Information Notice No. 86-107:Entry Into PWR Cavity with Retractable Incore Detector Thimbles Withdrawn
SSINS No.: 6835
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INCORE DETECTOR THIMBLES WITHDRAWN
All nuclear power reactor facilities holding an operating license or a
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are withdrawn.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withdrawn have occurred, leading to 6 personnel overexposures.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
IE Circular No. 76-03, "Radiation Exposure in Reactor Cavities," September
December 29, 1986
Page 2 of 4
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
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
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.
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.
December 29, 1986
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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
Thomas F. Dragon, RI
Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015