Transient light reactors

As with plain contact dermatitis, avoidance of contact with the photoallergen in a patient with PACD usually results in clearing of the dermatitis and the photosensitivity. Occasionally, however, the patient continues to be photosensitive that is, he or she continues to react to light, with the development of dermatitis. Such patients were first observed with antibacterial photoallergens and were referred to as persistent light reactors. In contrast, patients whose conditions cleared once the photoallergen was removed were called transient light reactors. 

As in all light water-moderated and low-enrichment reactors, the fuel Doppler reactivity coefficient is negative and prompt in its effect, opposing reactor power transients. When reactor power increases, UO2 temperature increases with minimum time delay, resulting in higher neutron absorption by resonance capture in the U-238. 

Anticipated Transients without Scram for Light Water Reactors, Vol. 1-3, December 1978. Haasl, D. F, et al., Fault Tree Handbook, January 1981. 

In the preceding sections we concentrated mainly on the coke-conversion selectivity aspects of various reactors. In this section we will briefly discuss the selectivities of major FCC products gasoline, LCO, HCO, and light gases in both transient and steady state reactors. Weekman (1-3) has looked at steady state and transient reactors for gasoline selectivity shifts. However, he did not include axial dispersion effects in his analysis which are important for laboratory FFB reactors, and are accounted for here. 

This order applies to all varieties of reactors including, but not limited to light water moderated reactors, heavy water moderated reactors, liquid metal cooled reactors, gas cooled reactors and short-pulse transient reactors. Space reactor power and propulsion systems and critical facilities require special design criteria. Attachment 4 is reserved for Nuclear Safety Design for critical facilities and space reactors. 

NUREG-0460, "Anticipated transients without scram for light water reactors," US Nuclear Regulatory Commission, March 1980. 

Prediction of the thermal margins of fuel elements to a harmful phenomenon like critical heat flux (CHF) during normal operation and transients is considered to be of the utmost importance. Mass flow rate in the core of the CAREM reactor is rather low compared to typical light water reactors and therefore available correlations or experimental data are not completely reliable in the range of interest. Thus, analytical data should be verified by ad-hoc experiments. 

Because of the effect of inelastic scattering in the spectrum softens as the proportion of fertile to fissile material is increased. Further softening is produced by the introduction of light elements, for example by the use of oxide or carbide fuel. As a result, the spectrum in a full-scale oxide-fueled fast reactor is considerably softer than that in the early compact cores of the EBR type. It may in fact be desirable deliberately to introduce a certain amount of additional moderation in order to improve the response of the reactor to power transients (see Section 11.3). 

Apart from the clad melt mentioned above, it is difficult to find plausible mechanisms for significant reactivity transients in a gas-cooled thermal reactor. The number of control rods tends to be large, so that the maximum reactivity worth of a single rod is usually of the order of 0.1 %, in comparison with the 2% or so possible in a light water reactor. Consequently, rapid... 

Identical initial DCPIPox concentrations within the reactor and transient asymmetric boundary conditions (inlet DCPIPox concentration or incident light intensities). ... 

In April 1978 the regulatory staff issued a new report, NUREG-0460, titled "Anticipated Transients Without Scram for Light Water Reactors." This report proposed a change in safety objective for an unacceptable ATWS from 10 per reactor-year as set forth in the WASH-1270 to lO per reactor-year. This was apparently based on the overall frequency of core melt predicted in the Reactor Safety Study... 

U. S. Nuclear Regulatory Conunission Staff Report, "Anticipated Transients Without Scram for Light Water Reactors, NUREG-0460, December, 1978. 

Y. Okano, S. Koshizuka, et al., Flow Induced Transient Analysis of a Supercritical Pressure, Light-Water-Cooled Fast Breeder Reactor, Proc. 3 rd JSME/ASME Joint International Conf. on Nuclear Engineering, Kyoto, Japan, April 23-27, 1995, 891-895 (1995)... 

K. Kitoh, S. Koshizuka and Y. Oka, Craitrol Rod, Pressiue and Flow-Induced Accident and Transient Analyses of a Direct-Cycle, Supercritical Pressure, Light-Water-Cooled Fast Breeder Reactor, Proc. ICONE-4, New Orleans, LA, April, March 10-14, 1996, Vol. 2, 537-545 (1996)... 

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