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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 53851 | 30 January 2019 15:10:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Secondary Containment Inoperable | At 0910 (CST) on January 30, 2019, the Dresden Station Heater Boiler 'B' tripped while placing the station Heater Boiler 'A' in service. With colder temperatures, the density of the supply air increased and contributed to a greater quantity of air entering the Reactor Building than what was previously being supplied with heating steam in service. The Reactor Building differential pressure (DP) degraded and dropped below 0.25 inches water column vacuum. This condition represents a failure to meet Technical Specification (TS) Surveillance Requirement 3.6.4.1.1. Entry into TS 3.6.4.1 Condition A was made due to Secondary Containment becoming inoperable. Standby Gas Treatment System was initiated to assist with Reactor Building DP control. Reactor Building DP was restored to greater than 0.25 inches water column vacuum. TS 3.6.4.1 Condition A was exited. This event is being reported under 10 CFR 50.72(b)(3)(v)(C), 'Any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to ... control the release of radioactive material.' The NRC Resident Inspector has been notified. | Secondary containment Standby Gas Treatment System | |
| ENS 52582 | 1 March 2017 00:25:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Short Duration Loss of Secondary Containment Due to Severe Weather | At 1825 (CST) on 02/28/2017, Dresden Station received unexpected alarm 923-5 C-1, RX BLDG DP LO (Reactor Building Differential Pressure Low). Reactor Building differential pressure was observed to briefly lose vacuum and return to a normal reading of 0.6 inches vacuum water gauge. At the time of the transient, Grundy County was under a Severe Weather Warning and gusts of wind were being monitored from the Main Control Room up to approximately 57 mph. The Reactor Building differential pressure returned to (greater than or equal to) 0.25 inches vacuum water gauge at 18:25 after 18 seconds with no operator action. Operators observed differential pressure reading to lose vacuum, below 0 inches vacuum water gauge, for approximately 3 seconds. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.1. As a result, entry into Technical Specifications 3.6.4.1 condition A was made due to Secondary Containment being inoperable. This event is being reported in accordance with 10CFR50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function. An issue report has been initiated and a 60-day Licensee Event Report will be submitted in accordance with 10CFR50.73(a)(2)(v)(C). The NRC Resident Inspector has been notified.
The purpose of this notification is to retract ENS notification 52582 made on 2/28/17 for Dresden Nuclear Power Station. The previous notification reported a potential loss of Reactor Building differential pressure due to high wind conditions and associated entry into Technical Specification 3.6.4.1 Condition A for failure to meet Surveillance Requirement 3.6.4.1.1 to maintain differential pressure above 0.25 inches vacuum water gauge. After further evaluation, it has been determined that the high winds caused a momentary low pressure pocket on the leeward side of the Reactor Building causing the differential pressure reading seen in the Main Control Room, but it did not challenge Reactor Building differential pressure or Secondary Containment. Reactor Building differential pressure indication utilizes four transmitters, one on each wall of the Reactor Building, and the most conservative reading is transmitted to the indicator in the Main Control Room. Wind conditions impacting a single transmitter would result in indication of low Reactor Building differential pressure in the Main Control Room. Procedures direct action to obtain local readings from all four Reactor Building differential pressure transmitters. After the low indication in the Main Control Room, Equipment Operators were dispatched to obtain local indication and all four transmitters were found to be indicating 0.6 inches vacuum water gauge. This was a short duration transient with no indications of an equipment failure that could impact Secondary Containment. The entire transient occurred within an 18 second window where differential pressure indication began at 0.6 inches vacuum water gauge, dropped to below 0 inches vacuum water gauge, and subsequently restored to 0.6 inches vacuum water gauge with no operator intervention. Furthermore, a significant change in Reactor Building differential pressure would impact readings on Drywell pressure because the Reactor Building pressure is used as a reference leg. Trends of Drywell pressure during the event indicated no adverse conditions implying that Reactor Building differential pressure was stable. Thus, it has been concluded that this was an indication issue and at no point during the transient would Secondary Containment have been unable to perform its safety function. Therefore, this event does not meet the criteria of 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function, and the ENS notification is being retracted. There is no longer a requirement for an associated 60-day Licensee Event Report in accordance with 10 CFR 50.73(a)(2)(v)(C). The NRC Resident Inspector has been notified. Notified R3DO (Jeffers). | Secondary containment | |
