05000498/LER-2014-001, Regarding Overpower Condition Relating to the Ultrasonic Flow Measurement System
| ML14119A068 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 03/24/2014 |
| From: | Gerry Powell South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-14003113 LER 14-001-00 | |
| Download: ML14119A068 (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)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 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)(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 |
| 4982014001R00 - NRC Website | |
text
V Nuclear Operating Company South Texas Pro/cd Electrc Generating Station P.. Box 289 adswortih. Tex-77483 March 24, 2014 NOC-AE-1 4003113 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Unit 1 Docket No. STN 50-498 Licensee Event Report 2014-001-00 LER 2014-001-00: South Texas Project (STP) Unit 1 Overpower Condition Relating to the Ultrasonic Flow Measurement System Pursuant to 10 CFR 50.73(a)(2)(i)(B) Condition prohibited by Technical Specifications, STP Nuclear Operating Company (STPNOC) submits the attached South Texas Project (STP) Unit 1 Licensee Event Report (LER) 2014-001-00 regarding overpower event that occurred in STP Unit 1 relating to the Ultrasonic Flow Measurement System.
This event did not have an adverse effect on the health and safety of the public and is further discussed in the Attachment.
There are no commitments in this letter. Corrective actions will be implemented in accordance with the STP Corrective Action Program.
If there are any questions, please contact Jim Morris at (361) 972-8652, or me at (361) 972-7566.
G. T. Powell Site Vice President RJG
Attachment:
Unit 1 LER 2014-001-00, South Texas Project (STP) Unit 1 Overpower Condition Relating to the Ultrasonic Flow Measurement System STI: 33847259
NOC-AE-14003113 Page 2 of 2 cc:
(electronic copy)
(paper copy)
Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 1600 East Lamar Boulevard Arlington, TX 76011-4511 Balwant K. Singal Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (MS 8 B1) 11555 Rockville Pike Rockville, MD 20852 NRC Resident Inspector U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MNl16 Wadsworth, TX 77483 Jim Collins City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 A. H. Gutterman, Esquire Morgan, Lewis & Bockius LLP Balwant K. Singal U. S. Nuclear Regulatory Commission John Ragan Chris O'Hara Jim von Suskil NRG South Texas LP Kevin Polio Richard Pelia L. D. Blaylock City Public Service Peter Nemeth Crain Caton & James, P.C.
C. Mele City of Austin Richard A. Ratliff Robert Free Texas Department of State Health Services NRC FORM 366 (02-2014)
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01131/2017 (02-201 4)
(02,201,4 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections SLICENSEE EVENT REPORT (LER)
Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget Washington, DC for each block) 20503. If a means used to impose an information collection does not display a currently valid OMB digits/characters
)control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE South Texas Unit 1 2014-001-00 05000498 1 OF 5
- 4. TITLE South Texas Project (STP) Unit 1 Overpower Condition Relating to the Ultrasonic Flow Measurement System
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED
- 1 I~
rFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FA NUMBER NO.
N/A N/A FACILITY NAME DOCKET NUMBER 01 23 2014 2014-001
- - 00 03 24 2014 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[1 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 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)
[] 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
__ 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
[E 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL 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)
El 20.2203(a)(2)(iii) 5l S0.36(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)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 1 8 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) 0 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify 3i6Absractbeloworin
- 12. LICENSEE CONTACT FOR THIS LER LEE CONTACT 12. LTELEPHONE NUMBER (Include Area Code)
Jim Morris 361-972-8652CAUSE SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TO EPIX D
SJ Fl AMAG N
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION 0
YES (Ifyes, complete 15. EXPECTED SUBMISSION DATE)
El NO DATE 4
30 2014 NBSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
This LER is being submitted due to an overpower event that occurred in South Texas Project (STP) Unit 1. It was discovered that the ultrasonic flow Feedwater correction factors had been trending in a non-conservative direction since installation resulting in an overpower of approximately 1.8% (max) for the period of 2.5 years.
