ML20058L837
| ML20058L837 | |
| Person / Time | |
|---|---|
| Site: | 05200001 |
| Issue date: | 05/07/1993 |
| From: | Fox J GENERAL ELECTRIC CO. |
| To: | Poslusny C Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9305130020 | |
| Download: ML20058L837 (14) | |
Text
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a GeneralElectrcCommy 175Curtner Avenue Sasicse.CA95125 i
May 7,1993 Docket No. STN 52-001
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i Chet Posiusny, Senior Project Manager Standardization Project Directorate Associate Directorate for Advanced Reactors and License Renewal Office of the Nuclear Reactor Regulation l
Subject:
Submittal Supporting Accelerated ABWR Review Schedule - Overpressure
'f Protection i
Dear Chet:
4 Enclosed are SSAR markups proposed for the overpressure protection system.
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Please provide a copy of this transmittal to Butch Burton.
Sincerely, l
l Jack Fox Advanced Reactor Programs-i
- cc: Jack Duncan (GE) j Norman Fletcher (DOE) l Bernie Genetti(GE)
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Jim 40 9305130020 930507 i
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23AMMAE Standard Plant Rev B Table 3.9-8 (Continued)
IN. SERVICE TESTING SAFETY-RELATED PUMPS AND VALVES T22 Standby Gas Treatment System Valves Safety Code Valve Test Test SSAR l
Class Cat.
Fune. Para freq. Fig.
No. Qty Description (h)(i)
(a)
(c)
(d)
(e)
(f)
(g)
F012 2 Filter train DOP samplingline valve 3
B P
El 651(23) 'f downstream of after HEPA j
F014 2 STGS sample line valve 3
B P
El 651(2,3)
(
FD15 2 PRM discharge to stack valve 3
B P
El 651(2,3)
)
F500 2 Filter unit vent line valve 3
B P
El 63-1(23) j' F501 2 Filter unit drain line valve 3
B P
El 651(2,3)
F504 2 Filter unit vent line vahr 3
B P
El 63-1(2,3)
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F505 2 Exhaust fan vent line valve 3
B P
El 63-1(2,3)
F506 2 Fdter train vent line valve 3
B P
El 651(2,3)
F507 2 Futer train vent line valve 3
B P
El 651(2,3)
F508 2 Filter train vent line valve 3
B P
El 63-1(2,3) -
F509 2 Fdter train vent line valve 3
B P
El 6.5-1(23)
F510 2 Filter train vent line valve 3
B P
El 63-1(2,3)
)
F511 2 Exhaust stack drain line valve 3
B P
El 63 1(23)
I F700 2 Filter unit demister dp instrument line valve 3
B P
El 63-1(2,3)
F701 7 Filter unit demister dp instrument line valve 3
B P
El 6.5-1(2,3)
F705 2 Futer train prefilter dp instrument line valve 3
B P
El 63-1(2,3) i F~o 2
Filter train prefilterdp instrument line valve 3
B P
El 63-1(2,3)
)
F707 2 Fdter train preHEPA dp instrument line valve 3 B
P El 651(2,3)
F708 2 Filter train preHEPA dp instrument line valve 3 B
P El 651(23)
F709 2 Fliter train charcoal adsorber dp inst. line viv 3 B
P El 651(2,3)
F710 2 Filter train charcoal adsorber dp inst line viv 3
B P
El 651(2,3)
)
F711 2 Fdter train after HEPA dp inst line valve 3
B P
El 651(2,3) r F712 2 Filter train after HEPA dp inst line valve 3
B P
El 651(2,3) 2 F713 2 Filter train exhaust flow instrument line valve 3 B
P El 63-1(23)
F714 2 Filter train exhaust flow instrument line valve 3 B
P El 63-1(23) A T31 Atmospheric Control System Valves F001 1 N2 supply line from Reac;or Building HVAC 2 A
1,A 1.,P 2 yrs 6.2-39(1)
S 3 mo F002 1 N2 supplyline to drywellinboard cont-2 A
1,A 1.,P 2 yrs 6.2-39(1) ainment isoaltion valve S
3 mo F003 1 N2 supply line to werwell inboard cont-2 A
I,A L,P 2>Ts 6 1-39(1) ainment isoaltion valve S
3 mo 2 7s 6.2-39(1)
FD04 1 Containment atmosphere exhaust line from 2
A 1,A L,1-3 drywelliscaltion vaht S
3mo 2 Ts 6.2-39(1)
F005 1 Drywell atmosphere exhaust line valve 2
A 1,A 1,P 3
T31-F004 bypass line S
3mo 2 Ts 6.2-39(1)
F006 1 Containment atmosphere exhaust line form 2
A 1A 1.,P 3
wetwellisolation valve S
3 mo Wetwell overpressure line valve (h 2) 2 A
P 1.,P 2 yrs 6.2-39(1)
F007 1 s
ao I
3 9 $8.27 1
Amendment /
6venterSS. Pa r.