| ENS 52355 | 8 November 2016 11:10:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Reactor Building to Atmosphere Differential Pressure Out of Specifications | On 11/8/16, Operators were performing Division I Undervoltage Testing Surveillance on Unit 3, when a 2 (psi) drywell signal was inserted, Reactor Building Ventilation tripped and SBGT initiated as expected. At 0510 (CST), reactor building to atmosphere differential pressure dropped below the (negative) 0.25 inches water. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.1. As a result, entry into Technical Specification 3.6.4.1 condition A was made due to Secondary Containment becoming inoperable. This event is being reported in accordance with 10CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function. At 0532, the 2/3 Reactor Building material interlock inner door was closed and Reactor Building (differential pressure) was restored to greater than (negative).25 inches of water column. An issue report has been initiated. An investigation will be conducted and a 60 day Licensee Event report will be submitted in accordance with 10 CFR 50.73(a)(2)(v)(C). The NRC Resident Inspector has been notified. | Secondary containment Reactor Building Ventilation | |
| ENS 51721 | 10 February 2016 03:42:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Secondary Containment Inoperable | At 2142 (CST) on February 9, 2016, Reactor Building differential pressure did not meet the required 0.25 inches of vacuum water gauge due to failure of the control system. At 2205, the Unit 3 Reactor Building Ventilation System was secured and manually isolated. The Reactor Building differential pressure returned to (greater than or equal to) 0.25 inches of vacuum water gauge at 2207. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.1. As a result, entry into Technical Specifications 3.6.4.1 condition A was made due to Secondary Containment being inoperable. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified. | Secondary containment Reactor Building Ventilation | |
| ENS 51374 | 5 September 2015 15:10:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Secondary Containment Inoperable Due to Loss of Vacuum from Open Inspection Hatch | At 1010 (CDT) on September 5, 2015, Reactor Building differential pressure did not meet the required 0.25 inches of vacuum due to an open inspection hatch. At 1018 (CDT), an inspection hatch was found to have fallen open and (was) subsequently closed (manually) on the Reactor Building exhaust fan damper access hatch. The damper is outside of the Reactor Building secondary containment isolation boundary. Following closure of the hatch, Reactor Building differential pressure returned to greater than or equal to 0.25 inches of vacuum water gauge. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.1. As a result, entry into Technical Specifications 3.6.4.1 condition A was made due to Secondary Containment being inoperable. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)c as a condition that could have prevented the fulfillment of a safety function. The NRC Senior Resident Inspector has been notified. | Secondary containment | |
| ENS 51371 | 4 September 2015 13:10:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Secondary Containment Inoperable Due to Both Airlock Doors Being Open Simultaneously | At 0810 (CDT) on September 4, 2015, two Secondary Containment doors in one access opening, were opened simultaneously. The interlock mechanism preventing both doors from operating simultaneously at the Unit 2 570 foot elevation Turbine to Reactor Building interlock did not operate as expected. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.2. As a result, entry into Technical Specifications 3.6.4.1 condition A was made due to Secondary Containment being inoperable. Secondary Containment differential pressure was maintained within specification. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function. The NRC Senior Resident Inspector has been notified. | Secondary containment | |
| ENS 49963 | 27 March 2014 06:51:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Failure of Secondary Containment Door Interlock | At 0151 (CDT) on March 27, 2014, indication was received in the Control Room that two Secondary Containment doors, in the 2/3 Diesel Generator Interlock, were opened simultaneously. An equipment operator, in the field at the time of the event, reported that while opening the reactor building side interlock doors, individuals were able to open the diesel side interlock doors. The interlock mechanism preventing both doors from operating simultaneously did not operate as expected. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.2, since two doors in a singular access opening were allowed to open. As a result, entry into Technical Specification 3.6.4.1 Condition A was made due to Secondary Containment being inoperable. The doors were open for approximately 5 seconds and were immediately secured. Secondary Containment differential pressure was maintained throughout the event. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified. | Secondary containment | |
| ENS 49590 | 28 November 2013 08:58:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Secondary Containment Declared Inoperable While Two Secondary Containment Doors Were Simultaneously Open | At 0258 CST on November 28, 2013, two individuals were removing materials from the main steam isolation valve room (X-Area) and defeated an interlock which allowed them to open two secondary containment doors simultaneously. The X-Area personnel access doors connect secondary containment to the turbine building and are part of the secondary containment boundary. At the time of this event, Dresden Unit 2 was in Mode 4 and secondary containment was not required. However, Dresden Unit 3 was in Mode 1 which requires secondary containment to be operable. Throughout this event, secondary containment differential pressure was maintained within technical specifications surveillance requirement 3.6.4.1.1 limits, and the individuals remained in the area with the capability to close the personnel access doors. This condition represents a failure to meet surveillance requirement 3.6.4.1.2, since both doors in a singular access opening were allowed to open. As a result, entry into technical specification 3.6.4.1 condition A was made, for Unit 3, due to secondary containment being inoperable. The doors were secured at 0311 and secondary containment was declared operable. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of the safety function. The NRC Resident Inspector has been notified. | Secondary containment Main Steam Isolation Valve | |
