ML20046B532
| ML20046B532 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 07/29/1993 |
| From: | Horn G NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-92-04, GL-92-4, IEB-93-003, IEB-93-3, NSD930885, TAC-M84275, NUDOCS 9308050066 | |
| Download: ML20046B532 (7) | |
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GENERAL OFFICE F.O. BOX 499. COLUMBUS. NEBRASKA 68602-0499 i
Nebraska Public Power District "T43&e'l!%**
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NSD930885 July 29, 1993 i
Nuclear Regulatory Commission Attention:
Document Control Desk Washington, DC 20555
Subject:
Response to NRC Bulletin 93-03 Cooper Nuclear Station Docket 50-298, DPR-46
References:
(1)
Letter from G.
R.
Horn to USNRC dated September 28, 1992,
" Response to NRC Generic Letter (GL) 92-04" (2)
Letter from Harry Rood (USNRC) to G. R. Horn dated April 27, 1993, " Additional Evaluation of Response to Generic Letter (GL) 92-04" (TAC No. M84275)
Gentlemen:
NRC Generic Letter (GL) 92-04, " Resolution of the Issues Related to Reactor Vessel Water Level Instrumentation in BWRs pursuant to 10CFR50.54(F)", was issued on August 19, 1992. The Generic Letter contained requesteil licensee actions and reporting requirements regarding the adequacy of, and corrective actions for; BWR water level instrumentation with respecc to the effect of noncondensible : gases
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on system operation.
In reference 1, the Nebraska Public Power District (District) responded to the requested actions contained in the NRC Generic Letter 92-04. In reference 2, the NRC concluded that the District response to Requested Action 3, of GL 92-04, was not acceptable, and requested that the District provide, by July 30, 1993, plans and a schedule, including any proposed hardware modifications necessary to ensure the water level instrumentation system design.
NRC Bulletin 93-03, " Resolution of Issues Related to Reactor Vessel Water Level Instrumentation in BWRs" was issued on May 28, 1993, and requested that the District submit a response by July 30, 1993.
The Bulletin contains Requested Licensee Actions and Reporting Requirements for BWR water level instrumentation with respect to the effect of noncondensible 5ases on system operation.
The requested actions and reporting requirements of the bulletin, duplicate the response requested by reference 2, and therefore only one response is being submitted.
As requested in reference 2, and by the bulletin, attached is the District's response to comply with the guidance, and resolve the concerns of NRC Bulletin 93-03. This response is submitted under oath in accordance with the provisions 10CFR50.54(f).
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l NSD'930885 Page 2 of 3 July 29, 1993 Please contact rne at this office if you have any questions.
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N G.
llorn Nuclear Power Group Manager
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NRC Regional Office Region IV Arlington, TX NRC Resident Inspector Cooper Nuclear Station i
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NSD930835 Page 3 July 29, 1993 STATE OF NEERASl% )
)ss PIATTE COUNTY
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G. R. Horn, being first duly sworn, deposes and says that he is an authorized representative of the Nebraska Public Power District, a public corporation and political subdivision of the State of Nebraska; that he is duly authorized to submit this response on behalf of Nebraska Public Power District; and that the statements contained herein are true to the best of his knowledge and belief.
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G. R. llorn Subscribed in my presence and sworn to before me this 29 O day of 3dL/
1993.
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Attachment to NSD930885 Page 1 of 4 NEBRASKA PUBLIC POWER DISTRICT'S i
RESPONSE TO NRC BULLETIN 93-03
" RESOLUTION OF THE ISSUES RELATED TO REACTOR VESSEL WATER LEVEL INSTRUMENTATION IN BWRs"
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INTRODUCTION NRC Generic Letter (GL) 92-04, " Resolution of the Issues Related to Reactor Vessel Water Level Instrumentation in BWRs", was issued on August 19, 1992.
On April 27, 1993,2 the NRC concluded that the District response to Requested Action 3, of GL 92-04, was not acceptable, and requested that the District provide, by July 30, 1993,-plans and a schedule, including any proposed hardware modifications necessary to ensure the water level instrumentation system design. On May 28,1993 the NRC issued Bulletin 93-03, " Resolution of the issues related to Reactor Vessel Water Level Instrumentation in BWRs."
