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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 51182 | 26 June 2015 05:00:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor | Two Reactor Vessel Level Channels Failed High | At 2200 PDT during startup from refueling outage 22, it was discovered that both level instruments used in reactor protection system (RPS) trip system 'A' for initiation of a reactor scram on low reactor pressure vessel (RPV) level were observed to have failed high. This resulted in the inability to generate a full reactor scram on low level (+13 inches). All remaining RPV level indications demonstrated that level was being maintained within normal operating bands. This constitutes a condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to shut down the reactor. The RPS trip logic at Columbia consists of two trip systems, RPS trip system 'A' and RPS trip system 'B'. There are two level instrument channels in each trip system. Columbia utilizes a 'one-out-of-two taken-twice' trip logic to generate a full scram signal. At least one channel in both trip systems must actuate to generate a full scram signal. With both level instruments in RPS system 'A' failed high, the RPS trip logic was unable to generate a full scram. At 2246 (PDT) and in accordance with TS LCO 3.3.1.1 Condition C, a half scram was generated on RPS trip system 'A' to restore full scram capability. The cause of the failure of the two level instruments associated with RPS Trip system 'A' is under investigation. The level channels are being calibrated prior to changing to mode 1 (power operations). The licensee will notify the NRC Resident Inspector. | Reactor Protection System Reactor Pressure Vessel |