United States Nuclear Regulatory Commission - Protecting People and the Environment


General Information or Other Event Number: 39392
REP ORG: GENERAL ELECTRIC COMPANY NOTIFICATION DATE: 11/22/2002
LICENSEE: GENERAL ELECTRIC COMPANY NOTIFICATION TIME: 13:43[EST]
CITY: SAN JOSE REGION: 4 EVENT DATE: 11/22/2002
COUNTY: STATE: CA EVENT TIME: 11:43[PST]
LICENSE#: AGREEMENT: Yes LAST UPDATE DATE: 11/22/2002
DOCKET: PERSON ORGANIZATION
DALE POWERS R4
MOHAMED SHANBAKY R1
NRC NOTIFIED BY: JASON POST (fax) DAVID AYRES R2
HQ OPS OFFICER: CHAUNCEY GOULD BRENT CLAYTON R3
EMERGENCY CLASS: NON EMERGENCY
10 CFR SECTION:
CCCC 21.21 UNSPECIFIED PARAGRAPH

EVENT TEXT

GENERAL ELECTRIC IDENTIFIED THE STABILITY OPTION Ill PERIOD BASED DETECTION ALGORITHM T- min SPECIFICATION HAS A DEFECT

"Stability solution Option Ill is implemented in the Oscillation Power Range Monitor (OPRM). Each OPRM channel contains 18 to 33 OPRM cells (depending upon plant size). Each OPRM cell signal is summed from three to four closely spaced Local Power Range Monitor (LPRM) signals. Each OPRM cell signal is processed through the Option III detection algorithms to determine when a trip is required. Trip of one OPRM cell causes its OPRM channel to trip, and when sufficient OPRM channels trip (one-out-of-two taken twice, or two-out-of-four), a reactor scram is initiated to terminate the oscillation.

An OPRM trip is enabled for plant operation within the OPRM Armed Region as defined on the power/flow map. The Armed Region extends from natural circulation to 60% of rated core flow. The licensing basis for the OPRM is to detect all expected oscillations within the OPRM Armed Region, and initiate a reactor trip to suppress the oscillation and provide Minimum Critical Power Limit (MCPR) safety limit protection.

GE LTR NEDO-31960-A, Supplement 1, "BWR Owners' Group Long-Term Stability Solutions Licensing Methodology (Supplement 1 )," November 1995, describes the Option III detection algorithms. The Period Based Detection Algorithm (PBDA) provides licensing basis MCPR safety limit protection. Other algorithms provide defense-in-depth protection. The PBDA includes two parameters called Tmin and Tmax. The PBDA will not evaluate oscillations if the period is less than Tmin or greater than Tmax because these would not be indicative of an expected coupled neutronic/thermal - hydraulic instability. The LTR specifies that "typical" Tmin values are in the range of 1.0 to 1.4 seconds and "typical" Tmax values are in the range of 3.0 to 3.5 seconds.

The expected period of a coupled neutronic/thermal-hydraulic instability depends upon the fluid transit time through the core, and therefore depends upon core flow rate. This has been demonstrated in reactor operation and is predicted by GE computer models. At high core flow, the expected oscillation period is shorter. At low core flow rate, the expected oscillation period is longer. The intent of the OPRM is that Tmin and Tmax provide a wide range with adequate margin to the expected oscillation period for operation within the OPRM Armed Region so that

11/22/2002 U.S. Nuclear Regulatory Commission Operations Center Event Report

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General Information or Other (PAR) Event# 39392 all expected coupled neutron ic/thermal-hydraulic instabilities will be detected by the PBDA".

