ML19309B109
| ML19309B109 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 03/25/1980 |
| From: | PUBLIC SERVICE CO. OF COLORADO |
| To: | |
| Shared Package | |
| ML19309B107 | List: |
| References | |
| EE-21-0004, EE-21-4, P-80064, NUDOCS 8004030132 | |
| Download: ML19309B109 (17) | |
Text
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Enclosure (2) to P-80064 4
I FORT ST. VRAIN INSERVICE INSPECTION AND TESTING PROGRAM l
1 SURVEILLANCE REQUIREMENTS REVIEW FOR THE PRIMARY COOLANT SYSTEM i
i HELIUM CIRCULATORS (21) i f
EE-21-0004 Rev. 1 March 25, 1980 4
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l EE-21-0004 Rev. 1 p.1 REPORT EE-21-0004 FORT ST. VRAIN INSERVICE INSPECTION AND TESTING PROGRAM SURVEILLANCE REQUIREMENTS REVIEW FOR THE PRIMARY COOLANT SYSTEM HELIUM CIRCULATORS A review was performed of the current' surveillance re-quirements for the primary coolant system helium circulators.
As ' result of this review, additional or modified surveillance requirements may have been recommended to meet the criteria established for the Fort St. Vrain inservice inspection and testing program which has been presented to the Nuclear Regulatory Commission.
This report consists of two parts, each one dedicated to the following equipment items:
Part A:
Helium circulators (compressor machine)
Part B:
Helium shutoff valves; diffuser and inlet ducting.
A list of the reference documents used in the course of this review is given individually for each part of this report.
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EE-21-0004 nev, 1 A.1
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REPORT EF-21-0004 PART A
'1 SURVEILLANCE REQUIREMENTS FOR THE FORT ST. VRAIN PRIMARY COOLANT SYSTEM (21)
.fELIUM CIRCULATORS (COMPRESSOR MACHINE)
I
EE-21-0004 Rev. 1 A. 2 1.
INTRODUCTION A review was performed of the current surveillance requirements for the primary coolant system helium circulator machines.
These machines, referred to in this report as circulators, include the drive shaft with its bearing and seals, the steam and water turbine drives, the compressor wheel, the static brake and shutdown seal, as well as the structures and pipes within the PCRV penetration which route the drive and service fluids to the machine.
The review included the reference documents listed in section 5 of this report and, in particular, the proposed ASME Code Section XI, Division 2 Draft.
An explanation is provided when the current and recommended surveillance operating experience with the circulators at the plant.
2.
SURVEILLANCE CLASSIFICATION The Fort St. Vrain helium circulators are used for core cooling during normal plant operation at power, or during shutdown with the reactor pressurized or depressurized.
The circulators also have a safety function where at least one of them assures emergency core cooling following all postulated accident conditions, except for design basis accident No. 1 (DBA 1) where total loss of forced circulation is assumed.
According to criteria 2.lb, 2.2b, and 2.3a of Ref.
1, the circulators are active equipment items assigned to surveillance class S2.
There are two active sub-components in each circulator, namely a shutdown seal and a brake.
The brake function is to prevent self turbining of the circulator rotor when the shutdown seal is to be applied.
The shutdown seal function is to prevent outleakage of primary coolant along the circulator shaft.
Actuation of both brake and shutdown seal is either automatic through the plant protection system or remote manual.
According to criteria 2.lc, 2.2c, and 2.3b of Ref.
1, the brake and shutdown seal is assigned to surveillance class S3.
The following applicable criteria of Ref. 1 are considered when performing the review of the surveillance requirements.
The operational readiness of compressors assigned to surveillance class S2 is to be demonstrated by normal operation, or by surveillance testing those compressors not normally in operation, at least once each quarter, according to rules and requirements based on the Draft ASME Code,Section XI Division 2 (criteria 3.2.lb).
The operational readiness of automatic isolation valves assigned to surveillance class S3 is to be demonstrated by normal operation, or by surveillance testing at least once each year to exercise those
EE-21-0004 Rev. 1 A.3 2.
(cont.)
values which do not normally operate, accordi.ng to rules and requirements based on the Draft ASME Code Section XI, Division 2 (criteria 3.2.2c).
3.
