05000335/LER-2018-001, Feedwater Heater Level Control Malfunctions Resulted in Lowering Steam Generator Water Level and Manual Reactor Trip
| ML18360A041 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 12/26/2018 |
| From: | Deboer D Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2018-236 LER 2018-001-00 | |
| Download: ML18360A041 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3352018001R00 - NRC Website | |
text
U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Re:
St. Lucie Unit 1 Docket No. 50-335 Reportable Event: 2018-001-00 Date of Event: October 29, 2018 D'EC 2 6 lU1ij Feedwater Heater Level Control Malfunctions Resulted In Lowering Steam Generator Water Level and Manual Reactor Trip L-2018-236 10 CFR 50.73 Licensee Event Report 2018-001 is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.
Respectfully, Daniel DeBoer Site Director St. Lucie Plant DD/ KWF Attaclunent cc:
St. Lucie NRC Senior Resident Inspector St. Lucie NRC Program Manager Florida Power & Light Company 6501 S. Ocean Drive, Jensen Beach, FL 34957
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150*0104 EXPIRES: 0313112020 (04-2018)
Estimated burden per response to comply with this mandatory ccllection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
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Reported lessons teamed are incorporated into the licensing process and fed back to industry.
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Send comments regarding burden estimate to the FOIA, Privacy and Information Collections
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- Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail
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LICENSEE EVENT REPORT (LER) to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory (See Page 2 for required number of digits/characters for each block)
Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a (See NUREG-1 022, R.3 for instruction and guidance for completing this form means used to impose an information ccllection does not display a cunently valid OMB centro!
htt~://www.nrc. govlreading-rm/doc-collectionslnuregslstalf/sr1022lr3D number, the NRC may not ccnduct or sponsor, and a person is not required to respond to, the information ccllection.
- 3. PAGE St. Lucie Unit 1 05000335 1 OF 4
- 4. TITLE Feedwater Heater Level Control Malfunctions Resulted In Lowering Steam Generator Water Level and Manual Reactor Trip
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.
MONTH DAY YEAR n/a 05000 FACILITY NAME DOCKET NUMBER 10 29 2018 2018 -
001 -
0 12 26 2018 n/a 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 0 20.2201(b) 0 20.2203(a)(3)(i) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) 0 20.2201(d) 0 20.2203(a)(3)(ii) 0 50. 73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B) 1 0
0 0 20.2203(a)(1) 0 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 0 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A)
~ 50. 73(a)(2)(iv)(A) 0 50.73(a)(2)(x)
- 10. POWER LEVEL 0 20.2203( a)(2)(ii) 0 50.36(c)(1)(ii)(A) 0 50. 73(a)(2)(v)(A) 0 73.71 (a)(4) 0 20.2203(a)(2)(iii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(B) 0 73.71 (a)(5) 0 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(C) 0 73.77(a)(1) 100 0 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(D) 0 73.77(a)(2)(i) 0 20.2203(a)(2)(vi) 0 50. 73(a)(2)(i)(B) 0 50.73(a)(2)(vii) 0 73.77(a)(2)(ii) 0 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in The non-nuclear safety HVD system has no safety functions and is designed to increase plant efficiency by increasing the temperature of the feedwater entering the steam generators. This is accomplished by pre-heating the condensate/feedwater using a series of heat exchangers called feedwater heaters. There are two FWH trains, each train has 5 FWHs. The feedwater heaters are tube and shell heat exchangers with sub-cooled condensate/feedwater flowing through the tubes and a saturated steam/water mixture on the shell side.
The heat given up to the feedwater causes the steam to condense and collect in the bottom of the heater shell where it then "drains" to the next lower pressure heater. The drain flow is not contiguous from high temperature to low temperature heater and into the condenser. It is split in the middle of each train, with condensate from heaters #5, #4 and the drain cooler all being returned to the feedwater (tube-side) by the heater drain pumps.
The condensate from heaters #3, #2, and #1 all ends up in the main condenser(s).
Heater level control is accomplished by the operation of level control valves specified as the normal and alternate drain valves. The normal drain valves maintain heater level by routing heater shell-side condensate to a downstream heater, or in the case of the #4 FWH, to its associated drain cooler tank. On above normal level, the alternate drain valves open and dump excess condensate directly into the main condenser.
The malfunction of the 4B FWH normal level controller prevented the normal level control valve from fully opening, reducing the drain cooler effluent flow to the main feedwater system. Additionally, as the 4B FWH shell side condensate level increased, the malfunction of the 4B FWH alternate level controller did not allow the alternate level control valve to modulate flow, so the valve went from full open to full close as the water level approached the water level control setpoints. The diversion of drain cooler flow from the feedwater system to the condenser resulted in the lowering SG water level.
The extent of condition evaluation results conclude that the Unit 1 and Unit 2 #1, #2, #3, and #4 FWHs use the same level controllers. The #1, #2, and #3 FWHs do not have a significant impact on heater drain pump performance or main feedwater pump performance and therefore, would not cause a similar result if they were to fail. The Unit 1 and Unit 2 #5 FWHs and the MSR drain collectors use digital controllers and are not susceptible to the same failure modes. Therefore the MSR, #5, #3, #2, and #1 FWH level controls are excluded from the extent of cause evaluations for the identified failure modes.
Based on the cause of the normal valve controller failure mode internal visual inspections of the normal level control valve controller level column for the Unit 1 4A FWH, Unit 2 4A FWH, and Unit 2 4B FWH will be performed to check for latent foreign material. Interim procedural controls are in place to enhance operator awareness of the issue until the inspections are complete.
0 Based on the cause of the alternate valve controller failure mode for the normally closed #4 FWH alternate drain valves, controller preventative maintenance calibration and overhaul frequencies have been increased from every 4 refueling outages to 1 R (calibration) and 3R (overhaul).
Safety Significance
When the low pressure 4B FWH normal level control valve could not maintain level in the heater, the alternate level control valve oscillations diverted flow from the 4B heater drain pump directly to the condenser. This resulted in decreased feedwater flow and decreasing steam generator level. The lowering level quickly reached the 50 percent narrow range operating limit, necessitating a manual trip of Unit 1 per procedure. The trip was uncomplicated. The Unit 1 risk remained Green. Unit 1 remained offline for approximately 1 day to complete troubleshooting and recovery.
The HVD and the main feedwater systems do not perform a safety function in the delivery of feedwater flow and are not required to mitigate the consequences of a design basis accident. The auxiliary feedwater (AFW) system provides feedwater for accident mitigation and low power conditions. SG level was maintained post-trip such that AFAS did not actuate.
All safety related systems functioned as designed. There were no safety systems actuations as a result of the trip. Given the response of the plant and the actions taken, the health and safety of the public was not affected by this event.
Corrective Actions
0
- 1. Foreign material was removed from the 48 FWH normal drain valve controller and the calibration check was performed satisfactorily.
- 2. The 48 FWH alternate drain valve controller was replaced.
- 3.
Internal visual inspections of the Unit 1 4A and Unit 2 4A and 48 FWRs normal drain valve controller level columns are scheduled.
- 4. Interim procedural controls are in place to enhance operator awareness of the issue until the inspections are complete.
- 5. Additional PM tasks on the Unit 1 and 2 #4 FWH alternate drain valve controllers will be added to perform the #4 FWH alternate level control valve controller calibration PM on a 1 R frequency and overhaul PM on a 3R frequency.
Failed Components Identified Tags:
Manufacturer:
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