NOV 22 '02 11:43AM GE NUCLEAR ENERGY P. 1/7

GE Nuclear Energy

General El;ectric Company
175 Curtner Ave. San Jose, CA 95125





November 22, 2002
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Document Control Desk
United States Nuclear Regulatory Commission
One White Flint North
11555 Rockvilie Pike
Rockville, Maryland 2O852-2738


Subject: Reportable Condition Stability Option ifi: Period ~ased Algorlthm Tmin Specification Reference: NEDO-3l960-A, BWR Owners' Group Long-Term Stability Solutions Licensing Methodology (Supplement 1), November 1995

This letter provides notification of a reportable condition with the reference GE Nuclear Energy (GE) Licensing Topical Report LTR) in accordance with §21.21(d). GE has identified that the stability Option III Period Based Detection Algorithm ~BDA) ~ specification is a defect as described below. GE recommends that ~ be set to no higher than 12' seconds to ensure that oscillations are detected and suppressed as intended for stability solution Option III. GE cannot determine how each licensee with stability Option III has implemented Tmin Therfore, this information is provided as a Transfer of Information in accordance with §2l.21(b) for each potentially affected licensee to evaluate if this concern applies to their plant.

Background, Stabillty Option III
Stability solution Option III is implemented in the Oscillation Power Range Monitor (OPRM) Each OPRM channel contains 18 to 33 OPRM cells (depending upon plant size) Each OPRM cell signal is summed from three to four closely spaced Local Power Range Monitor (LPRM) signals. Each OPRM cell signal is processed through the Option III detection algorithms to determine when a trip is required. Trip of one OPRM cell causes its OPRM channel to trip, and when sufficient OPRM channels trip (one-out-of- two taken twice, or two-out-of-four), a reactor scram is initiated to temi~te the oscillation.

An OPRM trip is enabled for plant operation within the OPRM Armed Region as defined on the power/flow map. The Armed Region extends from natural circulation to 60% of rated core flow. The licensing basis for the OPRM is to detect all expected oscillations

NOV 22 '02 11:43PM GE NUCLEAR ENERGY

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within tile OPRM Armed Region, and initiate a reactor trip to suppress the oscillation and provide Minimum Critical Power limit (MCPR) safety limit protection.

GE LTR NEDO-3l960-A, Supplement 1, "BWR Owners' Group Long-Term Stability Solutions Licensing Methodology (Supplement 1)," November 1995, describes the Option III detection algorithms. The Period Based Detection Algorithm PBDA) provides licensing basis MCPR safety limit protection. Other algorithms provide defense-in-depth protection. The PBDA includes two parameters called Tmin and Tmax. The PBDA because these would not be indicative of an expected coupled neutronic/thermal- hydraulic instability. The LTR specifies that "typical" Tmin values are in the range of 1.0 to 1.4 seconds and "typjcal" Tmax values are in the range of 3.0 to 3.5 seconds.

The expected period of a coupled neutronic/thermal-hydraulic instability depends upon the fluid transit time through the core, and therefore depends upon core flow rate. This has been demonstrated in reactor operation and is predicted by GE computer models. At high core flow, the expected oscillation period is shorter. At low core flow rate, the expected oscillation period is longer. The intent of the OPRM is that Tmin and Tmax provide a wide range with adequate margin to the expected oscillation period for operation within the OPRM Armed Region so that all expected coupled neutroniclthermal-hydraulic instabilities will be detected by the PBDA.
Basis for Reportable Condition

GE has performed calculations of oscillation period for different power/flow conditions with the GE frequency domain code ODYSY. Representative results from these calculations are shown in Figure 1 (attached). Calculations with other models and plant experience support these results.

The lowest value specified in the "typical" range for Tmax is 3.0 seconds. The results in Figure 1 show that all periods are less than 3.0 seconds and that there is a significant margin between the nominal calculated periods to the 3.0 seconds value. Therefore, even if a plant uses the lowest 1'typical" value for Tmax, it is expected to be greater than the actual period. Therefore, the "typical" range specified in Tmax causes no safety concern. The highest value in the specified allowable range for Tmin is IA seconds. The results in Figure 1 show that at high core flow, the expected oscillation period is below 1.4 seconds. The margin to Tmin of 1.4 second is not adequate since the use of this "typical" Tmin value could lead to failure of the PBDA to detect an expected oscillation1 Failure of automatic detection at this condition is not expected to result in fliel failures, but may lead to violation of the Technical Specification MCPR safety limit. This is considered to be a Reportable Condition on NEDO-31960-A, Supplement 1. GE analysis shows that for current licensed operation conditions, a generic Tmin value of 1.2 seconds provides adequate margin to expected oscillation periods.

