05000346/LER-2003-002, Re Potential Degradation of High Pressure Injection Pumps Due to Debris in Emergency Sump Fluid Post Accident
| ML031330187 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/05/2003 |
| From: | Myers L FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NP-33-03-002-00 LER 03-002-00 | |
| Download: ML031330187 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(vii)(B), Common Cause Inoperability |
| 3462003002R00 - NRC Website | |
text
FENOC FirstEnergy Nuclear Operating Company 5501 North State Route 2 Oak Harbor, Ohio 43449 Lew W. Mers Chief Operating Officer 419-321-7599 Fax: 419-321-7582 NP-33-03-002-00 Docket No. 50-346 License No. NPF-3 May 5, 2003 United States Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Ladies and Gentlemen:
LER 2003-002 Davis-Besse Nuclear Power Station, Unit No. 1 Date of Occurrence - October 22, 2002 Enclosed please find Licensee Event Report 2003-002, which is being submitted to provide written notification of an issue with the High Pressure Injection pumps. The issue concerns the potential for debris from the Containment Emergency Sump impacting the High Pressure Injection pumps following a design-basis accident whereby the pump internals may be damaged to the extent they would not be able to complete their intended safety function. This issue was identified as part of the Davis-Besse Return to Service Plan inspections. This LER is being submitted in accordance with I OCFR50.73(a)(2)(i)(B), 1 OCFR50.73(a)(2)(ii)(B),
1 OCFR50.73(a)(2)(v) and 1 OCFR50.73(a)(2)(vii).
Evaluation continues with respect to determining the final corrective action. Additional information as a result of the evaluation and final decision described herein will be provided in a supplement to this report within 30 days following restoration of High Pressure Injection Pumps operability.
Very tuly yours, JSP/s Enclosures cc:
Mr. J. E. Dyer, Regional Administrator, USNRC Region III Mr. C. S. Thomas, DB-1 NRC Senior Resident Inspector Utility Radiological Safety Board
6
Docket Number 50-346 License Number NPF-3 NP-33-03-002-00 Attachment Page 1 of 1 COMMITMENT LIST The following list identifies those actions committed to by the Davis-Besse Nuclear Power Station in this document.
Any other actions discussed in the submittal represent intended or planned actions by Davis-Besse. They are described only as information and are not regulatory
commitments
Please notify the Manager - Regulatory Affairs (419-321-8450) at Davis-Besse of any questions regarding this document or associated regulatory commitments.
COMMITMENTS
DUE DATE Submit supplemental information regarding the apparent cause and safety significance of this occurrence.
30 days following restoration of HPI Pump operability
Abstract
On October 22, 2002, with the reactor defueled, a potential deficiency was identified for the High Pressure Injection (HPI) pumps during the recirculation phase of postulated loss of coolant accidents (LOCA) and when the HPI pumps are used for post-LOCA boron precipitation control.
The HPI pumps may be damaged due to potential debris generated by certain postulated LOCAs and entrained in the pumped fluid.
The HPI pumps may be subject to this debris after the pump suctions are switched over from the borated water storage tank to the discharge of the Low Pressure Injection Pumps, which are taking suction on the containment emergency sump.
The HPI pumps use a process-fluid lubricated hydrostatic radial bearing on the outboard end of the pump shaft.
The hydrostatic bearing, an inter-stage bearing, and wear rings may be damaged by debris or particles in the pumped fluid.
An evaluation is being performed to determine pump operability during postulated accidents.
In parallel with the evaluation, modifications to the system design to mitigate the effects of debris are being considered.
NRC FORM 366 (72001)
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Formn 366A) (17)
DESCRIPTION OF OCCURRENCE (continued):
blocking internal lubricating ports would be too dense to be transported to the sump.
Documentation provided in 1975 by the nuclear steam system supplier addressed the acceptability of the pump design to function when provided with fluid supplied from the containment emergency sump.
It was noted that particles which could deteriorate the pump are in the range of 0.004 in.
to 0.015 in.
These particles can pass through the mechanical seals and wear rings.
However, if the mechanical seals failed from these particles, it will not prevent the pump from performing its intended function of supplying fluid to the system at the required pressures.
