ML20153D483
| ML20153D483 | |
| Person / Time | |
|---|---|
| Issue date: | 03/17/1997 |
| From: | Thatcher D NRC (Affiliation Not Assigned) |
| To: | Collins S NRC (Affiliation Not Assigned) |
| Shared Package | |
| ML20153D328 | List: |
| References | |
| NUDOCS 9809250071 | |
| Download: ML20153D483 (1) | |
Text
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. Collins, Director Office of Nuclear Reactor Regulation
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Electrical Engineering Branch Division of Engineering
. Office of Nuclear Reactor Regulation f FROM: Dale F. Thatcher, Section Chief Advanced Designs Section and Electrical Components
{ h' Electrical Engineering Branch Division of Engineering Office of Nuclear Reactor Regulation
SUBJECT:
DIFFERING PROFESSIONAL OPINION (DPV)
In accordance with the process established for handling DPVs, I am forwarding to you the attached DPV, " TECHNICAL SPECIFICATION SETPOINTS AND ALLOWABLE VALUES FOR INSTRUMENTATION."
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MEMORAlWUM T0: Data F. Thatcher, Section Chief Advanced Designs Section and Electrical Components
- Electrical Engineering Branch /
, . Division of Engineering FROM: Frederick H. Burrows, Electrical Engineer ,.
Advanced Designs Section and 5fL J ,
Electrical components T~
Electrical Engineering Branch Division of Engineering
SUBJECT:
DIFFERING. PROFESSIONAL '/IEW CONCERNING TECHNICAL SPECIFICATION SETP0lNTS AND ALLOWABLE VALUES FOR INSTRUNENTATION Attached is the subject Differing Professional View (DPV) which you should forward to our Office Director per the latest DPV policy guidelines.
Tom Dunning (TS8/NRR) and Virgil Beaston (EELB/NRR) are two qualified t
individuals who are willing to serve on the review panel for this DPV.
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DIFJERING PROFESS 10NAL UIEW CONCERNING TECHNICAL SPECIFICATION SETP0 N"S AND ALLOWABLE VALUM FOR INSTRUNENTATION E
FREDERICK H. BURA0WS
' In a memorandum to J. Wralel and C. Grimes dated March 6, 1996, I ex>ressed a concern that the recent staff efforts to improve and simplify Westingtouse Standard Technical Specifications (STS) have undemined efforts in the 1980s to produce a meaningful and technical concise approach'to satisfy 10 CFR 50.36. Specifically, it is my opinion that the use of an allowable value to detemine operability for an instrumentation channel in lieu of the channel's trip setpoint in technical specifications (TS) does not satisfy 10 CFR 50.36 and is not consistent with actual plant calculations that establish setpoints and with plant procedures that maintain the validity of those setpoints.
In a response of April 2, 1996, C. Grimes and J. Wermiel stated that it was not clear if I had raised a particular technical concern or policy concern refiarding the appropriate means to reflect setpoint calculations and related ma<ntenance practices into TS requirements. They also requested that I document my concerns so that they could be addressed before a revision to Regulatory Guide 1.105, " Instrument Setpoints for Safety Systems," or further improvements to the STS were made.
Instead of writing a Differing Professional View (DPV at that time, I chose to stay with the normal channels to express my concern)s in the hope that those efforts and the iraputs from others, such as Westinghouse, would convince the staff of what I believe is their failure to produce STS that satisfy 10.CFR
' 50.~36. .'Accordinelly, in a memorandum to J. Wemiel and C. . Grimes = dated
- August 94.1996, ' provided my comments on the proposed Revision 3 to m c Regulatorf Guide 1.105. In that memo I questioned whether the.. staff wa.s.~
espsistently. applying 10 CFR 50.36 and stated that the staffLw'sMownplaying a the imp'ortance of the nominal trip set >oint, and that the nominal'setpoint is the only.-setting that will satisfy 10 CFR 50.36. In a Ves'p~onsi'of! August.29, 1996,;C.. Grimes.and J. Werniel stated that my comments would be. considered ,
along~with those obtained from the public. .J . ;.jgg Now>tt' appears.that my comments and those by Westinghouse'w1N hrodecY D
.. . change in the staff's approach to undermining the important of'aichannel's
' trip setpoint. Therefore,withthisDPV,Iwishtoexpress"aredhcorns'as.
