POLICY ISSUE 

(Information) 

March 28, 2011 SECY-11-0044

FOR: The Commissioners 

FROM: Eric J. Leeds, Director 

Office of Nuclear Reactor Regulation 

SUBJECT: FISCAL YEAR 2010 RESULTS OF THE INDUSTRY TRENDS 

PROGRAM FOR OPERATING POWER REACTORS 

PURPOSE: 

The purpose of this paper is to inform the Commission of the results of the U.S. Nuclear 

Regulatory Commission’s (NRC’s) Industry Trends Program (ITP) for fiscal year (FY) 2010. 

This paper does not propose any new actions or commitments. 

BACKGROUND: 

The NRC staff implemented the ITP in 2001 to monitor for adverse trends in safety performance 

based on industry-level indicators. After the NRC assesses adverse trends for safety 

significance, it responds as necessary to any identified safety issues, including adjustments to 

the inspection and licensing programs. One important output of the ITP is the annual agency 

performance measures reported to Congress on the number of statistically significant adverse 

industry trends in safety performance. This outcome measure is part of the NRC Performance 

and Accountability Report. In addition, the NRC annually reviews the results of the ITP and any 

actions taken or planned during the Agency Action Review Meeting. The NRC reports the 

findings of this review to the Commission. This paper is the tenth annual report to the 

Commission on the ITP. 

NRC Inspection Manual Chapter 0313, “Industry Trends Program,” dated May 29, 2008, 

CONTACT: Kevin M Roche, NRR/DIRS 

 (301) 415-3106
The Commissioners 2 

contains details of the ITP, including definitions of monitored indicators and program 

descriptions. 

DISCUSSION: 

Using the ITP, the staff monitors industry safety performance to identify and address adverse 

industry trends. The indicators are comprehensive and are based on the best available data. 

An adverse trend exists if the slope of the regression line fitted to the long-term indicator data 

has a positive value. 

The ITP also uses precursor events identified by the Accident Sequence Precursor (ASP) 

Program to assess industry performance. The staff analyzes the occurrence rate of precursors 

to determine if an adverse trend exists. The staff uses the ASP results as one of the agency’s 

monitored indicators. 

 

In addition to the long-term indicators, the ITP uses a statistical approach based on prediction 

limits to identify potential short-term, year-to-year emergent issues before they become 

long-term trends. 

The ITP complements the Reactor Oversight Process (ROP); the ITP monitors industry-level 

performance, whereas the ROP provides oversight of individual plant conditions and events. 

FY 2010 LONG-TERM INDUSTRY TRENDS: 

Based on the ITP indicators and the ASP Program results, the staff did not identify any 

statistically significant adverse trends in industry safety performance through the end of 

FY 2010. The graphs in Enclosure 1 show the long-term ITP indicator trends and the ASP data. 

The ASP Program considers an event with a conditional core damage probability (CCDP) or an 

increase in core damage probability (ΔCDP) greater than or equal to 1x10-6 to be a precursor. 

The Office of Nuclear Regulatory Research (RES) staff evaluated precursor data from FY 2001 

to FY 2009 and identified no statistically significant trends for the occurrence rate of all 

precursors during that period (Figure 14 of Enclosure 1). Additionally, the staff identified 

statistically significant decreasing trends for precursors with a CCDP or ΔCDP greater than or 

equal to 1x10-4 and for precursors that occurred at pressurized-water reactors during this same 

period. The data period for ASP trending analysis will become a rolling 10-year period when the 

FY 2010 analyses are completed. 

The ASP Program also provides the basis for the safety performance measure of zero 

significant accident sequence precursors of a nuclear reactor accident. This is one measure 

that is associated with the safety goal that the NRC established in its Strategic Plan. A 

significant precursor is an event that has a probability of at least 1 in 1,000 (i.e., CCDP or ΔCDP 

greater than or equal to 1x10-3) of leading to a reactor accident. 

