ML19263F007
| ML19263F007 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/27/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Lewis M AFFILIATION NOT ASSIGNED |
| Shared Package | |
| ML19263F008 | List: |
| References | |
| NUDOCS 7910190308 | |
| Download: ML19263F007 (2) | |
Text
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SEP 2 71979 Mr. l4rvin I. Lewis 6504 Bradford Terrace Philadelphia, PA 19149
Dear Mr. Lewis:
Your letter of August 31,'1979, to the Comissioners about Class 9 accidents has been referred to me for reply.
The proposed Annex to ?ppendix D, 10 CFR Part 50, of the NRC Rules and
~ Regulations states that "the occurrences in Class 9 involve sequences of j's postulated successive failures more severe than those posculated for the design basis.for the protective systeins and engineered safety features of the plant." The accident at Three Mile Island Unit 2 involved a sequence of successive. failures (i.e., small-break loss-of-coolant accident. and failure of the emergency core cooling system) more tevere th n those postulated for the design basis of the plant. Therefore, we, conclude that the accident at Three Mile Island was a Class 9 event. However, at no time during the TMI-2 accident were the radiological consequences to the public more severe than those calcul c ed for the design basis of 'he plant..
The comon definition of Class 9 accidents are those events whose consequences ar. s ~ere but whose probability of occurrence is extremely low. The accident
'at Three Mile Island did occur, yet the release of radioactive material to
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the offsite population was very small. We conclude that the accident at j
TMI-2 can only be considered a Class 9 event from the standpoint of possible, i
rather than actual, radiological consequences of the given sequence of failures.
I f
An Ad Hoc Population Dose Assessment Group consisting of individuals from the Nuclear Regulatory Comission, the Environmental Protection Agency, and the l
Department of Health, Education and Welfare published a report on May 10,1979 on " Population Dose and Health Impact of the Accident at the Three Mile Island Nuclear Power Station" (NUREG-0558). The Ad Hoc Group concluded that "the l
offsite collective dose associated with radioactive material released during l
the period of March 28 to April 7,1973, represented minimal risks (that is, l
a very small number) of additional heslth effects to the offsite population."
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Mr. Marvin I. Lewis r A*) fg79 7 After the Three Mile Island accident, all holders of operating licens s were instructed to take a number of immediate actions to avoid repetition of errors that had cccurred in that accident. The prompt action t_aken by licensees contributed to assuring continued safe plant operation.
Operating plants designed by Babcock.and Wi'cox (the designer of the Three Mile Island plant) were shut down until they satisfactorily completed the short-tem actions required by the NRC and until the NRC staff completed an onsite verification of the plant readiness to resume operation.
In addition, each licen.see is to carry out certain long-tem modifications to further enhance the capability and reliability of the plant systems to respond to transient events.
15plementation action for other operating plants is being initiated as fim conclusions and recommendations develop from studies underway. For example, licensees of plants designed by llestinghouse and Combustion Engineering are being requested to initiate action t.)-improve the reliability of auxiliary feedwater systems or to propose design soiutions for NRC staff review.
The corrective actions taken as a msult of the Three Mile Island accidert permit the safe operation of pla'As with existing operating licenses. We shall continue to make every effort to ensure the protection of the public health and safety for plants currently in operation and for those that may come into operation in the future.
Sincerely, Original sipO!
E. G. Cast
/ Harold R. Denton, Dire'ctor
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