ML20147G968

Notifies of Plan to Amend Tech Specs,Changing Drop Time Limit for Shim Rod 3 to 2 Seconds.Change Will Be Requested Due to Gradual Loss of Excess Reactively Caused by Leakage of Water from Fuel Box Gasket & 880104 Event

ML20147G968
Person / Time
Site:	05000139
Issue date:	01/14/1988
From:	Robkin M WASHINGTON, UNIV. OF, SEATTLE, WA
To:	Murley T Office of Nuclear Reactor Regulation
References
NUDOCS 8801220212
Download: ML20147G968 (4)

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. -UNIVERSITY OF WASHINGTON SEATTLE, WASHINGTON 98105 College of Engineering Nuclear Reactor Laboratories Nuclear Reactor Building.

January 14, 1988 Dr. Thomas E. Murley Director Office of Nuclear Reactor Regulation U.S.N.R.C.

Washington, D.C. 20555 Docket No. 50-139

Dear Dr. Murley:

This letter i s to f orma l l y not i f y the N.R.C. of our plan to amend the Technical Specifications of the UWNR so that the drop time l imit for shim rod No. 3 wil I be 2 seconds. We wilI, in the near future, submit this request together with the required saf ety analysis showing that this amendment does not represent any safety problem. The drop time of shim rod number 3 was observed on January 4,1988 to f a l l in greater than the one second drop time currentl y specif ied in the Technical Specif ication of the University of Washington Nuclear Reactor (Docket No. 50-139). This failure was reported to Region Y by telephone on January 4, 1988. In addition, a gradual loss in excess reactivity due to leakage of water from the fuel box gasket (s) was a l so verba l l y reported.

Our Interpretation of the rod drop time delay is that during any extended per iod without operat ion, the grease lubricating the bearings hardens somewhat. During the prestartup checkout, it is observed that after some rod drops, the drop time Invariab l y decreases significantly. To correct the problem, we wilI exercise the rod every working day to maintain its freedom of action. We wilI measure the drop time of Shlm Rod No. 3 before each reactor run. As an operational procedure, we wi l I not operate un l ess the rod drop time is below one second, our current technical specification limit.

Our Interpretation of the gradual loss of excess reactivity is that a smal I l eak in one or more of the f uel boxs' l ower gaskets is al lowing some water to contact the graphite moderator during operation when the core boxes are filled with water. The water is absorbed into the graphite. The rate of reactivity loss is very slow and poses no particular safety concern. The enclosed graph shows our record of the excess reactiy Ity of the core at cold clean critical. As can be seen, the excess reactivity has 8801220212 880114 [D PDR ADOCK 05000139 l P DCD g

- .i changed very I l.ttl e during the l ast two years. We wil I continue to monitor the excess reactivity. If the loss of excess reactivity continues through June 30, 1988, we wil I not operate further without fixing the leaks. .The data show that, during periods of no operat ion, the ' Increase in excess reactivity is

-a l so very s l ow. Thus, it is not possib le f or the water in the graphite to be removed suddenl y. Therefore, the slow loss of excess reactivity does not represent a safety-problem.

Table I shows our data giving the readings f rom meters of the safety.

channels along with the thermal heat balance obtained from the '

coolant flow rate and temperature rise. Table 11 shows that the relative reading (current generated per unit power) is essentially unchanged from February 1983 to the present. Thus, the slow leakage of water into the graphite has not affected the r readings of any of the sensors in the core.

Sincerely, Se&MCf A Maurica A. Robkin Professor and Director Nuclear Engineering Laboratories c.c. John B. Martin Regional Administrator U.S.N.R.C. Region V <

A.L. Babb Chairman U.W.N.R. Advisory Committee University of Washington K.L. Garlid Chairman Department of Nuclear Engineering .

University of Washington i

t i

Summary of Thermal Calibrations for UWNR TABLE 1: Operations Data Record Date Hours Linear Safety Amp Log N Primary Delta KW at uamp #1 #2 uamp Flow Temp Thermal Power GPM Cent 2 22 83 1.6 440 65.5 63.5 55 21.94 16.65 96.1 3 1 84 1.8 440 65.0 63.0 50 22.10 16.31 94.8 5 2 84 1.8 440 65.5 64.0 50 22.10 16.26 94.5 10 19 84 1.7 430 63.0 61.5 50 21.94 16.27 93.9 21985 1+2 435 64.0 62.0 50 22.10 16.25 94.0 7 26 85 1.9 440 64.0 63.0 50 21.85 16.64 95.6 3 26 86 1.9 440 64.0 62.5 50 21.81 16.48 94.5 5 30 86 1.9 440 65.0 63.0 50 22.04 16.58 96.1 6 5 86 1.9 440 65.0 63.0 50 22.06 15.60 96.3 12 6 86 0.9 435 64.5 63.0 50 22.12 16.27 94.6 3 11 87 1.3 440 64.0 63.0 50 22.34 16.06 94.4 6 1 87 1.83 230 34.0 33.0 28 22.31 8.62 50.6 6 4 87 1.7 435 64.0 63.0 50 22.21 16.34 95.5 8 4 87 1.85 435 64.0 63.0 50 22.34 16.12 94.7 12 15 87 2.7 430 63.5 61.5 55 22.30 16.05 94.1 Table 11: Ratio of Meter Reading to Heat Balance Thermal Power Date Safety Amp Log N Linear Amp

1. 1 #2 uamp/KW uamp/KW uamp/KW uamp/KW 2 22 83 0.682 0.661 0.57 4.58 3 1 84 0.686 0.665 0.53 4.64 5 2 84 0.693 0.677 0.53 4.C6 10 19 84 0.671 0.655 0.53 4.58 2 19 85 0.681 0.660 0.53 4.63 7 26 85 0.669 0.659 0.52 4.60 3 26 86 0.677 C.661 0.53 4.66 5 30 86 0.676 0.656 0.52 4.58 6 5 86 0.675 0.654 0.52 4.57 12 6 86 0.682 0.666 0.53 4.60 3 11 87 0.678 0.667 0.53 4.66 6 1 87 0.672 0.652 0.55 4.55 0.670 6 4 87 0,660 0.52 4.55 8 4 87 0.676 0.665 0.53 4.59 12 15 87 0.675 0.654 0.58 4.57

University of Washington Nuclear Reactor Clean Core Excess Reactivity 1.20

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O 100 200 300 400 500 600 700 DAYS FROM January 1, 1986

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