ML20151E725
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| ML20151E725 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 04/07/1988 |
| From: | Kahle J, Marston R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML20151E619 | List: |
| References | |
| 50-416-88-05, 50-416-88-5, NUDOCS 8804150357 | |
| Download: ML20151E725 (14) | |
See also: IR 05000416/1988005
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UNITED STATES
NUCLEAR REGULATORY COMMISSION
REGION ll
4, 101 MARIETTA ST., N.W.
.....,o ATLANTA GEORGIA 30323
,
APR 0 71988
Report No.: 50-416/88-05
Licensee: System Energy Resources, Inc.
Jackson, MS 39205
Docket No.: 50-416 License No.: HPF-29
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Facility Name: Grand Gulf
Inspection Conducted: March 7-11, 1988
Inspectors:
R. R. Marston
N
Date Signed
Accompanying P,ers nnel: C. A. Hughey
Approved by:
J.
bid
. Kahle, Section Chief
e//f/8
Date 6igned
ision of Radiation Safety and Safeguards
SUMMARY
Scope: This special, announced inspection was conducted in the areas of offgas '
system hydrogen control and offsite dose assessments during charcoal bed
bypasses.
Results: No violations or deviations were identified.
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REPORT DETAILS
1. Persons Contacted
Licensee Employees
R. Brinkman, Radiological Engineer
*J. Cross, Site Director
*C. Elisaesser, Operations Coordinator
*R. Hutchinson, General Manager
J. Lassetter, HP/ Chemistry Specialist
*A. McCurdy, Manager, Plant Operations
*J. Parrish, Chem / Rad Superintendent
G. Smith, Plant Chemist
*J. Summers, Compliance Coordinator
Other licensee employees contacted included engineers, technicians,
cperators, and office personnel.
Other Organizations
L. Nesbitt, General Electric Company
Nuclear Ragulatory Commission
*R. Dutcher, Senior Resident inspector
*J. Mathis, Resident Inspector
* Attended exit interview
2. Exit Interview
The inspection scope and findings were summarized on March 11, 1988, with
those persons indicated in Paragraph 1. The inspector described the areas
- 4.nspected and discussed in detail the inspection findings listed below. ,
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No dissenting conments were received from the licensee. The licensee did
not identify as proprietary any of the material provided to or reviewed by
the inspector during this inspection.
l 3. Licensee Action on Previous Enforcement Matters
This subject was not addressed in the inspection.
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4. Introduction
On February 27, 1988, while changing from the "B" to the "A" steam jet air
ejector (SJAE), operations personnel noticed a sudden loss of offgas Flow
and spiking of the hydrogen (H,) inline analyzers located in the offgas
system. This was caused by a sudden burn of excess 2H within the offgas
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system. Although this burn apparently caused only minor equipment damage, l
there was a potential for major equipment damage and personnel injury,
exposure, and contamination.
The following paragraphs include a description of the event, the causes
and corrective actions related to the burn and the dose assessment
l relating to the increase in gaseous radioactivity discharged from the
plant.
5. General System Description
a. Design Objectives
The offgas system at Grand Gulf was designed to meet the following
regulatory objectives:
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The ALARA objectives of 10 CFR 50, Appendix 1
- The dose restrictions of 10 CFR 20, Appendix B
- General Design Criteria No. 60 (Control of Releases of
Radioactive Materials to the Environment) and No. 64 (Monitoring
of Radioactive Releases) of 10 CFR 50, Appendix A
The primary design objectives of the system were:
- To recombine hydrogen and oxygen gases produced in the reactor
by the radiolytic decomposition of water and therefore reduce
explosion hazards.
- To provide sufficient hold-up time for radioactive activation
products and fission products to decay prior to release.
- To minimize the release of the particulate daughter products of
noble gases.
- To provide for the controlled release of radioactive gases to
the environment during nonnal and off-normal operating
conditions.
b. System Description
The inspector reviewed system description:. from the FSAR and current
plant drawings, held discussions with licensee representatives, and
performed a walkdown of the system with a cognizant licensee
representative.
(1) There were two redundant offgas processing system trains, each
one capable of processing the entire offgas flow from the plant
(A and B trains). Each train was composed of systems to process
noncondensable gases and to control the release of radioactive
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effluents to the env'ronment. The condenser air removal system ,
and the offgas system perform these functions. Neither train )
contains rotating parts.
