Core damage frequency

Also, presented are the level-1 uncertainty analysis, results. The MLO mean core damage frequency from internal events is about an order of magnitude lower than that of full power operation. The mean core damage frequency due... 

On August 8, 1985, the U.S. Nuclear Regulatory Commission (NRCf requested the operators of nuclear power plants in the U.S. to perform Individual Plant Examinations (IPE) on their plants. IPEs are probabilistic analyses that estimate the core damage frequency (CDF) and containment performance for accidents initiated by internal events (including internal flooding, but excluding internal fire). Generic Letter (GL) 88-20 was issued to implement the IPE request to identify any plant-specific vulnerabilities to severe accidents and report the results to the Commission. ... 

The mean core damage frequency from all internal events is 1.8E-4/yr, with an error factor (95% percentile divided by the median) of 5.0. The percentage contributions to the core dai e frequencies are Large Reactivity Insertion 28% Large LOCA, 28% Reactivity Insertion L P ramp, 12% Spurious/normal shutdown, 11% Loss of commercial power, 10% and others, 5 ... 

Fault trees were developed using the IRRAS 2.0 code (Russell, 1988) which allows definition of individual sequences in an event tree, and generation of their cutsets, but does not generate cutsets for total core damage frequency. An in-house code was developed to combine the cutsets uf arictus sequences. Because IRRAS 2.0 was preliminary, use was also made of the SETS code (Worrel. 

At 40 MW operation, the core damage frequency is 3.7E-04/y. The proportion of accident classes is LOCA, 50% beam tube rupture, 27% ATWS, 17% LOOP, 4% and other transients, 2 7. Three minutes of forced flow are not required and large LOCAs with break size smaller than 2.8 inches can be mitigated. 

The point estimate core damage frequencies for the K-Reactor for both internal and external initiators are given in Table 11.3-6. 

The mean frequencies of events damaging more than 5% of the reactor core per year were found to be Internal Events 6.7E-5, Fire 1.7E-5, Seismic 1.7E-4, and total 2,5E-4. Thus, within the range of U. S. commercial light water reactors The core damage frequency itself, is only part of the story because many N-Reactor accident sequences damage only a small fraction of the core. The... 

M. T. Drouin, F. T. Harper and A. L. Camp, Analysis of Core Damage Frequency from Internal Events Methodology Guidelines, Vol. 1, September 1987. 

Core damage frequency (CDF), for nuclear power facilities, 17 540 Coreless induction furnaces, 12 309-311 Core level electron energy loss spectroscopy (CEELS), 24 74 Coremans, Paul, 11 398 Core-shell model, 14 464 Core-shell particles, in polymer blends, 20 354-355... 

Table 8 Core damage frequency for major initiating events...

Guidelines for the probabilistic safety analysis have been issued recently. In the guidelines, the analysis of initiating events in other operational states than full power is recommended if essential contributions to the total core damage frequency are to be expected. Efforts have therefore concentrated on limited shutdown analysis for a typical PWR and BWR. A low power and shutdown analysis for one PWR has been completed, one for a BWR will be finished soon and a third, major PWR analysis has just been started. 

While core damage frequency may be zero for those utilities that choose to off load fuel from the reactor vessel to the spent fuel pool, the shutdown PSA must account for the new location of the fuel and calculations should be performed to determine the susceptibility of the fuel damage in its new location. 

Safety goals core damage frequency lower than lO /RY and containment failure frequency lower than lO /RY. 

The current principles of risk-informed decisionmaking have been developed considering many parameters including the currently usual core damage frequencies (CDF) and the currently usual large early release frequencies (LERF). 

From those, a criterion closer to a direct evaluation of the probabilistic safety assessment results was derived, which states that the expected frequency of the large early releases from a NPP should be less than lOE-6/year. In addition, the core damage frequency should be proved to be below lE-4/year. 

The core damage frequency (CDF) is a risk measure, which shows, how likely the accident in a nuclear power plant is, i.e. the damage of the core in the nuclear reactor. 

Figure 1. Acceptance guidelines combining two risk measures (core damage frequency and large early release frequency).

E.g. the results of the new advanced nuclear power plants equipped with passive safety systems may indicate that the core damage frequency is assessed below the lE-06/ry, which is for orders of magnitude smaller than core damage frequency of existing plants. 

More than 100% increase of core damage frequency as a result of a certain modification could stiU be acceptable in such plants if the existing criteria is apphed, so new criteria are developed, which define the relative risk limit for changes in the plant in addition to existing absolute risk limit. 

Risk assessment of nuclear power plants is based on evaluation of core damage frequency (CDF). Thus we consider 1st and 2nd task category. Task category 1 defines all initiating events, which damage the reactor core. Task category 2 is focused to assess initiating events occurrence probability and to assess safety related systems malfunction probability. 

In the conventional quantification method (NRC 1983, EPRI/NRC 2005, KEPCO 2004) of a fire PRA, the core damage frequency (CDF) is calculated as below ... 

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