ML20059B152
| ML20059B152 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 12/15/1993 |
| From: | Rehn D DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-93-002, IEB-93-2, NUDOCS 9401030361 | |
| Download: ML20059B152 (6) | |
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.l-Duke n>w Company DLRmv Catawba Suclear Generauon Depanment Uce President.
4800 ConcordRoad (803}U14% office.
York, SC2976 (803)U13426 Fax DUKEPOWER December 15,1993 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555
Subject:
Catawba Nuclear Station, Units 1 and 2 Docket Nos. 50-413 and 50-414 NRC Bulletin 93-02, Debris Plugging of Emergency Core Cooling Suction Strainers Supplemental Response Duke Power's Catawba Nuclear Station supplemental response to NRC Bulletin 93-02, dated September 16,1993, described plans to remove both trains' Containment Air Charcoal Filter Unit (CACFU) pre-filters and high efficiency particulate adsorbers (HEPAs) during the next shutdown of each unit. These plans were developed as an interim solution to resolve concerns relative to debris plugging.of Emergency Core Cooling System (ECCS) Suction Strainers which could reduce net positive suction -
head to the Residual Heat Removal System (ND) Pumps which arn used for.
recirculation following a Loss of Coolant Accident (LOCA). Among the concerns was the potential for the strainers to become plugged due to the CACFU filter media becoming granular in size and neutrally buoyant as a result of.a direct spray-impingement, migrating to the ECCS Suction Strainer and " coating" the strainer.
On September 25,1993, the Unit 2 CACFU pre-filters and HEPAs (both trains) were removed from Unit 2 containment during a Unit 2 forced outage.
The supplemental response also described plans for a permanent solution to these concerns by performing a visual field inspection in Unit 1 lower containment, during the upcoming Unit ~1 refueling outage (1EOC7), to identify any high energy interactions which would have a potential for a direct spray impingement on the CACFU filters. The supplemental response indicated that if this inspection does not identify a potential for high energy interactions, an analysis would be performed and submitted to your staff as justification to leave these filters installed in during power operation of both units.
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U.S. Nuclear Regulatory Commission December 15,1993 Page 2 The Unit 1 refueling outage (1EOC7) began October 29, 1993 and the unit is scheduled to begin post-outage heat-up December 23, 1994. The visual field inspection in Unit 1 lower containment was completed December 8,1993. Please find attached, a revised response to Bulletin 93-02 which provides justification for leaving the HEPA filters in place during power operation of both units, with the pre-filters removed. Pending concurrence from your staff for this justification, the CACFU HEPAs and pre-filters will remain removed from Unit 2 containment and will be removed from Unit 1 containment prior to post-outage heat-up.
I declare, under penalties of perjury, that the statements set forth herein are true and correct to the best of my knowledge.
Very truly yours, D.L. Rehn, Site Vice-President Catawba Nuclear Station I
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S.D. Ebneter Regional Administrator, Region 11 R.E. Martin, ONRR R.J. Freudenberger Senior Resident inspector
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o Duke Power Company Catawba Nuciaar Station Evaluation of NRC Bulletin No. 93-02 1.
Introduction:
The purpose of this evaluation is to determine the applicability of NRC Bulletin No. 93-02 to Catawba Nuclear Station (CNS).
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Background:
NRC Bulletin No. 93-02, " Debris Plugging of Emergency Core Cooling Suction Strainers," raised -
the question of reducing post-LOCA recirculation capability due to blocking of the Emergency Core Cooling System (ECCS) sump screens. This concem was identified because of the potential to have " fibrous air filters or other temporary sources of fibrous material" in containment that is not designed to withstand the effects of a DBA-LOCA.
There are two (2) requested actions associated with this bulletin. These actions are:
(1) identify fibrous air filters or other temporary sources of fibrous material installed or stored in containment which are not designed to withstand a DBA-LOCA, and (2) take appropriate actions to assure these materials do not adversely affect the functional capability of the ECCS.
