ML18191A361
| ML18191A361 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 11/01/1974 |
| From: | Baldwin R, Murphy D Burns & Roe |
| To: | US Atomic Energy Commission (AEC) |
| References | |
| Download: ML18191A361 (29) | |
Text
CONCEPT FOR MAIN STEAM ISOLATION VALVE LEAKAGE CONTROL SYSTEM WPPSS-74-2-R6 Prepared for Washington Public Power Supply System
- Richland, Washington W.O.
2808
- November, 1974 Prepared by:
Approved by:
R. Baldwin Lead Nuclear Engineer D. Murphy Supervising Nuclear Engineer BURNS ANDROE, INC.
SNOINSSRS ANO CONSTRUCTORS 320 FULTON AVENUE HAMPSTEAD.NEW YORK 11550
CONCEPT FOR MAIN STEAM ISOLATION VALVE LEAKAGE CONTROL SYSTEM TABLE OF CONTENTS Pacae PREFACE I.
Design Bases II.
System Description
III.
Design Safety Evaluation 11 IV.
Tests and Inspection V.
Instrumentation Application 13 13 VI.
Radiological Dose Impact 14
PREFACE This report describes a concept for the main steam isolation valve leakage control system for Washington Public Power Supply System Nuclear Project No.
2 (Formerly Hanford No.
- 2).
This report is in response to the statement made in the Safety Evaluation Report for Hanford No.
2 in Paragraph 4.5 on page 47, and also responds to the request made during the October 17-18, 1973 Post-Construction Permit Meeting as de-scribed in Agenda Item No.
5 in the attachment to the letter from W.R. Butler (AEC) to J.J.
Stein (WPPSS) dated November 20, 1973.
This report is based on a draft report prepared by General Electric for the LaSalle County Generating Station main steam isolation valve leakage control system.
Figure 1
was prepared by Burns 6 Roe based on preliminary information provided by General Electric.
Main Steam Isolation Valve Leaka e Control S stem (MSIV-LCS').
The MSIV-LCS controls and minimizes the release of fission pro-ducts which could leak through the closed Main Steam Isolation Valves (MSIV's) after a
LOCA by directing the leakage through a bleed line into an area served by the Standby Gas Treatment System (SGTS) for processing prior to release to atmosphere.
Desi n Bases It a.
General Criteria.
The following general design cri-teria represent system design requirements.
1.
The offsite dose rate shall not exceed the guide-lines of 10 CFR Part 100 following a design basis LOCA resulting from a complete severance of the recirculation line.
2.
The fission product release model shall be based upon TID 14844.
I 3.
= The MSIV-LCS shall not prevent the SGTS from per-forming its function.
4.
Steam discharge from the MSIV-LCS shall be directed
.such that it will not affect functioning of struc-
- tures, systems, or components important to safety.
b.
Specific Criteria.
The following specific criteria delineate system performance requirements.
1.
.The MSIV-LCS,and any necessary, subsystems, shall be designed. in accordance with seismic Category I requirements.
2.
The MSIV-LCS,and any necessary subsystems, shall be capable of performing its safety function, when necessary, considering the design basis event.
effects including:
(a) internally generated mis-
- siles, (b) the dynamic effects associated with pipe whip and jet forces from the LOCA event and (c) normal operating and accident-caused local environmental conditions consistent with the de-sign basis event.
3
~
The MSIV-LCS shall be capable of performing its intended function following any single active component failure (including failure of any one of the main steam line isolation valves to close.)
4
~
The MSIV-LCS shall be capable of performing its intended function following a loss of all off-
>>te power coincident with the postulated design basis LOCA.
5.
The MSIV-LCS shall be designed with sufficient capacity and capability to control the leakage from the main steam lines consistent with con-tainment integrity under the conditions asso-ciated with the postulated design basis LOCA.
6.
The MSIV-LCS is manually initiated and controlled and shall be designed to permit actuation in a
-time period no sooner than 10 minutes following the postulated design basis LOCA.
The required actuation time period shall be consistent with loading requirements on the emergency electrical busses and with reasonable times for operator information, decision, and action.
7.
Instrumentation and controls necessary for the
.functioning of the MSIV-LCS shall be designed in accordance with standards applicable to nu-clear plant safety-related instrumentation and
~control systems.
