Module 6:Airborne Contamination

RPT 243Instructional Resources

Module 6:Airborne Contamination

Table of Contents:

Resources Key......

Module Readings and Homework......

Primary Scenario “Inhalation Uptake of 60Co”......

Transfer Scenario “Contamination and Uptake of Personnel from 58Co Airborne During Flood-up of the Reactor Refueling Cavity”

Transfer ScenarioOriginal Event Descriptions

Transfer Scenario “Contamination and Uptake of Personnel from 58Co Airborne During Flood-up of the Reactor Refueling Cavity”

Module Assessment Items......

Primary Scenario “Inhalation Uptake of 60Co”......

ACAD References......

Resources Key

Module Readings and Homework

Primary Scenario “Inhalation Uptake of 60Co”

Transfer Scenario “Contamination and Uptake of Personnel from 58Co Airborne During Flood-up of the Reactor Refueling Cavity”

• Refer to readings and homework for primary scenario above.
• The complete text of the event for this scenario is in the section “Transfer Scenario Original Event Descriptions” below.

Transfer ScenarioOriginal Event Descriptions

Use the complete text of these events to assess students’ ability to analyze the event, and apply appropriate safety and response procedures.

Transfer Scenario “Contamination and Uptake of Personnel from 58Co Airborne During Flood-up of the Reactor Refueling Cavity”

Description: On the ninth day of the refueling outage, the refueling cavity was being filled (flood-up) at the rate of about 1,160 gallons per minute. At 0056, a portable radioactive air sampler alarmed on the refueling floor. Non-essential personnel were directed to leave the refueling floor. A backup air sample was taken which indicated 87.3% Derived Air Concentration (DAC). At the time the reactor head lift was still in progress and the head was not set in its storage location until 0205. Thirty personnel were identified with EPRI Action Level I contamination, mostly 200-400 ccpm on their faces. Cobalt-58 was the predominant isotope identified in the personnel contaminations and area air samples.

Causes: The apparent cause of the airborne radioactivity is believed to be either (1) refueling water flow up through the reactor vessel that rapidly displaced air over dry surface contamination on the upper Reactor Internals or (2) water cascading down to the lower cavity causing sufficient turbulence to evolve airborne radioactivity.

Corrective Actions:

1. The Control Room and Outage Control Center were notified and the reactor building was posted as a "Airborne Radioactivity Area" and access was restricted.
2. Decontamination and whole body counts of the 30 contaminated personnel were completed within eight hours of the event. Each of the 30 workers received a low-level uptake of Cobalt 58, which was attributed to the airborne contamination. The estimated internal dose for each worker is 1-5 millirem.
3. The radiation protection manager met individually with each of the 30 contaminated workers to discuss the event and review their specific radiation exposure.
4. Depending on the results of the Root Cause Evaluation alternate means of flooding up the refueling cavity may be assessed and changes to both access and radiological controls may be instituted.

Module Assessment Items

Note: If instructors wish to increase the difficulty of any item,then we suggest you use it as the basis for an in-class discussion, and / or require students to write an explanation for why a particular choice is correct.

Primary Scenario “Inhalation Uptake of 60Co”

Sally, a Radiation Protection Technician at a nuclear power plant, is providing radiological coverage for a valve replacement. A six-inch valve in a radioactive system is being replaced with a new one. The old valve has been cut out of the system and both pipe ends dressed and beveled. The new valve was positioned and tack-welded in place. While the final weld is being made, a continuous airborne monitor alarms. Sally takes a portable air sample and has it analyzed and calculations indicate airborne activity of .2 DAC.

The facility’s procedures require an Airborne Contamination Area be posted at .2 DAC or above. They also require engineering controls such as ventilation systems to be used and minimizing Total Effective Dose Equivalent (TEDE) when determining respiratory protection needs. The dose rate in the welder’s work area is 2 mrem/hr. and it’s estimated that 2 hours are needed to complete the welding. Sally considers requiring the welder to wear a respirator for the remaining welding to reduce his Total Effective Dose Equivalent (TEDE). If he wears a respirator, the time to complete the welding is projected to be 3 hours. Sally requires the welder to wear a respirator.

1. (Inference) What is the likely cause of the airborne contamination?

a)Radioactive welding rods producing airborne activity

b)Activated corrosion products in the weld area (correct)

c)Fission product gases coming from inside the open pipes

d)Stellite metal valve seats in the replacement valve

1. (Prediction) If Sally required the welder to complete the job without a respirator, what would be the impact on his dose?

a)His total dose would be higher

b)His total dose would be lower (correct)

c)His external dose would be higher

d)His internal dose would be lower.

1. (Prediction) If the valve replacement involved a bolt-in valve instead of a welded-in valve, how would the welder’s dose be affected?

a)External dose would not change

b)Internal dose would be higher

c)Total dose would not change

d)Total dose would be lower(correct)

1. (Prediction) If the welder does not wear a respirator, how will his CEDE and TEDE change?

a)CEDE will increase and TEDE will decrease (correct)

b)CEDE will decrease and TEDE will increase

c)CEDE will increase and TEDE will increase

d)CEDE will decrease and TEDE will decrease

1. (Inference) Which of the following human performance tools did Sally fail to use in setting the radiological requirements for the job?

a)Clear communications

b)Procedure adherence (correct)

c)Self checking

d)Peer checking

ACAD References

Note: ACADs listed in the RPT 243 instructors’ guide introduction document may also apply.

• Explain exposure control including the following

• Operate the following air sampling equipment and describe when each is used:

• Describe methods used to protect against facial contamination such as face shield, "ski-mask" and specially designed hoods

• Identify the conditions in which the use of each type of containment device is to be considered

• Identify methods by which a work site can be prepared for the performance of highly contaminated work such as:

• Define cross-contamination and describe how it can result in the uncontrolled spread of contamination

• Describe techniques to minimize the spread of contamination when contaminated materials are brought out of posted areas

• Describe the purpose and use of a stepoff pad in controlling the spread of contamination

• Identify the isotopes of primary concern for airborne radioactivity at the plant (such as H3, Co-58, C0-60, CS-134, CS-137, I-131).

• Describe the procedures for posting areas as airborne radioactivity areas. (10CFR20)

• Explain the characteristic difference between particulate, iodine, tritium, and noble gases and how they affect the method of detecting and controlling airborne radioactivity.

• Explain the difference between low-volume, high volume, and lapel air samples, including when each is used.

• Discuss the purpose of using a continuous air monitor and identify situations in which continuous air monitors should be used.

• Evaluate trends in airborne radioactivity based on sampling results.

• Identify work situations and work practices that could produce airborne radioactivity, such as:

• Describe controls that can be used to reduce exposure to airborne radioactivity, such as:

• Define protection factor (10CFR20).

• Identify the protection factors, advantages, and disadvantages of each type of respirator used in radiological applications at the station.

• Describe the conditions under which each type of respiratory protection equipment must be used.

• Discuss the difference between paper filters and charcoal filters and when each is used.

• Identify and explain factors that determine the need for and type of protective clothing to be used during radiological work such as:

• Identify and explain factors that determine the need for and type of respiratory equipment to be used during radiological work, such as the following:

• Describe precautions to be used, when practical, to control airborne radioactivity, such as:

• Describe why some areas of the plant should not be decontaminated, such as:

Module 6Airborne Contamination

The Curators of the University of Missouri

Copyright © 2008-2009

A Product of DOL Grant #HG-15355-06-60

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