton Talk, Dec. 2008: http://r2.nrc.gov/videoarchive/ViewVideo.cfm?vlink=49. 

TMI 25th Anniversary Presentation 3/2004 at NRC: DVD available from OPA. 

 
Trends in Nuclear Plant Performance

There has been a significant increase in the safe operation of over 100 nuclear power plants over the 

past couple of decades. These charts depict those indicators of reactor performance the NRC uses to 

help monitor the operational safety of nuclear plants. In general, safety has increased and problems 

have decreased. Since the Three Mile Island accident in 1979, the agency has enhanced and sharpened 

its regulatory tools and requirements to ensure safe plant operation. The results can be seen clearly in 

the following charts. 

Significant Events - This chart shows that the 

number of significant events at each operating 

reactor has dramatically decreased from almost 2.5 

events per plant in 1985 down to 0.1 events per 

plant in 2007. Significant events are those events 

that have serious safety implications and include 

degraded safety equipment, a reactor shutdown 

with complications, an unexpected response to a 

change in a plant parameter, or a degraded fuel rod 

or coolant piping. Significant events are 

determined through detailed screening and 

evaluation of operating experience. 

Accident Precursors - NRC analyzes those events 

at plants that could lead to an accident where the 

reactor core melts as it did in the Three Mile 

Accident. A risk is assigned to each event relative 

to it leading to an accident. For example, risk of 

0.001 means that the event has a 1 in 1,000 chance 

of causing core damage. The data above show that 

over the years, these events have become much less 

frequent and less risky. This is due to many changes 

put in place to avoid these events in the future or to 

lessen the impact of such events should they occur. 

Safety Systems Actuations - Safety systems in a 

nuclear plant are activated either automatically or 

manually to deal with a problem detected in the 

reactor. Since 1985, there have been dramatically 

fewer activations of safety systems indicating fewer 

safety-related problems occurring in reactors. The 

average number of actuations is determined by 

dividing the total number of actuations occurring at 

operating reactors in any given year by the total 

number of operating plants in the fleet (~104). For 

example, in FY 2007, there were about 25 safety 

system actuations--far less than one per plant. 
Automatic Scrams While Critical - A nuclear 

plant is designed to automatically shut down 

(scram) if a safety problem is detected while 

operating. This chart shows the average number of 

scrams has decreased dramatically over the past 20 

years, indicating far fewer safety problems in plant 

operations. In FY 2007, there were about 50 

unplanned scrams among 104 operating plants 

compared to over 500 scrams in 1985. 

Collective Radiation Exposure - Total radiation 

dose accumulated by nuclear plant workers has 

decreased to less than 20 percent of the doses in 

1985. In 2007, those workers receiving a 

measurable dose of radiation received about 0.1 rem 

(rem is a unit that measures the amount of radiation 

absorbed by the human body). For comparison 

purposes, the average U.S. citizen receives 0.3 rem 

of radiation each year from natural sources in the 

environment.