February 4, 2013 

MEMORANDUM TO: Chairman Macfarlane 

Commissioner Svinicki 

Commissioner Apostolakis 

Commissioner Magwood 

Commissioner Ostendorff 

FROM: Eric J. Leeds, Director /RA/ 

Office of Nuclear Reactor Regulation 

SUBJECT: INDUSTRY TRENDS INDICATOR EXCEEDED IN 

FISCAL YEAR 2011 

This memorandum informs the Commission that, upon finalization of industry data, the 

Significant Events indicator exceeded its short-term (annual) prediction limit in fiscal year (FY) 

2011. As discussed in SECY-12-0056, “Fiscal Year 2011 Results of the Industry Trends 

Program for Operating Power Reactors,” dated April 9, 2012, the agency documented six 

events as Significant Events. As documented in SECY-12-0056, the staff had not yet finalized 

the probabilistic risk analyses for several other events. 

The staff determines Significant Events through a detailed screening and evaluation of 

operating experience. Inspection Manual Chapter 0313, “Industry Trends Program,” defines 

Significant Events as the following: 

• a Yellow or Red Reactor Oversight Process (ROP) finding or performance indicator, 

• an event with a conditional core damage probability (CCDP) or increase in core damage 

probability (ΔCDP) of 1x10-5 or higher, 

• an abnormal occurrence as defined by Management Directive 8.1, “Abnormal 

Occurrence Reporting Procedure,” and 

• an event rated at two or higher on the International Nuclear Events Scale. 

SECY-12-0056 noted the potential for a high number of significant events for FY 2011. As 

referenced above, the six documented events were related to Yellow or Red ROP findings, and 

the staff was still reviewing an additional seven events under the Accident Sequence Precursor 

(ASP) Program. The ASP Program, implemented by the Office of Nuclear Regulatory 

Research, systematically evaluates U.S. nuclear power plant operating experience to identify, 

document, and rank the operating events most likely to lead to inadequate core cooling and 

severe core 

CONTACT: Michael F. Balazik, NRR/DIRS 

 301-415-2856 
The Commissioners -2- 

damage (precursors). The ASP results of those seven events have been finalized since the 

staff submitted SECY-12-0133 on October 4, 2012, and indicate that all the events are 

significant with respect to CCDP. With the addition of these seven events, a total of 13 

Significant Events occurred in FY 2011, which exceeds the annual prediction limit of 11 events. 

 The annual prediction limit is a value established from industry baseline data that sets an upper 

bound on expected performance in a year. Industry data within the Industry Trends Program is 

normalized per unit. The additional seven Significant Events not documented in SECY-12-0056 

are the following: 

• On April 16, 2011, a loss of offsite power (LOOP) occurred at Surry, Units 1 and 2, when 

a tornado damaged the switchyard (Unit 1 CCDP = 9x10-5, Unit 2 CCDP = 7x10-5). 

• On April 27, 2011, a LOOP occurred at Browns Ferry, Units 1, 2, and 3, when high winds 

damaged the area’s transmission lines (Unit 1, 2, and 3 CCDP = 1x10-5). 

• On August 23, 2011, a LOOP occurred at North Anna, Units 1 and 2, during an 

earthquake (Unit 1 CCDP = 2x10-4, Unit 2 CCDP = 4x10-5). 

In each of these three events, natural phenomena beyond the control of the licensees resulted 

in a LOOP. The Significant Events indicator value was further amplified because each of these 

events occurred at a multi-unit site, resulting in seven units impacted by three external initiators. 

Equipment at Browns Ferry responded as expected early in the event. While Browns Ferry 

experienced two separate and independent emergency diesel generator-related failures that 

resulted in a short duration loss of shutdown cooling (less than one hour each), these failures 

had a negligible contribution to the overall significance of the event because redundant 

electrical power sources were available and the reactors were in cold shutdown at the time. 

Surry did not experience equipment failure throughout the event; therefore, the plant responded 

as expected. While the risk numbers for the North Anna event were driven higher by 

complications from an emergency diesel generator-related equipment failure, sufficient levels of 

defense-in-depth remained. The Browns Ferry, Surry, and North Anna events do not represent 

degradation in overall industry safety performance mainly because the reliability and availability 

of safety systems, along with operator response, minimized the overall risk significance of each 

event. 

