ML20062D724
| ML20062D724 | |
| Person / Time | |
|---|---|
| Site: | 05000112 |
| Issue date: | 07/31/1982 |
| From: | Terrell C OKLAHOMA, UNIV. OF, NORMAN, OK |
| To: | John Miller Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8208060197 | |
| Download: ML20062D724 (6) | |
Text
_ _ .
t The
- ((n/FerSily'O[ Oklahoma 865 Asp Avenue, Room 200 Norman, Oklahoma 73019 School of Aerospace, Mechanical and Nuclear Engineering July 31, 1982 Mr. James R. Miller, Chief Standardization & Special Projects Branch Division of Licensing Nuclear Esgulatory Commission Washington, DC 20555
Reference:
Docket 50-112
Subject:
Amendment of License R-53
Dear Mr. Miller:
We are requesting an amendment to our reactor operating license. The purpose of the amendment is to authorize an increase in the number of fuel elements from the current license limitation of 12 to 20 elements or less. The reason for the requested increase in fuel elements is to allow the reactor to operate in a flux trap configuration. The flux trap con-figuration results in a higher themal neutron flux in the central void and allows several valuable experiments to be added to the nuclear engin-eering laboratory courses.
We emphasize that no other aspect of licensed operation need be affected by going to a flux trap core configuration. The reactor power remains at 15 watts, and the maximum excess reactivity remains unchanged. The exact amount of excess reactivity of the flux trap core will be determined by a conventional critical experiment. To guarantee license compliance, a complete power calibration will be done for the flux trap core. In addition, the reactivity worth of the rods will be remeasured. We expect that the flux trap core will result in a slight change in these calibrations.
In summary, we request an amendment to License R-53 which permits operation of the reactor with a 20 fuel element (or less) plus graphite reflector core, as well as a standard 12 element plus graphite reflector core. No other aspect of the operating license would be changed.
To assist your evaluation of this requested amendment, we enclose Section F of our Safety Analysis Report submitted in April 1982 as part of our request for renewal of License R-53. Section F is pertinent to the flux trap core.
1 8208060197 820731 PDR ADOCK 05000112 PDR p
Mr. James R. Miller July-31, 1982 2
We will greatly appreciate a rapid response, as the requested change will very favorably affect our nuclear engineering program this fall.
Very truly yours,
&fp W. /
Charles W. Terrell Director, Nuclear Reactor CWT:et cc: Mr. J. James, Reactor Supervisor Dr. E. Klehr, Chairman, Reactor Safety Committee Dr. D. Egle, Director, AMNE i
1 l
rupture not a problem. The AGN fuel is unclad.
l E. Operation 100 Watts Operation of th reactor at 100 watts has b discussed and considered throughout the various s ions of the SAR. remains, perhaps, to be stated that we find no impediment to creasing e power from 15 to 100 watts. The UWV reactor operated at 75 watts period of years without problems to our knowledge. In order to keep the amma- level at or below 0.1 mr/hr at the operator's console, quarter ch iron plate ill be layed across the pool at power levels above 50 wa s. We have always use very conservative exposure policy because of th presence of students.
Additionall neutron and gamma radiation surveys ar d the reactor clearly. esta ish that the concrete shielding is fully adequat or 100 watt operatio The power increase will be undertaken in several steps th a peri of operation at each power step (25, 50, 75, 100) to allow time serve any unforseen effects.
F. Maximum Hypothetical Accident (MHA)
The University of Oklahoma AGN-211P is a homogeneous, thermal reactor, using 20 w/o U-235 oxide. The maximum permitted positive excess reactivity is limited to 0.65%. The effective beta for the reactor is estimated to be around 0.75%. Control of the excess is through a fuel loading limitation. To reach an excess of 0.65 'will require that the pool water be lowered substantially below 20 C. Thus, excess reactivity is controlled by a loading limitation as well as administrative procedure.
