ML19337A794

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Sys Design & Functional Description of Big Rock Point Plant Steam Drum/Reactor Vessel Level Instrument Mod, Revision 1
ML19337A794
Person / Time
Site: Big Rock Point File:Consumers Energy icon.png
Issue date: 09/09/1980
From:
ENERGY, INC.
To:
Shared Package
ML19337A792 List:
References
FD-CPW-002, FD-CPW-002-R1, FD-CPW-2, FD-CPW-2-R1, NUDOCS 8009300236
Download: ML19337A794 (18)
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{{#Wiki_filter:._ O / i SYSTEM DESIGN AND FUNCTIONAL DESCRIPTION OF BIG ROCK POINT PLANT STEAM DRUM / REACTOR VESSEL LEVEL INSTRUMENT MODIFICATION FD-CPW-002, REV.1 -w jgd@( g ENERGY INCORPORATED

t SYSTEM DESIGN AND FUNCTIONAL DESCRIPTION OF BIG ROCK POINT PLANT STEAM DRUM / REACTOR VESSEL LEVEL INSTRUMENT MODIFICATION 1 A FD-CPW-002, REV. 1 l k i j PREPARED FOR CONSUMERS POWER COMPANY G.W.0. 8424 FC 497 l i a i BY ENERGY INCORPORATED CONTRACT N0. CPW-13127-000 SEPTEMBER 9, 1980 E e 55-9

TABLE OF CONTENTS PAGE 1.0 INTR 000CTION........................................................ 1

2.0 DESCRIPTION

OF THE MODIFICATION..................................... 2 2.1 Purpose...................................................... .2 2.2 Design Bases................................................... 2 2.3 System Functions and Design Description........................ 4 LIST OF DRAWINGS 9223-A Reactor Vessel Constant Head Chamber Reference Leg Modification - Sheet 1 9479 Sheets 1, 2, and 3 Heat Trace Control Wiring Diagram Steam Drum and Reactor Vessel Level Instrument Modification 9480 Steam Drum and Reactor Vessel Level Instrument Modification Heat Trace Control Panel Assembly and Details 9494 St eam Drum Level Instrument Modification - LE-RE08A and LE-RE088 LIST OF FIGURES 4-1 Typical Heater Control Loop.................................... 6 55-9

SYSTEM DESIGN AND FUNCTIONAL DESCRIPTION OF BIG ROCK POINT PLANT STEAM DRUM / REACTOR VESSEL LEVEL INSTRUMENT MODIFICATION

1.0 INTRODUCTION

A modification will be made to the presently-installed Yarway constant head level chambers that are the primary elements in the steam drum and reactor vessel level measurement systems at the Big Rock Point Plant. This report discusses the design criteria used for the modification and describes the modification and its implementation.

i 55-9

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2.0 DESCRIPTION

OF THE MODIFICATION 2.1 Purpose This modification is being undertaken to stabilize the density of the water in the reference column of each level element. By doing this, plant level instrumentation and alarms can be calibrated with fixed tenperature compen-sation. Instrument errors will be reduced. The net results of the modificatioa will be a reduction of the probability of nuisance plant trips and restoration of operator confidence in reactor instrumen,tation. 2.2 Design Bases The design of the modification to the steam drum and reactor vessel level elements is based on the following constraints and information: 2.2.1 The modification must not change the qualification of presently-installed pipe systems. 2.2.2 The piping of the steam drum level elenents (LE-RE08A and LE-RE088) will not be modified, since temperatures measured on the reference columns of those level elements during plant operation are well below 250*F. 2.2.3 The reference columns of the reactor vessel level elements must be replaced with columns designed to minimize heat transfer into the reference column from the coolant in the reactor. 2.2.4 Each reference colunn shall be electrically heated and the average temperature over the heated portion of the column shall be controlled to 200*F 5*F. Each reference column shall be equipped with a primary and e epare heater. Each heater shall be terminated in a safe area to allow changeover to the spare if the primary herter should fail. 55-9

