a method for quantifying noble gas releases doug wahl limerick generating station
TRANSCRIPT
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) .
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.
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.
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
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.
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.
Hourly Average Monitor Readings for a 1-week Period
Value used asBackground for week
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.
Airborne Fission and Activation Gaseous Effluents Comparison by Year per BWR Reactor (Total Curies)
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
2000 Effluent Survey
• 19 Plants Participated.
• 11 Assigned Zero Activity for the Month if No Activity Found in Grab Sample.
• Survey Raised Several Questions?
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?
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.
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?
North Stack – A/B Monitor
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
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.
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.
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).
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.
Limerick’s Revised Approach
• Each Monitor’s Monthly Calculated Mean and 2 Standard Deviations was used as Background for the Month.
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
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”
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
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
Airborne Fission and Activation Gaseous Effluents Comparison by Year per BWR Reactor (Total Curies)