ML20247R137

Proposed Tech Specs Reducing Limit on Min Measured Flow Rate in RCS

ML20247R137
Person / Time
Site:	North Anna
Issue date:	05/23/1989
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
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ML20247R128	List: ML20247R122 ML20247R137
References
NUDOCS 8906070140
Download: ML20247R137 (19)

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PROPOSED TECHNICAL SPECIFICATIONS CHANGES FOR NORTH ANNA UNIT 1 l

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An POWER DISTRIBUTION LIMITS ~

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3/4.2.5 'DNB-PARAMETERS The limits.on the DNB related paramete'rs~ assure that each'of.the parameters.are maintained within the normal steady. state envelope of operation assumed :in the transient and accident analyses.-

.The limits have been analytically. demonstrated to be adequate to maintain

a. minimum.DNBR.. greater.

than fthe'. design limit throughout each analyzed transient.

Measurement uncertainties are accounted for in'the DNB design margin.

The 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> periodic surveillance of these parameters thru instrument readout is sufficient to. ensure that the parameters are restored within their limits following load changes and other expected transient operation.

The 18 month periodic' measurement 'of the RCS total flow rate is adequate to detect flow degradation and: ensure correlation of the flow indication channels with measured flow : such that the indicated percent flow will provide sufficient verification of flow rate on aL12 hour basis.

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-NORTH ANNA - UNIT 1 B 3/4 2-6

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ATTACHMENT 2 PROPOSED TECHNICAL SPECIFICATIONS CHANGES FOR NORTH ANNA UNIT 2 l

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POWER. DISTRIBUTION LIMITS BASES For purposes of monitoring QUADRANT POWER TILT RATIO when one excore detector is inoperable, the movable incore detectors are used to confirm that the normalized symmetric power distribution is consistent with the QUADuNT POWER TILT RATIO. The incore detector monitoring is done with a full intore flux map or two sets of 4 symmetric thimbles.

The two sets of 4 symmetric thimbles is a unique set of 8 detector locations. These locations are C-8, E-5, E-11, H-3, H-13, L-5, L-11, and N-8.

3/4.2.5 DNB PARAMETERS The limits on the DNB related parameters assure that each of the i

parameters are maintained within the normal steady state envelop of operation assumed in the transient and accident analyses.

The limits have been.

l analytically demonstrated to be adequate to maintain a minimum DNBR greater than the design limit throughout each analyzed transient.

Measurement uncertainties must be accounted for during the periodic surveillance.

The 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> periodic surveillance of these parameters thru instrument readout is sufficient to ensure that the parameters are restored within their i

limits following load changes and other expected transient operation. The 18 i

month periodic measurement of the RCS total flow rate is adequate to detect flow degradation and ensure correlation of the flow will provide sufficient verification of flow rate on a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> basis.

I NORTH ANNA - UNIT 2 B 3/4 2-6

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e-I ATTACHMENT 3 SAFETY EVALUATION IN SUPPORT OF REDUCED MINIMUM REACTOR COOLANT SYSTEM FLOW RATE FOR NORTH ANNA UNITS 1 AND 2

9 1.0. INTRODUCTION

-As required. by Technical. Specifications 3.2.5 and 4.2.5.2, the I

- Virginia Electric and Power Company performs reactor coolant system (RCS).

flow measurements at each of North Anna Units 1 and 2 once per fuel cycle.

Because the RCS flow:is sensitive to the steam generator tube plugging (SGTP).which has been performed during refueling outages, the. flow rates have been trended as. a ' function of SGTP.

The RCS flow - rates J have decreased predictably with increased SGTP.

. As additional tubes-are plugged, both units are expected to. approach the Technical Specifications

- flow limit.

This safety evaluation details how the. Technical Specifications.

minimum RCS flow rate may be reduced by absorbing a penalty in available DNBR ' design margin.

The flow rate for both units will be reduced to preserve consistency between the two sets of Technical Specifications.

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f 2.0 -TECHNICAL' SPECIFICATIONS CHANGES LThe Technical ~ Specifications must be updated in two places to' implement the RCS minimum, flow limit change as follows.

TS Table 3.2-1.

