05000333/LER-2013-002

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LER-2013-002, RCIC Condensate Storage Tank Level Switch Inoperable due to Corrosion
James A. Fitzpatrick Nuclear Power Plant
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3332013002R00 - NRC Website
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Background

Reactor Core Isolation Cooling (RCIC) System [BN] is comprised of various components which include pumps, valves, piping, and instrumentation. The RCIC System is designed to operate either automatically or manually following reactor pressure vessel isolation accompanied by a loss of coolant flow from the feedwater system to provide adequate core cooling and control the reactor water level under these conditions. The normal water source for the RCIC is the Condensate Storage Tanks (CST) [KA] 33TK-12A and 33TK-12B.

Low CST Level indicates the unavailability of an adequate supply of makeup water from this normal source (CST). Normally, the suction valve between the RCIC pump and the CSTs is open and, upon receiving a RCIC initiation signal, water for RCIC injection would be taken from the CSTs. However, if the water level in both CSTs falls below a preselected level, the water source is automatically changed to the suppression pool. This ensures that an adequate supply of makeup water is available to the RCIC pump.

Level switches detect the water level for the 2 CSTs. Each tank has 2 RCIC instrumentation level switches, 131_5-76A and 131_5-77A for the "A" tank and 13LS-76B or 13LS-77B for the "B" Tank. Four channels of low CST level function are available and are required to be Operable when RCIC is required to be Operable to ensure that no single instrument failure can preclude RCIC automatic suction source alignment to suppression pool source.

Preceding events On 01-04-2013, 131_5-77B did not actuate (trip) on low CST water level during ISP-75-1. The other three level switches operated satisfactory. The 13LS-77B was then re-tested and operated satisfactory. The switch was disassembled and water was found in the switch casing. The Apparent Cause for the source of the water was from the environmental conditions in the CST pit. Water penetrated through the junction box (JB-CIC-31) into a conduit to the level switch assembly. The junction box has weep holes to drain water; however, it was evident that there was a buildup of water in the junction box due to foreign material blocking the weep hole. The weep hole was cleaned and the contacts in the level switch were replaced. The excessive water in the switch affected the switch operation by causing intermittent failure.

On 03-28-2013, ISP-75-1 was performed successfully for all 4 RCIC CST level switches.

EVENT DESCRIPTION

On 07-16-2013, 13LS-76B did not trip on low CST water level during ISP-75-1. The other three level switches actuated (tripped) properly. When the top cover was removed the technician stated that it took excessive force to manually actuate the switch. Once the switch was freed up it worked repeatedly. There was evidence of corrosion due to water intrusion into the electrical top works and that the water was apparently coming from within the upstream conduit and junction box; however, water was not present.

On 08-19-2013, 13LS-76B and 13LS-77B did not trip on low CST water level during ISP-75-1. The plant was at 100% power. Corrosion formation due to water exposure prevented the switch from changing state. The other two "A" CST level switches operated satisfactory.

EVENT ANALYSIS

The failures of 13LS-77B and 131_5-76B both stem from water intrusion into the switch casing from their shared junction box (JB-CIC-31) and associated conduit. The junction box and level switches are not Environmentally Qualified devices. Rain water or run off water from conditions in the CST pit were able to penetrate the junction box and make its way through the conduit to the level switch assembly. Only one of two level switches (13LS- 76B or 131_5-77B) for "B" CST and one of the two level switches (13LS-76A or 131_5-77A) for "A" CST are required to perform the swap from the CST to the suppression pool. This condition only affects the "B" CST level In January, water present in the switch directly caused the failure of 13LS-77B. There is no firm evidence that the level switches continued to be Inoperable as a result of excessive water after the January event. On March 28, 2013, ISP-75-1 was performed successfully for all RCIC CST level switches. Later, in July and August, both "B" CST level switches (13LS-76B and 13LS-77B) experienced corrosion on the trip mechanism from water exposure.

Whenever a level switch was tested and did not trip repairs were performed and the level switch was restored to Operable status prior to exiting the maintenance activity. However, as a consequence of corrosion, the "B" CST level switches were Inoperable from July 16, 2013, until restoring the level switches to Operable status after the event of August 19, 2013.

