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BLD-NUCL84-06 · Lesson 3 · 30 clock hours · theory

10 CFR Part 20: Radiation Protection Standards

Objective. Students will apply occupational dose limits, ALARAprinciples, and controlled/restricted area requirements from 10 CFR Part 20 to given exposure scenarios and determine compliance.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional engineer or master tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Overview of 10 CFR Part 20

Title 10 of the Code of Federal Regulations, Part 20 (10 CFR Part 20), titled Standards for Protection Against Radiation, is the primary federal regulation governing radiation protection at NRC-licensed nuclear facilities. Every licensed nuclear power plant must operate within the dose limits and administrative controls established by Part 20. Violating these limits is not just a safety concern — it is a federal regulatory violation that can result in enforcement action, civil penalties, and loss of operating license.

As a nuclear plant technician or operator, you will encounter Part 20 daily. You must be able to read a dosimetry record, compare it against the applicable limit, identify an ALARA concern, and recommend corrective action. This lesson builds exactly those skills.

Occupational Dose Limits

Part 20 sets annual dose limits for occupational workers — adults who work with or near radiation sources as part of their job. The key limits are:

These are regulatory ceilings, not targets. A worker whose dose approaches these limits without a strong justification has almost certainly violated the spirit of Part 20 and plant ALARA policy, even if the numerical ceiling has not been crossed.

Declared Pregnant Worker Limits

When a worker voluntarily and in writing declares her pregnancy to the licensee, a separate, more protective limit applies. Part 20 limits the total dose equivalent to the embryo/fetus to 0.5 rem (5 mSv) over the entire gestation period, with the additional requirement that dose be spread as evenly as practicable over the pregnancy. This limit is roughly one-tenth of the general occupational whole-body annual limit. Once a pregnancy is declared, the licensee must immediately reassign or reroute the worker as needed to ensure the fetal dose limit can be met.

Controlled Areas and Restricted Areas

Part 20 defines two key geographic categories:

Plant radiological postings (Radiation Area, High Radiation Area, Very High Radiation Area, Airborne Radioactivity Area) are required signage tied to dose-rate and contamination thresholds defined in Part 20 and plant Technical Specifications. These postings trigger specific PPE and work-control requirements.

The ALARA Principle

ALARA stands for As Low As Reasonably Achievable. Part 20 requires licensees to make every reasonable effort to maintain radiation exposures — to workers and the public — as far below the regulatory limits as is achievable, taking into account economic, technological, and social factors. ALARA is not optional guidance; it is a regulatory requirement embedded in Part 20.

In practice, plants set administrative action levels (AALs) well below the Part 20 limits. A common structure uses two investigation levels: if a worker's dose exceeds a lower threshold, supervisors investigate; if it exceeds a higher threshold, work stops pending review. Being within the Part 20 numerical limits but above an administrative action level still requires investigation and corrective action under ALARA.

Monitoring and Records

Licensees must monitor occupational dose for workers who are likely to receive a dose above specified thresholds. Personal dosimetry — typically thermoluminescent dosimeters (TLDs) or electronic personal dosimeters (EPDs) — is the primary monitoring tool. Workers must also provide prior occupational dose records when starting a new assignment so the licensee can verify the worker will not exceed annual limits from combined exposures.

Dose records must be maintained for the duration of employment plus additional years specified in Part 20, and workers must be informed of their dose upon request and at least annually.

Safety-Critical Reminders

Connecting to Credentials

For the NRC Non-Licensed Operator and Reactor Operator license pathways, Part 20 knowledge is tested directly. The NRRPT examination and the NEI NUCP Uniform Curriculum also assess radiation protection standards. OSHA 10 reinforces general hazard recognition habits. Mastery of Part 20 dose limits, ALARA requirements, and area controls is foundational to every credential in this program.

