United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-107: Entry Into PWR Cavity with Retractable Incore Detector Thimbles Withdrawn

                                                       SSINS No.:  6835    
                                                       IN 86-107 

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                              December 29, 1986

Information Notice No. 86-107:  ENTRY INTO PWR CAVITY WITH RETRACTABLE 
                                   INCORE DETECTOR THIMBLES WITHDRAWN 

2Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit. 

Purpose and Summary: 

This notice is provided to alert licensees of a recurring event where 
workers were allowed to enter the reactor vessel (RV) sump room at a PWR 
[cavity beneath the RV] while the retractable incore detector (RID) thimbles 
are withdrawn. With the RID thimbles retracted, radiation levels of 
thousands of roentgens per hour (R/hr) can exist in the reactor cavity area. 
Although established. administrative, procedural, and physical controls 
failed to prevent this latest entry, no excessive personnel exposure 
occurred because the accompanying health physics (HP) technician acted in a 
timely, proper manner. Licensee corrective actions to prevent a reoccurrence 
are discussed below. 

Since 1972, 11 unauthorized entries into PWR cavities with the RID thimbles 
withdrawn have occurred, leading to 6 personnel overexposures. It is 
suggested that recipients review this notice for applicability to 
high-radiation area work-controls programs at their facilities and consider 
actions, if appropriate, to preclude the occurrence of a similar problem at 
their facilities. Suggestions contained in this information notice do not 
constitute NRC requirements; therefore, no specific action or written 
response is required at this time. 

Past Related Correspondence: 

INPO Significant Operating Experience Report (SOER) 85-3, "Excessive 
Personnel Radiation Exposures," April 30, 1985. 

Information Notice No. 84-19, "Two Events Involving Unauthorized Entries 
Into PWR Reactor Cavities," March 21, 1984. 

Information Notice No. 82-51, "Overexposure in PWR Cavities," December 
21, 1982. 

IE Circular No. 76-03, "Radiation Exposure in Reactor Cavities," September 
13, 1976. 

8612230089 

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Description of Circumstances: 

On March 30, 1986 the Salem Generating Station Unit 1 was in cold shutdown 
for refueling with the RID thimbles retracted. While the reactor refueling 
cavity was being filled, the Unit 1 Shift Supervisor (SS) directed the con-
tainment equipment operator (EO) to check the RV sump for water leaks 
through the inflatable cavity seal. The EO and an accompanying HP technician 
attempted to enter the locked entrance door to the seal table room. When the 
high radiation exclusion area key did not open the door (wrong key) the EO 
jammed the door and entered the seal table room. The began a descent down 
the ladder into the RV sump with the HP technician in the lead taking 
radiation survey readings. When the radiation level indicated 3R/hr, the HP 
technician aborted the entry, the leak inspection was terminated, and both 
personnel exited the area. Seal water leakage was noted. Total personnel 
radiation doses were less than 50 millirem. 

The licensee conducted a thorough fact-finding investigation immediately 
after the event. The following chief causal factors evolved from the review:

1.   Lack of Understanding of RV Sump Room's Radiological Hazards 

     The SS who directed the sump entry was aware that the RID thimbles were
     withdrawn, but did not know that these thimbles presented significant 
     radiological hazards. However, the SS did check and ensure that the 
     movable incore detectors were safely stored. Some other plant super-
     visors also did not understand the thimbles can create intense 
     radiation fields of such magnitude as to jeopardize personnel health 
     and safety. 

     As noted in Information Notice No. 82-51, radiation levels of thousands 
     of R/hr are possible within a few feet of the thimbles. That same 
     notice suggested that each licensee senior reactor operator (SRO) be 
     given a copy of the notice. 

2.   Lack of Communication Between Work Groups 

     The on-shift containment HPs and operation personnel generally under-
     stood the RID thimble hazards, but were not informed by shift 
     management that thimbles had been withdrawn. 

3.   Work-Control Procedures Not Followed 

     Procedures for installing safety tags, high-radiation area access key 
     control, and the operating procedure for filling the reactor refueling 
     cavity apparently were not followed properly. 

The three causal factors listed above are recurring factors that have lead 
to the numerous unauthorized/improper RV sump entries described in the past 
related correspondence. As a result of the investigation, the licensee 
committed to institute the following corrective actions: 

1.   As a long-term action, the licensee will upgrade the training (and 
     retraining) program for reactor operators and HP technicians to include
     RV sump area transient radiation hazards (from the incore detector and 
     the RID thimbles). As a short-term action, the plant General Manager  

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                                                         IN 86-107 
                                                         December 29, 1986 
                                                         Page 3 of 4 

     issued a letter to all plant staff, reviewing the RV sump area radio-
     logical hazards. Reinforcing this action, the Operations Manager will 
     personally provide upgraded radiological training to shift operations 
     management, focusing on operations overall responsibility for plant 
     worker radiological safety. 

2.   The licensee will perform a reevaluation and review of other,plant 
     areas and operations as requested by IE Circular 76-06. This 
     reexamination effort should help ensure high-radiation areas 
     (particularly transient) are properly identified and controlled. Within 
     1 day of the incident, known, existing high-radiation areas locking 
     mechanisms were checked and improved when necessary by the licensee. 

3.   Procedural controls will be reviewed and upgraded to provide more 
     effective, improved access controls to all high-radiation areas. This 
     administrative effort includes a detailed review of pertinent 
     operations procedures (filling reactor refueling cavity, thimble 
     retraction, etc.) to ensure these documents have appropriate radiation 
     protection hold points to protect the workers. These procedures also 
     will be revised to require appropriate notification and hazards 
     description to maintenance, HP, operations, and other personnel when 
     the RID thimbles are retracted. 

     Hazards posting will be provided in the control room and HP control 
     point in containment to help ensure personnel are aware of thimble 
     position and RV sump entry requirements. The radiation work permit 
     (RWP) procedure will be changed to specifically require a special RWP 
     to enter the RV sump area. This location-specific, single-purpose RWP 
     will require approval by the HP/Chemistry Manager. 

Discussion: 

Irradiated components such as RID thimbles can create radiation fields in a 
reactor cavity where permissible occupational dose standards can be exceeded
in less than 1 minute. These extremely hazardous areas can present life-
threatening radiation situations where acute exposures, sufficient to cause 
serious radiation injury, are possible with just a few minutes exposure. A 
reactor cavity is often a hostile physical environment (with poor access and
limited visibility) and can be a likely place for personal accidents and 
mishaps to occur. 

As a result of a similar event at Salem in 1980, the licensee had initiated 
corrective actions to improve radiological controls of the RV sump. In an 
October 3, 1986 letter to Region I describing licensee corrective actions 
and commitments for programmatic improvements resulting from the 1986 event,
the licensee noted that previous actions as a result of the 1980 event ". . 
. appeared to be effective in the short term, were apparently not incorpor-
ated into station programs in a manner that perpetuated their effectiveness 
. . . ." The 1986 Salem event clearly demonstrates that these unforgiving 
areas demand continued management efforts and,oversight to ensure that ade-
quate controls persist and remain effective. 

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                                                         IN 86-107 
                                                         December 29, 1986 
                                                         Page 4 of 4 

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office. 


                                   Edward L. Jordan, Director
                                   Division of Emergency Preparedness
                                     and Engineering Response
                                   Office of Inspection and Enforcement

Technical Contacts:  James E. Wigginton, IE
                     (301) 492-4967

                     Thomas F. Dragon, RI
                     (215) 337-5373

Attachment:    List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, November 12, 2013