05000338/LER-1979-041-01, /01T-0 on 790329:info Received from Westinghouse of Potential Nonconservatism in Analysis of Single Dropped Rod Event.Caused by Improper Analysis of Accident by NSSS Vendor

/01T-0 on 790329:info Received from Westinghouse of Potential Nonconservatism in Analysis of Single Dropped Rod Event.Caused by Improper Analysis of Accident by NSSS Vendor

ML19263D778
Person / Time
Site:	North Anna
Issue date:	04/10/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19263D775	List: 05000338/LER-1979-041, Forwards LER 79-041/01T-0 05000338/LER-1979-041-01, /01T-0 on 790329:info Received from Westinghouse of Potential Nonconservatism in Analysis of Single Dropped Rod Event.Caused by Improper Analysis of Accident by NSSS Vendor
References
LER-79-041-01T, LER-79-41-1T, NUDOCS 7904130249
Download: ML19263D778 (2)

LER-1979-041, /01T-0 on 790329:info Received from Westinghouse of Potential Nonconservatism in Analysis of Single Dropped Rod Event.Caused by Improper Analysis of Accident by NSSS Vendor

Event date:
Report date:
3381979041R01 - NRC Website

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Virginia Electric and Power Company North Anna Power Station, Unit #1 Attachrent:

Page 1 of I Docket No. 50-338 Report No. LER 79-041/01T-0 Lescription of Event on 3/29/79, s t e-ion personnel were informed by the NSSS Vendor of a potential nonconsertatism associated with the atalysis of the single dropped rod accident. This nonconservatism could lead to a lower calculated DNB ratio for the single dropped rod accident.

Probable Consequences of Occurrence This event assumes that a single dropped rod near the power range detector channel (N-44) feeding the automatic rod control system will cause the automatic rod control system to respon.1 to the sensed reduction in nuclear power by a rod withdrawal. This subsequent rod withdrawal could result in an overpower condition in which DNB conditions would be achieved.

Since the steady state operation control rod position would normally limit a

reactivity insertion of less than 100 PCM by rod withdrawal, this event would not result in the overpower condition necessary to achieve DNB.

The re f ore, the health and safety of the general public would be unaffected by this event.

Cause of Occurrence This event was caused by reartlysis of the single dropped rod event in conjunction with the rod bow r aalty. This reanalysis was found to produce a potential nonconservatiom under certain conditions depending upon the response of the automatic rod control system.

Immediate Corrective Action

The immediate corrective action was to limit the steady state power operation control rod position such that in automatic rod control a maximum of 100 PCM of positive reactivity could be inserted if such an event were to occur. This corresponds to a D bank rod position of 214 steps. The value of 100 pcm is the typical dropped rod worth assumed in the analysis.

Scheduled Corrective Action The scheduled corrective action is to perform a more specific analysis of this event in relation to the present design and to determine the necessary corrective actions required to provide for the required DNB safety margin.

Actions Taken To Prevent Recurrence No further action is required.