A07623, Responds to NRC Re Generic Ltr 88-17, Loss of Dhr. Equipment Mods for Programmed Enhancements Accomplished During 1990 Refueling Outage.Summary of Instrumentation Used to Monitor Status of RCS Encl

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Responds to NRC Re Generic Ltr 88-17, Loss of Dhr. Equipment Mods for Programmed Enhancements Accomplished During 1990 Refueling Outage.Summary of Instrumentation Used to Monitor Status of RCS Encl
ML20066J815
Person / Time
Site: Millstone Dominion icon.png
Issue date: 01/30/1991
From: Mroczka E
NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
A07623, A7623, B13691, GL-88-17, TAC-69754, NUDOCS 9102050114
Download: ML20066J815 (13)
v • d • e


Text

{{#Wiki_filter:. + NORTimAST UTILITIES o.no,.i on,e.. . seio.n si,..i. o.,nn. conn.ei cui 9 *i ,. um m. o a u-~ P.O Box 270 en.u w. w" HARTFORD. CONNECTICUT 061410270 k k J N.2C.~2',C (2031 665 5000 l January 30, 1991 l Docket No. 50 336 A07623 B13691 , Re: Generic Letter 88-17 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555

References:

(1) D. M. Crutchfield letter to All Holders of Operating Licens~es or Construction Permits for. Pressurized Water Reactors, " Loss of Decay Heat Removal (Generic _ Letter No. 88-17), 10CFR50.54(f)," dated October 17,-1988. 

                                                                                                                               ~

(2) E. J. Mroczka. letter . to U.S. Nuclear Regulatory Commis-sion, " Loss of Decay Heat Removal--GL 88 17," dated December 23, 1988. (3) E. J. Mroczka letter to U.S. Nuclear Regulatory Commis-sion, " Loss of Decay Heat Removal--GL 88 17 " dated January 31, 1989. (4) G. S. Vissing letter to E. J. Mroczka, " Programmed Enhancements for Generic Letter 8817, loss of Decay Heat Removal for Millstone Unit 2," dated May 29, 1990. Gentlemen: Millstone Nuclear Power Station, Unit No. 2 Loss of Decay Heat Removal Generic letter 88 17 (TAC No. 69754) On - Octob'er 17, 1988, the NRC issued Generic letter (GL) 88-17 to request information from licensees regarding the actions taken to implement the i identified expediti_ous actions, and plans and schedules to implement the identified programmed enhancements concerning operation of the Nuclear Steam Supply System during shutdown cooling or during conditions where such cooling would normal _ly be provided. These expeditious actions and programmed enhance-ments apply whenever there is irradiated fuel in the - reactor vessel. The 

               . Staff requested, within- 60 days of receipt of Reference (1), that licensees submit a description of actions taken to implement each of the eight recom-mended expeditious actions identified in the attachment to GL 88-17. In Reference (2),        Northeast Nuclear Energy Company             (NNECO),        on      behalf     of Millstone Unit No. 2, provided a response to each of the eight recommended osam ntv 4-88 9102050114 910130

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l . . V.S. Nuclear Regulatory Commission I B13691/Page 2 January 30, 1991 expeditious actions. The expeditious actions were implemented to support the 1989 refueling outage. In addition, the Staff requested, within 90 days of receipt of Reference (1), that all licensees submit a description of enhancements, specific plans, and a schedule for implementation for each of the six programmed enhancements identified in the attachment to GL 88 17. In Reference (3), NNECO, on behalf of Millstone Unit No. 2 provided a response to this request. Reference (4) discussed NNECO's responses contained in Reference (3) and requested notification of any significant schedule changes, notification of implementation, and notification of modification completion. The equipment modifications for programmed enhancements were accomplished on schedule during the 1990 refueling outage. These modifications are now complete and are operational. Attachment I summarizes the Millstone Unit No. 2 instrumentation that will be used to monitor the status of the reactor coolant system during a reduced inventory condition. We trust you find this information satisfactory and responsive. As always, we are available to address any questions the NRC Staff may have. Very truly yours, NORTHEAST NVCLEAR ENERGY COMPANY 