8.
The MSIU-LCS controls shall be provided with in-terlocks actuated from appropriately designed safety systems or circuits to prevent inadver-tent MSIV-LCS operation.
9.
The MSIV-LCS shall be designed to permit testing of the operability of controls and actuating de-vices during power operation to the extent prac-tical, and testing of the complete functioning of the system during plant shutdowns.
10.
The MSIV-LCS shall be designed so that effects resulting from a sealing system single active component failure will not affect the integrity of the main steam lines or MSIV's.
c.
Codes and Standards.
The detailed design and construc-tion criteria are provided by published
- codes, stan-dards, regulatory guides and recommendations.
All piping systems and components for the MSIV-LCS will comply with the applicable
- codes, addenda, code cases and errata in effect at the time the equipment is pro-cured.
Currently in effect is the:
ASME Boiler and Pressure Vessel Code Section III, Nuclear Power Plant Components.
The piping and com-ponents at the point of connection on the main steam line and including the pressure retaining system valves are Class l. All other piping and components are Class 2.
Subsections NA, NB, and NC of the Code apply to the MSIV-LCS.
The equipment and piping of the MSIV-LCS, in order to meet specified seismic capabilities, are designed to the requirements of Seismic Category I.
This class includes all structures and equipments essential to the safe shutdown and isolation, of the reactor, or the failure or damage of which could result in undue risk to the.chealth and safety of the public.
Refer to Table 1, "Reactor Coolant Pressure Bound-ary Materials" for a presentation of the specifications which generally apply to the selection of materials used in the MSIV-LCS.
Nonmetallic materials such as lubricants,
- seals, packings, paints and primers, insula-tion, as well as metallic materials, etc.,
are se-lected as a result of an engineering review and evalu-ation for compatibility with other materials in the system and the surroundings with concern for chemical, radiolytic, mechanical and nuclear effects.
The MSIV-LCS shall be designed to IEEE Std. 279-1971 (Criteria for Protection Systems for Nuclear Power Generating Stations),
IEEE Std. 323-1971 (General Guide for Qualifying Class I Electric Equipment for Nuclear Power Generating Stations) and IEEE 344-1971 (Guide for Seismic Qualification of Class I Electric Equip-ment for Nuclear Power Generating Stations).
II.
S stem Descri tion a.
General Descri tion.
The MSIV-LCS is designed to minimize the release of fission products which could by pass the Standby Gas Treatment System (SGTS) after a reactor LOCA.
This is accomplished by directing the, leakage through the closed. main steam isolation valves (MSIV's) to a bleed line into an area served by SGTS.
The flow is effected by a small blower which maintains the pressure in the steam lines. negative with respect to atmosphere, thus assuring that the MSIV leakage will pass through the blower and on into SGTS prior to release to atmosphere.
The flow diagram of the MSIV-LCS is shown on the PAID (Figure l).
As indicated, two independent sys-tems (an outboard system and an inboard) system are provided to accomplish the leakage control function.
The inboard system receives power from one electrical division and the outboard system from the other elec-trical division of the emergency power supply.
The outboard system is connected to the segments of the 'main steam lines, between fast closing MSIV's outside containment and the downstream block valves (Figure l).
The bleed line from each 'main"'steam line connects to a bleed header.
The bleed header outlet is provided with two valves in series to permit the main steam lines to be depressurized by venting fol-lowing a LOCA.
A parallel set of valves is provided which are opened following depressurization to con-nect the blower suction to the steam lines.
Pressure sensors are used for depressurization interlock con-trol to prevent any accidental actuation of the sys-tem during normal reactor operation.
Another pres-sure sensor is used for interlock control on the valves in the line to the blower suction to prevent accidental actuation when pressure is appreciably greater than atmospheric.
Pressure indicators are provided for monitoring the pressure in'he main steam lines between the fast closing MSIV's outside containment and the downstream block valves.
The major flow to the blower suction is dilution air from the building served by stand-by gas treatment.
This dilution air greatly reduces the temperature of the MSIV leakage as it passes through the blower.
A di-
lution air flow indicator is provided to monitor blower flow rate.
A timer is used to actuate a high steam line pressure alarm within a pre-set time period after system actuation if a sub-atmospheric main steam line pressure is not established.
Manual switches are provided for functional testing of the bleed valves.
