ML19318B464
| ML19318B464 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 06/23/1980 |
| From: | Smith I Atomic Safety and Licensing Board Panel |
| To: | |
| References | |
| NUDOCS 8006260194 | |
| Download: ML19318B464 (3) | |
Text
Bd 6/23/80 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION G
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ATOMIC SAFETY AND LICENSING BOARD
'll/N 2
Ivan W. Smith, Chairman C #l&8 h.
Dr. Walter H. Jordan Dr. Linda W. Little 9%
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,,s'y In the Matter of
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METROPOLITAN EDISON COMPANY
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Docket No. 50-289 SP
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(Three Mile Island Nuclear Station, Unit No. 1)
)
MEMORANDUM ON NRC STAFF ACCIDENT SEOUENCES REPORT We have received and studied the staff document entitled -
"TMI-l Potential Core Damage Accident Sequences and Preventive and Mitigative Measures".
The sequences involving success or failure of the engineered safety features following a main feed-water transient and/or a small-break LOCA are diagrammed on pp. 13 and 14.
(Whether those are the only or dominant sequences will be questioned later.)
We also note that the staff has pro-vided a number of useful tables which list proposed actions that will reduce the likelihood of failure of the particular engineered safety feature.
Many of these actions are those included in the Commission August 9 order.
We accept the document as a presently adequate response to,our March 31 order.
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8 0 0.626 0 / N D
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, 4 We observe that the staff has not listed any probabilities in connection with any cf the accident sequences nor have they j identified which sequences are most likely.
They do refer to Action Plan II-C as one of the measures proposed for identifying the high risk paths and the associated mitigating actions.
We are concerned as to whether the adequacy of the proposed actions can be assumed until some such study has been completed.
For e st closely example, the staff points out that the sequence T 827 approximates the TMI-2 accident.
This accident has been identi-fied as having a probability (Kemeny report, p. 32) so high as to be likely within 400 years.
We will inquire as to the basis l
for any claims by licensee or staff that the proposed actions I
will reduce the probability by several orders of magnitude.
We further observe that in the past when the staff has identified a particular accident sequence as being of concern, they have required that the probability be reduced to less than 10-6/yr.
We have in mind, for example, the probability of a l
heavy aircraft crash causing unacceptable damage -- or an ATWS event followed by pressure vessel rupture.
Will the staff con-clude that the particular sequences identified in the staff docu-ment will each have a probability of less than 10-6/yr following the proposed mitigating actions?
To our mind, evidence to that effect would be very important in support of a position that the proposed actions are necessary and sufficient.
- We are not at this time telling the staff what we will require in the nature of evidence.
We are trying only to inform the parties of the nature of our concern in the matter. of safety at TMI-1.
t We require no response to this memorandum at this time.
We dxpect that our concern will be addressed by written testimony.
THE ATOMIC SAFETY ANJ LICENSING BOARD
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V72 ric4/ PAY A van W. Smith, Chairman Bethesda, Maryland June 23, 1980 1
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