ML24057A303

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Attachment 1: Braidwood Station Regulatory Conference Information
ML24057A303
Person / Time
Site: Braidwood Constellation icon.png
Issue date: 02/26/2024
From:
Constellation Energy Generation
To:
NRC/RGN-III
Shared Package
ML24057A301 List:
References
BW240007
Download: ML24057A303 (1)
v • d • e


Text

-~

.~t* Constellation.

Braidwood Clean Energy Center Diesel Driven Auxiliary Feedwater (AF)

Pump Regulatory Conference

Constellation Representatives

~ Greg Gugle Donnie Hudak

,, Steve Macartney

" Kevin Mores

~ Gary Thompson

,. David Gullatt

" Kevin Lueshen Site Vice President, Braidwood Plant Manager, Braidwood Director Engineering, Braidwood Senior License Holder and Operations Senior Manager, Braidwood Diesel Technical Expert, MPR Vice President Licensing and Regulated Programs, Constellation Director of Licensing, Constellation

~ Roy Linthicum Senior Manager, Risk Management, Constellation

" Marri Marchionda-Palmer Senior Vice President Operations, Constellation

~

~.c' Constellation

2 Agenda

~ Purpose

,. Overview and Timeline & Causal Product

~ Engineering Analysis of Lube Oil Dilution Testing

  • - Test Engine Selection & Differences
  • - Leakage Considerations Lube Oil Considerations
    • - Load Profile Evaluation Industry Operating Experience Conclusion of Testing

~ Greg Gugle, Site Vice President

@ Donnie Hudak, Plant Manager Steve Macartney, Director Engineering

~ Risk Sensitivity Evaluation and Operations Response

~ Roy Linthicum, Sr. Mgr. Risk Management Risk Sensitivity Evaluation Operator Response to Loss of Heat Sink

  • -* Additional Margin from FLEX

" Constellation Perspective

@ Closing Remarks

" Kevin Mores, Braidwood Senior License Holder

$ David Gullatt, VP Licensing & Regulated Programs

@ Marri Marchionda-Palmer, Sr. VP Operations j ~

~,; Constellation

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Purpose

~ Provide a comprehensive overview of the event, causal analysis, and corrective actions

~ Establish a common understanding of the factors that influence the final significance of the Regulatory Finding:

Impact of lube oil dilution on continued operation of diesel driven Auxiliary Feedwater (AF) pump Use of FLEX strategies to provide feedwater to steam generators in a loss of heat sink scenario Communicate the potential risk impact of the performance deficiency

~,* Constellation

4 Preliminary Greater-than-Green Finding

~ Apparent violation of 10 CFR 50, Appendix B, Criterion XVI, Corrective Actions

-Failed to document anomalous lube oil sample results in Corrective Action Program (CAP) and correct issue

~ NRC finding determined to be preliminarily of greater than very low safety significance

-Preliminary evaluation concluded increase in Core Damage Frequency (ilCDF) related to 2B AF Engine lube oil dilution is greater than green

~** Constellation

5 Overview and Timeline - Oil Sample Anomalies and Corrective Actions

., May 2023 - 28 AF Engine maintenance completed during refuel outage, Post-Maintenance Testing (PMT) run completed satisfactorily, oil sample drawn June 2023 - Oil sample results returned, indicating viscosity outside of expected range and no data for Fuel Oil Concentration was recorded

.. September 2023 - 2B AF Pump quarterly run complete, oil sample drawn September 21st - Initial oil sample results indicate viscosity and fuel oil concentration exceeding procedural acceptance criteria, confirmatory samples performed September 23rd - Results received confirming initial sample results, 28 AF Pump removed from service, repairs were performed, and lube oil drained and refilled. 28 AF pump returned-to-service. PMT run completed satisfactorily.

.. October 2023 - 28 AF Pump removed from service for engine bearing inspection, additional fuel leak identified and repaired, all fuel injectors replaced, and 2B AF Pump returned to service. PMT run completed satisfactorily.

