Effect of Xenon Oscillations on CANDU Power Cycles

Progress in Nuclear Energy, 2012

Large quantities of nuclear waste plutonium and minor actinides (MAs) have been accumulated in the civilian light water reactors (LWRs) and CANDU reactors. These trans uranium (TRU) elements are all fissionable, and thus can be considered as fissile fuel materials in form of mixed fuel with thorium or naturanium in the latter. CANDU fuel compacts made of tristructural-isotropic (TRISO) type pellets would withstand very high burn ups without fuel change. As carbide fuels allow higher fissile material density than oxide fuels, following fuel compositions have been selected for investigations: ① 90% nat-UC þ 10% TRUC, ② 70% nat-UC þ 30% TRUC and ③ 50% nat-UC þ 50% TRUC. Higher TRUC charge leads to longer power plant operation periods without fuel change. The behavior of the criticality k N and the burn up values of the reactor have been pursued by full power operation for > w12 years. For these selected fuel compositions, the reactor criticality starts by k N ¼ 1.4443, 1.4872 and 1.5238, where corresponding reactor operation times and burn up values have been calculated as 2.8 years, 8 years and 12.5 years, and 62, 430 MW.D/MT, 176,000 and 280,000 MW.D/ MT, with fuel consumption rates of w16, 5.68 and 3.57 g/MW.D respectively. These high burn ups would reduce the nuclear waste mass per unit energy output drastically. The study has show clearly that TRU in form of TRISO fuel pellets will provide sufficient criticality as well as reasonable burn up for CANDU reactors in order to justify their consideration as alternative fuel.

IEEE Transactions on Nuclear Science, 2005

The regional overpower protection (ROP) system of a Canada deuterium uranium (CANDU) reactor was assessed for the direct use of spent pressurized water reactor fuel in CANDU reactors (DUPIC), including the validation of the Winfrith improved multigroup scheme (WIMS)/reactor fuelling simulation program (RFSP)/reduction power (ROVER) code system used for the calculation of the ROP trip setpoint (TSP). Comparative calculations showed that the WIMS/RFSP/ROVER code system produced results consistent with the current design code system for estimating the ROP TSP of the standard natural uranium CANDU reactor. For the DUPIC fuel CANDU core, the ROP TSP was estimated to be 123.4%, which was almost the same as that of the standard natural uranium core. The extra margin of the ROP TSP for the DUPIC fuel system was enhanced by the flattened axial channel power distribution as well as the reduced refueling ripple of the channel power. This study has shown that the DUPIC fuel does not deteriorate the current ROP TSP designed for the natural uranium CANDU reactor.

World Journal of Nuclear Science and Technology, 2011

In these studies the isotopic inventories and corresponding activities of important nuclides for different fuel cycles of a CANDU reactor have been compared. The calculations have been performed using the computer code WIMSD4. The isotopic inventories and activities have been calculated versus the fuel burn-up for the natural UO 2 fuel, 1.2% enriched UO 2 fuel and for the 0.45% PuO 2-UO 2 fuel. It is found that 1.2% enriched uranium fuel has the lowest activity as compared to other two fuel cycles and vice versa for the 0.45% PuO 2-UO 2 fuel.

Fusion Technology, 1992

Radioactivity induced in a typical fusion power reactor was calculated for all elements with atomic number Z < 84 and for different irradiation times. It was shown that the shutdown activity varies widely with the duration of the irradiation time. In general, the activity induced by radionuclides with halflives that are significantly longer than the period of irradiation increases with increasing the irradiation time. On the other hand, the level of activity generated by any radionuclide with a half-life which is significantly shorter than the reactor lifetime reaches a peak early during irradiation and then may starts to drop to lower value before the end of irradiation. The severity of this peaking is determined by the destruction rate of the parent element The activities generated by long-lived nuclides (important for waste management) in any fusion reactor with life time in the order of 30 years reach their peak values at end-of-life. In the mean time, using the activity and decay heat values generated by short and intermediate-lived radionuclides at the end of reactor life to represent the worst case values used in safety analyses related to a loss of coolant accident (LOCA) and accidental release of radioactive inventory might lead to a substantial underestimation of the results.

Nuclear Engineering and Design, 2006

Weapon grade plutonium is used as a booster fissile fuel material in the form of mixed ThO 2 /PuO 2 fuel in a Canada Deuterium Uranium (CANDU) fuel bundle in order to assure the initial criticality at startup. Two different fuel compositions have been used: (1) 97% thoria (ThO 2) + 3%PuO 2 and (2) 92% ThO 2 + 5% UO 2 + 3% PuO 2. The latter is used to denaturize the new 233 U fuel with 238 U. The temporal variation of the criticality k ∞ and the burn-up values of the reactor have been calculated by full power operation for a period of 20 years. The criticality starts by k ∞ = ∼1.48 for both fuel compositions. A sharp decrease of the criticality has been observed in the first year as a consequence of rapid plutonium burnout. The criticality becomes quasi constant after the second year and remains above k ∞ > 1.06 for ∼20 years. After the second year, the CANDU reactor begins to operate practically as a thorium burner. Very high burn up could be achieved with the same fuel material (up to 500,000 MW•D/T), provided that the fuel rod claddings would be replaced periodically (after every 50,000 or 100,000 MW•D/T). The reactor criticality will be sufficient until a great fraction of the thorium fuel is burnt up. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically.