GE does not have responsibility for the Tmin value used by each plant that has selected Option III. Furthennore, GE does not kuow if any licensee has developed a plant- specific basis to support the Tmin value used. Consequently, all Option in plants are


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NOV 22 'O2 11:44AM GE NUCLEAR ENERGY P.3/7

November 22,2002
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potentially affected and this is a Transfer of Information to all Option III plants under l0CFR21.
Corrective Action
1) Absent plant-specific justification of a higher value, tile OPRM is not considered to be operable with a Tmin value greater than 1.2 seconds; Tmin should be set to 1.2 seconds or lower. With Tmin set to 1.2 seconds or lower, the OPRM is considered to be operable. However, GE recommends that plants corsider using a value of 1.0 second to provide additional margin to the expected period range.

2) The OPRM is considered operable for values of Tmax set to 3.0 seconds or higher. However, absent plant-specific justification, GE recommends using a Tmax value of 3.5 seconds or higher to provide additional margin to the expected period range.

3) A tighter Tmin/Tmax range may be justified based on plant-specific analysis and/or experience

If you have any questions, please call me at (408) 925-5362.
Sincerely,



Jason. S. Post, Manager
Engineering Quality and Safety Evaluations

cc.' S D. Alexander (NRG-NRR/DISP/PSIB) Mail Stop 6 F2
J. W. Foster ~RC-NRR/DISP/PSIB) Mail Stop 12 H2
J. F. Kiapproth (GE-NE)
H. J. Neems (GB-NE)
PRC File

Attachments:
1. Figure 1. Expected Oscillation Period vs. Core Flow
2. Information per §21,21(d)(4)
3. Potentially Affected Plants


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Attachment 1 - Figure 1. Expected Oscll1ation Period vs. Core Flow
See ADAMS DOCUMENT

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NOV 22 '02 11:44AM GE NUCLEAR ENERGY P.5/7

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Attachment 2- information per §21.21(d)(4)
(i) Name and address of the individual informing the Commission:

Jason S. Post, Manager, Engineering Quality & Safety Evaluation, GE Nuclear Energy, 175 Curtner Avenue, San Jose, CA 95125 (ii) Identification of the facility, the activity, or the basic component supplied for such facility or such activity within the United States which fails to comply or contains a defect:

All stability solution Option III plants are potentially affected. These plants are listed in Attachment 3.

(iii) Identification of the firm constructing the facility or supplying the basic component which fails to comply or contains a defect:

GE Nuclear Energy, San Jose, California

(iv) Nature of the defect or failure to comply and safety hazard which is created or could be created by such defect or failure to comply:

The specification of the Tmin parameter in licensing topical report NEDO-31960- A, BWR Owners' Group Long-Term Stability Solutions Licensing Methodology (Supplement 1), November 1995 is defective. This report provides a "typical" range of values for Tmin as 1.0 to 1.4 seconds. However, plants may have been using this as a generically approved range. GE has detenmned that expected oscillation period may be less than l.4 seconds for a portion of the power/flow operating domain where the Option III system is to be armed. If a plant used a Tmin value of 1.4 seconds and the actual oscillation period was less than 1.4 seconds, the oscillation would not be detected. Thus, automatic protection for the Minimum Critical Power Ratio (MCPR) Technical Specification safety limit would not be provided by the Option III system as intended. Fuel failures are not expected as many minutes are available for tile operator to take action to mitigate this event.

