United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-63, Supplement 2: High Radiation Hazards from Irradiated Incore Detectors and Cables

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                                June 25, 1991

                                                 IRRADIATED INCORE DETECTORS
                                                 AND CABLES  


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


The U.S. Nuclear Regulatory Commission (NRC) issued Information Notice 
(IN) 88-63 on August 15, 1988, and IN 88-63, Supplement 1, on October 5, 1990,
to alert addressees to uncontrolled radiation exposures experienced at the 
Surry Power Station, Unit 2, the Duane Arnold Energy Center, and the Brunswick
Steam Electric Plant, Unit 1.  These exposures resulted from irradiated incore
detectors and drive cables that were not adequately evaluated.  This supplement
alerts addressees to a similar recent event in which a substantial potential
for an overexposure occurred.  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 February 11, 1991, at the Edwin I. Hatch Nuclear Plant, Unit 1, a contract
vendor operated the controls of the traversing incore probe (TIP) system
without the knowledge of control room personnel and in violation of plant

While troubleshooting a problem with the process computer (PC), the reactor 
engineer (RE), the shift technical advisor (STA), and a contract vendor were 
performing TIP traces to reproduce previously observed computer problems.  When
these attempts failed to evoke the prescribed PC response, they temporarily
halted work.  They agreed that they would continue troubleshooting after lunch
and verified that the TIPs were in their indexers before leaving.

Shortly thereafter, in preparing to perform a radiation contamination survey,
the health physics (HP) supervisor called the control room to obtain permission
for an HP technician to enter the Unit 1 TIP room.  The HP supervisor asked if 

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                                                  June 25, 1991  
                                                  Page 2 of 4

the TIPs were being moved.  The Unit 1 reactor operator informed the HP super-
visor that the STA had gone to lunch and that no one would be operating the

In preparing to enter the Unit 1 TIP room, the HP technician observed a reading
of 1 R/hr at the exterior of the wire mesh door leading into the TIP room
(Attachment 1).  The HP technician telephoned the HP supervisor to inquire
about the reason for the high radiation levels.  The HP supervisor then called
the Unit 1 control room operator. 

While the HP supervisor was on the telephone with the reactor operator, the STA
arrived at the Unit 1 control room.  The operator asked the STA if anyone was
operating the TIPs.  The STA replied that, to his knowledge, no one was operat-
ing the TIPs.  The STA then asked the same question of the RE, who said that he
was not operating the TIPs, but was unaware of the contract vendor's actions. 
The STA immediately proceeded to the TIP operating panels in back of the main
control boards.  When the STA arrived, he found that the contract vendor had
withdrawn one TIP into the shield from the indexer and was operating another 
in an attempt to resolve the PC problem.  The STA told the contract vendor to
"hold on" and verified that HP personnel were out of the TIP room area.  The
STA then returned the TIPs to the indexer in the drywell.  The contract vendor
failed to realize that he was violating station procedures and could have
overexposed personnel.  As part of the licensee's evaluation of this event, the
Health Physics Department processed the HP technician's thermoluminescent
dosimeter and recorded a reading of 5 mrem. 

The licensee and NRC regional personnel subsequently reviewed the event and 
identified several key factors that contributed to the incident. 

1.   Unauthorized operation of the TIP system by the contract vendor. 

     An unauthorized person operated the TIP system without the knowledge of    
     the control room operators.  Because the PC troubleshooting activities had 
    taken several days, the contract vendor had become less sensitive to the    
    requirements for operating the equipment.  Therefore, on the day of the
     incident, he operated the equipment without authorization and without the
     knowledge of control room personnel. 

2.   Poor adherence to procedural communication requirements between the      
     operators of the TIP system and the Health Physics Department. 

     The procedure used to troubleshoot the problem with the PC is the same     
     procedure used to perform the monthly surveillance required by Technical
     Specifications.  The procedure warns that extremely high radiation levels
     will exist in the TIP room when the TIP probes and cables emerge from the
     shields or during the traverse.  The procedure requires that the HP
     Department be notified when this procedure is performed.  The NRC reviewed
     both the STA and the HP desk logs for the 2 months before the event and
     found that, of the 14 times the STA log documented TIP operation, the HP
     Department was notified of only 4 of these operations.  The HP log also
     listed 6 additional TIP operations that were not reflected in the STA log.