As requested in the April 27, 1993, correspondence,2 and by the bulletin, attached is the District's response _ to comply with the guidance, and resolve the concerns of NRC Bulletin 93-03. The following is the Nebraska Public Power District's Response to those requested actions. The requested actions and reporting requirements of the bulletin, duplicate the response requested by 1, and therefore only one response is being provided.
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ELqt!FSTED ACTIONS i
1.
Short Term Compensatory Actions (a)
Within 15 days of the date of this bulletin or prior to startup, whichever is later, each licensee is requested to implement the'following measures to ensure that potential level errors caused by reference leg de-gassing will not result in improper system response or improper operator actions during transients and accident scenarios initiated from reduced pressure cor.ditions (Mode 3):
t (1)
Establish enhanced monitoring of all RPV level instruments to provide early detection of level anomalies associated with de-gassing from the reference legs,
Response
Cooper Nuclear Station (CNS) currently has enhanced RPV level monitoring in place during normal planned depressurizations. This enhanced monitoring consists of sampling Plant Management Information System (PMIS) data points such that real-time level data is available to the Control Room operators and video taping of the local instruments racks (RPV water level instruments from hot Yarways) for a cross reference in case of an reference legs anomaly.
No notching in RPV water level instrumentation from the Letter Harry Rood (USNRC) to G.
R.
Horn dated April 27, 1993, 2
Additional Evaluation of response to Generic Letter 92-04, " Resolution of the Issues Relatt.d to Reactor Water Level Instrumentation in Boiling Water Reactors (TAC No. M84275).
Attachment to NSD930885 Page 2 of 4 cold reference legs has been observed during the past two planned depressurizations.
(2)
Develop enhanced procedures or. additional restrictions and controls for valve alignments and maintenance that have a potential to drain the RPV during Mode 3.
Response
Valve operations are currently restricted by operating procedures, Clearance Orders, and Plant Temporary Modifications controls when in I
Shutdown Cooling (SDC). Valve-to-valve interlocks and prespecified clearance orders preclude RPV drain-down events.
In addition, the RHR loop which is selected for SDC is a shutdown risk management protected system. No maintenance is allowed to be performed on this system, which could potentially result in a loss of SDC or breach the Reactor Coolit.g System boundary, without the necessary I
contingencies in plc ce and proper management approval of those l
l contingencies.
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(3)
Alert operators to potentially confusing or misleading level indication that may occur during accident or transients initiating from Mode 3.
For example, a drain-down event could lead to i
automatic initiation of high-pressure emergency core cooling systems (ECCS) without automatic system isolation or low-pressure ECCS
_i actuation.
Response
Licensed Operators (L0s) and Shift Technical Advisors (STAS) have been alerted to the potential of loss of the level 3 SCRAM signal and the Groups 2, 3, and'6 isolations due to noncondensible Cas (NCC) errors while in Mode 3.
Also, in training cycle 93-05 all Los and STAS received industry events training, which specifically discussed this NRC bulletin.
Cooper Nuclear Station (CNS) was in a cold shutdown when this Bulletin was issued on May 28, 1993, Short Term Compensatory Actions 1.a.1, l.a.2, and 1.a.3 vere completed within 15 days of the date of this Bulletin, while the plant was in cold shutdown.
i (b)
By July 3G, 1993, each licensee is requested to complete augmented operator training on loss of RPV inventory scenarios during Mode 3, including RPV drain-down events and cracks and breaks in piping.
Response
In Training cycle 93-02 conducted between February 1, 1993 and March 12, 1993, two simulator training sessions were completed.
These training sessions included Los and STAS and were part of the Shutdown Risk Management Training.
The scenarios developed and trained on dealt with loss of RPV inventory during Mode 3, including RPV drain-down events and cracks or breaks in piping.
Also, in training cycle 93-05 L0s and STAS received industry events training, which discussed this NRC bulletin.
l Attachment to NSD930885 Page 3 of 4 The Short Term Compensatory Actions described above will remain in effect until the concerns of Generic Letter 92-04, and NRC Bulletin 93-03 are resolved, or until the hardware modification described below has been implemented.
