ML20044D664
| ML20044D664 | |
| Person / Time | |
|---|---|
| Issue date: | 05/10/1993 |
| From: | Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | |
| References | |
| SECY-93-125, NUDOCS 9305200130 | |
| Download: ML20044D664 (7) | |
Text
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POLICY ISSUE May 10, 1993 (InfOrmation)
SECY-93-125 FOR:
The Commissioners FROM:
James M. Taylor Executive Director for Operations
SUBJECT:
NRC BULLETIN 93-XX, " DEBRIS PLUGGING 0F EMERGENCY CORE COOLING SUCTION STRAINERS" PURPOSE:
To inform the Commission, in accordance with the guidance in th December 20, 1991, memorandum from Samuel J. Chilk to James M. Taylor regarding SECY-91-172, " Regulatory Impact Survey Report-Final," of the staff intent to issue the sutject bulletin.
In the enclosed bulletin, we notify power reactor l
licensees of a previously unrecognized contributor to the potential loss of net positive suction head for the emergency core cooling system (ECCS) pumps l
during the recirculation phase of a loss-of-coolant accident (LOCA) and request that licensees take corrective actions.
DISCUSSION:
In March 1993, the Cleveland Electric Illuminating Company found that the ECCS pump strainers were clogged at its Perry Nuclear Plant.
This latest strainer clogging event occurred only 2 months after the licensee had replaced the strainers and thoroughly cleaned the suppression pool.
Investigation indicated that the clogging was caused by debris, consisting of (1) glass fibers from air filter material that had been inadvertently introduced into the suppression pool and (2) corrosion products that had been filtered from the pool by the glass fibers adhering to the surface of the strainer. This Perry event indicated that the filtering action of fibrous material on corrosion products, dust, and other debris from the drywell during a LOCA may cause an unexpectedly rapid loss of net positive suction head for the ECCS pumps when they are needed to perform their intended function. The NOTE:
TO BE MADE PU.BLICLY AVAILABLE IN 10 WORKING DAYS FROM THE DATE OF THIS PAPER 64011D
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The Commissioners operability of the ECCS suction for recirculation is required to meet the requirements of Section 50.46 of Title 10 of the Code of Federal Reuulations (10 CFR 50.46). The actions requested by the proposed bulletin are necessary to ensure that licensees are in compliance with existing NRC rules and regulations. Therefore, rulemaking is not a consideration at this time.
Because of the urgency of this issue, the staff has not published this proposed bulletin for public comment. The staff will determine the need for additional actions based on the ongoing evaluation of the domestic events and foreign event described in the bulletin and recent information notices.
On May 7, 1993, the Committee to Review Generic Requirements (CRGR) reviewed and recommended issuing the proposed bulletin. The staff has incorporated all comments provided by the CRGR in that meeting.
The Office of the General Counsel reviewed this proposed bulletin and has no legal objection to issuing it.
The staff intends to issue this bulletin immediately.
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J mes M. Ta or xecncive Director for Operations
Enclosure:
Proposed NRC Bulletin DISTRIBUTION:
Conghissioners OGC OCAA OIG OPA OCA OPP REGIONAL OFFICES EDO ACRS SECY
Enclosure T*p OMB No.: 3150-0011 NRCB 93-UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 May
, 1993 NRC BULLETIN NO. 93-
- DEBRIS PLUGGING 0F EMERGENCY CORE COOLING SUCTION STRAINERS Addressees For Action:
All holders of operating licenses for nuclear power reactors.
For Information:
All holders of construction permits for nuclear power reactors.
Purpose This bulletin notifies licensees of a previously unrecognized contributor to the potential loss of net positive suction head (NPSH) for the Emergency Core Cooling Systems (ECCS) for Light Water Reactors during the recirculation phase of a loss-of-coolant accident (LOCA). All operating reac. tor licensees are requested to take the recommended actions, and are required to provide the U.S. Nuclear Regulatory Commission (NRC) with a written response describing the actions taken associated with this bulletin.