Outside the Industry Trends Program, the Operating Experience Branch, within the Office of 

Nuclear Reactor Regulation, is reviewing significant events from the past 5 years to determine if 

there is any trend of concern that the Nuclear Regulatory Commission will need to address. 

The staff will document any conclusions or recommendations resulting from this review in the 

FY 2012 Industry Trends annual report. In addition, the staff will evaluate the conclusions and 

recommendations to determine if changes to the ROP are warranted as part of the ROP SelfAssessment Process. 

cc: SECY 

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 OPA
The Commissioners -2- 

damage (precursors). The ASP results of those seven events have been finalized since the staff submitted 

SECY-12-0133 on October 4, 2012, and indicate that all the events are significant with respect to CCDP. With 

the addition of these seven events, a total of 13 Significant Events occurred in FY 2011, which exceeds the 

annual prediction limit of 11 events. The annual prediction limit is a value established from industry baseline 

data that sets an upper bound on expected performance in a year. Industry data within the Industry Trends 

Program is normalized per unit. The additional seven Significant Events not documented in SECY-12-0056 

are the following: 

• On April 16, 2011, a loss of offsite power (LOOP) occurred at Surry, Units 1 and 2, when a tornado 

damaged the switchyard (Unit 1 CCDP = 9x10-5, Unit 2 CCDP = 7x10-5). 

• On April 27, 2011, a LOOP occurred at Browns Ferry, Units 1, 2, and 3, when high winds damaged the 

area’s transmission lines (Unit 1, 2, and 3 CCDP = 1x10-5). 

• On August 23, 2011, a LOOP occurred at North Anna, Units 1 and 2, during an earthquake (Unit 1 

CCDP = 2x10-4, Unit 2 CCDP = 4x10-5). 

In each of these three events, natural phenomena beyond the control of the licensees resulted in a LOOP. 

The Significant Events indicator value was further amplified because each of these events occurred at a multiunit site, resulting in seven units impacted by three external initiators. Equipment at Browns Ferry responded 

as expected early in the event. While Browns Ferry experienced two separate and independent emergency 

diesel generator-related failures that resulted in a short duration loss of shutdown cooling (less than one hour 

each), these failures had a negligible contribution to the overall significance of the event because redundant 

electrical power sources were available and the reactors were in cold shutdown at the time. Surry did not 

experience equipment failure throughout the event; therefore, the plant responded as expected. While the risk 

numbers for the North Anna event were driven higher by complications from an emergency diesel generatorrelated equipment failure, sufficient levels of defense-in-depth remained. The Browns Ferry, Surry, and North 

Anna events do not represent degradation in overall industry safety performance mainly because the reliability 

and availability of safety systems, along with operator response, minimized the overall risk significance of each 

event. 

Outside the Industry Trends Program, the Operating Experience Branch, within the Office of Nuclear Reactor 

Regulation, is reviewing significant events from the past 5 years to determine if there is any trend of concern 

that the Nuclear Regulatory Commission will need to address. The staff will document any conclusions or 

recommendations resulting from this review in the FY 2012 Industry Trends annual report. In addition, the staff 

will evaluate the conclusions and recommendations to determine if changes to the ROP are warranted as part 

of the ROP Self-Assessment Process. 

cc: SECY OPA 

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 ADAMS Accession Number: ML12347A034 *concurred via email

OFFICE NRR/DIRS/IPAB BC:NRR/DIRS/IPAB BC:NRR/DIRS/IOEB BC:NRR/PMDA/BFEB 

NAME MBalazik RFranovich HChernoff CHsu* 

DATE 12/17/12 01/14/13 01/22/13 11/ 28/12 

OFFICE D:NRR/DIRS OGC (NLO) RES D:NRR 

NAME HNieh BHarris* BSheron* ELeeds 

DATE 01/15/13 01/ 07/13 01/10/13 02/04/13 
The Commissioners -2- 

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