NRC-91-0119, Application for Amend to License NPF-43,changing Tech Specs to Revise Instrumentation Setpoints for Rod Block Monitor Downscale Trip Function

Application for Amend to License NPF-43,changing Tech Specs to Revise Instrumentation Setpoints for Rod Block Monitor Downscale Trip Function

ML20083D875
Person / Time
Site:	Fermi
Issue date:	09/24/1991
From:	Orser W DETROIT EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20083D876	List: ML20083D878 NRC-91-0119, Application for Amend to License NPF-43,changing Tech Specs to Revise Instrumentation Setpoints for Rod Block Monitor Downscale Trip Function
References
CON-NRC-91-0119, CON-NRC-91-119 NUDOCS 9110020003
Download: ML20083D875 (7)

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September 24 1991 NRC-91-0119 U. S. Nuclear Regulet ery Commission Attni Doctuent Cont rol Ucck _

Washingt on, D. c. 20555 Ref e t encei; 1) icini 2 NRC socket No. 50-341 NRC License No. NPF-43

2) Det roit Edison let t er to NRC.

NRC-90-0125 dat ed August 20 1990

3) Detroit Edison let t er t o NRC, NRC-91-0102 et ed Sept ember 24 1991

Subject:

Proposed Technical Specification Change (License An;enda.ent) - Rod Block Monitor Downscale Inst rument ation Setpoints Pursuant to 10CFR$0.90. Detroit Edison Company hereby proposes to amend Operating License NFF-43 for the Fermi 2 plant by incorporating the enclosed changes into the Plant Techt.ical Specifications. The proposed change revises the instrtmientaticn setpoints f or the Rod Block Monitor (REM) downscale t rip f unction. The change reflects a design modification n.ade to the RBM during Yetmi 2's second refueling out age which resulted in a mor e conservative means of applying the downscale trip function. The RBM design changes were described in the Refetence 2 licence amendment application which resulted in Amendment i 69 to the Fertti 2 Operating License. Subsequent t o this amendment. It has been determined that an additional change to the Technical Specifications would be appropriate.

As discussed in Enclosure 1. the actual setpoint for the downscale trip as a result of the design change han leen in full compliance with the cur rent Technical Specification at all times. Because the cetpoint in no longet expressed in terms of % rated power, however, a change in Technical Specification is necescaty for clarif1 cation.

Detroit Edison has evaluated the propor,ed Technical Specifications egainst the crit eria of 10CFR50.92 and det etwined that no significant hazards consideration is involved. The Fermi 2 Gi. cit e Review Organization has spproved and the Nuc3 aat Safe Rev iew Group han m oowon mm o i PD9 ADOCV 05000341

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< U S fiRC Sept est cr 24, 1991 6

i 14RC-91-0119

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i reviewed the propoud Technical Specifications and concurs with the l

enclosed det erminations. In accordance with 10CFR50.91 Detroit Edison has provided a copy cf this letter to the State of Michigan. )

If you have any questionn, please cont act Mr. Glen D. Ohlemacher at (313) 586-4275. l S ince r el y ,

l Enclosure cw

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l cci A. B. Davis R. W. DeFoyet t e J. F, Stang S. Stasek Supe rvis or, Elect . e Ope r at ors. Michigan Public Service Cu:: mission - J. R. Pad get t l

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USNRC September 24, 1991 NRC-91-0119 Page 3 I, WILLI AM S. ORSER, do hereby af firm that the f oregoing statunento are based an f acts and circumstances which are t rue and accurat e t o the best of my knwledge and belief.

J 'l/M WILLI AM S. ORSER Senior Vice Presiden.

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day of gjf I/5 & L i, 1991, before me per:onally appeared William S. /Orcer, being first duly sworn and says that 'ne e.~ecut ui the foregoing as his f ree act and deed .

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Notary Pablic CCT4 " ' ?u ,"KiiA Notory FubHC. f.'c nta County, kW NY M M O M CI##L%L1992

. Enclosura to NRC-91-0119 Page 1 INTRODUCTION In Reference 2, Detroit Edison applied for Technical Specification changes associated with the Maximum Extended Operating Domain (MEOD) and APRM/ Rod Block / Technical Specifications ( ARTS) program. The MEOD/ ARTS program includes design changes for the Rod Block Monitor (RBM) system. The new RPM replaced the flow-biased rod block setpoints with power based setpoints.

The new design also changed the method of applying the downscale trip setpoint. However, the downscale setpoint changes associated with the new design were not included in Reference 2. The purpose of this change is to make the necessary setpoint changes for the RBM downscale trip setpoint.

EVALUATION The RBM system ia provided to prevent local fuel damage that may result from a single rod witildrawal error. The RBM also provides a signal to allow the operator to evaluate the change in relative power level near a control rod during the rod's movement.

To provide a measure of local power change th3 RBM uses Local Power Range Monitor (LPRM) detectors located in the vicinity of the selected rod. Two RBM channels compute an average of all assigned unbypassed LPRMs. An RBM channel inoperatie rod withdrawal block occurs if an autosatic count of active LPRMs determines that too rev detectors are available for use and the RBM is not bypassed. If the .eference Average Power Range Monitor (APRM) associated with a channel is indicating less than 30% power, the RBM is bypassed automatically.