,M1~, Constellation

6 Overview and Timeline - Test Diesel Engine

" November 2023 - Same model test diesel engine procured and arrives on site in Texas for set-up and tuning. Initial test runs were performed to set baseline operating conditions and ensure performance consistent with our installed AF diesel engines.

,, December 2023 - Lube Oil Dilution testing complete. Test diesel engine ran for 24.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> with continuous dilution of lube oil and no degradation in performance.

- Following testing, a controlled engine shutdown was completed per approved test plan.

" January 2024-Final MPR test report received and accepted via formal Engineering Product

~

.t
:" Constellation

7 Causal Product Investigation Conclusions and Extent of Condition Root Cause/Contributing Cause

" Vendor performance/quality control gaps in refurbishing quality level 1 fuel injectors (Root Cause)

~ Personnel behaviors, oil sampling, and analysis process did not identify abnormal conditions (Contributing Cause)

" The model work order did not include a fuel system pressure test (Contributing Cause)

Corrective Actions

" Discontinued use of faulty parts

~ Addressed site accountability in the oil sample reviews & improved the review process

., Ensured engine overhaul work instructions include pressure testing fuel injectors prior to return to service

.. Fleet-wide corrective actions related to oil sampling/testing requirements and behavioral lessons learned Extent of Condition

~ Historical oil sample results and fuel injector parts for 1B AF pump were reviewed

" Other site diesel engines were reviewed and do not have same design considerations

., Part 21 Submitted by vendor in December 2023, parts removed from sites and returned to vendor

        • Constellation

8 Engineering Analysis of lube Oil ilution Impact

  • Constellation explored methods to evaluate impact on 2B AF diesel performance with high fuel concentration in lube oil

- Industry expertise was engaged to assist in evaluation (MPR)

Engineering and MPR determined that no applicable analytical methods of evaluation exist

  • Constellation procured a diesel engine to perform empirical testing to assess the impact of lube oil dilution on 2B AF diesel performance

- Tested same model diesel engine (Detroit Diesel Model 149)

MPR performed detailed engine comparison and established test plan

--- Dilution testing was performed by Southwest Research Institute (SwRI) at the SwRI Locomotive Technology Center in San Antonio, Texas Purpose of the test: Simulate same conditions experienced at Braidwood to understand impact of lube oil dilution on engine's ability to operate for Technical Specification and PRA mission time

~

~,, Constellation

9 Test Engine Selection

" Both are Model 149 engines manufactured by Detroit Diesel Company Two-stroke diesel engines with four turbochargers Same displacement per cylinder, cylinder bore, and stroke length, with similar continuous rating per cylinder Plant and Test engine speeds were matched Main seals are common design e Differences between the engines Plant Engine has 16 cylinders vs. 12 cylinders for the Test Engine

-- Test Engine has more than twice the run time of installed Plant Engine

=,,,, Constellation

10 Analysis of Test Engine Differences

'I> Air intake temperature Bounding Plant Engine design would be 47°F higher than Test Engine (140°F vs. 93°F)

" Jacket Water (JW) heat exchanger has sufficient cooling margin to account for higher temperatures Expect lube oil and JW to have small temperature increase with minimal impact on lube oil pressure and viscosity

.. lntercooler (cools compressed air from turbocharger)

.. _ Test Engine did not have intercooler like the Plant Engine

" Results in higher temperatures in Test Engine than Plant Engine (conservative)

.=,:,' Constellation

11 Analysis of Test ne Differences Turbochargers Plant Engine turbos are insulated whereas Test Engine is not Visual monitoring was in place as a compensatory measure (nothing noteworthy observed)

" Lube oil is cooled by jacket water (with sufficient margin), both system parameters remained stable during testing Nearly identical design, similar size, and operate at similar speed Temperatures not recorded on Test or Plant Engine

~

,!4,::-, Constellation

12 Leakage Considerations e Leak rate Plant Engine oil analysis results and collective runtime duration (6.39 hours4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br />) determined leak rate Leak rate was scaled to Test Engine lube oil volume