(2) Condenser Air Removal System
The condenser air removal system consists of a first stage steam
jet air ejector (SJAE), an intercondenser and a second stage
SJAE. Main steam flows to the air ejectors to:
- Pump noncondensable gases from the main condenser
- Provide the motive force for the offgas system
- Dilute the offgas stream to less than 4% hydrogen
concentration, and
- Remove noncondensables from the offgas flow.
An intercondenser is located between the first and second stage
SJAEs. The intercondenser is cooled by plant service water
(PSW) and functions to remove moisture from the offgas flow.
The significant gaseous wastes removed from the main turbine
condenser by the SJAEs consist of the following:
- Radiolytic hydrogen and oxygen
- Condenser air inleakage
- Nitrogen-13, Nitrogen-16, and Oxygen-19
- Krypton, Xenon, and Iodine isotopes
These gases are produced in the core region and travel to the
main condenser along with the main steam.
(3) Offgas System
The offgas system begins at the outlet of the second stage SJAE
and ends at a connection to the radwaste ventilation system.
The following is a brief sequential discussion of the major
system components and their operating functions.
(a) The offgas reheater (heat exchanger) superheats the gases
and steam from the second stage SJAE to about 300*F before
l entering the recombiner. This increases the recombiner
catalyst efficiency by eliminating moisture. Main steam is
used as a heat source.
(b) The catalytic recombiner recombines the hydrogen and oxygen
produced by radiolytic decomposition by passing the process
flow over trays of a platinum alloy catalyst. The water
vapor temperature at the exit of the recombiner is normally
in excess of 600'F. Gas flow rate prior to the recombiner
is in excess of 100 standard cubic feet per minute (SCFM)
and is 20 SCFM as it exits the recombiner. This latter
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flow rate remains constant through the rest of the offgas
system.
(c) The superheated water vapor and inleakage air mixture from
the recombiner flows through the offgas condenser where the
bulk of the water vapor is cooled (160 F), condensed and
removed. This condenser (heat exchanger) is cooled by
Turbine Plant Cooling Water (TPCW) flow through the tube
side.
(d) The process flow enters a water separator where entrained
water droplets are removed as the flow passes through a
stainless steel wire mesh de-entraining element.
(e) Two redundant inline hydrogen analyzers continuously
monitor the H7 concentrations in the offgas process flow
prior to entering the hold-up line. If a preset value on
the monitors is exceeded, a main control room annunciator
is actuated. An inline pretreatment radiation monitor also
monitors the radioactivity of the process flow prior to
entering the hold-up line. A more detailed discussion of
these monitors is included in Paragraph 5.c.
(f) A hold-up line, consisting of a straight run of piping
500 feet long and 6 inches I.D. provides a delay of
approximately seven and one-half minutes to allow for the
decay of short-lived radionuclides.
(g) The cooler condenser (heat exchanger) cools the process
flow by means of a glycol refrigeration system to as low as
possible without freezing (35 F). This removes moisture
from the process flow.
l (h) Another moisture separator removes any moisture droplets in
the process ficw that are not removed in the cooler
condenser.
(i) A high efficiency particulate air prefilter element
(aluminum separator and glass fiber filter elements)
removes particulate daughter products of fission product
gases from the process flow.
(j) Any additional moisture is removed by passing the process
flow through one of four desiccant dryer beds. The dryer
beds are regenerated on a regular basis using an electric
heater / dryer chiller system. The dewpoint of the process
flow after the desiccant cryers is normally about -80 F.
(k) Two redundant dewpoint analyzers continuously monitor the
process flow relative humidity. Excess moisture in the
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process flow reduces the adsorption efficiency of noble
gases on the charcoal beds.
(1) . The gas coolers further cool the process flow prior to
entering the charcoal adsorber beds by means of a glycol
refrigeration system. This cooling helps increase charcoal
adsorption efficiency.
(m) Eight charcoal adsorber vessels, each containing about
three tons of charcoal, adsorb radioactive fission product
gases (xenon and krypton) thereby allowing significant
delay and allowing for their decay. Any particulate
daughter products, aloag with radioactive isotopes c~
iodine, are retained in the charcoal beds. The gas coolers
and adsorber beds are enclosed in a refrigerated vault kept
at 0 F.
A bypass line is constructed around the gas coolers and
adsorber beds and is used during startup.
(n) Two redundant post-treatment radiation monitors
continuously monitor radiation levels within the process
stream. These monitors provide for automatic termination
of offgas releases in case of high radiation levels in the
process stream. A more detailed discussion of these
monitors is included in Paragraph 5.c.
(o) The process flow is then filtered through high efficiency
particulate air (HEPA) after-filters to remove any
remaining particulate daughter products and carbon dust.
