ML20237H338
| ML20237H338 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/18/1987 |
| From: | Hukill H GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 5211-87-2160, NUDOCS 8709030214 | |
| Download: ML20237H338 (4) | |
Text
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GPU Nuclear Corporation o Q Nuclear
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Middletown, Pennsylvania 17057 0191 717 944 7621 TELEX 84 2386 Writer's Direct Dial Nurnber:
August 18, 1987 5211-87-2160 U.S. Nuclear Regulatory Commission Attn: Document Control Desk
. Washington, DC 20555 Gentlemen:
Three Mile Island Nuclear Station, Unit 1 (TMI-1)
Operating License No. OPR-50 Docket No. 50-289 Safety Parameter Display System Isolation Device Reactor Coolant Pump Power Monitors
Reference:
GPUN Letter 5211-87-2062, " Safety Parameter Display System Isolation Device Test Results dated March 13, 1987 The purpose of this letter is to update and clarify information provided in the referenced submittal, as discussed in a series of telephone conversations with mernbers of the NRC Staff.
Figure 1 is a simplified sketch of the RC pump power monitor.
The output circuit of the watt transducer is considered Class 1E from a functional standpoint, per the original plant design. The isolator associated with the Reactor Protection System (Rochester Instrument Model SC 1300) wac not part of the original design, but was later added based on circuit loading considerations. The SC-1300 isolator does not perform a Class 1E isolation function.
The RIS Model SC-1302 isolator isolates a Class 1E circuit from the computer (non-Class 1E), and therefore it is appropriate to address the input impedance af ter the postulated destruction of the device due to a 120 VAC fault on the output. GPUN has recognized that input impedance could increase sufficiently to affect the Class 1E circuit function, i.e., to indicate erroneously an RC pump trip to the RPS.
On trip of one RCP, the RPS will not trip the reactor (two RCP's must be tripped for reactor trip).
Since the effect of the 120 VAC fault in itself does not result in RPS action, and the only possible consequence of such a fault would be reactor trip resulting from an actual trip of only one reactor coolant pump (since the
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fault could result in an erroneous indication of trip of another pump), a safety concern does not exist.
GPUN intends to upgrade circuit design during
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Outage 7R to preclude erroneous indication of RC pump trip to the RPS.
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8709030214 870810 PDR ADDCK 05000209 j
P PDR GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation gp m
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5211-87-2160 August 18, 1987 As a related concern, the NRC reviewer recognized that four RC pump inputs are routed to the computer multiplexer (MX), and he theorized that a fault could
-propagate. GPUN has determined that the MX, although not a qualified Class 1E isolator, provides 120 db. of isolation between inputs for 140 VAC input faults. A fault, therefore, could affect only one.RCP input to the RPS.-
t 3incerely,
. D.
kill Vice President and Director, TMI-1 HDH/SMK/rna 5101g/0967A cc:
G. Edison W. Russell R. Conte
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ATTACHMENT 1 RPS A
RC PUMP POWER SC-1300 CTS y
RIS C
N WAIT
+ CLASS lE) 0-1 MAMP
^"3" PTS (INTO 0-10,000 OHM)
SC-DUCEh.
1302 4 COMPUTER CLASS 1E ISOLATOR SIMPLIFIED S"ETCR OF RC PU"P POWER "0NITOR FIGURE 1 (nilw-D-
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