Headquarters Daily Report APRIL 04, 1996 *************************************************************************** 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 APRIL 4, 1996 MR Number: H-96-0025 NRR DAILY REPORT ITEM SIGNIFICANT EVENTS Subject: SOUTH TEXAS, UNIT 1, REACTOR TRIP WITH CONTROL ROD INSERTION PROBLEMS, CLASSIFIED AS A SIGNIFICANT EVENT The NRR/AEOD/RES Events Assessment Panel on March 26, 1996, classified the South Texas, Unit 1, reactor trip with complications on December 18, 1995, as a Significant Event for the Performance Indicator Program. The significant event classification was based on a reactor trip with complications, specifically, on non-compliance with emergency operating procedures (EOPs) having a potential for impacting plant safety; however, the failure to emergency borate had negligible impact to plant safety. From a generic aspect, the failure of control rods to insert fully could have an effect on the shutdown margin. On December 18, 1995, with Unit 1 at 100 percent power, a main transformer lock out resulted in a turbine trip and reactor trip. In response to the trip, three control rod bottom lights failed to light and the digital rod position indicated six steps out for each rod. Following the transient, one rod drifted to the bottom, and the other two were manually inserted. During subsequent rod testing, an additional control rod failed to insert fully. South Texas has a 14 foot core with Westinghouse Standard XL, Standard XLR, and VANTAGE 5H 17 x 17 fuel assemblies, and the affected control rods were found in twice burned Standard XLR fuel with burnup greater then 42,880 megawatt days(MWD)/metric ton uranium(MTU). Without sufficient evidence to support their decision, the operating crew concluded that the rod position indications were inaccurate, and the three control rods were at the bottom limit of travel. This permitted the crew to declare all of the control rods had fully inserted and proceed with scram recovery without initiating emergency boration. An expected recovery response was an automatic shift of charging pump suction to the refueling water storage tank, which was considered an acceptable alternative to emergency boration. The trip was within the design basis and all systems functioned effectively. With respect to the stuck control rods, the rod worth for the last six steps has minimal affect to adequate shut down margin. The follow-up safety evaluation demonstrated shutdown margin would be maintained to the end of fuel cycle with the assumption that 32 control assemblies stop at 12 steps from the bottom following a presumed reactor trip. Information Notice 96-12, "Control Rod Insertion Problems," dated February 15, 1996, discussed details of both the South Texas trip and the Wolf Creek trip on January 30, 1996. Subsequently, Bulletin 96-01, dated March 8, 1996, requested Westinghouse utilities to conduct specified control rod tests. Root cause of the control rod problem is still under investigation. On March 15, 1996, Region IV cited South Texas with a severity level IV violation, on the basis that the non-compliance with HEADQUARTERS MORNING REPORT PAGE 2 APRIL 4, 1996 MR Number: H-96-0025 (cont.) EOPs had a potential for impacting plant safety, but the failure to emergency borate had no actual impact to plant safety. Contact: Stephen S. Koenick, NRR/DRPM/PECB (301) 415-2841 _ Headquarters Daily Report APRIL 04, 1996 *************************************************************************** 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 APRIL 4, 1996 MR Number: H-96-0025 NRR DAILY REPORT ITEM SIGNIFICANT EVENTS Subject: SOUTH TEXAS, UNIT 1, REACTOR TRIP WITH CONTROL ROD INSERTION PROBLEMS, CLASSIFIED AS A SIGNIFICANT EVENT The NRR/AEOD/RES Events Assessment Panel on March 26, 1996, classified the South Texas, Unit 1, reactor trip with complications on December 18, 1995, as a Significant Event for the Performance Indicator Program. The significant event classification was based on a reactor trip with complications, specifically, on non-compliance with emergency operating procedures (EOPs) having a potential for impacting plant safety; however, the failure to emergency borate had negligible impact to plant safety. From a generic aspect, the failure of control rods to insert fully could have an effect on the shutdown margin. On December 18, 1995, with Unit 1 at 100 percent power, a main transformer lock out resulted in a turbine trip and reactor trip. In response to the trip, three control rod bottom lights failed to light and the digital rod position indicated six steps out for each rod. Following the transient, one rod drifted to the bottom, and the other two were manually inserted. During subsequent rod testing, an additional control rod failed to insert fully. South Texas has a 14 foot core with Westinghouse Standard XL, Standard XLR, and VANTAGE 5H 17 x 17 fuel assemblies, and the affected control rods were found in twice burned Standard XLR fuel with burnup greater then 42,880 megawatt days(MWD)/metric ton uranium(MTU). Without sufficient evidence to support their decision, the operating crew concluded that the rod position indications were inaccurate, and the three control rods were at the bottom limit of travel. This permitted the crew to declare all of the control rods had fully inserted and proceed with scram recovery without initiating emergency boration. An expected recovery response was an automatic shift of charging pump suction to the refueling water storage tank, which was considered an acceptable alternative to emergency boration. The trip was within the design basis and all systems functioned effectively. With respect to the stuck control rods, the rod worth for the last six steps has minimal affect to adequate shut down margin. The follow-up safety evaluation demonstrated shutdown margin would be maintained to the end of fuel cycle with the assumption that 32 control assemblies stop at 12 steps from the bottom following a presumed reactor trip. Information Notice 96-12, "Control Rod Insertion Problems," dated February 15, 1996, discussed details of both the South Texas trip and the Wolf Creek trip on January 30, 1996. Subsequently, Bulletin 96-01, dated March 8, 1996, requested Westinghouse utilities to conduct specified control rod tests. Root cause of the control rod problem is still under investigation. On March 15, 1996, Region IV cited South Texas with a severity level IV violation, on the basis that the non-compliance with HEADQUARTERS MORNING REPORT PAGE 2 APRIL 4, 1996 MR Number: H-96-0025 (cont.) EOPs had a potential for impacting plant safety, but the failure to emergency borate had no actual impact to plant safety. Contact: Stephen S. Koenick, NRR/DRPM/PECB (301) 415-2841 _