ENS 40287
ENS Event | |
|---|---|
01:00 Nov 2, 2003 | |
| Title | an Event That Could Have Prevented Fulfillment of the Safety Function to Mitigate the Consequences of an Accident, |
| Event Description | {{#Wiki_filter:On November 1, 2003, the plant was performing testing on the Control Room Envelope for Unfiltered In-Leakage Tracer gas Test. During this test the control room ventilation is set up to simulate system line up following an F [high drywell pressure initiation signal], A [low reactor pressure vessel level], or Z [high containment building radiation] signal. This dual pressurization line up consists of both control room emergency filtration (CREF) fans running with the normal and one of two remote air intakes isolated. This line up caused a low-flow condition to occur on both trains of CREF, rendering both trains of CREF to become inoperable. The inoperability of the CREF is due to losing the permissive to allow the heaters located in each of the fresh air ducts to the emergency filters to energize. These heaters reduce the relative humidity of air entering the emergency filters to 70%. Without the heaters the 30-day dose limits to control room personnel of GDC 19 of 10CFR50, Appendix A could be exceeded during a Design Basis Accident.
The isolation of a single remote air intake is a condition allowed under technical specification 3.3.7.1 and is also required for certain radiological and HAZMAT conditions. During an FAZ with an isolated remote air intake both trains of CREF will become inoperable until one train is shutdown. Once both trains of CREF were inoperable the plant entered LCO 3.0.3. per technical specification 3.7.3. At 1728 the plant opened the isolation valves for the second remote air intake and the low-flow condition cleared for one train of CREF and LCO 3.0.3 was exited. The plant is currently in a 7 day LCO to shutdown for having one train of CREF inoperable per 3.7.3. The NRC Resident Inspector was notified.
On 11/1/2003 at 2344 [PST], Columbia Generating Station (CGS) reported (EN# 40287) both trains of Control Room Emergency Filtration (CREF) were made inoperable during performance of tracer gas testing. This condition was reported to NRC headquarters pursuant to 10 CFR � 50.72(b)(3)(v)(D) as a condition that at the time of discovery, could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident. After further evaluation, the 8-hour report is being retracted based on the following: At 1646 (PST) on 11/1/2003, with the plant in mode 1, testing was being performed to measure control room in-leakage using (ASTM 741) tracer gas methodology. In accordance with the test procedure, the CREF system was configured in a non-standard manner that would create the most limiting in-leakage conditions. Specifically, the configuration was a dual-pressurization mode with both trains of CREF running and the normal, and one of the two remote intakes closed. This line-up caused a low-flow condition to occur in both CREF trains, and prevented electric heaters from energizing in each of the CREF air ducts containing the emergency filters. Differential pressure switches monitor the differential pressure across HEPA filters in each of the CREF trains. These switches provide a high/low alarm in the main control room to alert operators of either low airflow, fan failure, or dirt loading. Additionally, a low differential pressure setpoint provides an interlock permissive for automatic operation of an upstream duct heater. This design feature ensures the 5 KW heater has adequate airflow to prevent damage to the heater elements. When this low flow permissive is satisfied, the associated heater will cycle on and off to maintain the relative humidity of the air entering the CREF unit to 70% or lower. When the low-flow condition occurred on 11/1/2003, plant operators declared both trains of CREF inoperable and entered Technical Specifications Limiting Condition for Operation (LCO) 3.0.3 as directed by Technical Specifications LCO 3.7.3 condition D.1. This condition existed for approximately 45 minutes until 1728 (PST) when operators opened the second remote intake and the low-flow condition cleared. During the time the heaters were inoperable, meteorological conditions were recorded as: Relative Humidity (RH) between 31.5 to 34.0% RH, temperature between 39.2 to 40.3 degrees F, wind speed between 5.3 to 9.8 mph, and wind direction from the southeast. A postulated Main Steam or Feedwater line break outside of primary containment provides a potential for the RH conditions at the remote intake that was open during this event to exceed the measured ambient 34% RH. However, each of the remote intake lines are routed underground, then up through the interior of the building containing the control room, the intake ducts traverse the full length of the Control Room, and continue up to the 525 foot elevation where they join into a common line. Because the pipe is buried and routed through relatively warm internal building areas, the temperature of this fresh air makeup increases during this time of year. Test data collected in the same CREF alignment (i.e. dual train, single remote intake) showed a significant temperature increase (preliminary information indicates greater than 40 degrees F). Considering