Calculation of Fuel Temperature Coefficient, Reactivity Loss and Temperature of BAEC TRIGA Research Reactor

Transcription

1 Asian Journal of Applied Science and Engineering, Volume 6, No 2/2017 ISSN X(p); (e) Calculation of Fuel Temperature Coefficient, Reactivity Loss and Temperature of BAEC TRIGA Research Reactor Md. Iqbal Hosan 1, M.A.M. Soner 2, Khorshed Ahmad Kabir 3 1,3 Department of Nuclear Engineering, University of Dhaka, Dhaka- 1000, BANGLADESH 2 Centre for Research Reactor, Bangladesh Atomic Energy Commission (BAEC), Savar, Dhaka, BANGLADESH *Corresponding Contact iqbalhosan@du.ac.bd ARTICLE INFO Article URL: Source of Support: None No Conflict of Interest: Declared ABSTRACT Fuel temperature reactivity coefficient is important for reactivity and power excursion transient analysis where power feedback effects depend on the sign, rate and time delay of the fuel temperature reactivity effects. In this study reactivity loss are measured at different fuel temperatures and various reactor power levels. Temperature coefficient of reactivity is measured for BTRR reactor power ranges from 0 to 3 MW. Fuel temperature and water temperature also measured at different reactor power levels. The measured values were found to be within the safety limit as mentioned in the Safety Analysis Report (SAR) of the BTRR. The present study will strengthen reactor operational safety and provide an experimental database for validation of computer codes of the nuclear reactor. Key Words: TRIGA Reactor, Fuel temperature coefficient, reactivity loss, Reactor power How to Cite: Hosan, M., Soner, M., & Kabir, K. (2017). Calculation of Fuel Temperature Coefficient, Reactivity Loss and Temperature of BAEC TRIGA Research Reactor. Asian Journal of Applied Science and Engineering, 6(2). This article is is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Attribution-NonCommercial (CC BY-NC) license lets others remix, tweak, and build upon work noncommercially, and although the new works must also acknowledge & be non-commercial. INTRODUCTION The BTRR (BAEC TRIGA Research Reactor) is the only nuclear reactor in the country. The reactor has been designed and constructed by the General Atomics (GA) of USA [A. Zahed Chowdhury et al., 2013]. The BTRR is a pool type, light water cooled, graphite reflected reactor which is used for manpower training, radioisotope production and various R&D activities in the field of Neutron Activation Analysis (NAA), Neutron Radiography (NR), and Neutron Scattering (NS) etc.[mi Hosan 2015, MI Hosan 2017] BTRR fuel is a solid homogeneous Copyright CC-BY-NC 2014, Asian Business Consortium AJASE Page 89