2.
Hardware Modifications Each licensee is requested to implement hardware modifications necessary to ensure the level instrumentation system design is of high functional reliability for long term operation. This includes level instrumentation performance during and af ter transient and accident scenarios initiated from both high pressure and reduced pressure conditions. Since the level instrumentation plays an important 6
role in plant safety and is required for both normal and accident conditions, the staff requests that the hardware modifications be implemented at the next cold I
shutdown beginning after July 30, 1993.
Response
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The District is installing a continuous backfill modification into the two divisional RPV water level instrumentation cold reference legs using the Control Rod Drive (CRD) system.
This modification will be similar to the one used by Northeast Utilities Co., at Millstone-l. As stated by the NRC in Bulletin 93-03, this hardware modification will prevent buildup of noncondensible gases in the RPV level instrumentation cold reference legs. Installation of this continuous backfill modification is expected to be completed on August 6, 1993.
Post modification acceptance testing will still need to be performed and some of the testing requires that the plant to be in a hot condition in order to verify proper instrumentation response in the presence of the continuous reference. leg backfill injection.
Bulletin 93-03 requests each licensee, whose facility is in cold shutdown on
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July 30,1993, to implement the hardware modifications prior to starting up from their outage.
CNS is presently in a cold shutdown condition with plans to July 29, 1993.
However, delays to the startup plant startup on commence a schedule may be incurred such that the plant would still be in cold shutdown some. time on July 30, 1993 while in the process of startup. The District requests NRC consideration of the acceptability of our plans to complete the hardware modifications on August 6, 1993, while allowing for the plant to proceed with startup from an outage on or af ter July 30, 1993. The District has a high degree i
of confidence that the hardware installation will be completed on or before August 6,1993 and does not believe postponement of startup is warranted for the remaining amount of time needed to complete the installation.
l As stated earlier, this response covers both the required actions of Bulletin 93-03, and the April 27, 1993 letter requesting that the District provide, by July 30, 1993, plans and a schedule, including any proposed hardware modifications necessary ta ensure the water level instrumentation system design is of high functional reliability for long term operation.
1 Attachment to NSD930885 Page 4 of 4 REPORTING REOUIREMENTS Written Reports are required as follows:
(1)
Addressees choosing not to take the requested short term actions must submit a report within 15 days of the date of this bulletin containing a description of the proposed alternative course of action, the schedule for completing it, and a justification for any deviation from the requested actions.
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Response
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The District implemented Short Term Compensatory Actions described in 1.a.1, 1.a.2, and 1.a.3, these actions were completed within 15 days of the date of this bulletin. The District also provided simulator training on loss of RPV inventory 4
scenarios to LOs and STAS prior to July 30, 1993.
(2)
By July 30, 1993, all addressees must submit a report providing:
(a) the description of the short term compensatory actions taken,.and (b)
A description of the hardware modifications to be implemented at the next 4
cold shutdown after July 30, 1993.
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Response
f The District response to Requested Actions 1.a, and 1.b, (Short Term Compensatory Actions) provides a description of all the short term compensatory actions taken j
to address the concerns of Generic Letter 92-04, and NRC Bulletin 93-03. All of The Short Term Compensatory Actions described in this response will remain in
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effect until the concerns of Generic Letter 92-04, and NRC Bulletin 93-03 are resolved, or until the hardware modification described herein has been completed and implemented.
The District response to Requested Action 2, (Hardware Modifications) provides a description of the hardware modifications to be implemented at CNS to prevent s
buildup of noncondensible gases in the RPV level instrumentation cold reference legs. This modification should resolve the concerns of Generic Letter 92-04, and NRC Bulletin 93-03.
(3)
Within 30 days of completion of the requested hardware modifications, a report confirming completion and describing the modification implemented shall be submitted.
Response
The District will notify the NRC within 30 days upon completion of the hardware modification described herein, that the hardware modification installed to prevent buildup of noncondensible gases in the RPV level instrumentation cold referenca legs has been implemented and acceptance testing completed.
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