Integral Rod Worth

Table n gives a comparison of the measured and calculated temperature coefficients and eigenvalues between 74 and 464 F. The temperature defect between 74° and 464 F was estimated from integrated rod worths to be about 3%. Rod worths and temperature coefficients were b d on a calci ted effective delayed neutron fraction fi of 0.0074 (i.e., p/p = 1.16). In addition to having a small absolute bias (all calculated eigenvalues are within + 0.5 and - 0.9% of measured values), the model describes the temperature effects quite accurately. 

Explain (sketches might make it easier) the difference between differential and integral rod worth curves for UWNR. 

Which ONE of the following correctly describes the relationship between Differential Rod Worth (DRW) and Integral Rod Worth (IRW) ... 

Using the Integral Rod Worth Curve provided identify which ONE of the following represents ""Excess Reactivity"" ... 

The integral rod worth curve is a plot of the summed area under the differential curve up to a designated rod position. The value of the integral worth is the cumulative effect of withdrawing a control rod a specific distance from the core. 

Construct an integral rod worth curve from a differential curve or from differential data. 

Construction of an integral rod worth curve from a differential worth curve is illustrated in Figure 7.2. Starting at the bottom of the core, move up one inch of rod position. At that point, observe the differential worth value. That value is not truly representative of the differential worth over the first inch. Some lower value is. The product of the estimated differential worth times the inch of motion is the cross hatched rectangular area shown on Figure 7.2.a. The cross should be equal to the actual area under the curve position. The actual area, which is the summed or up to that position, is shown dotted in Figure 7.2. of the hatched area are differential worth (AK/K/in... 

The integral rod worth curve is S shaped, As the rod is withdrawn from the low flux bottom of the core, cumulative reactivity is added slowly. Reactivity is added rapidly at midcore where flux is highest. As the rod is withdrawn toward the top of the core, the slope of the curve diminishes again because the rate of reactivity addition tapers off. 

Typical Integral Rod Worth as a Function of Axial Rod Position... 

The number and location of the top entry control rods and the diverse reserve shutdown control have been specified to assure that the reactor thermal power is controlled both for normal and off-normal conditions. The radial thickness of the active core annulus was specified on the basis of assuring that the control rod worths of the reflector-located rods would meet all shutdown and operating control worth requirements. The choice of reflector control, coupled with the choice of a control system withdrawal sequence and safety classification was made to assure that the control rod integrity is maintained during passive decay heat removal. 

Sketch and label an integral control rod worth curve. 

Reactor physical characteristics have also drawn much attention. The control rod worth, including the differential worth and integral worth, were calculated by the Monte Carlo code for neutron and photon transport (MCNP) for the 2 MW TMSR-SE (Zhou and Liu, 2013). The measurement of the neutron energy spectrum was also theoretically and experimentally studied (Zhou, 2013). Parametric study of the thorium-uranium conversion rate was conducted to optimize the core structure for the improvement of the economics of the TMSR using the standardized computer analyses for licensing evaluation (SCALE) code (Wang and Cai, 2013). 

The CPT is responsible for integration and implementation of the core design and safety analyses, which includes responsibility for design specifications, verification that fuel received is within specifications, verification that core conditions lie within core design and safety analysis criteria, operating limits, physics ihd thermal-hydraulic data for operational assessment and operational data for core design and safety analyses. The CPT is also responsible for core performance analysis which includes estimated critical position predictions, shutdown reactivity predictions, control rod worth curves, operational anomaly analysis and observed performance summaries. 

Theoretically, a single rod may reach a worth of two per cent or more (as an example, a rod at the centre of the core with all the other rods inserted, which increases the worth of the rod) but the reactivity corresponding to the ejection of any rod (one of the DBAs) is always kept below the prompt reactivity value (0.6 per cent) typically a limit of 0.5 per cent is adopted. The integrated worth of a control rod has the shape shown in Figure 4-5. 

A weighted least-squares method was used to fit a straight line to the inverse cube root of the differential worth vs rod-bank height. Hie integral of the differential worth from the critical rod-bank configuration to an all-rods-out configuration was then taken to be the excess reactivity of that particular core configuration. 

Continue the evaluation and summation of areas as shown in Figures 7.2.c and 7.2.d over the entire length of the rod, The final integral worth curve is shown in Figure 7.2.d. The left... 

A reactor is critical at low power. The integral reactivity of a bank of rods is 1.2 XAK/K rod bank worth IS linear over its 12 ft length. The bank is withdrawn 12 inches at a speed of 1.2 in/sec. 

Figure 5 of Reference 2 can be used to determine the negative reactivity input required to produce a given flux response as a function of time. Use of these curves presupposes that the reactor is in a "one-slab loading" condition and that the assembly is critical. If these conditions are fulfilled, one need merely cause the control rod being calibrated to be inserted fully and rapidly into the assembly by means of the rod-drop pushbutton on the reactor console and to read the flux response of the system from detection instruments and strip-chart recorders provided (see Fig. 3.6). This procedure will be iterated with successively larger reactivity inputs, noting the portion of the rod travel for each input, until finally the entire rod travel is used as an input. The reactivity values thus obtained can be plotted versus the position from which the rod began to fall to obtain an integral calibration or "worth" curve.

The completed flight power unit was to be received from the core vendor. Zero-power physics tests were to be performed to confirm that no significant manufacturing errors exist, and to obtain an initial physics characterization of the reactor. Measurements include reflector critical positions, differential and integral worth of reflectors, and integral worth of safety rod. 

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