On March 28, 2010, an event occurred at H.B. Robinson Steam Electric Plant involving 

electrical equipment fires, a reactor trip, a subsequent safety injection actuation, and an Alert 

emergency declaration. Based on information provided in Inspection Report 
The Commissioners 3 

05000261/2010009, “H.B. Robinson Steam Electric Plant—Augmented Inspection Team 

Report,” dated July 2, 2010 (Agencywide Documents Access and Management System 

(ADAMS) Accession No. ML101830101), the NRC staff initially performed an ASP screening 

analysis and determined that the event was not a potential significant precursor. Subsequently, 

the staff reported in SECY-10-0125, “Status of the Accident Sequence Precursor Program and 

the Standardized Plant Analysis Risk Models,” dated September 29, 2010 (ADAMS Accession 

No. ML102100313), that no significant precursors had been identified in FY 2010. However, 

RES staff received new information in December 2010 that could lead to the event being a 

potential significant precursor. The ASP analysis is currently ongoing. If the final ASP analysis 

results in a significant precursor, the NRC will report this event in next year’s Abnormal 

Occurrence Report and in the FY 2011 Performance and Accountability Report to Congress. 

FY 2010 SHORT-TERM INDUSTRY PERFORMANCE: 

In addition to the long-term trend monitoring, the staff uses a statistical approach based on 

prediction limits to identify potential short-term, year-to-year emergent issues before they 

become long-term trends. Enclosure 2 shows the short-term results and the prediction limits for 

each of the ITP indicators. None of the indicators exceeded its prediction limit in FY 2010; 

however, the number of significant events (SEs) did increase. These events were unrelated 

and appear to have no common theme. Furthermore, the number of SEs is inflated because 

yellow inspection findings were identified for each reactor unit at two three-unit sites, essentially 

tripling the number of SEs for those sites because SEs are counted on a per-unit basis. 

Short-term FY 2010 data did not reveal any emerging trends that warranted additional analysis 

or significant adjustments to the nuclear reactor safety inspection or licensing programs. The 

NRC Staff and Industry have noted issues related to human performance and training. The ITP 

has captured those issues that have manifested themselves as significant events or one of the 

other ITP performance indicators; never the less, no statistically significant increase has been 

noted. 

FY 2010 RESULTS OF BASELINE RISK INDEX FOR INITIATING EVENTS: 

In 2008, the NRC staff implemented the Baseline Risk Index for Initiating Events (BRIIE) as part 

of the ITP. The BRIIE (1) tracks several types of events that could potentially start (“initiate”) a 

challenge to a plant’s safety systems, (2) assigns a value to each initiating event according to its 

relative importance to the plant’s overall risk of damage to the reactor core, and (3) calculates 

an overall indicator of industry safety performance. 

The BRIIE concept provides a two-level approach to industry performance monitoring. The first 

level (referred to as Tier 1 performance monitoring) tracks and counts the number of times the 

initiating events that have an impact on plant safety occur in nuclear power plants during the 

year. Nine initiating event categories are monitored for boiling-water reactors and 10 for 

pressurized-water reactors. The number of times that each event occurs is compared to a 

predetermined number of occurrences for that event. If the predetermined number is exceeded, 

one can infer the possible degradation of industry safety performance. This annual tracking 

allows the NRC to intervene and engage the nuclear industry before any long-term adverse 

trends in performance emerge. 

 
The Commissioners 4 

The second level (referred to as Tier 2 performance monitoring) addresses the risk to plant 

safety and core damage that each of the initiating events contributes. Each event is assigned 

an importance value, a ranking according to its relative contribution to overall risk to plant 

safety. The greater the contribution of the event to overall risk, the higher the importance value 

that is assigned to it. Using statistical methods, the importance values are combined with the 

number of times the events occur during the year to calculate a number that indicates how 

much the overall industry risk of damage to the reactor core has changed from a baseline value. 

If the BRIIE-combined industry value reaches or exceeds a threshold value of 1x10-5 per reactor 

critical year, the NRC informs Congress of this performance outcome, along with actions that 

have already been taken or are planned in response, in the NRC Performance and 

Accountability Report. 

Enclosure 3 provides the Tier 1 and Tier 2 BRIIE results. None of the initiating events tracked in 

Tier 1 exceeded its prediction limit in FY 2010. Figure 15 of Enclosure 3 shows that the BRIIE 

combined industry value in FY 2010 (-3.39x10-6 per reactor critical year) indicates better than 

baseline industry performance and is well below the established reporting threshold of 

∆CDF = 1.0x10-5 per reactor critical year. 