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3.   Lack of procedural control of the TIP system and of understanding who      
     is authorized to operate the TIP system. 

     Because the control panel for the TIP system is located behind the main    
     control boards, the TIP system can be operated without the knowledge of    
     control room personnel.  The control room operators believed that the      
     procedure required the STA to be physically present for the TIPs to be     
     operated.  In fact, the procedure also allows the RE to move the TIPs.     
     Shift personnel authorized HP technicians to enter the TIP room because    
     the STA had gone to lunch and they believed the STA had to be present      
     before the TIP system could be operated. 

To avoid repeating this event, the licensee initiated the following corrective

1.   Procedural controls have been added to the HP and Chemistry Department     
     procedure, "High Radiation Area Access Control," requiring that a danger
     tag be affixed to the TIP control panel when personnel are to enter the
     TIP room.  The HP technician obtains a sub-clearance on the tagout which
     prevents the tagout being released before personnel exit the TIP room.  

2.   A positive control "key exchange program" was instituted by which the HP
     technician obtains the TIP control panel key from the main control room
     with the shift supervisor's permission and exchanges the TIP control panel
     key for the TIP room door key controlled by the health physics supervisor. 
     Similarly, the RE or STA must obtain the TIP room door key prior to
     operating the TIP controls.

3.   The Engineering Support Department will transfer the TIP operating proce-
dure to the Operations Department.  This transfer should give the Opera-
tions Department more direct control over TIP movement. 

4.   The Operations Department will affix a warning placard to the TIP control
     panel requiring that the HP Department be notified before the TIP system
     is operated.

5.   HP technicians will wear digital alarming dosimeters "chirpers" for entry
     into the TIP room and other very high radiation areas (greater than 1 R/hr
     at 18 inches). 

The licensee is investigating the feasibility of erecting a shield at the front
of the TIP room door to reduce exterior dose rates when the TIPs are activated. 
The licensee is considering placing a radiation monitoring device in the TIP
room and other areas where very high radiation levels  could exist which, at a
predetermined dose rate, would activate an audible  alarm and/or a flashing
warning light.


The unauthorized movement of the TIPs by the contract vendor is a significant
safety concern because it could have caused personnel to receive substantial 
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exposures in excess of the limits prescribed in Part 20 of Title 10
Code of Federal Regulations (10 CFR Part 20).  Further, this action indicates
that the licensee failed to control the manipulation of plant  equipment from
the control room.  The root causes of this event were an inadequate procedure
that did not provide clear controls of TIP-related activities and inadequate
communication between the involved personnel.  It is also evident that the
contract vendor had not received adequate training and instruction on the
procedural controls and restrictions that apply to the manipulation of the

If the HP technician had arrived at the TIP room earlier, he may have entered
the room and completed his initial radiation survey before the unauthorized TIP
movement began.  He would then have proceeded with his contamination survey
inside the TIP room and, not being equipped with an alarming dosimeter, could
have been unaware of the subsequent TIP operations and the higher dose rates. 

HP technicians may realize the radiation hazard that exists in the TIP room 
while the TIPs are operated, but, in this high noise area, they may not hear 
or associate the noise of the TIP drive mechanism with TIP operation.  Site  
HP technicians stated that a typical TIP room survey of this type would take 
between 10 and 15 minutes.  With all of the TIPs present and activated, general
area whole body radiation levels in the TIP room could range up to several
hundred R/hr.  Based on these radiation levels, a dose in excess of 10 CFR Part
20 whole body limits could have been received within a few minutes. 

On April 15, 1991, the NRC issued a Notice of Violation and Proposed Civil 
Penalty in the amount of $50,000 for the Hatch event.  The NRC issued this 
violation to emphasize the importance of developing and implementing adequate
procedures and of communicating precisely in order to ensure positive control
over the operation of plant systems, specifically the TIP system.  

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact one
of the technical contacts listed below or the appropriate NRR project manager. 

                                   Charles E. Rossi, Director 
                                   Division of Operational Events Assessment 
                                   Office of Nuclear Reactor Regulation 

Technical Contacts:  Daniel R. Carter, NRR 
                     (301) 492-1848

                     Roger B. Shortridge, RII
                     (404) 841-4717

1.  Figure 1, Typical Tip Room Layout  
2.  List of Recently Issued NRC Information Notices 

Page Last Reviewed/Updated Friday, May 22, 2015