Key terms8

Total Effective Dose Equivalent (TEDE)The sum of the deep-dose equivalent (from external radiation) and the committed effective dose equivalent (from internal radiation); the primary whole-body dose quantity used in Part 20, with an annual occupational limit of 5 rem.
ALARAAs Low As Reasonably Achievable; a regulatory requirement under 10 CFR Part 20 mandating that licensees keep all radiation doses — to workers and the public — as far below regulatory limits as technology, economics, and practicality permit.
Restricted AreaUnder Part 20, any area to which access is controlled by the licensee for purposes of protecting individuals from radiation exposure or radioactive material; requires posting and access controls.
Declared Pregnant WorkerAn occupational worker who has voluntarily submitted a written declaration of pregnancy to the licensee; subject to a separate fetal dose limit of 0.5 rem (5 mSv) over the entire gestation period under Part 20.
Administrative Action Level (AAL)A dose threshold set by a licensee's ALARA program — well below the Part 20 regulatory limit — that triggers investigation, work review, or corrective action when a worker's dose reaches it.
Extremity DoseThe shallow-dose equivalent measured at the hands, forearms, feet, or ankles; subject to a separate Part 20 annual occupational limit of 50 rem, distinct from the whole-body TEDE limit.
Electronic Personal Dosimeter (EPD)An active, real-time radiation monitoring device worn by workers in radiologically controlled areas; provides immediate dose-rate and accumulated dose readout and can alarm at preset thresholds.
Uncontrolled AreaAny area outside a restricted area; dose to members of the public in uncontrolled areas is limited under Part 20 to 0.1 rem (1 mSv) per year from licensed operations.

Worked examples4

1. A radiation worker's annual dosimetry record shows a deep-dose equivalent of 3.8 rem and a committed effective dose equivalent from internal sources of 0.9 rem. Is the worker within the Part 20 annual TEDE limit?
  1. Recall the Part 20 annual TEDE limit for occupational workers: 5 rem.
  2. Calculate TEDE: TEDE = deep-dose equivalent + committed effective dose equivalent = 3.8 rem + 0.9 rem = 4.7 rem.
  3. Compare to the limit: 4.7 rem < 5 rem, so the worker is within the regulatory limit.
  4. Assess ALARA: 4.7 rem is 94% of the 5-rem limit. This is very close to the ceiling and would almost certainly exceed the plant's administrative action levels, triggering mandatory investigation and corrective action even though no Part 20 ceiling was broken.
Answer: The worker is within the Part 20 TEDE limit (4.7 rem < 5 rem), but the dose is 94% of the regulatory ceiling. An ALARA concern clearly exists; the licensee must investigate and take corrective action per its ALARA program.
2. A declared pregnant worker's cumulative fetal dose at the end of her seventh month of pregnancy is recorded as 0.42 rem. She has approximately two months of gestation remaining. Is she at risk of exceeding the Part 20 fetal dose limit?
  1. Recall the Part 20 limit for the embryo/fetus: 0.5 rem over the entire gestation period.
  2. Determine dose already received: 0.42 rem.
  3. Calculate remaining dose budget: 0.5 rem − 0.42 rem = 0.08 rem remaining for the final two months.
  4. Assess risk: With 0.08 rem left and two months remaining, even a modest exposure rate could cause her to exceed the limit. At her current average monthly rate (0.42 rem ÷ 7 months ≈ 0.06 rem/month), two more months at the same rate would add approximately 0.12 rem, exceeding the budget by about 0.04 rem.
  5. Recommended action: Notify the Radiation Protection manager immediately. Reassign or repost the worker to minimize further fetal exposure for the remainder of the pregnancy.
Answer: At the current exposure rate, the fetal dose limit of 0.5 rem will be exceeded before term. Immediate reassignment or administrative control is required; this is both an ALARA concern and a pending regulatory violation.
3. A maintenance technician performs work in a high-radiation area and receives a shallow-dose equivalent to the hands of 38 rem during the year. A separate dosimetry record shows a whole-body TEDE of 2.1 rem. Which limits apply to each measurement, and is the worker in compliance?
  1. Identify the applicable limits. For TEDE (whole body): 5 rem/year. For extremities (hands): 50 rem/year.
  2. Check whole-body TEDE: 2.1 rem < 5 rem — within the limit.
  3. Check extremity dose: 38 rem < 50 rem — within the Part 20 extremity limit.
  4. Assess ALARA for extremity dose: 38 rem is 76% of the extremity limit. Most plant ALARA programs set administrative action levels far below this. The licensee must investigate the source of high hand dose (e.g., inadequate shielding, tool selection, or technique) and implement corrective actions.
Answer: Both doses are within their respective Part 20 limits (TEDE: 2.1/5 rem; extremity: 38/50 rem). However, the hand dose at 76% of the regulatory ceiling is an ALARA concern requiring investigation and corrective action by the licensee.
4. A plant's ALARA program sets an administrative action level of 1.25 rem per quarter (5 rem annual prorated). A worker receives 1.40 rem in the first quarter alone. Part 20 annual TEDE limit is 5 rem. Is there a Part 20 violation? Is there an ALARA concern?
  1. Check annual TEDE: The worker has received 1.40 rem in one quarter. If work continues at this rate, projected annual TEDE = 1.40 rem × 4 quarters = 5.6 rem, which would exceed the 5-rem annual limit.
  2. Check for current Part 20 violation: At this moment, 1.40 rem for the year-to-date is below 5 rem — no current regulatory violation.
  3. Check against the administrative action level: 1.40 rem > 1.25 rem quarterly AAL — the AAL has been exceeded, triggering mandatory ALARA investigation.
  4. Project forward: If the quarterly rate is not reduced, the annual limit will likely be exceeded, creating a future Part 20 violation. The licensee must act now — investigate root cause, modify work practices, rotate the worker, or add shielding — to prevent exceeding 5 rem by year-end.
Answer: No Part 20 violation exists yet (1.40 rem year-to-date is below 5 rem), but the quarterly administrative action level has been exceeded, and the projected annual dose of approximately 5.6 rem would violate Part 20. ALARA corrective action is required immediately.