                                                     . .       jrtzka           4' Senior Vice President cc:  T. T. Martin, Region 1 Administrator G. S. Vissing, NRC Project Manager, Millstone Unit No. 2 W. J. Raymond, Senior Resident inspector, Millstone Unit Nos. 1, 2, and 3

1 

       ,                                                                                      1 Docket No. 50 331
A07623 E11b1L l

l l l Attachment Millstone Nuclear Power Station, Unit No. 2 Implementation of Generic Letter 88 17 Programmed Enhancements item 1--Instrumentation i l l January 1991 1. i l

U.S. Niclear .Ngulatory Commission

- 81369'./ Attachment /Page1 January 30, 1991 Millstone Nuclear Power SthlioI, Unit No. 2 Implementation of Generic l' tter 8817 '

Programmed Gnhancenants Ilcm 1--InRGLED.ta tion In response to Generic Letter 8817. Loss of Decay Heat Removal, Millstone t Unit No. 2 has completed implementation of Item 1, Instrumentation. The following describes the features of this completed instellation. Item 1 - Insttumentation 

                          --Provide reliable indication of parameters that describe the state of the reactor coolant system (RCS)-and the performance of systems normally used to cool-the RCS for both normal and accident conditions. At a minimum, provide the following in the control room (CR):
. Two independent RCS level indications.

. 2. At least two independent temperature measurements representative of the l core exit whenever the reactor vessel (RV) head is located on top of the RV. (We suggest that temperature indications be provided at all times.)

3. The capatility of continuously e.)nitoring decay heat removal- (DHR) system performant.e whenever a'0HR system is being used for cooling the RCS. ,
4. Visible and Mudible indications of abnormal conditions in temperature. -

level, and DHRMystem performance. Response -

1. RCS Hot Leg Level Instrumentation Additions Level detection instrumentation is installed for monitoring RCS hot- leg level. The instrumentation provides input to the integrated control
                                      . system (ICS) for indication (Figures 2 through 4) and alarms on C03F.

Diverse level sensing methods which are unaffected by pressure perturba-tions or process flow effects are used. These methods are illustrated in Figure ~1.

a. RCS Hot leg No.1 Level Detection A continuous level detection system is provided in the Hot leg No. I loop area. The scheme (see Figure 1) includes sensors for both -

local -indication and remote indication and alarms. The sensor measures RCS level during reduced inventory conditions via the Hot Leg No. 1 drain line. J 

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b U.S. Nuclear Regulatory Commission B13691/ Attachment /Page 2 January 30, 1991 The sensor providing the signal for mote indication and alarms of RCS level in the CR is a thermal disper> tin continuous level sensor manufactured by fluid Components Inc. (FCI). The Model CL86 level sensor (LE-ll2) is installed in a standpipe provided by FCI. The standpipe is connected (valved-in) to existing hot leg drain volves (2-RC-214 and 2-RC-433) and RCS common vent header (2 RC 419) only during Modes 5 and 6 evolutions including RCS draindown, reduced inventory, midloop, and fill. The standpipe is isolated (valved-out) for all other operational modes (1 through 4). Existing Tygon* tubing connections required to vent the pressurizer and RCS via the f' reactor vessel hnad vent is replaced with hard tubing. A transition tubing assembly is provided with quick disconnects to connect the RCS head vent on the control element assembly (CEA) shroud to a vent header provirled on the steam generator (S/G) No.1 enclosure wall at approximately the refueling deck level. A level transmitter (LT ll2) located in the east electr; cal penetra-tion room generates a 4-20 milliamp direct current (madc) output (proportional to the level sensor output) to the ICS for remote indication (Figures 3 and 4) and provide reduced RCS level and Loop 1 hot leg level low alarm contact outputs to RC22 for annunciation on control room (CR) reactivity control panel (C04). The reduced RCS level alarm alerts the operator that level is approaching reduced inventory conditions; i.e., approximately 3 feet below the reactor vessel flange. The Loop 1 hot leg level low alarm alerts the operator that RCS hot leg level has fallen to a point where air entrainment and possibly onset of vortexing is likely at shutdown cooling (SDC) flows > 1200 gpm. Power for the transmitter is provided at the local racks from VRll. Local indication is provided via a GEMS Sure Site