The bleed line depressuriza-tion branch is to be terminated at an appropriate location where steam can be discharged; and processed by SGTS while depressurizinq the steam lines, without adversely affecting safety related equipment.
The blower discharge line is terminated at, a location where the discharge flow will pass to the stand-by gas treatment system.
The inboard system is connected to the segments of the main steam lines between the fast closing MSIV's outside containment (Figure 1).
An individually controlled bleed line is provided for each main steam line.
For each bleed line two bleed valves, which are of the motor operated gate type, are connected in s'eries followed by a flow element and a motor operated by-pass valve.
Flow through the four flow elements passes to a common blower which dis-charges to a building volume served by stand-by gas treatment.
Discharge through the flow element by-pass valve is similarly routed to stand-by gas treat-ment.
Pressure sensors are used for interlock con-trol to prevent any accidental actuation of the sys-tem during normal reactor operation.
Pressure indi-cators are provided for monitoring the pressure in the main steam lines between the fast closing MSIV's outside containment and those inside, containment.
A delay timer and pressure sensor are used for reclos-ing the bleed valves aft.er the inboard system is activated in case of gross leakage through the in-board MSIV.
Another timer together with a high flow limiter, is used to monitor and reclose the bleed valves should the total leakages through both MSIV's exceed the high flow set point.
Electric heaters are used, one at the low point of each bleed line, to boil off any condensate and pass it through the flow limiter.
A flow indicator is provided to moni-tor blower flow rate.
Manual switches are provided for functional testing of the bleed valves.
The bleed line depressuriza-tion branches are to be terminated at a location in the building volume served by the SGTS where steam can be discharged, while depressurizing the steam lines, without adversely affecting safety related equipment.
The blower discharge line is also term-inated at a location where the discharge flow will pass to the standby gas treatment system.
b.
S stem Operation.
The MSIV-LCS will be actuated manually (both inboard and outboard system) after it has been ascertained that a LOCA has occuired and after pressure in the steam lines is below the pressure permissive interlock set point.
In the outboard system the valves in the depressuri-zation branch line are opened to permit the steam lines beyond, the fast closing MSIV's outside con-tainment to depressurize and the'blower is started.
When the steam lines have depressurized to approxi-mately atmospheric pressure the valves in the branch line to the blower are automatically opened and the valves in the depressurization branch are automa-tically closed.
This establishes a sub-atmospheric pressure in the steam lines and MSIV leakage is routed to standby gas treatment.
If a sub-atmos-pheric pressure is not established in the main steam lines within the estimated time required to depres-
- surize, the timer will actuate the high pressure alarm, indicating failure of a component required for the system to function.
Inboard system actuation automatically depressurizes the main steam lines through the flow limiter by-pass valves which reclose automatically to route the flow through the flow limiter.
The electric heaters are turned on from the system actuation signal.
The blower also starts from the system actuation signal and establishes a sub-atmospheric pressure in the main steam lines after the flow limiter by-pass valves re-close.
MSIV leakage is routed to standby gas treat-ment during both depressurization and exhaust stages of operation.
The'nboard system is designed to automatically re-close in the event of excessive MSIV leakage.
Auto-matic reclosure capability is provided on the bleed system for each individual steam line.
Each steam line has its own bleed valves, electric heater, flow limiter, flow limiter by-pass valve, timers and pressure instrumentation.
Assuming that the leak-age through thy isolation valves is at the techni-cal specification value, the depressurization ofthe steam line volume between the MSIV's can be com-puted as shown in Figure 2 for a typical BWR.
The depressurization rate is varied as a function of the equivalent length of the bleed-off line flow resis-tance.
Figure 3 shows the steam line pressure decay curves with the bleed-off line equivalent to 100,
- 200, 300, and 400 ft of 1" Schedule 80 pipe.
For illustration
- purposes, assume the bledd-off line is 100 ft.
The steam line pressure between the two MSIV's one min-ute after the system initiation will be approximately 19 psia.
The first timer circuit will open for one minute after system initiation.
After a period of one minute, if the steam line pressure between MSIV's is over 5 psig, the bleed valves will close.
Over-pressure indicates gross inboard MSIV leakage.
Otherwise, the valves will be kept open and bleed>off continues.