2.2.5 Each reference column shall be insulated to minimize heater require-ments and reduce ambient temperature effects on level measurement. 2.2.6 Failure of the taperature control system shall result in more conservative plant operation. That is, if a temperature control loop should fail off, the corresponding reference column will become cooler. The effect of a cooler reference column is to cause the measured fluid level to appear to be lower (closer to low level setpoints) than it actually is, resulting in more conservative plant operation. 2.2.7 Abnonnally high or low reference column temperature shall set an alann on an annunciator in the main control room. 2.2.8 Each channel of the temperature control systen shall have additional built-in safety features: (a) Controller shutdown in case of input thermocouple burnout; (b) Adjustable transformer to limit the maximum voltage that can be applied to a heater if the controller fails full on; and (c) Automatic interruption of power to the heater if reference column tenperature reaches a value 10 F higher than the setpoint. 2.2.9 Piping modifications shall confona to the ANSI B31.1 Power Piping Code. 1967 Edition. Heater elements and, temperature controls shall j conform to codes and standards concerned with Class 2 systems and separation from and protection of Class 1E systems and circuits. 2.2.10 The tenperature control panel shall be installed inside containment to reduce the number of electrical penetrations required for the modification. 55-9 4

2.3 Systen Functions and Design Description 2.3.1 Reference Column Piping Madifications The four level elements on the reactor vessel (LE-RE09A, B, C, and D) each are to have a new reference column installed as shown on Drawing 9223-A. presently-installed reference column is to be removed and the opening in the constant head chamber plugged. The design of the new pipe spool piece is such that heat transfer from the steam / water interface in the constant head chamber to the fluid in the reference column is minimized. The level element supports will not be modified since the new reference (.. 'umn is not significantly different from the existing column other than tc.: bent shape. The reference columns of the steam drum level elements (LE-RE08A and B) operate at low enough temperatures that 'the piping of the reference columns of those level elements will not be altered. 2.3.2 Reference Column Heaters In order to stabilize the density of the water in the reference columns, each column will be heated electrically and the temperature controlled to 200 F 15 F. Nelson Electric Company mineral-insulated, stainless-steel-sheathed heating elements have been selected for use on the columns. They will be banded to the reference column as shown on Drawings 9223-A and 9494. Each reference column will be fitted with a primary and a spare heating element. The power cable to each heater will be extended to a terminal box outside the reactor and steam drum shielding enclosure in order to pennit changeover from the primary to the spare h, eater during plant operation. l 2.3.3 Heat Element Watt Density The power density required to maintain the desired reference column temper-ature is 3.5 watts per foot of pipe. The heaters selected can operate as 4-55-9

high as 15 watts per foot at 200 F. Variable autotransfomers will be used to reduce the voltage applied to the heaters so that the maximum power density output is 8 watts per foot. At 8 watts per foot, the reference column can be maintained at a temperature of 200 F with the heater operating 50% of the time. The autotransformers may be adjusted to a different voltage setting to improve the system performance or further restrict the power density of the heaters. 2.3.4 Reference Column Temperature Control Temperature control will be provided for each indivioual reference column. The controllers selected for use are manufactured by Research Incorporated. They are three-mode (proportional plus integral plus deri-vative) electronic controllers, with type K thermocouple input and time j proportioned 5 VDC output. The controller output will control the switching of a solid state relay in the heater circuit. Additional fea-tures of the controller include digital temperature setpoint, deviation. meter, deviation alarm, and downscale thermocouple burnout protection. j Figure 2-1 depicts a typical temperature control loop, and Drawing 9479, Sheets 1 through 3, is the wiring diagram for the complete six-loop ) reference column temperature control system. 2.3.5 Temperature Measurement j The temperature of a reference column will be measured by four typ: K thermocouples. Average temperature measurement will be achieved by installing the four themocouples at different points along the column and then connecting the thermocouple leads in parallel. A swamping resistor in each themocouple circuit will compensate for differences in themocouple anc extension cable resistar.ces. Refer to Drawings 9223-A, 9494, and 9479 for details of the installation and wiring of the themocouples and resistors. The temperature measuring scheme allows operation of the controller with 1, 2, 3, or all 4 themocouples functional. The thermocouple signals wil be averaged in pairs and then the pair of averaged signals from one level element will be averaged again. By the ' 55-9