OPERATIONAL READINESS 3.1 OPERATIONAL READINESS OF THE CIRCULATORS a)
Current surveillance requirements:
Technical specification SR 5.2.7 addresses the surveillance of the circulator water turbine drive system which is required for the circulator to perform its safety function.
Item (a) of SR 5.2.7 includes the circulator as part of the system, the remaining items applying to circulator auxiliary system equipment items, which will be covered in a separate report.
This specification requires that one circulator and the associated water supply valving in each loop be functionally tested annuall: by operation on water turbine drive using feedwater, condensate, and boosted condensate (supplied to the firewater booster pumps at firewater pump discharge pressure).
Technical specifications SR 5.2.8 and SR 5.2.9 address the surveillance for the bearing water supply, but have no requirements directly related with the circulator.
Technical specifications SR 5.2.17 and SR 5.2.18 specify the requirements for inspection of the circulators.
SR 5.2.17 addresses in particulas. a one-time inspection of one Pelton wheel to assure the adequacy of the change in the design following the discovery of cracks in Pelton wheel coupling original design.
SR 5.2.18 requires that one circulator unit be removed in its entirety from the PCRV and be thoroughly inspected for signs of abnormal wear or component degradation.
Such in-spection includes examination of bearing surfaces, seal sur-faces, brake system, buffer seal system, and labyrinth seals.
The compressor wheel rotor, the turbine wheel and the Pelton wheel are to be inspected for both surface and subsurface defects in accordance with the appropriate methods, procedures, and associated acceptance criteria specified for Class 1 components in Subarticle NB-2500,Section III of the ASME Code.
The frequency for such inspection is for one circulator to be removed for inspection at the time of the first main turbine generator overhaul, then a previously uninspected circulator i
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EE-21-0004 Rev. 1 A.4 3.la (cont.)
is removed for inspection at approximately 10 year intervals thereafter.
The examination results are to be submitted to NRC for review, and are to be evaluated to determine the need for scheduling additional future inspections.
b)
Recommended surveillance requirements:
b.1) General description of the helium circulators:
The circulators are single stage compressors.
The com-pressor wheel is attached at one end of the shaft within the reactor cavity.
The ottar end of the shaft, in the interspace betwee. primary and secondary closures, is provided with a steam turbine and with a water turbine (Pelton wheel).
The steam turbine can be driven by either cold reheat steam or, when no such steam is available during startup and shutdown, by steam produced by the auxiliary boiler.
The Pelton wheel provides a means of driving the compressor when no steam is available.
The drive fluid in this case can be either one of several diverse water supply sources:
feedwater, condensate, or firewater.
Operation of the circulators on water drive is sufficient for plant startup and snutdown, as well as for residual heat removal following accidents.
The bearings are water lubricated.
A controlled leakage i
l buffer helium seal prevents bearing water from leaking into the reactor cavity and primary helium from leaking out of the i
reactor cavity.
Only the bearings and bearing water supply have a function related to circulator operation; the buffer helium seal functions as part the reactor coolant boundary.
b.2) Surveillance of the helium circulators:
As outlined in the basis for technical specification SR 5.2.18, the circulators operate during normal operation of the plant, and their performance is monitored by instruments provided to measure compressor differential pressure and flow, bearing temperatures, bearing water temperature and flow, J
buffer helium flow, and shaft speed and vibration.
During operation of the plant at power, the circulators normally operate on steam drive.
During operation of the plant at shut-down, the circulators normally operate on water drive.
There-fore, operation of the circulators is adequate to demonstrate their operational readiness on both steam and water drive, according to criteria 3.2.lb of Ref.
1.
Additional assurance of operational readiness of the circulators on water drive is provided by the surveillance test of SR 5.2.7a-A which requires that each circulator be operated at conditions simulating the several alternate water drive fluids, and that a verification be made that the minimum required circulator spc d corresponding to each water drive supply can be achieved.
'1 EE-21-0004 Rev. 1 A.5 3.lb (cont.)
Preliminary results of the examination performed on the Pelton wheel as required by technical specification SR 5.2.17 have been reviewed.
No defects or area of concern were identified which would require that further inspection or examination be per-formed in addition to that required by technical specification SR 5.2.18.
