ML20215M978
| ML20215M978 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 10/31/1986 |
| From: | Whittier G Maine Yankee |
| To: | Thadani A Office of Nuclear Reactor Regulation |
| References | |
| 8089L-LMO, GDW-86-256, MN-86-131, NUDOCS 8611040117 | |
| Download: ML20215M978 (10) | |
Text
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MAIRE HARHEE ATOMICPOWERCalRPARUe
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(207) 623-3521 O
October 31, 1986 MN-86-131 GDH-86-256 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington, D. C.
20555 Attention:
Mr. Ashok C. Thadani, Director PHR Project Directorate #8 Division of Licensing
References:
(a) License No. DPR-36 (Docket No. 50-309)
Subject:
Inadequate Core Cooling Instrumentation (ICCI) System Gentlemen:
As a result of our August 25, 1986 meeting, and as we discussed on September 8, 1986, Maine Yankee hereby proposes several changes to our existing ICCI system.
These changes should adequately address your concerns-regarding Primary Inventory Trending System (PITS), Subcooled Margin Monitor System (SMM), and Core Exit Thermocouples (CETs).
This submittal, Attachment 1, describes the ICCI system as it would be implemented with the changes in place. The design analysis and accuracy evaluation of the ICCI system will be performed following your approval.
He trust this design proposal should adequately address your concerns.
If you should have any questions, please do not hesitate to call us.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY khW G. D. Whittier, Manager Nuclear Engineering and Licensing GDH/bjp Enclosure cc: Dr. Thomas E. Murley Mr. Pat Sears Mr. Cornelius F. Holoen
$Ch05000309 17 861031 P
8089L-LM0 POR
MAINE YANKEE ATOMIC POWER COMPAP$Y 1
ATTACHMENT 1 CONCEPTUAL DESCRIPTION OF PROPOSED ICCI SYSTEM Maine Yankee's Inadequate Core Cooling Instrumentation System consists of three subsystems:
the subcooled margin monitor (SMM), the core exit 4
thermocouple system (CETS), and the primary inventory trend system (PITS)-.
e These three subsystems are used together to provide an indication of the adequacy of core cooling under various plant conditions. A description _of the use of the ICCI subsystems during a postulated small break loss of coolant accident is provided below.
4 Following a small break loss of coolant accident, subcooled~ margin would decrease providing the first indication of an approach to inadequate core f
cooling. When the margin decreases to 25'F, the operators would, by procedure, trip the reactor coolant pumps.
If subcooled margin is completely lost, the reactor coolant system would be in a saturated condition with bulk boiling occurring in the core. The core exit thermocouples track temperature changes within the vessel and provide an indication of possible core uncovery. A reduction in coolant level below the j-top of the core would result in the exit thermocouples indicating a superheated condition.
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. The Primary Inventory Trending System (PITS) monitors coolant level in the reactor vessel after the reactor coo a,nt pumps are secured. A loss of saturation margin could lead to a steam void developing under the reactor head. The PITS would monitor the growth of the steam void and consequential level decrease.
It would further track diminishing level through core uncovery.
Together these three subsystems constitute a comprehensive and diverse system capable of providing an unambiguous indication of inadequate core cooling.
8089L-LHO
MAINE YANKEE ATOMIC POWER COMPANY SUBC00 LED MARGIN MONITOR I
l The Subcooled Margin Monitor provides an indication of the adequacy of core cooling when system overpressure exists. Coolant temperature and I
pressure infctmation is input to the SMM for calculation of the margin to saturation. When the SMM reads 25'F, the operators are required by procedure to trip the reactor coolant pumps, thus avoiding cavitation of the reactor coolant pumps and possible consequential damage.
The SMM system has two redundant channels.
Each channel receives a pressure input from a separate pressurizer pressure channel and a temperature input from a separate group of eight CETs. A selector switch is used to choose one of the eight CETs for input into the saturation margin monitor.
The margin to saturation is displayed on a digital monitor on the main control board.
Each channel is powered from a separate Class 1E power supply.
Operating Range Method of Indication Ranae Disolay*
2 T-SAT 0-750*F MCB/H/SPDS l
Method of Display MCB/M - Main Control Board Meter Indication SPDS - Safety Parameter Display System 8089L-LM0
MAINE YANKEE ATOMIC POWER STATION PROPOSED SUBCOOLED MARGIN MONITOR SYSTEM PRESSURE CHANNEL, P1 PRESSURE CHANNEL, P2 PZR CEfs 9-16 CETs 1-8 7
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b CORE PLANT COMPUTER e PRESSURE g
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INPUT P1 SATURATION POWER M
1 SUPPLY MARGIN gP Y
NO. 1 CETs 1-8 MONITOR #1 SELECTOR SWITCH Pi.A T
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COMPUTER
- PRESSURE
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POWER INPUT P2 SA ATION MONITOR #2 SfLY SUPPLY NO. 2 CETs 9-16
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SELECTOR SWITCH
% ISOLATION DEVICE e NOT PART OF ICCI
M AINE YANMEE ATOMIC POWER COMPANY CORE EXIT THERM 0 COUPLES Core Exit Thermocouples (CETs) provide temperature output to the computer for mapping and trending of coolant temperatures at the core exit.
