ML20087F695
| ML20087F695 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 03/31/1995 |
| From: | Marchleuba J OAK RIDGE NATIONAL LABORATORY |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20087F613 | List: |
| References | |
| CON-FIN-L-1697 ORNL-NRC-LTR-95, ORNL-NRC-LTR-95-08, ORNL-NRC-LTR-95-8, NUDOCS 9508150390 | |
| Download: ML20087F695 (5) | |
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1 ORNL/NRC/LTR-95/08 Contract Program:
Technical Support for the Reactor Systems Branch (Ll697/P2)
Subject of Document:
Review of Proposed Technical Specification Changes for Interim implementation of Solution I-D in Vermont Yankee Type of Document:
Technical Evaluation Report j
Author:
Jose March-Leuba Date of Document:
March 1995 NRC Monitor:
T. L. Iluang, Office of Nuclear Reactor Regulation 1
i Prepared for U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation under DOE Interagency Agreement 1886-8169-7A NRC JCN No. Ll697, Project 2, Task 19 Prepared by Instrumentation and Controls Division OAK RIDGE NATIONAL LABORATORY managed by MARTIN MARIETTA ENERGY SYSTEMS. INC.
for the U.S. DEPARTMENT OF ENERGY under Contract No. DE-AC05-840R21400 81g0%
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SUMMARY
This technical evaluation report addresses the Technical Specification char :es proposed by Vermont Yankee (VY) to implement a Long Term Stability Solution of I-D type, which were submitted to NRC in Ref 1 ("VY proposed change #173", dated March 31, 1994). The main conclusion from this review is that the proposed changes are an adequate interim implementation of Solution I-D. These changes are not, however, a full implementation of Solution I-D because they do not address power distribution controls or reload confirmation procedures, it is our understanding that the licensee has plans to address the remaining implementation issues by the startup of Cycle 19 which is expected in January 1996.
INTRODUCTION a
Our initial review of the proposed changes' indicated that the I-D implementation was not complete because it did not include provisions for reload conGrmation analyses or power distribution controls. The results of our preliminary review were discussed with the licensee in a meeting held on August 10, 1994. The conclusion reached in the August 10 meeting was that NRC would issue a " generic" Solution I-D SER, which would recognize that Solution I-D is an acceptable Long Term Solution. The generic SER would also specify the minimum requirements that a Solution 1-D implementation must satisfy in the area of power distribution controls and reload confirmation procedures. A TER addressing the technical issues that will be covered in the generic SER was issued in September 1994.2 During a February 8,1995, meeting at NRC headquarters, the licensee described their proposed power distribution controls and reload confirmation analyses. It appears that Vermont Yankee will complete the implementation of Solution I-D when the SOLOMON Monitor / Predictor software (a GE product based in the ODYSY code) is installed to guarantee power distribution controls. The protection provided by the flow-biased scram for core-wide oscillations will be confirmed when the new BWROG delta-CPR correlation becomes available in mid 1995. The licensee also indicated that they plan to use the LAPUR code to calculate exclusion regions for reload confirmation analyses. During this meeting, l
the licensee stated that they plan to have a full Solution 1-D implementation ready by the startup of Cycle 19, which is expected in January 1996.
PROPOSED TECilNICAL SPECIFICATION CllANGES There are three major moo'fications proposed to the Vermou Yankee Technical Specifications:'
(1)
An exclusion region wil! be deOned in the Core Operating Limits Report (COLR) 2
h (2) The reactor cannot be operated intentionally within the power-flow exclusion region.
If the reactor has entered the exclusion region, the operator is instructed to exit the region immediately by either: (a) inserting control rods, or (b) increasing recirculation flow.
(3)
Eliminate the current requirements to acquire baseline neutron noise data, and to monitor neutron noise levels while operating in the exclusion region.
Other proposed modifications melude:
(1)
Revise the basis for the APRM flux scram setting. Previously, this section only addressed the 120% high flux scram; he revised procedures state that the plant is now taking credit for the flow-biased scram.
(2)
Single loop operation is allowed but only outside the exclusion region.