Since the adequacy of the Pelton wheel design modification has been demonstrated, it is recommended that the surveillance requirements of technical specification SR 5.2.17 be deleted.
The surveillance inspection required by SR 5.2.18, in addition to the previous test and to monitoring of normal operation, provides assurance that no abnormal wear or component degradation occured during circulator operation, and allows an assessment of circulator operating life, to confirn that the circulators will be available to perform their safety function throughout plant lifetime.
Preliminary results of the first circulator inspection required by technical specification SR 5.2.18 have also been reviewed.
No evidence of abnormal wear or component degradation was indicated during this inspection, and therefore, no area of concern has been raised which would require that 'he next inspection be performed at shorter intervals than currently required.
Since the objective was to verify the design adequacy of these first of a kind machines (similar to the Pelton wheel inspection required by technical specification SR 5.2.17), the first circulator inspection was very thorough and complete.
In order to examine such items as the bearings, the brake and shutdown seal, and the shaft, circulator parts exposed to primary coolant had to be decontaminated to allow for manual handling and complete disassembly.
It is expected that the contamina-tion level of the next circulator scheduled to undergo examination will be greater than experienced with the first one, which re-quired chemical decontamination.
Decontamination of the next circulator may not be adequate to allow manual handl.ng and inspection.
Development of tooling to perform theae operations remotely would be a major task and increase the risk of damaging the equipment and having to replace such parts.
Considering the extensive capability available at the plant to monitor circulator performance, particularly shaft vibrations and bearing temperatures as well as bearing water temperature and flow, it is recommended that future inspections be limited to the currently specified examinations of the compressor rotor, the turbine rotor and the Pelton wheel and that other components accessible without further dissassembly be visually examined.
Ea-
EE-21-0004 Rev. 1 A.6 3.lb (cont.)
The recommended surveillance exceeds the requirements of Rcf. 1 and, therefore, is considered adequate.
c)
Proposed ASME Code requirements:
Subsection IGQ of the proposed Code gives the requirements for inservice testing of core auxiliary cooling system com-pressors.
It should be noted that the proposed Code was written for the large HTGR design which was provided with auxiliary co.? pressors and which, conttIry to Fort St. Vrain, were not used during plant operation.
The main steam turbine driven circul ; rs of the large HTGR design are not covered by the proposed Code (see IGQ-1100: Scope).
Consequently, the inservice tests are divided in a monthly readiness test (essentially a start up test and short time operation in con-ditions which do not perturb normal operation) and an annual full flv' test at maximum service speed and with flow condi-tions ar.
gas compositions thu; demonstrate the intended service for the compressor (IGQ-3110 and IGQ-31'.0).
During both tests, several parameters characteristic of compressor operation are to be measured or observed:
rotative speed, absolute compressor inlet temperature and pressure, differential pressure across the compressor, vibration amplitude, lubricant level or pressure, bearing temperature.
In addition, the flow-rate is to be measured during the annual full flow test.
P At Fort St. Vrain, the circulators are in permanent operation.
Monitoring the parameters characteristic of their operation exceeds the proposed Cc'a requirement for a monthly test intended to demonstrate the operational readiness of circulators not normally in operation.
The surveillance test of SR 5.2.7a-A is equivalent to the full flow test required by the proposed Code.
The difference in test frequency for each machine is justified:
in the large HTGR, all the auxiliary circulators are required to be operable, while at Fort St. Vrain, only one circulator in each loop is required to be o prable (LCO 4.2.1), so that both tests provide the same degree c' assurance that the required minimum number of circulators will be available to perform the safety function.
The proposed Code has no requirement for circulator exami-nation, which is recommended for the Fort St. Vrain circulators.
Therefore, the recommended surveillance generally excoeds the proposed Code requirements.
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EE-21-0004 Rev. 1 o
A.7 s
3.2 OPERATIONAL READINESS OF THE BRAKE AND SHUTDOWN SEAL a)
Current surveillance requirements:
The shutdown seal and brake systems are to be examined during the circulator examination required by technical spe-cification SR 5.2.18, as out ined in paragraph 3.la above.
There are no further current surveillance requirements.
b)
Recommended surveillance requirements:
The brake and shutdown seal are actua~ted each time that a circulator is shutdown or tripped and the auxiliaries isolated.