follows.:
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- 1. Regulstory position'3 in the staff's draft RegulatoryMKDMN48f
' "(proposed (circa October 1996) Revision 3 to Regulato$t.uidi1:105) states: -
The. allowable value, in conjunction with the trip setpoint, will determine the limits on instrument ATTADOIENT
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operability and must be specified in the TS in order !
j to meet 10 CFR 50.36. The LSSS should be developed in accordance with the setpoint methodology based on the i standard, with the allowable value listed in the TS l and the relationship of the trip setpoint to the
{ allowable value must be documented and controlled by j the setpoint methodology.
i 10 CFR 50.36 states that TS will include limiting safety system settings (LSSS) and "where a limiting safety system setting is specified for a i
variable on which a safety limit has been placed, the setting must be so i
chosen that automatic protective action will correct the abnormal situation before a safety limit is exceeded." In a typical setpoint >
a methodology for instrumentation, it is only the trip setpoint which i satisfies this requirement since its value i accounts for all the instrumentation errors (pndThis not is thesupported allowablebyvalue) i ISA-S67.04-1994 which states that " trip setpoints in nuclear safety-i related instruments shall be selected to provide sufficient allowance between the trip setpoint and the safety limit to account for i uncertainties." Further, the standard states that "an allowance shall i be provided between the trip setpoint and the analytical limit to ensure <
a trip before the analytical limit is reached" and "the trip setpoint should be the value that the final setpoint device is set to actuate."
- Therefore, it is my view that the trip setpoint by itself should be i
considered the LSSS. To use the allowable value as the LSSS or to include it as part of an LSSS (as the above quote from the draft revision to Regulatory Guide 1.105 does) serves no useful purpose and
] only adds confusion to TS.
! 2. In the TS for Westinghouse plants issued in the 1980s, a Limiting
{ Condition of Operation (LCO) for safety-related instrumentation would typically state ' hat an instrument channel was operable if its setpoint was set consisv sc with values shown for the trip setpoints. Contrary to this, the current Westinghouse STS states in the Bases that "if the measured setpoint does not exceed the allowable value, the bistable is considered operable." It is my opinion that an instrument channel can only be considered operable if it is adjusted to the trip setpoint within the calibration tolerance specified in the associated setpoint calculations since, as stated above, it is only the trip setpoint value (and not the allowable value) that accounts for all the instrumentation errors, and it is so chosen that automatic protective action will correct the abnormal situation before a safety limit is exceeded.
' ISA-567.04-1994 states that an allowable value may include instrument calibration uncertainties, instrument uncertainties during normal operation, and instrument drift associated with the portion of the instrument channel being tested. It further states that the allowance for the trip setpoint shall account for all applicable design-basis events and process uncertainties (including those associated with the allowable value) unless they were included in the determination of the analytical limit.
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s-From my viewpoint, the TS should focus on the trip setpoint value and not the allowable vtlue. The sole purpose of an allowable value is to use it as a limit for instrument uncertainties actually encountered during periodic t testing. If actual test results exceed the allowable value, then the l corresponding assumptions in the setpoint methodology must be revisited to l ensure continued validity of the trip setpoint selection. This is supported by ISA-S67.04-1994, which states:
The purpose of the allowable value is to identify a value that, if exceeded, may mean that the instrument has not performed within the assumptions of the setpoint calculation. A channel whose trip setpoint as-found condition exceeds the allowable value should be evaluated for operability taking into account the setpoint calculation methodology.
In this quote, " operability" means future operability based on the revisited l setpoint methodology assumptions and the setpoint set back to the specified trip setpoint value.
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