Headquarters Daily Report OCTOBER 07, 1998 *************************************************************************** REPORT NEGATIVE NO INPUT ATTACHED INPUT RECEIVED RECEIVED HEADQUARTERS û REGION I û REGION II û REGION III û REGION IV û PRIORITY ATTENTION REQUIRED MORNING REPORT - HEADQUARTERS OCTOBER 7, 1998 MR Number: H-98-0146 NRR DAILY REPORT ITEM SIGNIFICANT EVENTS Subject: SUSQUEHANNA, UNIT 2 - AUTOMATIC SCRAM DURING START UP ON 7/2/98 CLASSIFIED AS A SIGNIFICANT EVENT On 9/28/98, the NRR/AEOD/RES Events Assessment Panel classified the automatic scram at Susquehanna, Unit 2, as a Significant Event for the Performance Indicator program based on information provided in the licensee event report (LER 50/388 98-010, Accession #9808070296). Although the safety significance of this event was minimal because of the low power at which the event occurred (less than 1%), the panel determined that there was a significant breakdown of command and control on the part of the control room staff and operating procedure inadequacies that resulted in the reactor scram on 7/2/98. The plant was starting up in accordance with the licensee's general operating procedure. In addition to the Shift Supervisor, the Unit-2 operating crew consisted of a Unit Supervisor and an additional senior reactor operator (SRO) who was specifically assigned the reactivity management aspects of the startup, one operator (RO-1) in charge of making reactivity changes, one operator (RO-2) acting as a control rod position verifier and one operator (RO-3) responsible for balance of plant activities. The plant achieved criticality at 02:58am with rods in Group 2 of the rod pull sheets. Overlap testing of the start up range monitor (SRM)/intermediate range monitor (IRM) systems was performed and the SRMs were withdrawn from the core and the IRM chart recorders were placed in slow speed. Single notch control rod withdrawal was continued from 03:10am to 03:12am until a reactor period of 200 seconds was reached. At that point, further rod withdrawal was suspended so that the operators could perform other start up activities, including opening of the main steam isolation valves (MSIVs). At 04:15am, the SRO assigned for reactivity management and RO-1 and RO-2 discussed the resumption of control rod withdrawal. They decided to perform a continuous rod withdrawal until a response was observed on the SRMs. The crew did not recognize that the reactor had become sub-critical while they had performed the other start up activities. The next rod on the pull sheet was continuously withdrawn by RO-1 from position 22 to position 48. A slight increase in IRM indications was observed before settling out. The next rod was selected and continuously withdrawn by RO-1 from position 00 (full in) to position 24. Reactor power began increasing. Post scram reconstitution of digital IRM data determined that power had increased on a 30 second period but this digital data is not available to the operators. The SRO directed RO-2 to up range the E' IRM. RO-2 inadvertently ranged the IRM from 5 to 7 (two positions instead of one). Recognizing the error, RO-2 immediately down ranged the IRM to position 6. RO-2 next attempted to up range 'C' IRM from 5 to 6, but inadvertently ranged it from 5 to 4, causing a half scram signal on the Division I IRM upscale trip. Three seconds later, RO-1 inadvertently ranged the D' IRM from position 6 to position 5 (instead of position 7), resulting in a Division II IRM upscale trip and completing the logic for HEADQUARTERS MORNING REPORT PAGE 2 OCTOBER 7, 1998 MR Number: H-98-0146 (cont.) a reactor scram at 04:17am. Several breakdowns in the licensee's defense in depth philosophy combined to result in the reactor scram: (1) procedures were less than adequate. Criticality occurred in Group 2 of the rod pull sequence. Whereas procedures direct operators to perform notch withdrawal, including Group 2 rods, when the reactor is close to being critical, the procedures did not restrict control rod withdrawal for Group 2 rods following initial criticality. Group 2 rods are permitted to go from full in to full out. Restrictions did exist for the Group 3 rods in the rod pull sequence. Also, per procedure, the SRMs were withdrawn from the core and the IRM recorders switched to slow speed after SRM/IRM overlap was achieved. With SRMs withdrawn from the core, a power change in the core will not be immediately detected by the SRMs, and with the IRM recorders in slow speed the recorders do not provide useful trend information for changes in reactor power. (2) the SRO responsible for reactivity management and the 2 ROs did not recognize that the reactor had become sub critical during the delay to open the MSIVs. After initially reaching criticality, the operators did not check to see if the reactor was still critical after nearly an hour delay in further rod withdrawals while other start up activities were addressed. Operating crews at Susquehanna are trained on the simulator for unit start up from the point of criticality to 50øF above the point of adding heat with decay heats similar to that observed on July 2, 1998. The simulator training did not include suspending rod withdrawals while attending to other start up activities with the reactor just above the point of criticality. (3) team dynamics were inadequate. RO-2, as the verifier, should not have manipulated any controls on the board. Only RO-1 should have been ranging the IRMs during the power increase. The failure to maintain defined roles allowed both channels of the scram logic to be completed, and caused the scram when the two operators both made the same error of down ranging the IRMs. It is important to note that is likely that even if RO-1 was the only operator manipulating the IRM range switches, a reactor scram would have occurred due to an IRM upscale trip because of the relatively high power increase rate that occurred because of the continuous rod withdrawal. (4) management and supervisory oversight failed. The SRO responsible for reactivity management determined that it was acceptable to continuously withdraw control rods. The Shift Supervisor and the Unit Supervisor in the control room were not involved in the decision to continue the startup with a continuous rod withdrawal after rod pulls were suspended while the MSIVs were opened. (5) during a previous startup, several days earlier, a similar event occurred that resulted in a similar core response. The RO-1 on duty during that startup terminated the rate of power increase by partially inserting a control rod. Because this earlier event was not documented, it was not identified and corrected by the licensee prior to the July 2, 1998 event. HEADQUARTERS MORNING REPORT PAGE 3 OCTOBER 7, 1998 MR Number: H-98-0146 (cont.) Contacts: Cliff Anderson, Region I (610) 337-5227 E-mail: cja@nrc.gov Dave Skeen, NRR/PECB (301) 415-1174 E-mail: dls@nrc.gov _