pp :x of g
.Q\\q 23A6100AE Standard Plant an, n Table 3.9-8 (Continued)
IN-SERVICE TESTING SAFETY-RELATED PUMPS AND VALVES T31 Atmospheric Control System Valves Safety Code Valve Test Test SSAR Class Cat. Func. Para Freq. Fig.
No.
Qty Description (h)(1)
(a)
(c)
(d)
(c)
(f)
(g) hF008 1
Containment atmosphere exhaust line 2
A 1,A 1,P 2 yrs 6.2-39(1) 5 to SGTS S
3mo kFD09 1 Containment atmosphere exhaust line to 2
A I,A 1,P 2 yrs 6.2-39(1)
S 3mo j
R/B HVAC Drywell overpressure line valve (b 2 )
2 A
P 1,P, 2 yrs 6.2-39(1)
& FD10 1 5
F025 1 N2 supply line from K-5 outboard cont-2 A
I,A 1,P' 2 yrs 6.2-39(1) f ainment isolation valve S
3 mo
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F039 1 N2 supply line from K-5 outboard cont-2 A
I,A 1,P 2 yrs 6.2-39(1) ainment isolation valve S
3mo F040 1 N2 supply line from K-5 to drywellinboard 2
A I.A 1,P 2 yrs 6.2-39(1) isolation valve S
3mo
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F041 1 N2 supply line from K-5 to wetwellinboard 2
A I.A 1,P 2 yrs 6.2-39(1) isolation valve S
3mo I
F044 8 Drywell/wetwell vacuum breaker valve 2
C A
P RO 6.2-39(2)
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R D
/ F050 1 N2 supply line to drywell test line valve 2
B P
El 6.2-39(1)
F051 1 Containment atmosphere exhaust line test 2
B P
El 6.2-39(1) line valve i
F054 1 Drywell personnel air lock hatch test 2
B P
El 6.2-39(2) i line valve F055 1 N2 supply line from test line valve 2
B P
El 6.2-39(1)
F056 1 Wetwell personnel air lock hatch test 2
B P
El 6.2-39(2) line valve F700 1 N2 supplyline to drywell FE upstream 2
B P
El 6.2-39(1) instrument line
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F701 1 N2 supply line to drywell FE downstream 2
B P
El 6.2-39(1) instrument line F702 1 N2 supplyline to wetwell FE upstream 2
B P
El 6.2-39(1) mstrument line
,) F703 1 N2 supply line to wetwell FE downstream 2
B P
El 6.2-39(1)
I instrument line F720 8 DW/WW vacuum breaker valve N2 supply 2
A I,P L
RO 6.2-39(2) lineisolation vaht F730 1 Drywell pressure instrument line isolation 2
B P
El 6.2-39(2) valve I
F731 1 Drywell pressure instrument line solenoid 2
A I,P I,P RO 6.2-39(2) isolation vahe l
F732 2 Drywell pressure instrument line valve 2
B P
El 6.2-39(2)
F733 2 Drywell pressure instrument line solenoid 2
A 1,P 1,P RO 6.2-39(2)
)
isolation vahc
( F734 4 Drywell pressure instrument line for NBS 2
B P
El 6.2-39(2) c' valve 3958.26 Amendmentg
f j
gg MA fMM. PR'Tgg d 13
' Standard Plant REV C t
l 1-required, through a pathway from the wetwell l
(16) The primary containment purge system will 1
aid in the long-term post accident cleanup airspace to the stack. The pathway is isolated j
operation. The primary containment during normal operation with@upture disf j
i 4
I atmosphere will be purged through the SGIS 4
i to the outside environment. Nitrogen makeup The following modes of operation are provided:
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j will be available during the purging l
operation.