There are a total of sixteen CETS with one group of eight qualified CETs available to each channel of the ICCI system.
Each group contains two CET's per quadrant.
The output of each CET group is sent to a separate SMM channel.
Instruments associated with each group of eight CETs are powered by a different Class lE power supply. One CET is chosen by a selector switch for saturation margin calculations. This CET also provides an input to a PITS channel for automatic t
density compensation calculation and a digital display indicating the CETs actual value.
Operating Range Method of Indication Range Disclav*
16 T/Cs 200-2250*F
- Computer, MCB/M/SPDS Method of Display MC8/M - Main Control Board Meter Indication SPDS - Safety Parameter Display System i
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MAINE YANKEE ATOMIC POWER STATION PROPOSED SYSTEM FOR CORE EXIT THERMOCOUPLE MEASUREMENT CET DISPLAY NO.1 ON MCB INPUT TO SMM NO.1 PITS DENSITY
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COMPENSATE NO.1 NO. 1 1
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2 SELECTOR 7
S TCH PLANT COMPUTER
- 6 MC8 5
4 (T1 T2 T3 T4 T5 T6 T7 T8
)
ARDS POWER SUPPLY NO.1 16 QUAUFIED CETS 2 PER QUADRANT PER TRAIN, 4 PER QUADRANT TOTAL T
T/C REF POWER
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T9 T10 T11 T12 T13 T14 T15 T16 J CARDS SUPPLY NO. 2 A
NO. 2 g
16 10 CET S
CM 15 SWITCH 11 ON CET DISPLAY 13 12 NO. 2 ON MCB INPUT TO SMW NO. 2 PITS DENSITY COMPENSATOR NO. 2 y-PLANT COMPUTER
- hh== ISOLATION DEVICE
- NOT PART OF ICCI
F M AINE YANKEE ATOMIC POWER COMPANY
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PRIMARY INVENTORY TRENDING SYSTEM The Primary Inventory Trending System (PITS) provides the operator with a continuous indication of the reactor coolant level in the reactor vessel when the RCP's are not running.
The PITS system consists of two redundant I
channels.
Each channel includes a pressure transmitter which measures the pressure differential between.the top and the bottom of the ~ reactor vessel.
The delta P signal is then automatically compensated for coolant density changes in the reactor core and in the reference leg.
For each PITS channel, temperature compensation input is provided to its calculator' by an RTD on the reference leg and by the CET selected by the operator for the SMM for the variable leg.
Each channel output is indicated on a separate strip chart recorder on the main control board showing 0-100%
full scale from the bottom to the top of the reactor pressure vessel.
Separate Class lE power supplies are provided for each PITS channel.
Operating Range Method of Indication Range Disolay*
2 dp 0 to 100%-
MCB/R/SPDS Hethod of Display MCB/R - Main Control Board Recorder Indication SPDS - Safety Parameter Display System 8089L-LMO.
MAINE YANKEE ATOMIC POWER STATION PROPOSED PRIMARY INVENTORY TRENDING ~ SYSTEM CET's 9-16%
CET's 1 [\\
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f 4H REFERENCE LEG RTD-1 4H REFERENCE LEG RTD-2 CORE PT A DIFFERENTIAL PRESSURE
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ICI TUBE PLANT *
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g COMPUTER D/P TRANS. PT-3001 POWER AUTO DENSITY PT-3001 SUPPLY COMPENSATION LEVEL N O. 1
=
=
RTD-1 CALCULATOR RECORDER CET'S 1-8
=
SELECTOR SWITCH PLANT *
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- COMPUTER, D/P TRANS. PT-3002 POWER AUTO DENSITY PT-3002 SUPPLY REF. LEG COMPENSATION LEVEL NO. 2
=
=
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RTD-2 CALCULATOR RECORDER CET*S 9-16 SELECTOR SYATCH D ISOLATION DEVICE
- NOT PART OF ICCI
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MAINE YANKEE ATOMIC POWER COMPANY CONCLUSION The ICCI system is designed so that a single active failure will not result in the loss of any of the three ICCI subsystem functions. That is, at least one channel of Subcooled Margin Monitoring, Primary Inventory Trend, and Core Exit Thermocouples will be functional following any single active failure.
The ICCI-system is not designed for passive failures.
This is acceptable because of the extremely low probability of passive failures coincident with the need for the system.
The system meets Maine Yankee's original electrical separation criteria.
8089L-LM0
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