**NRC INSPECTION MANUAL** IOLB

INSPECTION PROCEDURE 83501

SIGNIFICANT UNCONTROLLED RADIATION EXPOSURES

PROGRAM APPLICABILITY: 2515

83501‑01 INSPECTION OBJECTIVE

To evaluate the licensee=s response to events that involved significant
uncontrolled radiation exposures of plant staff, contractors, or
visitors that resulted in or could have resulted in the dose limits in
10 CFR Part 20 being exceeded.

83501‑02 INSPECTION REQUIREMENTS

02.01 [Risk Assessment]{.underline}. The inspector should perform the
following, if a significant uncontrolled exposure event occurred or
could have occurred.

a.  Evaluate whether the licensee=s initial dose or risk estimate is
    consistent with the known sequence of events.

b.  Evaluate whether the licensee=s immediate response to the event is
    commensurate with the initial risk estimate. Consider whether the
    following actions are needed, and were taken by the licensee as
    appropriate;

    1.  Additional controls on source(s) of exposure/intake.

    2.  Medical screening or treatment of involved individual(s).

    3.  Stop work to limit additional risk to other individuals.

    4.  In-vivo or in-vitro bioassay for those events that involve or
        may involve significant intakes of radioactive material.

    5.  Evaluation to determine if other individuals may have been
        exposed to radiation source(s).

02.02 [Event Reconstruction]{.underline}. Evaluate whether the
licensee=s understanding of the event is supported by the facts.
Evaluate whether assumptions made concerning the sequence of events
(i.e., exposure, proximity to the source, time interval, etc.) are
reasonably conservative and are supported by the logical extension of
verifiable facts.

02.03 [Significance Determination]{.underline}. In light of the findings
from the above, determine if the significance of the event(s) has been
appropriately characterized.

02.04 [Root Causes and Corrective Actions]{.underline}. Evaluate whether
the licensee has adequately determined the causes of the uncontrolled
exposure(s) and has instituted corrective actions sufficient to prevent
reoccurrence.

83501‑03 INSPECTION GUIDANCE

[General Guidance]{.underline}

This inspection procedure applies to situations where the licensee has
experienced one or more events involving the uncontrolled exposure(s) of
individual(s) at the site that resulted in, or had a substantial
potential for, personnel exposures in excess of regulatory limits. This
procedure does not address unintended exposures that only have a
significant impact on collective dose and not individual dose . As
discussed below, necessary licensee actions can be time sensitive.
Nothing in this procedure should be interpreted as limiting or
interfering with the licensee=s ability to take those actions the
licensee deems necessary to preclude additional exposures from, mitigate
the health impact of, or properly characterize the consequences of, the
exposure event.

[Specific Guidance]{.underline}

03.01 [Risk Assessment]{.underline}

In cases of serious radiation exposures, immediate licensee actions
necessary to minimize the health impact may be warranted or prudent.
These actions may include medical examination and intervention for
individuals that have received doses from external sources several times
the dose limits. In addition to the early medical considerations, the
need to initiate prompt in-vivo or in-vitro bioassay (for significant
intakes) should be evaluated. These are judgement calls by the licensee
usually made early in the event, and may be based on incomplete
information. Inspector review of these actions may start prior to
arriving at the site, (e.g., telephone discussions with the licensee).

Verify that the licensee=s methods of quantifying the dose, such as time
and motion studies, classification of radionuclide transportability, and
intake dose factors, are complete and appropriate for the exposure
situation. For example, verify; whether the licensee has contacted and
interviewed all individuals who may have been exposed during the event
or during previously undetected instances, whether all potential intakes
of radioactive materials or dose pathways have been considered, and
whether the licensee has fully evaluated the source term (e.g.,
unidentified pure beta or alpha emitters) for purposes of dose
calculation. If the licensee is focused on whole body effective dose
(TEDE), verify whether a different dose limit (i.e., fetal dose or
extremity dose) is more limiting.

The risk assessment should review all appropriate or reasonable outcomes
as well as the actual consequences (dose) of the event. For example,
uncontrolled exposure events in Very High Radiation Areas could result
in life threatening exposures.

03.02 [Event Reconstruction]{.underline}

Uncontrolled exposure events are typically identified after the event by
alarming electronic dosimeters, results of TLD dosimeter processing,
access point monitor alarms, or other actions, and require
reconstruction of the event to model the exposure condition and doses
received. In addition, the initial risk or dose assessment made by the
licensee is followed by a more thorough review of the event.

The licensee=s investigation of the event(s) may be ongoing during this
inspection. Additional information, as it becomes available, should be
evaluated in terms of impact on the initial risk assessment.
Notwithstanding, the inspector should conduct sufficient independent
review to evaluate the reasonableness of the exposure circumstances and
dose evaluation. The review may include interviews of exposed
individuals.

Assumptions concerning the course of the event and the related risk
assessment should be directly supported by verifiable facts. In some
cases, a time and motion re-enactment of the event can verify or
quantify the sequence of events.

