05000446/LER-2015-001
| Comanche Peak Nuclear Power Plant | |
| Event date: | 07-10-2015 |
|---|---|
| Report date: | 09-18-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4462015001R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION:
Reportable per 10 CFR 50.73(a)(2)(i)(B), "Operation in a condition prohibited by Technical Specifications.
B. PLANT CONDITION PRIOR TO EVENT:
At the time of discovery, Unit 2 was in MODE 1 (Power Operation) at 100 percent power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE INOPERABLE AT THE
START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
There were no structures, components or systems (SSC) that were inoperable at the start of the event and that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES:
While performing a quarterly system walkdown on 7/7/2015, the SI System Engineer discovered a boric acid accumulation coming out of the insulation on pipe segment SI-2-070 beneath 2SI-0055 and accumulating on the floor. The insulation was removed within an hour of identifying the accumulation. Upon removal, a through wall leak was discovered in the socket weld beneath test vent 2SI-0055. T.S. LCO 3.5.2 Condition B was entered immediately upon discovery of the through wall leak on 7/7/2015 at 1304. The socket weld was reworked as an emergent activity under WO-5087339. An enhanced weld design was implemented to improve the fatigue life of the socket weld by using a 2:1 weld leg ratio. Repairs took a total of 82 hours9.490741e-4 days <br />0.0228 hours <br />1.35582e-4 weeks <br />3.1201e-5 months <br /> and 56 minutes. A Notification of Enforcement Discretion (NOED) was approved which allowed Unit 2 to remain at power despite exceeding the allowed LCO time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for Condition B.1 plus 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> for Condition C.1.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL
PERSONNEL ERROR
While performing a quarterly system walkdown on 7/7/2015, the SI system Engineer discovered a boric acid accumulation coming out of the insulation on pipe segment SI-2-070 beneath 2SI-0055 and accumulating on the floor. Upon removal of the piping insulation, a through wall leak was discovered in the socket weld beneath test vent 2SI-0055.
II. COMPONENT OR SYSTEM FAILURES
A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
An original weld defect resulted in a stress concentration that allowed otherwise acceptable tensile loads to cause propagation of a through-wall crack.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
Cracking of the socket weld beneath 2SI-0055 allowed system fluid to leak through the resulting weld fracture. Cracking was evident by visual inspection which indicated that the failure was brittle in nature since there was a lack of deformation in the failed socket weld.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS
WITH MULTIPLE FUNCTIONS
The sole safety function of the socket weld was pressure boundary integrity in support of the train B ECCS. No other safety functions or components with multiple safety functions were affected.
D. FAILED COMPONENT INFORMATION
Through-wall crack of the socket weld beneath 2SI-0055, a cantilever connected, 3/4" vent valve near the Unit 2, Train B Safety Injection pump suction.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not applicable - No safety system responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Unit 2, Train B Safety Injection System was declared inoperable at 1304 Central Time on July 7, 2015 and was restored to operable at 0000 Central Time on July 11, 2015. The total time Unit 2, Train B Safety Injection System was inoperable was 82 hours9.490741e-4 days <br />0.0228 hours <br />1.35582e-4 weeks <br />3.1201e-5 months <br /> and 56 minutes.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
During the time the Unit 2, Train B Safety Injection system was inoperable, the Unit 2 Train A Safety Injection system was operable and fully capable of performing the intended safety functions of the Safety Injection system. Prior to discovery, Train A SI had been operable since completion of the pre-summer cleaning of the 2-01 CCW/SSW heat exchanger on June 20, 2015 at 0233. Since the Train A Safety Injection system was capable of performing the intended function during the period of inoperability, there was no impact to public health and safety.
IV. CAUSE OF THE EVENT
An original weld defect added a stress concentration which allowed otherwise acceptable tensile loads to cause propagation of a through-wall crack.
V. CORRECTIVE ACTIONS
The failed socket weld was replaced with an improved 2:1 weld leg ratio. As a part of the CPNPP Corrective Action Program, Engineering has reviewed the extent of condition for this event and plans to perform dye penetrant testing and volumetric inspections, capable of detecting subsurface indications, of the process pipe to vent and drain pipe socket welds for other potential locations where the condition may exist.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at Comanche Peak Nuclear Power Plant (CPNPP) in the last three years.
Comanche Peak Nuclear Power Plant
2. DOCKET
05000 - 446