ML19308B816
| ML19308B816 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 07/09/1976 |
| From: | Rowden M NRC COMMISSION (OCM) |
| To: | Gossick L NRC COMMISSION (OCM) |
| Shared Package | |
| ML19308B807 | List: |
| References | |
| TASK-TF, TASK-TMR NUDOCS 8001170355 | |
| Download: ML19308B816 (3) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION I
W ASHINGTON, D. C. 20555 I
JUL S 1976 FOR OFFICIAL'USE ONLY caa'a aN MEMORANDUM FOR:
Lee V. Gossick, Executive Director for 0 erations FROM:
Mar owden, Chairman
SUBJECT:
LIGHTNING PROTECTION FOR NUCLEAR POWER STATIONS A concern relating to lightning phenomena and the safe operations of nuclea'r power plants has been identified to the Commission as a potential safety issue that is not being adequately addressed in NRC licensing reviews. You are requested to report to the Commission 1
by August 6, 1976 the staff position with respect to the following questions:
- To what extent does the staff consider the effects of lightning on nuclear power station design?
- Is lightning a safety issue that should be included in the Standard Format and Standard Review Plans?
- What is th technical basis for the staff positions with respe~ct to the above questions? This technical basis need not be limited to unclassified information.
- What has been the actual experience to date with respect to' lightning impacts at nuclear power plants?
Attached is a more iletailed discussion of the alleged problem which also should be addressed i.n your response.
If you have any questions concerning this request, contact Hugh Thompson of my staff (634-1429).
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b ATTACHMEllT 1
Alleged Problem Lightning is a natural phenomenon about which little information is available.
Applicable research which has been done and can be found 1
outside classified literature is scarce. On the assumption that the large quantities of energy transferred during a lightning strike could conceivably affect a nuclear power station, we can justify exploring possible effects.
If this exercise shows chains of events which could conceivably result in compromising the integrity of engineered safety features, a more detailed examination seems warranted.
ALLEGED POSSIBLE EFFECTS 1.
Direct Strikes One would assume that electrical and other components within a nuclear reactor would be shielded from the effects of a direct strike by the conductive steel reinforcing bar, liners, etc.,
acting as a faraday cage.
Several considerations make this a less tenable assumption.
a.
Constructors will not guarantr^ the electrical continuity nor complete grounding of the rebar".
- b..A strike could travel along a conductive portion of the containment, reach an area of high resistance, the resultant heat generation could produce steam from the water of hydration in the surrounding concrete and either spall or penetrate the containment. This might not be noticed until this engineered safety feature was called upon to fulfill its function, at which point it might fail.
c.
Auxiliary generators and other critical structures are not always within containment and these could be disabled by direct strikes.
The massive ground system required by an electrical generating statian, plus a system of lightning rods, would seem to greatly minimize this aspect of concern if we had assurance that the system was desioned and constructed on sound principles.
j Can one feel confident of this in present plants?
2.
Indirect Strikes a.
Strikes on transmission lines, auxiliary generating facilities, etc., could cause large surges to enter the plant, possibly damaging critical equipment or electrical l
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circuitry. All electrical generating plants have interruptors installed to prevent damage from just such an event. Un-fortunately, these mechanisms are installed to protect the generators, transformers and other large pieces of expensive j
gear from damage from massive charges. They are not set sensitively enough to protect the type of electronic equip-ment now being used in engineered safeguard controls and instrumentation.
In addition, " reaction time" of the in-terruption is much too slow to prevent short duration pulses from entering the system. The above insensitive settings are understandable as the operators of the plant do not wish it to be shut down unnecessarily or frequently.
Has a thorough analysis of the effects of surges on the control instruments of a nuclear plant been conducted?
b.
Magnectic Fields Electronic circuitry, particularly integrated circuitry, is susceptible to magnetic influence.
Lightning strikes produce significant perturbations in the earth's magnetic field. Many modern designs of engineered safeguard systems are using integrated circuits. The effects of lightning strikes near a nuclear power plant on these circuits is unknown but probably significant.
Are the following alleged events possible at nuclear power stations?
If so, please indicate the impact of the event or, if not, please indicate why the event is not considered possible.
1.
A strike could put the emergency generating equipment out of action.
2.
Control instrumentation could be damaged so that reactivity is added at the same time that " scram" systems are disabled.
3.
If a lightning-induced power surge could cause a turbine trip with simultaneous loss of auxiliary power, we might be well on our way ~
toward an event which could lead to a reactivity surge resulting in steam generator tube failure with resultant release of radio-activity.
4.
If surges or magnetic field fluctuation disable the overlaod or overspeed controls on the turbine, a runaway turbine condition could develop.
5.
Surges, etc., could cause instrumentation to falsely represent
- operating conditions causing plant operators to take inappropriate
'or dangerous actions.
6.
Alarms or automatic scram controls might be disabled in a manner which leaves the operator unaware of impending problems.
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