RCIC Instrumentation Limiting Condition of Operation (LCO) 3.3.5.2 requires that the RCIC System instrumentation for each 4 channels of Low CST water level be Operable while in Mode 1, Mode 2, and Mode 3 with reactor steam dome pressure > 150 psig. When the channel was inoperable, Condition D action required that the channel be placed in trip. When this condition was not met Condition E required that RCIC be declared inoperable.

LCO 3.5.3 required RCIC be restored to Operable within 14 days or be in Mode 3.

Since both level switches 13L5-76B and 13L5-77B were Inoperable between July 16, 2013 and August 19, 2013. This period of time is longer than allowed by the Technical Specifications (TS); therefore, JAF had a condition reportable per 10 CFR 50.73(a)(2)(i)(B) as prohibited by TS.

High Pressure Coolant Injection (HPCI) Operability [BJ] LCO 3.5.1 Condition C states that if HPCI is Inoperable then verify RCIC is Operable administratively. When RCIC is concurrently Inoperable then Condition G requires the plant to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The history of HPCI Operability was verified since January 1, 2013. All Inoperable instances were associated with the performance of normal surveillance procedures. At no point was HPCI Inoperable for greater than 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

Therefore, this condition was not prohibited by TS 3.5.1 or the corresponding RCIC TS 3.5.3 Condition B.

CAUSE OF EVENT

The Apparent Cause of the failure of Reactor Core Isolation Cooling (RCIC) instrumentation for the "B" Condensate Storage Tank (CST) level switches was corrosion initiated by water intrusion. The source of the water into the level switches assembly came from junction box JB-CIC-31 shared by the level switches (13LS- 76B and 13LS-77B).

EXTENT OF CONDITION

The only susceptible level switches to this condition were those associated with the "B" CST (131_5-76B and 131_5-77B) due to a shared junction box. There is no evidence that supports that either the "A" CST level switches 13LS-76A or 131_5-77A were inoperable or that the corresponding HPCI level switches 23LS-74A, 23LS-75A, 23LS-74B, 23LS-75B were inoperable.

FAILED COMPONENT IDENTIFICATION:

Manufacturer:

Manufacturer Model Number:

NPRDS Manufacturer Code:

NPRDS Component Code:

FitzPatrick Component ID:

Robertshaw Controls 51_301-A2XS11-C31-1 R290

LS

131_5-76B and 13LS-77B

Completed Actions

  • Replaced affected components of 13LS-77B on 1/10/13
  • Opened junction box JB-CIC-31 and cleared obstruction on 1/10/13
  • Temporarily increased ISP-75-1 frequency to 45 days.
  • Revise ISP-75-1 and ISP-75 to inspect and verify satisfactory condition of the junction box, switches, and corresponding conduit during the quarterly surveillance tests.

Post 8-19-13

  • 13LS-77B corroded components replaced and level switch returned to Operable status Future Actions
  • Examine the extent of the Corrosion Condition in the "A" CST level switches and the four corresponding HPCI level switches.
  • Evaluate and implement a method to prevent of reduce water intrusion into HPCI and RCIC CST level switches.

SAFETY SIGNIFICANCE

Nuclear Safety There were no actual nuclear safety consequences during this period as a result of this event.

The potential consequence was that the RCIC system may not have operated as designed. If RCIC was called upon to Operate during an accident scenario and the CSTs ran low on water then RCIC may not have detected channels of RCIC low level CST instrumentation, in order to prevent the required function of the low level CST function both 13LS-76B and 13LS-77B need to fail to trip concurrently. Also, Operators have the ability to manually perform this swap.

JAF accident analysis does not take credit for the operation of the RCIC system. The accident analysis assumes the operation of the HPCI system and operation of the Automatic Depressurization System in conjunction with the Low Pressure Coolant Injection System. These systems were unaffected by the identified condition.

Therefore, the potential consequences of the RCIC system inoperable during this period were minimal.

Radiological Safety No radiological impact or dose associated with this condition.

Industrial Safety No safety events or abnormal increases to personnel risk.

SIMILAR EVENTS

There are no historical cases of RCIC or HPCI level switches not functioning as a result of corrosion at JAF.

REFERENCES

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