... Plant Engine leak was due to mechanical defect on a sealing surface of injectors

-- Leak rate remains constant with the mechanical defect

-- Testing also concluded load changes do not influence fuel pressure or leak rate 11 Leak location Plant Engine leak was above cylinder head and Test Engine simulated leak was into oil pan Flow path in Test Engine is representative of Plant Engine (passages from top of engine down to oil pan)

-- No stratification will occur as both oil pumps produce >100 GPM of lube oil flow creating sufficient recirculation

  • k Constellation

13 Lube Oil Considerations

~ Oil Level Test Engine has smaller oil capacity Accounted for in test plan development

,. Oil level conservatively reaches reciprocating components and creates seal leakage earlier on Test Engine

@ Burn Rate

-- Test Engine burn rate scales proportionally to Plant Engine due to cylinder design similarities Test Engine burning of diluted lube oil is representative of the Plant Engine as lube oil volume is only replenished by leaking fuel Scaled burn rate and larger oil system volume in the Plant Engine are accurately represented in Test Engine

.~

t Constellation

14 Load Profile Evaluation Loading of the Test Diesel:

  • Plant Engine loading was simulated and scaled to the Test Engine

~

24 hr. profile was determined from the maximum of the following:

-- Design Basis Accident (OBA) fuel consumption calculation

- PRA thermal-hydraulic analysis

- Natural circulation cooldown

  • Actual loading for each test interval was 1-5% higher than the test plan 750

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Actual Dilution Test Load Profile

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10 lS 20 25 Elapsed Test Time (hrs)

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15 Bearing Performance i!

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Note: #3, #6, and #7 bearing pictures in the MPR report show consistent results.

" Low viscosity lube oil can lead to bearing failure

  • Lube oil system adequately maintained heat load
  • Impact on Bearings:

Condition of the main bearings, pre/post test, were unchanged with no signs of abnormal degradation Main bearing inspections show the lubrication film barrier was maintained with high lube oil dilution No signs of metal-to-metal contact during testing No increase in wear metal concentrations recorded during post test lube oil analysis.

" Results support that other lubricated components (e.g., engine/turbocharger bearings) were not damaged

~

'" Constellation

16 Lube Oil Analysis and Concentration Measured fuel concentration in the lube oil sample results were lower than actual fuel concentration The oil sample analysis methodology initially used was per ASTM D3524 standards in accordance with the vendor manual. This test method identifies a lower fuel concentration limit than the test conditions and is not normally calibrated above the limit. This should have been identified in the original test plan preparation.

-- An alternative analysis method was developed to determine accurate fuel concentrations based on the dilution of lube oil additive elements

~ Upon receipt of the results, actual fuel concentration was lower than identified in the test plan

--- The drained engine contained a small volume of residual undiluted lube oil when the diluted oil was added prior to the test, reducing the overall initial fuel concentration

-- This was anticipated and included in the preparation of the diluted oil, but the estimated residual lube oil volume was less than the actual residual volume

-- The fuel oil addition rate was achieved per the test plan and confirmed by frequent weight checks

  • = Constellation

17 Viscosity Test Results Initial measured viscosity matched the as-tound plant engine viscosity Test analysis determined 6 additional hours of run time would achieve the target final concentration The dilution test adequately simulated the conditions that the Plant Engine would have encountered 10 Pure Lube Oil 1-l li

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2B AF Engine Diluted LO Test

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18 Oil Pressure and Temperature Performance 70 en ~'"~3/4----

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  • Diluted Test
  • Lube oil pressure lowered by 7 psig over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> with significant margin remaining to acceptance criteria
  • No adverse impact to bearing performance expected over at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />
      • Constellation

19 OU Seal Inspection Oil and fuel was observed leaking from the rear side of the Test Engine during dilution testing (expected condition per vendor)

External leakage was not tested due to contamination (contact with test cell floor)

Post test inspection results of rear main seal:

Dust shield had minor damage (no impact)

Seal assembly was intact in correct installation position and orientation with no damage (other than dust shield)

,~

Seal leakage:

Removes lube/fuel oil mixture while only fuel is added to lube oil system Seal leakage increases fuel oil concentration Common seal design for both Plant and Test Engine

~

,=;, Constellation

20 Industry Operating Experience (OE)

No Direct Operating Experience for a Detroit Diesel Engine.

