ML20212Q156
| ML20212Q156 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 08/19/1986 |
| From: | Allen C COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-CR-3453 1928K, NUDOCS 8609040031 | |
| Download: ML20212Q156 (3) | |
Text
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COmHHulwoolth Eclistut i
One First Nabonal Plaza, Chica00. lHinois
< X3Oross Reply to: Post Omce Box 767 b/ Chicago,lilinois 60690 0767 August 19, 1986 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
LaSalle County Station Units 1 and 2 SPDS Isolator Qualification NRC Docket Nos. 50-373 and 50-374
Dear Mr. Denton:
As a result of the Nuclear Regulatory Commission concerns for additional testing (maximum credible fault) of the Validyne Isolator Model CM 249, Commonwealth Edison has reviewed the overall component arrangement of the Validyne System and its use in regards to the Safety Parameter Display System (SPDS). This evaluation and the conclusion that an additional test is not required are discussed below.
The review consisted of examining both internal and external failures to the isolator system. It also included review of the EG&G prepared report entitled Electronic Isolators Used in Safety Systems of U.S.
Nuclear Power Plants.
(NUREG/CR 3453, dated March 1986)
Specifically, the need for the test suggested by your staff was evaluated by Sargent and Lundy as follows:
Fault _: Application of 120V AC power at remote safety related panel to excitation power input or signal output terminals of CM249 isolator.
Frequency of Occurrence: Rare since 120V AC power terminals are normally not located in close proximity to low level instrumentation circuit terminals.
I ilo i
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r-4 Mr. H. R. Denton August 19, 1986 Evaluation Results (1): The test fault current would blow the 1/4A input fuse (s) at the CM249 isolator and/or destroy excitation power or the signal transformer (i.e., open circuit it). Destruction of the transformer would cause no damage external to the CM249 isolator since the isolator and transformers are encapsulated and metal encased.
(2): No loss of multiple SPDS/TSC input points will occur from backfeeding of 120V AC power to CD173 demodulators to Validyne power supply.
(3): No effect on safety signal circuit because of no expected energy is let through (output to input) based on results of BGGG major fault tests of similar types of isolators.
(i.e., Test results show no energy let through for fused isolators for 120V, 20A fault.)
(4): External power supply will be affected and could affect safety circuits if supply is safety-related, however, only one division would be affected and this is considered a single failure.
Based on the results of this detailed evaluation, commonwealth Edison believes that the requested additional testing is not necessary for the following reasons:
1.
SPDS use of the validyne Isolator CM 249 ir consistent with the design for the STARTREC System.
2.
The Va11 dyne CM 249 Isolator has no high voltage power (above 5 volts) connections.
3.
Credit must be given for the internal 1/4A fuse on the output circuit side of the model CM 249.
4.
CM249 isolators are physically constructed such that their circuits are encapsulated (potted) and metal encased (canned).
5.
physical panel arrangement with Validyne System has sufficient barriers (conduit, metal enclosures, separate bays) between high voltage power (120 VAC) and signal processing equipment. Safety divisional separation within panels has been maintained properly (one safety division per panel or panel section).
r-b Mr. H. R. Denton August 19, 1986 l
6.
The EG&G report, referenced above, observed no effect at the input when a 120V AC major fault was applied to the output of electronic isolators that have fused outputs.
(
Reference:
Report Table 6 Code Groups KA-2, WA-2, and TA-3.)
If you have any additional comments regarding this matter, please contact this office.
i One signed original and fifteen copies of this transmittal are provided for NRC use.
Very truly yours, I
C. M. Allen Nuclear Licensing Administrator 1m cc:
A. Bournia - NRR LSCS Resident Inspector l
l 1928K
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