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Nuclear Power Operation Safety and Environment Part 5

Tham khảo tài liệu 'nuclear power operation safety and environment part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Low Power and Shutdown PSA for the Nuclear Power Plants with WWER440 Type Reactors 109 estimate of the effective dose that could be avoided by implementing a particular countermeasure the lower and upper emergency reference levels are defined. Below the lower level introduction of the countermeasure would not be justified because of the harm that it would cause. The upper level is the dose level at which every effort should be done to introduce the countermeasure except in exceptional circumstances. It is set at ten times the dose of the lower level. The lower and upper levels for sheltering are a dose of 5 mSv and 50 mSv respectively. For evacuation they are 50 mSv and 500 mSv. These are higher than the recommended dose limit for routine exposure which is 1 mSv per year for the public. This is because the dose levels are not intended to represent the boundary between what is safe and what is unsafe but to represent an acceptable balance between the harms and benefits of an action. In case of fission product release the release is large if more than 1 caesium is released to the environment from the core inventory. It can correspond to the dose of 50 mSv y for the public. Large early release is a release to the environment before implementation of required countermeasure before evacuation . For the purpose of the WWER440 units it is considered that the evacuation can not be performed until 10 h from the beginning of the accident. The release until 10 h is the early release. For the groups G0 G1 a G2 the Large early release frequency LERF is given as sum of frequencies of the following source term categories STC7 STC9 STC13 STC16 STC17. For group G3 the LERF is given by STC14 and STC15 the reactor vessel is open the containment is open . For group G4 the LERF is given by STC8 the spent fuel pool is outside the containment . 3.7 Results The source term category 14 for group G3 is presented in Table 4 for illustration of the results. The fission product groups Xe I and