United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 95-46: Unplanned, Undetected Release of Radioactivity from the Exhaust Ventilation System of a Boiling Water Reactor

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                         WASHINGTON, D.C.  20555-0001

                                October 6, 1995


NRC INFORMATION NOTICE 95-46:  UNPLANNED, UNDETECTED RELEASE OF RADIOACTIVITY
                               FROM THE EXHAUST VENTILATION SYSTEM OF A        
                               BOILING WATER REACTOR


Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to inform addressees of an undetected release of radioactive material,
from a liquid radwaste evaporator.  The vapor from this evaporator is normally
released directly to the environment.  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 are not NRC requirements; therefore, no
specific action or written response is required.

Description of Circumstances

On April 5, 1995, the licensee for the Hope Creek Nuclear Station, the Public
Service Electric & Gas Company, was using the decontamination solution
evaporator to process liquid waste from the chemical waste tank.  The
evaporator was equipped with a demister and an exhaust vent piped directly to
the south plant vent.  On two occasions, alarms caused by high differential
pressure across the demister prompted the operator to spray the demister.  The
spraying, combined with a continuous supply of heating steam to the
evaporator, caused a buildup of steam in the vapor body and an increase in
evaporator pressure, which was suddenly relieved when the operator stopped
spraying.

Unknown to the operator, these two depressurizations caused two momentary high
steam flows in the 15-cm-diameter [6-in-diameter] effluent exhaust pipe from
the evaporator, ejecting 227 L [60 gal] of approximately 26 MBq/L [0.7 �Ci/mL]
radioactive water and steam mixture to the south plant vent upstream of the
effluent radiation monitor.  About half this liquid, containing an estimated
3,100 MBq [85 mCi] of mixed corrosion products, was released to the
environment and blown downwind, thus contaminating a large area within the
site protected area as well as onsite buildings and vehicles.  The remainder
of the mixture was deposited as radioactive liquid in the south plant vent
ducting, thus causing radiation alarms in the nearby reactor building
ventilation system exhaust and radwaste area exhaust systems.  However, the
south plant vent effluent monitor did not indicate any ongoing or previous 

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                                                            October 6, 1995
                                                            Page 2 of 3


release to the environment, even though the mixture passed isokinetic sampling
probes in the exhaust duct.  These releases occurred between midnight and
1:00 a.m. 

The licensee initiated abnormal operating procedures and an investigation.
after observing a hot spot in the south plant vent duct (approximately 1.2
mSv/hr [120 mrem/hr] on contact and 0.15 mSv/hr [15 mrem/hr] at 30 cm [1 ft])
and a radioactive reddish-brown liquid dripping from the duct into a
previously installed drip bag.  Despite these indications, the licensee
believed no release had occurred because a sample of the evaporator effluent
indicated no unusual conditions and because the south plant vent effluent
monitor did not indicate any abnormal radioactivity on an effluent sample. 
The licensee assumed the reddish liquid drip to be a preexisting condition and
that the hot spot was caused by a piece of solid material (possibly a piece of
a filter) that had been deposited in the duct.  The licensee focused on
preventing a release of radioactivity from occurring once the radioactive
liquid drips subsequently dried.  The licensee also attempted to locate the
source and the extent of contamination.

While questioning plant staff during the afternoon shift turnover, the
licensee also surveyed the turbine building roof and found elevated levels of
removable contamination.  The licensee then surveyed the yard areas and found
radioactive contamination in the protected area at approximately 4:00 p.m.
Vehicles that had left the site the day of the release were identified,
located, and surveyed.

Discussion

The NRC review of the event is documented in NRC Inspection Report No. 
50-354/95-05, dated May 30, 1995.  The release of radioactive contamination
did not have a significant radiological impact on the public, onsite workers,
or the environment.  However, several significant weaknesses were revealed: 
insufficient understanding and review of the design basis and operation of the
decontamination solution evaporator and the south plant vent effluent
monitoring system, inadequate communications and integrated assessment of
incoming information, operation of the evaporator neither in accordance with
its design basis nor with commitments in the Final Safety Analysis Report, an
erroneous belief, unchallenged by several 10 CFR 50.59 safety evaluations,
that the evaporator could not cause a radioactive release, and untimely
notification of workers of the release and onsite contamination.

Although radwaste systems typically are not safety related, proper operation
of such systems is essential for controlling onsite and offsite personnel
exposures within the limits of Parts 20 and 50 of Title 10 of the Code of
Federal Regulations.

This event and an event at the James A. FitzPatrick Nuclear Power Plant, which
was discussed in a previous information notice 91-40 (referenced below), have
common root causes:  weaknesses in design review or implementation, operating
procedures, and management oversight of radwaste system operations..                                                            IN 95-46 
                                                            October 6, 1995
                                                            Page 3 of 3


Related Generic Communications

      Information Notice 91-40, "Contamination of Nonradioactive System and
      Resulting Possibility for Unmonitored, Uncontrolled Release to the
      Environment," June 19, 1991.

      Circular No. 80-18, "10 CFR 50.59 Safety Evaluations for Changes to
      Radioactive Waste Treatment Systems," August 22, 1980.


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 Office of
Nuclear Reactor Regulation (NRR) project manager.

                                    /s/'d by DMCrutchfield


                                    Dennis M. Crutchfield, Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation


Technical contacts:  Ronald L. Nimitz, RI       John White, RI
                     (610) 337-5267             (610) 337-5114

                     Tracy Walker, RI           Scott Morris, RI
                     (610) 337-5381             (609) 935-3850
Page Last Reviewed/Updated Monday, November 18, 2013