After another aninutq the second delay timer will close the bypass gate valve and direct the bleed-off flow through the flow meter.
Another one-half minute is allowed by the third timer for the space between MSIV's to drop to subatmospheric pres-sure and for the flow to settle down to a steady value reflecting MSIV leakage flow. If the measured flow is lower than the preset value, the bleed-off will continue.
The effects on the pressure decay with respect to either one of the isolation valves in the same main steam line are shown in Figure 3.
A gross leakage, such as the inboard isolation valve fails to close, will cause the bleed valves to be'isolated after one minute.
Excessive leakage through either the in-board or outboard MSIV will close the bleed-off valves after two minutes.
c.
E ui ment Description
~Pi in'.
Process piping is 1 in-or l-l/2 in.
sch 80 welded carbon steel pipe throughout.
That portion from the main steam piping between
, MSIV's up to second MSIV-LCS isolation valve is designed and constructed to ASME III Class 1.
The remainder is designed and constructed to AMSE III, Class 2 code.
The components and piping installation is designed to withstand seismic Category I loads.
2.
Valves.
Motor operated to provide about 12"/min opening and closing speed and constructed to the ASME III code class appropriate to the piping in which they are installed.
3.
4 ~
Blower.
Rated at about 50 cfm at about -20 in.
H20 suction pressure.
I
. LCS will add about 50 scfm of load to the SGTS during the exhaust phase.
This is less than 2% of the rated capacity of the SGTS and will be conditioned to be compatible with the SGTS temperature and humidity operating limits.
The MSIV-LCS will add no more than 80 lbs of s'team to the building volume served by the SGTS during steam line depressurization, where it will be diluted before entering the SGTS.
III.
Desi n Safet Evaluation.
A point by point evaluation in conformance with the design bases of Section I follows.
The numbering of the bases is retained.
The components and structures necessary to the performance of the mission of the MSIV-LCS are designed and constructed to operate during and following the application of seismic Category I design loads in conjunction with operating loads associated with the LOCA.
2.
The MSIV-LCS equipment is arranged so as to mini-mize the exposure of the system components to
- missiles, pipe deformations and jet forces by limiting the equipment in the vicinity of the steam lines and other high energy lines to only those valves and piping necessary for pressure
. boundary isolation.
The remaining equipment is
- located outside the steam tunnel and is removed and shielded from such effects by'he concrete walls of the pipe tunnel.
The inboard and out-board systems are physically separated.
The equipment, is designed to operate under the ex-pected LOCA environmental conditions appropriate to the equipment location.
3.
The MSIV-LCS will function following any active component failure (including failure of any one MSIV to close) by virtue of two redundant systems.
The systems are independently powered from dif.-
ferent divisions of the power supp'ly.
4, The use of the engineered safeguard power source
'to power the components of the system assures system operation during the loss;of offsite power.
5.
The discussion of the activity released to the environment by way of the SGTS is discussed in the radiological evaluation in Section VI.
I 6.
The manual initiation of the system need not occur until the-,,pressure of steam trapped be-tween the isolation valves decreases to the vessel pressure and abnormally high radiation is present.
The pressure decay between the MSIV's due to MSIV leakage at an estimated maxi-mum rate of 11.5 scfh 9 29 psid, is such that the line pressure will exceed vessel pressure
'or about one hour at which time the vessel and trapped line pressure will be about 35 psia.
There would be no need to actuate any portion of the MSIV-LCS when the pressure between valves is higher than containment pressure since clean
- steam, trapped between the valves when they "closed, would be leaking toward the containment.
As set forth in Section I-b (6), the emergency electrical busses are well able to "provide the estimated 15 KW required for system operation.
7.
The instrumentation necessary for control and status indication of the MSIV-LCS are classified
's essential
'and as such are designed and quali-fied, per IEEE 344-1971, IEEE 279-1971 and IEEE
'23-1971, to function under seismic Category I and LOCA environmental loading conditions appropri-ate to their installation with the control cir-cuits designed to satisfy the mechanical and electrical separation criteria.
8.
The system will detect high steam line pressure and prevent system actuation and also detect high leakage and prevent excessive release of leakage to the SGTS.
9.
Components of the system downstream of the system
- isolation valves may be tested at any time during
~ plant operation.
The isolation valves may also be operated sequentially at any time during plant operation.