  • Level Indicator (LI-ll2), Model 87120. The local level indicator is continuously monitored via camera on a remote CR Tv monitor and can be used for cross channel checks of the other RCS ' level sensors. This levcl indicator consists of a float in a standpipe similar to the stand-pipe being provided for the FCl sensor. Indication is provided by high visibility magnetic ' flags' attached to the standpipe which are positioned depending on the elevation cf the internal float. The FCI and GEMS standpipe assemblies are cunnected via flange adaptors,
b. RCS Ilot leg No. 2 level Detection A continuous level detection system is provided on Hot Leg No. 2.

The scheme (see Figure 1) includes an ultrasonic level sensor, - preamplifier, and remote electronics for driving indication and - alarms. This ultrasonic level sensing system is provided by Westinghouse. It measures Hot leg No. 2 water level nonobtrusively by sensing

  • s i
              'U.S. Nuclear Regulatory Commission                                                             1 B13691/ Attachment /Page3                                                                       t Vanuary 30, 1991
                         -water levol ultrasonically through the RCS pipe wall _. The pipe surface is finished to meet the senson interface requirements.

Piping insulation has been modified to accommodate the sensor. The sensor is. designed to remain strapped to the bottom of the RCS , hot leg pipe dwing operation as well;as shutdown. A is located in the containment outer loop (-3' 6") preamplifier , area near l Rack C-146. The signal processor or level transmitter (LT 122) is f located outside of containment in the west electrical penetration .! area near-Rack C-263. The processor includes functions which fail  ! 

                          -the transmitter output low, i.e., < 4 made, if either the sensor or preamplifier # .ls, or the actual level drops below = -17" (below                  .l the centerline . The processor cannot reliably detect water levels _                 i of less - than - = 4" above the pipe bottom. Once -level rises to 1 = 4", the processor will reinitialize and resume normal operation.                    >
                          .The cransmitter pmvidss a 4-20 made output- signal proportional to                       ;

RCS Hot Leg No. 2. level for display by the..ICS (Figures 3 and 4) and  ; generation of alarms on CR reactivity control panel-(C04) by Foxboro-f 7 SPEC 200 instrumentation located in Cabinet RC-310. Alarms include-RCS level at hot leg and Loop 2 hot leg level hw. _.The RCS Level at l 

                           ' hot leg alarm alerts the operator that level is below the to) of the hot leg, and that. SDC flow should be: reduced, . by procecure, to
                            < 2500 gpm. The Loop 2 hot leg level low alarm is redundant to the                      '

loop 1 hot leg level low alarm, and alerts the operator that RCS hot 

                                                                          ~

leg level -has fallen to a point wh'ere air entrainment- and onset of vortexing is possible at SDC' flows > 1200 gpm. An alarm bypass is 

                            .provided on-C03R to eliminate off normal alarms from this instrumen-tation during normal plant operating = temperature conditions. The hypass is -keylocked and administratively controlled to prevent inadvertent bypass during reduced inventory conditions. Power for the preamplifier ar.J Uansmitter is _provided at the local- racks from VR21.

a

c. Additional RCS Level Indications  ;

Although not specificillv credited for level . monitoring. during reduced invento'ry conditions, two independent channels = of the feactor vessel level monitoring system (RVLMS) are available for.RCS temperature monitoring purposes when the RCS-is in a reduced inven- 

                            ' tory condition with =the reactor vessel head located on top of the reactor-vessel. The _RVLHS level channels each provide the operator with eight discrete indication' points above the reactor core. Three discrete' points correspond to the top, center, and bottom of the hot leg. The RVLMS sensors are continuously displayed on any of three ICS-ICC display pages, as illustrated in Figures 2 through 4.

