ML20072T933
| ML20072T933 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 09/09/1994 |
| From: | Reid D VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20072T939 | List: |
| References | |
| BVY-94-90, NUDOCS 9409160045 | |
| Download: ML20072T933 (4) | |
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VERMONT YANKEE NUCLEAR POWER CORPORATION j
Ferry Road, Brattleboro, VT 05301-7002 ENGINE R N OFFICE
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580 MAIN STREET BOLTON. MA 01740 (508) 779-6711 September 9,1994 l
BW 94-90 United States Nuclear Regulatory Commission j
Attention: Document Control Desk-Washington, DC 20555
References:
(a)
License No. DPR-28 (Docket No. 50-271)
(b).
Letter, USNRC to WNPC, NW 94-84, June 9,1994
Subject:
Response to Request for Additional information Regarding Proposed Change No.173 to the Vermont Yankee Technical l
Specifications l
l The NRC has requested additional information [ Reference (b)] to complete its review of the application of BWR Owners' Group long-term stability solution Option 1-D to Vermont Yankee. Enclosure A addresses this request and provides revised wording
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to the proposed Technical Specification bases to address NRC' concerns. The Information provided should aid the NRC in completing its review of the applicability
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of Option 1-D to Vermont Yankee.
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Should you have any questions or require additional technical details, please contact us.
Sincerely, j
l VERMONTYANKEE NUCLEAR POWERCORP.
C Donald A. Reid i
j Vice President - Operations LAT/mma Enclosure :
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USNRC Region i Administrator USNRC Resident inspector - WNPS USNRC Project Manager - WNPS 9409160045 9409o9 PDR ADOCK o5o00271 P
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ENCLOSURE A l
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Response to Request for Additionalinformation
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1.
Provide a Detailed Description of the Power Distribution Controls and i
the Administrative Procedures Used to implement Them i
j Power Distribution Controls (PDCs) will be implemented to monitor plant conditions and assess stability margins for either core wide or out-of-phase.
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conditions that may occur during low power operation near the. power / flow
' exclusion region. The PDCs. employ on-line. software which, when given pertinent plant input, calculates the core and channel decay ratios. The monitored plant conditions which are known to affect plant stability include 1
power, flow, power distribution, and feedwater temperature. This form of PDC l
l-is often referred to as a monitor / predictor since it may be used to evaluate and plan plant operation as well as providing the on-line stability status.
The monitor / predictor software will be integrated with the plant process computer. The process computer environment contains all parameters needed to perform decay ratio calculations with this software.' integration of the monitor / predictor with the other process computer software simplifies software maintenance.
Use-of PDCs will automatically occur within'a 5% power / flow buffer zone outside of the exclusion region..The buffer zone represents an analytical i
uncertainty of approximately 20% in decay ratio or " stability margin". This 20%
uncertainty will bound any uncertainty in power peaking, feedwater temperature or xenon concentration at Vermont Yankee. In its plant monitoring mode, the monitor / predictor will be automatically initiated ty recognition of the buffer zone
'l power / flow boundary. The monitor / predictor will also have an off-line capability
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to allow evaluation of planned plant maneuvers, in this predictive mode, plant stability margins would be predicted by input frora a reactor engineer.
The monitor / predictor software is currently not expected to be available until January 31, 1996.
Until that-time and at any other time when the monitor / predictor software is not available, the plant operators will be trained to avoid the 5% power / flow buffer zone.
Plant procedures and training will provide operators the information to use the plant stability information derived from the on-line monitor / predictor. The operators will monitor core and channel decay ratios as well as power and flow in the control room. Action required by the operator, upon reaching the decay ratio A 0.8 will be to increase flow or insert control rods to ensure plant stability. This is the same action required of the operator upon entering'the exclusion region.
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VEloloNT YA%I:E Nrcs.i:An Pown;n Conrustrinos
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t ENCLOSURE A Response to Request for Additional Information (Continued)
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l 2.
Provide an Operator Trainina Plan and/or Channes in Proposed Technical Specifications to Address Concerns About the Possibility of Out-Of-Phase Oscillation As part of implementing BWR Owners' Group (BWROG) Option 1-D, a defense-in-depth strategy will be employed to ensure the potential for.out-of-phase instabilities is recognized. Vermont Yankee intends to train plant operators prior to the start of Cycle 18 (currently planned for Spring of 1995) on the 1-D requirements, and the procedural actions required to avoid an instability or to recognize an instability if it occurs. Plant operators will be trained to recognize a regional oscillation through plant instrumentation which will mainly focus on j
information received from the LPRMs. The LPRM information available to the operator includes individual readings and alarms based on the instrument upscale and downscale. ranges.
The plant operators would observe the periodicity or the magnitude of an instability with the LPRM data and alarms which could signal the need to manually scram the plant. Additionally, the operator training plan will provide information related to the differences in global and out of-phase instabilities. This includes discussion of oscillation -
phenomena, characteristics of plant operation that affect stability and review of BWR instability events.
Further, operators will be trained on how to use the monitor / predictor prior to its implementation which is expected to be by January 31,1996. The on-line monitor / predictor, discussed in the response to item 1, has the capability to recognize the approaches to an out-of phase oscillation and is a primary means for prevention of these oscillation occurrences. The monitor / predictor will provide core and channel decay ratios and other information which would alert plant operators to a possible out-of-phase oscillation.
Vermont Yankee will change the wording in the ' proposed - Technical Specifications bases prior to the start of Cycle 18 as shown in the attached Page 125-a to clearly recognize the potential for out-of-phase as well as core wide instability.
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VERMONT YANKEE NUCLEAR POWER CORPORATION ENCLOSURE A Response to Reauest for AdditionalInformation (Continued) 3.
Provide a Description of the Reload Confirmation or Exclusion Realon Definition Process-The reload confirmation process consists of a two-part calculation to provide justification for use of the APRM flow-biased scram setpoints and definition of the exclusion region boundary. Vermont Yankee will perform these evaluations using BWROG approved methodology. 'A detailed procedure. is now under -
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development for the detect and suppress (flow-blased scram) portion within the BWROG. This procedure provides a checklist of parameters for comparison to those obtained from the reload analysis. For~ situations where the reload i
parameters fall outside the checklist criteria, a specific analysis. is required.
The reload procedure provides two alternatives for the utility at this point, vendor analysis or utility analysis. The utility analysis will require benchmarking to standard detect and suppress problems provided as part of the procedure.
l A detailed topical report describing the reload procedure is planned for -
I-submittal by the BWROG in late Fall of 1994.
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Vermont Yankee currently plans to submit its analysis methods for the exclusion I
region at the end of the first quarter 1995. The contents of this submittal will demonstrate use of the LAPUR code in calculating the exclusion region boundary and checking the BWROG stability mode criterion map for the potential for out-of-phase oscillations.
This demonstration will consist of benchmarks to the 1981 Vermont Yankee stability tests and vendor calculations for Cycle 15. It should be noted that large changes in the exclusion region are not anticipated. However, to allow for any change, the exclusion region will be contained in the Vermont Yankee Core Operating Limits Report.
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