ML18139B609

Proposed Tech Specs Revising Min Number of Thimbles Required for in-core Flux Mapping to Adopt Less Restrictive But Equally Safe Limit

ML18139B609
Person / Time
Site:	Surry
Issue date:	11/05/1981
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML18139B608	List: ML18139B607 ML18139B609
References
NUDOCS 8111100618
Download: ML18139B609 (3)

Text

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TS 3.12-15 It should be noted that the enthalpy rise factors are based on intergrals and are used as such in the DNB and LOCA calculations. Local heat fluxes are obtained by using hot channel and adjacent channel explicit power shapes which take into account variations in radial (x-y) power shapes throughout the core.

Thus, the radial power shape at the point of maximum heat flux is not necessarily directly related to the enthalpy rise factors. The results of the loss of coolant ac~ident analyses are conservative with respect to the ECCS acceptance criteria as specified in 10 CFR 50.46 using an upper bound envelope of 2.18 times the hot channel factor normalized operating envelope given by TS Figure 3.12-8.

When an FQ measurement is taken, measuremen*t error, manufacturing tolerances, and the effects of rod bow must be allowed for. Five percent is the appropriate allowance for measurement error for a full core map (~38 thimbles monitored) taken with the movable incore detector flux mapping system, three percent is the appropriate allowance for manufacturing tolerances, and five per-cent is the appropriate allowance for rod bow. These uncertainties are statistically combined and result in a net increase of 1.08 that is applied to the measured value of FQ.

In the specified limit o f ~ there is an eight percent allowance for uncer-tainties, which means that normal operation of the core is expected to result in F~ ~ 1.55 (1+0.2 (1-P))/1.08. The logic behind the larger uncertainty in this case is that (a) normal perturbations in the radial power shape N

(e.g., rod misalignment) affect F~, in most cases without necessarily affecting FQ' (b) the operator has a direct influence on FQ through movement of rods and can limit it to the desired value; he has no direct control over~' and (c) an error in the predictions for radial*power shape, which 8111100618 811105 PDR ADOCK 05000280 p _ PDR _

l may be detected during_J;_t_ar.tup physics tests and which may influence FQ, can

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TS 3.12-16 be compensated for by tighter axial control. Four percent is the appropriate allowance for measurement uncertainty for F~ obtained from a full core map

(~38 thimbles monitored) taken with the movable incore detector flux mapping system.

Measurement of the hot channel factors are required as part of startup physics tests, during each effective full power month of operation, and whenever abnormal power distribution conditions require a reduction of core power to a level based on measured hot channel factors. -The incore map taken following core loading provides confirmation of the basic nuclear design bases including proper fuel loading patterns. The periodic incore mapping provides additional assurance that the nuclear design bases remain inviolate and identify opera-tional anomalies which would, otherwise, affect these bases.

For normal operation, it has been determined that, provided certain condi-tions are observed, the enthalpy rise hot channel factor F~ limit will be met. These conditions are as follows:

1. Control rods in a single bank move together with no individual rod insertion differing by more than 15 inches from the bank demand position. An indicated misalignment limit of 13 steps precludes a rod misalignment no greater than 15 inches with consideration of maximum instrumentation error.

2. Control rod banks are sequenced with overlapping banks as shown in TS Figures 3.12-lA, 3.12-lB, and 3.12-2.

3. The full length control bank insertion limits are not violated.

4. Axial power distribution control procedures, which are given in terms of flux difference control and control bank insertion limits are observed. Flux difference refers to the difference

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• COMMONWEALTH OF VIRGINIA)

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CITY OF RICHMOND )

The foregoing document was acknowledged before me, in and for the City and Commonwealth aforesaid, today by W. L, Stewart, who is Manager-Nuclear Operations and Maintenance, of the Virginia Electric and Power Company. He is duly authorized to execute and file the foregoing document in behalf of that Company, and the statements in the document are true to the best of his knowledge and belief.

,-tL. 71 Acknowledged before me this .S day of P t ~ , 19

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My Commission expires: ---~-_-_::i- s

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Notary Public (SEAL)

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