Surry Power Station (SPS) LER 84-027-00 Emergency Diesel Generator (EDG) turbocharger bearing failure and subsequent fire with 40% lube oil dilution Differences of OE to Test and Plant Engine:

Surry turbocharger was a vulnerable design as noted in EPRI Manual 3002004359 and GL 84-15

~ Industry turbocharger failure occurrences were experienced in the Electro Motive Diesel EDG design

,, Vulnerabilities subsequently addressed by the industry Engine failure occurred at seven minutes after start with significantly higher initial fuel concentration

- Surry turbochargers utilize gear drive and clutch assembly which the Detroit Diesel does not have

,,, Less subcomponent failure modes in the simpler Detroit Diesel turbocharger design

-- Detroit Diesel turbocharger operates with larger lubrication margin due to higher operating speed and slower starting sequence compared to the Surry EDG. Detroit Diesel vendor guidance does not include turbocharger inspection following a dilution event.

-, During the Braidwood 2B AF demonstration test, the turbocharger did not display any abnormalities

. ~

~" Constellation

21 Conclusion of Testing

  • The Dilution Test demonstrates the ability of the 2B AF Diesel Engine to perform its safety function and operate beyond its Technical Specification and PRA mission times

- Actual test loads exceeded accident requirements

      • Lube oil pressure was maintained (with margin)

- Jacket Water (JW) temperature remained stable during testing (Note: Plant Engine JW cooler is oversized)

The main bearings showed no abnormal wear Lube oil analyses showed no increase in wear metal concentrations Test provides assurance that film barrier would be maintained on the Plant Engine Main seals are same design (Test Engine results are representative of the Plant Engine)

-- Lube oil recirculation rate prevents the diluted oil mixture to stratify

" This ensures fuel will not settle on top and flow out of seal first

.=r Constellation

22 Risk Sensitivity Evaluation e Based on best available information, 2B AF Engine was always operable and capable of meeting its PRA mission time (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />)

~ Sensitivity Evaluations were performed to determine the risk significance assuming the engine would not have met its PRA mission time

.. NOTE:

SPAR Model and Braidwood Model are in close alignment following changes to both to ensure as-built as-operated modeling

  • -Use of similar assumptions yields similar SOP results

.~

="' Constellation

23 Critical Sensitivity Assumptions

~ Engine testing is representative of installed engine 4J Results of Detroit Diesel test engine impact on the model sensitivities

-"-Engine loading is conservative

  • -Engine run time

~ Minimum run time of 1.88 hours0.00102 days <br />0.0244 hours <br />1.455026e-4 weeks <br />3.3484e-5 months <br /> allows sufficient time for alternate Steam Generator feed sources (e.g., Medium Head FLEX pump)

,~

i1t,, Constellation

24 AF Engine Runtime and Available Time to Restore Steam Generator Feed

  • Following a reactor trip, additional personnel are called according to Braidwood's Forced Outage Plan.
  • With minimum assumed runtime, additional resources would be available to align FLEX equipment per Braidwood procedures AF Engine Run time after reactor trip Time Available to Implement FLEX after AF Engine Failure 1.88 hours0.00102 days <br />0.0244 hours <br />1.455026e-4 weeks <br />3.3484e-5 months <br /> 4 hours 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> 4.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 3 hours 4.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> 4 hours 4.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> 12 hours 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />

~z,,, Constellation

25 28 AF Engine Extended Run Time Benefits

~ Longer engine run times provides significant benefit in Operator response

-- Post trip actions would be completed

., Reduced operator stress Not working in multiple procedures simultaneously Lower reactor decay heat slows Steam Generator dryout, providing additional time to complete actions and reducing Human Error Probabilities Additional resources would be available to support FLEX deployment

