Information Notice No. 88-63: High Radiation Hazards from Irradiated Incore Detectors and Cables
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
August 15, 1988
Information Notice No. 88-63: HIGH RADIATION HAZARDS FROM IRRADIATED
INCORE DETECTORS AND CABLES
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors, research reactors and test reactors.
Purpose:
This information notice is being provided to alert addressees to the recent
high exposure event at Surry Unit 2 resulting from the failure to adequately
evaluate the radiation hazards present during work involving irradiated incore
neutron detectors. Similar events have occurred at other facilities and are
summarized in Attachment 3. It is expected that recipients will review the
information for applicability to their facilities and consider actions, as
appropriate, to avoid similar problems. However, suggestions contained in
this information notice do not constitute NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances:
On March 3, 1988, with Unit 2 at 100-percent power and the containment at
subatmospheric pressure, two instrument and control (I&C) technicians and one
health physics (HP) technician entered the Surry Unit 2 containment to free a
stuck incore detector and drive cable, transfer it to a storage location, and
replace the detector and associated drive cable with new equipment (see
Figure 1). According to the licensee's event investigation report, the "A"
detector cable became mechanically bound in the "B" 10-path transfer device
(the incore detector system was being operated in the "Emergency" mode at the
time because the "B" incore detector was inoperable). This resulted in the
"A" detector and cable being lodged in the core. The binding was a result of
the 10-path transfer device becoming misaligned when the 10-path transfer
device attempted to rotate to the next core thimble position while the cable
was still inserted in the previous core thimble location. The bound cable
could not be electrically retracted from the core.
During efforts to dislodge the detector, about 100 feet of the cable attached
to the detector were manually pulled into the Seal Table Room, through the
polar crane wall, and taken up on the "A"-drive-unit reel assembly in the
outer annulus area. As the incore detector was pulled up to the penetration
through
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. IN 88-63
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the crane wall (see Figure 2), the HP technician noted rapidly increasing
radiation levels near the transfer tube which soon exceeded the maximum
onscale reading of his survey meter (1000 R/hr). He then ordered the work
stopped and the work platform evacuated. Dose estimates performed by the
licensee show that whole body doses for the three workers ranged from
approximately 700-1000 mrem. The worker who held and pulled the cable
received a dose of 800 mrem to his hand. The beta dose contribution to the
workers was small because the stainless steel tube casing through which the
activated drive cable was inserted effectively attenuated the beta radiation.
Subsequent licensee and NRC regional review of the event revealed several key
factors that contributed to the incident.
1. Failure To Adequately Evaluate the Radiation Hazards Present During Work
on an Incore Detector
Licensee personnel had freed stuck detectors several times in the past.
Radiation levels associated with the detector typically ranged between 5
and 35 R/hr; the drive cable had never exhibited significant induced
activity. The principal radionuclide of concern in the drive cables used
at Surry is manganese-56, which has a half-life of 2.56 hours and which
accounts for 99 percent of the dose rate once it has reached equilibrium
in the core. (NOTE: the principal radionuclide of concern may vary
depending on drive cable composition and core irradiation/decay time.)
The reason for the typically low activity levels of the drive cable in
the past at Surry is that either the cable had resided in the core for
only a short time or that it was allowed to decay to background levels
between the time it was removed from the core and the time it was
withdrawn into the Seal Table Room. However, in this event, the drive
cable (which had been in the core at 100-percent power for 26 days) had
decayed for only 15 minutes before being withdrawn through the Seal Table
Room into the outer annulus area and, therefore, was highly radioactive.
The licensee failed to evaluate the radiation hazards from the drive
cable and several feet of activated cable were manually pulled into the
outer annulus area before the HP technician halted work and ordered all
personnel out of the area. Survey meter readings of more than 1000 R/hr
were measured 12 inches from the cable.
2. Use of Inadequate Procedures With Insufficient Radiological Controls
Because no special procedure was available for freeing the stuck incore
detector, the licensee wrote a temporary change to the normal procedure
for replacing the detector to cover this operation. This procedure
change did not offer any precautions about assessing the detector's
location and stay time (irradiation time) in the core or the resultant
detector or cable radiation levels. It also did not contain any
stop-work limitations based on measured radiation levels or steps to
permit withdrawal of the detector through the Seal Table Room and up to
the polar crane wall.