It is expected that, between normal and abnormal occurences, each brake and shutdown seal will be exercised about once every year.
Therefore, normal operation provides the exercising frequency required by criteria 3.2.2c of Ref. 1 for automatic isolation valves (both the brake and shutdown seal are con-sidered analagous to automatic isolation valves).
Proper operation of the brake and shutdown seal is monitored by in-strumentation of the circulator ausiliary systems, and a malfunction or failure would be raadily detected.
Therefore, normal operation is considerea on adequate means of assuring operational readiness of the circulator brakes and shutdown seals.
No additional surveillance is recommended for these components.
c)
Proposed ASME Code requirements:
Since the brake actuator can be compared to a valve actuator, and since the brake is not required to be leaktight, the proposed Code requirements for category B valves (IGV-2100) are considered applicable in this review.
The shutdown seal can also be compared to a Code category B valve, since leaktightness is only required when a circulator is shutdown, the reactor is pressurized and there is no buffer helium.
Further, seat leakage is not expected to result in unacceptable releale of radioactivity, since backup isolation can be provided by a water seal in the bearing cartridge.
IGV-3412 raquires that valves, which cannot be full stroke exercised during plant operation (which is the case of the brake and shutdown seal), be.part stroke exercised at least once every three months and full stroke exercised during each cold shutdown.
d)
Interlocks are provided in the brake and shutdown seal actuation systems which prevent their operation while the cir-culator operates.
Therefore, partial stroking is not practical during plant operation.
Normal actuation of the brake and shutdown seal otherwise meets the proposed Code requirement for valve exercising at each shutdown for the circulators which do not operate during that shutdown.
EE-21-0004 Rey, 1 A.8 3.3 OPERATIONAL READINESS OF INSTRUMENTATION AND CONTROLS The surveillance for the circulator speed, vibration and temperature instrumentation, which appears on system diagrams PI-21-1 and PI-21-2, will be reviewed in a separate report covering the circulator auxiliary system.
4.
STRUCTU"aL INTEGRITY The reructural integrity of those components of the cir-culators which function e.s primary and secondary closures for the PCTS penetrations bas been reviewed in the reports on the PCRV ead PCRV auxilia.y systems (references EE-ll-0001 and EE-ll-0002).
The structural integrity cf those components of the cir-culators which direct drive steam and water to and from the circulators will be reviewed in the report which cavers the secondary coolant system (system 22).
The structural integrity of those components of the cir-culators which direct service fluids to-and from the circulators will be reviewed in the report which covers the circulator auxiliary system (system 21).
The structural integrity of the remaining parts of the circulators is assured by the examination required by technical specification SR 5.2.18 as outlined in paragraph 3.1 above.
5.
LIST OF REFERENCES t
References:
1.
PSC report EE-SR-0001.
Surveillance inspection and test criteria for the Fort St. Vrain nuclear generating station.
2.
Fort St. Vrain FSAR - Sections 4.1, 4.2.1, 4.2.2, 6.2 3.
FSV system description - SD-21-1, SD-21-2, SD-93-ll-2.
4.
FSV system diagram - PI-21-1, PI-21-2, IC-ll-1 through -3.
5.
FSV drawings - R 1100-100, C2101-300, C2101-500
-,m EE-21-0004 ney. 1 A.9 i
5.
(cont.)
6.
FSV technical specifications - LCO 4.2.1, LCO 4.,2.2, LCO 4.2.3, SR 5.2.7, SR 5.2.8, SR 5.2.9, SR 5.2.17, SR 5.2.18, SR 5.3.4.
7.
FSV surveillance procedures - SR 5.2.7a-A, SR 5.2.7b-A, SR 5.2.7cd-Q, SR 5.2.7d-A, SR 5.2.8a-Q, SR 5.2.8abc-Q, SR 5.2.8c-A, SR 5.2.9-M, SR 5.2.9-A, SR 5.2.17-X/5.2.18-X, SR 5.3.4-SA/5.3.3c-A.
8.
ASME Code section XI, Division 2, Draft.
9.
Report GA-A 10349 - Operation and maintenance manual for the Fort St. Vrain 330MW(e) HTGR helium circulators.
10.