.The minimum allowable Reactor ' Coolant System. Total Flow Rate will be-changed from 289,200 gpm to 284,000 gpm.. This limit change is off set by a penalty'on' retained DNBR margin as described in the following sections.

TS Bases 3/4.2.5.

A flow limit of 289,200 gpm was assumed in:the currently docketed Updated Final Safety Analysis Report (UFSAR) accident a.

analyses which. were performed with the Westinghouse Improved Thermal Design' Procedure (ITDP2).

The new ~ limit no longer - reflects.this

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assumption and the -Technical Specifications Bases will be revised accor'ingly.

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b 3.0 ' JUSTIFICATION FOR FLOW REDUCTION

.v Two different flow rates have been used in the currently docketed analyses for North. Anna which were approved as a part'of the 1986' core-uprating.2 These are the ITDP flow rate which is' used. for statistical DNBR analysis and a lower, non-ITDP flow-rate which is used for non-statistical analysis of both DNB and non-DNB events (e.g., LOCA).

Key methodology differences as pertain to the flow measurement issue are highlighted in Table 3.1.

The Technical Specifications require that the RCS flow rate be measured

- every 18 months in. order to verify the assumed ITDP flow rate of 289,200 No uncertainty is applied because the measurement uncertainty has

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been statistically absorbed by the ITDP methodology. No comparison with the non-ITDP flow rate is necessary since, even with the application of the required measurement uncertainty, the 284,000 gpm limit is substantially below the ITDP value.

Sufficient analysis margin exists to lower the minimum measured flow rate from the ITDP limit of 289,200 gpm to the non-ITDP limit of 284,000 gpm.

As a part of the Reload Safety Evaluation process for each cycle, a table of retained DNBR margin (derived from Technical Specification Bases 3/4.2.3) is prepared for the reload cores.

Generally, about 10%

retained DNBR margin remains available after all pertinent penalties have been absorbed.

This available margin can be used to offset the desired flow limit reduction.

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The' maximum DNBR sensitivity to flow rate for North Anna is 1.6% per p,

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. percent flow. This ; sensitivity was determined over a range of statepoints whicn bound all operating and DNB-related accident conditions as a part of the Statistical DNBR Methodology

• which has been proposed" for l

implementation at North Anna. Further, it is slightly more conservative than the ITDP sensitivity which was used to develop the DNBR limit for the North Anna core uprating.2 Based upon this sensitivity, each percent' reduction of the 289,200 gpm limit must be offset by a 1.6% penalty on retained DNBR margin.

Such a penalty may be applied without requiring reanalysis of the ITDP events for North Anna. Enough DNBR design margin exists to lower the Technical Specification for minimum measured RCS flow to the non-ITDP flow limit of 284,000 gpm.

This proposed limit is 1.8%

below 289,200 gpm, so that the retained margin DNBR penalty would be (1.8% flow) * (1.6% DNBR/% flow) = 2.9% DNBR The Reactor Coolant System. flow limit of Technical Specifications Table 3.2-1 may therefore be lowered to 284,000 gpm. This reduction will be offset by a retained DNBR margin penalty of 2.9%, which is easily absorbed by the available retained DNBR margin. The total remaining DNBR margin will still be approximately 7%. Measured flows below the 284,000 gpm level would invalidate the assumptions of the non-ITDP accident analyses of UFSAR Chapter 15 and are therefore unacceptable at this time.

There are no other areas which are impacted by the limit change.

Flow-related items such as loop transport times or RTD response times either include substantial margin in the safety analyses when compared 4

to a change of less than 2% or are insensitive to the actual value of the flow (i.e.,

they are sensitive only to relative changes such as a fractional deviation from the measured full power AT).

Therefore it is only necessary,to absorb the penalty on retained DNBR margin in order to support the flow limit reduction.

