Deterministic safety analysis

The deterministic approach studies the behaviour of the plant in operational states and under specific accident conditions originally identified on the basis of evaluations of prudent engineering or for compliance with the chosen criteria. Today, probabilistic techniques are sometimes used to aid decisions concerning the deterministic approach, for example if a new candidate appears (e.g. from research or operating experience) for inclusion in the list of Design Basis Accidents (DBAs), the decision on inclusion or not can be aided by a probabilistic comparison with other situations already inserted in the DBA list. Usually the deterministic analyses are performed using conservative assumptions on input data, intermediate parameters for the analyses and on the behaviour of plant systems (single failure, etc.). Consequently, the behaviour of the plant as evaluated could be rather different from the most 

The deterministic analyses have been used for a longer time and, therefore, they are based on a well-consolidated basis, at least for the rare events included among the DBAs. 

Severe accidents are now also part of the deterministic analyses. However, because of then-very low probability, the conservative assumptions used for DBAs are not used. A best estimate treatment of the phenomena is preferred in this case. 

Safety analysis should consider normal operation, operational occurrences and accidents.  

Anticipated operational occurrences are off-normal events, usually plant transients, which can be coped with by the plant protection systems and normal plant systems but which could have the potential to damage the reactor if some additional malfunction should happen. Their typical frequency of occurrence may be more than 10 year Some of the anticipated occurrences (PIEs - postulated initiating events) are due to the increase of reactor heat removal (as might occur for an inadvertent opening of a steam relief valve, malfunctions in control systems, etc.). Some are due to the decrease of reactor heat removal (such as for feed-water pumps tripping, loss of condenser vacuum and control systems malfunctions). Some are due to a decrease in reactor coolant system flow rate, as in the case of a trip of one or more coolant pumps. Some are connected with reactivity and power distribution anomalies, such as for an inadvertent control rod withdrawal or unwanted boron dilution due to a malfunction of the volume control system for a PWR. Events entailing the increase or decrease of the reactor coolant inventory may also happen, due to malfunctions of the volume control system or small leaks. Finally, releases of radioactive substances from components may occur. 

---

Deterministic safety analysis (frequently referred to as accident analysis) is an important tool for confirming the adequacy and efficiency of provisions for the safety of nuclear power plants in accordance with the defence in depth concept. Owing to the close interrelation between accident analysis and safety, an analysis that lacks consistency, is incomplete or is of poor quahty is considered a safety issue for a given nuclear power plant. The development of IAEA guidance publications for accident analysis is thus an important step towards resolving this issue. 

The objective of the review of the deterministic safety analysis is to determine to what extent the existing deterministic safety analysis remains valid when the following aspects have been taken into account actual plant design the actual condition of SSCs and their predicted state at the end of the period covered by the PSR current deterministic methods and current safety standards and knowledge. In addition, the review should also identify any weaknesses relating to the application of the defence in depth concept. 

A deterministic safety analysis should be conducted for each nuclear power plant, should confirm the design basis for items important to safety and should describe the plant behaviour for postulated initiating events [6]. Therefore, a documented safety design basis (original and updated) should be... 

Procedures should be comprehensive, validated, formally approved and subject to rigorous change control. In addition, they should be unambiguous and relevant to the actual plant (with modifications taken into account), and should reflect current practice and due consideration of human factor aspects (for example, it should be considered whether the procedures are user friendly). The review should focus on those procedures that are of high safety significance it should not entail a technical review of all procedures. (The safety significance can be determined from a deterministic safety analysis and a PSA.) The system for the development and control of procedures should be reviewed. (As far as possible, staff should participate in the development of the procedures that they use.) The review of this safety factor should include ... 

The availability or unavailability status of systems for PIEs to be considered in deterministic safety analysis ... 

For the purposes of the deterministic safety analysis, those safety functions that are used to determine compliance with acceptance criteria should be performed using classified SSCs only. 

The starting point for the safety analysis is the set of PIEs that need to be addressed. A PIE is defined in Ref. [1] as an identified event that leads to anticipated operational occurrences or accident conditions . PIEs include events such as equipment failure, human errors and human induced or natural events. The deterministic safety analysis and the PSA should normally use a common set of PIEs. 

Uncertainty studies in the framework of deterministic safety analysis are meant as statistical combinations of the influence of the plant conditions, code models and associated phenomena on the results. These studies should be used to confirm that the actual plant parameters will be bounded by the results of calculation plus uncertainty with a specified high confidence. A combination of sensitivity studies, code to code comparisons, code to data comparisons and expert judgements are typically used to estimate uncertainties. 

Deterministic safety analysis is performed with the set of calculation codes developed by OKBM and proven in calculations of stationary and non-stationary modes of plant operation. The codes take into account specific features of the plant design, circulation circuit, steam generator, aftercooling systems, control system, etc., and are based on experimentally proven methods of calculation and correlations and have a long-term experience of application. 

In the deterministic safety analysis, it is confirmed that operational limits are in compliance with the assumptions and intent of design for normal operation of the SMART. The safety analysis is performed on initiating events listed in SRDBE that are appropriate for the... 

International Atomic Energy Agency, 2009. Deterministic Safety Analysis for Nuclear Power Plants. Vienna IAEA. 

In this section of the SAR all the deterministic analyses performed to evaluate and justify plant safety should be considered. Deterministic safety analysis predicts the plant response to PIEs in specific predetermined operational states. It applies specific rules and uses specific acceptance criteria. The analyses typically focus on neutronics and thermal-hydraulic, structural and radiological aspects that are analysed with different computational tools. As is stated in para. 4.19 of Ref. [4] In general, the deterministic analysis for design purposes should be conservative. The analysis of beyond design basis accidents is generally less conservative than that of design basis accidents. It is acceptable that best estimate codes are used for deterministic analyses provided that they are either combined with a reasonably conservative... 

This publication establishes design requirements for stractures, systems and components important to safety that must be met for safe operation of a nnclear power plant, and for preventing or mitigating the consequences of events that could jeopardize safety. It also establishes requirements for a comprehensive safety assessment, which is carried out in order to identify the potential hazards that may arise from the operation of the plant, under the various plant states (operational states and accident conditions). The safety assessment process includes the complementary techniqnes of deterministic safety analysis and probabilistic safety analysis. These analyses necessitate consideration of postulated initiating events (PIEs), which include mat r factors that, singly or in combination, may affect safety and which may ... 

The deterministic safety analysis shall include the following ... 

---