ML20136B881
| ML20136B881 | |
| Person / Time | |
|---|---|
| Issue date: | 12/18/1985 |
| From: | Palladino N NRC COMMISSION (OCM) |
| To: | Ward D Advisory Committee on Reactor Safeguards |
| References | |
| NUDOCS 8601030060 | |
| Download: ML20136B881 (10) | |
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December 18, 1985-CHAIRMAN Mr. David A. Ward Chairman Advisory Committee on Reactor Safeguards U.S. Nuclear Regulatory Commission Washington, D. C.
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Dear Mr. Ward:
On October 16, 1985, you provided me with the ACRS report relating the impacts of natural phenomena on off-site emergency response.
The specific issues addressed in this letter were:
(1) the range of probabilities for the occurrence of various natural phenomena, (2) the potential of various_ natural phenomena causing severe core damage, and (3) the relati've potential of different natural phenomena having a significant impact on off-site emergency response.
On October 17, 1985, you provided me with ACRS-comments on the consideration of earthquakes in off-site emergency planning.
This letter focused on:
(1) establishing a lower bound on the occurrence frequencies for events'which must be considered, (2) the importance of seismic events as they relate to off-site emergency planning, and (3) the potential difficulty in implementing the staff's recommendation outlined in SECY-85-283.
Both reports were fully discussed with the ACRS at the Commission meeting held on November 7., 1985.
I can assure-you that both reports will be given consideration by the Commission in its future deliberations on this topic.
Sincerely, l
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Nunzio J. Palladino l'
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NUCLEAR REGULATORY COMMISSION g
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WASMNGTON D. C. 20666 October 16, 1985 s
Honorable Nunzio J. Palladino Chairman U. S. Nuclear Regulatory Connission Washington, D. C. 20555
Dear Dr. Palladino:
SUBJECT:
ACRS REPORT ON IMPACTS OF NATURAL PHENOMENA ON OFF-SITE EMERGENCY RESPONSE During its 306th meeting, October 10-12, 1985, the Advisory Comittee on Reactor Safeguards, in response to the oral requests made by Comis-sioners Asselstine, Bernthal, and Zech during our meeting with the Comission on September 9,1985, met with the NRC Staff to review and evaluate the relative importance of various na tural phenomena which could initiate, or occur in coincidence with, accidents at nuclear power plants and which have the potential for significant impacts on off-site emergency response. The specific matters addressed were:
1.
The range of probabilities for the occurrence of various natural
' phenomena, 2.
Their relative potential for causing severe core damage, and 3.
Their relative potential for having a significant impact on off-site emergency response.
These matters were also the subject of a joint meeting of our Subcomit-tees on Site Evaluation and Extreme External Phenomena held on October 9, 1985.
Our evaluations were made in the following context:
1.
The probability for occurrence, the severity, and the potential contribution of individual natural phenomena to nuclear power plant accidents are site-specific.
The potential impact of various natural phenomena on off-site emergency response is also site-specific.
For example, although the effects of hurricanes may be an important consideration for plants located in coastal areas, they would not be important for plants located in the Midwest.
Similarly, the effects of blizzards might be a consideration for plants located in the North, but would not be significant for plants located in the Sunbelt.
2.
The capabilities of nuclear power plants to resist the impacts of various natural phenomena cover a wide range. For example, plant
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Honorable Nunzio J. Palladino October 16, 1985 designs to withstand the. impacts of a design basis tornado are based on events that may have a probability of occurrence as low as 10-0/yr.
Plant designs to withstand the impacts of earthquakes, on the other hand, are based on events that may have a probability of occurrence of 10-3 to 10-4/yr.
3.
Warning times in advance of the impset of natural phenomena vary over a wida range.
The arrival time of a hurricane or a tsunami may in some cases be anticipated from tens of hours to several days, whereas an earthquake normally occurs without warning.
As a result, supplementary precautionary measures that may be taken in preparation for a hurricane are generally not possible in the case ~
of an earthquake.
4.
There is a wide variation in the spatial impact of natural events.
The extent of the impact of a tornado may be limited to a small area, whereas the impact of a flood, hurricane, or earthquake may be widespread.
Although a tornado that strikes a nuclear power plant might have some detrimental _effect on the plant itself, the irpact on off-site facilities, and particularly on the capabilities for off-site emergency response, might be negligible.
In our evaluations, we reviewed SECY 85-283, " Final Amendments to 10 CFR Part 50, Appendix E; Consideration of Earthquakes in Emergency Plan-ning," dated August 21, 1985 and discussed key issues with our con-sultants and the NRC Staff.
As a result of these deliberations, a considerable amount of data addressing portions of the three-items cited above was assembled. On the basis of our review of this information, we make the following observations:
1.
Probabilistic Risk Assessments indicate that some natural phenom-ena, such as heavy rains, blizzards, and fog, are not important as accident initiators.
However, because the occurrence of such phenomena is relatively frequent compared to the occurrence of other natural events such as earthquakes and tornadoes, the poten-tial for their occurrence contemporaneous 1y with a major nuclear power plant accident due t to some other cause must be taken into consideration in off-sitet emergency planning.