The math in this lesson1

Learners sum deep and committed dose into TEDE and compute percent of the 5-rem limit.
7.RP.3
Brush up in the math halls at newSchoolWorks.com:
In class: Work through a set of 10 scenario cards showing hypothetical annual dose records; determine for each whether the worker is within Part 20 occupational limits, note any ALARA concern, and recommend corrective action where warranted. · Compare the Part 20 dose-limit structure (whole-body, extremity, lens of eye, declared pregnant worker) using a structured comparison table; then apply limits to two sample plant dosimetry records. · Classroom debate: given a scenario where a worker's dose is within limits but not ALARA, one group argues a procedural violation has occurred and the other argues it has not; both groups cite Part 20 sections to support their position.
Materials: 10 CFR Part 20 (current edition), scenario dose-record cards, comparison-table worksheet, sample dosimetry printouts (simulated)
Check: Written exam of 20 questions requiring limit calculations and compliance determinations; pass mark 80%.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NRC Radiation Protection Standards
1. Under 10 CFR Part 20, what is the annual occupational dose limit for the Total Effective Dose Equivalent (TEDE) to an adult radiation worker?
NRC Radiation Protection Standards
2. A declared pregnant worker has accumulated 0.48 rem of fetal dose equivalent with six weeks remaining in her pregnancy. Which action best reflects compliance with 10 CFR Part 20?
NRC Radiation Protection Standards
3. A technician's annual dosimetry record shows a hand (extremity) dose of 42 rem and a whole-body TEDE of 3.2 rem. Which statement correctly evaluates compliance with 10 CFR Part 20?
NRC Radiation Protection Standards
4. ALARA is best described as which of the following under 10 CFR Part 20?
NRC Radiation Protection Standards
5. Under 10 CFR Part 20, what is the annual dose limit for members of the public from licensed operations in an unrestricted (uncontrolled) area?
NRC Radiation Protection Standards
6. A worker's first-quarter dose is 1.6 rem. The plant's ALARA administrative action level is 1.25 rem per quarter. The annual Part 20 TEDE limit is 5 rem. Which of the following is the most accurate regulatory assessment?
NRC Radiation Protection Standards
7. Which Part 20 dose limit applies specifically to the lens of the eye for occupational workers?
NRC Radiation Protection Standards
8. A supervisor argues that because a worker's annual dose is within Part 20 regulatory limits, no further action is needed, even though the dose is above the plant's ALARA administrative action level. Which response best reflects the correct regulatory position?
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