RESOURCES: 

The staff of the Office of Nuclear Reactor Regulation (NRR) estimates resource needs of 

approximately 0.5 full-time equivalent (FTE) staff and $510,000 for ongoing ITP implementation 

in FY 2011, and 0.5 FTE and $535,000 in FY 2012. The resources are included in the FY 2011 

budget and FY 2012 budget request as part of the ROP in Subprogram: Reactor Oversight; 

Planned Activity: Reactor Performance Assessment. 

RES provides indirect support to the ITP in the areas of operating experience data and models 

that are developed and budgeted under other RES programs such as the Standardized Plant 

Analysis Risk Model Development Program, the ASP Program, and the Reactor Operating 

Experience Data Collection and Analysis Program. The ITP uses the results of RES work in the 

ASP Program to assess industry performance, although the funding and performance of RES 

work are completely separate from the ITP. The resources budgeted in NRR and RES are 

adequate for ongoing ITP implementation. Resources required in future years beyond FY 2012 

would be addressed during the Planning, Budgeting, and Performance Management process of 

the respective year. 
The Commissioners 5 

COORDINATION: 

The Office of the Chief Financial Officer has reviewed this paper and concurs. The Office of the 

General Counsel has reviewed this paper and has no legal objection. 

 /RA/ 

 Eric J. Leeds, Director 

Office of Nuclear Reactor Regulation 

Enclosures: 

1. Fiscal Year 2010 Long-Term Industry 

 Trend Results 

2. Fiscal Year 2010 Short-Term Industry 

 Performance 

3. Summary of Baseline Risk Index for 

 Initiating Events: Annual Graphs 

 through Fiscal Year 2010
The Commissioners 6 

COORDINATION: 

The Office of the Chief Financial Officer has reviewed this paper and concurs. The Office of the 

General Counsel has reviewed this paper and has no legal objection. 

 

 Eric J. Leeds, Director 

Office of Nuclear Reactor Regulation 

Enclosures: 

1. Fiscal Year 2010 Long-Term Industry 

 Trend Results 

2. Fiscal Year 2010 Short-Term Industry 

 Performance 

3. Summary of Baseline Risk Index for 

 Initiating Events: Annual Graphs 

 through Fiscal Year 2010

WITS 200100034/EDATS: SECY-2010-0368 

ADAMS Accession Number: ML110320544 *concurred via email 

OFFICE NRR/DIRS/IPAB BC:NRR/DIRS/IPAB Tech Editor* BC:NRR/DIRS/IOEB* BC:NRR/PMDA/BFEB*

NAME KRoche RFranovich KAzariah-Kribbs JThorp HLe 

DATE 02/05/11 02/15/11 02/08/11 02/14/11 02/17/11 

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

NAME FBrown (MCheok for) GPeterson EWilliamson BSheron (DCoe for) ELeeds 

DATE 02/23/11 03/10/11 03/09/11 03/02/11 03/28/11 

OFFICIAL RECORD COPY
ENCLOSURE 1 

FISCAL YEAR 2010 LONG-TERM INDUSTRY TREND RESULTS 

The staff of the U.S. Nuclear Regulatory Commission did not observe any statistically significant 

adverse trends in the Industry Trends Program performance indicator data from the most recent 

10 years (fiscal years 2001–2010), as indicated by the figures below.

Figure 1 Automatic scrams while critical

0.57

0.44

0.75

0.56

0.47

0.32

0.48

0.29

0.36

0.44

0.00

0.50

1.00

1.50

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Scrams per Unit

Fiscal Year

Automatic Scrams While Critical

Industry Average

Industry Average Trend
2 

Figure 2 Safety system actuations

Figure 3 Significant events

0.19 0.18

0.42

0.24

0.38

0.22

0.25

0.14

0.23

0.18

0

0.2

0.4

0.6

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Actuations per Unit

Fiscal Year

Safety System Actuations

Industry Average

Industry Average Trend

0.07

0.05

0.07

0.04

0.05

0.03

0.02 0.02

0.00

0.09

0

0.04

0.08

0.12

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per Unit

Fiscal Year

Significant Events

Industry Average

Industry Average Trend
3

Figure 4 Safety system failures 

Figure 5 Forced outage rate

0.83 0.87

0.96

0.78

0.99

0.60

0.68 0.71 0.70

0.89

0.0

0.5

1.0

1.5

2.0

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Failures per Unit

Fiscal Year

Safety System Failures

Industry Average

Industry Average Trend

3.00

1.70

3.04

1.88

2.44

1.47 1.41 1.34

2.21

1.74

0

2

4

6

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Forced Outage Rate (%)