2 Hosan et al.: Calculation of Fuel Temperature Coefficient, Reactivity Loss and Temperature of BAEC TRIGA Research Reactor (89-94) mixture of E-U-ZrH alloy containing about 20% by weight of uranium enriched to about 19.7% U-235 and about 0.47% by weight of erbium. The hydrogen-to-zirconium atom ratio of the fuel-moderator material is about 1.6 to 1[Annual Report, 2013]. The important safety feature of BTRR is the Prompt Negative Temperature Coefficient of Reactivity (PNTCR). The nominal value of PNTCR for the BTRR is about % k/k/ C. [GA, SAR, 1986] The BTRR reactor is controlled by six control rods, which contain Boron Carbide (B4C) as the neutron absorber material. The reactor is licensed by the Bangladesh Atomic Energy Commission (BAEC) to operate at a maximum steady state power of 3 MW (thermal) and can also be pulsed up to a peak power of about 852 MW with a maximum reactivity insertion of up to $2.00 having a half maximum pulse width of nearly 18.6 milliseconds. [MA Salam 2014a, MA Salam 2014b] Reactor Operation and Maintenance Unit (ROMU) of AERE, Saver is responsible for operation and maintenance of the research reactor. THEORETICAL BACKGROUND The fuel temperature coefficient is defined as the change in reactivity over the change in temperature of fuel [Lamarsh 1966]. One of the main safety features of the BTRR fuel is the strong negative fuel temperature coefficient [Rhodes 1993]. This is accomplished by the incorporation of Uranium-Zirconium-Hydride (UZrH) alloy as reactor fuel. When positive reactivity is added into the reactor through the withdrawal of control rods, the power of the reactor will start to increase [DOE/NE-0088, Cohen 1983]. As a result, the fuel temperature will increase. Simultaneously, the temperature of the Zirconium- Hydride (ZrH) in the fuel matrix will increase. The high concentration of hydrogen mixed within the fuel will increase the energy of the incoming neutrons (also known as up-scattering) and therefore decrease the fission rates in the fuel [Groves 1975, Smyth 1976]. This is because a rise in fuel temperature will increase the probability that a thermal neutron (0.025eV) will gain energy after interacting with the ZrH matrix and therefore escape out of the fuel rather than fission due to the increased mean free path for interaction [Cohen 1983].This, then, will decrease the power of the reactor immediately and in turn, inherently control the reactor power [Rhodes 1988, Cantelon 1980]. The RTP core consists of a lattice of cylindrical fuel-moderator elements, in which the zirconium-hydride moderator is homogeneously combined with20%-235u, and graphite elements. The fuel consists of UZrH 1.6 with a uranium content of 8.5 wt%, 12 wt% and 20 wt% with a cladding of stainless steel. The power level of the reactor is controlled by 6 control rods: transient, shim-1, shim-2, shim-3, shim-4 and regulating. Fuel temperature was obtained through the use of an instrumented fuel element (IFE) with shim thermocouples embedded in the zirconium center line pin. Fuel temperature measurements were taken in the position C1 (ring C) and D3 (ring F). This reactivity coefficient is defined by: α g = ρ T Figure 1: Core configuration of the reactor Page 90 Volume 6, No 2/2017 AJASE

3 Asian Journal of Applied Science and Engineering, Volume 6, No 2/2017 EXPERIMENTAL PROCEDURE ISSN X(p); (e) To measure fuel temperature reactivity coefficient the power is gradually increased from 1 kw to the power of 3000 kw by withdrawal of control rods. The fuel temperature is measured in a fuel element, containing a thermocouple. The last step brings the reactor to 3000 kw power. The temperature coefficient is calculated on the basis of the control rods movements, the known calibration curves for control rods and corresponding temperature changes. The experiment was performed by increasing the reactor power, and consequently, the fuel temperature by withdrawing the control rods in a number of steps. Initially, the reactor was critical at 1 kw, until thermal steady-state conditions were reached in the core, and the fuel temperatures were 27 in the C ring and 31 in the D ring. Note that the reactor hall temperature was estimated around 30 C. The power was raised until a specific value, and then reached a new steady higher level, and the fuel temperatures raised as well. From the fact that the power level is limited to a given reactivity insertion, one can conclude that the power coefficient of reactivity is negative. The reactor power, the fuel temperatures and the control rod positions were recorded for each steady-state power level. The reactivity change ρ was determined from the calibrated control rod curve, considering each critical rod position, before and after each step. DATA COLLECTION AND ANALYSIS The effects of the negative temperature are considered at fuel temperatures above 40 C [Edelson 1994, MA Salam 2014b]. Therefore, one can measure the temperature effects during regular BTRR operations at all temperatures above 40 C and average these values to derive the average negative temperature coefficient of the BTRR of the C-1 and D-4 fuel elements. The increase in fuel temperature adds a negative amount of reactivity that is equal to the reactivity inserted into the reactor by the withdrawal of the control rods. The temperature distributions across the fuel element in ring-c and in ring-d are plotted in figure 2 and temperature distributions in the pool are plotted in figure 3 at different power level are given below: Figure 2: Fuel temperature distributions across the fuel element at different power level Copyright CC-BY-NC 2014, Asian Business Consortium AJASE Page 91

4 Hosan et al.: Calculation of Fuel Temperature Coefficient, Reactivity Loss and Temperature of BAEC TRIGA Research Reactor (89-94) Figure 3: Water temperature at different power level Figure 5 shows the reactivity losses as a function of the fuel temperatures measured at C and F rings. The reactivity loss increases as the fuel temperature rises. If these relationships assumed to be linear, the temperature coefficient of reactivity is related to the slope of the curve. Figure 4: Temperature coefficient of reactivity at different power level. Page 92 Volume 6, No 2/2017 AJASE