TC-1 TC 2 TC-3 TC 4 b b b b CH AL CH AL CH AL CH AL r--- k R, i kR R S2 33 R l S 34 l 5200A 5 5 l l TYP { l I l i L___.__.-___._.__.__________ ~- INSULATED ENCLOSURE WITH THERMOCOUPLE ALLOY TERMINAL STRIP AND PRECISION SWAMPING RESISTORS,2 PLACES i 1 VARIABLE AUTOTRANSFORMER 7-._-. \\ O-120/140 VAC, 700 VA l i R (SET AT 26 VAC OUT) S5 RS6h I 2K.tL 120 VAC AL +20 % L_,_--__----__J 0 E v i NEUTRAL hO RELA'Y y FROM SOLID STATE RELAY j 9.fL/FT MEUTRA l2l0l0l NOOFF HEATER l LO AO - (HI) TO _ ALARM EXISTING O "oou'5 AaauaciAroa + TO ALARM I MODULE AM SETPolNT s s 120 VOLT 1 ' ALARM l / AC POWEft ) ALARM A HANDOFF T 'A' y (+0R-DEVIATION) ,v s TO EXISTING ~ power ANNUNCIATOR CONTROLLER FIGURE 2-1 TYPICAL HEATER CONTROL LOOP double ave-aging scheme, the single failure of a thennocouple or extension cable will not congletely disable a control loop. 2.3.6 Reference Column insulation Each reference column will be insulated over its heated length with one-inch-thick preformed chloride-free fiberglass insulation (MIL-I-24244). The insulation will be sheathed with a.010-inch stainless steel jacket. All joints in the jacket will be sealed with clear silicone sealant to keep moisture out of the insulation. Drawings 9223-A and 9494 show the method of installation of the insulation and sheathing. 2.3.7 Alarms and Interlocks Each of the six tenperature controllers (ref. Section 2.3.4) will have an integral adjustable deviation alarm. Thr; alarm contacts will close when the preset deviation above or below the temperature setpoint is exceeded. Each temperature control loop will also hcve an electronic temperature alarm module which monitors the same temperature input. as the contrclier. The alarm output contacts will operate when referencr. column average tem-perature exceeds the setpoint of the alarm module. Simultaneously, another set of contacts in the alarm module will operate to disconnect power from the reference column heater. The alarm signals from each of the six temperature controllers and the six alarm modules are to be connected in parallel to a unit in the Reactor Building Ventilation System annunciator panel inside the containment building. All of the alarms from that panel are retransmitted to a unit in an annunciator panel in the main control room. 55-9

i 2.3.8 Control Panel All of the tenperature controllers, alarm modules, autotransfonners, elec-trical protective devices, and terminal strips are to be installed in a dust tight instrument enclosure inside the containnent sphere. The base af the enclosure is to be bolted to floor grating, and brackets near the top of the rear of the enclosure will be used ta attach it to the wall. Drawing 9480 shows the panel assembly and details. 2.3.9 Power and Grounding The power source selected for the heat trace system is Motor Control Center Bus 28 in the Station Povier Area. The 480 volt-to-120 volt transformer and electrical protective devices are to be installed in the "A" stack of Motor Control Center 28. An analysis of the loading of Motor Control Center 2B (MCC-2B) has been made and addition of the reference column heating will not result in an overloaded condition. Coordination af the circuit breakers and fusing has been done to assure that faults in the heater circuits will not cause the MCC-2B to be tripped. Equipment is to be grounded to the station ground bus. No grounding con-ductors will be carried through electrical penetrations. 2.3.10 Electrical Penetration 120-volt power from outside containnent will be passed through general-purpose power penetration assembly H45 to the heat trace temperature con-trol panel. 2.3.11 Raceways and Cables All thermocouple extension cables will be run in dedicated galvanized steel conduits. Heater and supply power cables will be laid in existing cable trays where it is convenient to do so; otherwise, galvanized steel conduits will be used. Conduits are sized for 40% fill at initial installation. 55-9

Conduits will be supported by steel channel brackets with pipe clamps. The brackets will be anchored to concrete walls or ceilings or clamped to existing building structural members. All cables will have radiation-cured cross-linked polyethylene insulation and flame retardant jackets. 2.3.12 Junction and Terminal Boxes All junction box and terminal box enclosures will have a gasketed clamp cover and galvanized steel finish. The enclosures will be anchored to concrete walls or bolted to specially constructed steel structures. 4 l ~ ~ 55-9 i w -v.,,. -,,. - - ~

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