Fiscal Year

Forced Outage Rate (%)

Industry Average

Industry Average Trend
4

Figure 6 Equipment forced outages per 1,000 commercial critical hours 

Figure 7 Collective radiation exposure

0.11

0.12

0.16

0.15

0.13

0.10

0.11

0.08

0.09

0.10

0

0.1

0.2

0.3

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Equipment Forced Outages/

1000 Comm. Crit. Hours

Fiscal Year

Equipment Forced Outages/1000 Commercial Critical Hours

Industry Average

Industry Average Trend

123

111

125

100

117

93

109

96

87

92

0

50

100

150

200

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Average Exposure per Unit

(Person-REM)

Fiscal Year

Collective Radiation Exposure

Industry Average

Industry Average Trend
5

Figure 8 Unplanned power changes

Figure 9 Reactor coolant system activity

1.21

1.07

1.15

1.00 0.97 0.91 0.91 0.92

0.56

0.85

0.0

0.5

1.0

1.5

2.0

2.5

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Power Changes per 7000 Critical Hours

Fiscal Year

Unplanned Power Changes

Industry Average

Industry Average Trend

0.52 0.51

0.40 0.42 0.41

0.60

0.45 0.48

0.32

0.19

0.0

0.5

1.0

1.5

2.0

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Maximum Percentage of Technical

Specification Limits

Fiscal Year

Reactor Coolant System Activity

Industry Average

Industry Average Trend
6

Figure 10 Reactor coolant system leakage

Figure 11 Drill/exercise performance

5.86

5.16

4.82 4.64 4.45

4.08

4.35 4.25

3.97 4.08

0

4

8

12

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Maximum Percentage of

Technical Specification Limits

Fiscal Year

Reactor Coolant System Leakage

Industry Average

Industry Average Trend

95.44 95.28

95.73 95.64

95.85

96.03 96.17 96.25

97.06

96.84

92

94

96

98

100

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Percentage Timely and Accurate

Fiscal Year

Drill/Exercise Performance

Industry Average

Industry Average Trend
7

Figure 12 Emergency response organization drill participation

Figure 13 Alert and notification system reliability

96.30

97.10

97.74

97.87

98.19

97.96

97.58

98.14

98.65

98.93

94

96

98

100

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Percentage of Key Personnel

Fiscal Year

ERO Drill Participation

Industry Average

Industry Average Trend

98.53

98.79

98.92

99.24

99.34

99.48 99.45

99.52 99.57 99.59

97

98

99

100

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Percentage of Tests Successful

Fiscal Year

Alert and Notification System Reliability

Industry Average

Industry Average Trend
8

Accident Sequence Precursors 

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

2001 2002 2003 2004 2005 2006 2007 2008 2009

All Precursors Occurrence Rate

Fiscal Year

Precursors (FYs 2001–2009)

Figure 14 Accident sequence precursors
ENCLOSURE 2 

FISCAL YEAR 2010 SHORT-TERM INDUSTRY PERFORMANCE

The annual industry trend analysis compares the data for the most recent year to established 

short-term “prediction limits.” The prediction limits are 95th percentiles of predictive distributions 

for the data. The predictive distributions are statistical probability distributions that describe 

expected future performance. They are derived from performance during “baseline” periods for 

each performance indicator (PI). Baseline periods are periods for each PI during which the data 

can be regarded as fairly constant and indicative of “current” performance. 

The results of the evaluation of the fiscal year (FY) 2010 Industry Trends Program PIs, using the 

established prediction limits, indicate that no PI exceeded its associated prediction limit in 

FY 2010, as shown in the following figures for each PI with its FY 2010 data and associated 

prediction limit. 