The RBM channel also is bypassed if the selected control rod has one or more adjacent fuel bundles located in the outer boundary of the reactor core, in this case, the high neutron leakage prevents over-limit conditions. In addition, an RBM channel may be manually bypassed. An RBH channel reading downscale and not bypassed is considered to have failed and an RBM Downscale red withdrawal block occurs.

The RBM computes the average of all unbypassed LPRMS assigned te the channel. The average is modified automatically by a gain adjustment in the RBM whenever a control rod is selected. This gain adjustment factor can never be less than one. There is a momentary rod block wnile the gain adjustment is made. The gain adjustment is then held until a new control rod is selected.

The REM automatically limits the local thermal margin changes by causing a rod withdrawal block if the local average neutron flux j

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. . , Enclorur3 to 4 NRC-91-0119 Page 2 indications increases by more than a controlled amount. Only one of the two RBM channels is required to trip to prevent rod withdrawal.

The previous RBM design set the gain adjustment factor to adjust the RBM signal to read the same as the reference APRM signal which, when the RBM was not automatically bypassed, could vary from 30% to 100% of rated thermal power. If the RBM channel signal increased to a recirculation flow-t;iased setpoint or decreased to the fixed downscale setpoint of 5% of rated thermal power, a rod withdrawal block

. occurred. j i

The new PBM design sets the gain adjustment factor to adjust the BBM i signal to a fixed (constant) reference level.- The upscale and downscale trip levels are set as percentages of the reference signal.

The downscale trip setpoint is determined to detect abnormally low signal levels.

.The RBM system vendor, GE Nuclear Energy, recommended t5at the i downscale trip setpoint be set at 94% of the reference signal. This recommendation was included in the GE analysis which was part of the i Reference 2 submittal. The actual trip setpoint has also been set in accordance with.this recommendation.

The recommended setpoint provides a conservative downscale trip when compared to the former scheme. The 5% of rated thermal power setpoint required the RBM signal to decrease by at least 835 to cause a downscale trip. The new 94% of reference. signal setpoint only requires a 6% decrease. Since the new fixed reference signal has been selected to be the same as the-old 100% power reference APRM signal, the gain adjustment factors for the new RBM will be the same or greater than for the old system. These effects compound to provide the new system with a-much greater sensitivity to downscale conditions

. 'in an RBM channel. This greater sensitivity also assures that, when set at 94% of the reference signal, the RBM -stops' rod withdrawal sooner than when set at 5% of rated thermal power with the gain -

adjustment made to the reference APRM signal.

The necessary setpoints were determined in-Design Calculation 4608.

The proposed trip setpoint is greater than or equal to 94% of the reference level .with an allowable value of greater than or equal to 92 3% of the reference level. These values are provided on the attached proposed Technical Specification page. This change is

' independent of.the proposed changes for the Fermi 2 power uprate 1 program (Reference' 3) which also affect this page.

In summary, the proposed change provides RBM downscale instrumentation setpoints_ consistent with the new RBM design which provides greater

Enclosure to NRC-91-0119 Page 3 sensitivity to RBM downscale conditions. For this reason the change enhances safety and is acceptable.

SIGNIFICANT HAZAEDS CONSIDERATION In accordance with 10CFRSO.92, Detroit Edison has made a determination that the proposed amendment involves no significant hazards considerations. To make this determination, Detroit Edison must establish that operation in accordance with the proposed amendment would not: 1) involve a significant increase in the probability er consequences of an accident previously evaluated, or 2) create the possibility of a new or different kind of accident from any accident previously evaluated, or 3) involve a significant reduction in a margin of safety.

The proposed change modifies the Rod Block Monitor (RBM) system downscale instrument setpoints to be consistent with a recently implemented design change which allows greater sensitivity to RBM channel downscale conditions.

The proposed change does not:

1) Involve a significant increase in the probability or consequences of an accident previously evaluated. The change makes setpoint modifications consistent with RBM system design changes such that the system will have greater sensitivity to RBM channel downscale conditions. Therefore, the RBM will terninate rod withdrawal sooner under these inappropriate conditions. The change does not affect the reliability of the RBM system. Therefore, the change does not involve a significant increase in the probability or consequences of any previously evaluated accident.

2) Create the possibility of a new or different kind of accident from any accident previously evaluated. The RBM downscale trip setpoint continues to function on abnormally low RBM channel signal output and acts to halt rod motion in the same manner.

Therefore, no new accider.t scenarios are created.

3) Involve a significant reduction in a margin of safety. By providing greater sensitivity to RBM channel downscale condition safety nargins are maintained.

Based on the above, Detroit Edison has determined that the proposed amendment does not involve a significant hazards consideration.

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i Encloruro to NRC-91-0119 Page 4 ENVIRONMENTAL IMPACT Detroit Edison has reviewed the proposed Technical Specification changes against the criteria of 10CFR51.22 for environmental considerations. The proposed change does not involve a significant hazards consideration, nor significantly change the types or significantly increase the amounts of effluents that may be releasad offsite, nor significantly increase individual or cumulative occupational radiation exposures. Based on the foregoing, Detroit Edison concludes that the proposed Technical Specifications do meet the criteria given in 10CFR51.22(c)(9) for a categorical exclusion from the requirements for an Environmental Impact Statement.

00NCLUSION Based on the evaluation above: 1) there is reasonable assurance that the health and safety of the public will rot be endangered by operation in the proposed manner, and 2) such activities will be conducted in compliance with the Commission's regulations and preposed amendments will not be inimical to the common defense and security or to the health and safety of the public.

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