a method for quantifying noble gas releases doug wahl limerick generating station

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A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

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Page 1: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

A Method for Quantifying Noble Gas Releases

Doug Wahl

Limerick Generating Station

Page 2: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Radiation Monitoring Display System (RMDS)

• Design– Continuous monitoring

gaseous effluents.

– Alert Operations to abnormal releases.

– Quantify gaseous effluents for reporting and dose calculations.

– Sensitivity of 1E-06 uCi/cc (Xe-133) .

Page 3: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Effluent Monitoring History

• RMDS Computer System failed in 1997.• System continued to function, but data was not

stored for more than a one-hour period.– Live time available for emergency dose calculation.– Data was over written with new data.

• No record of effluent releases.• Relied on grab samples for quantifying effluent

releases.• Reported 0 curies of Noble Gas released in 1997

and 1998.

Page 4: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Effluent Monitoring History

• New computer system installed in 1999.• Received an NRC violation in 1999.

– Failure to maintain records of effluent releases - Tech. Spec. violation.

• Inspector’s Philosophy– Power plants are not zero release.– Accuracy of numbers reported.

• Urged Limerick to develop a means to quantify effluent monitor results.

Page 5: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

New RMDS

• Drawback– Electronic files not

available except by IT.

– Available as hard copy printouts only.

– Don’t know when normal releases are occurring.

– No Trending of data

Page 6: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Method of Quantification

• Obtained the Weekly 1-hour Average Radiation Effluent Monitor Data Printout.

• Determined the Daily High and Low 1-hour Readings (uCi/cc).

• Averaged the Daily High and Daily Low to Obtain Daily Average.

Page 7: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Method of Quantification

• Assigned the Lowest 1- hour Reading for the Week as Background (uCi/cc).

• Subtracted the Background from each Daily Average.

• Multiply by Flow and Time to obtain Curies released for Week.

• In 1999 Reported 1412 Curies released.

Page 8: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Hourly Average Monitor Readings for a 1-week Period

Value used asBackground for week

Page 9: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Consequences of Method

• More than 1400 Curies of Noble Gas Released Annually from 1999 through 2002.

• Limerick is in INPO’s Worst Quartile for Gaseous Releases. • Gaseous Effluents is one of the Twelve Areas of Plant

Performance Measured by ANI’s Engineering Rating Factor.• Portion of Nuclear Plant’ Liability Premium is Redistributed.

– Best performers – 20 percent credit– Worst performers – 30 percent surcharge.

• Limerick Pays a Surcharge of about $40,000.

Page 10: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Airborne Fission and Activation Gaseous Effluents Comparison by Year per BWR Reactor (Total Curies)

Page 11: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Why the ANI Surcharge?

• A Perceived Increase Risk of Litigation.– ACE - Alliance for Clean Environment

• Tooth Fairy Project

• Limerick “Part of the Toxic Triangle”

Occ

iden

tal

Limerick

Waste Management

Page 12: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

2000 Effluent Survey

• 19 Plants Participated.

• 11 Assigned Zero Activity for the Month if No Activity Found in Grab Sample.

• Survey Raised Several Questions?

Page 13: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

2000 Effluent Survey

• Is it Appropriate to Rely on the Monthly NG Grab Sample as the Station’s Sole Record of Release?

• If No NG Activity is Found in the Grab Sample, Should you Report Zero Activity for the Month?

• Are INPO’s Rankings Comparing Apples to Apples?

• What is Background?

Page 14: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Noble Gas Grab Sampling

• Monthly Requirement.• Additional Sampling as Warranted.

– Increase Release Rate as Observed by Control Room

• One Point in Time.– It doesn’t tell you what happened yesterday

• Qualitative.– Nuclides being seen by rad monitors.

Page 15: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Noble Gas Grab Sampling

• In 2003 No Activity was found in the Monthly Grab Samples.

• Does that Mean there were No Releases for the Year?

• If No Activity is Found – How to Quantify Gaseous Effluents?

Page 16: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

North Stack – A/B Monitor

Page 17: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

North Stack 4/23/03

0.00E+00

4.00E-07

8.00E-07

1.20E-06

1.60E-06

2.00E-06

A - MonitorB - Monitor

Page 18: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Goal

• Develop a Method to Better Estimate Noble Gas Releases.– Statistically Driven– Determine a “Reasonable” Background

• Understand the Role of the Noble Gas Grab Sample.