Figure 1 Automatic scrams while critical

0.00

0.25

0.50

0.75

1.00

1.25

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Scrams per Unit

Fiscal Year

Automatic Scrams While Critical

Industry Average

Prediction Limit (0.673)

Baseline Industry Average (0.534), 1997-2002
2 

Figure 2 Safety system actuations 

Figure 3 Significant events

0.00

0.25

0.50

0.75

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Actuations per Unit

Fiscal Year

Safety System Actuations

Industry Average

Excluded August 2003 Blackout Event

Prediction Limit (0.375)

0.00

0.03

0.06

0.09

0.12

0.15

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per Unit

Fiscal Year

Significant Events

Industry Average

Prediction Limit (0.106)

Baseline Industry Average (0.524), 2000-2004
3 

Figure 4 Safety system failures 

Figure 5 Forced outage rate

0.00

0.50

1.00

1.50

2.00

2.50

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Failures per Unit

Fiscal Year

Safety System Failures

Industry Average

Prediction Limit (1.04)

Baseline Industry Average (0.859), 2001-2004

0

2

4

6

8

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Forced Outage Rate %

Fiscal Year

Forced Outage Rate

Industry Average

Prediction Limit (4.28)

Baseline Industry Average (2.40), 2001-2004
4 

Figure 6 Forced outage rate of equipment per 1,000 commercial critical hours

Figure 7 Collective radiation exposure

0.00

0.05

0.10

0.15

0.20

0.25

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Equipment Forced Outage Rate

Fiscal Year

Equipment Forced Outages/1000 Commercial Critical Hours

Industry Average

Prediction Limit (0.180)

Baseline Industry Average (0.142), 1998-2004

0

50

100

150

200

250

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Average Exposure per Unit (Person-REM)

Fiscal Year

Collective Radition Exposure

Industry Average

Prediction Limit (139)

Baseline Industry Average (119), 1999-2002
5 

Figure 8 Unplanned power changes per 7,000 critical hours

Figure 9 Reactor coolant system activity

0.0

0.5

1.0

1.5

2.0

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Power Changes per 7000 Critical Hours

Fiscal Year

Unplanned Power Changes

Industry Average

Prediction Limit 1.30

Baseline Industry Average (1.10), 2001-2004

0.00

0.25

0.50

0.75

1.00

Maximum Percentage of Tech. Spec. Limits

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Fiscal Year

Reactor Coolant System Activity

Industry Average

Prediction Limit (0.646)

Baseline Industry Average (0.462), 2001-2004
6 

Figure 10 Reactor coolant system leakage

Figure 11 Drill/exercise performance

0

2

4

6

8

10

Maximum Percentage of Tech. Spec. Limits

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Fiscal Year

Reactor Coolant System Leakage

Industry Average

Prediction Limit (6.32)

Baseline Industry Average (5.14), 2000-2004

92

94

96

98

100

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Percentage Timely and Accurate

Fiscal Year

Drill/Exercise Performance

Industry Average

Prediction Limit (95.2)

Baseline Industry Average (95.6), 2000-2004
7 

Figure 12 Emergency response organization drill participation

Figure 13 Alert and notification system reliability 

94

96

98

100

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Percentage of Key Personnel

Fiscal Year

ERO Drill Participation

Industry Average

Prediction Limit (97.5)

Baseline Industry Average (97.9), 2003-2007

97

98

99

100

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Percentage of Tests Successful

Fiscal Year

Alert and Notification System Reliability

Industry Average

Prediction Limit (98.3)

Baseline Industry Average (98.9), 2001-2004
8 

Note that the 2003 blackout event in the safety system actuations graph (Figure 2) and the 2000 

steam generator tube rupture event at Indian Point Nuclear Generating Unit 2 in the reactor 

coolant system leakage graph (Figure 10) were not included in the short-term data for the 

purpose of determining prediction limits. They were excluded from the development of the 

prediction limit models because they are considered outlier events that overly influenced the 

statistical analysis of the industry-wide data. This treatment results in a more conservative 

prediction limit. 
ENCLOSURE 3 

SUMMARY OF BASELINE RISK INDEX FOR INITIATING EVENTS: 

ANNUAL GRAPHS THROUGH FISCAL YEAR 2010 

The Baseline Risk Index for Initiating Events (BRIIE) addresses the initiating event (IE) 

cornerstone in the U.S. Nuclear Regulatory Commission’s Reactor Oversight Process for 

monitoring commercial nuclear power plants. It is based on plant performance for the 10 

initiator events listed in the table below. 