(p) The final effluent from the offgas system is incorporated
into the radwaste ventilation system which is monitored for
radioactivity prior to release to the environment. A more
detailed discussion of the radiation monitors is included
in Paragraph 5.c.
(q) Several water-filled loop seals are located along each
train to prevent gas escape from the process flow through
various system drains.
c. Radiologicai Monitoring Systems
The following systems were evaluated:
(1) Offgas Pretreatment Radiation Monitoring System
This system monitors radioactivity in the condenser offgas at
the inlet to the hold-up piping after it has passed through the
offgas condenser and moisture separator. A continuous sample is
extracted from the offgas pipe via a sample line. It is then
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passed through a sample chamber and sample panel before being
returned to the suction side of the steam jet air ejector
(SJAE). The sample panel can be purged with room air to check
detector response to background radiation. The sample panel
measures and indicates sample line flow. A Geiger-Muller (GM)
tube is positioned adjacent to the vertical sample chamber and
monitoring is provideg locally and to the control room. The
monitor range is 1-10 mR/hr on a six decade log scale. The
principal gases detected are Kr-85, Kr-87, Kr-88, Xe-133m, and
Xe-135. Three trip circuits provide alarm functions only.
Readings are displayed on a r9diation monitor and actuate the
- following control room annunciators
- Offgas high-high, offgas
high, and offgas downscale. High or low sample line flow
measured at the sample panel actuates a control room offgas
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sample high-low flow annunciator. The radiation level output of
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the monitor can be directly correlated to the concentration of
the noble gases by using the semiautomatic vial sample panel to
obtain a grab sample. The sample is analyzed in the plant
counting room with the multichannel analyzer (MCA) and the
results correlated with the monitor reading.
(2) Carbon Bed Vault Monitor
The carbon vault is monitored for gross gamma radiation levels
with a single channe16 GM tube monitor. The monitor reads out
over a range of 1-10 mR/hr over a six decade logarithmic scale.
The principal nuclides detected are Xe-135, Xe-135m, Kr-87, and
Kr-88. The channel includes a sensor and converter, an
indicator and trip unit, and a locally mounted auxiliary ut.it.
The indicator and trip unit is located in the control room. The
channel provides for both loeg1 and remote readout of gama
radiation over a range of 1-10 mR/hr. The indicator and trip
unit has one adjustable upscale trip for alarm and one downscale
trip. The trip circuits may be verified by means of test
signals or through use of portable gamma sources. A licensee
representative stated that the decector was located near the
room ventilation exhaust duct.
(3) Offgas Post-treatment Radiation Monitor
This system monitors radioactivity in the offgas piping
downstream of the offgas charcoal adsorbers and upstream of the
offgas system discharge valve. A continuous sample is passed
through the offgas post-treatment sample panel for monitoring
and sampling and returned to the effgas system piping. The
sample panel has a pair of filters (one for particulate
collection and one for halogen collection) in parallel (with
respect to the flow) with two identical gross radiation
detection assemblies (for determination of noble gases). Each
gross radiation detection assembly consists of a shielded
chamber, a set of GM tubes and a check source. Two radiation
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monitors in the control room displag the measured gross
radiation level over a range of 10-10 over five decades on a
logarithmic scale. The principal nuclides detected are Kr-85
and Xe-133.
The sample panel shielded chambers can be purged with room air
to check detector response to background radiation. The sample
panel measures and indictes sample line flow. A check source
for each detection assemoly operated from the control room can
be used to check operability of the gross radiation chamber.
Each radiation monitor has three trip circuits: two-upscale
(high-high-high, and high) and one downscale (low). Each trip
is visually displayed on the radiation monitor. These three
trips actuate corresponding control room annunciators: offgas
post-treatment high-high-high radiation offgas post-treatment
high radiation, and offgas post-treatment downscale. A trip
circuit on the recorder actuates an offgas post-treatment
high-high radiation annunciator. High or low sample flow
actuates a control room annunciator.
A trip auxiliary unit in the control room takes the
high-high-high and downscale trip setpoint and initiates closure
of the offgas system discharge and drain valves if its logic is
satisfied. A vial sampler panel similar to the pretreatment
sampler panel is provided for grab sample collection to allow
isotopic analysis and gross monitor calibration.
