Information Notice No. 83-52: Radioactive Waste Gas System Events
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
August 9, 1983
Information Notice No. 83-52: RADIOACTIVE WASTE GAS SYSTEM EVENTS
All nuclear power reactor facilities holding an operating license (OL) or
construction permit (CP).
This information notice is issued to alert licensees to two recent events
involving radioactive waste gas systems. The PWR event involved the
inadvertent, offsite release of the contents of a waste gas decay tank
(WGDT) over a 7-hour period. The BWR event involved power operation for a
25-hour period without the automatic isolation function capability on the
condenser offgas system.
In both events the offsite radiological consequences were negligible.
However, these events clearly demonstrate that the level of attention given
to the status and procedural controls for the operation and maintenance of
these radioactive waste gas systems can be significantly improved. The
corrective actions taken by the licensees to prevent reccurences are
presented. Attachment No. 1 contains nine summaries of related events taken
mainly from the Licensee Event Report files. It is expected that recipients
will review this information for applicability to their facilities. No
specific action or response is required.
Description of BWR Event:
During the 2330 shift turnover on May 9, 1983, the Brunswick Unit 2 on-duty
Shift Operating Supervisor (SOS) noted unusually low readings (for existing
reactor power level) on both main condenser steam jet air ejector (SJAE)
offgas radiation monitors. After the proper operability of these monitors
and was verified, local flow at the SJAE monitors was found to be 3.5 - 5.5
CFM (normal should be 12 - 15). Subsequent investigations revealed SJAE
monitor readings were not consistent with the main stack monitor readings
which were properly following the ongoing power ascensions. At 0315 on May
10 the operations shift personnel, having exhausted other potential causes
of the problem, checked the positions of the radiation monitors' manual root
isolation valves (2-06-V35 and V36). Both valves were found to be shut and
when opened, all control room SJAE related indications including radiation
level and hi-lo flow, annunciator returned to normal levels/conditions.
A subsequent licensee investigation of the events leading up to the SJAE
monitor isolation incident revealed that a plant modification of the offgas
system had required a valve clearance (30 valves), which included shutting
August 9, 1983
Page 2 of 4
valves V35 and V36 on April 10. On April 17, the clearance was partially
restored (21 valves) with V35 and V36 to be restored to their normal open
positions. On April 25 a Unit 2 startup was in progress with the SJAE's
started briefly but not maintained in service because of low supply steam,
pressure and a Group 1 isolation--main steamline isolation valve closures.
With the unit shut down on April 26, the plant chemistry group wrote a
"trouble ticket" for the low flow condition on the SJAE monitor; no work was
ever performed and the ticket was eventually cancelled since (in a shutdown
condition) no flow is normal.
On May 8, SJAEs A and B were placed in half-load condition with Unit 2 in
startup mode. Operations personnel judged no immediate action was necessary
in response to the annunciator for hi-lo SJAE flow -- a history of past
problems during startup existed, because of sample line condensation removal
problems and low supply steam pressure (which would clear shortly as startup
progressed). Poor performance of loop seal drains further compounded the
problem of putting the SJAEs on line. Three different operations shifts
(from May 8, 2300 to May 19, 2300) during the Unit 2 startup failed to
identify and act on the abnormally low SJAE radiation monitor readings.
While the hi-lo flow SJAE annunciator was noted, it was not a shift turnover
action item, and hence, no followup was performed. Other indications
available to the operations staff for problem identification were:
1. Failure of SJAE monitor readings to track with the main steam line
radiation monitors and main stack monitor during the power ascension
from 0800 - 2300 period.
2. Hi-lo flow SJAE annunciator alarm.
3. Virtually the same SJAE radiation monitor reading recorded in Daily
Surveillance Report over power ramp up to 55%.
The licensee initiated the following corrective actions to prevent
1. Upgraded Operations On-shift Training Program by stressing: need for
increased awareness of available control room indications, strict
adherence to clearance procedure, and importance of valve positioning.
2. Added specific requirement for each shift to review and update
3. Increased involvement of operations engineering staff through
evaluation of impact of major maintenance activities and communication
of potential concerns to on-shift operations management.
4. Clearance procedure will be reviewed and revised as necessary to
provide for better tracking and auditability of equipment status (e.g.,
valve position be determinable by time and date.
5. Personnel involved with the incident will have their individual
performance reviewed for possible disciplinary action, employee
counseling, and possible training/retraining.
August 9, 1983
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The licensee reported that a comparison of primary coolant Iodine-131 Dose
Equivalent values, SJAE radiation monitor readings, and main stack release
rates for periods before and after the event were very similar, indicating
health and safety of public were not affected the incident.
Description of PWR Event:
On February 27, 1983, during normal power operation of Turkey Point Unit 3,
the contents of waste gas decay tank (WGDT) No. 2 were inadvertently
released to the environs via the auxiliary building exhaust fan to the plant
vent. The licensee reported that over a 7-hour period beginning at 1700, the
waste gas decay pressure decreased from a reading of 98 psig to a reading of
only 10 psig. This low pressure reading prompted a review of associated
process radiation monitoring equipment printouts (SPING-4 gas monitor and
R-14 vent monitor) which confirmed that a radioactive release had occurred
during the WGDT pressure decay period. Samples of the remaining WGDT
contents were taken and analyzed and together with the radiation monitoring
system printouts, the licensee determined approximately 18 curies of gaseous
activity were released. This reported release quantity is about 0.02% of the
allowable quarterly release limit for total gaseous releases.