 INITIATOR ACRONYM APPLICABLE PLANTS 

 General transient TRAN Both plant types, separately 

 Loss of condenser heat sink LOCHS Both plant types, separately 

 Loss of main feedwater LOMFW Both plant types 

 Loss of offsite power LOOP Both plant types 

Loss of vital alternating 

current bus LOAC Both plant types 

Loss of vital direct current 

bus LODC Both plant types 

Stuck-open safety/relief 

valve SORV Both plant types, separately 

 Loss of instrument air LOIA Both plant types, separately 

Very small loss-of-coolant 

accident VSLOCA Both plant types 

Steam generator tube 

rupture SGTR Pressurized-water reactors (PWRs) only 

The BRIIE program, described in NUREG/CR-6932, “Baseline Risk Index for Initiating Events 

(BRIIE),” issued June 2007, consists of two levels or tiers. The first tier considers individual IEs 

and evaluates performance based on statistical prediction limits. This evaluation is for the 

ongoing monitoring and early detection of possible industry-level deficiencies. A second tier is a 

risk-based integrated measure evaluated for each plant type. Because four of the initiators 

have separate data for each plant type, there are a total of 14 Tier 1 graphs. 

The units for the Tier 1 IE frequency graphs are event counts for a fiscal year divided by the 

industry critical time for the year. The Tier 1 graphs also show the average frequency for an 

established “baseline period” and 95-percent prediction limits for a future year if occurrences 

continue at the same rate as in the baseline period. If industry data shift as time progresses, 

the baseline periods used to determine the prediction limits may no longer be relevant. The 

periods were originally developed to describe, roughly, calendar years 1998–2002. 

In early 2010, the events were reviewed, and several events in the loss of condenser heat sink 

and loss of main feedwater categories were reclassified to more accurately reflect the actual 

impact on the plant. After the data were reclassified, the existing baseline periods were 

checked to see if any trends were present that would make the periods no longer appropriate for 

describing the ongoing data. Because such trends were not found, the baseline periods were 

not changed. However, new prediction limits were identified for these categories with reduced 

data that are more appropriate for the way ongoing events are now classified and that allow the 

Tier 1 BRIIE assessment to remain realistic and not overly conservative. 

The prediction limits depend on the expected critical years of reactor operation in the upcoming 
2

year and on the baseline occurrence rate for each indicator. A rate can exceed a limit by having 

more events than expected or by having the same number of events and less critical time than 

expected. In recent years, U.S. nuclear power plant availability has been approximately 

90 percent at the industry level. This figure enters into the calculations that determine the 

bounds on the number of events that might be expected. 

For all of the initiators, the 2010 occurrence rates are lower than the associated Tier 1 prediction 

limits. 

The Tier 2 integrated index includes, for each plant type, the relative contribution of each 

initiator to the risk of core damage, based on the events that occurred in each fiscal year. The 

event frequencies are converted to core damage frequency (CDF) estimates by multiplying by 

Birnbaum risk coefficients. These coefficients are industry averages of the contribution to core 

damage from each initiator as reflected in the industry standardized plant analysis risk models. 

Figure 15 shows annual differences in estimated industry CDF compared to the established 

baseline levels of these quantities. The combined industry BRIIE value for 2010 (-3.39x10-6 per 

reactor critical year) indicates better than baseline industry performance and is well below the 

established reporting threshold of ∆CDF = 1.0x10-5 per reactor critical year. 