IIL Scope:
This evaluation addresses the possibility of degrading the ability of the ECCS system to cool containment during a DBA-LOCA at Catawba Nuclear Station (CNS). The degradation is due to the ECCS sump screens being blocked by fibrous air filter media or other temporary sources of fibrous material. The potential to block the screens with insulation or paint flakes has been previously analyzed and is not included in this evaluation.
IV. Discussion:
The containment recirculation screen structure (ECCS sump screens) consists of a low, steel enclosure covered with horizontal, vertical and slanted stainless steel mesh screens that surround the redundant ECCS suction lines. This arrangement provides a maximum available screen area with a minimum depth of water in the containment sump (floor)i The potential to block the sump screens with insulation or paint flakes has been previously analyzed and shown not to be a concern at CNS. However, due to recent problems at other nuclear plants, it has become apparent that the potential to block the sump screens with fibrous materials, such as air filters, should also be unalyzed. Therefore, an investigation was conducted to ascertain the potential to block the sump screens with temporary fibrous materials or with permanently installed fibrous air filter media. This investigation focused on (1) fibrous materials that could be temporarily used or stored in containment, and (2) air filters in containment that are not designed to withstand the effects of a DBA-LOCA. The three (3) types of filter units in containment at CNS.
that contain fibrous filter media are the Upper Containment Ventilation Units (UCVUs), the incore Instrumentation Room Ventilation Units (llRVUs) and the Containment Auxiliary Carbon Filter I
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Revision 2 Units (CACFUs). This evaluation addresses the potential for temporary fibrous materials and the permanently installed air filters in the UCVUs, llRVUs and the CACFUs to migrate to the ECCS sump and adversely impact the ability to cool containment and the reactor core.
Temocrari1v Used or Stored Fibrous Materials Temporary fibrous materials used during inspections or routine maintenance are controlled por Station Directive 3.1.2, " Access to Containment," and Site Directive 3.11.1. " Housekeeping, Cleanliness Levels, and Use of Tobacco Products." These directives include specific guidance to ensure temporary materials are not left in containment. Therefore, temporary fibrous materials associated with inspections and maintenance do not pose a sump screen blockage concern.
Fibrous materials that could be installed as part of a temporary modification are controlled by the Temporary Station Modification (TSM) process in addition to the two directives mentioned above.
These station procedures assure that any materials used in a temporary modification are properly reviewed and/or analyzed prior to allowing them to be left in containment.
Since entry into containment is very restricted during operation, it would be difficult to transport a substantia! quantity of fibrous material into containment. During an outage, when entry into containment is less restricted, other procedures are in place to ensure temporary materials are removed from containment. Operations Procedure PT/0/A/4200/02, " Containment Cleanliness inspection," requires a visual inspection of all areas in containment to verify cleanliness of areas and that the ECCS sump is free of -debris prior to entering Mode 4. This procedure was performed on October 12,1992 on Unit 1, and on March 25,1993 on Unit P Station Directive 3.1.30,
- Unit Shutdown Configuration Control," serves to ensure that during shutdown and low power operation, the containment sump recirculation function is operable. These measures assure that materials are not inadvertently left in containment prior to mode escalation.
Rega'rding stored fibrous materials, these types of materials are not allowed to be stored in containment. Therefore, it is coacluded that temporarily used or stored fibrous materials are not a potential ECCS sump screen - xage concem at CNS.
Permanentiv Installed Materials Permanently installed fibrous materials used in containment consist of the air filters on the Upper Containment Ventilation Units (UCVUs), the incore Instrumentation Room Ventilation Units (llRVUs) and the Containment Auxiliary Carbon Filter Units (CACFUs). The scenarios that could cause these filters to dislodge from their holding frames and become a potential sump blockage concem are either a flood in containment or fluid spray from a pipe break. The potential for permanently installed fibrous filter media to degrade the ECCS sump is addressed below for each containment filter unit.