(d) Offgas and Radwaste Building Ventilation Radioactivity
Monitoring System
The system monitors for gaseous radioactivity in the offgas and
Radwaste Building discharge, including radwaste storage tank
vents for gross radiation level, and collects halogen and
particulate samples. The gross radiation detection assembly
consists of a shielded chamber, a beta sensitive GM tube, and a
check source. A radiation monitor in the control room analyzes
and visually dgsplays the measured gross radiation level over a
range of 10-10 cpm. The sample panel shielded chamber can be
purged with room air to check detector response to background
radiation. The sample panel measures and indicates sample line
flow. /, check source operated from the control room can be used
to check operability of the gross radiation channel.
The radiation
(high-high and monitor
high) andhas
onethree trip (circuits;
downscale low). two upscale
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6. Event Description
On Friday, February 26, 1988, at approximately 1630 hours, preparations
were begun by operations personnel for changeover from "B" SJAE to "A"
SJAE. A 20 SCFM air purge was placed through the "A" SJAE until the
changeover froa the "B" SJAE at about 1700 hours the. next evening,
Saturday, February 27, 1988. At the time of the changeover on' Saturday,
the following conditions existed:
- Plant was at 100% power
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Preheater "B" outlet temperature was 305*F
Preheater "A" outlet temperature was 295 F
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Recombiner "A" outlet temperature was 395 F
Recombiner "B" outlet temperature was 600*F
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Preheater "B" steam pressure was 110 psig
Preheater "A" steam pressure was 100 psig
- Offgas flow rate was 40 SCFM (including purge flow)
- Post-treatment radiation monitor was indicating 60-65 cpm
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"A" H analyzer was in auto in "zero purge" mode
"B" analyzer was in manual and "sample" mode reading 0.2-0.5 H2
conce tration.
After placing the second stage of the "A" SJAE in service, the steam
supply pressure was being raised to the normal operating pressure of
130 psig, when operations personnel received a second stage low steam flow
alarm. Steam supply pressure was reduced to 80 psig while instrument
(I&C) technicians were called to vent the pressure transmitters. This
venting cleared the alarms and steam supply pressure was brought back up
to 130 psig.
The final step in changcover from the "B" to the "A" SJAE was begun by
"bumping" open the suction valve (F003A) from the low pressure condenser
to the first stage "A" SJAE, as per procedure. As offgas flow to "A"
recombiner increased "B" recombiner temperature started to decrease as
expected. However, there was no corresponding incresse in "A" recombiner
temperature. (The 2H,+0 9 to 2H
9 0 recombination is an exothermic reaction).
The "A" reconbiner pressure differential was normal; therefore, operations
personnel continued to "bump" open F003A in an attempt to increase offgas
flow and therefore raise "A" recombiner outlet temperature.
At about 1745 hours, operations personnel noticed spiking of both in-line
hydrogen analyzers (analyzers indicate 0-5% 9H ) and a loss of offgas flow.
Water induction into the recombiner was sGspected at that time.
OperaLions personnel opened the "B" drain valves and then the "A"
recombiner drain valves as per procedure. Subsequently, offgas flow
indication returned. The hydrogen monitors were reset within ten minutes
after flow return. The " A" recombiner outlet temperature quickly
increased to 600'F (normal operating tenperature) from an indicated 400*F.
It was later discovered that the recorder could not indicate below 400'F
because of recorder mechanical problems.
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The first charcoal adsorber beds in each of the two parallel trains were
determined. to be hot imediately after the burn. Charcoal adsorber bed
D012B was at 140 F and and D012A was at 110'F. (Offgas flows in parallel
through two trains of four charcoal beds and one gas cooler each).
Inline dewpoint indicators also pegged out high. It was later determined
that high system temperature during the burn had destroyed the electrodes
associated with the instruments.
Because of the hydrogen burn, plant power was reduced to 75%. Health
physics personnel were requested to survey offgas system areas. No
significant increases in airborne radiation levels were detected,
indicating that no offgas system loop seals had been blown. This was also
an indication that no major pressure transients occurred during the burn
because any system pressure exce.eding approximately six (6) psig dould
have blown loop seals. Normal system operating pressure was one (1) psig.
By 1845 hours, the charcoal treatment system was bypassed. Plant power
had been reduced to 55% to help ensure that offgas process flow radiation
levels stayed below radiation monitor trip-points.
By 1945 hours, nitrogen purging of the charcoal adsorber beds had begun.
Temperatures peaked at 443'F in bed D012A and 700'F in bed 0012B at about
2300 hours. By March 1, 1988, the bed temperatures had decreased to the
20-30*F range with the nitrogen purge continuing.