To Ann xiv Preface removes any drudgery that might otherwise be entailed. Selected problems require the use of one of the earlier mentioned high level computing languages for the solution of transcendental or differential equations. These are marked with an asterisk. The preparation of this text would have been immensely more difficult if not impossible without the help and encouragement of many friends, colleagues, and students. Advice and assistance from the staff of the Nuclear Engineering Division of Argonne National Laboratory have been invaluable in the text's preparation. Won Sik Yang, in particular, has provided advice, reactor parameters, graphical illustrations, and more as well-taking the time to proofread the draft manuscript in its entirety.

Journal of Engineering, 2013

This paper looks at the existing challenges with steady-state Liquid Zone control at some CANDU (CANada Deuterium Uranium) stations, where—contrary to expectations for equilibrium flow—Liquid Zone Control Valve oscillations have proven to be a chronic, unanticipated challenge. Currently, the exact causes of this behaviour are not fully understood, although it is confirmed that the Control Valve oscillations are not due to automatic power adjustment requests or zone level changes due to process leaks. This phenomenon was analysed based on a case study of one domestic nuclear power station to determine whether it could be attributed to inherent controller properties. Next, a proposal is made in an attempt to improve current performance with minimal changes to the existing system hardware and logic using conventional technologies. Finally, a proposal was made to consider Model Predictive Control-based technology to minimize the undesirable Control Valve oscillations at steady state bas...

International Journal of Energy Research, 2016

Spent nuclear fuel out of conventional light water reactors contains significant amount of even plutonium isotopes, so called reactor grade plutonium. Excellent neutron economy of Canada deuterium uranium (CANDU) reactors can further burn reactor grade plutonium, which has been used as a booster fissile fuel material in form of mixed ThO 2 /PuO 2 fuel in a CANDU fuel bundle in order to assure reactor criticality. The paper investigates incineration of nuclear waste and the prospects of exploitation of rich world thorium reserves in CANDU reactors. In the present work, the criticality calculations have been performed with 3-D geometrical modeling of a CANDU reactor, where the structure of all fuel rods and bundles is represented individually. In the course of time calculations, nuclear transformation and radioactive decay of all actinide elements as well as fission products are considered. Four different fuel compositions have been selected for investigations: ① 95% thoria (ThO 2) + 5% PuO 2 , ② 90% ThO 2 + 10% PuO 2 , ③ 85% ThO 2 + 15% PuO 2 and ④ 80% ThO 2 + 20% PuO 2. The latter is used for the purpose of denaturing the new 233 U fuel with 238 U. The behavior of the criticality k ∞ and the burnup values of the reactor have been pursued by full power operation for~10 years. Among the investigated four modes, 90% ThO 2 + 10% PuO 2 seems a reasonable choice. This mixed fuel would continue make possible extensive exploitation of thorium resources with respect to reactor criticality. Reactor will run with the same fuel charge for~7 years and allow a fuel burnup~55 GWd/t.

Energy Conversion and Management, 2004

A neutronic analysis has been performed to assess a prospective utilization of light water reactor (LWR) spent fuel in Canada deuterium uranium (CANDU) reactors mixed with thoria (ThO 2 ). The study is conducted for mixture grades with 50%, 60% and 100% LWR spent fuel and 50%, 40% and 0% thoria, respectively.

ICONE28, 2020

One sees eerie similarities here in Canada to the incestuous, cozy relationship between regulator and utilities in pre-Fukushima Japan. This has created conditions that are ripe for a nuclear disaster. Operating reactors have barely seen any substantive risk reduction upgrades seven eight years after Fukushima, hoopla around some minor improvements and closure of regulatory 'Fukushima Action Items' notwithstanding .notwithstanding. At less than 0.7 atm(g) design pressure and design leakage ~500 times the 0.1%/day norm in newer PWRs, the multi unit CANDU reactors sport some of the weakest containments; have high steam and air oxidation potential in 10km of low carbon steel feeder piping and twice the Zircaloy of LWRs. Combustible gas detection and mitigation systems are unfortunately designed for Hydrogen instead of Deuterium gas in these PHWRs. With no reactor pressure vessel to isolate the overheating core debris, the leaky containments become immediate recipients for copious quantities of combustible Deuterium and fission products. Reactor geometries and interconnected reactors promote combustible gas explosion potential. The pressure relief systems in cooling and moderating systems are dangerously inadequate, resulting likely in containment bypass and vessel failures. Even more dangerous are the unsubstantiated claims being made of near impossibility of off-site releases by clueless, irresponsible management without nay a challenge by the regulators, eager to rubber stamp all industry requests. The life management issues of ageing, elongating, thinning, hydriding, embrittling and deforming pressure tubes is yet to be resolved but these obsolete reactors keep getting ever longer license extensions (over 50% beyond original Pickering pressure tube design life). Proposed engineering fixes that can be undertaken to overcome some critical vulnerabilities are groundlessly rejected in ingrained obdurate industry intransigence against changes. Emergency preparedness by civil authorities has been conditioned for smallest source terms and available response time for mitigation measures irresponsibly exaggerated. A number of early mitigation measures, common to all PWRs, will not work due to an unusually low, below core, placement of Pressurizer that will divert much primary coolant in detriment of potential fuel cooling restoration by re-flooded boilers inducing natural circulation flows. These are signs of impending implosions in Canadian nuclear industry that has avoided resilience engineering. Not likely, but perhaps disaster can be avoided by a return to the principles, and not mere slogans, of 'safety first'. Right now, an unmitigated station blackout in a CANDU multi-unit station will make Fukushima disaster look like a walk in the park.