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Topical Aspects on Monitoring Airborne Radioactive Effluents from NPPs

Topical Aspects on Monitoring Airborne Radioactive Effluents from NPPs. Wan-tae KIM. Contents. Concepts of Monitoring Guidelines of Monitoring Status of Monitoring. I. Concepts of Monitoring. WHAT. MONITORING. WHEN. WHY. HOW. WHERE. Monitoring What.

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Topical Aspects on Monitoring Airborne Radioactive Effluents from NPPs

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  1. Topical Aspects on Monitoring Airborne Radioactive Effluents from NPPs Wan-tae KIM

  2. Contents • Concepts of Monitoring • Guidelines of Monitoring • Status of Monitoring

  3. I. Concepts of Monitoring WHAT MONITORING WHEN WHY HOW WHERE

  4. Monitoring What • All radioactive effluents to the environment • Two broad source types at NPPs • Point source : stacks and ducts • Nonpoint source : all other sources • Focus on aerosol effluents from point source

  5. Monitoring Why • For evaluation • the environmental impact • the potential annual radiation doses to the public • adequacy and performance of containment, waste treatment methods, and effluent controls • To ascertain • regulatory requirements and LCO have been met • concentrations have been kept ALARA

  6. Monitoring When • Continuously or periodically • At all conditions of reactor operation • Normal • Off-normal • Anticipated operational occurrences • Post-accident • Off-normal case should consider leakage of particles through filter media, filter seals, and cracks in filter frames

  7. Monitoring Where (1) • All major and potentially significant paths • In 40 CFR Part 61.93 (4)(i) : continuous monitor at release points that have the potential effective dose equivalent (EDE) ≥ 0.1 mrem/yr • NUREG-0800, SRP 11.5, table 1 lists all paths

  8. Monitoring Where (2) NUREG-0800 11.5 Table 1

  9. Monitoring How • Combination of direct measurement, sample extraction, and analysis • Sample extraction is performed with sampling system • Sampling system is very useful, but there are a lot of complexities for getting representative samples

  10. Sampling System Generic Sampling System (from ANSI N13.1-1999)

  11. Continuous Air Monitor P&ID of a CAM Sampler

  12. II. Guidelines of Monitoring ANSI N13.1-1969 1977 CAAA : EPA limit emission to air 1983 EPA : propose NESHAP – DOE &NRC 1987EPA:Case of VCD-reconsider NESHAP 1981 NRC : SRP 11.5 ver.3 - ANSI N13.1(1969) 1989 EPA:promulgate-40 CFR 61, Subpart I & H Decision-making : VCD & benzene policy No member of public exceeds 0.1 mSv/yr 1989 NRC : petition for regulation duplicate 1990 EPA: publish Rad NESHAP - 0.1 mSv/yr EPA(1993a) : ANSI N13.1-1969 EPA(1993b) : “8-2 rule” or “duct diameter” 1990 DOE : follow Rad NESHAP-ANSI N13.1(1969) 1993, propose ANSI N13.1-199X 1996 NRC : announce new Constraint Rule - transfer 0.1 mSv/yr to 10 CFR 20 1996 NRC : SRP11.5 Draft ver.4-ANSI N13.1(1993) 1997 EPA : rescind - 40 CFR 61, Subpart I 1997 KINS : SRP 11.5 ver.0 - ANSI N13.1(1969) ANSI N13.1-1999 2000 DOE : present DOE Position to EPA - No supporting complete retrofitting &replacement of all existing monitoring devices 2002 EPA : update - Rad NESHAP ANSI N13.1-1999 use for new & modified Impose additional inspection on existing 2007 NRC : SRP 11.5 ver.4 - ANSI N13.1(1999)

  13. Rad NESHAP (40 CFR 61, Subpart H) • Rad NESHAP standard for public dose limit • from 1 mSv/yr to 0.1 mSv /yr • from all pathway to just only air pathway • The technical requirements for determining dose to the public became more rigidly defined • So, called out the ANSI N13.1-1969 as in USEPA(1993a) • In addition, sampling sites are required to be selected following procedures in USEPA(1993b)

  14. Deficiency in USEPA(1993b) • USEPA(1993b) require that sampling should be done at least 5 - 8 diameters downstream from a disturbance and at least 2 diameters upstream flow disturbances • Techniques is clear, but no criteria • Assumption : the degree of flow development and mixing are directly related to the distance from disturbance • This, unfortunately, is not necessarily true

  15. Deficiency in USEPA(1993a) - 1 • USEPA(1993a) assumes nothing about flow development and mixing and calls out ANSI recommendations for probe design • However, other characteristics of the bulk effluent (i.e., the degree of flow development and particulate mixing) are also critical to determine the design requirements of the probe • ANSI N13.1(1969) provides guidance for particulate sampling probes that utilize a multinozzle array to accomodate any deficiencies in the flow development or mixing

  16. Deficiency in USEPA(1993a) – 2 from ANSI N13.1-1969 • This scheme has a significant drawback • As additional nozzles are added, the loss of particles increase due to impaction in the small nozzle inlet and tube bends • Depending upon the density of the particulates at a ratio 2.0, particulates are underestimated by 10 to 50%

  17. ANSI N13.1-1999 • ANSI N13.1-1999 compensate the deficiencies in USEPA(1993a) and USEPA(1993b) • ANSI N13.1-1999 is a performance-based standard rather than the prescriptive 1969 version • To assure a representative sample is collected, the standard established required sampling system performance criteria

  18. Performance Criteria (1) • Total transport of 10 μm AD particles and vaporous contaminants shall be 〉50% from the free stream to the collector/analyzer • Sampler nozzle inlet shall have a transmission ratio between 80% and 130% for 10 μm AD particles • Sampler nozzle shall have an aspiration ratio that does not exceed 150% for 10 μm AD particles

  19. Performance Criteria (2) • Characteristics of a suitable sampling location are : • coefficients of variation over the central 2/3 area of the cross section within ±20% for 10 μm AD particles, gaseous tracer, and gas velocity • flow angle 〈 20° relative to the long axis of the stack and nozzle inlet • the tracer gas concentration shall not vary from the mean 〉30% at any point on a 40 CFR 60, Appendix A, Method 1 velocity mapping grid

  20. Performance Criteria (3) • Effluent flowrate continuous measurement required if flow variation is 〉± 20% in a year • Effluent and sample flow rate shall be measured within ±10% • Continuous sample flowrate measurement and control required if flow varies 〉±20% during a sample interval • flow control shall be within ±15%

  21. III. Status of Monitoring • 20 units under operation • 6 units under construction • All NPPs under operation use stacks (and ducts) sampling system with isokinetic multiple small-diameter nozzles • Besides, the APR-1000 and APR-1400 have much more number of stacks and ducts

  22. Design Differences • Status of sampling system at 4 units has been surveyed during regular inspection in 2007 • Considerable matters are listed : • the ratio of effluent/sample flow rate ranges from 10000 to 100000 • unbalance seems to exist among the components • transport line seems too long, lots of bends • information related sampling location, nozzle, and transport line for old system is absent • no total procedures to maintain sampling system • no method to inspect the inner sampling site

  23. Data Comparability • Uniform method can provide a uniform basis for data comparison from the different facilities • Uniform method can be maintained with • Periodic inspections of nozzle, transport lines, sample and effluent flowmeters shall be conducted • Periodic calibrations of effluent and sample flowmeters, CAMs, and sample analysis instrumentation shall be conducted

  24. Under Tasks • New plants under construction in Korea are planning to use ANSI N13.1-1999 • The performance criteria of ANSI N13.1-1999 have been studied to impose on the existing facilities

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