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l' 9 U.S. Nuclear Regulatory Comission B13691/ Attachment /Page4 January _30, 1991 _

2. RCS Temperatura Monitoring As discussed in 1.c above, NNECO plans to' maintain two independent  ;

channels of- the RVLMS--operable- when the RCS is in a reduced inventory 

                   - condition = with. the reactor vessel head located on -top of the. reactor vessel. The unheated .thermocouples utilized in- each sensor assembly -

provide a measure of RCS temperature, when in contact with the RCS water, and are available for display on the ICS-ICC display page. Pages 2 and 3 of the 10S 100 pages display the bottom two thermocouples for each RVLMS sensor, as illt.strated on Figures 3 and 4. 

         - 3.         SDC System Performance Monitoring Substantial SDC system performance monitoring data is available- to the CR operator in the form of continuously updated graphic displays on the ICS.

Figure 5 illustrates the SDC display page. The ICS also provides trend , capabilities for selection by the operator and computer-generated alarms. Previous monitoring capabilities included the following:

a. -SDC inlet and outlet temperatures.
b. SDC heat exchar.ger outlet temperatures. .
c. .SDC low pressure safety injection pump (LPSI) discherge pressure. *
d. SDC system flow.
e. LPSI -injection header flows,
f. LPSI pump motor current.

Audible, visible and computer alarms are presently available .to the CR ccorator, as follows:

a. LPSI pump tripped annunciators,
b. LPSI Injection Headers 1A, 2A, IB, 28 high/ low flow, c.-
                     -d. . .LPSI  Pomps Shutdown        Heat    A and    B high/ low Exchangers         discharge A and           pressure.

B high/ low discharge temperature. SDC System Instrumentation Uoarades Additional SDC instrumentation 'is installed to provide the operator with enhanced SDC performance monitoring capabilities. The completed instal-lations are described as follows:

a. LPSI Pump A and B Sucti6n Pressure Indication and Alarms Tees -and new tubing 'are added between existing root valves and local suction pressure gauges. (PI-3051, 3053).. New Foxboro= Model 821GM electronic pressure transmitters (PT-3051,-3053) are added to provide a 20 made analog output for remote signal processing.

Foxboro SPEC 200 Cabinets RC-31C and 310 perform signal processing

? .l U S. Nuclear Regulatory Commission B13691/ Attachment /Page 5 ' January 30, 1991 for retransmission to the ICS system for remote indication (Fig-ure 5), and generation of LPSI Pump A suction pressure lo and LPSI Pump B suction pressure lo alarms at CR engineered safeguards panel (C01). The purpose of the low suction pressure alarm is to provide a qualitative alert to the operator that pump suction pressure has fallen below that expected during midloop operhtion. These alarms are interlocked with the LPSI pump motor control- switches to elimi-note board alarms when the switches (HS-3017, 3018) are in the off puition.-

b. LPSI Purbp A and B High/ Low Motor Current Alarms Current transmitters and signal processing electronics are -installed for measuring LPSI pump motor current and provide LPSI Pump A motor current _ hi/lo and LPSI Pump B motor current hi/lo alarms at CR engineered safeguards panel-(C01). The purpose of the high/ low pump motor current alarm is to provide a qualitative alert to the opera-tor that pump motor current has gene outside that range expected for various SDC flow rates during midloop operation. The AC current' sensor provides a 4 20 made output signal proportional to a single phase of the LPSI pump motor current._ The AC current ser.sor is powered by signal processing electronics located in Foxboro SPEC 200-cabinets (RC31C and RC310) which also generate alarm outputs for-annunciation on CR Engineered Safeguards Panel C01F. These alarms are interlocked with the I. PSI purra motor control switches to elimi-nate board alarms when the Li sl pump motor- control switches (HS-3017,3018) are in the off position.
4. Available Alarm and Trend Capabilities ,

Visible and audible-indications of abnormal conditions in temperature, 

            . level, and SDC system performance are described- in Items 1, 2, and 3 above.

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15:03:49 SHUTDOWN RCS LEVEL Icgi337;'a l, TESTER HOST B 1 i Uessel HJTC 

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