Backaround On December 3,1985, the NRC issued Generir. Letter 85-22, "Fotential for Loss of j
Post-LOCA Recirculation Capability Due to Insulation Debris Blockage," which-i recommended that Regulatory Guide 1.82, Revision 1, " Water Sources for Long-Term Recirculation Cooling Following a loss of Coolant Accident," be used as guidance for 10 CFR 50.59 reviews dealing with modification of thermal insulation.
Regulatory Guide 1.82, Rev. I discussed, among other things, the blockage of strainers due to fibrous debris.
On September 30, 1992, the NRC issued Information Notice (IN) 92-71, " Partial Plugging of Suppression Pool Strainers at a Foreign BWR,". which provided information on the plugging of two ECCS suction strainers by mineral wool insulating material that had been dislodged by steam from an open safety valve. On April 26, 1993, the NRC issued Information Notice 93-34, " Potential for Loss of Emergency Cooling Function Due to a Combination of Operational and Post-LOCA Debris in Containment," which described two incidents of debris identified in suppression pools associated with damaged and clogged strainers, and the identification of a significant source of material in a PWR with the potential to restrict the flow through the sump debris screen.
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NRCB 93-May
, 1993 Page 2 of 5 DescriDtion of Circumstances Information Notice 93-34 and Supplement 1 to IN 93-34 issued on May 6, 1993, described clogging of ECCS pump suction strainers that occurred at the Perry Nuclear Plant, a BWR-6.
The event involving deposition of filter fibers in residual heat removal strainers occurred in Marct.,1993, two months after the strainers at Perry had been replaced and the suppression pool had been thoroughly cleaned.
Subsequent to issuance of IN 93-34, the licensee chemically analyzed the debris on the strainer.
The debris consisted of glass fibers from temporary drywell cooling filters that had been inadvertently dropped into the suppression pool, and corrosion products that had been filtered from the pool by the glass fibers adhering to the surface of the strainer.
A small amount of the fibrous filter material was also found in the suppression pool near the weir wall.
The licensee used the fibrous material as a filter in the drywell in three cooling air return ducts that each have a surface area of about 5.6 square meters (60 square feet].
In addition, there were six similar air filters in containment.
4 The purpose of the filters is to maintain cleanliness in containment and the drywell during reactor outages.
It has been the licensee's practice to replace the filter material at the end of each outage and to leave the material in the drywell and containment during operation of the plant at power. As a result of the March 1993 event, the licensee will remove the filters from the drywell and containment prior to startup.
They will also remove fibrous insulation from ducting in the pool-swell area of the containment.
In aJdition, Perry has thoroughly cleaned the drywell, containment, and suppression pool to reduce dirt, dust, and foreign material which could contribute to the clogging of the strainers.
They have also initiated a program to periodically monitor RHR strainer differential pressure. They have replaced their strainers, significantly increasing the flow area.
In addition, a procedure has been developed to use existing equipment to backflush the strainers in the event of clogging.
Discussion Section 50.46 of Title 10 of the Code of Federal Regulations (10 CFR 50.46) requires that each operating nuclear power plant have an ECCS that provides, among other characteristics, long-term cooling capability.
For the LOCA sequence, this long-term cooling capability is provided through recirculation of the coolant from the Boiling Water Reactor (BWR) suppression pool or the Pressurized Water Reactor (PWR) sump back to the reactor vessel. Appendix A to 10 CFR Part 50, General Design Criterion (GDC) 35, " Emergency Core Cooling," GDC 36, " Inspection of Emergency Core Cooling System," and GDC 37, " Testing of Emergency Core Cooling System," require appropriate design, inspectability and testability of the Emergency Core Cooling Systems. This includes the ability of the ECCS to provide long term core cooling.
NRC8 93-jp May
, 1993 Page 3 of 5 NUREG-0897, Rev. 1, " Containment Emergency Sump Performance," wh'ch was written in conjunction with resolution of Unresolved Safety Issue (USI) A-43, addressed transport of fibrous thermal insulation from the containment to the strainers during a LOCA.
Resolution of USI A-43 was based in part on strainer head loss tests with fibrous thermal insulation obstructing flow.
The consequences on head loss of the filtering action of the fibrous material on the strainer was beyond the scope of USI A-43.