a worst-case postulated accident condition that results in remote intake inlet air containing 100% RH, only a minor temperature increase (i.e. approximately 2 degrees F) of the ambient fresh air makeup would be required to ensure that the resulting relative humidity of the air entering the CREF units was less than 95% RH. Therefore, taking into consideration the meteorological conditions, distance of the intake from CREF unit, and applying engineering judgment, it is reasonable to conclude that at all times during the approximately 45-minute event, the CREF inlet air relative humidity remained at or less than the design basis 95% RH and most likely less than the heater-controlled limit of 70% RH. As discussed in NRC Generic Letter 99-02 "Laboratory Testing of Nuclear-Grade Activated Charcoal," if ESF filtration systems have humidity control (i.e. heaters), then carbon lab testing should be in accordance with ASTM D3803-89 "Standard Test Method for Nuclear-Grade Activated Carbon" at 30 degrees C (86 degrees F) and 70% RH. For systems without humidity control the laboratory test conditions are 30 degrees C (86 degrees F) and 95% RH. Columbia's Technical Specification 5.5.7.c requires testing to demonstrate methyl iodide penetration for a sample of the CREF system charcoal adsorber is less than 2.5% when tested in accordance with ASTM D3803-89 at a temperature of (30 degrees C) 86 degrees F and 70% RH. The lower than normal flow conditions during the tracer gas test effectively resulted in a CREF system without humidity control, which per GL 99-02 would require lab testing at 30 degrees C (86 degrees F) and 95% RH. Figure A 5.1 of ASTM D3803-89 illustrates the impact of CREF unit operation with no humidity control. This figure provides the relative effect of carbon methyl iodide penetration versus % RH on new carbon. As shown by this figure, the methyl iodide penetration at 95% RH is 670% (which includes standard deviation) of penetration value at 70% RH. The most recent laboratory carbon test data for Columbia's filters provided methyl iodine penetration test results of 0.31% for train A and 0.13% for train B. Applying a multiplier of 6.7 (for the no-humidity control test 95% RH value) to these test results yields penetration values of 2.08% for train A and 0,87% for train B when no credit is taken for humidity control. A teleconference was conducted with an industry recognized charcoal testing laboratory to corroborate this carbon efficiency impact analysis. The laboratory stated they had observed an increase in penetration for used carbon of 300 to 500% (or 3 to 5 times) when varying RH from 70 to 95%. This analysis demonstrates that without reliance on the CREF heaters, the allowable methyl iodide penetration of 2.5% as specified in TS 5.5.7.c would not be exceeded and the penetration remains well below the more conservative analytical design limit of 5% (CGS accident analysis assumes 95% iodine removal efficiency for the CREF system). Therefore, the condition experienced at Columbia, on 11/1/2003 at 2344 (PST) where the CREF heaters did not energize during the low-flow condition, would not have prevented the CREF system from performing its design safety function and does not meet the criterion for reporting under 10 CFR � 50.72(b)(3)(v)(D) as "a condition that at the time of discovery, could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident. The licensee notified the NRC Resident Inspector. Notified R4DO Linda Smith. }}[[Event description::Description::{{#Regex_clear:On November 1, 2003, the plant was performing testing on the Control Room Envelope for Unfiltered In-Leakage Tracer gas Test. During this test the control room ventilation is set up to simulate system line up following an F [high drywell pressure initiation signal], A [low reactor pressure vessel level], or Z [high containment building radiation] signal. This dual pressurization line up consists of both control room emergency filtration (CREF) fans running with the normal and one of two remote air intakes isolated. This line up caused a low-flow condition to occur on both trains of CREF, rendering both trains of CREF to become inoperable. The inoperability of the CREF is due to losing the permissive to allow the heaters located in each of the fresh air ducts to the emergency filters to energize. These heaters reduce the relative humidity of air entering the emergency filters to 70%. Without the heaters the 30-day dose limits to control room personnel of GDC 19 of 10CFR50, Appendix A could be exceeded during a Design Basis Accident. The isolation of a single remote air intake is a condition allowed under technical specification 3.3.7.1 and is also required for certain radiological and HAZMAT conditions. During an FAZ with an isolated remote air intake both trains of CREF will become inoperable until one train is shutdown. Once both trains of CREF were inoperable the plant entered LCO 3.0.3. per technical specification 3.7.3. At 1728 the plant opened the isolation valves for the second remote air intake and the low-flow condition cleared for one train of CREF and LCO 3.0.3 was exited. The plant is currently in a 7 day LCO to shutdown for having one train of CREF inoperable per 3.7.3. The NRC Resident Inspector was notified.
