ML20114B625
| ML20114B625 | |
| Person / Time | |
|---|---|
| Site: | University of Utah |
| Issue date: | 01/23/1985 |
| From: | Linder C LOS ALAMOS NATIONAL LABORATORY |
| To: | Thomas C Office of Nuclear Reactor Regulation |
| References | |
| Q-6-85-187, NUDOCS 8501290371 | |
| Download: ML20114B625 (7) | |
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IN REPLY REFER TO:
January 23, 1985 Q-6-85-187_(R649)
Los Alamos NationalLaboratory ma. stoa: K557 LosAlamos NewMexico87545 retemo"E (505) 667-7000 FTS 843-7020 Safety Assessment Mr. C. O. Thomas, Chief Standardization & Special Projects Branch Division of Licensing Mail Stop 340-Phil US Nuclear Regulatory Commission Washington, DC 20555
Dear Sir:
Enclosed are pages of the University of Utah TRIGA Reactor (UUTR)
Technical Evaluation Report (TER) that have been changed to reflect the new excess reactivity limit of 1.96% Ak/k (2.805) in accordance with the instructions received from your staff. Also enclosed is a completed version of Table 14.2, " Calculated Radiation Dose Rates," of the subject TER that incorporates additional details just received from the licensee.
If you have any questions about these revisions, please call me at the above number or, in my absence, call A. E. Sanchez-Pope on FTS 843-9746.
Sincerely,
/
C. A. Linder CAL /jl Cy: H. N. Berkow, NRC/NRR M. G. Stevenson/W. L. Kirk, Q-00, w/o enc., MS E561 L. H. Sullivan/J. R. Ireland,Q-D0/RS, MS K552 R. A. Haarman/W. S. Gregory, Q-6, MS K557 J. E. Hyder, Q-6, MS K557 CRM-4 (2), MS A150 Q-6 File 8501290371 850123 PDR ADOCK 05000407 P PDR l
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' An Equal opportunny Employer / Operated try the UrWversny of Cakforrus t
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- 4. REACTOR The University of Utah TRIGA Reactor (UUTR) is a General Atomic Mark I reactor that operates at a maximum steady-state power level of 100 kW. It uses solid uranium-zirconium-hydride fuel containing 8 and/or 8.5 weight-per cent uranium and is enriched to <20% 8 3 5U. The UUTR contains a mixed core of stainless-steel-clad and aluminum-clad elements. Light water serves as the moderator and coolant. The reactor power is regulated by inserting or withdrawing neutron-absorbing control rods.
The UUTR initially attained criticality in October 1975. It is used principally as a neutron source for activation analysis studies, academic research, and the limited production of radioactive isotopes. It also is used as a tra.ning i
facility for the engineering program. Currently it operates an averacs of 10 MWh/yr. The principal design parameters for the current core configuration are listed in Table 4.1.
4.1. Reactor Building Facility Layout The reactor is located on the University of Utah campus in Room 1001 of the Merrill Engineering Building. Only Rooms 1001E and 1001F are restricted areas; they form a confinement enclosure for the reactor. The reactor room is 42 ft by 23 ft by 20 ft high (12.8 m by 7.0 m by 6.1 m high) and has a structural steel frame construction with a concrete floor and ceiling. An AGN-201M 5-W nuclear reactor that is occasionally used for teaching and training purposes also is located in the reactor room. However, no neutronic interaction or hazard coupling between the TRIGA and the AGN-201M is considered credible. The UUTR facility layout is shown in Fig. 4.1.
4.2. Reactor The UUTR is located in a 24-ft-deep, 8-ft-diam (7.5-m-deep, 2.4-ft-diam) reactor pool. The reactor core heat is dissipated by natural convection of the bulk pool water. The UUTR maximum reactivity loading is limited by the Technical Specifications to 1.96% Ak/k (2.80$) excess reactivity above the cold critical condition. The UUTR has no pulsing capabilities.
