ML20247N973
| ML20247N973 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/28/1989 |
| From: | NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20247E174 | List: |
| References | |
| TASK-AE, TASK-T903 AEOD-T903, NUDOCS 8904060365 | |
| Download: ML20247N973 (3) | |
Text
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O AE0D TECHNICAL REVIEW REPORT UNIT:
Browns Ferry Nuclear Plant Unit 2 TR REPORT N0.: AE0D/T903 DOCKET NO.:
50-260 DATE: March 28, 1989 LICENSEE:
Tennessee Valley Authority EVALUATOR / CONTACT:
T. M. Su NSSS/AE:
General Electric /TVA
SUBJECT:
GENERIC IMPLICATION OF BROWNS FERRY FIRE ON NOVEMBER 2,1987
SUMMARY
This technical review documents the results of evaluation of an event at Browns Ferry Unit 2 which involved a fire inside the drywell.
The fire burned for thirty minutes and damaged hundreds of cables of safety-related and non-safety equipment. The burn rate in this event was more rapid than expected.
Investigation of this event indicated that gasoline was detected in samples of the affected cables and that the fire was likely caused by arson.
In addition, the rapid propagation of the fire was in part due to electrical cables without fire retardant coatings exposed to the atmosphere during the outage. Our review on the adequacy of current regulation also concludes that the requirements specified in 10 CFR 50 Appendix R and BTP CMEB 9.5-1 to SRP 9.5.1 are adequate for fire protection and need not be modified due to this event. No further AE0D review or AE0D actions is recommended.
DISCUSSION On November 2,1987, a fire occurred at Browns Ferry Nuclear Plant Unit 2.
The fire, which originated inside the drywell, burned for thirty minutes and damaged hundreds of cables of safety-related and non-safety-related equipment.
The detailed description of the fire is described in the NRC Inspection Reports (Ref. 1).
The burn rate in this event was more rapid than expected. Because of this concern, AE0D performed this review to determine if this event might have a generic impact on current fire protection regulations.
Results of our evaluation are provided in the following sections.
The Browns Ferry Fire is evaluated in the following areas:
The cause of the fire; Safety implications of the fire; Adequacy of current regulations for fire protection.
l a.
The Causes of the Fire The NRC Inspection Reports identified the potential causes to be:
(a) fire of suspicious origin and (b) fire due to. modification work activities.
Following the initial inspection, laboratory examination of 12 residue 8904060365 890324 4
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samples from the damaged equipment indicated that gasoline was detected in three samples.
Consequently, the Bureau of Alcohol, Tabacco, and Fireatus (ATF),
and the Federal Bureau of Investigation (FBI) were asked to investigate a potential cause of sabotage. The AFT and FBI investigation concluded that the fire was caused by arson (Ref. 2).
Both the TVA and NRC teams also investigated the possibility that the fire was caused by an electrical short between temporary power cable connections used for the modification work. These temporary power cable connections were routed through penetration EE, near where the fire was initially observed. The investigation resulted in no conclusive findings.
Searches of the SCSS (Sequence Coding and Search Syctem) database identified no similar event in other operating plants since 1980.
b.
Safety Implication of the Fire The fire resulted.in destruction of the cables in the affected section of the cable trays and melting of two aluminum conduits above a penetration i
splice box.
Control circuitry to the main steam system, reactor recircula-tion system, neutron monitoring and other non-safety related systems was damaged. No other equipment was damaged by the fire.
Since the drywell houses the reactor and other safety-related equipment, a fire in the drywell is a serious event. A fire in the drywell is considered highly unlikely to occur during plant operation -- Mark I and II containments are inerted resulting in an oxygen concentration less than 3.5% by volume and the inerted atmosphere prevents fires.
For Mark III and PWR containments which are not inerted, 10 CFR 50 Appendix R requires fire protection means to be provided in the containment.
During plant startup and shutdown of BWRs with Mark I and II containments, when the containment is not inerted, the regulatory position is that the short duration of the deinerted condition results in a low probability of fire and is an acceptable risk. Also, the redundancy and diversity of systems to provide water to the core make it unlikely that a fire inside the drywell could disable them all; and some of these systems have all their active components outside the drywell.
c.
Adequacy of Current Regulations for Fire Protection Tho ir.vestigation conducted by the FBI and the ATF concluded that the fire was caused by arson.
It indicated that gasoline or other accelerators must be present to cause such a rapid fire. This explains the phenomenon of the rapid horizontal burn propagation along the cables. A fire caused by arson is not considered in current requirements for equipment for fire protection. The requirements for separation of cable for equipment and fire barriers will not necessarily provide protection where both trains are consumed by fire due to arson.
The current regulations do not address the criterion of acceptable burn rate. The guidelines specify that electric cable insulation should pass the flame test in the current IEEE Standard 383, or cables should be coated with a fire retardant. The IEEE Standard requires that "the cable does not
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~in the area of flame impingement." It is noced that most of the cables in the Browns. Ferry drywell do not meet IEEE 383, but, in most cases, have a fire retarAnt coating.' In the area where the fire occurred, they are not
. coated with a fire retardant coating (Ref.,1) because the drywell. is~inerted
' during power' operation.. This may. explain the observation of rapid propaga-tion of the fire:as the drywell was not inerted during the. extended outage.
The NRC Safety Evaluation Report issued March 1976.found these cables'
. acceptable (Ref. 1).
The current regulation specifies. strict administrative control during all.
phases of operation, including maintenance, iuodification, or refueling operations. There were many-areas of_ concern raised by the NRC inspection team (Ref. 1). 'However, it is reasonable to conclude that a fire at.
' Browns Ferry.could b~e confined and damages would be limited if fire protection features required by the current regulations were implemented
.and the appropriate administrative controls enforced by the licensee.
CONCLUSIONS The Browns Ferry fire was likely caused by arson.
In addition, the rapid propagation' of the fire was: due to electrical cables without fire retardant coatings exposed to.the atmosphere during the cutage. Administrative controls were not enforced as the licensee did not pay close attention to-the temporary electrical' connections for the modification work. We also conclude that the requirements specified in 10 CFR 50 Appendix R and BTP CMEB-9.5-1 to SRP 9.5-1 are' adequate for fire protection and need not be modified due.to this event.
Enforcement of these requirements'and appropriate safeguards to preclude arson need to be maintained.to prevent recurrence.
No further AE0D. review or AEOD action is recomended.
REFERENCES 1.
NRC Inspection Report Hos. 50-259/87-43, 50-260/87-43, and 50-296/87-43, December 30, 1987.
2.
TVA Serious Accident Investigation Team " Preliminary Accident Analysis Report, Browns Ferry Nuclear Plant Unit 2 Drywell Fire, November 2,1987."
December 2, 1987; Final Version April 13, 1988.
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