ML20209E635
| ML20209E635 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 07/08/1985 |
| From: | Fiedler P GENERAL PUBLIC UTILITIES CORP. |
| To: | Zwolinski J Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8507120047 | |
| Download: ML20209E635 (6) | |
Text
.
GPU Nuclear Corporation Nuclear
=ggra88 Forked River, New Jersey 08731-0388 609 971-4000 Writer's Direct Dial Number:
July 8,1985 Mr. John A. Zwolinski, Chief Operating Reactors Branch No. 5 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Mr. Zwolinski:
Subject:
Oyster Creek Nuclear Generating Station Docket No. 50-219 Integrated Plant Safety Assessment (IPSAR) Section 4.27, Isolation of Reactor Protection System From Nonsafety Systems, Including Qualifications of Isolation Devices GPUN letter dated August 3,1984 transmitted the results of the evaluation concerning the subject matter.
Subsequently, the NRC staff concluded that there is insufficient information to support the conclusfor. made in the submittal and requested additional information by the letter dated October 23, 1984.
Following information provides our response to the request.
NRC Question 1:
The evaluation did not address the resistor isolation buffer circuitry between the RPS and the process computer.
Response
There are two potential paths a failure in the process computer could take to propagate into the RPS. The one is a direct path between the computer and RPS, and the other is a propagation via nuclear instrumentation.
Isolation features of both paths are discussed below.
Isolation between the plant computer and the RPS is provided by the contact isolation, i.e. the computer tie-ins are accessed on separate contacts of the particular relays associated with RPS logic. This method provides an electrical isolation as recommended by IEEE criteria (IEEE-384-1981) for independence of Class IE equipment; no failure may propagate into RPS.
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PUR doi GPU Nuclear Corporahon is a subsutiary of the General Pubhc Utihtms Corporation
, Isolation capability between the plant process computer and nuclear instrumentation is provided by an isolation amplifier which feeds the multiplexer for the plant computer.
Design criteria of the isolation circuits are given in Supplement No.
6 (Addendum No.
1) to the application for a full term license dated November 21, 1983 (Answer to Question SC).
The isolation amplifier will prevent a failure in the plant process computer from propagating into RPS via the nuclear instrumentation.
I Therefore it is concluded that RPS is protected from a failure in the plant process computer.
NRC Question 2:
The previous GPUN evaluation concludes that the probability of maximum recorder input voltage being applied across the recorder input signal terminals (or R-18) is negligible.
- However, no justification is presented to support this conclusion.
Response
The sketch of Figure 1
shows the IRM/APRM general arrangement and their association with the RPS.
A single failure at one IRM/APRM process recorder can affect at most one APRM (or IRM when in the startup mode), and therefore affect only one subchannel of the RPS.
This is I
afforded via two
- separate, independent measuring and recording systems within each RIOS recorder.
This prevents the total failure of the subchannel and the possibility of spurious trips.
Because RPS logic is wired in one-out-of-two-twice logic, a failure of a single f
subchannel will not compromise RPS logic to provide a j
reactor scram.
I The maximum voltage supplied to the reactor is 115 VAC.
Within the recorder this voltage supplies the recorder servomotor and amplifier.
At the amplifier input transformer, the 115 V is stepped down to several smaller
(
operating voltages.
Therefore, the maximum credible i
voltage available at the R-18 resistor (and, thus the individual IRM/APRMs) is less than 115 VAC due to c. fault internal to the recorder.
Propagation of a 115 VAC fault to the IRMs and APRMs could result in failure of IRM/APRM Dual Trip Unit and/or DC Amplifier.
However, as it can be seen in the attached sketch (Figure 1), a failure at a single IRM/APRM process recorder can affect at most one APRM (or one IRM when in the startup mode) and therefore affect only one subchannel of the RPS.
This is afforded via two separate, independent measuring and recording systems within each RIOS recorder.
This prevents the
- total failure of the subchannel and the possibility of spurious trips.
Because RPS logic is wired in 1
. one-out-of-two-twice logic, a failure of a single subchannel will not compromise RPS logic capability to provide a reactor scram.
Therefore, faults in a single subchannel will only affect that subchannel within the RPS since power supply separation (see attached Figure 2) exists between individual IRM/APRMs.
NRC Question 3:
The evaluation does not describe any periodic testing for stray voltages and system capability to withstand maximum credible voltages, as required by IEEE 279-1971 and IEEE 379-1977.
In the. absence of such testing, redundancy does not provide sufficient protection.
Response
Stray voltage requiements are not addressed in IEEE 279 (1971) and 379 (1977).
IRM/APRM are checked during weekly surveillance channel calibrations and are also overhauled bi-annually.
However, recorder operation is continually verified via operator observation.
This is outined below:
A.
An hourly log reading is taken by the control room operator.
B. The recorders are front panel mounted in direct view of control room operator so that operation may be easily observed.
C. The APRM meters are input to the plant computer.
The computer compares the actual APRM reading with a value that it projects from a heat balance calculation.
When the actual and projected value of the APRM reading deviate by more than 57., the computer provides indication that gain settings require adjustment.
This output adjustment using the operational type heat balance during power operation is required to be performed at least once per three days by Technical Specifications (Table 4.1.1, Section 4.1).
Calibration and maintenance on the IRM/APRM is performed according to the
" Calibration Check",
and
" Trouble i
Shooting" sections of the GE Instruction Manual 4530K70-712 " Type 521 Two Pen Recorder."
. He believe that questions transmitted by your letter of October 23, 1984 are adequately responded to in this letter.
Should you have any further que:tions, please contact M. Laggart, Manager, BWR Licensing.
V t ly y -
.8 Y
er itc P sident & Director i
er' Creek Ir/1781f cc: Administrator Region I U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pa.
19406 fiRC Resident Inspector Oyster Creek Nuclear Generating Station Forked River, N. J. 08731 1781f
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- NOTE: Two independent channels are contained within one APRM drawer.
Each is electrically separated and derive their operating power from individual PRM's.
FIGURE 2: Power Supply Separation S
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