Report FGLP-2113 - Procedure for helium circulator 2xamination in compliance with technical specification requirements.
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EE-21 0004 Rev. 1 B.1 i
I a
PART B 1
i 1
a SURVEILLANCE REQUIREMENTS REVIEW i
FOR THE i
FORT ST. VRAIK
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l PRIMARY COOLANT SYSTEM (21) o HELIUM SHUTOFF VALVE o DIFFUSER AND INLET DUCTING f
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EE-21-0004 Rev. 1 B.2 1.
INTRODUCTION A review was performed of the surveillance requirements for the circulator diffuser and inlet duct assemblies.
These assemblies include the inlet and outlet structures,.which conduct the primary helium flow to and from the compressor wheel, and the helium shutoff valves which prevent flow re-versal when a circulator is shutdown.
The review included the reference documents listed in section 5 and, in particular, the proposed ASME Code,Section XI Division 2 Draft, the requirements of which are identified.
An explanation is provided when the current and recommended surveillance differ from the proposed Code requirements.
The review also included the operationa) experience with the equipment at the plant.
2.
SURVEILLANCE CLASSIFICATION The diffuser and inlet duct assembly is a passive structure which, by its geometry, progressively accelerates the flow from the circulator inlet plenum to the compressor wheel, then, once passed the compression stage, progressively decelerater he flow to the circulator outlet plenum, thereby preventing >.anecessary pressure losses.
The assembly also has a function of instrumentation support.
Therefore, according to criteria 2.2c and 2.3b of Ref. 1, the diffuser and inlet assembly ducting is assigned to surveillance class S3.
The helium shutoff valve is an active component, and functions as a check valve to close on shutdown of a circula-tor, thereby preventing bypass flow around the core, so that adequate primary coolant flow is available for core cooling.
According to criteria 2.2b and 2.3a of Ref.
1, the helium shutoff valves are assigned to surveillance class S2.
l The following criteria of Ref. 1 apply when reviewing the surveillance of the above equipment items.
The opera-tional readiness of check valves assigned to surveillance class S2 shall be det'anstrated by normal operation or by surveillance testing at least once each year, to exercise those valves which do not normally operate, according to rules and requirements based on the Draft ASME Code,Section XI, Division 2 (criteria 3.2.2b).
The structural integrity of equipment items assigned to surveillance class S3 need j
not be demonstrated for equipment which operate at condi-l tions not expected to degrade their integrity during normal l
operation, when compared to design conditions, or for equip-ment the failure of which does not prevent the performance of an active safety function and does not lead to unacceptable release of radioactivity (criteria 3. 3.lc).
When required,
EE-21-0004 Rev. 1 B.3 2.
(Cont.)
structural integrity can be demonstrated by leakage moni-toring (criteria 3. 3. la).
3.
OPERATIONAL READINESS OF THE HELIUM SHUTOFF._ VALVES -
a)
Current surveillance requirements:
None.
b)
Proposed surveillance requirements:
Each of the primary coolant circulators is orovided with a helium shutoff valve whose purpose is to minimize reverse coolant flow through a shutdown circulator and, thereby prevent large amounts of primary coolant from bypassing the core, re-sulting in potentially inadequate cooling.
The helium shutoff valves also function to isolate a primary coolant loop when both circulators in that loop are shutdown.
The helium shutoff valves are self-actuated, split flapper check valves located in the circulator diffusers.
The flappers are designed to open using circulator discharge pressure, and to close upon initiation of reverse flow through the corres-ponding circulator and/or by gravity.
The two flat metallic f'appers are articulated on horizontal hinge pins.
When the helium shutoff valve opens, the flappers move to a vertical position, as provided by mechanical stops.
One airfoil is welded to each flapper and provides aerodynamic forces to main-tain the valve open and prevent fluttering or chattering, and to initiate valve closure upon flow reversal.
A small reverse flow is allowed by design past the flappers when the valve is closed; therefore, there are no concerns with respect to valve tightness.
Should a helium shutoff valve fail to close, a low resistance flow path between the circulator outlet plenum (at higher pressure) and the circulator inlet plenum (at 1cwer pressure) would result, through which a fraction of the reactor coolant would circulate instead of circulating through the reactor core.
