ML20086T279
| ML20086T279 | |
| Person / Time | |
|---|---|
| Site: | University of Missouri-Rolla |
| Issue date: | 07/26/1995 |
| From: | Freeman D MISSOURI, UNIV. OF, ROLLA, MO |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20086T282 | List: |
| References | |
| NUDOCS 9508020300 | |
| Download: ML20086T279 (4) | |
Text
s' Nuclear Reactor Reactor Facility UNIVERSITY OF MISSOURI-ROLLA Rolla, Mo 654010249 Missourfs TechnologicalUniversity Telephone (314)341-4236 FAX (314) 341-4237 July 26,1995 yIM ,
Document Control Room U.S. Nuclear Regulatory Commission MS 10-D-21 Washington, D.C. 20555
Dear Sirs:
The UMR Reactor Facility respectfully requests a change in Technical Specifications that will remove the descriptive reference to our magnet contact lights.
Technical Specification Section 5.3.4, " Control Rod Drive Mechanisms" provides three descriptive paragraphs pertaining to the rod drive mechanisms. Paragraph (3) states:
" Lights are provided on the operator's console to indicate upper limit, lower limit, shim range, and magnet contact for each shim / safety rod." ;
We request this paragraph be changed to remove the reference to the magnet contact. The new wording we request is as follows:
" Lights are provided on the operator's console to indicate upper limit, lower limit, and shim range for each shim / safety rod." ;
The rationale for the revision is that the magnet contact lights are a convenience item and are not l safety related. Due to poor engineering design of the magnet contact switch mechanism, the magnet i I
contact switches have never operated properly. From conversations with personnel that used to work at the facility, it appears the switching mechanisms have always been a problem as far back as the early 1960s. Years ago this was discussed with the then AEC and an accommodation was made whereby we could continue to operate without the magnet contact switches operating if we l procedurally verified that the rods dropped on a scram signal by audio and visual means.
We now seek to put this matter to rest by removing the reference to the magnet contact lights in our Technical Specifications. We feel that the reference to magnet contact lights in the Technical Specifications is descriptive of the system design and not a safety requirement. l Normally, magnet contact light switches for control rod I and 3 are inoperable and magnet contact light switch 2 operates fine. The switches have been repaired many times over the years. When I l anived as the new Reactor Manager in 1990, one of the first things I did was initiate repair of contact l light switches I and 3. I was cautioned by the staff that the repair had been attempted many times in the past and that the renaired switches would fail within a matter of days. Additionally, I was
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cautiongd that the repair was risky in that it required the breakdown of the rod system and caused wear on old and very worn aluminum threads susceptible to galling on the control rod mechanisms. ,
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The aluminum threads are on the actual rod mechaaisms and cannot be replaced without
.. remanufacturing an entire mechanism assembly.
We proceeded with the repair and as predicted by the staffit or ly lasted a matter of days. We again attempted a repair and had the same results. ;
The design ofour control rod magnets is such that the actual magnet is located under about 20 feet of water and directly contacts the control rod. The magnet contact switch is a microswitch that is supposed to be actuated by a iron plunger that resides in a hole bored in the center of the magnet iron core. In theory, when the magnet contacts the top of the control rod, the magnetic field in the vicinity l of the plunger is perturbed to the extent that the plunger is moved downward thus actuating the ;
microswitch. In practice, the plunger frequently binds rendering the magnet switch inoperable.
The function of the magnet contact switch is to provide information to the operator that the magnet and drive are magnetically coupled. . In the case that the switch is inoperable, this information is not available to the operator. We see this a matter of convenience to the operator and not as a matter j ofsafety significance. _r During a reactor startup the status of the magnet contact is most useful to the operator. In some i instances, an operator may try to start the reactor without one or all of the rods being magnetically j coupled to the drives. In such an instance, the operator could attempt to startup without one (or l more) of his rods. In this case, the attempted startup would be halted early on because the required
- increase in startup count rate could not be obtained. At this point, the operator would have to suspend the stanup, reinsert his rods and try to remedy the problem. In most cases the cause of not picking up a rod is that either the magnet was off(or had inadequate current applied) or the magnet j i
was energized while the rod drive was liftedt ' hus not allowing the magnet to pick up the rod. In either case, the presence of an operating magnet contact light would save the operator the wasted ,
time spent (about 5 minutes overall) in attempting the stanup without one (or more) rods. In this !
i instance the operation of the magnet contact lights is clearly a convenience and not at all safety related.
The other function of the magnet contact light is to give the operator a visual indication that rods have dropped in a scram situation. The operator has several other redundant means of assuring rods l have dropped following a scram The primary indicators that the reactor has properly scrammed are ;
the power monitoring channels. The operators are trained and SOPS are written such that the j operator first verifies a scram by observing the appropriate power decrease following the scram. The ,
UMR Reactor has five neutron instrument channels that all can provide redundant information i verifying a proper scram has taken place. Additionally, the operator can clearly hear the characteristic
. loud audible " clang' of the rods falling and landing in the grid plate. Finally, the rods can be seen visually through long slots cut in the housing.
J We have looked into new above water magnet mechanisms that would have magnet contact switches that are directly mechanically actuated with rod contact - a feature not possible with underwater
magnets. The cost of the new mechanisms alone have been quoted at about $300,000. Additionally, the change would require NRC review and approval which can also be very costly for a small facility 2 such as ours. It should be noted thr.t our interest in acquiring the new mechanisms is not to remedy y the magnet contact light issue but rather update our old mechanisms with an above water magnet system that would be easy to maintenance, i I In summary, the magnet contact lights at our facility have never properly functioned. This was l 1
realized by the old AEC who accommodated the situation. We now seek to finally resolve the issue
- by having it removed from the descriptive section of our Technical Specifications. The presence of l the magnet contact lights are a matter of convenience and not a safety issue.
i Please contact me with questions or comments. Thank you in advance for your attention to this matter.
i Sincerely -
lB '
David W. Freeman UMR Reactor Manager cc: Dr. Albert E. Bolon, Reactor Director [
Dr. Nord Gale, Chairman, Radiation Safety Committee 1 Signed before me this l'} day of M ,199 6.
Notary Public SUE HUPHAM WARY PUBLIC STATE OF MIS 6OURI PHELPs COUMry W COMMrssioN EXP. AUC. 30,1996 I
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ATTACHMENT A Proposed Technical Specification Change l
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