05000389/LER-2005-002
| St. Lucie Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3892005002R00 - NRC Website | |
St. Lucie Unit 2 05000389 1=i
Description of the Event
On May 13, 2005, with Unit 2 in Mode 1 operation at 100 percent reactor power, valve V07408, the 2A hydrazine pump discharge to storage tank relief bypass valve (EIIS:BE], was found to be in a locked open position, instead of the required locked closed position. The error was discovered by a Unit 2 non-licensed senior nuclear plant operator (SNPO) while performing the quarterly valve lineup for the containment spray and iodine removal system (IRS). The 'A' IRS train was subsequently declared inoperable, and a 72-hour shutdown action statement was entered. The 'A! IRS train was restored to service by placing valve V07408 in its required locked closed position in accordance with 2-NOP-07.41, "Containment Spray System Initial Alignment." Additionally, valve V07409, the 2B hydrazine pump discharge to storage tank relief bypass on the opposite train, was verified locked closed as required.
Cause of the Event
The last time V07408 was operated was approximately 78 hours9.027778e-4 days <br />0.0217 hours <br />1.289683e-4 weeks <br />2.9679e-5 months <br /> earlier, on May 10, following the 2A containment spray pump surveillance test. During that surveillance testing, the hydrazine pump recirculation valve was throttled open to establish 35 psig discharge pressure to simulate hydrazine pump flow conditions that would be seen during the post accident containment spray injection phase. However, non-licensed operator human errors during the surveillance testing restoration activities led to valve V07408 being mispositioned.
The causes for the mispositioning of valve V07408 were the failure to use self- checking when initially restoring the valve position, and the failure to follow the restoration steps of the surveillance procedure when performing the independent verification of the valve position.
The operators involved in the incident received remediation and were placed back on shift. Additionally, Training is developing a non-licensed operator lesson plan to reinforce human performance fundamentals.
Analysis of the Event
Unit 2 Technical Specification 3.6.2.2, "Iodine Removal System," states that the allowed outage time for an inoperable hydrazine pump is 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Based on the timeline developed during the event investigation, the 'A' IRS train was inoperable for a time longer than allowed by Technical Specifications. Therefore, this condition is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B).
Analysis of Safety Significance The containment spray system (CSS) is provided to perform the dual functions of removing heat and fission products from a post-accident containment atmosphere. The heat removal capability of the CSS is discussed in the Unit 2 Updated Final Safety Analysis Report (UFSAR) Section 6.2.2. The fission product removal function is carried out by the IRS, operating in conjunction with the CSS. The IRS is credited for removing radio-iodines from the containment atmosphere following a loss of coolant accident (LOCA) by adding controlled amounts of hydrazine to containment spray water.
The 1/2-inch recirculation lines for the 2A and 2B hydrazine pumps protect the pumps from damage by recirculating flow back to the hydrazine storage tank when the pumps are running with closed discharge header valves. The hydrazine pumps are slow speed St. Lucie Unit 2 05000389 positive displacement pumps. With valve V07408 open, flow would be diverted back to the hydrazine tank, adversely affecting the pH buffering flow to the 'A' CCS train.
This condition did not affect the design function of the CSS to provide containment heat removal, nor did it adversely affect the 'B' IRS train. The 'B' IRS train was always available to provide the required redundant 100 percent CSS radio-iodine removal capacity.
The St. Lucie licensing and design bases credit the use of the IRS during post accident conditions for a LOCA event. However, the need to use hydrazine for iodine removal or pH control was the subject of the recent St. Lucie alternate source term (AST) license amendment request. FPL letter L-2004-203, dated September 21, 2004, documents that hydrazine is no longer needed for pH control and iodine removal in the analysis supporting AST. The containment sump pH for Unit 2 is 6.93 at the most conservative time for recirculation and 7.1 at one hour. NUREG/CR-5950 indicates that at a pH of 6.93 and higher, no iodine re-evolution would occur. Considering the actual St. Lucie Unit 2 inputs at the time of recirculation, the fraction of iodine that may re-evolve is less than 0.000003. Numbers much larger than this value were already assumed in the AST analysis. Therefore, the radiological consequences after a design basis accident are not expected to increase due to inoperability of valve V07408 at the beginning of the accident. FPL concludes that this condition would not have had a significant effect on post-accident control room or offsite doses.
This condition is not applicable to the Unit 1 IRS as it does not have injection pumps-or the associated recirculation valves. Additionally, FPL determined that valve mispositioning events concurrent with faulty independent verification are infrequent events. A review of St. Lucie Licensee Event Reports for the last five years concluded that no reportable events were due to this particular combination of human performance deficiencies.
Corrective Actions
1. Upon discovery the 'A' IRS train was restored to operable status and the '13' IRS train valve positions were verified correct.
2. The operators involved in the incident completed their remedial training on June 1, 2005.
3. The St. Lucie Training department is developing a Human Performance Fundamental class for cycle 5.5 of non-licensed operator requalification training. This training is to include self-checking, procedural use and compliance, and independent verification. This training will include a case study of this event.
The class will be developed by August 19, 2005.
Other Information None