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u c.e Sent Mag Card to Gower on 2/9/78 E 3 1 4 1973 MEMORANDG4 FOR:
E. L. Jordan, Executive Officer for Operations Support, IE:HQ FROM:
B. H. Grier. Director, NRC: Region I
SUBJECT:
ANALYSIS OF LICENSEE REPORT ON HILLST0tE I 0FF-GAS EXPLOSION (AITS H61628F1)
The enclosed analysis responds to the above subject track item. Electronic submittal of the enclosure was effected on February 9,1978.
B. H. Grier Director
Enclosure:
As Stated bec:
E. Brunner T. Elsasser E. McCabe T. Shedlosky RO&NS Millstone 1 File RO&NS TRACK File J. Devlin
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ENCLOSURE 1 ANALYSIS OF NORViEAST UTILITIES' FOLLOW-UP REPORT ON MILLSTONE I 0FF-GAS SYSTEM GAS EXPLOSIONS A.
Licensee Description of the Event The licensee's description is basically vaTid. The explosions were chemical reactions. There was no damage to nuclear safety-related equipment. No radiation exposures reached or exceeded federal limits. The most significant discrepancy noted follows.
The licensee's report states "The first event was a hydrogen explosion confined to a massive underground pipe that was designed to withstand such an incident." flRC inspection indicates that, because broken gage glass faces in the Instru-ment Building adjacent to the stack were attributed to the first explosion, that explosion's effect was not totally confined to underground piping.
B.
Causes of the Explosions The licensee attributes the first explosion to touching of an off-gas system instrument line with welding equipment. URC inspection also indicates that action is the cause of the first explosion.
The licensee attributes the second explosion to buildup of explosive gases in the stack base because of inadequate restoration of the off-gas drain line loop seal after the first explosion, with detonation initiated by a spark from a level switch from a stack base sum pag. NRC inspection also indicates that condition caused the second explosion.
C.
Licensee Reaction The licensee report and NRC inspection indicate that actions taken to combat the damaging explosion were proper. There was no hazard to the public, and no need to call for special assistance (except to treat the injured man).
The incident did identify areas where the licensee response could have been better.
If the action taken to restore loop seals had been effective, the second explosion could have been prevented.
Additional means of measuring loop seal adequacy or a hydrogen concentration would, therefore, have been valuable. Corrective actions do prevent recurrence b escape paths for explosive gas.y elimination of the loop seals as 1
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A second area for improvement is licensee comunications in situations where incomplete knowledge and rumor could cause undue concern.
Public reaction to phrases like " explosion at a nuclear power plant" or " radiation release" could be inappropriate if licensees do not pro @tly place such incidents in perspective. Connecticut officials criticized licensee comunications in this case, and the licensee comitted to making his comunications plan acceptable to the State of Connecticut.
D.
Licensee Analysis and Corrective Actions The license report and NRC Region I inspection Report 50-245/77-33 show that the licensee identified the cause of the explosion and effected multiple corrective actions to prevent recurrence. NRC concurrenca in the adequacy of corrective action was obtained before operation was resumed.
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ese se t NoRTHE AST HuCLE AR ENERGY COMPANY A NoRTHE Alt utiLifitt CCMPANY March 2, 1978 Docket No. 50-245 Mr. Boyce H. Grier, Director Office of Inspection and Enforcement U. S. Nuclear Regulatory Conmission Region 1 631 Park Avenue King of Prussia, PA 19406
Reference:
!E Bulletin No. 78-03 Gentlemen:
The above referenced IE Bulletin was generated as a result of events
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occurring at our Millstone Nuclear Power Station Unit No.1.
In your December 14, 1977 letter to NNECO. you requested detailed information concerning these events. We responded on December 22, 1977 with this information which included the concerns expressed in IE Bulletin 78-03. We therefore feel no further response is required to IE Bulletin 78-03.
Very truly yours.
NORTilEAST NUCLEAR ENERGY COMPANY b
h D. C. Switzer President
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