Headquarters Daily Report SEPTEMBER 03, 1997 *************************************************************************** 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 SEP. 03, 1997 MR Number: H-97-0106 NRR DAILY REPORT ITEM SIGNIFICANT EVENTS Subject: POTENTIAL LOSS OF COOLING CAPABILITY DUE TO GAS ACCUMULATION IN REACTOR VESSEL HEAD The NRR/AEOD/RES Events Assessment Panel on June 17, 1997, classified the potential loss of cooling capability due to gas accumulation in the reactor vessel head at Zion Unit 2, as a Significant Event for the Performance Indicator Program. On March 7, 1997, with Unit 2 in cold shutdown, the licensee identified a gas bubble in the reactor vessel head. The void was discovered when an operator questioned the computer trend plots for the volume control tank (VCT) and pressurizer levels. The head was vented and approximately 6900 gallons of water were required to refill the head. It was later determined that vessel level had decreased to approximately 2.6 feet below the vessel flange. The source of the gas was the nitrogen blanket on the VCT. Since nitrogen is water soluble, the nitrogen gas present in the free space of the VCT tends to go into solution until an equilibrium is established. Because the VCT temperature was lower than that of the RCS, the solubility of nitrogen in the RCS was less than that of the VCT. When water was transferred from the VCT to the RCS, the water was heated, causing nitrogen gas to come out of solution and accumulate in the reactor vessel head. Given the geometry and configuration of the facility, the plant conditions and the operating practices at that time, the potential existed for a void to have been created in the reactor vessel that could have impacted decay heat removal. Additionally, the accumulation of gas in the steam generators could have prevented the preferred alternative method of RCS cooling due to the obstruction of natural circulation flow. The Reactor Vessel Level Indicating System (RVLIS) was available but not in service during this event. The licensee's procedures did not require RVLIS to be in service and did not direct the operators to monitor RVLIS during this mode of operation (cold shutdown) nor during a loss-of-shutdown-cooling condition. A precursor to this event occurred on Unit 1 in September of 1996 when Unit 1 experienced an unexpected gas accumulation in the reactor vessel head. The licensee initiated a root cause investigation, however, approval of the investigation and implementation of the corrective actions were postponed by plant management pending completion of the on-going Unit 2 refueling outage. If the identified corrective actions had been implemented in a timely manner on both units, the March 7 event probably would not have occurred. Further, if the licensee had more aggressively reviewed operating experience and applied industry lessons learned, possibly neither event HEADQUARTERS MORNING REPORT PAGE 2 SEP. 03, 1997 MR Number: H-97-0106 (cont.) would have occurred. CONTACT: William F. Burton, NRR/DRPM/PECB (301) 415-2853 _ HEADQUARTERS MORNING REPORT PAGE 2 SEPTEMBER 3, 1997 MR Number: H-97-0107 NRR DAILY REPORT ITEM SIGNIFICANT EVENTS Subject: POTENTIAL LOSS OF COOLING CAPABILITY DUE TO VOIDING IN THE REFERENCE LEG OF THE PRESSURIZER LEVEL INSTRUMENT The NRR/AEOD/RES Events Assessment Panel on June 17, 1997, classified the potential loss of cooling capability due to voiding in the reference leg of the pressurizer level instrument at Sequoyah Unit 1, as a Significant Event for the Performance Indicator Program. On March 23, 1997, Sequoyah Unit 1 was depressurized from approximately 325 psig to approximately 30 psig in preparation for entering cold shutdown. On March 24, 1997, a draindown was initiated to reduce the reactor coolant system (RCS) inventory from solid conditions to approximately 25 percent pressurizer level. As a result of the earlier depressurization, dissolved gases in the reference leg came out of solution, partially voiding the reference leg of the cold-calibrated level instrument, and causing an erroneous pressurizer level indication. As a result of the incorrect level indication and a lack of understanding of the plant configuration and operation, the level was reduced below 25 percent. A low level alarm was initiated at approximately 17 percent pressurizer level based on the hot-calibrated instrument. An operator later recognized the plant condition, secured the draindown, and refilled the system to approximately 25 percent. Shutdown cooling was not affected and RCS temperature remained at approximately 140F degrees throughout the event. However, had the operator not recognized that an excessive inventory loss had occurred, level could have decreased to the point of affecting shutdown cooling. A similar event occurred on Unit 1 in 1993 when approximately 10,000 gallons of water were drained from the RCS due to inaccurate level indication caused by voiding of the reference leg of the cold-calibrated level instrument. The corrective actions which were developed as a result of this event included modifications to plant procedures instructing the operators to use various pressurizer level indications during plant evolutions. However, these modifications were not implemented in all applicable procedures. Had lessons learned from the earlier event been fully implemented, this second loss of inventory probably would not have occurred. CONTACT: William F. Burton, NRR/DRPM/PECB (301) 415-2853 _ REGION III MORNING REPORT PAGE 3 SEPTEMBER 3, 1997 Licensee/Facility: Notification: Indiana Department Of Transportation MR Number: 3-97-0091 Indiana Department Of Transportatio Date: 09/02/97 Greenfield,Indiana TELEPHONIC FIELDSITE INSPECTION Dockets: 03032463 License No: 13-26341-01 Subject: MOISTURE DENSITY GAUGE DAMAGED BY VEHICLE Discussion: On August 27, 1997, at approximately 3:30 a.m., a Troxler moisture density gauge, Model 3440, was damaged by a vehicle on I-70 in Indianapolis, Indiana. The gauge contained a nominal 8 millicurie (0.3 GBq) of cesium-137 sealed source and 40 millicurie (1.48 GBq) americium-241 sealed source. The incident occurred on I-70 in a coned off (restricted for public use) area. After completing measurements with the nuclear gauge, the gauge technician was in the process of preparing for the next test when an automobile crossed the coned area at a high rate of speed and ran over the gauge. The automobile did not stop after the gauge was run over. No one was injured during the incident. The housing unit was damaged; however, the sources appeared to remain intact and shielded within the device. The nuclear gauge was located next to the gauge technician prior to the incident. The gauge user notified the area engineer and together loaded the gauge into its Type A shipping container. The radiation safety officer (RSO) was contacted at approximately 9:18 a.m. regarding the damaged gauge by the area engineer. The RSO made a radiation survey of the gauge and did not identify any abnormal radiation levels. The gauge is at the licensee's Greenfield office in a secure area. The licensee will perform a leak test of the gauge and supply the NRC with the test results in the next few days. The gauge will be returned to the manufacturer for disposal. The State of Indiana and NMSS have been notified of this event. Contact: MICHAEL M. LAFRANZO (630)829-9865 JOHN R. MADERA (630)829-9834 _