Simultaneous operation of the isolation
, valves and complete system testing or isolation
~ valve leak testing, can be performed only during reactor shutdown in order not to interfere with normal plant operation.
10.
Double series isolation valves electrically and physically separated and operated by separate sensors and controls insure that no single ac-tive failure will affect the integrity of the main steam lines.
'h In addition, this system, by exhausting leakage steam and gases, does not introduce or expose the steam piping or valves to thermal or mass loadings different from that experienced in normal isolation
.valve service and, therefore, cannot affect or de-grade the sealing ability of the MSIV's.
The additional design criteria of I-a and I-c are
~,discussed above except the I-a (3) which requires that, the gas treatment load of the MSIV-LCS not exceed the capacity of the SGTS.
The maximum pro-cess loads imposed by the MSIV-LCS are 80 lbs of steam 9
35 psig saturated initial conditions vented to the, building volume served by the SGTS, followed 10
by the continuous MSIV leakage flow.
The initial discharge will have no significant effect on building pressure buildup.
The continuous flow is considered negligible
.compared to the SGTS rated flow.
The MSIV-LCS conditions the exhaust.
temperature and humidity to the requirements of the SGTS prior to delivery to the SGTS inlet.
a.
Failure Anal sis.
Inasmuch as the MSIV-LCS is con-structed to withstand seismic Category I and LOCA accident loadings, no passive (i.e., structural) failures are considered.
The consequences of single active component or sub-system failures are as follows:
Malfunction Conse uences Inboard MSIV l of 4 fails to close (excessive leakage)
OUTBOARD LCS System functions to collect leakage through 3
sets of 2 MSIV's in series and one outboard MSIV and deliver it to SGTS for treatment.
Inboard system isolates open MSIV but is available to collect leakage from 3 of 4
inboard MSIV's, but not re-quired.
Outboard MSIV l of 4 fails to close (excessive leakage)
Outboard LCS system functions to collect leakage through 3
sets of 2 MSIV's in series and one inboard MSIV, and deliver it to SGTS for treatment.
Inboard LCS is available to collect leakage from 3 of 4
inboard MSIV's and deliver it to SGTS for treatment.
The inboard LCS serving the failed.
outboard MSIV will have auto-matically recXosed.
Malfunction Downstream Block Valves fails to close (excessive leakage)
Outboard LCS functions but capacity is insufficient to positively control MSIV leak-age.
Inboard LCS functions to collect leakage through inboard MSIV and deliver it to SGTS for treatment.
Inboard LCS,.'-
fails to oper-blower ate, or loss Inboard LCS emer-of power gency power Inboard LCS switch Inboard LCS inoperative.
Outboard LCS powered by other electrical division functions to collect leak-age through 4 sets of 2
MSIV's in series and de-liver it to SGTS for treat-ment.
Outboard LCS blower Outboard LCS=-:
power supply Outboard LCS switch Outboard LCS bleed valve fail to oper-ate, or loss of power, or fails to open Outboard LCS inoperative.
Inboard LCS powered by the other division of emergency power operates to collect leakage through 4 inboard MSIV's and deliver it to SGTS for treatment.
Inboard LCS BleeQ valve fails to open Inboard LCS collects leak-age from 3 of 4 inboard MSIV's.
Outboard LCS func-tions to collect leakage through 4 of 4 sets of 2 MSIV's in series.
Inboard LCS Depressuri-zation Valve fail to open One main steam line between MSIV will not depressurize in time giving a false in-board MSIV excessive leak-age signal, and resulting in isolation of 1/4 of in-board LCS.
3/4 of inboard LCS continues to function.
12
Com nent
,Malfunction Outboard LCS Depressuriza-tion Valve fails to close Gas from SGTS building volume is recirculated thru blower, decreasing its effective cap-acity.
The LCS continues to function inboard.
Inboard LCS heater fails to heat Leakage relative humidity will be high, condensation may plug pipe and decrease inboard LCS capacity.
Outboard system continues to function.
IV.
Tests and Ins ections a ~
Prep erational Tests.
Preoperational tests are con-ducted prior to initial startup.
The tests assure functioning of all controls, instrumentation and all active components.
Functional testing and flow meas-urements are accomplished with compressed air.
