05000457/LER-2008-001, A Essential Service Water Train Inoperable Due to Strainer Fouling from Bryozoa Deposition and Growth
| ML083450328 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 12/08/2008 |
| From: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BW080117 LER-08-001-00 | |
| Download: ML083450328 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4572008001R00 - NRC Website | |
text
10 CFR 50.73 December 8, 2008 BW080117 U, S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Unit 2 Facility Operating License No. NPF-77 NRC Docket No. STN 50-457
Subject:
Licensee Event Report Number 2008-001-00 2A Essential Service Water Train Inoperable due to Strainer Fouling from Bryozoa Deposition and Growth The enclosed Licensee Event Report (LER) is being submitted in accordance with 10 CFR 50.73, Licensee event report system, paragraph (a)(2)(i)(B) as a condition prohibited by the plant Technical Specifications (TS). On October 8, 2008, Braidwood Station determined that the 2A Essential Service Water Train was inoperable from September 2, 2008 until September 6, 2008, which is longer then allowed by TS 3.7.8, Condition A. 10 CFR 50.73(a) requires an LER to be submitted within 60 days following discovery of the event. Therefore, this report is being submitted by December 8, 2008, 60 days from the October 8, 2008 discovery date.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. David Gullott, Regulatory Assurance Manager, at (815) 417-2800.
Respectfully, ryan Hanson Site Vice President Braidwood Station
Enclosure:
LER Number 2008-001-00
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMiSSION
~9-20O7 LICENSEE EVENT REPORT (LER)
(See reverse ior requtre num er Oi digits/Characters for each block)
APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 0831 2010 Estmated, the NRC may not conduct or sponsor, and a person s not requ red to respond to the nfnrm~tnr, nnh,~rtWn
- 1. FACILITY NAME Braidwood Station, Unit 2
- 2. DOCKET NUMBER
- 3. PAGE 05000457 1
OF 4
I. TITLE 2A Essential Service Water Train Inoperable due to Strainer Fouling from Bryozoa Deposition and Growth
- 5. EVENT DATE I
MONTH DAY YEAR
~
09 02 2008
.). OPERATING MODE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED Il
~OCKETNUMBER
~
MONTH DAY YEAR Braidwood Station, Unit 1 05000456
~LITYNAMED~NUMBER 2008 001 00 12 08 2008 N/A N/A
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check & that apply) 1 o 20.2201(b) 0 20.2203(a)(3)(i)
El 50.73(a)(2)(iXC)
[1 50.73(a)(2)(vii)
El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50,73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(vUi)(B)
El 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
El 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x) o 20.2203(aX2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)Øi)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
~
50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in The OW forebay inspection identified live bryozoa colonies in all six OW forebays (lA/B/C and 2AJB/O). The inspection results indicated that significant bryozoa mass existed in the Unit 1 forebays immediately upstream of the intakes that supply the 1A and 2A SX pumps. The bryozoa mass in the Unit 2 forebays immediately upstream of the intakes that supply the 1 B and 2B SX pumps was approximately 30% less than the Unit 1 side.
Live bryozoa was discovered previously in the OW forebays in October 2005 and in September 2002. During the previous events, all forebays indicated the presence of bryozoan colonies to varying degrees. In those instances, however, the amount of bryozoa present did not result in failure of flow rate surveillances, or a declaration of system inoperability. The corrective actions following the 2005 bryozoa event included mechanical cleaning of the forebays, completion of a lake bryozoa study forcontrol and mitigation of bryozoa, development of an adverse condition monitoring plan, and additional forebay inspections prior to and after the summer months.
Following the events of September 2008, a root cause evaluation was performed. This evaluation determined two causes of the 2008 event:
1.
The site organization did not understand the bryozoa life cycle and the bryozoa deposition and growth mechanism downstream of the OW forebay traveling screens. The previously established bryozoa monitoring plans did not inspectfor byrozoa during peak growth periods, and sampling skids installed on the bar racks just outside the forebays were not indicative of the bryozoa growth and deposition near the SX pump intakes.
2.
A lack of questioning attitude existed regarding the SX strainer designs ability to address rapid fouling challenges. Previous reviews for re-affirming the SX strainer design basis did not fully consider what could occur to cause rapid strainer fouling events nor how these events could negate the compensatory actions that the station could take to restore the strainers.
).
Safety Consequences
There were no actual safety consequences as a result of this event. Both units remained at 100% power and non-essential power [EA] was available to support the SX strainer backwash function.
The impacts of bryozoa on safety related heat exchangers were reviewed using current and five year historical data. There has been no reporting of live bryozoa in safety related plant systems. Periodic maintenance inspections of the safety related heat exchangers confirm that current chemical treatment, flushing, and operating practices are sufficient to maintain equipment in a condition that meets the requirements of NRC Generic Letter (GL) 89-13, Service Water System Problems Affecting Safety-Related Equipment, and ASME Code Inservice Inspection (ISI) standards.
The evaluation of the effects of the bryozoa fouling indicates that both units and trains of SX strainers were capable of mitigating the effects of bryozoa into the SX system when non-essential power was maintained to the SX strainer backwash components.
Power can be restored to strainer backwash in the event of LOOP. The non-essential buses servicing the strainer backwash components can be powered from the emergency diesel generators [EK] by closing the essential to non-essential power crosstie breaker. This evolution is governed by procedure, and operators are trained to perform this activity.
An evaluation is being performed to determine the bounding impact on the SX system, the plants ability to mitigate events, and the associated change in risk. A supplement to this report will be issued with the conclusions of this evaluation and the associated risk impact.
Corrective Actions
Corrective actions to prevent recurrence include:
1.
Development and implementation of a lake macro-biological program, to include; 1) monitoring, 2) inspection, and 3) mitigation. This will provide the strategies and bases for monitoring of bryozoa and other biological challenges in the lake and the forebays, inspections of forebays, and forebay cleaning threshold ensuring that the GL 89-13 program requirements are met.
2.
Establishment of a process for utilization of a Devils Advocate in situations where key decisions are made for the performance of the safety related systems.
Additional Corrective Actions include:
1.
Installation of a mechanical debris removal system such as a sparger to provide flushing capability to prevent accumulation of bryozoa (and other materials) downstream of the traveling screens during summer months.
2.
Evaluate use of a non-intrusive forebay monitoring system for monitoring bryozoa growth and deposition in the forebays.
3.
Develop actions to improve the design of the SX pump discharge strainers by providing the SX pump discharge strainers power supply, alarms and controls with a permanent safety related power source.
4.
Development of a case study of this event, and provide in continuing training for appropriate Braidwood Station personnel.
Previous Occurrences
There have been no similar Licensee Event Report events at Braidwood Station in the last three years.
Two other events occurred at Braidwood Station relating to SX strainer differential pressure and bryozoa growth in the circulating water forebays:
September 2002:
During forebay inspections, silt buildup and bryozoa growth was found.
October 2005:
Bryozoan growth discovered following SX strainer differential pressure alarms. An equipment apparent cause evaluation was performed. Corrective actions included mechanical cleaning of the forebays, completion of a lake bryozoa study for control and mitigation of bryozoa, development of an adverse condition monitoring plan, and additional forebay inspections prior to and after the summer months.
. Component Failure Data:
Manufacturer Nomenclature Model Mfq. Part Number N/A N/A N/A N/APRINTED ON RECYCLED PAPER