| ENS 49543 | 16 November 2013 16:19:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Failure of Secondary Containment Interlock Mechanism | At 10:19:02 (CST) on November 16, 2013, indication was received in the Control Room that two Secondary Containment doors, in one access opening, were open simultaneously. The interlock mechanism preventing both doors from operating simultaneously did not operate as expected. A worker was staged in the interlock to operate the doors as an interim action while a modification to prevent additional failures was being developed. The worker reported that while opening the reactor building side door the Turbine Building side door opened several inches. Both doors were immediately closed and the interlock was removed from use. Secondary Containment differential pressure remained within Technical Specification required values during the short time both doors were open. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.2. As a result, entry into Technical Specification 3.6.4.1 Condition A was made momentarily due to Secondary Containment being inoperable. The doors were secured at 10:19:07 (CST) and Secondary Containment was declared Operable. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of the safety function. The NRC Resident Inspector has been notified. | Secondary containment | |
| ENS 49503 | 5 November 2013 14:42:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Secondary Containment Declared Inoperable Due to Failure of Interlock Mechanism | At 08:42 (CST) on November 5, 2013, indication was received in the Control Room that two Secondary Containment doors, in one access opening, were opened simultaneously. The interlock mechanism preventing both doors from operating simultaneously did not operate as expected. A worker in the field reported that the Turbine Building side door was opened, and simultaneously the Reactor Building side door opened several inches and then quickly re-closed. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.2. As a result, entry into Technical Specification 3.6.4.1, Condition A, was made momentarily due to Secondary Containment being inoperable. The doors were secured at 08:42 and Secondary Containment was declared Operable. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified. See similar events 49153 and 49379. The licensee is tracking the failure as Incident Report 01581320. | Secondary containment | |
| ENS 49379 | 23 September 2013 21:55:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Both Secondary Containment Access Doors Opened Simultaneously | At 16:55:59 (CDT) on September 23, 2013, indication was received in the Control Room that two Secondary Containment doors, in one access opening, were opened simultaneously. The interlock mechanism preventing both doors from operating simultaneously did not operate as expected. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.2. As a result, entry into Technical Specifications 3.6.4.1 condition A was made due to Secondary Containment being inoperable. The doors were secured at 16:56:04 and Secondary Containment was declared operable. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified. | Secondary containment | |
| ENS 49153 | 28 June 2013 12:49:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Door Interlock Malfunction Resulted in Brief Loss of Secondary Containment | At 0749 CDT on June 28, 2013, indication was received in the Control Room that two Secondary Containment doors, in one access opening, were opened simultaneously. The interlock mechanism preventing both doors from operating simultaneously did not operate as expected. This condition represents a failure to meet Surveillance Requirement 3.6.4.1.2. As a result, entry into Technical Specifications 3.6.4.1 Condition A was made due to Secondary Containment being declared inoperable. The doors were secured at 0749 CDT (total time with both doors open was 7 seconds) and Secondary Containment was declared operable. This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified. | Secondary containment | |
| ENS 47540 | 21 December 2011 06:46:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Both Unit Two Secondary Containment Doors Were Inadvertently Left Open | On 12/21/11 at 0046 Secondary Containment integrity was lost when both U2 Reactor Building interlock doors were open simultaneously. Interlock door electrical checks were in progress. TS LCORA 3.6.4.1.Condition A was entered. Reactor Building differential pressure remained within Tech Spec limits. The doors were both open for approximately 9 seconds. The cause of the event is being investigated. The NRC Resident Inspector has been notified. The State of Illinois Inspector will be notified.
On 12/21/2011, EN 47540 was made describing a condition where secondary containment was declared inoperable due to not meeting the surveillance requirement for having one access door closed. This was reported as a loss of safety function for the secondary containment. This condition occurred during a planned maintenance activity. During a maintenance activity both doors unexpectedly opened. As a part of the maintenance, the inner door was opened by maintenance personnel using the normal control pushbutton. Upon personnel observing the outer door opening, the inner door button was released and the functional door automatically closed. Although both doors were briefly open, the negative pressure required to ensure secondary containment integrity was maintained at all times. Based on the door immediately closing and negative pressure being maintained, this is not considered a loss of safety function. Therefore this EN is being retracted. The NRC Resident Inspector has been notified. Notified R3DO (Giessner). | Secondary containment |