05000247/LER-2014-001
| Indian Point 2 | |
| Event date: | 02-20-2014 |
|---|---|
| Report date: | 04-07-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii) |
| 2472014001R00 - NRC Website | |
Note: The Energy Industry Identification System Codes are identified within the brackets {}.
DESCRIPTION OF EVENT
On February 20, 2014, Entergy identified a failure to comply with Technical Specification (TS) 3.4.3 [Reactor Coolant System (RCS) Pressure and Temperature (P/T) Limits] after review of a Westinghouse PWR Owners Group (PWROG) correspondence (0G-14- 66) dated February 19, 2014. The PWROG correspondence discussed a Non-cited Violation at Perry Nuclear Plant for failure to comply with their TS for RCS P/T limits when operating the plant with a vacuum in the reactor pressure vessel (RPV) during cold startups and cooldowns. A review of the Indian Point Units 2 and 3 TS 3.4.3 determined that TS 3.4.3 P/T limits for heatup and cooldown only provide for values greater than or equal to 0 psig. TS 3.4.3 requires that the RCS pressures and temperatures be maintained within limits at all times specified in TS Figures 3.4.3-1 and 3.4.3-2. The P/T Figures provide curves with a pressure starting at 0 psig. During past operation at both units, TS 3.4.3 P/T limits were not complied with when performing vacuum refill in Mode 5 as this process results in RCS pressures less than 0 psig. The condition was recorded in the Indian Point Energy Center corrective action program (CAP) as CR-IP2- 2014-00877.
TS 3.4.3, RCS Pressure and Temperature (P/T) Limits, Limiting Condition for Operation (LCO) requires RCS pressure, temperature and RCS heatup and cooldown rates be maintained within the limits specified in Figure 3.4.3-1 and Figure 3.4.3-2.
Applicability is at all times. All components of the RCS are designed to withstand the effects of cyclic loads due to system pressure and temperature changes. The LCO limits the pressure and temperature changes during RCS heatup and cooldown, within the design assumptions and the stress limits for cyclic operation. Figure 3.4.3-1 and Figure 3.4.3-2 contain P/T limit curves for heatup, cooldown, in-service leak and hydrostatic testing, and data for the maximum rate of change of reactor coolant temperature. Each P/T limit curve defines an acceptable region for normal operation. The usual use of the curves is operational guidance during heatup or cooldown maneuvering, when pressure and temperature indications are monitored and compared to the applicable curve to determine that operation is within the allowable region. The TS LCO establishes operating limits that provide a margin to brittle failure of the reactor vessel and piping of the reactor coolant pressure boundary (RCPB). The P/T limit curves are composite curves established by superimposing limits derived from stress analyses of those portions of the reactor vessel and head that are the most restrictive. The P/T curves do not graphically go below 0 psig and no basis explanation is provided for vacuum refill conditions.
The RCS P/T limits LCO provides a definition of acceptable operation for prevention on non-ductile failure in accordance with 10CFR50, Appendix G. 10CFR50, Appendix G requires the establishment of P/T limits for specific material fracture toughness requirements of the Reactor Coolant Pressure Boundary (RCPB) materials. These limits represent an adequate margin to brittle failure during normal operation, anticipated operational occurrences, and system hydrostatic tests. The P/T curves are composite curves established by superimposing limits derived from stress analysis of those portions of the reactor vessel and head that are the most restrictive. The primary concern for the reactor vessel, in terms of pressure, is a low temperature overpressure condition. A pressure greater than an allowable value increases the likelihood of non- ductile failure. The P/T limits represented by the TS figures are considered acceptable limits because they preclude operation in an unanalyzed condition
Cause of Event
The cause of the event was a failure to recognize that a negative pressure was not allowed by the TS. The change to the use of vacuum fill of the RCS had technical justification that there was no adverse impact on the RCS but the safety evaluation for the change concluded there was no affect on the TS. Direction in procedures and reinforced during training stressed that compliance with the governing TS P/T curves is preserved as long as the conditions within the RCS are maintained to the right of the effective curve.
Corrective Actions
The following corrective actions have been or will be performed under Entergy's Corrective Action Program to address the cause and prevent recurrence:
- A proposed change to Indian Point Unit 2 TS 3.4.3 was submitted to the NRC by Entergy letter dated February 24, 2014, and amendment number 274 was issued by NRC letter dated March 5, 2014, that included changes to TS 3.4.3 for P/T limits for vacuum fill.
- A proposed change to TS 3.4.3 will be prepared and submitted to the NRC for amending the Unit 3 TS 3.4.3 for P/T limits for vacuum fill.
Event Analysis
The event is reportable under 10CFR50.73(a)(2)(i)(B). The licensee shall report any operation or condition which was prohibited by the plant's TS. This condition meets the reporting criteria because during past operation following each refueling outage, the RCS pressure was reduced to less than 0.0 psig for RCS vacuum fill and vent activities.
The Indian point Unit 2 and Unit 3 TS 3.4.3, Figures 3.4.3-1 and Figure 3.4.3-2 heatup and cooldown limits only contain values for RCS pressures equal to or greater than 0.0 psig. TS 3.4.3 requires that RCS pressures and temperatures be maintained within the limits specified in the TS at all times. During startup from previous refueling outages, the RCS was made water solid, and during filling of the RCS, a vacuum was drawn so as to expel any air/non-condensibles from the RCS. During this evolution, the RCS was below 0.0 psig, which is outside the range of the TS 3.4.3 figures. The TS 3.4.3 requirements were not complied with during vacuum fill of the RCS and is therefore a TS prohibited condition.
The condition is not reportable in accordance with 10CFR50.73(a)(2)(ii), Any event or condition that resulted in (A) The condition of the power plant, including its principal safety barriers, being seriously degraded; or (B) the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety. The heatup, cooldown limitation curves remain valid during vacuum fill in accordance with current regulations. These limitation curves were established in compliance with the methodology used to calculate and predict effects of radiation embrittlement of the Reactor Pressure Vessel beltline materials and remain valid during vacuum fill. Since operation was within the limitation curves, the RCS materials behaved in a non-brittle manner consistent with the original design basis. Therefore, there was no principal safety barriers seriously degraded nor was there any condition that significantly degraded plant safety.
Past Similar Events
A review was performed of the past three years for Licensee Event Reports (LERs) reporting a TS prohibited condition due to a non-compliant TS. No LERs were identified.
Safety Significance
This event had no effect on the health and safety of the public.
The RCS pressure boundary is a barrier against the release of radioactivity generated within the reactor and is designed to ensure a high degree of integrity throughout the life of the plant. The RCS pressure boundary is capable of accommodating the temperatures and pressures associated with operational transients. The RCS components containing the reactor coolant (i.e., reactor vessel, reactor coolant pumps, pressurizer, steam generator tubes, and RCS piping) are designed with sufficient wall thickness to withstand full system pressure. The minimum wall thickness for the RCS components to withstand full vacuum (0 psia) is below the existing wall thickness of the reactor vessel, pressurizer, steam generator tubes, and the RCS piping.
Performance of RCS vacuum fill and vent process to reduce RCS pressure up to and including full vacuum will not adversely affect the integrity of RCS components. The NRC review of the proposed changes to the TS P/T figures that included reference to vacuum fill of the RCS performed in Mode 5 under sub-atmospheric pressure and isothermal condition, verified that the proposed P/T limits are in accordance with Appendix G to Section XI of the ASME code and satisfy the requirements of Appendix G to 10CFR50. Therefore, RCS vacuum fill and vent is not considered to be safety significant.