For exposure events involving uncontrolled intakes at plants with poor
fuel performance, determine whether the licensee has considered the
potential for intakes of transuranic and other hard-to-measure
radionuclides. The inspector should evaluate the adequacy of the
licensee characterization of the intake source term by reviewing results
of independent analyses made by the licensee including 10 CFR Part 61
analyses of waste streams. In addition, intake assessments may be
complicated by specific characteristics of the in-vivo counters. For
example, the following questions should be considered: Does the
licensee=s whole body counter treat the intake as total body or organ
specific? For the in-vitro analyses, are samples being analyzed for the
appropriate excretion pathway? Are analyses of lower limits of detection
(LLDs) appropriate? Specifically, are the LLDs sufficiently low enough
to detect the specific radionuclide of importance and thus be useful in
providing a meaningful indication of excretion rate for purposes of
intake determination?

For external exposure events, the inspector should evaluate the
characterization of the source term and the adequacy of the
instrumentation/dosimetry used to evaluate or measure the dose. Note
that underwater exposure events may involve significant dose
determination problems including potential changes of energy of
radiation.

03.03 [Significance Determination]{.underline}

An event presents a substantial potential for overexposure when it was
fortuitous that the resulting exposure did not exceed the limits of 10
CFR Part 20. The concern is not the significance of the actual resulting
(or potential) exposure, but whether the licensee exercised adequate
control over the situation, as required, to prevent exceeding the 10 CFR
Part 20 limits.

When evaluating whether an exposure event could have a substantial
potential for overexposure, the inspector should attempt to construct a
reasonable scenario in which a minor alteration of circumstances would
have resulted in a violation of 10 CFR Part 20 limits. Circumstances
such as (a) timing, (b) source strength, (c) distance, and (d) shielding
should be considered.

a.  Timing: Could the exposure period have reasonably been longer?

> Example: An individual in the proximity of an unknown source of
> radiation receives an unplanned excessive exposure. Because of the
> duration of the exposure, no limits were exceeded; however, the
> individual could reasonably have stayed in proximity to the source
> long enough to be overexposed.

b.  Source Strength: Could the radiation source have reasonably been
    stronger?

> Example: An inadvertent release results from a worker venting the
> wrong waste gas decay tank. Although the release did not exceed Part
> 20 limits, the same mistake could have as easily resulted in venting a
> decay tank with enough activity to exceed the limits.

c.  Distance: Could the person have reasonably been closer to the
    source?

> Example: In the example in paragraph (a) above, the individual could
> have been overexposed by standing closer to the source of radiation.

d.  Shielding: Could some unintended shielding have reasonably been
    removed?

> Example: A radioactive source was accidently left in an office area.
> Shielding afforded by a desk prevented the overexposure of an
> individual worker in the office. However, nothing prevented the source
> from being left in an area of the office that would not have been
> shielded by the desk, such that the individual would likely have been
> overexposed.

03.04 [Root Causes and Corrective Actions]{.underline}

Verify that the licensee directed sufficient management attention to the
event to evaluate its significance. Verify that the licensee has
provided reasonable assurance that the root causes have been identified
and that corrective actions have been taken to prevent reoccurrence of
the event. Note, in some cases, the licensee may curtail certain
activities until full corrective action can be implemented. The licensee
may establish and implement immediate, interim, and long-term corrective
actions.

Experience has shown that uncontrolled exposures have resulted from one
or more of the following:

a.  Poor hazards evaluation, including failure to survey or
    inappropriate surveys.

b.  Inadequate instructions to the workers, including incomplete
    requirements or briefings.

c.  Poor response to changing conditions by the Health Physics coverage.

d.  Failure to follow procedures.

e.  Lack of Supervisory involvement.

f.  Lack of Management support.

g.  Lack of effective communication between departments (e.g., radiation
    protection and operations).

These areas may be interrelated: any one of them may be a symptom of a
deeper underlying cause. For example, the chronic failure to follow
procedures or inadequate corrective actions for similar previous
problems may be symptoms of lack of management support for the Radiation
Protection Program and/or insufficient involvement in work activities by
the first line supervisors.

83501-04 RESOURCE ESTIMATES

It is estimated that approximately 25-35 hours will be needed to
complete the requirements of this procedure.

83501-05 REFERENCES

NUREG/CR 4884, AInterpretation of Bioassay Measurements@

Regulatory Guide 8.9, AAcceptable Concepts, Models, Equations, and
Assumptions for a Bioassay Program@

Regulatory Guide 8.26, AApplication of Bioassay for Fission and
Activation Products@

Regulatory Guide 8.34, AMonitoring Criteria and Methods to Calculate
Occupational Radiation Doses@

Regulatory Guide 8.38, AControl of Access to High and Very High
Radiation Areas of Nuclear Plants@

NUREG/BR-0195, ANRC Enforcement Manual@ (definition of substantial
potential for overexposures)

END