ML20052H325

Proposed Changes to Tech Specs 3/4.2.4 Re Core Protection Computer Rod Bow Penalties

ML20052H325
Person / Time
Site:	Arkansas Nuclear
Issue date:	05/03/1982
From:	ARKANSAS POWER & LIGHT CO.
To:
Shared Package
ML20052H322	List: ML20052H321 ML20052H325
References
NUDOCS 8205200215
Download: ML20052H325 (4)

Text

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POWER DISTRIBUTION LIMITS BASES P /P tilt untilt is the ratio of the power at a core location in the presence of a tilt to the power at that location with no tilt.

3/4.2.'4. DNBR MARGIN The limitation on DNBR as a function of AXIAL SHAPE INDEX represents a conservative envelope of operating conditions consistent with the safety analysis assumptions and which have been analytically demonstrated adequate to maintain an acceptable minimum DNBR throughout all anticipated operational occurrences, of which the loss of flow transient is the most limiting. Operation of the core with a DNBR at or about this limit provides assurance that an acceptable minimum will be maintained in the event of a loss of flow transient.

Either of the two core pcwer distribution monitoring systems, the Core Operating Limit Supervisory System (COLSS) and the DNBR channels in the Core Protection Calculators (CPCs), provide adequate monitoring of the core ocler distribution and are capable of verifying that the DNBR does not violate its limits. The COLSS performs this function by continuously monitoring the core power distribution and calculating a core operating limit corresponding to the allowable minimum DNBR. Reactor operation at or below this calculated power level assures that the limits of Figures 3.2-3 are not violated. The COLSS calculation of the core power operating limit based on DNBR includes appropriate uncertainty and penalty factors necessary to provide a 95/95 confidence level that the core power at which a DNBR of less than 1.24 could occur, as calculated by COLSS, is less than or equal to that which would actually be required in the core. To ensure that the design margin to safety is maintained, the COLSS computer program includes an F measurement uncertainty factor of 1.053, an engineering uncertainty fac N r of 1.02 and appropriate uncertainty and penalty factors for flux peaking augmentation and rod bow.

Parameters required to maintain the margin to DNB and total core power are also monitored by the CPCs. Therefore, in the event that the COLSS is not being used, operation within the limits of Figure 3.2-4 can be maintained by utilizing a predetermined DNBR as a function of AXIAL SHAPE INDEX and by monitoring the CPC trip channels. The above listed uncertainty and penalty factors are also included in the CPC.

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l 8205200215 820503 PDR ADOCK 05000368 l P- PDR

The DNBR~ penalty factors listed in section 4.2.4.4 are penalties used to accomodate the effects of rod bow. The amount of rod bow in each assembly is dependent upon the average burnup experienced by that l'

assembly. - Fuel assemblies that incur higher average burnup will experience a greater magnitude'of rod bow. Conversely, lower burnup assemblies will experience less rod bow. The penalty for each batch required to compensate for rod bow is determined from a batch's maximum average assembly burnup applied to the batch's maximum integrated planar-radial power peak. A single net penalty for COLSS and CPC is then determined from the penalties associated with each batch, accounting-for the offsetting margins due to the lower radial power peaks in the higher burnup batches.

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POWER DISTRIBUTION LIMITS SURVEILLANCE REQUIREMENTS (Continued) 4.2.2.4 The following DNBR penalty factors shall be verified to be included in the COLSS and CPC DNBR calculations at least once per 31 days:

Burnup (MTU) DNBR Penalty (%)

0-30 2.0 t

30-40 3.5 40-50 5.5 l

The penalty for each batch will be determined from the batch's maximum burnup assembly and applied to the batch's maximum radial power peak assemply. A single net penalty for COLSS and CPC will be determined from the penalties associated with each batch, accounting for the offsetting.

margins due to the lower radial power peaks in the higher burnup batches.

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FIGURE G-2 PENALTY ON MINIMUM DNBR DUE TO FUEL ROD BOWING AS A FUNCTION OF BURNUP 6 , , , ,

FOR 14 x14 FUEL DESIGN 5 -

FOR 16 x16 FUEL DESIGN 4

4 -

8 ' -

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5 b Z 3 -

=

Q 2 -

1 -

0 -

a I t 0 10000 20000 30000 40000 50000 BURNUP, MWD /MTU d

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