(1) Startup - Inerting. Liquid nitrogen is t
vaporized with steam or electric heaters to
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(17) The system is also designed to release a temperature greater than 200F and is l
containment pressure before uncontrolled injected into the wetwell and the drywell.
l containment failure could occur.
The nitrogen will be mixed with the primary containment atmosphere by the drywell j
6.2.5.2 System Design coolers in the drywell and, if necessary, by the sprays in the wetwell.
6.2.5.2.1 General c
(2) Normal - Maintenance of Inert Condition. A The ACS provides control over hydrogen and nitrogen makeup system automatically sup-l oxygen generated following a LOCA. In an inerted plies nitrogen to the wetwell and upper i
containment, mixing of any hydrogen generated is drywell to maintain a slightly positive i
not required. Any oxygen evolution from pressure in the drywell and wetwell to pre-i
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radiolysis is very slow such that natural clude air leakage from the secondary to the l
convection and molecular diffusion is sufficient primary containment. An increase in con-i to provide mixing. Spray operation will provide tainment pressure is controlled by venting l
further assurance that the drywell or wetwell is through the drywell bleed line.
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uniformly mixed. The system consists of the following features:
(3) Shutdown - Deinerting. Air is provided to the drywell and wetwell by the primary j
(1) Atmospheric mixing is achieved by natural containment HVAC purge supply fan. Exhaust processes. Mixing will be enhanced by is through the drywell exhaust lines and l
operation af the containment sprays, which wetwell to the plant vent, through the HVAC l
are used to control pressure in the primary or SGTS, as required.
l containment.
(4) Overpressure Protection, 11 the wetwell l
(2) The primary containment nitrogen purge pressure increases to about 5.6 establishes and maintains an oxygen -
kg/cm g, the rupture disks will open.
l 2
The overall containment pressure deficient atmosphere (13.5 volume percent) as venting continues.JLater, the operator,D(les in the primary containment during normal operation.
(can close the two 350A air-operated No l
butterfly valves to re-establishe5 (3) The redundant oxygen analyzer system (CAMS) containment isolation as required.
L measures oxygen in the drywell and suppression chamber. Oxygen concentration The following interfaces with other systems i
are displayed in the main control room.
are provided-Description of safety-related display l
instrumentation for containment monitoring (1) Residual Heat Removal System (RHR-Ell).
is provided in Chapter 7.
Electrical The RHR provides post-accident suppression l
requirements for equipment associated with pool cooling as necessary following heat the combustible gas control system are in dumps to the pool, including the exothermic accordance with the appropriate IEEE heat of reaction released by the design j
standards as referenced in Chapter 7.
basis metal-water reaction. This heat of reaction is very small and has no real In addition, the ACS provides overpressure affect on pool temperature or RHR heat
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protectican to relieve containment pressure, as exchanger sizing. The wetwell spray Ammendment#f 6.2-33
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i ABWR ow4mun,Pdor 2W100AB Standa rd PInnt prv c limit completion of either the inerting or nitrogen gas supply system is supplied from deinerting process and provides a the ACS nitrogen storage tank.
y representative oxygen sample for the ACS
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oxygen sensors. Should the arrangement of the RPV insulation leave a significant gap between itself and the RPV, forced l
circulation will be provided to that area. (5) Standby Gas Treatment System (SGTS-T22).
Alternatively, the major portion of the The SGTS processes any drywell bleedoff, drywell will be inerted to sufficiently inerting, and deinerting flows, as required below 3.5% such that the bulk average crygen by offsite release constraints.
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concentration does not exceed 3.5% percent
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2 pd Slw Nwn wnhng f (3) HVAC System (U41). The HVAC a ccommodat es the drywell and wetwell exhaust flow during (6) Containment Atmosphere Monitoring System in e rting3Mincrting, accommodate (CAMS D23). The CAMS monitors oxygen drywell bleedoff flows during startup,gha.-
levels in the wetwell and drywell during I
([ormal operatioO"frovides sufficient air accident conditions to confirm the primary flow to limit the concentration of any containment is inert.
nitrogen leaking from the primary containment into the secondary containment, Radiation monitoring in the plant vent, part c
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and supplies air for purging the primary f Process Radiation Monitoring (PRM-D11),
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g containment during deinerting. The real detects high radiation during deinerting.