. IN 88-63
August 15, 1988
Page 3 of 4
Finally, this procedure did not have any requirements for using extremity
dosimeters while manually retracting the drive cable. If this procedure
had been formally reviewed (as is required by the licensee's Technical
Specifications when the purpose of the procedure is changed), the radio-
logical controls described above might have been included.
3. Lack of Communication Among Individuals and Work Groups
Performance of this job under a Standing Radiation Work Permit (RWP)
instead of under a Special RWP allowed the job to be carried out without
prior review by Health Physics personnel or establishment of special
radiological controls. The HP technician covering the job did not
receive an adequate pre-job briefing and was not provided with
sound-powered headphones to communicate with the control room during the
job, as were the other two technicians performing the work. Therefore,
he was not aware of the detector's location as it was being withdrawn.
In addition, all three individuals performing the work were wearing
respirators (because of reduced oxygen in the subatmospheric
containment), further hindering communications among the members of the
work party.
As a result of this event, the licensee has initiated certain corrective
actions which include the following:
(a) Revision of the procedure to replace incore detectors to include steps to
free stuck detectors. Performance of this procedure will require the
approval of the HP Shift Supervisor, the use of a Special RWP,
limitations on manual withdrawal of the detector drive cable, and an
evaluation of radiological hazards and detector location.
(b) Revision of appropriate training programs and procedures to incorporate
the lessons learned from this event.
(c) Informing appropriate station personnel of the key points and lessons
learned from this event.
Discussion:
Irradiated components, such as incore flux detectors and attached drive
cables, can create radiation fields in which permissible occupational dose
standards can be exceeded in less than a few seconds and acute exposures,
sufficient to cause serious radiation injury, are possible with just several
minutes of exposure. The event at Surry and a similar incident involving the
manual freeing of a stuck incore detector at Indian Point 3 in 1980 were both
the result of the licensee's failure to evaluate the radiation hazard from the
neutron activation of the incore flux detector drive cable. In both cases,
the irradiated drive cable itself, which had not been allowed to decay
sufficiently after being removed from the core, was the contributing factor to
the high exposures at Surry and the overexposures at Indian Point.
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The Surry event is just one in a series of overexposures or near overexposures
in which a lack of management oversight led to inadequate radiological assess-
ment and a resultant lack of proper control over work activities involving
irradiated components. Several NRC and Institute of Nuclear Power Operations
(INPO) generic communications have been issued over the last several years
informing licensees of the dangers involved with entry into high radiation
areas (see Attachment 4). On June 13, 1988, the NRC issued a Notice of Viola-
tion and Proposed Imposition of Civil Penalty in the amount of $100,000 for
the Surry event to emphasize the importance of using proper radiological
procedures in high radiation areas.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni-
cal contacts listed below or the Regional Administrator of the appropriate
regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Charles S. Hinson, NRR
(301) 492-3148
Craig Bassett, RII
(404) 242-5570
Attachments:
1. Figure 1, Typical Westinghouse Incore Neutron Monitoring System
2. Figure 2, Relative Positions of Individuals During Incident
3. Related Event Summaries
4. Past Related Correspondence
5. List of Recently Issued NRC Information Notices
. Attachment 3
IN 88-63
August 15, 1988
Page 1 of 2
Related Event Summaries
Overexposure of Workers Retrieving Stuck Incore Neutron Detector
(Indian Point 3, PWR)
Inspection
Report No.: 50-286/80-09
Event Date: 6/24/80
Event Cause: Lack of Maintenance Procedure
Abstract: When a problem developed with retrieval of a neutron flux
detector, two instrument and control (I&C) personnel and a
health physics (HP) technician entered the containment to
inspect and repair the moveable detector system. When it was
discovered that the drive cable was severed, the workers
decided to retract the cable by hand (without benefit of
approved procedural guidance). After withdrawing, cutting, and
bagging approximately 90 percent of the cable, the remaining
8-10 feet of cable were extracted. The detector was cut off
and put in a shielded container; the remaining cable was bagged
and set between one of the I&C workers and the HP technician.