5 Asian Journal of Applied Science and Engineering, Volume 6, No 2/2017 ISSN X(p); (e) Figure 5: Loss of reactivity at different power level. Figure 6: reactivity loss versus fuel temperature in ring-c and ring-d CONCLUSION Measurement and validation of safety parameters of a nuclear reactor are mandatory for reactor start up, normal power operation, experimental research and shutdown. To ensure the operational safety of the BAEC TRIGA research reactor (BTRR) nuclear safety parameters were measured with the PC based digital instrumentation and control (I&C) system. The fuel elements temperature is proportional to fuel elements power, which in turn is proportional to reactor power. As the control rods are withdrawn, positive reactivity is inserted. As a result, the reactor power increases, the fuel element temperature increases, Copyright CC-BY-NC 2014, Asian Business Consortium AJASE Page 93

6 Hosan et al.: Calculation of Fuel Temperature Coefficient, Reactivity Loss and Temperature of BAEC TRIGA Research Reactor (89-94) causing a negative reactivity insertion in return. The fuel temperature coefficient in C-ring is 0.51cent/ and in D-ring is 0.59 cent/.in average, these value give 0.55 cent/ (3.85x10-05 / ) which is lower than the value in SAR report of BTRR. The accuracy of the results depends on the measurement of ρ and T. Further analysis and measurement is needed to fully understand this discrepancy. REFERENCES BAEC. Annual report of the reactor operation and maintenance unit. Atomic Energy research Establishment, Bangladesh Atomic Energy Commission, July Cantelon, Philip, and Robert C. Williams. Crisis, The Department of Energy at Three Mile Island: A History, Washington, D.C.: U.S. Department of Energy, Cohen, Bernard L., Before It s Too Late, A Scientist s Case for Nuclear Energy, New York: Plenum Press, DOE/NE -0088, The history of nuclear energy. Edelson, Edward, The Journalist's Guide to Nuclear Energy, Nuclear Energy Institute, General Atomics (GA), Safety Analysis Report of BAEC 3 MW TRIGA Mark-II Research Reactor. Groves, Leslie R., Now It Can Be Told, The Story of the Manhattan Project, New York: Harper, Lamarsh, J.R., Introduction to Nuclear Reactor Theory, Addison-Wesley, 1966, Chapter 3. MI Hosan, MAM Soner, KA Kabir, MA Salam, MF Huq, (2015). Study on neutronic safety parameters of BAEC TRIGA research reactor. Annals of Nuclear Energy 80, MI Hosan, MAM Soner, MF Huq, KA Kabir, (2017). Measurement and Comparison of control rod worth of BTRR using Inhour Equation and Period reactivity conversion table. Journal of Bangladesh academy of sciences 41(1), Rhodes, Richard, Nuclear Renewal: Common Sense about Energy, Viking, Rhodes, Richard, The Making of the Atomic Bomb, Touchstone, Salam, M. A., M. A. M. Soner, M. A. Sarder, A. Haque, M. M. Uddin, M.M Sarker, S. M. A. Islam. 2014a. Measurement of control rod reactivity and shutdown margin of 3 MW TRIGA Mark-II research reactor using analogue and digital I&C system. Annals of Nuclear Energy 68: Salam, M. A., M. A. M. Soner, M. A. Sarder, A. Haque, M. M. Uddin and A. Rahaman, 2014b.Measurement of neutronic safety parameters of the 3 MW TRIGA Mark-II research reactor. Progess in Nuclear Energy 74: Smyth, Henry D., Atomic Energy for Military Purposes, Princeton: Princeton University Press, Zahed Chowdhury, A., M. A. Zulquarnain, A. Kalam, A. Rahman, M. A. Salam, M. A. Sarder, M. R. I. Khondoker and M. M. Rahman Beam Port Leakage Problem in the BAEC TRIGA Mark-II Research Reactor and the Corrective Measures Implemented. International Journal of Scientific & Engineering Research, 4(4): Page 94 Volume 6, No 2/2017 AJASE