Licensee followup of the event focused on the safety valve and the two
normally closed valves (4638B and RCV-014) in the line from the WGDT to the
waste gas release header. A special test of the associated waste gas safety
(relief) valve verified its proper operation. The licensee determined that
the 4638B valve had apparently not seated properly, and the hand controller
for the RCV-014 valve was found to be slightly off zero leaving the valve
As a result of the investigation, the licensee took the following corrective
1. Verified proper operation of the 4638B valve and installed a new
diaphragm (although old diaphragm had no apparent damage).
2. Revised the plant operating WGDT release procedure to ensure that the
RCV-014 valve will be "failed" closed after each controlled release.
The attachment contains nine summaries of other related events involving
various equipment and personnel problems associated with radioactive waste
gas systems and their operation. These summaries are provided to illustrate
the wide scope of potential problems with these systems.
August 9, 1983
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If you have any questions regarding this matter, please contact the
Regional, Administrator of the appropriate NRC Regional office, or this
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: J. E. Wigginton, IE
1. Related Summaries
2. List of Recently Issued IE Information Notices
August 9, 1983
Page 1 of 3
SJAE RADIATION MONITOR ISOLATED (Brunswick,2, BWR)
RO-76-12 EVENT DATE: 1/19/76
CAUSE: Improper valve position POWER LEVEL: 84%
ABSTRACT: While increasing power to 95%, control room operator observed that
SJAE offgas radiation monitor reading was not increasing with
power. Investigation revealed no SJAE monitor sample flow because
of shut sample supply valve; likely to have been shut during
12/27/75 investigation of loss of condenser vacuum.
SJAE RADIATION MONITORS ISOLATED (Monticello, BWR)
RO-77-06 EVENT DATE: 3/21/77
CAUSE: Undetermined POWER LEVEL: 55%
ABSTRACT: During plant startup, both SJAE radiation monitors were found to
be isolated. Work control process and startup procedures were
revised to prevent recurrence.
SJAE RADIATION MONITOR ISOLATED (Pilgrim 1, BWR)
LER 78-052/03L EVENT DATE: 10/28/78
CAUSE: SJAE isolation (block) shut POWER LEVEL: 58%
ABSTRACT: While conducting routine startup, low level SJAE radiation monitor
readings were noted and investigation revealed that the block
valve to SJAE monitor was shut. Licensee could not determine
reason for mispositioning of block valve.
UNPLANNED GASEOUS RELEASE (Maine Yankee, PWR)
LER 81-003 (REV 1) EVENT DATE: 4/17/81
CAUSE: Containment sampling valve left open POWER LEVEL: 97%
ABSTRACT: Licensee discovered a 1/4 temporary line off the containment air
particulate detector (APD) had been left open nine days, following
sampling of containment. The resulting containment leakage rate
exceeded plant Technical Specification limits. The temporary
sampling valve was not included in formal valve control
August 9, 1983
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NO OFFGAS STACK SAMPLE FLOW (Duane Arnold, BWR)
LER 81-002E EVENT DATE: 4/27/81
CAUSE: Open breaker POWER LEVEL: Shut down
ABSTRACT: During a refueling and maintenance shutdown, the breaker supplying
power to the offgas stack radiation monitor sample pumps was found
open (not tripped). Reason for open breaker not determined;
breaker was marked as spare, rather than sample, pump breaker.
Operations personnel acknowledged alarm for low sample flow, but
took no action at time of alarm.
INADVERTENT WGDT RELEASE (Cook 1, PWR)
LER 81-035 EVENT DATE: 8/26/81
CAUSE: Drain valves left open POWER LEVEL: 100%
ABSTRACT: Leakage pathway occurred from waste gas vent header through spent
resin storage tank (SRST) drain valves via the clean sump tank
vent out the unit ventilation system. A non-licensed operator left
SRST drain valves open after draining operation,, resulting in a
substantial pressure drop in waste gas decay tank pressure (but
negligible amount of gaseous activity released).
INADVERTENT WGDT DEPRESSURIZATION (San Onofre 1, PWR)
LER 82-017 EVENT DATE: 6/14/82
CAUSE: Waste gas system back-leakage POWER LEVEL: Shut down
ABSTRACT: During a 24-hour period between surveillances, a WGDT
depressurized from 25 psig to O psig (no actual radiological
release occurred). Followup comprehensive helium leak testing
verified leakage path was back through WGDT system.
CONTAINMENT-PLANT VENT AIR PARTICULATE DETECTOR (APD) INOPERABLE (Salem 1,
LER 82-078 EVENT DATE: 10/17/82
CAUSE: Personnel Error--capped sample line POWER LEVEL: O%
ABSTRACT: During containment purge operations, licensee noted APD sample
line to the plant vent had been erroneously capped during
TMI-design change. APD had been isolated since before unit
start-up in April 1982.
August 9, 1983
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INOPERABLE MAIN STEAMLINE RADIATION MONITORS (Nine Mile Point 1, BWR)
EVENT DATE: 7/17/83 POWER LEVEL: 90%
CAUSE: Defective detector cables
ABSTRACT: On July 18, the NRC Senior Resident Inspector (SRI) identified two
of the four main steamline radiation monitors were reading too low
for existing reactor power level (90%). Subsequent licensee
investigation revealed the two monitors were inoperable for
approximately 27 hours because of defective radiation detector
cabling. The detector cabling was repaired, recalibrations
performed, and monitors returned to service.
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