Pipe wall thickness measurements were then taken in the Unit 1 Feedwater piping in the vicinity of the Ultrasonic Flow Measurement System (UTF), and it was determined that pipe wall thicknesses were less than the original values resulting in increased flow diameters. The overpower condition in Unit 1 resulted in reactor trip instrumentation being inoperable longer than allowed by Technical Specifications (TS), thus reportable under 50.73(a)(2)(i)(B) Condition prohibited by TS. The Root Cause for this event is that the STP License Amendment Request implementation process did not require a formal, documented review of plant specific requirements and recommendations from vendor supplied documents that are used as a basis for a license amendments. The corrective action to prevent recurrence of this event is to develop or revise a Licensing procedure accordingly to require a formalized, documented review.
- 1.
DESCRIPTION OF EVENT
A.
REPORTABLE EVENT CLASSIFICATION
This event is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) as a Condition prohibited by Technical Specifications.
B.
PLANT OPERATING CONDITIONS PRIOR TO EVENT
Unit 1 was operating in Mode 1 at 100% indicated power, (101.8% actual).
C.
STATUS OF STRUCTURES, SYSTEMS, AND COMPONENTS THAT WERE INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT The Unit 1 overpower value of approximately 1.8% was above the Trip Setpoint Total Allowable value for the Power Range Nuclear Instruments (PRNI) High Trip. The Unit 1 overpower value exceeded the PRNI High Total Allowable value by 0.1%. This exceedence has been attributed to gradual pipe erosion which has taken place since the UTF was commissioned in 1999. Thus, this instrumentation was inoperable longer than the associated allowed outage time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
A reportability evaluation was performed that recommended that this issue be considered REPORTABLE against 50.73(a)(2)(i)(B) - as "Any operation or condition which was prohibited by the plant's Technical Specifications", i.e. Reactor Trip PRNI High Set-points Exceeding the Total Allowable Value of TS 2.2.1, and the associated allowable outage time of LCO 3.3.1.
D.
NARRATIVE SUMMARY OF THE EVENT
The Unit 1 Correction Factors for the UTF had been trending in the non-conservative direction since initial installation. After measuring the feed water piping, it was identified that feed water pipe internal diameter measurements were outside the allowances of the UTF calculation. Preliminary analysis indicates that STP Unit 1 exceeded operating limits for thermal output for at least 2.5 years. This condition occurred because pipe internal diameters were not periodically monitored, and the results of the monitoring were not used as a basis to update the calculation.
This condition also occurred in STP Unit 2. This is not reportable in Unit 2 since all the technical specification requirements were met and did not exceed the system set-point allowable values.
E.
METHOD OF DISCOVERY
After measuring the feed water piping in December 2013, it was identified that feed water pipe internal diameter measurements were outside the allowances of the respective UTF calculation. Preliminary analysis indicates that STP Unit 1 exceeded operating limits for thermal output for at least 2.5 years.
II.
EVENT-DRIVEN INFORMATION A.
SAFETY SYSTEMS THAT RESPONDED There were no safety systems that responded to this event.
B.
DURATION OF SAFETY SYSTEM INOPERABILITY
One of the PRNI instruments was inoperable for the past 2.5 years. This exceeded the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> TS associated allowable outage time.
C.
SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT An assessment of the safety consequences and implications is as follows:
Nuclear Safety: Accident Analyses were reviewed to ensure a 2% overpower condition did not consume the Nuclear Safety Margin, and the review concluded that margin remains. Therefore, the overpower conditions of approximately 1.8% in Unit 1 does not result in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety.
The above information is reflected in the PRA in the following way:
- - Initiating Events There is no impact on the frequency of initiating events. However, the overpower condition may effect some reactor trip set points such as Power Range, Neutron Flux High and Low, Over-temperature AT, and Overpower AT were set at a higher power level than assumed in the safety analysis.
- - Mitigating Systems There is no effect on the PRA mitigating systems directly, but because the plant operated at a higher power there was an associated increase in the decay heat. This small increase in decay heat is not significant, and does not impact the function of these systems.
