ML20137L089

Proposed Tech Spec Re Surveillance Requirements for end-of- Cycle Moderator Temp Coefficient to Permit Suspension of Further Coefficient Measurements When Equilibrium Boron Concentration Reached.Safety Evaluation Encl

ML20137L089
Person / Time
Site:	North Anna
Issue date:	01/20/1986
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML20137L086	List: ML20137L083 ML20137L089
References
NUDOCS 8601240358
Download: ML20137L089 (7)

Text

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REACTIVITY CONTROL SYSTEMS MODERATOR TEMPERATURE COEFFICIENT SURVEILLANCE REQUIREMENTS 4.1.1.4 The MTC shall be determined to be within its limits during each fuel cycle as follows:

a. The MTC shall be measured and compared to the BOL Limit of Specification 3.1.1.4a above, prior to initial operation above 5% of RATED THERMAL POWER, after each fuel loading.

! b. The MTC shall be measured at any THERMAL POWER and compared to -3.1 x

-4 Ak/k/*F (all rods withdrawn, RATED THERMAL POWER condition)

! 10 within 7 EFPD af ter reaching an equilibrium boron concentration of 300 ppm. In the event this comparison indicated the MTC is aore

~4 negative than -3.1 x 10 Ak/k/*F, the MTC shall be remeasured, and compared to the EOL MTC limit of specification 3.1.1.4.b, at least once per 14 EFPD during the remainder of the fuel cycle.(1)

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a (1) For fuel cycle 4 only, further measurements may be suspended once an equilibrium boron concentration (all rods withdrawn, RATED THERMAL POWER condition) of 20 ppm or less is reached.

l DR A O P

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

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i ATTACHMENT 2 SAFEn' EVALUATION January, 1986

Safety Evaluation End-Of-Cycle Moderator Temperature Coefficient Surveillance Virginia Electric and Power Company is proposing a change to the North Anna Ur it 2 Technical Specifications to permit suspension of further moderator temperature coefficient (MTC) measurements once an equilibrum boron concentration (all rods withdrawn, rated thermal power condition) of 20 ppm or less is reached for the current fuel cycle (cycle 4) only. It has been determined that the proposed change is acceptable from a nuclear safety viewpoint on the basis that the MTC limiting condition for operation of -40 pcm/ 'T will not be reached during the current fuel cycle.

This determination was based on calculations and actual measurements of MTC performed over the past two and one-half months of plant operations.

The attached graph shows calculated and "best-fit" lines of MTC as a function of boron concentration. The calculated line is based on reactor physics calculations for Unit 2, Cycle 4. The "best-fit" line is based on actual MTC measurements. The "best-fit" line predicts an extrapolated MTC value of -38 pcm/ 'F at 0 ppm boron. As stated in the Bases to the Technical Specifications, "The Surveillance requirements for measurement of MTC ..... are adequate to confirm that the MTC remains within its limits since this coefficient changes slowly due. principctly to the reduction in RCS boron concentration associated with fuel burnup " Thus the MTC is not expected to change appreciably after reaching 0 ppm boron.

However, during the power coastdown to the licensed burnup limit, the MTC is calculated to change by no more than 0.9 pcm/ 'F. Therefore, based on

the seven MTC measurements taken to date for North Anna Unit 2, Cycle 4, it is expected that the end-of-cycle MTC value will remain within the Technical Specifications limit of -40 pcm/ 'F. Further, the calculated end-of-cycle MTC is also above this limit.

10 CFR 50.59 Safety Evaluation It has been determined that the proposed change to allow suppension of further MTC measurements during Unit 2, Cycle 4 operation does not involve an unreviewed safety question as defined in 10 CFR 50.59. Specifically;

1. The probability of occurrence or the consequences of any accidents or malfunction of equipment important to safety previously evaluated in the safety analysis report is not increased. The MTC measurements taken to date provide adequate assurance that the Technical Specifications limit of -40 pcm/ 'F will not be exceeded during cycle

4. Further, reactor physics calculations also indicate that end-of-cycle MTC will remain above the limit. Thus, the current safety analyses remains bounding.

2. The possibility for an accident or malfunction of equipment of a different type than previously evaluated - in the safety analyses report is not created. The proposed change does not involve any alterations to the physical plant or procedures which would introduce any new or unique operational modes or accident precursors.

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3. The margin of safety as defined in the basis for any technical i

specification is not reduced by the proposed change. Since the end-of-cycle MTC limit is not changed and the current safety analyses L

remains bounding, the margin of safety is not reduced.

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10 CFR 50.92 Significant Hazards Considerations Analyses It has also been determined that the proposed change does not involve a significant hazards consideration as defined in 10 CFR 50.92. This i

determination was based on the foregoing 10 CFR 50.59 safety evaluation.

Specifically, the change does not:

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1. Involve a significant increase in the probability or consequences of

an accident'previously evaluated. For the reasons stated above the s

change has no effect on the probability or consequences of accidents t

previously evaluated.

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2. Create the possibility of a new or different kind of accident than previously evaluated. As discussed in . the safety evaluation the

change does not introduce any new or unique operational modes or accident precursors.

3. Involve a significant' reduction in the margin of safety. As noted in the safety evaluation the change has no effect on the margin of safety inherent in the basis for any technical specification, f

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We have also reviewed the examples of types of amendments which the NRC considers not likely to involve significant hazards considerations (48FR14870, 4/6/83) and found that none of the examples were directly comparable to the proposed change. However, one example was found to be similar to the proposed change. This example (iv) states in part: "A I

relief granted upon determination of acceptable operation from an operating restriction that was imposed because acceptable operation was not yet demonstrated." The proposed change would provide relief from a surveillance requirement which has demonstrated acceptable operation but which is now considered impractical because a suitable measurement can no longer be performed.

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NORTH ANNA 2, CYCLE 4 i CALCULATED VS MEASURED MODERATOR TEMPERATURE COEFFICIENT BEST-Fli LINE BASED ON INDIVIDUAL BORATION/ DILUTION POINTS MTC D

D LE

-32z g AST. QUARES

-34h a NEASuggy P AlculATEo E

OINTS D U

-36 o

0

-40 g 1

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4' l' 5' '&' '4' 'e' '4- 'l' ~5' '&' '4' e

, 3 2 2 2 2 2 1 1 1 1 1 1

0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 MEASURED BORON CONCENTRATION

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