1 On March 2,1988, at about 0900, three beds of the "A" charcoal train were
placed back in service. Nitrogen purging of D012A and all of "B" train
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beds continued.
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Radiological Significance of Event
The inspector evaluated the radiological aspects of the event through
discussion with licensee representatives, review of records, and
examination of radiation sampling, monitoring, and analysis equipment used
in conjunction with the offgas system. The inspector also reviewed
calculations of monitor setpoints and dose assessment for releases during
the event.
) While the offgas flow was bypassed the Radwaste Building Ventilation
Exhaust Radiation Monitor reading peaked at 2.0 E+3 counts per minute
(cpm) at 0645 CST on February 29, compared to a pre-event reading of
1.0 E-2 cpm.
1 The maximum effluent rate (61.9 microcuries per second) occurred at i 0327 CST on February 29. The effluent monitor gross reading peaked at a '
later time due to increasing background radiation. The instantaneous dose
rate at the plant boundary corresponding to the maximum source term was
2.10 mrem per year, well within allowable limits.
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The inspector reviewed Technical Specification and procedural requirements
for the:
Offgas Pretreatment Monitor;
Carbon Bed Vault Radiation Monitor;
Offgas Post Treatment Monitor;
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Offgas and Radwaste Building Ventilation Exhaust Radiation Monitor; -{
Hydrogen Analyz es; and
* Charcoal and HEPA filter testing (Offgas Af ter Filters and Radwaste
Building Ventilation Exhaust filters).
Operating and surveillance requirements for the offgas pretreatment
monitor, the offgas post-treatment monitor, the offgas and radwaste
monitor, and the hydrogen analyzers were found in Technical Specification (
Tables 3.3.7.12-1, ano 4.3.7.12-1. Technical Specification Table 4.4.5-1
provided additional surveillance requirements for the offgas pretreatment
monitor. Technical Specification Tables 3.3.7.1-1 and 4.3.7.1-1 provided
operating and surveillance requirements for the carbon bed vault radiation
monitor, and Technical Specification Tables 3.3.7.5-1 and 4.3.7.5-1
orovided additional operating and surveillance requirements for the Offgas
and Radwaste Building ventilation exhaust radiation monitor. Technical
Specification Sections 3.11.2 and 4.11.2 also provided operating and
surveillance requirements for the monitors and 'ie hydrogen analyzers.
The inspector selectively reviewed procedures implementing the Technical
Specification requirements and reviewed licensee documentation showing
that surveillances (calibrations, functional tests, filter testing, and
dose calculations) had been performed within the required frequencies.
The radiation monitors appeared to have been functioning properly at the
time of the event. The hydrogen analyzer recorders went offscale (greater
than 5 percent) at the time of the event, so grab samples were taken and
analyzed. Procedure 06-CH-IN62-0051, "Offgas Hydrogen Concentration,"
' Revision 23, was used for this operation. The first sample was taken at
7:47 pm on February 27. Since licensee personnel were concerned about the
operability of the gas chromatograph, a "pop" test was conducted on the
' tampl e. The test indicated that the concentration of hydrogen in the
Ople was less than 4 percent by volume. Two more samples were taken
over the next five hours and were analyzed on the gas chromatograph, which
had tven determined to be operational and and had been functionally
checkJd. The results indicated concentrations by volume of 0.03 percent
hydrogen and 0.04 percent hydrogen. The hydrogen analyzers were reading
b ck on scale by this time.
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CauseW Conclusions / Corrective Actions
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After the event, tre licensee assembled a task force consisting of the
e , Manager-Plant Opera.tions, key onshift personnel involved with the event,
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i various pynt derFtment representatives and a vendor (GE) expert in the
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- design ani, operation of the offgas system to determine the root causes,
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i' condusio' )! /and cor.'ective actions.
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a. Equipment Damage
As a result of the ignition, the licensee noted the following
equipment damage:
(1) The inservice prefilter had been damaged with partial melting of
the aluminum separator material. The filter was subsequently
removed and the other filter was placed in service.
(2) The inline dewpoint indicator electrodes had been destroyed.
(These electrodes were considered to be possible ignition
sources.)
(3) About 25 pounds total of charcoal (calculated value) was burned
in the charcoal beds. Each bed contains approximately 3 tons of
charcoal. The licensee considered this an insignificant loss
and did not plan to replace or add charcoal.