Page 19: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Limerick’s Revised Approach

• Obtain the 2003 RMDS 1-hour Average Data from Information Technology.

• Plot the Data, Observe and Investigate Anomalous Results.

• Obtain the 2003 RMDS 15-minute Average Data for the Days that the Noble Gas Grab Sample was taken; as well as, for Days that Appeared to Show a Release from the 1-hour Data.

Page 20: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Limerick’s Revised Approach

• Background Arbitrarily Chosen from 15-minute Data One Hour before the NG Grab Sample and One Hour after.– Assumed that if No Activity Found in Grab

Sample then Effluent Radiation Monitor Reading was Background

– Provided 8 data points for Statistics

• Action taken for All Six Effluent Radiation Monitors (2 per release point).

Page 21: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Limerick’s Revised Approach

• If 15-minute Data not Available or Suspect, then data from the Previous Month was used as Background.

• Likewise, if Positive Activity were found in the NG Grab Sample, then Background Based upon a Previous Month where No Activity was Found.

Page 22: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Limerick’s Revised Approach

• Each Monitor’s Monthly Calculated Mean and 2 Standard Deviations was used as Background for the Month.

Page 23: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Monthly Background ValuesMean + 2 SD of 15-Minute Data

Month

Common

North Stack

A

Common

North Stack

B

Unit 1

South Stack

A

Unit 1

South Stack

B

Unit B

South Stack

A

Unit 2

South Stack

B

Jan 7.59E-07 6.54E-07 5.71E-07 6.83E-07 7.73E-07 5.44E-07

Feb 7.91E-07 5.34E-07 6.40E-07 8.11E-07 7.85E-07 3.44E-07

Mar 7.63E-07 5.65E-07 5.63E-07 6.85E-07 6.22E-07 4.99E-07

Apr 7.62E-07 6.40E-07 6.12E-07 1.05E-06 8.17E-07 4.05E-07

May 7.58E-07 5.08E-07 6.46E-07 8.57E-07 1.06E-06 3.53E-07

Jun 6.31E-07 5.77E-07 5.17E-07 8.47E-07 6.82E-07 4.88E-07

Jul 7.01E-07 5.08E-07 4.84E-07 1.32E-06 5.63E-07 3.30E-07

Aug 6.56E-07 4.42E-07 5.73E-07 7.12E-07 7.12E-07 3.38E-07

Sep 7.28E-07 4.97E-07 5.71E-07 9.34E-07 6.08E-07 4.57E-07

Oct 7.48E-07 5.71E-07 6.10E-07 6.49E-07 8.48E-07 4.12E-07

Nov 6.04E-07 4.73E-07 5.22E-07 6.49E-07 7.47E-07 3.48E-07

Dec 7.16E-07 4.73E-07 5.05E-07 5.77E-07 7.45E-07 4.88E-07

Page 24: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Limerick’s Revised Approach

• Each Monitors Background Number was Subtracted off Each Valid Hourly Reading.

• Net Activity from the A and B Monitors were Averaged to obtain the Net Activity in uCi/cc.– Net Activity below Zero was Classified as Zero

or “No Release”

Page 25: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Limerick’s Revised Approach

• For Each Hour of Positive Net Activity the Number of Microcuries Released was Determined by the Formula:

hrccCiccVolumeStack

hrCi /sec3600*/*(sec) 604800

)(/

Where:Stack Volume (cc) = Total weekly stack volume604800 (sec) = Number of seconds in a weekuCi/cc = Net average hourly rate for the A and B monitor3600 = conversion from seconds to hour

Page 26: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Limerick’s Revised Approach

• Nuclide Mix Reported in FSAR Used to Calculate Dose

• Using this Method Limerick Reported in the 2003 Annual Effluent Release Report 4.26 Curies of Noble Gas.– Significantly lower than the 1447 Ci reported in 2002.

– Contribute to a Reduction in the ANI Surcharge

– From INPO’s Worst Quartile to Best Quartile

Page 27: A Method for Quantifying Noble Gas Releases Doug Wahl Limerick Generating Station

Airborne Fission and Activation Gaseous Effluents Comparison by Year per BWR Reactor (Total Curies)