ML19345D615
| ML19345D615 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 12/01/1980 |
| From: | Minogue R NRC OFFICE OF STANDARDS DEVELOPMENT |
| To: | Kocen S AFFILIATION NOT ASSIGNED |
| Shared Package | |
| ML19345D616 | List: |
| References | |
| NUDOCS 8012160253 | |
| Download: ML19345D615 (2) | |
Text
PDR Copy
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 yo
/
V DEC 1 1980 Mr. Samuel Kocen 3
d 7814 South Kenton b
er a
Chicago, Illinois 60652
Dear Mr. Kocen:
In response to your letter to Dr. Hendrie and the other Commissioners, I thank you for your interest in improving the safety of nuclear power plants. Your letter shows both interest and understanding of the technical issues we are facing.
Your suggestions of utilizing infrared photoelectric detectors to detect flow interruptions in pipes and vessels and the use of a spring-loaded flow sensing vane to monitor pipe flow have been reviewed within the Office of Nuclear Regulatory Research.
The use of infrared photoelectric detectors to detect flow changes in reactor cooling pipes has some inherent disadvantages. Because of the thickness of the main cooling pipes, which are typically three inches or greater, the response time between a temperature change in the coolant and that on the outside wall of the pipe will be relatively long, thus reducing the usefulness of the instrument. Our current safety requirements make it necessary to detect the loss of main coolant flow within a few seconds of the change. We feel that, as far as the detection of loss of main coolant flow is concerned, it can be accurately and reliably detected with current power plant instrumentation, and operating experience to date has confimed this.
l You also suggested the use of infrared photoelectric detectors to measure flow changes within the reactor vessel. The measurement of flow through and level of the fluid in the reactor vessel is an issue that is currently receiving additional attention by NRC. The basic problem in making i
vessel flow and level measurements is that during a transient, the flow patterns are a complex function of both time and location within the I
vessel. Two-phase conditions (. steam and water), as well as gas entrainment, are also complicating factors. For these reasons, vessql f,1uid temperature is not a very sensitive measurement of vessel coolant level.
Furthemore, because of the shielding around the reactor vessel, it would be diffic' ult to obtain a direct signal from the vessel wall by a photoelectric detector.
We are currently conducting research to better understand fluid changes in the vessel during transient conditions. Based on what we have learned to date, it appears that in-vessel measurements offer the best solution to this measurement problem.
l l
l l
l 8012160
Mr. Samuel Kocen 2
In addition to the use of infrared photoelectric detection, we have also considered your suggestion to use a spring-loaded flow sensing vane to monitor pipe flow.
Instruments of this type are currently in use in the l
chemical process industries and, to a limited extent, on auxiliary systems in nuclear power plants. Although they do offer an accurate, direct and immediate indication of flow stoppage, they have the disadvantage of creating a passible source of flow blockage if portions of the instru-i ment break off in the fluid stream. This type of instrument would also require pipe penetrations. The reactor heat removal system is designed with a minicum of penetrations to reduce the potential leak paths and, as a result, this type of flow sensor has not been used on the main coolant pipes.
If you would like additional information, we would be pleased to have you discuss these problems with one of the national laboratories conducting research for NRC on these measurements.
Sincerely, 8&d8 Robert B. Mincgue, Director Office of Nuclear Regulatory Research O
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