ML20155F804

Forwards AEOD/S803, AEOD Concerns Re Power Oscillation Event at LaSalle 2 (BWR-5). Rept Details AEOD Concerns Re Facility Power Oscillation Event of 880309.Significant Concerns & Associated Recommendations Listed

ML20155F804
Person / Time
Site:	LaSalle
Issue date:	06/08/1988
From:	Jordan E NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:	Beckjord E, Murley T Office of Nuclear Reactor Regulation, NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
Shared Package
ML20155F805	List: ML20155F804 ML20155F844
References
REF-GTECI-B-19, REF-GTECI-B-59, REF-GTECI-ES, REF-GTECI-TH, TASK-B-19, TASK-B-59, TASK-OR AEOD-S803, NUDOCS 8806170060
Download: ML20155F804 (6)

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MEMORANDUM FOR:

Thomas E. Murley, Director Office of Nuclear Reactor Regulation Eric S. Beck,iord, Director Office of Nuclear Regulatory Research FROM:

Edward L. Jordan, Director Office for Analysis and Evaluation of Operational Data SUEJECT:

AE0D CONCERNS REGAPDING THE MARCH 9, 1988 POWER OSCILLATION EVENT AT LASALLE 2 Enclosed is an AE00 Special Report detailing our concerns about the LaSalle 2 power oscillation event of March 9,1988. We have reviewed calculations performed by Brookhaven on the BWR Nuclear Plant Analyzer, as well as the licensee's LER and other foreign and U.S. infonnation. Although this is the first event of this type at a domestic reactor, similar events have occurred in foreign reactors.

Based on this review, we classify this event as an important precursor event with significant safety concerns. Our most significant concerns and associated recomendations are described below.

1.

The laSalle event raises questions about the adequacy of the analysis used to meet the cora stability requirements of GDC-12 when both recirculation pumps are tripped. The event also points out the difficulties the operators face in rapid diagnosis of and response to an event which readily promotes significant complicating factors such as j

subsequent loss of feedwater heating and reactor water level fluctuations.

Simple and unambiguous procedures are needed to assure prompt proper operator response which ensures compliance with GDC-12.

GE SIL 380 does not provide adequate guidance.

2.

During startup and shutdown, BWCs routinely enter regions of potential thermal-hydraulic-neutron kinetics instability.

This operation can be avoided without large impact on plant operations by nrodifying plant operating procedures to increase recirculation flow slightly early in the startup and by inserting control rods sooner during shutdcen.

Several foreign reactors operate with power / flow operating restrictions that avoid the unstable region. Addit %lly, reduction or loss of forced recirculation flow during plarc hansients can result in the plant entering regions of potential instability.

Prudent operator action is needed to restore stable plant operation and to avoid actions which could initiate events with more significant consequences.

For example, restart of recirculation pumps following loss of feedwater heating or MSIV closure i

could result in additional reactivity insei tion while the reactor was exhibiting power oscillations.

3.

This event has implications regarding the reactor transient response to a recirculation pump trip during an ATWS.

In par;icular, the power oscilla-tions may substantially exceed previously predicted values and thus raise ouestions regarding previous fuel integrity etaluations.

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Thomas E. Murley i Conclusion The March 9 LaSalle event indicates serious deficiencies in the core stability analysis for LaSalle and perhaps other BWRs.

Further, such undamped power oscillations call for prompt operator recognition and action, yet at LaSalle, operators were not trained to recognize or respond to such oscillations.

Adequate plant procedures did not exist at LaSalle, and few, if any, plant simulators in the U.S. are capable of modeling these typm of oscillations.

i It is not at all clear at this time that we understand ). nature end potential consequence of such power oscillations considering such factors as improper or no operator action, alternative core configurations and equipment failures, or divergent localized power oscillations.

Since it will take time to thoroughly analyze and understand the LaSalle event and its implications on other BWRs, we j

conclude that, at least in this interim period, action is warranted to minimize i

the potential for core instability.

Our recommendations in this regard are presented below.

We anticipate a written response to these recommendations within 45 days as discussed in NRC Manual Chapter 0515.

Recommendation to NRR Pending a full understanding of tne LaSalle event and its implications, we i

believe that all BWRs should be required to; l

(a)

Immediately insert control rods to below the 80% rod line following reduction or loss of recirculation flow or other transients which result in entry into potentially unstable regions of the power / flow map.

(b)

Increase recirculation flow during routine reactor startups and insert some control rods prior to reducing recirculation flow below 50% during shutdowns to avoid operation in potentially unstable areas of the power /

flow map.

(c)

Immediately scram the reactor if (a) or (b) above are not successful.