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TA8LE 4.1 PRINCIPAL DESIGN PARAMETERS Parameter Descriotion Reactor type TRIGA Mark I Maximum steady-state power level 100 kN h Fuel element design Fuel-moderator material U-ZrH1.6 and U-ZrH1 .0 Uranium inventory 3.35 kg ***U (current core configuration)
Uranium conter.t 8 and 8.5 weight-per cent
, (aluminum and stainless-steel clad)
Uranium enrichment (20s 885U Shape Cylindrical tength of fuel 14 in. (35.6 cm) Al clad elements 15 in. (30.1 cm) SS clad elements Diameter of fuel 1.47 in. (3.7 cm)
Cladding material and nominal thickness 304 stainless steel [0.02 in.
(0.05 cm) thick] and aluminum
[0.03 in. (0.076 cm) thick]
bioight 8 8 8U/ fuel element ~37 g (8 weight-per cent Al clad fuel) and ~39 g (8.5 weight-per cent SS clad fuel)
Alumber of fuel elements 72 (minimum core) or 80 (current core)
Reactivity worths Encess reactivity 0.03% Ak/k (1.tel) [1.96% Ak/k (2.00$) Tech. Spec, maximum limit with cold, clean, critical condition]
Safety-transient rod (1) 1.25% Ak/k (1.76$)
Shim rod (1) 1.005 8k/k (1.55$)
Regulating rort (1) 0.32% Ak/k (0.46$)
Total reactivity of rods 2.64% Ak/k (3.77$)
Reactor cooling hatural convection of pool water Reflector bioter, D2 0-filled trapezoidal tanks, and cylindrical D2 0-filled elements 8 effective 0.7% Ak/k aFor stainless-steel-clad elements, the nominal ratio is 1.60 and the maalmum value is 1.67. For aluminuse-clad elements, the nominal ratio is 0.9 and the
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GA-4314, 1980; GA-0471, 1958). This inherent shutdown property of U-ZrH, fuel has been the basis for designing the TRIGA reactors with a pulsing capability as a normal mode of operation. The automatic compensation provided by the prompt negative temperature coefficient for step excess reactivity insertions is capable of terminating any resulting power excursion in the pulsing mode without using any i.echanical or electrical safety systems or operator action.
Because the UUTR only operates in the steady-state mode, this serves as a backup safety feature for the mitigation of accidental reactivity insertion effects (Simnad et al., 1976; CA-4314, 1980; GA-0471, 1958). (See also Sec. 14.2.)
4.5.1. Excess Reactivity and Shutdown Margin The Technical Specifications require that the control rods provide a shutdown margin greater than 0.35% ok/k (0.50$) with the highest worth control rod fully withdrawn and with the highest worth nonsecured experiment in its most reactive state under any conditions of operations.
The Technical Specifications for the UUTR limit the maximum core excess reactivity to 1.96% ak/k (2.80$) above the cold, clean, critical, xenon-free condition. The Technical Specifications limit experiment reactivity worths to 1.96% ok/k (2.80$) for any single experiment and 0.7% Ak/k (1.00$) for any single nonsecured experiment.
The current core configuration has an excess reactivity of 0.83% Ak/k (1.18$). The individual control rod worths are shown in Table 4.1; the total rod worth is 2.64% ak/k (3.77$). The shutdown margin for the current core configuration with the highest worth rod fully withdrawn is 0.58% ok/k
(= 2.64 - 1.23 - 0.83) or 0.83$ (= 3.77 - 1.76 - 1.18). Therefore, the current core configuration meets the shutdown requirements. With all rods fully inserted, the current core is subcritical by 1.81% ak/k (2.59$).
SECOND REVISION a'
occupational personnel and to the public in unrestricted areas would be below the limits stipulated in 10 CFR 20. Accordingly , there would be no significant risk to the health and safety of the public.
