05000316/LER-2001-001

LER-2001-001,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown
3162001001R00 - NRC Website

Conditions Prior to Event Unit 2 was in Mode 1 at 25% power.

Description of Event

On January 22, 2001 at 1948 hours0.0225 days <br />0.541 hours <br />0.00322 weeks <br />7.41214e-4 months <br />, with the reactor at approximately 25% power, maintenance personnel began troubleshooting the control system for shutdown bank "C and D". This troubleshooting was initiated in response to a failure of shutdown bank "C" to respond to a demand for movement during performance of surveillance testing required by Technical Specification (T.S.) 4.1.3.1.2. As part of this troubleshooting activity, on January 23, 2001, shutdown bank "D" was inserted eight steps from fully withdrawn. Individual rod motion was observed on the Individual Rod Position Indications (IRPI) during insertion but not during the subsequent withdrawal attempt. Operations personnel then attempted to withdraw shutdown bank "D", four steps in one step increments, but were unsuccessful. There was no change observed in the IRPIs, confirming that shutdown bank `D' had not moved.

Technical Specification 3.1.3.5 states that all shutdown rods shall be limited in physical insertion as specified in the Core Operating Limits Report (COLR) except for surveillance testing. The action statement of this T.S. allows for a maximum of one shutdown rod inserted beyond the insertion limit specified in the COLR. The insertion limit specified in the COLR for shutdown bank "D" is the fully withdrawn position. When the shutdown bank "D" withdrawal attempt failed and with all four shutdown bank "D" rods beyond the COLR insertion limit, T.S. 3.1.3.5 could not be met and T.S. 3.0.3 was entered. T.S.

3.0.3 requires that, within one hour, actions shall be initiated to place the unit in Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

Accordingly, a unit shutdown was commenced at 0619 hours0.00716 days <br />0.172 hours <br />0.00102 weeks <br />2.355295e-4 months <br />, and was completed when the unit reached mode 3 at 1102.

In accordance with 10 CFR 50.72(b)(2)(i), a 4-hour ENS notification was made to the NRC at 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br /> on January 23, 2001 as a condition that requires a plant shutdown. This LER is being submitted in accordance with 10 CFR 50.73(a)(2)(i)(A), for completion of a plant shutdown required by the Technical Specifications.

Cause of Event

Following plant shutdown, further troubleshooting revealed that the terminal connection in the shutdown "CD" power cabinet was approximately two turns loose. This connection is in the signal path for the lift coil signal to the shutdown "CD" lift circuit firing card. A loss of continuity in this signal path prevented the generation of full current to the lift coil, thus preventing rod withdrawal.

The apparent cause for this event was determined to be an inadequate cleaning and inspection program that failed to ensure proper tightening of the terminal connection. The existing program was inadequate in that the Recurring Task Job Order for the program required only a visual inspection of wiring terminations in the control rod drive system cabinets. This method of inspection did not verify adequate tightness of the wiring terminations.

Analysis of Event

It was concluded that the loose connection affected the withdrawal of shutdown bank "D". During the troubleshooting activities, shutdown bank "D" was inserted eight steps and did not exhibit any indication of mechanical interference. The event would not have impacted the ability of shutdown bank "D" rods from inserting into the core in the event of a reactor trip thus, the shutdown margin was not affected. The insertion of shutdown bank "D" eight steps is within the practice of normal surveillance procedures. These surveillance procedures have had the appropriate reviews to show that there was minimal impact on the safety and accident analyses. There is significant design margin at 25% reactor power to the FACILITY NAME (1) DOCKET NUMBER(2) LER NUMBER (6) PAGE (3) Donald C. Cook Nuclear Plant Unit 2 05000-316 license and safety limits, which would not be compromised by this event. As such, there was minimal safety significance associated with this event.

Corrective Actions

Immediate corrective actions that were taken included tightening the loose connection and initiating an inspection of all terminal board connections in all Unit 2 rod control cabinets. This inspection required technicians to physically touch each wire rather than perform the inspection visually. During this inspection, six additional loose terminal board connections were discovered in the rod control cabinets. All the identified loose connections were tightened in accordance with appropriate work instructions. The Unit 1 rod control cabinet terminal connections were physically inspected during a unit shutdown that occurred on February 15, 2001. Loose connections were identified and tightened.

Actions are being formulated to address the problems associated with loose electrical connections in the rod control system.

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