- - PRA Success Criteria and Human Actions The identified overpower condition has a potential impact on PRA success criteria and operator action timing. The impact to these items is not significant because the overpower condition is very small.
Therefore any increase in core damage or large early release risk due to this condition is considered very small.
Security Safety: This condition has no effect on the physical security program at STP. There is no interface between the described condition and security's execution of processes and procedures which implement the requirements of 10 CFR 73.55.
Emergency Preparedness: The described problem has no impact on emergency preparedness equipment and/or systems and on their capability to perform the various required functions.
Radiological Safety: The event did not affect and could not affect the radiological safety of workers. The event was determined to be a level 5 reactivity event and does not affect radioactive process fluids, sources of radiation, safe shutdown of the reactor or an EECS function. Therefore, the event could not cause or increase the likelihood or severity of unintentional exposure to workers.
Safety of station personnel: The event did not affect and could not affect the radiological safety of workers. The event was determined to be a level 5 reactivity event and does not affect radioactive process fluids, sources of radiation, safe shutdown of the reactor or an ECCS function. Therefore, the event could not cause or increase the likelihood or severity of unintentional exposure to workers.
Safety of the public: The event did not affect and could not affect the radiological safety of public, nor could it cause the release of radioactive material. This level 5 reactivity event does not affect radioactive process fluids, sources of radiation, safe shutdown of the reactor or an ECCS function. Therefore, the event could not cause, nor increase the likelihood or severity, of unintentional exposure to the public.
A risk assessment was performed for this event. There was no initiating event or impact to the capability of mitigating systems or other plant equipment to perform required safety functions. Therefore, there is no incremental core damage or large early release risk associated with this event.
Operability/functionality of equipment: The decrease in feed water pipe wall thickness resulted in an increased diameter and corresponding flow area which, in the absence of any other documentation, should have resulted in a higher mass flow rate and corresponding increased secondary calorimetric indication of power. Since the diameter is a constant in the CROSSFLOW computer, the CROSSFLOW computer "under reported" power. The "under reported" power led to calibrating the PRNI, the Overtemperature Delta-Temperature (OTAT), and the Overpower Delta-Temperature (OTAT) trip settings non-conservatively. The diameter change led to the conclusion that overpower was approximately 1.8%
for Unit 1.
Ill.
CAUSE OF THE EVENT
The cause of the event has been attributed to an absence of prescriptive procedural requirements for a formal technical review of license changes. STP License Amendment Request implementation process does not require a formal, documented review of plant specific requirements and recommendations from vendor supplied documents that are used as a basis for a license amendment.
IV.
CORRECTIVE ACTIONS
Once STP was aware of a potential problem, the vendor, Advance Measurement and Analysis Group (AMAG) was contracted to conduct pipe wall measurements on the Feedwater pipe in the vicinity of the UTF.
This action was performed in December 2013, and was to validate STP pipe inner diameter measurements.
The pipe internal diameter measurements performed by AMAG confirmed that pipe internal diameters were outside uncertainty assumptions. The UTF system was declared unreliable, removed from service, and both units were reduced in power to 3838 mWt. Design changes were issued for the affected units, and the new pipe wall diameters were entered. Unit 1 was returned to full power on 1/17/14.
The following Corrective Action to Prevent Recurrence has been put in place:
Develop or revise a Licensing procedure to require a formal, documented review of plant specific requirements and recommendations from vendor supplied documents to support license amendments.
Corrective actions will be implemented in accordance with the STP Corrective Action Program.
V.
PREVIOUS SIMILAR EVENTS
There have been no similar reportable events at STP within the last three years related to this issue.
VI.
ADDITIONAL INFORMATION
A supplemental LER report is planned to be submitted to provide additional information regarding the overpower event. A more detail study is being performed by two independent vendors to provide a more detailed analysis of the overpower condition. This submission date of the supplement is projected to be April 30, 2014.