ML042090263

E-mail from M. Hamer of Vermont Yankee to Various, Regarding CR-VTY-2004-00092: Over Power Condition

ML042090263
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	03/01/2004
From:	Hamer M Vermont Yankee
To:	Bronson K, Desilets M, Devincentis J, Dreyfuss J, Fales N, Stasolla J, Wierzbowski G - No Known Affiliation, Office of Nuclear Reactor Regulation
References
FOIA/PA-2004-0267
Download: ML042090263 (9)

Text

I Sienel, Beth From:

Sent:

To:

Hamer, Mike Monday, March 01, 2004 5:41 PM Bronson, Kevin; Wierzbowski, George; Devincentis, Jim; Desilets, Mike; Fales, Neil; Stasolla, John; Dreyfuss, John Pelton, David; Sienel, Beth CR-VTY-2004-00092: Over Power Condition Cc:

Subject:

The over power condition documented in CR-VTY-2004-00092 was subsequently determined to not have exceeded the licensed limit for core thermal power. Please see the attached PRO and supporting documentation. An LER will not be required. This item may be removed from the White Board.

LS E s..

PRO-0400092.pdf Memo (93 KB)

)04-023.pdf (163 KE Have a Nice Day, Mike Hamer A\\

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.INTEROFFICE MEMORANDUM REGULATORY COMPLIANCE POTENTIALLY REPORTABLE OCCURRENCE REPORT

'TO:.

MIKE DESILETS, TECHNICAL SUPPORT MANAGER FROM:

MIKE HAMER, TECHNICAL SPECIALIST III

SUBJECT:

CR-VTY-2004-00092: CALCULATED CORE THERMAL POWER (CTP)

EXCEEDED DATE:

FEBRUARY 17, 2004

-PRO NUMBER: PRO-0400092 EVENT DESCRIPTION:

On 01114104, during full power operations, a reactor overpower event occurred. The event was discovered at 15:00hrs via the Crossflow System and immediately reported to the control room.

Operators immediately took actions to reduce power and terminate the event. The overpower condition was no more than 0.1% (later determined to be 0.05%) of rated thermal power for a duration of no more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. All of the CrossflowE System parameters and connections were che6ked, found to be satisfactory and all applicable ERFIS data was analyzed. The Crossflow System was confirmed to be operating properly and the analysis of ERFIS data showed no conditions that would justify the observed change in power. It was therefore believed that this event was the result of an actual process change within the plant. The Crossflow System is completely functional and fully operable.

The initial thought is that changes to plant chemistry and the continuing effects of HWC caused a sudden defouling of the feedwater nozzles that led to rise in actual (vice indicated) core thermal power.

-The restart of hydrogen water chemistry has an impact upon the overall plant processes, and specifically a new variable is introduced with respect to feedwater nozzle fouling I defouling characteristics: These characteristics have been altered and have required constant monitoring vigilance to ensure the proper correction factors are installed to provide a sufficient margin between actual and indicated reactor-power.

Prior to HWC, the feedwater nozzles historically slowly fouled over the cycle. Crossflow correction factors trended slowly downwards during the cycle to reflect this nozzle fouling, and over the short term were stable and predictable. Post HWC, data to date shows the nozzles are defouling over the cycle, and Crossflow correction factors are trending upwards to reflect this. Additionally, over the short term the data is exhibiting great variability and non-predictability.

I

Since the startup of HWC and based on initial observed instability, monitoring and performance calculations are performed virtually daily, with adjustments made as required and far more frequently as compared to the historical pre-HWC performance. The additional monitoring, calculation, and trending will continue to be necessary until HWC flow rates settle and plant chemistry stabilizes.

The following regulation and license condition were considered when determining reportability of this event.

Operation or Condition Prohibited by Technical Specifications

§50.73(a)(2)(i)(B) "[The licensee shall report:] Any operation or condition which was prohibited by the plant's Technical Specifications except when: (exceptions do not apply).

DPR-28 Ucense Condition g.3.A.