(3)
Delete the figure showing the staouity exclusion regions in the current specifications; the new region has been moved to the COLR, (4) The bases for thermal hydraulic stability ic revised to reflect the current Solution I-D approach. Reference to thermal hydraulic stability is removed from the bases of single loop operation and the recirculation system.
SOLUTION 1-D IMPLEMENTATION The technical bases for Solution I-D are discussed in detail in references 3 and 4 and were 2
reviewed in ref. 2. A solution 1 D implementation must satisfy the following criteria:
(1)
A exch sion region is defined conservatively and intentional operation is not allowed inside,he region. Instabilities are only likely if the reactor is operated inside the exclusion region unintentionally, which reduces significantly the probability of occurrc nee.
(2) in case an instability occurs in a Solution 1-D plant, it is likely to be an core-wide instability because Solution I-D plants have: (a) tight inlet orifices, and (b) small cores. Both of these characteristics make out-of-phase instabilities unlikely when reasonable power distribution controls are in place.
(3) The flow-biased scram provides automatic protection against core-wide instabilities, which is the most likely oscillation mode, and little or no protection for the out-of-phase mode, which is highly unlikMy. Thus, the probability that unstable power oscillations will result in fuel design limits violations is low in Solution 1-D plants.
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4 The proposed changes to Technical Specifications represent an adequate interim implementation of Solution I-D from the technical point of view because they satisfy criteria numbers (1) and (3) described above. Solution I-D will be completely implemented in Vermont Yankee when criteria number (2)is satisfied by implementing power distribution controls and reload confirmation procedures.
j The proposed changes satisfy criterion number (1) because they provide a requirement that a cycle-specific exclusion region be defined in the COLR and also provide administrative controls to avoid the region. Note that the requirement is that the exclusion region must be reviewed and confirmed in a cycle-to-cycle bases, not that it must be changed every cycle.
Criterion number (3) is satisfied by the calculations provided in ref. 5. Those calculations' show that the flow-biased scram will provide automatic protection before fuel limits are violated if large amplitude power oscillations develop because of a core-wide mode instability. We must note that the calculations shown in reference 3 are based on an interim delta-CPR correlation based on preliminary analyses of the impact on CPR of power oscillations that were performed by GE. The gnal delta-CPR correlation is expected in mid 1995, but the conclusions from ref. 5 are not elpected to be qualitatively different when the more accurate correlation is used became SoluLon I-D is only required to show protection for core-wide oscillations.
Criterion number (2) is partially satisfied by Vermont Yankee because it is a small-core plant with tight (i.e., higher friction) bundle inlet oritices. These characteristics make out-of-phase instabilities unlikely as long as reasonable power distribution controls are in place. The criterion is only partially satisfied by the proposed Technical Specification changes because power distribution controls are not addressed. It is our understanding that these controls will be addressed by plant procedures rather than by a Technical Specification change.
CONCLUSIONS Based on our present review of the Technical Specification changes proposed in reference 1, we conclude that this changes represent an adequate interim implementation of Long Term Stability Solution I-D. Complete implementation of Solution 1-D will require additional plant procedures to cover power distribution controls and exclusion region confirmation analyses for new fuel cycles.
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.C REFERENCES 1
1.
Letter, Vermont Yankee Nuclear P,o, wer Corporation to U.S. NRC, Proposed Change No.173, BWR Thermal Hydraulic Stability and Plant-Information Requimmentsfor.
BWROG Option 1-D Long Term Stability Solution. BVY 94-36, March 31,1994.
2.
ORNLINRCILTR-93/23, Review of Technical issues Related to Long Term Solution I-D " Regional Exclusion with Flow Bia. sed Scram" September i994.
3.
General Electric Company, BWR Owners' Group Long-Term Stability Solutions Licensing Methodology, NEDO-31960, May 199'.
j 4.
General Electric Company, BWR Owners ' Group Long-Tenn Stability Solutions Licensing Methodology, NEDO-31960 Supplement 1. March 1992.
S.
General Electric Company, Application of the " Regional Exclusicm with Flow-Biased j
APRM Neutron Flux Scram" Stability Solution (Option I-D) to the Vermont Yankee
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Nuclear Power Plant, GENE-637-018-0793, DRF A00-04021, July 1993.
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