ML20138D832
| ML20138D832 | |
| Person / Time | |
|---|---|
| Issue date: | 04/28/1997 |
| From: | Chaffee A NRC (Affiliation Not Assigned) |
| To: | Simpson J GAMMA-METRICS, INC. |
| References | |
| NUDOCS 9705010248 | |
| Download: ML20138D832 (4) | |
Text
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- h April 28, 1997 Mr. James D. Simpson Sales and Programs Manager l
Gamma Metrics 5788 Pacific Center Blvd.
San Diego,. California 92121 -
SUBJECT:
REQUEST.FOR-A TECHNICAL. REVIEW 0F A DRAFT INFORMATION NOTICE i
REGARDING FAILURES OF WIDE RANGE LINEAR. NEUTRON FLUX CHANNELS l
Dear Mr. Simpson:
7' The U.S. Nuclear Regulatory Com$1ssion (NRC) is planning to issue an information notice to discuss failures that have occurred in Gamma Metrics wide range linear neutron flux channels; that have the potential to defeat the scram function of the channels to ensure that' all non-power reactor licensees receive the informatio'n.- We ask that you review the enclosed draft of that information notice to ensure-that the technical information is accurate.
Your cooperation in,this matter 'is appreciated.. Please return any comments you may 4
have within 10 days of'the date of this.lett.er.. A copy of this request and your response will'be placed in the Public Document Room for review by the i
public.
Yourresponseshouldbe^mailedtol U.S. Nuclear Regulatory Commission ATTN: Alexander-Adams, Jr., NRR/PDND M.S. 0-11-B-20 Washington, DC 20555-0001 Please address any questions you may have on this matter to Alexander Adams.
Mr. Adams may be reached by phone (301) 415-1127 or E-mail (axaenrc. gov).
If no comments are received by the close of the 10-day period, we will assume the technical information in the notice is correct.
Sincerely, Original signed by:
Alfred E. Chaffee, Chief Events Assessment and Generic Communications Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation
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Enclosure:
Draft Information Notice
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April 28, 1997 Mr. James D. Simpson Sales and Programs Manager Gamma Metrics 5788 Pacific Center Blvd.
San Diego, California 92121
SUBJECT:
REQUEST FOR A TECHNICAL REVIEW 0F A DRAFT INFORMATION NOTICE REGARDING FAILURES OF WIDE RANGE LINEAR NEUTRON FLUX CHAWNELS
Dear Mr. Simpson:
The U.S. Nuclear Regulatory Commission (NRC) is planning to issue an information notice to discuss failures that have occurred in Gamma Metrics wide range linear neutron flux channels that have the potential to defeat the scram function of the channels to ensure that all non-power reactor licensees receive the information. We ask that you review the enclosed draft of that information notice to ensure that the technical information is accurate.
Your cooperation in this matter is appreciated.
Please return any comments you may have within 10 days of the date of this letter. A copy of this request and your response will be placed in the Public Document Room for review by the public.
Your response should be mailed to:
U.S. Nuclear Regulatory Commission ATTN: Alaxander Adams, Jr., NRR/PDND M.S. 0-11-B-20 Washington, DC 20555-0001 Please address any questions you may have cn this matter to Alexander Adams.
Mr. Adams may be reached by phone (301) 415-1127 or E-mail (axa@nrc. gov).
If no comments are received by the close of the 10-day period, we will assume the technical information in the notice is correct.
Sincerely, Gid 1D 1
Alfred E. Chaffee,
/
Events Assessment and Generic
's Communications Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation l
Enclosure:
Draft Information Notice
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555-0001 April xx.1997 NRC INFORMATION NOTICE 97-XX: FAILURES OF GAMMA METRICS WIDE-RANGE LINEAF. NEUTRON FLUX CHANNELS Addressees All holders of operating licenses or construction pemiits for test and research reactors.
Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform addressees of failures that have occurred in Gamma Metrics wide-range linear neutron flux channels that have the potential to defeat the scram function of the channels. It is expected that recipients will review the information for applice' ility to their facilities ana consider action, v
as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required.
Description of Circumstances The non-power reactor at North Carolina State University (NCSU) has two Gamma Metrics wide range linear neutron flux channels. One unit is used as a linear channel for power monitoring and control and provides a high-power-level scram. The other unit is used as a safety channel that provides a high-power-level scram.
The channels used at NCSU can be operated in different modes for ranging and scram functions. These units can be operated in an auto-ranging mode in which the unit changes scales automatically or in a manual range-change mode in which the reactor operator changes the range displayed on the channpl to follow the reactor power level or leaves the channel set on one range. These units can also be operated with the smart bistable set in a
" standard" mode in which the scram function is present on each range at a set percentage of range, or in a " smart" mode in which the scram function is present at a set percentage of range only on one specific range.
The initial problem observed by the licensee was that the linear channel unit failed to uprange automatically with the unit in the reactor console in the auto-ranging mode and the smart bistable set in the " smart" mode. While testing the unit in the reactor console f.er repair, the unit failed to uprange and exhibited spurious automatic range-changing while operating in the " standard" mode. During pre-startup console testing following modification of the unit, it was found that actuation of the rod reverse demand would cause a range change with the range control in manual mode. During benchtop testing following repairs, the unit exhibited spurious range changes, including oscillatory behavior, it was also cbserved that l
the unit increased range to greater than the maximum range even though this unit has by i
design a maximum range limit function.
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IN 97-xx April xx,19" Page 2 of 2 l
The unit used as a safety channel exhibited spurious down ranging during reactor operation in the manual mode with the bistable set in the " standard" mode.
Discussion It is possible for a malfunction of these units to disable the scram function, which, depending on the use of the unit, may be a high-power-level scram required by the technical specifications (TS). For the scram to be disabled, the unit bistable would have to be in the j
" smart" mode while a spurious down ranging occurs, which places the unit on a range without scram protection when such protection is needed. Being on the wrong range disables the scram function because the reactor could be operated beyond the scram setpoint power level. Operating the unit with the bistable in the " standard" mode with the scram enabled on all ranges alleviates this problem.
If a spurious uprange malfunction occurs in which the range goes beyond the maximum range limit, the scram function, if still present, will not actuate at the proper setpoint even with the unit bistable in the " standard" mode. This result occurs because the scram is set for a percentage vf the range on all ranges, which will be above the scram setpoint when it is beyond the maximum range. Licensees should be aware of this type of behavior The impact of this type of problem is reduced by the TS requirement for multiple high-power-level scrams using redundant channels. The possibility of a problem is further reduced if the redundant channels are also diverse.
The fact that the unit is on an incorrect scale can be readily detected by the reactor operator by observation of the unit display. The operator can then take whatever action is necessary to respond to the specific situation.
This information notice requires no specific action or written response. If you have any questions about the informaton in this notice, please contact the technical contact listed below.
Thomas T. Martin, Director Division of Reactor Program Management Office of Nuclear Reactor Regulation TECHNICAL CONTACT: Alexander Adams, Jr., NRR (301) 415-1127 E-mail: axa@nrc. gov
Attachment:
List of Recently issued NRC Information Notices l
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