05000528/LER-2003-002
| Docket Number03 27 2003 2003 - 002 - 01 04 ?? 2006 05000 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 5282003002R01 - NRC Website | |
1. REPORTING REQUIREMENT(S):
Arizona Public Service Company (APS) is reporting this condition pursuant to 10 CFR 50.73 (a) (2) (iv) (A) due to the manual actuation of the reactor protective system (RPS)i:ElIC Code: JC). Pursuant to 10 CFR 50.72 (b) (2) (iv) (B), a notification was made to the headquarters operation officer on March 27, 2003 (reference ENS 39705).
2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The main condenser tube plug that was found to be degraded is a PLUG, PUSH & SEAL CONDENSER, SIZE 1-1/8IN, 18-22 GAUGE, BUNA N RUBBER manufactured by JNT Technical Services Inc.
3. INITIAL PLANT CONDITIONS and EVENT DESCRIPTION:
On March 27, 2003 with Unit 1 operating in Mode 1, Power Operation, at approximately 97 per cent power, the main condenser (EIIC Code: COND) HOTWELL A HIGH SODIUM alarm (EIIS Code: AA) was received in the chemistry lab at approximately 09:27 MST. Chemistry personnel responded to the alarm and determined that hotwell 1A sodium in-line monitoring indication (EIIC Code: MON) was trending up and that condensate demineralizer (EIIS Code: DEM) influent (CDI) sodium indication was also trending up. The control room was notified and a chemistry technician proceeded to obtain a grab sample from the 1A hotwell. At the time of the event the unit was operating in the condensate demineralizer by-pass mode.
By 09:35 MST sodium levels in both steam generators (SGs) (EIIC Code: SG) were noted by a second chemistry technician to be 5000 ppb. Control room personnel were notified of this condition and the Condenser Tube Rupture abnormal operating (AO) procedure, 40A0-9ZZ10, was entered. SG sodium levels continued to increase and at approximately 09:43 MST, in accordance with appendix I of the AO procedure, the Control Room Supervisor (CRS) directed a manual reactor trip be initiated.
Standard post trip actions were taken and the Shift Manager classified the event as an uncomplicated reactor trip. Due to the amount of contaminant ingress to the SGs, the plant was cooled down and entered Mode 5 at 01:28 MST on March 28 to facilitate cleanup of the SGs.
There were no inoperable systems at the start of the event that contributed to the event.
Shortly after the manual reactor trip a problem was noted by the control room operators with letdown flow (EIIS Code: CB). A pressure relief valve (1JCHNPSV0345) (EIIS Code: RV) lifted twice and reset in response to a pressure surge in the letdown line as a result of the reactor trip transient and the pressurizer level control system response to the transient.
4. ASSESSMENT OF SAFETY CONSEQUENCES:
The manual reactor trip did not result in a transient more severe than those already analyzed in the updated Final Safety Evaluation Report Chapters 6 and 15. The primary system and secondary pressure boundary limits were not approached and no violations of the specified acceptable fuel design limits (SAFDL) occurred.
The condition would not have prevented the fulfillment of any safety function and did not result in a safety system functional failure as defined by 10CFR50.73(a)(2)(v).
The event did not result in any challenges to the fission product barriers or result in the release of radioactive materials. Therefore, there were no adverse safety consequences or implications as a result of this event and the event did not adversely affect the safe operation of the plant or health and safety of the public.
5. CAUSE OF THE EVENT:
The cause of the event was determined to be the failure of a previously installed main condenser tube plug. The cause of the plug failure has been determined to be a manufacturing defect that may have been aggravated during the installation of the plug. The plug exhibited a tear in the tip of the plug that allowed circulating water used to cool the condenser to enter the condenser hotwell and then enter the SGs.
Laboratory examination revealed that the plug had developed a "de-bonding" flaw that initiated within the body of the part and then extended by fracture to both the interior and exterior surfaces of the plug. Since the plug is injection molded, it is highly probable that the initial defect occurred at the time of manufacture (i.e. gas inclusion, blister, micro-fracture, contamination impurity, etc.). After six months of service, the pressure differential that the plug experienced combined with the plug "relaxing" from being distended during installation caused the defect to extend until the plug was breached.
6. CORRECTIVE ACTIONS:
The degraded plug was replaced. SG chemistry was cleaned up, with the plant in Mode 5, by draining and refilling the SGs.
Condenser tube plug types were evaluated to determine the best one to be used at PVNGS. Various plants were contacted to obtain information on the type of the tube plug used and any problems connected with them. After evaluation, the Push'N Seal plug with plastic insert was selected for use at PVNGS. The condenser tube plugs in Units 1, 2 and 3 have been replaced with Push'N Seal plugs with plastic inserts.
7. PREVIOUS SIMILAR EVENTS:
There has been no similar event reported to the NRC by the Palo Verde Nuclear Station in the past three years.