Maximum Power Level "Entergy Nuclear Operations, Inc. is authorized to operate the facility at reactor core power levels not to exceed 1593 megawatts thermal in accordance with the Technical Specifications (Appendix A) appended hereto."

DISCUSSION/BASES:

The Crossflow correction factor calculation is inherently a conservative calculation: a small conservative bias is always included within the final correction factor. This bias, however, is not a given constant but rather a variable dependent primarily upon the plant specific process at the time of the calculation. The determination of the exact value of this bias requires a case-specific data evaluation. For this reason such margin is'not typically credited, even though it is always there.

For the event in question, a case-specific data evaluation has been calculated. The result of this case-specific data evaluation has determined that the nozzle fouling correction factors were non-conservative by -0.011% (rather than -0.09% as previously reported). Therefore, indicated CTP was biased non-conservatively low by 0.175 MWth (rather than 1.4 MWth as previously reported).

Since indicated core thermal power at the time of the event was 1592.4 MWth, actual core thermal power was 1592.575 MWth (not 1593.8 MWth as previously reported). Therefore, actual reactor power was 99.97%, not 100.05% as previously reported.

Additionally, the previously calculated 100.05% power level was fully bounded by plant analyses.

The fuel reload analysis assumes a CIP level in excess of 102% for all the UFSAR accident analysis and feedwater flow uncertainty of 1.8% for transient analysis. The plant's safety significant protection systems were unaffected and the limiting condition achieved during the event was fully bounded by plant analyses.

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CONCLUSION:

This event is not reportable as an LER pursuant to exceeding License Condition g.3.A. or §50.73(a)(2)()(B)

/ W,

RECOMMENDED:

APPROVED:

/ 2-l w-01 Michael J. Hamer Date Technical Specialist III Licensing Department iaeP.Desets Date Technical Support Manager 3.

M E M E R A N D U M S y s t e m E n g i n e e r i n g TO:

G. WIERZBOWSKI DATE:

FEBRUARY 23, 2004 FROM:

N. Fales, J. Stasolla, A. Cardine ID #:

SYSENG 2004 - 023

SUBJECT:

SUPPORTING INFORMATION FOR DETERMINING REPORTABILITY The purpose of this memo is to provide information in support of the determination that Root Cause CR.2004-0092 was ultimately not an overpower event. Initial calculation results from the Crossflow system revealed that an overpower condition resulted from defouling on the Feed Water Nozzles by 0.9 MWT. Further investigation into the conservatism built into Crossflow shows that an overpower did not occur.

The Crossflow correction factor.calculation Is inherently a conservative calculation: a small conservative bias Is always included within the final correction factor. This bias, however, is not a given constant but rather a variable dependent primarily upon the plant specific process at the time of the calculation. The determination of the exact value of this bias requires a case-specific data evaluation. For this reason such margin is not typically credited, even though it is always there.

A case specific data evaluation has now been completed and discussed as follows. The attached Crossflow Analysis sheets are used to determine the correction factor used in the calorimetric equation. The bottom of the sheet lists the proposed MAXFLOW value (nozzle correction factor) and the Percent Difference: Original MAXFLOW to New MAXFLOW.. The conservatively calculated values are on top, nonconservative values are in the middle and the nominal value is on the bottom. When the apparent overpower condition was indicated by Crossf low results, the conservative value was used in the calculation. The amount of apparent overpower was calculated as shown below.

Case 1 - Results Durinq Root Cause Investigation The two Feed Water loops percent difference between original MAXFLOW to New MAXFLOW are added together:

(-0.09754%) + (-0.00952%) = -0.10706%

The difference In power, as calculated by the calorimetric, is as follows, where 0.9 is a factor representing that Feed Water flow Is approximately 90% of the calorimetric equation:

0.9 x (0.00107 x 1593) = 1.534 MWT PAGE 1 OF 2

Since operations actually operates the plant slightly less than 1593, the power level of the plant during the event was an average of 1592.4 MWT. When the nonconservative difference in power of 1.534 MWT is added to 1592.4 MWT, the result is 1593.9 MWT (100.06% power).