On 11/1/2003 at 2344 [PST], Columbia Generating Station (CGS) reported (EN# 40287) both trains of Control Room Emergency Filtration (CREF) were made inoperable during performance of tracer gas testing. This condition was reported to NRC headquarters pursuant to 10 CFR � 50.72(b)(3)(v)(D) as a condition that at the time of discovery, could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident. After further evaluation, the 8-hour report is being retracted based on the following: At 1646 (PST) on 11/1/2003, with the plant in mode 1, testing was being performed to measure control room in-leakage using (ASTM 741) tracer gas methodology. In accordance with the test procedure, the CREF system was configured in a non-standard manner that would create the most limiting in-leakage conditions. Specifically, the configuration was a dual-pressurization mode with both trains of CREF running and the normal, and one of the two remote intakes closed. This line-up caused a low-flow condition to occur in both CREF trains, and prevented electric heaters from energizing in each of the CREF air ducts containing the emergency filters. Differential pressure switches monitor the differential pressure across HEPA filters in each of the CREF trains. These switches provide a high/low alarm in the main control room to alert operators of either low airflow, fan failure, or dirt loading. Additionally, a low differential pressure setpoint provides an interlock permissive for automatic operation of an upstream duct heater. This design feature ensures the 5 KW heater has adequate airflow to prevent damage to the heater elements. When this low flow permissive is satisfied, the associated heater will cycle on and off to maintain the relative humidity of the air entering the CREF unit to 70% or lower. When the low-flow condition occurred on 11/1/2003, plant operators declared both trains of CREF inoperable and entered Technical Specifications Limiting Condition for Operation (LCO) 3.0.3 as directed by Technical Specifications LCO 3.7.3 condition D.1. This condition existed for approximately 45 minutes until 1728 (PST) when operators opened the second remote intake and the low-flow condition cleared. During the time the heaters were inoperable, meteorological conditions were recorded as: Relative Humidity (RH) between 31.5 to 34.0% RH, temperature between 39.2 to 40.3 degrees F, wind speed between 5.3 to 9.8 mph, and wind direction from the southeast. A postulated Main Steam or Feedwater line break outside of primary containment provides a potential for the RH conditions at the remote intake that was open during this event to exceed the measured ambient 34% RH. However, each of the remote intake lines are routed underground, then up through the interior of the building containing the control room, the intake ducts traverse the full length of the Control Room, and continue up to the 525 foot elevation where they join into a common line. Because the pipe is buried and routed through relatively warm internal building areas, the temperature of this fresh air makeup increases during this time of year. Test data collected in the same CREF alignment (i.e. dual train, single remote intake) showed a significant temperature increase (preliminary information indicates greater than 40 degrees F). Considering a worst-case postulated accident condition that results in remote intake inlet air containing 100% RH, only a minor temperature increase (i.e. approximately 2 degrees F) of the ambient fresh air makeup would be required to ensure that the resulting relative humidity of the air entering the CREF units was less than 95% RH. Therefore, taking into consideration the meteorological conditions, distance of the intake from CREF unit, and applying engineering judgment, it is reasonable to conclude that at all times during the approximately 45-minute event, the CREF inlet air relative humidity remained at or less than the design basis 95% RH and most likely less than the heater-controlled limit of 70% RH. As discussed in NRC Generic Letter 99-02 "Laboratory Testing of Nuclear-Grade Activated Charcoal," if ESF filtration systems have humidity control (i.e. heaters), then carbon lab testing should be in accordance with ASTM D3803-89 "Standard Test Method for Nuclear-Grade Activated Carbon" at 30 degrees C (86 degrees F) and 70% RH. For systems without humidity control the laboratory test conditions are 30 degrees C (86 degrees F) and 95% RH. Columbia's Technical Specification 5.5.7.c requires testing to demonstrate methyl iodide penetration for a sample of the CREF system charcoal adsorber is less than 2.5% when tested in accordance with ASTM D3803-89 at a temperature of (30 degrees C) 86 degrees F and 70% RH. The lower than normal flow conditions during the tracer gas test effectively resulted in a CREF system without humidity control, which per GL 99-02 would require lab testing at 30 degrees C (86 degrees F) and 95% RH. Figure A 5.1 of ASTM D3803-89 illustrates the impact of CREF unit operation with no humidity control. This figure provides the relative effect of carbon methyl iodide penetration versus % RH on new carbon. As shown by this figure, the methyl iodide penetration at 95% RH is 670% (which includes standard deviation) of penetration value at 70% RH. The most recent laboratory carbon test data for Columbia's filters provided methyl iodine penetration test results of 0.31% for train A and 0.13% for train B. Applying a multiplier of 6.7 (for the no-humidity control test 95% RH value) to these test results yields penetration values of 2.08% for train A and 0,87% for train B when no credit is taken for humidity control. A teleconference was conducted with an industry recognized charcoal testing laboratory to corroborate this carbon efficiency impact analysis. The laboratory stated they had observed an increase in penetration for used carbon of 300 to 500% (or 3 to 5 times) when varying RH from 70 to 95%. This analysis demonstrates that without reliance on the CREF heaters, the allowable methyl iodide penetration of 2.5% as specified in TS 5.5.7.c would not be exceeded and the penetration remains well below the more conservative analytical design limit of 5% (CGS accident analysis assumes 95% iodine removal efficiency for the CREF system). Therefore, the condition experienced at Columbia, on 11/1/2003 at 2344 (PST) where the CREF heaters did not energize during the low-flow condition, would not have prevented the CREF system from performing its design safety function and does not meet the criterion for reporting under 10 CFR � 50.72(b)(3)(v)(D) as "a condition that at the time of discovery, could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident. The licensee notified the NRC Resident Inspector. Notified R4DO Linda Smith. }}| ]] |
| Where | |
|---|---|
Columbia Generating Station  Washington (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+1.73 h0.0721 days <br />0.0103 weeks <br />0.00237 months <br />) | |
| Opened: | Stephen Magill 02:44 Nov 2, 2003 |
| NRC Officer: | Chauncey Gould |
| Last Updated: | Dec 26, 2003 |
| 40287 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |