United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-63: High Radiation Hazards from Irradiated Incore Detectors and Cables

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                 August 15, 1988

                                   INCORE DETECTORS AND CABLES


All holders of operating licenses or construction permits for nuclear power 
reactors, research reactors and test reactors.  


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 

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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.
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     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.


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

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
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                             Related Event Summaries

Overexposure of Workers Retrieving Stuck Incore Neutron Detector
(Indian Point 3, PWR)

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)

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
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               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 

.                                                            Attachment 4
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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 
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                                                            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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