Therefore, 1593.9 MWT (100.06% power) resulted in power being 0.9 MWT (0.06% power) above VY's license power limit.

Case 2-Results During Investigation into Determining Reportabilitv The two Feed Water loops percent difference between original MAXFLOW to New MAXFLOW are added together in the same.manner as above the results are:

-0.05769 + (+0.04669%) = -0.01100%

The difference in power, as calculated by the calorimetric, is as follows, where 0.9 is a factor representing that Feed Water flow is approximately 90% of the calorimetric equation:

0.9 x (0.011 x 1593) = 0.158 MWT When this non conservative difference in power of 0.158 MWT is added to 1592.4 MWT the result is 1592.6 MWT (99.97% power) which is less than 100% power, therefore not an overpower as previously reported. This results in power being 0.4 MWT below VY's license power limit.

Conclusion Based on the above review and analysis, an overpower event did not occur.

Prepared By:

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"A" Loop Crossflow Analysis ERFIS Data Crossflow Data Initial Date Final Date Initial Time 1/13/04 22:00:00 Final Time 1/14/04 10:00:00 Initial Date 1/13/04 Final Date 01/14/04 Initial Time 22:00:32 Final Time 10:00:03 Standard Deviation (Mlbslhr) 0.01049 Average Flowrate (Mlb/hr) 3.23973 Standard Deviation (Mlbs/hr) 0.01232 Average Flowrate (Mlb/hr) 3.24218 Average Core Thermal Power (C047) 1592.54 Number of ERFIS data points (N1) 721 Number of Crossflow data points (N 2) 492 I

Degrees of Freedom u (pooled: N1 +N2 -2) 1211 t - for a 95% C.I. And Pooled Degrees of Freedom = 1211 1.96

'Pooled Standard Deviation 0.01127 Confidence Interval Difference of Two Means (Mlb/hr)

Diff of Lower Limit

-0.00374 Two

-0.00245 Upper Limit

-0.00116 Difference between the ERFIS and Crossflow Average Flowrates are Statisically Signficant.

A change to MAXFLOW is required.

Crossf low Correction Term (Mlb/hr) 3.24347 3.240888155 3.24218 New MAXFLOW (millivolt)

Percent Difference:

ERFIS to Crossflow Flowrates Percent Difference:

Original MAXFLOW to New MAXFLOW

-0.09754

-0.017848809

-0.057694684 3.97643 3.973269055 3.974851956

-0.11542

-0.035718365

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"B" Loop Crossflow Analysis ERFIS Data Initial Date Initial Time 1/13/04 22:00:00 Final Date Final Time 1/14/04 10:00:00 Standard Deviation Average Flowrate (Mlbs/hr)

(Mlb/hr) 0.01076 3.17506 Crossf low Data Initial Date Initial Time 1/13/04 21:59:48 Final Date Final Time 01/14/04 10:00:47 Standard Deviation (Mlbslhr) 0.02068 Average Flowrate (Mlb/hr) 3.17167 Average Core Thermal Power (C047) 1592.54 Number of ERFIS data points (N.)

721 Number of Crossf low Data Points (N2) 493 M
-

Degrees of Freedom u t - for a 95% C.I..And Pooled (pooled: N. +N2 -2)

Degrees of Freedom = 1212 1212 1.96 Pooled Standard Deviation 0.01557 Confidence Interval Difference of Two Means (Mlb/hr)

Diff of Two Lower Limit 0.00161 Means 0.00339 Upper Limit 0.00517 Difference between the ERFIS and Crossf low Average Flowrates are Statisically Signficant.

A change to MAXFLOW Is required.

Crossflow Correction Term (Mlb/hr) 3.17346 3.169888582 3.17167 New MAXFLOW (millivolt) 3.98338 3.978901771 3.981140388 Percent Difference:

ERFIS to Crossflow Flowrates 0.05056 0.162901481 0.106730959 Percent Difference:

Original MAXFLOW to New MAXFLOW

-0.00952 0.102893011 0.046688728

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