ML20072T954

Proposed TS Bases Page 125-a,recognizing Potential for out- of-phase as Well as Core Wide Instability

ML20072T954
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	09/09/1994
From:	VERMONT YANKEE NUCLEAR POWER CORP.
To:
Shared Package
ML20072T939	List: ML20072T933 ML20072T954
References
NUDOCS 9409160049
Download: ML20072T954 (1)

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BASES: 3.6 and 4.6 (Continued) $ -

l J. Thermal Hydraulic Stability -

The reactor design criteria is such that thermal hydraulic oscillations are prevented or can- be 9j readily detected and suppressed without exceeding specified fuel design limits. To minimize the xg likelihood of an - instability, a power / flow exclusion region to - be avoided during normal

- . operation is calculated ' using the approved methodology as stated . in 6.7.A.4. Since the 00 exclusion region may change each fuel cycle, the limits are contained in the Core Operating Limits Report. Specific directions are provided to avoid operation in this region and to S$ immediately exit upon an entry. Entries into the exclusion region are not part of' normal oo Operation. An entry may occur as a result of an abnormal event, such eis a single recirculation ute pump trip. In these events, operation in the exclusion region may be . needed to prevent o8 equipment damage, but actual time spent inside the exclusion region is minimized. Though each MS operator action can prevent the occurrence and protect the reactor from an instability, the APRM Uy flow-biased scram function is designed to suppress global oscillations, the most likely mode of oscillation, prior to exceeding the fuel safety limit. While global oscillations are the most likely mode, protection from out-of-phase oscillations are:provided through avoidance of the exclusion region.and administrative controls on reactor conditions.which are primary factors affecting reactor stability.

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l j' Amendment No. 125-a i

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