|Pilgrim Nuclear Power Station|
|Reporting criterion:||10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications|
10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
|2932017003R01 - NRC Website|
|Person / Time|
|From:||Perkins E P|
Entergy Nuclear Operations
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17163A180 (6)|
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to NEOB-10202, (3150-0104), Office of Management and Bli.dget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Pilgrim Nuclear Power Station 05000-293
The suppression pool water provides the heat sink for the reactor primary system energy release following a postulated rupture of the system. The suppression pool water volume must absorb the associated decay and structural sensible heat released during primary system blow-down. The design volume of the suppression pool (water and air) was obtained by considering that the total volume of reactor coolant to be condensed is discharged to the suppression pool and that the drywell volume is purged to the suppression pool.
The suppression pool is designed to absorb the sudden input of heat from the primary system. In the long term, the pool continues to absorb residual heat generated by fuel in the reactor core.
On March 31, 2017, at 1155 [EDT], with the reactor at 97 percent core thermal power and steady state conditions, operators were restoring a valve lineup after performing planned operations when a pathway was created through valve manipulation that allowed water in the Condensate Storage Tank to be diverted to the suppression pool. The rise in suppression pool water level to (+) 6.3 inches exceeded the maximum suppression pool water level specified in Technical Specification (TS) and the TS limit for differential pressure was lowered to less than 1.17psid between the drywell and suppression pool.
With suppression pool water level and differential pressure outside of TS limits, both Limiting Condition for Operation Action Statement (LCOAS) 3.7.A.5 and 3.7.A.8.c were entered. In addition, Emergency Operating Procedures-03, Primary Containment Control, was also entered due to high suppression pool water level.
Investigation into the cause of diverting water to the suppression pool was initiated. Appropriate procedural guidance was followed to begin lowering suppression pool water level below the limit specified in the TS.
With suppression pool water level and differential pressure both returned to within TS limits, LCOAS 3.7.A.8.c and 3.7.A.5 were both exited at 1515 and 1540 respectively.
The direct cause of the condition was that the control room operator opened the Core Spray Pump A Suppression Pool Suction Valve prior to verifying closed the Core Spray Pump Suction Valve from the Condensate Storage Tank and the Condensate Supply to Core Spray System Valve.
Upon discovery of the suppression pool high water level condition, Operations returned the suppression pool water level to the required level using appropriate procedural guidance.
The Control Room Supervisor and the Reactor Operator were disqualified.
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection
- Pilgrim Nuclear Power Station 05000-293
The safety function of the suppression pool system was not adversely affected due to the high water level condition in the suppression pool. A preliminary assessment has demonstrated that the suppression pool water level was within a volume range that will accommodate all normal, transient, emergency, and accident events within the design capabilities of the primary containment system. As such, there are no consequences to general safety of the public, nuclear safety, industrial safety and radiological safety from this condition.
Maintaining a drywell to suppression pool pressure differential to keep the downcomer legs clear of water significantly reduces suppression pool post LOCA hydrodynamic loads. A pressure of 1.17psid is required to sufficiently clear the water legs of the downcomers without bubbling nitrogen into the suppression pool at the 3.00 ft. downcomer submergence level.
The suppression pool remained available and functional and capable of performing its intended safety function during the event. As such, there was no actual loss of safety function.
The engineering evaluation that was performed concluded that this event did not constitute a Safety System Functional Failure. (Reference NEI 99-02, Revision 7, Regulatory Assessment Performance Indicator Guideline, Section 2.2, Mitigating Systems Cornerstone, Safety System Functional Failures, Clarifying Notes, Engineering Analyses.) As such, this event will not be reported in the NRC Performance Indicator for Safety System Functional Failures since an engineering evaluation was performed which determined that the system was capable of performing its safety function during this event.
This event was initially reported under 10 CFR 50.73(a)(2)(i)(B), as a condition that was prohibited by TS.
Subsequent to submission of the initial Licensee Event Report, based on NRC questions, it was concluded that this notification should have more precisely been made in accordance with 10 CFR 50.73(a)(2)(v)(D), event or condition that could have potentially prevented fulfillment of a safety function of structures or systems that are needed to mitigate the consequences of an accident.
A review of PNPS Licensee Event Reports for the past five years did not identify any similar occurrences of declaring the suppression pool inoperable due to a high water level condition.