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SME Associates LLCProviding Innovative Solutions

RMS- OPTIMIZATION OF SAMPLING SYSTEMS

JAMES P. MENGE PE, CHP

2Background

Every day various quantities of particulates, vapors, gases and radionuclides are discharged to the environment from various power generation plants and production facilities.

In general, the airborne effluent from nuclear power plants is discharged continuously through one or more vents or stacks of various heights.  

3Background (cont’d)

The released airborne radioactive pollutants can be summarized into the following categories: Gaseous Vapor Particulate

The radionuclides are produced by a result of two processes: The first process is the formation of fission products, which are produced

when uranium atoms in the fuel are split. The second process is activation, which occurs when atoms of other

material within the system are made radioactive by neutron bombardment.

4Key Terms• A term used as a single dimension to describe a particle size in a

fluid medium.Aerodynamic Equivalent

Diameter (AED)

• The particle size distribution curve relating to one size particleMonodisperse

• Dimension less number that relates variables describing flow, velocity, density and viscosity.Reynolds Number

• The percent of particulate that is transported from the nozzle to the collection media.Transport Efficiency

• The region of Reynolds numbers between laminar (<2500) and turbulent flow (>4000) which relates variables describing flow, velocity, density and viscosity.

Transition Region

5System Description The system draws a continuous air sample from

the sampling probe located high in the effluent stack.

The air sample is drawn through the sample lines to a series of filters consisting of a particulate filter, an iodine filter, a noble gas chamber and a pump then discharged to the stack.

6Sampling Systems FAQ’s Is there one “Universal” monitoring system configuration?

No. Various monitoring system configurations are used by the nuclear power plant operators or utilities to comply with NUREG 0737 and Reg Guide 1.97.

Why do the sampling systems have problems? These sampling systems can have inherent problems associated with representative

sampling because of the complexity and length of the sampling line. How effective are the sampling systems?

One utility initiated a program to measure the effectiveness of the sampling systems and found several mechanical problems (fans, baffles, probes, etc.) that affected their effluent monitoring program.

What did reviews of the stacks show? Reviews performed for stacks found that the stack flows and the flow profiles were

significantly different than the design flows used in their emission calculations.

7Sampling System FAQ’s (cont’d)

What is the purpose of a sample system model? A sample system model provides an insight of which factors can influence the sample

transport efficiency of a sampling system. The sample flow velocity (v) is an important factor in the transport efficiency of

particles through a sampling system.

What are the various design parameters, and what do they do?

The sample flow rate, tubing diameter and Reynolds Number are design parameters that directly determine the flow velocity through the sample system

8Particle Transmission Efficiency –Fx of Sample Flow & Reynolds Number

9Sampling System Maintenance

Perform a maintenance check on the sampling system actual pump flow variance

Check each probe and sample line for cleanliness.

Check system installation for the number of bends and bend curvature radius. Higher transport efficiencies can be achieved when sampling line

installations minimize flow direction changes.

Check Moisture content residual in sampling lines

Pressure test for Air-Leakage within Sample lines

A periodic check of the flow profile should be performed to check the effluent stream characteristics for sampling location.

10Sampling Point Challenges

The sampling point available for use may not provide a valid representation sample of the effluent.

A flow profile should be generated for each sample point location. This ensures that under varying plant conditions, the sample point is representative of the system stream.

11RMS: A Dynamic System

Flow rate and tubing diameter will affect transport efficiency based on particle sizing, plate out and impaction.

The transport efficiency of particles through a sample line may vary by 50% or more due to sample flow rate, and tubing diameter.

The RMS accuracy increases by reducing the sampling error and the extent of the scaling factors used to determine the particulate effluent release.

The effluent particulate monitoring repeatability increases due to the transport efficiency being optimized.

12Transport Efficiency The transport efficiency is a function of particle size: as the particle size increases,

the transport efficiency decreases. The median particle aerodynamic size should be determined for the distribution range of the mixture.

The limitation of the sample transport efficiency of the radiation monitoring sampling system is that it is based on a particular particle size and not the mixture.

13Optimization of Design Parameters

The transmission of a 5μm AED particle with a density of 1.5 g/cm3 drawn through the sample system model at 56.630 l/min yields only a 26% transmission efficiency.

The transmission efficiency of a particle is a function of the sample tube diameter. The optimum internal diameter for this sample system model with the design flow of 56.630 l/min is 22.926 mm.

The sample line transmission efficiency for this sample system model can be increased to 27% for a 5μm AED particle with a density of 1.5 g/cm3 by increasing the flow to approximately 70 l/min. The transmission efficiency of all particles less than 10μm AED is increased by raising the sample flow rate to 70 l/min.

14Particle Transport Efficiency

15Optimization of Design Parameters

The transmission efficiency of particles is a function that is inversely proportionate to the particle density. As the particle density increases, the transmission efficiency decreases.

At the optimum sample flow rate of 70 l/min, the transmission efficiency for AED particle with a density range of 1.00 to 2.00 g/cm3 varies by only 0.1%.

The sampling system Reynolds number is in the transition region to achieve optimum transport efficiency.

16Recommendations: Sampling System Perform an analysis of the sample stream to

determine the range of particle sizes and density.

Develop a model for the sampling system to determine the transmission efficiency for the system based on particle size and density. It is not a monodisperse particle.

• Determine the optimum sample flow rate for the sampling system. Do not rely on what the vendor or manufacturer has stated the sample flow rate should be for their radiation monitoring system skid.

17Filter Efficiency vs Particle Size• Review the filter collection media specifications to

ensure the filter is sized appropriately for the flow velocity.

18Conclusions

The RMS Sampling System is key to proper system operation and dose measurement

RMS Sampling systems need periodic maintenance

It’s important to understand what the design parameters are for the sampling system

Performing detailed reviews will ensure system is not operationally challenged

19References

Menge J, (1997); “Optimization of Airborne Effluent Sampling Systems for Nuclear Power Plants”

Schmidt, A (1988); “ A Three-Part Strategy for Continuous Extractive Monitoring for Hazardous Particulate Emissions from Exhaust Stacks”

Schwendiman, Stegen, Glissmeyer (1975); “Methods and Aids for Assessing Particle Losses in Sampling Lines”

ANSI N13.1-1995; American National Standard Institute “Guide to Monitoring Releases of Airborne Radioactive Substances from Ducts and Stacks of Nuclear Facilities”.

NUREG 0737 (1983); “Clarification of TMI Action Plan Requirements” US NRC Regulatory Guide 1.97 Rev 3 (1983); “Instrumentation for Light-Cooled

Nuclear Power Plants to Assess Plant and Environs Conditions During and Following an Accident”

20RMS- Optimization of Sampling Systems

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