14.2. Rapid Insertion of Reactivity (Nuclear Excursion)
The U-ZrH fuel in the UUTR exhibits a strong, prompt, negative temperature coef ficient of reactivity, as discussed in Sec. 4.5. This temperature coefficient terminates any pulse or nuclear excursion and decreases the amount of reactivity as the steady-state temperature of the fuel increases. These results have been verified at many operating TRIGA reactors. Although it may be possible theoretically to rapidly insert sufficient excess reactivity ur. der accident conditions to create an excursion such that fuel damage would occur before the excursion could be terminated, the limits imposed by the Technical Specifications of the UUTR make such an event unlikely.
14.2.1. Scenario The maximum power excursion transient that is postulated to occur is the event in which the total available amount of excess reactivity is inserted into the core instantaneously. The UUTR is limited by the cuerant license to 1.96% Ak/k (2.80$) e> cess reactivity above a cold, critical condition.
However, the Los Alamos review has not been able to identify a credible method for instantaneously inserting all of the available excess reactivity.
Los Alamos has considered the scenario of the reactor operating at some steady-state power level between 0 and 100 kW, at which time all the remaining excess reactivity is inserted rapidly into the core. The analysis conservatively neglected the reactivity loss as a result of the xenon (185Xe) buildup. Los Alamos found that the worst case would be the initiation of a 1.96% Ok/k (2.80$) step insertion with the core at ambient temperature and essentially zero initial power. The potential significant reactivity insertion accident cansequences that were considered by Los Alamos are melting of the fuel or cladding material, failure of the cladding as a result of high internal gas pressures, and/or phase changes in the fuel matrix. The major cause of fuel element cladding failure at elevated SECOND REVISION
4 The fuel experienced no melting effects because of the temperature increase, and the fuel element cladding integrity was maintained. Thus, a 1.96% ak/k (2.80$) step reactivity insertion accident on a nonpulsing reactor such as the UUTR will not result in a loss of cladding integrity or mechanical damage to the fuel. Because the radial temperature distribution in a fuel element immediately following a step insertion of reactivity is similar to the radial power distribution, the peak temperature immediately following a step insertion of reactivity is located at the periphery of the hottest fuel element. This temperature decreases rapidly (within seconds) as the heat flows towards the cladding and the fuel center.
Based on the above analysis, Los Alamos concludes that the rapid insertion into the UUTR core of the 1.96% ak/k (2.80$) available excess reactivity will not result in fuel melting nor a cladding ' allure due to high internal gas pressure or high temperature. Therefore, there is reasonable assurance that the fission products contained in the fuel will not be released to the environment as a result of the rapid insertion of reactivity accident.
'.3.
Loss-of-Coolant Accident The rapid loss of shielding and cooling water following reactor operation is considered to be a potential accident that would result in the increase of fuel and cladding temperatures. Because the water provides for the major SECOND REVISION
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TABLE 14.2 CALCULATED RADIATION DOSE RATES Instantaneous Loss of Reactor Pool Water Direct Radiation Levels (rem /h or 10-2 Sv/h)
Time after shutdown Top of Pool Floor of Laboratorva 0.1 h 440.0 4.1 1.0 h 236.0 2.3 10.0 h 112.0 1.1 1.0 day 80.0 0.69 1.0 week 36.4 0.36 1.0 month 6.6 0.065 Decrease in Pool Water Level at 0.4 m/h Direct Radiation Levels (mrem /h or 10-2 mSv/h)
Time after Water Depth shutdown over core (m) Top of Pool Floor of Laboratorya 0.1 h 6.1 10-3 10-10 1.0 h 5.6 10-3 10-10 5.0 h 4.1 10-3 2.1 x 10-10 10.0 h 2.1 3.0 x 10-2 0.051
.15.2 h 0 8.3 x 104 880.0 24.0 h 0 6.6 x 104 692.0 mLocated on second level floor directly above the reactor.
SECOND REVISION