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 MONITORING WHAT WHEN WHY HOW WHERE

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

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

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

Monitoring Where (1) All major and potentially significant paths In 40 CFR Part (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

Monitoring Where (2) NUREG Table 1

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

Sampling System Generic Sampling System (from ANSI N )

Continuous Air Monitor P&ID of a CAM Sampler

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

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 N as in USEPA(1993a) In addition, sampling sites are required to be selected following procedures in USEPA(1993b)

Deficiency in USEPA(1993b) USEPA(1993b) require that sampling should be done at least 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

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

Deficiency in USEPA(1993a) – 2 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% from ANSI N

ANSI N ANSI N compensate the deficiencies in USEPA(1993a) and USEPA(1993b) ANSI N 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

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

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

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%

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

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 to 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

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

Under Tasks New plants under construction in Korea are planning to use ANSI N The performance criteria of ANSI N have been studied to impose on the existing facilities