When the HP technician noticed that the dose rate above the
bagged end cable section was nearly 200 R/hr, he evacuated the
area. This incident resulted in quarterly exposures to the two
I&C workers of 4.2 and 4.1 rem whole body, 7.1 and 8.2 rem
skin, and 43.7 and 17.1 rem extremity, respectively. One of
the corrective actions taken by the licensee to prevent a
recurrence of this event was the preparation of a procedure for
removing and replacing incore detectors.
Traversing Incore Probe (TIP) Room Entry (Vermont Yankee, BWR)
Inspection
Report No.: 50-271/85-21
INPO SER 50-85
Event Date: 8/8/85
Event Cause: Inexperienced HP Technician
Abstract: After a TIP probe had remained in the core at 90 percent power
for more than 2 hours (because of a TIP drive power loss from a
shorted TIP ball valve solenoid), the probe was manually
cranked into its storage area inside the TIP room. Since a
radiation work permit (RWP) was required in order to enter the
room to
. Attachment 3
IN 88-63
August 15, 1988
Page 2 of 2
repair the ball valve solenoid, a backshift HP technician
prepared to survey the area to gather information to fill out
the RWP. After notifying the shift supervisor, the HP techni-
cian and an auxiliary operator entered the room. Using a
hand-held ionization chamber, the HP technician measured dose
rates near the door of 200 R/hr. The HP technician then pro-
ceeded further into the room and measured dose rates of
1000 R/hr near the core probes using a teletector. After the
HP technician noticed that his 0-500 mR dosimeter was offscale,
the two individuals left the room. The HP technician received
1.3 rem; the auxiliary operator received 270 mrem. The
radiation hazards of an activated TIP and cable were
inadequately evaluat-ed because the HP technician had little
experience on what precautionary actions to take upon
encountering the high exposure rates that existed in the TIP
room. Among the corrective actions taken by the licensee to
prevent recurrence of this event were issuance of procedures
for TIP room entrance (including an RWP requirement for all
entries), HP training on the lessons learned from this
incident, and installation of a TIP room remote area radiation
monitor.
. Attachment 4
IN 88-63
August 15, 1988
Page 1 of 1
Past Related Correspondence:
INPO Significant Event Report (SER) 6-88, "Uncontrolled Radiation Exposure,"
March 9, 1988.
Information Notice No. 86-44, "Failure To Follow Procedures When Working in
High Radiation Areas," June 10, 1986.
INPO Significant Event Report (SER) 50-85, "Uncontrolled Personnel Radiation
Exposure," November 4, 1985 (discusses two events).
INPO Significant Operating Experience Report (SOER) 85-3, "Excessive Personnel
Radiation Exposures," April 30, 1985.
. Attachment 5
IN 88-63
August 15, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-62 Recent Findings Concerning 8/12/88 All holders of NRC
Implementation of Quality quality assurance
Assurance Programs by program approval
Suppliers of Transport for radioactive
Packages material packages.
88-61 Control Room Habitability - 8/11/88 All holders of OLs
Recent Reviews of Operating or CPs for nuclear
Experience power reactors.
88-60 Inadequate Design and 8/11/88 All holders of OLs
Installation of Watertight or CPs for nuclear
Penetration Seals power reactors.
88-04, Inadequate Qualification 8/9/88 All holders of OLs
Supplement 1 and Documentation of Fire or CPs for nuclear
Barrier Penetration Seals power reactors.
88-59 Main Steam Isolation Valve 8/9/88 All holders of OLs
Guide Rail Failure at or CPs for nuclear
Waterford Unit 3 power reactors.
88-58 Potential Problems with 8/8/88 All holders of OLs
ASEA Brown Boveri ITE-51L or CPs for nuclear
Time-Overcurrent Relays power reactors.
88-57 Potential Loss of Safe 8/8/88 All holders of OLs
Shutdown Equipment Due to or CPs for nuclear
Premature Silicon Controlled power reactors.
Rectifier Failure
88-56 Potential Problems with 8/4/88 All holders of OLs
Silicone Foam Fire Barrier or CPs for nuclear
Penetration Seals power reactors.
88-55 Potential Problems Caused 8/3/88 All holders of OLs
by Single Failure of an or CPs for nuclear
Engineered Safety Feature power reactors.
Swing Bus
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
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