Information Notice No. 87-13: Potential for High Radiation Fields Following Loss of Water from Fuel Pool

                                                        SSINS No.: 6835 
                                                          IN 87-13 

                               UNITED STATES 
                           WASHINGTON, D.C. 20555

                              February 24, 1987

Information Notice No. 87-13:   POTENTIAL FOR HIGH RADIATION FIELDS 
                                   FOLLOWING LOSS OF WATER FROM FUEL POOL 


All holders of a nuclear power reactor operating license (OL) or a 
construction permit (CP) except Fort St. Vrain. 


This information notice is to alert addressees of the potential for high 
radiation fields following the inadvertent loss of water from the spent fuel 
pool or transfer canal. Recipients are expected to review the information 
for applicability to their facilities and consider actions, if appropriate, 
to preclude similar problems occurring at their facilities. 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 December 2 and 3, 1986, the Hatch nuclear power plant lost 141,000 
gallons of water from the spent fuel pool because of a leak from pneumatic 
seals in the transfer canal, between Units l and 2. The redundant pneumatic 
seals leaked because of a single failure. A valve in the single air supply 
line to the seal was mistakenly closed. Although water level dropped about 5 
feet and low level alarms in the spent fuel pool worked, the leak was not 
specifically identified for several hours because a leak detection device 
was valved out and none of the seals were instrumented to alarm on loss of 
air pressure. 

Analysis by the licensee after the event has shown that, if water had been 
completely lost from the transfer canal, radiation fields would be high 
enough that remedial measures may be difficult. High radiation fields would 
be present because irradiated control blades are stored on short hanger rods 
clipped over the side of the spent fuel pool. A control blade's roller 
bearing is typically made of cobalt-rich stellite which, when activated, has 
radiation levels of 8,000 to 10,000 R/hr on contact. Some of the control 
blades would be completely uncovered if the water level dropped to the 
bottom of the transfer canal. This drop in water level would result in 
general area radiation levels of about 100 R/hr at the edge of the spent 
fuel pool and 1 R/hr 6 feet from the edge of the pool. About 2 feet of water 
would remain over the top of the spent fuel at the minimum level resulting 
from draining via the transfer canal; so, there was no likelihood of fuel 
damage because of fuel uncovery. 


                                                       IN 87-13 
                                                       February 24, 1987 
                                                       Page 2 of 2 


The potential for this general type of event was discussed in IE Information 
Notice No. 84-93, "Potential for Loss of Water from the Refueling Cavity," 
issued on December 14, 1984 and IE Bulletin No. 84-03, "Refueling Cavity 
Water Seal," issued on August 24, 1984. The transfer canal between the Hatch 
units is an unusual design that illustrates yet another way a single failure 
resulted in substantial loss of water from the spent fuel pool. 

Although recipients of IN 84-93 and IEB 84-03 may have evaluated the 
potential uncovering of spent fuel, recipients may not have fully evaluated 
the potential for high radiation fields because of the potential uncovering 
of short hangers or other short fixtures holding irradiated material such as 
used control rods or neutron detectors. 

Since the event, concern has been raised about the design of the leak 
detection system for the seals. The leak detection system consists of a 
level switch that is piped between the first and second pneumatic seals to 
detect water leakage that gets past the first seal. The NRC is currently 
evaluating this design to determine whether water would flow past the leak 
detector if all seals failed and thus fail to detect the leak. 

As corrective measures, the licensee has separated the air supply to the 
transfer canal seals and the air supply to the inner and outer gates between 
the transfer canal and the spent fuel pools and is studying other changes to 
assure greater reliability. The licensee also is shipping the used control 
rods in the spent fuel pool off the site. 

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

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

Technical Contact:  Eric Weiss, IE
                    (301) 492-9005

                    Floyd Cantrell, Region II
                    (404) 331-5534

Attachment: List of Recently Issued IE Information Notices

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