I effect of leaking nitrogen from the primary containment is insignificant and does not There are no potential sources of oxygen in impact HVAC design.
containment other than that resulting from d[,
radiolysis of the reactor coolant.
Consideration of potential sources of leakage of oxygen into the containment included not only normal plant conditions but also postulated I
loss of-coolant accident conditions. Potential p'
sources of leakage are instrument air systems, service air lines, leakage control systems, The intake of the control room portion of purge lines, and inflatable door seals.
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the HVAC system is located to protect Nitrogen is substituted for air service wherever
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personnel in the control room in the event leakage into the inerted containment could bc
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of a nitrogen pipe or storage tank rupture. postulated.
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Similarly, suction for all HVAC systems is located to rninimize the introduction of 6.23.2.2 Inerting Equipment
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nitrogen from a break into occupied areas of the plant.
The inerting subsystem is capable of reducing the wetwell and drywell oxygen (4) High Pressure Nitrogen Gas Supply System concentrations from atmospherie conditions to (HPIN P54). Because the containment is less than 3.5 percent in less than four hours.
p inerted, all pneumatically operated The inerting vaporizers are sized to provide at (
components in the primary containment are least 2.5 times the containment (wetwell and p
normally supplied with nitrogen. The drywell) free volume of nitrogen within the pneumatic devices in the primary containment allotted four hours. The specified oxygen limit or those which could leak into the primary of 3.5 volume percent must be adjusted for p
containment are supplied with nitrogen for initial containment conditions, instrumentation f
the purpose of preventing oxyge t addition to errors, operator and equipment response time, the inerted volumes. The high pressure and equipment performance to ensure that the actual Ammendmentf
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. ABM o>nerus.rsor 9 se a 21 moan Standard Plant nry c l-elevation which would be covered by post LOCA the same time and made from the same sheet flooding for unloading the fuel, to provide uniformity of relief pressure.
m3 ER T4,,2,b7 2. (, (i )
6.2.5.2.5 Pressure Control (6) [T h e r u p t u r e dis k(~a r c c a p a ble o f j withstanding full vacuum in the wetwell I
(1) In general, during startup, normal, and Qapor space without leakage.
i abnormal operation, the ~wetwell and drywell pressures is maintained greater than 0 psig (7) The piping material is carbon steel. The g
to prevent leakage of air (oxygen) into the design pressure is 10.5 kg/cm g (150 primary containment from secondary psi)g and the design temperature is containment but less than the nominal 2 psig 171 C.
scram set point. Sufficient margin is provided such that normal containment 6.2.5.2.7 Recombloer temperature and pressure fluctuations do not cause either of the two limits to be reached (1) Two permanently installed safety-related d considering variations in initial recombiners are located in secondary containment conditions, instrumentation containment. Each recombiner, as shown in i
errors, operator and equipment response Figure 6.2-40, takes suction from the time, and equipment performance.
drywell, passes the process flow through a neating section, a reactor chamber, and a (2) Nitrogen ngakeup automatically maintains a spray cooler. The gas is returned to the 530 kg/m (0.75 psig) positive pressure wetwell.
to avoid leakage of air from the secondary into the primary containment.
(2) The recombiners are normally initiated on high levels as determined by CAMS (if l
(3) The drywell bleed sizing is capable of hydrogen _ is not present, oxygen
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l maintaining the primary, containment pressure concentrations are controlled by nitrogen l
less than 880 kg/m (1.25 psig) during makeup).
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the maximum containment atmospheric heating which could occur during plant startup.
6.2.5.3 Design Evaluation 6.2.5.2.6 Overpressure Protection The ACS is designed to maintain the 4,3 containment in an inert condition except for (1) The system is designed to passively reliev nitrogen makeup needed to maintain a positive I
the wejwell vapor space pressure at containment pressure and prevent air (0 )
3 kg/cm g,The system valves are capable leakage from the secondary into the primaiy containment.
fjeeMedgot being closed from the main control room ME 2M* using AC power and pneumatic air.