The UCVUs are located in upper containment above the postulated flood level. They are, therefore, unaffected by flooding events. These units are also not subject to the consequences of a pipe break since there are no credible high energy pipe breaks in upper containment. The filter units could, however, be sprayed by the Containment Spray (NS) Systom. This is of little concern since the fibrous filter media is enclosed by the metal panel sides of the UCVUs and are not directly exposed to any NS water spray. This prevents the Containment Spray (NS) System from dislodging the filter media and carrying it to the refueling cavity drains. These drains return water from the upper containment through the divider deck to the lower containment. The drains are open six (6) inch pipes without screen covers. Even if the UCVU filter media become dislodged from the filter holding frames, there is no reasonable mechanism to get the filter media into the ECCS sump screens and it is unrealistic to assume that the fibrous filter media from the UCVUs could clog the refueling cavity drains. Any dislodged filter media would most likely be 2
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trapped within the UCVU housing. Assuming the dislodged filters floated ano did get out of the UCVU housing, they would not be able to reach the sump screens since the screens are underwater. Filter media that got out of the filter unit housing and was heavier than water would sink and be caught on numerous curbs or other physical obstructions and prevented from reaching the sump screens. Therefore, the filters media installed in the UCVUs are not an ECCS sump blockage concern.
The air filters used in the llRVUs are not considered to be a sump blockage concem due to their location in the instrumentation area in lower containment. This area is separated from the rest of lower containment and is isolated from postulated pipe breaks, Containment Spray and other sources of water which could wash loose filter media into the containment sump. The filter units are also located above the postulated containment flood level. A stainless steel screen covers the filter media which adds additional protection against loose filter media getting out of the filter unit. Therefore, the filter media in the llRVUs is not an ECCS sump blockage concern.
The CACFUs are the only in-containment filter units containing fibrous filter media that are located in an area affected by both pipe rupture and flooding. They are located in lower containment inside the polar crane wall. It is important to note that the ECCS sump screens are also located in lower containment, however, they are located in the pipe tunnel outside the polar crane wall The flow path from the CACFUs to the ECCS sump are through seventy (70) 8" diameter pipe sleeves in the crane wall. All of the sleeves are above floor level in order to determine if the CACFUs are subject to fluid spray from a pipe break, a visual field inspection was recently conducted on the Unit 1 filter units. This inspection showed that, even though there are potential pipe break locations near the CACFUs, an adverse jet interaction which could damage the filter units and dislodge the filters (HEPAs or prefilters) is not possible due to the extensive amount of pipe, structural and framing steel between the potential break locations and the filter units. Since the Unit 2 CACFUs and piping configurations are similar to the Unit 1 arrangement, neither Unit's CACFUs are subject to adverse pipe break interaction which could dislodge the filter media.
Flooding is the only othe r. 4chanism which could dislodge fibrous filter material from the l
CACFUs. The CACFUs contain two (2) types of fibrous filter media: prefilters and HEPA filters.
Flooding, however, only affects the profilters; it is not a concern for the HEPA filters due to their construction. The HEPAs are manufactured from a fiberglass mesh bonded to a steel frame with a water proof neoprene adhesive. Besides the adhesive the filter media is held in the frame with a wire mesh screen across both ends of the filter cell. This assures that flooding will not cause the HEPA media to come out of its frame. The construction of the prefilters is not as substantial as that of the HEPA filters. It is reasonable to assume that, should the CACFUs be flooded, the prefilters could become dislodged and loose in containment. Therefore, the prefilters will be removed from the CACFUs. They will not be replaced with another type of filter (metal or otherwise) as this is unnecessary.
It should also be noted that there are no filters installed in the Lower Containment Ventilation Units (LCVUs) which are the only other ventilation units in containment.
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V. Conclusion:==
The fibrous materials in containment identified for NRC Bulletin 93-02 are:
(1) air filters in the UCVUs (32 ft2 total ared (2) air filters in the llRVUs (11 fF total area; (3) air filters in the CACFUs (48 ft2 total area) 3 q
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.J in summary, the above justification is provided to show that only the profilters in the CACFUs
- pose an ECCS sump blockage concem. All other in-containment filters, as well as other temporary fibrous materials in containment, do not pose a potential to degrade the ECCS system. The CACFU prefilters will be removed to assure the functional capability of the Emergency Core Cooling System.
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