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Table 3.1 Key Features of ITDP and Non-ITDP Analysis

'as Pertain to'the RCS Flow Measurement Methodology-ITDP Non-ITDP Applicati"n Statistical Non-statistical DNBR DNBR analysis and non-DNBR analysis UFSAR Events Full power Other accidents Condition II DNBR events plus Loss of Flow Treatment of-Absorbed in-Must be added to-Flow Measurement DNBR limit analysis assumption-Uncertainty before' comparison to limit Current Flow 289,200 gpm 284,000 gpm Limit plus-(no uncertainty (including Applicable required) uncertainty)

Uncertainty Proposed. Flow 284,000 gpm 284,000 gpm Limit plus (no uncertainty (including Applicable required) uncertainty)

Uncertainty 6

F l 4' 0 ~ 10 CFR 50.59 EVALUATION When tested J against the.. criteria ' of '.10 CFR - 50.59, these i proposed

changes are found < to create no unreviewed safety questions.

The basis r s for this determination is as follows.

The probability of occurrence or the consequences of.an accident or

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malfunction of equipment'important to Safety previously evaluated in j.

the safety analysis report does not increase. Accident probability is not dependent upon the flow' limit and as such is not affected by the limit change.

Potential accident consequences remain within the bounds of the UFSAR accident analyses because.the flow limit reduction

'is fully compensated by a penalty on retained DNBR margin.

As such there is no increase in potential consequences, No possibility for an accident or malfunction of. a different type than-

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y any evaluated previously in the - safety analysis report has-been created.

The absence of a hardware change means that the accident-initiators remain unaffected, so that the proposed RCS flow limit change.cannot create the probability of any accident which has not already been analyzed in the UFSAR.

The margin of safety as ' defined in the basis of the Technical

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Specifications has not been reduced.

These changes. simply reflect the use of part of the available retained DNBR margin in order to offset the flow limit reduction.

The margin of safety for accident analysis does not include retained DNBR margin and thus is not impacted by this proposed' change.

In summary, the proposed changes do not create an unreviewed safety question as defined by the criteria of 10 CFR 50.59.

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-5.0- CONCLUSIONS i

l, The minimum measured RCS flow rate at North Anna may be reduced. from 289,200 gpm to 284,000 gpm without reanalysis of ~ the UFSAR Chapter 15 l

accidents. 'A 2.9% penalty will be extracted from available retained DNBR I'

margin-(approximately 10%) in order to compensate for.this flow reduction.

Further reductions would require reanalysis. or re-evaluation of all of the UFSAR Chapter 15 - events.

This limit change does not create an unreviewed safety question as defined by 10 CFR 50.59.

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i REFERENCES

1. ' Chelemer, H.,' et al. : " Improved Thermal Design Procedure," WCAP-8567

(July,1975).

2.

Letter. from L. B. Engle (NRC) to W. L. Stewart (Vir; inia Power), dated August 25, 1986.

j 3.

Anderson, R.

C.:

" Statistical DNBR Evaluation l Methodology,"

VEP-NE-2-A (June, 1987).

4.

Letter from W.

L'. Stewart (Virginia Power) to United States Nuclear Regulatory Commission, " Virginia Electric and Power Company North

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Anna Power Station Units 1 and 2 Proposed Technical Specifications Change,". Serial No.87-231,' dated June 17, 1987.

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9-ATTACHMENT 4 10 CFR 50.92 EVALUATION

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10-CFR 50.92 EVALUATION

.The proposed change in the North Anna: Technical Specifications minimum measured reactor coolant system flow from 289,200 gpm to 284,000 gpm does e

.not -involve a significant hazards consideration.

The. basis for this o

determination is as follows.

There is no significant increase in the probability or consequences

=

of an' accident previously evaluated.

Accident probability is not dependent upon the flow limit and as such is not affected by the limit change.

Potential accident consequences remain within the bounds of the UFSAR accident analyses because the flow limit reduction is fully compensated by a penalty on retained DNBR margin..As such there is no increase in potential consequences.

.The possibility of a new or different kind of accident from any

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accident ~ previously evaluated is not created.

The absence of a hardware change means that the accident initiators remain unaffected, so that no unique accident probability is created.

No sig9fficant reduction in the margin of safety is involved. These

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changes simply reflect the use of part of the available retained DNBR margin. in order to. offset the flow limit reduction.

The margin of safety -for accident analysis does not include - retained DNBR margin and thus is not impacted by this proposed change.

In summary, the proposed changes _do not involve a significant hazards consideration as defined by the criteria of 10 CFR 50.92.

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