(v) The date on which the information of such defect or failure to comply was obtained:

September 23,2002

(vi) In the case of a basic component which contains a defect or failure to comply, the number and locations of all such components in use at, supplied for, or being supplied for one or more facilities or activities subject to the regulations in this part:

The potentially affected plants are listed in Attachment 2.



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NOV 22 '02 11:45PM GE NUCLEAR ENERGY P.6/7

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(vii) The corrective action which has been is being, or will be taken; the name of the individual or organization responsible for the action; and the length of time that has been or will be taken to complete the action (note, these are actions specifically associated with the identified Reportable Condition):

All potentially affected licensees have been notified by a Transfer of Information per §2l.21(b) on this date.

Each potentially affected licensee must initiate action to determine if they are affected by this concern within their Part 21 program

o If a licensee is using Tmin = 1.4 seconds and does not have a plant specific justification for use of this value, the OPRM should be declared inoperable until the value is changed to Tmin less than or equal to 1.2 seconds, or a plant-specific justification for continued use of Tmin = 1.4 seconds is completed.

o If a licensee is using Tmin less than or equal to 1.2 seconds, it is not necessary to declare the OPRM inoperable. However, it is recommended that the licensee consider reducing the value to 1 ~0 seconds

GE will modify the user's manual for plants which use the GE supplied Power Range Neutron Monitor to limit the Tmin setting, with allowance to use a higher value if applicable, based on a plant-specific justification.


(viii) Any advice related to the defect or failure to comply about the facility, activity, or basic component that has been, is being, or will be given to purchasers or licensees:

1. Absent plant-specific justification of a higher value, Tmin should be set to 1.2 seconds or lower. GE recommends that plants consider using a value of 1.0 second to provide additional margin to the expected period range.

2. The Tmax value specified in the reference licensing topical report is not identified as being reportable because values over the entire "typicaI" range of 3.0 to 3.5 seconds will not prevent detection of expected oscillations. However, GE recommends using a value of 3.5 seconds or higher to provide additional margin to the expected period range.

3. A tighter range of values for Tmin and Tmax may bejustified based on plant- specific analysis and/or experience.


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Attachment 3 - Potentially Affected Plants
Utility Plant

x AmerGen Energy Co. Clinton
AmerGen Energy Co. Oyster Creek
x Carolina Power & Light Co. Brunswick 1
x Carolina Power & Ligbt Co. Brunswick 2
Constellation Nuclear Nine Mile Point 1
x Constellation Nuclear. Nine Mile Point 2
x Detroit Edison Co. Fermi 2
Dominion Generation Millstone 1
x Energy Northwest Columbia
Entergy Nuclear Northeast Fitzatrick
Entergy Nuclear Northeast Pilgrim
Entergy Operations, Inc. Grand Gulf
Entergy Operations, Inc. River IBend
Entergy Nuclear Northeast Vermont Yankee
Exelon Generation Co. CRIT Facility
x Exelon Generation Co. Dresden 2
x Exelon Generation Co. Dresden 3
x Exelon Generation Co. LaSalle 1
x Exelon Generation Co. LaSalle 2
x Exelon Generation Co. Limerick I
x Exelon Generation Co. Limerick2
x Exelon Generation Co. Peach Bottom 2
x Exelon Generation Co. Peach Bottom 3
x Exelon Generation Co. Quad Cities 1
x Exelon Generation Co. Quad Cities 2
x FirstEnergy Nuclear Operating Co. Perry l
Nebraska Public Power District Cooper
Nuclear Management Co. Duane Arnold
Nuclear Management Co. Monticello
Pooled Equipment Inventory Co. PIM
x PPL Susquehanna LLC. Susquehanna 1
x PPL Susquehanna LLC Susquehanna 2
x Public Service Electric & Gas Co. Hope Creek
x Southern Nuclear Operating Co. Hatch 1
x Southern Nuclear Operating Co. Hatch 2
Tennessee Valley Authority Browns Ferry 1
x Tennessee Valley Authority Browns Ferry 2
x Tennessee Valley Authority Browns Ferry 3

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