The staff has in place a program to systematically evaluate the larger implications of the Perry experience and the aforementioned foreign reactor event. This will include consideration of strainer area, containment housekeeping, pool cleanliness, and measures to cope with clogged strainers.
The Perry event showed that filtering of corrosion products, dust, and other debris from the drywell, as occurred at Perry, may cause an unexpectedly rapid loss of net positive suction head for the ECCS pumps when they are needed to perform their intended function.
Fibrous air filters and other temporary material appear to be likely sources of such fibrous material.
This bulletin deals with the presence of such material in reactor containments.
Reouested Actions All holders of operating licenses for nuclear power reactors, immediately upon receiving this bulletin, are requested to take the following actions:
Identify fibrous air filters or other temporary sources of fibrous material, not designed to withstand a LOCA, which are installed or stored in your primary containment.
Take any immediate compensatory measures which may be required to assure the functional capability of the ECCS.
Take prompt action to remove any such material.
Because of the low probability of a LOCA event, the staff considers removal of this material at the next shutdown, or within 120 days, whichever comes first, to be sufficiently prompt.
If the facility is currently in a shutdown, you are requested to remove such material prior to restart.
Renortina Reauirements All action addressees are required to submit the following written reports:
1.
Within 30 days of the date of this bulletin, a written response stating whether the actions requested above have been or will be performed.
If the use of such material is identified, this written response shall also include the locations and quantity of use, any immediate compensatory measures taken, and the current schedule for removal of the material.
2.
Within 30 days of completion of the requested actions, a report confirming completion.
3.
If an addressee proposes not to take the actions requested in this bulletin, provide to the NRC staff, within 30 days of the date of this bulletin, your proposed alternative course of action and a justification for any deviations from the requested actions.
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NRCB 93-May
, 1993 Page 4 of 5 proposed alternative course of action and a justification for any deviations from the requested actions.
Address the required written reports to the U.S. Nuclear Regulatory Commission, ATTN:
Document Control Desk, Washington, D.C. 20555, under oath or affirmation under the provisions of Section 182a, Atomic Energy Act of 1954, as amended, and 10 CFR 50.54(f).
In addition, submit a copy to the appropriate regional administrator.
flackfit Discussion The operability of the ECCS suction for recirculation is requir1d to meet a condition of a plant operating license and the requirements of Section 50.46 of 10 CFR.
The actions requested by this bulletin represent a new staff position and are considered necessary to ensure that licensees are in compliance with existing NRC rules and regulations where these conditions are applicable. Therefore, this bulletin is being issued as a compliance backfit under the terms of 50.109(a)(4),
and is being issued as an immediately effective action (10 CFR 50.109(a)(6)).
Panerwork Reduction Act Statement This bulletin contains information collection requirements that are subject to the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.).
These requirements were approved by the Office of Management and Budget, approval number 3150-0011.
The public reporting burden for this collection of information is estimated to average 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for further reducing reporting burden, to the Information and Records Management Branch (MNBB-7714), U.S. Nuclear Regulatory Commission, Washington, D.C. 20555; and to the Desk Officer, Office of Information and Regulatory Affairs, NE0B-3019, (3150-0011), Office of Management and Budget, Washington, D.C. 20503.
Compliance with the following request for information is purely voluntary.
The information would assist NRC in evaluating the cost of complying with this bulletin:
(1) the licensee staff time and costs to perform requested inspections, corrective actions, and associated testing; (2) the licensee staff time and costs to prepare the requested reports and documentation; I
(3) the additional short-term costs incurred as a result of the inspection findings such as the costs of the corrective actions or the costs of down time;
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NRCB 93-May
, 1993 Page 5 of 5 (4) an estimate of the additional long-term costs which will be incurred in the future as a result of implementing conaitments such as the estimated costs of conducting future inspections or increased maintenance.
If you should have any questions about this matter, please contact one of the technical contacts listed below or the appropriate NRR project manager.
James G. Partlow, Associate Director Division of Reactor Projects Office of Nuclear Reactor Regulation Technical contacts:
Roger Woodruff (301) 504-2917 John B. Hickman (301) 504-3017
Attachment:
List of Recently Issued NRC Bulletins J