Bulletin 78-08: Radiation Levels from Fuel Element Transfer Tubes
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
June 12, 1978
IE Bulletin 78-08
RADIATION LEVELS FROM FUEL ELEMENT TRANSFER TUBES
Description of Circumstances:
On April 5, 1978, two radiation protection technicians at Portland General
Electric Company's Trojan Nuclear Power Plant received whole body radiation
doses of 27.3 and 17.1 rem while performing a survey adjacent to an exposed
section of the fuel element transfer tube during the plant's first refueling
outage. The exposures occurred in a shielded space inside the containment
building which housed one of two fuel element transfer tube seismic relief
bellows. The second bellows outside of containment had been provided with
removable shielding and appropriate access controls. The bellows space
inside containment was constructed with labyrinth-type shielding, however,
access to the space was not controlled. The technicians were performing
surveys in an attempt to identify a reported possible source of higher than
expected radiation and had scheduled the survey to coincide with the passage
of a fuel element through tile fuel element transfer tube. The technicians
believed that the fuel element transfer tube was buried in the concrete
beyond the compartment they occupied and assumed that the structure passing
through the compartment was a ventilation duct.
The licensee staff had performed surveys of all areas of the plant during
the outage in an attempt to identify intermittent sources of radiation
resulting from refueling activities; however, nothing significant was
identified because of the transient nature of the resulting radiation
fields. Subsequent to the exposures, the licensee performed surveys in
numerous areas surrounding the general area of the fuel transfer tube with
an irradiated fuel element stopped in the transfer tube. The surveys
identified a number of areas previously unidentified where significant
radiation streaming was present. The principal paths of radiation streaming
were the narrow seismic relief spaces between the containment and internal
and external structures.
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IE Bulletin 78-08 June 12, 1978
Action To Be Taken By Licensees:
While the exposures above occurred at a pressurized water reactor, similar
situations could occur at any reactor facility designed to transfer spent
fuel between the reactor refueling canal and a spent fuel storage pool
outside of containment by means of a fuel element transfer tube.
Accordingly, holders of power, test and research reactor operating licenses
where plant design incorporates a fuel element transfer tube, are to take
the following actions:
1. Perform a thorough review of shielding design of plant areas adjacent
to the fuel transfer tube to identify potential high radiation areas,
both continuous and transient, as defined in 10 CFR 20.202(b).
2. Assure that positive control of access exists or is included in the
facility design for entryways into potential high radiation areas where
a portion of a fuel transfer tube is accessible in an unshielded
condition.
3. Assure that points of access to potential high radiation areas
associated with accessible unshielded portions of a fuel transfer tube
are conspicuously posted in accordance with 10 CFR 20.203(c).
4. If the Action from Paragraph 1 above identifies the potential for
radiation streaming from shielded spaces, plan and conduct special
radiation surveys during the next refueling to identify and control
such areas. It is not necessary to survey in areas where the transfer
tube is exposed, but if it is found desirable, extreme care should be
exercised to control and limit personnel exposure. Care should also be
taken in planning surveys and fuel movements such that survey
requirements do not override any technical limitations on fuel
movement.
5. Confirm by written reply to the NRC Regional Office within 60 days that
the actions for Items 1-4 above have been or are being taken. A record,
detailing findings, actions taken, and actions to be taken, should be
retained for review by NRC during subsequent radiological safety
inspection.
Approved by GAO, B180225 (R0072); clearance expires 7-31-80. Approval was
given under a blanket clearance specifically for identified generic
problems.
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