The only other possible effect would be increased wear on the wear rings, which could result in a minor loss of efficiency (approximately 5% if the wear ring clearance is doubled), and a slight decrease in discharge pressure.
Again, this will not prevent the HPI pump from performing its intended function.'
The effect of these particles on the hydrostatic bearing was not addressed.
Communications with the current vendor for the HPI pumps identified clearances of various rotating parts and noted that debris that is small enough to pass through the bearing may cause localized erosion of mating material surfaces, but would not lead to imminent failure of the bearing.
The pump vendor also noted larger debris could block flow to the hydrostatic bearing, resulting in bearing damage.
On March 4, 2003, review of a spare hydrostatic bearing assembly revealed the existence of a threaded plug with a 0.11 inch diameter hole in each of the five feed holes (0.315 inch in diameter) to the bearing that was not documented in the vendor manual.
Since these openings are smaller than the sump screen openings, they may become clogged with debris.
It was also identified that the radial clearances on the impeller wear rings could be eroded by the debris, resulting in a reduction in pump efficiency and capacity.
Thus, although not quantified, a range of debris or particles was recognized that could possibly result in degradation of the HPI pumps.
The complete extent of potential HPI pump degradation due to debris in the pumped fluid has not yet been determined.
APPARENT CAUSE OF OCCURRENCE:
When the plant design was developed, the design of the HPI pump and the use of a hydrostatic bearing was apparently not adequately evaluated for the potential impact of post-LOCA debris that was smaller than the containment emergency sump screen openings.
Evaluation continues with respect to the apparent cause(s) of this issue, and pertinent additional information that may be developed will be provided in a revision to this report.
(If more space is required, use additional copies of NRC Forn 366A) (7)
ANALYSIS OF OCCURRENCE:
The HPI pumps are automatically started upon receipt of a Safety Features Actuation System (SFAS) [JE] signal with suction aligned to BWST to provide flow to the RCS.
Depending on the size of the postulated break, HPI Pump suction may switched over from the BWST to the LPI Pump discharge in order to maintain flow from the containment emergency sump to the RCS.
While the LPI pumps are utilized to mitigate the largest of RCS piping breaks, the HPI pumps are utilized on smaller breaks.
Additionally, the HPI pumps are utilized to control boron concentration post-LOCA that may result from boiling heat transfer within the core.
Technical Specification 3.5.2 requires that two independent ECCS subsystems be operable during Modes 1, 2, and 3. Each subsystem includes one Operable HPI pump with an Operable flow path initially from the BWST with suction transferred to the containment emergency sump during the recirculation phase of operation.
This condition is being reported under 10 CFR 50.73 (a)(2)(i)(B) as operation or condition prohibited by the plant's technical specifications since the condition existed for a time longer than permitted by the DBNPS Technical Specifications.
This condition is also being reported under 10 CFR 50.73 (a)(2)(v) as a condition that could have prevented the fulfillment of the safety function of a system needed to maintain the reactor in a safe shutdown condition and remove residual heat.
Likewise, this condition is being reported under 10 CFR 50.73(a)(2)(vii)(B) as a single condition that caused two independent trains to become inoperable in a single system designed to remove residual heat, and under 10 CFR 50.73 (a)(2)(ii)(B) as a condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety.
A non-emergency eight hour notification per 10 CFR 50.72 (b)(3)(ii)(B) was provided to the NRC as Event Number 39740 on April 7, 2003.
Evaluation into the safety significance of this issue is ongoing, and the results of the evaluation will be provided in a revision to this report.
CORRECTIVE ACTIONS
An evaluation is being performed to determine pump operability during postulated accidents.
Additionally, modifications to the system design to mitigate the effects of debris are being formulated, which may result in incorporation of strainers to eliminate debris or particles of concern, replacement of the bearing with a new design, or replacement of the entire pump.
The results of this evaluation, and the resultant modifications performed to restore operability of the HPI pumps will be provided in a revision to this report.
(If more space is required, use additional copies of NRC Form
PREVIOUS SIMILAR EVENTS
There have been no LERs in the previous two years involving similar deficiencies associated potential damage of hydrostatic bearings or other pump internals due to debris entrained in the pumped fluid.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
NP-33-03-002-00 CR 2002-08492, CR 2003-01738.