Figure 1 Pressurized-water reactor (PWR) general transients

0.76

0.54

1.2

0.72

0.51 0.52

0.65

0.56 0.57

0.88

0.0

0.5

1.0

1.5

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

PWR General Transients

Baseline period: 1998 - 2002

Baseline industry average

95% prediction limit for one year
3

Figure 2 Boiling-water reactor (BWR) general transients

Figure 3 PWR loss of condenser heat sink

0.69

0.81

0.96

0.81 0.84

0.56

0.97

0.55

0.87

0.63

0.0

0.5

1.0

1.5

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

BWR General Transients

Baseline period: 1997 - 2002

Baseline industry average

95% prediction limit for one year

0.081

0.032

0.065

0.11

0.064 0.064

0.032

0.016

0.047

0.082

0.00

0.05

0.10

0.15

0.20

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

PWR Loss of Condenser Heat Sink

Baseline period: 1995 - 2002

Baseline industry average

95% prediction limit for one year 
4

Figure 4 BWR loss of condenser heat sink 

Figure 5 Loss of main feedwater

0.063 0.063

0.26

0.16 0.16

0.031

0.16

0.091 0.093

0.060

0.0

0.1

0.2

0.3

0.4

0.5

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

BWR Loss of Condenser Heat Sink

Baseline period: 1996 - 2002

Baseline industry average

95% prediction limit for one year 

0.064

0.021

0.075

0.084 0.086

0.042

0.063

0.042 0.042

0

0.00

0.05

0.10

0.15

0.20

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

Loss of Main Feedwater

Baseline period: 1993 - 2002

Baseline industry average

95% prediction limit for one year 
5

Figure 6 Loss of offsite power 

Note that the prediction limit for loss of offsite power was calculated under the assumption that the nine such events 

that occurred during the 2003 blackout were a single event. This treatment results in a more conservative prediction 

limit. 

Figure 7 Loss of vital alternating current bus

0.021

0

0.13

0.053

0

0.021

0.011

0

0.031

0

0.00

0.05

0.10

0.15

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

Loss of Offsite Power

Baseline period: 1997 - 2004

Baseline industry average

95% prediction limit for one year 

0.021

0

0.011

000000

0.021

0.00

0.02

0.04

0.06

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

Loss of Vital AC Bus

Baseline period: 1992 - 2002

Baseline industry average

95% prediction limit for one year
6

Figure 8 Loss of vital direct current bus

Figure 9 PWR stuck-open safety/relief valve

0000000000

0.00

0.01

0.02

0.03

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

Loss of Vital DC Bus

Baseline period: 1988 - 2002

Baseline industry average

95% prediction limit for one year

0000000000

0.00

0.01

0.02

0.03

0.04

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

PWR Stuck Open SRV

Baseline period: 1988 - 2002

Baseline industry average

95% prediction limit for one year
7

Figure 10 BWR stuck-open safety/relief valve

Figure 11 PWR loss of instrument air

0.063

0.031 0.032 0.031

0000

0.031

0

0.00

0.03

0.06

0.09

0.12

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

BWR Stuck Open SRV

Baseline period: 1993 - 2002

Baseline industry average

95% prediction limit for one year

0.016 0.016 0.016

0 0

0.016 0.016

0 0

0.016

0.00

0.02

0.04

0.06

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

PWR Loss of Instrument Air

Baseline period: 1997 - 2002

Baseline industry average

95% prediction limit for one year
8

Figure 12 BWR loss of instrument air

Figure 13 Very small loss-of-coolant accident

00000

0.031

0000

0.00

0.02

0.04

0.06

0.08

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

BWR Loss of Instrument Air

Baseline period: 1991 - 2002

Baseline industry average

95% prediction limit for one year

0000

0.011

00000

0.00

0.01

0.02

0.03

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

Very Small LOCA

Baseline period: 1992 - 2002

Baseline industry average

95% prediction limit for one year
9

Figure 14 PWR steam generator tube rupture

 

0000000000

0.00

0.01

0.02

0.03

0.04

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Events per reactor critical year

Fiscal Year

PWR Steam Generator Tube Rupture

Baseline period: 1991 - 2002

Baseline industry average

95% prediction limit for one year
10

Figure 15 BRIIE Tier 2 (change in CDF)

-1.0E-05

-5.0E-06

0.0E+00

5.0E-06

1.0E-05

1.5E-05

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Delta CDF (1/rcry)

Fiscal Year

BRIIE Tier 2 (Change in CDF)

PWR BWR Industry Using Bayesian updates of annual frequencies

Industry BRIIE threshold for one year of data: 1.E-5