We are not able to define a design basis accident (CBA) for an AGN-211 reactor. No insertion or moderation or fuel into the reactor (anywhere) can result in much more than a scram on period, Jerking a small piece of cadmium 10
from the glory hole will result in an instantaneous period of 5 second (period scram setting). This is with an excess of 0.45%.
We can, he 'er, define a maximum hypothetical accident (MHA). Our license renewal asks for approval to operate in more than one core configuration. This is important in the training of students in that several different critical experiments may be run. Changes in rod worths among different cores could now be demonstrated.
We have asked for approval to operate in two basic core configurations.
These are shown in Figure 2. The standard core is a 12 element parallelepiped with a graphite reflector. The flux trap core will be either a 15, 16, 17 or 18 element core depending on the excess reactivity needed. The missing element at the center produces a neutron pileup which results in a thermal flux of about a factor of two over that in the standard core. (Both ANISN And EXTERMINATOR computer codes have been used to compute the flux in the hole.)
Such flexibility in core configuration is highly beneficial to the nuclear engineering program, both research and teaching.
Studies of the flux trap configuration have, however, pointed to what we feel make define the MHA.
Consider: The flux trap configuration is present. The pool water is at 20*C, the glory hole is empty and the excess reactivity is measured to be, say 0.a%. The reactor is shutdown by -4.6% (all four rods in). We now postulate the accident senario.
Unbeknown to the operator, a student loads a plastic rod in the GH (absolute violation of operative procedure). This has a positive worth of
- 0.1%. The reactor is now shutdown by -4.5%.
A new operator takes over and is told to change to a standard core. In
! absolute violation of procedure he loads a fuel element into the empty flux 11
R R R R R R R A R R R R f;)G U R E JE'.
R R F F F C R R F F F F R R F
F F F '
R R R R R R p- F u EL P L era EAIT g R R R R 17 = O SA P'" 'I #
R R EFL EC TO A ELE /k ENT A. Standard Core Configuration R 'R R 'R ' It R R R R R R
R F F F F W= WAT'A I' F F w w P F R R I
P F F F R R R R p
R R R R R R
- 8. Flux Trap Core Configuration 12 i
L
trap. That element is estimated to be worth 4.6% (three group EXTERMINATOR CALCULATIONS). The reactor, with all four rods in,, is now delayed critical, having a 0.1 excess. The resulting period will be about 60 seconds. This means that if the operator does not take an emergency corrective action within about 7 minutes, the reactor power will have reached 1000 watts. The large negative temperature coefficient (- 3.0 x 10-4/ *C) will simply shut the system down. The reactor operator would be expected to shove a cadmium sleeve in the glory hole or pour boric acid in the pool to secure a shutdown.
This accident is the only possible way we can postulate any large reactivity addition to an AGN-211P.
The result of a 2% step input was calculated by AEROJECT General in the original hazards analysis for the AGN. In summary, a 2% step would result in a period of 5-10 milliseconds. The excursion would last about 100 milliseconds. The core temperature would have reached 70*C -80*C, distorting the polyethylene fuel and terminating the reaction. The total energy release is estimated to be about 4 megajoules. Since a temperature of at least 200*C is required to melt the polythylene, no large fission product release would occur. The excursion would result in a dose of 1 to 2 R should a person be standing looking down into the pool. We note also that the 2% step would produce about 100 milliscuries of I-131.
While the consequences of these accident are relatively mild, steps must be taken to ensure that they do not occur. Such steps encompass both administrative and physical assurances.
13
_ __ -_._.__....m.__
T By procedure, to effect a change inL a, core configuration (flux trap to standard or reverse)
- 1. A SR0 will be present
- 2. A second person will be present
of the core change-over resulting in a large additional negative l reactivity (therefore, preventing the MHA postulated).
- 4. The change-over will be conducted form a written procedure.
Finally, it is noted that the greatest safety feature of the AGN polythylene fuel is its large negative temperature coefficient (3.6 x 10-4*C).
l i
14
- - . .. ~ . . - - - , _.
- . _ . - . - . - _