Com-pressed air testing is conservative compared to opera-tion of the system with steam blowdown under post ac-cident conditions.
For the hot steam blowdown case, compared to the preoperational test case with 70 F
air, the space between MSIV's will depressurize faster and the 5 psig trip shtting has additional margin against reclosure.
System reference characteristics such as timer setpoints and flow rates are documented during the preoperational testing and are used as base points for measurements obtained in subsequent opera-tional tests.
b.
0 erational Tests.
During plant operations,
- valves, piping, instrumentation, wiring, and other components outside the steam tunnel can be inspected visually at any time.
Components inside the tunnel can be in-spected only when it is open for access.
Valves loc-ated in the tunnel are capable of being exercised peri-odically during normal operation.
Test frequency is consistent with the requirements of the Plant Operating Technical Specifications.
V.
Instrument A lication.
Refer to Figure l.
13
VI.
Radiolo ical Dose Im act a.
Activit Released to Environment.
The QDose or increase in dose by application of the MSIV-XCS will be dis-cussed in the FSAR.
14
TABLE 1'EACTOR COOLANT PRESSURE BOUNDARY MATERIALS
~Com anent Form Material Specification (ASTM/ASME)
Reactor Vessel Rolled Plate or Low Alloy Steel SA 533 Gr.
B or
- Heads, Shells Forgings Welds Low Alloy Steel SA 508 C1.2 SFA 5.5 Closure Flange Forged Ring Low Alloy Steel SA 508 Cl.2 Welds Low Alloy Steel SFA 5.5 Nozzles
'Cladding Forged Shapes Welds Weld Overlay Low Alloy Steel SFA 5.5 Austenitic Stainless Steel SFA 5.9'or SFA 5.4 TP 309 with carbon content on final surface limit to 0.08% maximum Low Alloy Steel 'A 508 C1.2 Control Rod
. Pipe Drive Housings Welds Austenitic Stainless Sterol Stainless Steel SA 312 SFA 5.9 TP." 308 or 316 or SFA 5.4 TP.
308 or 316 In-Core Housings Pipe Welds Austenitic Stainless Steel Stainless Steel SA 213 SFA 5.9 or 5.4 TP.
308L or 316L Additional RCPB component materials and specifications to be used are specified below.
Depending on whether impact tests are required and, depending on the lowest service metal temperature when impact tests are required, the following ferritic materials and specifications are to be used:
Pipe Valves Fittings SA-106" Grade B; SA-333 Grade 6 and SA-155 Grade KCF-70 SA-105 Grade II> SA-350 Grade LFl and SA-216 Grade WCB SA-420 Grade WPLl or WPL6 15
Table 1 (Continued)
Bolting SA-193 Grade B7> SA-194 Grades 7 and 2H; and SA-540 Grade B22, B23 and B24 Welding Material SFA-5.1 (E-705, E-7016, E7018)
SFA 5,5 (E-7010A1, E-7015, E-7016, E-7018)
SFA-5.17, SFA-5.18 For those systems or portions of systems, such as the reactor recirculation
- system, which require austenitic stainless
- steel, the following materials and specifications are to be used:
Pipe Valves Pump Flanges Bolting SA-376 Type 304; SA-312 Type 304; SA;358 Type 304.
SA-182 Grade F-304>
SA-351 Grades CF-8 and CF-8M SA-182 Grade F-'304'A-351 Grades CF-8 and CF-8M SA-182 Grade F-316 SA-193 Grade B7g SA-194 Grades 7 and 2H; SA-540 Grades
- B22, B23 and B24 Welding Material SFA-5.4 (E308-15, E308L-15, E316-15)g SFA 5 9 (ER 308'R 308Lg ER 316)
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FLOW DIASitAM IIAINS'fEAVISOLATIONVALVE LEAKASE CONTltOL SYSTEM.
RCACTOR SUI Dirlt WASHINGTON PUEMC POWER SUPPLY STTtCN
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Figure 2 Main Steam Line Between Isolation Valve Decompression vs Elapsed Time
DECO,"Jt? RESSION BLEEDNFF n
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'S 30 INCREASING INBOARD ViSIV LFAKAGE PAESSURE SrVITCH r
SET PO<NT INBOARD ViSIV
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Figure 3-Steam Line Pressure Between MSIV During Decompression and Bleed-Off