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b. Causes and Corrective Actions
(1) Intercondenser Fouling
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During the week prior to the ignition, plant performance
monitoring personnel had noted a degradation of plant
efficiency. Low pressure (LP) condencer pressure had equalized
with intermediate pressure (IP) condenser pressure resulting in
a 5-6 megawatt loss in plant electrical output. This
degradation was the result of fouling problems within the
i intercondenser of the inservice "B" SJAE. Flow through both
intercondensers is cooled by Plant Service Water (PSW).
Biological fouling within the Intercondenser (tube-side) lowered
its ability to condense first stage SJAE effluent and therefore
maintain sufficient pressure differential across the air
ejector. This degradation was the main reason for initiating
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the swap to the "A" SJAE.
Biocides and dispersants added to the PSW in the past had been
ineffective in preventing intercondenser fouling. Periodic
mechanical or hydraulic cleaning had been required to keep these
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- heat exchangers clean. The licensee had very recently changed
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to a different biocide / dispersant treatment regime in order to
reduce fouling. Biological fouling (macro and micro) had been
- an ongoiag problem in general at Grand Gulf Nuclear Station.
(2) Recombinor Wetting
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Wetting and subsequent cooling of the "A" recombiner catalyst
j resulted in the buildup of H 7 in the offgas system prior to i ignition. This wetting occurred as a result of the proccdural
sequence for opening a arain valve in a low area between the
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preheater and recombiner. Condensation collects in this area
due to piping configuration and needs to be drained.
Wetting of the recombiner catalytt v.as not detected during the
event because the recombiner temperature recorder (located in
the main control room) had pegged low at about 400'F due to a
mechanical failure of the recorder. Temperature history of the
recombiner below 400'F cannot, therefore, be reproduced.
The licensee had subsequently revised System Operating
Instructions 01-1-01-N62-1, Offgas System, to: (a) revise the
sequence for opening the offgas header to the recombiner drain
valves to ensure that any condensation and moisture had been
drained prior to initiating offgas flow and (b) establish
procedural holdpoints for verification of proper recombiner
temperature profile.
(3) Ignition Source
At the time of the inspection the licensee had not positively
identified the f gnition source. Because of the stoichiometric
concentrations v. hydrogen, oxygen and humidity in the process
flow at the time of ignition only a small amount of energy would
have been required to ignite the mixture. The licensee
suspected that the ignition occurred in the area of the
desiccant dryers. The licensee and the inspector agreed that by
insuring proper recombiner operation, ignition sources become a
secondary consideration.
(4) Preheater Steam Supply Pressure
Several design problems existed in the main steam supply to the
preheaters. Sufficient steam pressure could not be supplied to
both A and B preheaters to allow simultaneous operation of both
of the condenser air removal /offgas trains or to make a rapid
changeover between trains. Insufficient steam supply to the
preheaters reduced their ability to preheat process flow to the
proper recombiner inlet temperature. A rapid switch from one
train to another could slug the recombiner with water.
To alleviate this problem, a Design Change Request (No. 87/113,
dated 9/25/87) had been previously authorized to redesign the
piping runs between the main steam equalizing header and the
preheaters to allow sufficient steam supply pressure with both
preheaters inservice.
The licensee had also experienced cycling problems with solenoid
valves in the steam supply lines to the preheaters. During
plant startup in January 1988, with the plant at 3% power, a
valve in the steam supply line to the inservice preheater
inadvertently closed, shuttir, off steam supply to the
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, preheater. Subsequent wetting of the recombiner resulted in H2
concentration of 14% in the offgas system. There was ne
ignition at that time.
Design Change Request No. 87/113 also included provisions for
replacing each solenoid valve with two manual valves. The
. J.
licensee indicated that modifications described in the DCR would
be completed during the next refueling outage. The inspectors
urged the licensee to ensure that these modifications be
completed as scheduled.
-
8. Radiological Considerations
The licensee performed an analysis of the radiological output from the
plant which could result from operating with only three charcoal beds
operating in the offgas treatment system instead of the normal eight. The
analysis showed that the plant could be expected to. operate within
,
!
Technical Specification limits for effluents.
9. Sumary and Conclusions
,
The hydrogen burn took place in a system which was designed to contain
such burns and detonations. .The burn was fully contained.
, j The licensee was still in the process of evaluating the event at the time ! of the inspection. The integrity of the offgas system boundary did not
appear to have been violated. The licensee had identified contributing
, i causes of the incident, though the ignition source had not been ,
identified,
f
The licensee had evaluated the event and had identified corrective
' actions, some definite and some tentative, depending on what further
- analysis might reveal. No radiological effluent restrictions were
5 exceeded during the event.
No violations or deviations were identified.
e ! l i ! ! < }}