The primary containment atmosphere will be f
(2) The vent system is sized so that residual inerted with nitrogen during normal operation of core thermal power in the form of steam can the plant. Oxygen concentration in the primary be passed through the relief piping to the containment will be maintained below 3.5 volume stack.
percent measured on a dry basis.
(3) The initial driving force for pressure Following an accident, hydrogen concentration relief is assumed to be the expected will increase due to the addition of hydrogen pressure setpoint of the rupture disk #." from the specified design-basis metal water.
/E5e#T4,f.f'2,4(a/)
_ reaction. Hydrogen concentration will also j
(4)(The rupture diskt aTt. constructed o increase due to radiolysis. Any increase in stainless steel or a material of similar hydrogen concentration is of lesser concern
[corrision resistance.
because the containment is inerted. Due to dilution, additional hydrogen moves the (5) A number of rupture disks are procured at operating point of the containment atmosphere farther from the envelope of flammability.
1 6.2-36 Amendment 26 l
i
i outrypu. /98E Jy i of 13 Revise ABWR SSAR Paragraph 6.2.5.2.6, sub-paragraphs (4) and (6) to read:
195 Egr G 2.O. 6 (4)
(4)
The rupture disk is designed to prevent flow in the containment overpressure relief piping until a specified rupture pressure is reached.
It is constructed of stainless steel or a material of similar corrosion I
resistance.
M 5t'R T 6**Je f, 2,4 (4)
(6)
The rupture disk is part of the primary containment boundary and is able to withstand the containment design pressure (3.16 kg/cm2) with no i
leakage to the environment. It is also capable of withstanding full vacuum in the wetwell vapor space without leakage. The disk ruptures at 6.3 kg/cm8 due to overpressurization during a severe accident as required to assure containment structural integrity. As potential backup to a leaking, fractured or improperly sealed rupture disk,the two valves upstream of the disk can be closed. These valves are safety-related and i
ate subjected to all testing required for normal isolation valves.
I i
5 f
I I
QQ 00EFffBf /hr PJ '? ef 8 Kenndard Plant arv c Containment oxygen concentration also increases temporary plugs. Hydrostatic testing of piping h c.due to radiolysis. During plant operation, there systems will be performed at a pressure 1.5 \\
i
( are no other sources of oxygen in the times the design pressure, but in no case at i
/ containment.
less than 75 psig. The test pressure will be i
held for a minimum of 30 minutes. Pneumatic In the ABWR, there are no design basis events testing may be substituted for hydrostatic I
that result in core uncovery or core heatup testing in accordance with the applicable codes.
sufficient to cause significant metal water reaction. Therefore, per Regulatory Guide 1.7, Preoperational testing will demonstrate the i
the design basis metal water reaction is that ' ability of the ACS to meet design requirements.
l equivalent to the reaction of the active clad to Each valve will be exercised both opened and j
a depth of 0.00023 inches. This is equivalent to closed and position indication verified. Trip l
0 Radiolysis is and alarm logic signals will also be check'ed.
l b ca.72% of the active clad.
l lculated based on Regulatory Guide 1.7 source The tests assure correct functioning of all terms. Hydrogen and oxygen concentration controls, instrumentation, compressors, I
/ profiles in containment after the design basis recombiners, piping and valves. System LOCA are provided as Figure 6.2-41.
reference characteristics, such as pressure l
Overpressure relief is provided to passively i
j relieve the containment pressure, as required, by venting the wetwell armosphere to the plant j
i stack. Venting the wetwell airspace to the plant stack precludes an uncontrolled containment l
l failure. Venting from the wetwell, as opposed to l
the drywell, takes adventage of the decontamination factor provided by the l
suppression pool. Venting to the stack provides a monitored, elevated release. Precluding l
containment failure limits the maximum fission j
j product release as shown in Figure 19E.3 2.
Details of the effect of overpressure relief on ABWR performance goals are found in Subsections 19.5.2 and 19.5.3.
l t
i Unintended opening of the overpressure relief
/ rupture is highly unlikely and would be characterized by opening of ne
't e rupture disig place. Unintended operation at a lower l
j pressure, such as during a design basis accident, would not significantly affect offsite doses, since no fuel failures would be expected.