Such a situa-tion would be sensed by the instrumentation which monitors reactor operation, and its cause would be confirmed by the instrumentation which monitors pressure differentials across the circulator, since instrument indications are different when the valve is open and when it is closed.
(See figure 1 for a schematic diagram of the circulator instrumentation).
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EE-21-0004 R:v. 1 B. 4 3.
(Cont.)
Each helium shutoff valve operates when the corresponding circulator is shutdown.
Between anticipated and unanticipated shutdown or trip of any circulator, it is expected that the helium shutoff valves operate at least about once a year, which satisfies the exercising frequency required by criteria 3.2.2b of Ref.1. However, it is recommended that-the operational readiness of the helium shutoff valves to close be formally determined by periodic surveillance monitoring.
Such monitoring should be performed for each helium shutoff valve approximately once each year, i.e. at the next scheduled plant shutdown if it has not been performed during the previous year.
The surveillance requirements for the instrumentation, used to verify the operational readiness of the helium shutoff valves, will be covered in a separate report on System 93.
c)
Proposed ASME Code requirements:
The helium shutoff valves are considered Code category C (IGV-2100) since they function as check valves.
Paragraph IGV-3521 requires that check valves be exercised at least every 3 months with the exceptions provided by paragraph IGV-3522, i.e., unless valve exercising is not practical during plant operation, which is the case for these valves.
If only limited operation of the check valve is practical during plant operation, paragraph IGV-3522 requires that the check valve be part stroke exercised during plant operdion and full stroke exercised during each cold shutdown.
For normally open valves, confirmation that the disc is on its seat is to be provided by visual observation, by position indication instruments, by observation of appropriate pressure indications in the system, or by other positive means.
d)
A difference exists between the recomended surveillance and the proposed Code requirements, because part stroke exercising of these valves is not practical during plant operation.
The recommended test frequency is consistent with criteria 3.2.2b of Ref.1, and tM recomended rules for observation of valve operation are otherwise consistent with the proposed Code requirements as specified by criteria 3.2.2b.
4.
STRUCTURAL INTEGRITY OF THE DIFFUSER AND INLET ASSEMBLIES a)
Current surveillance requirements:
None.
b)
Recomended surveillance requirements:
The diffuser and inlet assemblies have no pressure retaining or load bearing function.
They experience only the pressure differential between circulator inlet and outlet plenums.
They are not exposed to temperature gradients, since they operate at reactor inlet temperature, and their thermal expansion is not restrained.
No area of concern has been identified with respect to their structural integrity.
Further, they could only be accessible with major difficulties for partial visual examination.
EE-21-0004 Rev.1 B. 5 Therefore, no surveillance is recommended for these equipment items.
c)
Proposed ASME Code requirements:
Not applicable.
5.
LIST OF REFERENCES References 1.
PSC report EE-SR-0001.
Surveillance inspection and test criteria for the Fort St. Vrain nuclear generating station.
2.
FSV System description 5D-21-1, 50-93-11-2.
3.
FSV Drawings R1100-100, C2101-200, -210 through -213, -270, -430
-600 through -603.
4.
FSV I & C diagram 1C-11-3.
5.
FSV technical specifications - LC0 4.2.1, LC0 4.2.2, LCO 4.2.3, SR 5.2.7, SR 5.2.8, SR 5.2.9, SR 5.2.17, SR 5.2.18.
6.
Fort St. Vrain FSAR - Sections 4.1 and 4.2 7.
Draft ASME Code,Section XI, Division 2 4
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CIRCULATOR AP A
f, Diffuser *
,s.
,ei pil Helium Shutoff DIFFUSER AP B
N M'.
valve
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== 4 1 Q
sD Compressor Wheel COMPRESSOR AP C
n t
FLOW AP p
,E Inlet Low range /High range 1
=
A B
C D
E PDE-PDE-PDE-PDE-PDE-CIRCULATOR 1179 1165 1161 1157-2 1157-1 C 2101 1181 1167 1163 1159-2 1159-1 C 2102 1180 1166 1162 1158-2 1158-1 C 2103 1182 1168 1164 1160-2 1160-1 C 2104 m
to I
C PJ 6*
Circulator Instrumentation (Schematic Diagram) g$
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