NRRPT - National Registry of Radiation Protection Technicians Contamination and Airborne Control Questions and Answers — Questions and Answers
Question 1: A technician performs a wipe survey for removable contamination. The wipe is counted in an instrument with a 35% efficiency for the beta emitter of concern. If the net count rate for the wipe is 700 cpm, what is the removable contamination level in disintegrations per minute (dpm)?
- 245 dpm
- 700 dpm
- 1225 dpm
- 2000 dpm (Correct answer)
Correct answer: 2000 dpm
To convert from counts per minute (cpm) to disintegrations per minute (dpm), the count rate must be divided by the detector's efficiency for the specific radionuclide and geometry being counted. In this case: dpm = cpm / efficiency = 700 cpm / 0.35 = 2000 dpm.
Question 2: According to 10 CFR 20, which of the following conditions requires an area to be posted as an "Airborne Radioactivity Area"?
- The measured concentration of airborne radioactive material exceeds 10% of the DAC.
- An individual present in the area without respiratory protection could exceed 12 DAC-hours in a week. (Correct answer)
- The use of any respiratory protection is mandatory for entry.
- An individual could receive an intake of 1% of the Annual Limit on Intake (ALI).
Correct answer: An individual present in the area without respiratory protection could exceed 12 DAC-hours in a week.
10 CFR 20.1003 defines an "Airborne Radioactivity Area" as a room or area where airborne radioactive materials exist in concentrations that either (1) are in excess of the Derived Air Concentrations (DACs) or (2) are such that an individual could exceed an intake of 0.6 percent of the Annual Limit on Intake (ALI) or 12 DAC-hours in a week.
Question 3: A worker must enter an area with a general airborne concentration of a specific radionuclide measured at 20 DAC. The worker will wear a full-face, air-purifying respirator. What is the effective airborne concentration inside the respirator mask?
- 2.0 DAC
- 1000 DAC
- 0.4 DAC (Correct answer)
- 20 DAC
Correct answer: 0.4 DAC
A full-face air-purifying respirator has an OSHA-mandated Assigned Protection Factor (APF) of 50. The effective concentration inside the mask is the ambient concentration divided by the APF. Therefore, Effective DAC = 20 DAC / 50 = 0.4 DAC.
Question 4: Which of the following describes the primary function of a High-Efficiency Particulate Air (HEPA) filter used in nuclear ventilation systems?
- To absorb radioactive noble gases from the exhaust airstream.
- To cool the air being exhausted to prevent thermal damage to ductwork.
- To remove at least 99.97% of airborne particles with a size of 0.3 micrometers. (Correct answer)
- To remove moisture from the air to prevent condensation in the system.
Correct answer: To remove at least 99.97% of airborne particles with a size of 0.3 micrometers.
The standard definition of a HEPA filter is one that is certified to remove at least 99.97% of airborne particles that are 0.3 micrometers (µm) in diameter. This particle size is considered the most penetrating. HEPA filters are designed for particulates and are not effective for removing radioactive gases.
Question 5: During a routine survey, a worker is found to have a small spot of removable radioactive contamination on their forearm. What is the most appropriate initial action?
- Immediately apply duct tape to the spot to lift the contamination.
- Scrub the area vigorously with a stiff brush and industrial solvent.
- Gently wash the affected area with mild soap and lukewarm water. (Correct answer)
- Report directly to an off-site medical facility for evaluation.
Correct answer: Gently wash the affected area with mild soap and lukewarm water.
Standard procedure for personnel decontamination is to begin with the least aggressive method first. Gentle washing with mild soap and lukewarm water is effective at removing loose contamination without abrading or damaging the skin, which could lead to an intake or prevent further, more aggressive decontamination if needed.
Question 6: What is the primary purpose of maintaining a negative pressure differential in a radiological containment enclosure, such as a glovebox or hot cell, relative to the surrounding room?
- To increase the efficiency of the HEPA filters by creating higher airflow.
- To ensure that any potential leakage flows from the surrounding room into the containment. (Correct answer)
- To provide a constant flow of fresh air to cool internal components.
- To reduce the external radiation dose rate for personnel outside the containment.
Correct answer: To ensure that any potential leakage flows from the surrounding room into the containment.
Maintaining negative pressure ensures that the direction of airflow is always from the cleaner area (the surrounding room) into the more contaminated area (the containment). This engineering control prevents the out-leakage and spread of airborne radioactive contaminants should there be a breach in the containment.