I g _ Failure ofSoiWiiipture dis 8ould be required for this unintended operation. In addition, the l
butterfly-valves could be closed if in line radiation monitoring indicated unexplained flow in the relief line.
6.23.4 Tests and Inspections Complete process systems are pressure tested i
to the maximum practicable extent. Piping l
systems will be hydrostatically tested in their entirety, utilizing available valves or 6.2 11 a%g i
l u- - - - - - - _ --- - - - - - - - - - - - _ - _ -., - -.- - - - - _ - - - -, - - -
---r n-
-W M
w
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0*'E!MtJiripr /nr. 9g g )3 l
' ABM wt=s l-Standard Plant PJV C differentials and flow rates, are documented monitored. Low makeup vaporizer nitrogen outlet l
during the preoperational tests and are used as temperature alarms (only) in the main control base points for measurements in subsequent room. Auxiliary steam feeding the main inerting operational tests.
vaporizer (s) is controlled to regulate the j
inerting vaporizer nitrogen outlet temper -
l During plant operation, the ACS, its valves, ature. Low inerting vaporizer nitrogen outlet l
instrumentation, wiring and other components temperature sounds a local alarm and low-low I
outside the containment can be inspected visually temperature isolates the main inerting line. It at any time. Testing frequencies of the ACS com-is intended that the local panel be attended ponents are generally correlated with testing full-time during all main inerting operations.
frequencies of the associated controls and in-All locally-mounted instruments are easily read
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strumentation. When a valve control is tested, from the local ACS panel. Keylocked switches in j
the operability of that valve and its associated the main control room are provided to override instrumentation are generally tested by the same the containment isolation signal to the valves action. In addition, inservice inspection of all providing nitrogen makeup to the drywell and -
l ASME,Section III, Class 3 components is done in wetwell and the small 50 mm drywell vent line. d
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accordance with Subsection 6.6.5.
Position indication in the main control room is provided for all remotely-operated valves.
l Preoperational tests of the combustible gas control system are conducted during the final Backup purge and the addition of makeup stages of plant construction prior to initial nitrogen is initiated at the operator's startup.
discretion.
The overpressure protection concept was Design details and logic of the designed to minimize any adverse impact on normal instrumentation is discussed in Chapter 7.
operation or maintenance. Initially, several l
rupture disks from a batch of rupture disks could As discussed in 5cction 6.2.5.2, safety-grade i
be tested to verify the opening characteristics oxygen monitoring is provided in the wetwell and and setpoint. The diskdould be replaced every drywell by the CAMS. This monitoring function five years according to normal industry practice. is not used for normal operation. Separate The installation of the diskfould not impact oxygen monitoring is included in the ACS for use containment leakage tests, since disk integrity is during non-accident plant operation to determine expected to be essentially perfect.
when the primary containment is inert and l
l nitrogen purging may be terminated and when the The overpressure protection valves would be primary containment is de-inerted and personnel teste d during preoperational testing and re-entry procedures may be initiated.
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periodically durincdrurveinns testing to verify 35v b sco t e'm 5. 9. 4 3"NE their normally opch position and their ability to The ACS oxygen monitors for assuring safe I
close using AC power and pneumatic air.
personnel entry and an inert condition during l
l startup, normal, and abnormal operating l
l 6.2.5.5 Instrumentation Requirements conditions have a range from 0 to 25 percent at 100 percent relative humidity. The maximum and 7
Separate inerting flow indication to both the minimum inlet temperature to the oxygen monitor drywell and wetwell are provided. Drywell will be 10 and 650C, respectively. Two sample pressure and makeup flow are monitored and points are provided in both the drywell and
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recorded in the main control room. Additional wetwell, high and low in their respective drywell pressure instrumentation, with a lower compartments and in opposing quadrants. Each serpoint, provided in addition to the redundant, airlock is also sampled.
safety-grade drywell pressure instrumentation of the nuclear boiler system. If drywell pressure The sample lines are sized and sloped to exceeds a given setpoint, the makeup and inerting assure draining condensation to the containment.
l valves are closed. The temperature of the makeup and inerting vaporizers nitrogen outlet are l
Amendment /
62-3'
i
- Nd O f '/ '3
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ABWR metoors l
Standar' Plant gyy,
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l 19E.2.8 Severe Accident Design penetrations in the drywell rather than drywell head i
Feature Considerations failure.). To compare the consequences of se,ere l
accidents resultmg in fission product releases ua I
drywell head failure to those with releases through the l
Although the frequency of core damage is very low COPS, MAAP was.used to simulate a senes of severe
' in the ABWR design, features were added to the design ccident sequences f r both release mechanisms.These
' to ensure a robust response of the contamment to a severe accident sequences are desenbed in Secuon j
severe accident. This secuon discusses the important 19E..,...,,. Failure pressure of the drywell head was
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considerauons for the severe accident design features.
assumed to be equal to its median ulumate strength.