Reconnendation to RES Review resolution of GIs B-19 and B-59 and ATWS mitigation in light of the LaSalle operating experience.

Please let me know if we can provide any clarification or additional assis-tance.

If you have questions regarding the enclosed Special Report, please call Jack Rosenthal on x24440.

D(,ginal $6aed By:

E: D 'Judan Edward L. Jordan, Director Office for Analysis and Evaluation of Operational Data

Enclosure:

As stated Distribution:

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• SEE PREVIOUS C0hCURRENCE

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Thomas E. Murley Conclusion The March 9 LaSalle event indicates serious deficiencies in the core stability analysis for LaSalle and perhaps other BWRs.

Further, such undamped power oscillations call for prompt operator recognition and action, yet at LaSalle, operators were not trained to recognize or respond to such oscillations.

Adequate plant procedures did not exist at LaSalle, and few, if any, plant i

simulators in the U.S. are capable of modeling these types of oscillations.

It is not at all clear at this time that we understand the nature and potential consequence of such power oscillations considering such factors as improper or no operator action, alternative core configurations and equipment failures, or divergent localized power oscillations.

Since it will take time to thoroughly analyze and understand the LaSalle event and its implications on other BWRs, we conclude that, at least in this interim period, action is warranted to minimize the potential for core instability. Our recommendations in this regard are presented below.

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. jg Recomendations 1.

Pending a full understanding of the LaSalle event and its implications, we believe that all BWRs should be required to:

(a)

Immediately insert control rods to below the 80% rod line following loss of all recirculation flow or other transients which result in entry into potentially unstable regions of the power / flow map.

(b)

Increase recirculation flow during routine reactor startups and insert some control rods prior to reducing recirculation flow below 50% durir.g shutdowns to avoid operation in potentially unstable areas of the power / flow map.

(c)

Immediately scram the reactor if (a) or (b) above are not successful.

frA 2.

NRR should revisit GIs 8-19 and B-59 and ATWS mitigation in light of the LaSalle operating experience.

Please let me know if we can provide any clarification or additional assis-tance.

If you have questions regarding the enclosed Engineering Evaluation, please call Jack Rosenthal on x24440.

Edward L. Jordan, Director Office for Analysis and Evaluation of Operational Data

Enclosure:

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109

Thomas E. Murley 3.

This event has apparent implications regarding reactor response to recirculation pump trip during an ATWS.

In particular, it is not clear where the power oscillations would peak and whether fuel would be damaged.

Recomendation Issue a generic communication which would require all BWRs to:

a)

Immediately insert control rods to below the 80% rod line following loss of all recirculation flow, trip of a recirculation pump, or loss of feedwater heatina.

b)

Increase recirct. tion flow during routine reactor startups and insert some control rods prior to reducing recirculation flow during shutdowns to l

avoid operation in potentially unstable areas of the power / flow map.

c)

Immediately scram the reactor if a) or b) above are not successful in l

preventing and suppressing oscillations.

Under separate correspondence, we are recommending that RES revisit GIs B-19 and B-59 and ATWS mitigation in light of the LaSalle operating experience.

Conclusion Adequate justification exists for an appropriate generic communication that ensures prudent operations.

In addition, adequate justification exists for revisiting the technical bases of previously resolved issues in light of the LaSalle operating experience.

Edward L. Jordan, Director Office for Analysis and Evaluation of Operational Data

Enclosure:

As stated Distribution:

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Thomas E. Murley Recomendation Issue a generic comunication which would require all BWRs to:

Imediately implement procedures to scram the plant on loss of all forced circulation.

Based on the LaSalle event, imediately train plant operators regarding the magnitude of the power oscillations observed, the short time to onset of these oscillations, and the factors which contribute to core instability.

Imediately implement the requirements of GE SIL 380, regardless of calculated decay catio, until improved analytical methods are approved by the NRC.

Implement procedures which prevent routine operation in or near the unstable region and which address operator response to transients which put the reactor in the unstable region.

Recommendation Because of current reliance on operator action to meet GDCs 10 and 12, perform a thorough, integrated review of procedures, operator training, Control Room aids, and instrumentation used for response to and identification of power oscillation events.

Recommendation On a lower priority, revisit Generic Issues B-19 and B-59 and the BWR ATWS mitigation studies in light of the LaSalle operating experience.

Conclusion Adequate justification exists for an appropriate generic comunication that ensures prudent operations.

In addition, adequate justification exists for revisting the technical bases of previously resolved issues in light of the LaSalle operating experience and for performing a review of items required for adequate operator response to power oscillation events.

Edward L. Jordon, Director-Office for Analysis and Evaluation of Operational Data

Enclosure:

As stated Distribution:

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