~ For Fire events, fire response would be completed Ii For Non-Fire events, additional time allows improved likelihood of recovery offsite power

~~, Constellation

26 28 AF Pump Fail-to-Run (FTR) Sensitivity (No Additional Margin) e Best available information supports no change to nominal failure probabilities

" Results do not quantitatively credit extended engine run time 2B AF Pump FTR Probability Comparison to IMC 0609 Thresholds No Change {2.7%)

0 2x Failure Probability (5.4%)

8E-7 10%

2E-6 50%

8E-6 Assumed Failure (100%)

2E-5

~*** Constellation

27 Operator Response to Loss of Heat Sink T-+10:0;4, '

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13 Minutes from complete loss of FW to direction to EOs to use Medium Head FLEX pumps - Modeling assumes 20 minutes

~° Constellation

28 Additional Margin from FLEX G Model utilizes Human Error Probability (HEP) of 6E-2 for the Medium Head (MH) FLEX pump, with suction from the Refueling Water Storage Tank (RWST), to inject water into the steam generator developed in accordance with PRA standards

  • Simulator exercise confirmed prompt implementation of FLEX

~Assumes no AF flow at time of reactor trip Post reactor trip actions performed concurrent with actions to recover SG Flow

-~

..=fh Constellation

29 Additional Margin from FLEX e HEP timeline uses 20 minutes after plant trip as the point at which the operators are directed to align the MH FLEX pump Operators required 13 minutes, demonstrated in the simulator under higher stress conditions than would be expected with pump running for 1.88 hours0.00102 days <br />0.0244 hours <br />1.455026e-4 weeks <br />3.3484e-5 months <br />

, Performed concurrent with post-trip actions Demonstrates adequate procedures, training, cues, and time to successfully complete this task, confirming PRA credit is acceptable

@ BwFR-H.1 Step 13.b clearly directs use of the MH FLEX pump to feed Steam Generators "TRY TO ESTABLISH FEED FLOW FROM ANY AVAILABLE LOW PRESSURE SOURCE TO AT LEAST ONE SG: Align one of the following feedwater sources with the final isolation valve closed: Medium head FLEX pump per 2BwFSG-3, ALTERNATE LOW PRESSURE FEEDWATER" 0 Operators are highly trained and well-practiced in implementing hose alignments

, Constellation

Combined Sensitivity Results FLEX HEP

  • 6.3E-2 0.3 No Credit 2B AF Pump FTR (Total Failure (Total Failure (Total Failure Probability::: 0.3)

Probability::: 0.5)

Probability =1.0)

Probability

  • No Change (2.7%)

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4E-6 6E-6 'Pact 8E-6 Assumed Failure 8E-6 lE-5 2E-5 30

~, Constellation

31 Constellation Perspective lmpactful event for Braidwood Station and Constellation fleet Actions taken to improve parts quality and correct organizational causes

--- Fleetwide actions: changes to oil sampling/testing requirements, behavioral lessons shared

~ Tested Detroit Diesel Series 149 model engine to understand impact of lube oil dilution No measurable or observable impact to performance during 24-hour test

- Safety maintained - engine remained operable and capable of performing design basis safety function Differences in test engine and test performance do not impact conclusion

.. IMC 0609, Appendix A, Exhibit 2.A "Mitigating SSCs and PRA Functionality" questions should be answered "NO" - screen to green Dilution did not result in a loss of safety function or PRA function (function and mission times met)

  • Detailed Risk Evaluation must consider dilution test as best available information
      • No technical basis to use an expected engine failure rate beyond baseline

-- Doubling of baseline failure rate still results in LlCDF below lE-6 threshold

    • - FLEX strategies provide additional margin below threshold due to available implementation time

~" Constellation

Closing Remarks

~

32

~,,,, Constellation

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