1.025 MPa (134 psig). He results of these runs show 19 E.2.8.1 Containment Oserpressure micases d volaule fission products, after 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. for l
Protection System the COPS cases to be several orders of magnitude less than for the corresponding drywell head failure cases.
ABWR has a very low core damage frequency.
The Csl release fractions are compared in Table Furthermore, in the unlikely event of an. accident 19E.2 25. Most accident sequences show this large resulting in core damage, the fission products are difference in releases between drywell head failure and typically trapped in the containment and there is no COPS cases.
i release to the environment. Nonetheless, in order to mitigate the consequences of a severe accident which 19 E.2.8.1.1 Pressure C-tpoint results in the release of fission products and to limit the Deterinisation effects of uncertainties m severe accident phenomena, ABWR is equipped with a Containment Overpressure Sevd ktws e mM 6 enE W l
Protection System (COPS). This system is intended to Optimum pressure setpoint for the rupture disk. The t
l provide protection against the rare sequences in which results of the previous analysis show that it is desirable structural integnty of the contamment is challenged by to avoid drywell head failure. His can be assured by l overpressurization. It has been determined that theserare sequences comprise only 16 p pressure that would begin to challenge the structural Providing a rupture disk pressure setpoint below the j
hypothesized severe accident sequences.
mtegnty of the containment. However, as the pressure p
nt MW, de mne to catammem W aM j
The COPS is part of the/a ospheric control f ssi n Product release is also reduced. Thus, the system and consists of
-inch diameteL setPoint of the rupture disk must optimize these overpressure tchef rupture dis moumed i I DB-inch hne which connects the wetwell ai[n M Wa competing factors: minimizing the probability of j
pece to the drywell head failure while maximtztng time before stack. The COPS provides a fission product release 6Ss n Product release m 6e ennonment.
l point at a time prior to containment structural failure.
(
Thus, the containment structure will not fail. By ne service level C capability of the containment i
engineenng the release point in the wetwell airspace, serves as one indicadon d 6e stnictural imegnty d the the escaping fission products are forced through the containment. As shown in Appendix 19F.,the semce j
suppression pool. In a core damage event initiated by a level C for the ABWR,s 97 psig, hmited by the i
transient in which the vessel does not fail, fission drywell head. Thus, it ts desirable to set the rupture l
i producu are directed to the suppression pool via the
&sk setpoim below 6is value.
j SRVs, scrubbing any potential release. In a severe I
accident with core damage and vessel failure or in a he disdbudon o drywell head failure pressure l
1.OCA which leads m core damage, the fission products and the distnbution of rupture disk burst pressure were will be directed from the vessel and drywell through the also considered m, determining the burst pressure. As t
drywell connecting vents and into the suppression pool stated in Attachment A to Appendix 19F, the drywell l
again insuring any release is scrubbed. Eventually, if head failure pressure is assumed to have a lognormal the containment pressure cannot be controlled, the distnbution with a median failure pressure equal to its.
rupture disk opens. Any fission product release to the ultimate strength of 1.025 MPa (134 psig). The environment is greatly reduced by the scrubbing variability of rupture disk opening pressures is best provided by the suppression pool..
modeled with a normal or Gaussian distribuuon.
Typical high quality rupture disks exhibit a tolerance of In the absence of the COPS, unmitigated m d 6e mean opening pressure. Tests have shown j
overpressurization of the containment will resuit in that this 15% tolerance spans 22 to 2.5 standard failure of the drywell head for most severe accident deviations of the rupture disk population.His analysi>
scenarios (Some high-pressure core melt sequences of the Containment Overpressure Protection System i result in fission product leakage through the moveable 19E M 1-
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