Current regulations recognize this need, and we believe they are adequate.
S impacts of those natural phenomena, such as hurri-2.
The potential canes, external floods, a(d tsunamis, for which warning times can be provided, can be consfaerably ameliorated by shutting a nuclear power plant down prior to hheir arrival..For example, this type of precautionary action was 'taken by the operators of several East Coast nuclear power plants during Hurricane Gloria in September 1985. The wisdom of incorporating requirements for such actions I
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3 HonorabIeNunzioJ.Palladino October 16, 1985 frnto the Technical Specifications should continue to be assessed through evaluation of appropriate probabilistic risk assessments on a plant-specific basis.
This could also be done as part of the severe accident policy review.
3.
At the present time there is some question as to the frequency with which extremely rare, natural phenomena must occur to be considered in off-site emergency planning. We believe that useful guidance on this subject is available in the Standard Review Plan, Section 2.2.3, which provides limitations on off-site hazards that must be considered in nuclear power plant safety evaluations. For example, Section 2.2.3 recomends that of f-site events having a probability of. occurrence greater than 10-6/yr of causfng on-site accidents leading to off-site doses in excess of the limits prescribed in 10 CFR Part 100 must be taken into consideration.
Based on the above considerations and observations, we offer the follow-ing reconnendations:
1.
Our review indicates that, of all natural pheiomena, an earthquake is the only event that nomally provides no warning of its im-pending occurrence and that has a significant potential for causing severe core damage and contemporaneous major disruption of off-site emergency response. The peak ground acceleration of an earthquake having this potential, however, is generally considered to be several times the safe shutdown earthquake and its proba-bility for occurrence is low.
Nonetheless, because such earth-quakes have a finite probability of occurrence, we recommend that such events receive appropriate limited consideration in off-site emergency planning. For further discussion on this matter, see our letter to you of June 10, 1985.
2.
The probability for the contemporaneous occurrence of an earthquake that impairs the capabilities for off-site emergency response and a major nuclear power plant accident due to some other cause is extremely remote.
For tnis reason, the contemporaneous occurrence of two -such events need not be specifically considered from the standpoint of off-site emergency planning.
3.
Of secondary importance, compared to earthquakes, are tornadoes, hurricanes, and external floods.
Tornadoes are placed in this category because of their limited spatial impacts and the conser-vatisms that exist in the designs of nuclear power plants to resist
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their impacts. Although hurricanes and external floods are both of concern because of their potential for causing extended disruptions in the supply of off-site power, the occurrence of these two natural phenomena is preceded, in general, by a warning time of r
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HonorabYeNunzioJ.Palladino October 16, 1985 hours0.023 days <br />0.551 hours <br />0.00328 weeks <br />7.552925e-4 months <br /> to days. This fact, coupled with the fact that nuclear power plants are designed to cope with the impacts of these events, should considerably limit their contributions to severe core damage and the associated need to consider their impacts on off-site emergency response.
Sincerely, David A. Ward Chaiman l
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%,*****/e October :7,1985 Honorable Nunzio J. Palladino Chairman U.-S. Nuclear Regulatory Commission Washington, D. C. 20555
Dear Dr. Palladino:
SUBJECT:
ACRS COMMENTS ON CONSIDERATION OF EARTHQUAKES IN OFF-SITE EMERGENCY PLANNING During its 306th meeting, October 10-12, 1985, the Advisory Comittee on Reactor Safeguards continued its review of the Proposed Final Amendments to 10 CFR Part 50, Appendix E, Consideration of Earthquakes in Emergency Planning.
The primary document considered in this review was SECY '283, dated August 21, 1985. This topic was also the subject of a joint meeting of our Subcommittees on Site Evaluation and Extreme External Phenomena held on October 9, 1985.
We had previously written a letter to you on this matter on June 10, 1985.
On the basis of this review, we offer the following additional coments:
1.
Al though we realize that the NRC Staff plans to address many classes and types of low frequency natural phenomena in its con-siderations of their complicating effects on off-site emergency planning, the ACRS believes that seismic events warrant specific attention.
Our reasons for making this recomendation are covered in a sepa, ate letter to you dated October 16, 1985, "ACPS Report on Impacts of Natural Phenomena on Off-site Emergency Response."
2.
If the Comission desires to address low frequency natural phe-nomena on a generic basis, we would urge that a lower bound be set on the occurrence frequencies for events that must be considered.
Useful guidance on this subject is available in the Standard Review Plan, Section 2.2.3.
3.
Although we concur, in general, with the four recomended changes in 10 CFR Part 50, Appendix E, as expressed in SECY-85-283, we believe that implementation of the recomendation for the develop-ment of a capability for. augmenting the staff at a nuclear power plant under emergency conditions should not occur without con-sideration of the nature and extent of the accident.
For example, what should be done if exposure rates in the vicinity of the plant preclude transporting people into the site? We also believe that nl-M M)$QN~
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Honorable Nunzio J. Palladino October 17, 1985 i't would be useful for the utility to supply an appropriately limited study of potential seismically induced effects which are relevant to off-site emergency planning.
. We hope you will find these comments helpful.
Sincerely.
David A. Ward Chainnan 4
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