Risk modelling of ageing nuclear reactor systems

Optimisation of nuclear reactor primary coolant design and maintenance parameters

“…The Petri net modelling in this work was realised with Macchiato, 22 developed in-house at the University of Nottingham.…”

“…Having generated a set of optimisation parameters, the corresponding Petri net structure was generated, as discussed in Section 4, and was simulated 10 6 times. On the order of 10 5 iterations would be sufficient when typical system parameter values are used, 22 but to guarantee that an adequate body of data is collected even in the case of the more exotic parameter combinations, this larger sample size was used, with the total expenditure of computational time summing to 15,000 core hours on the Hydra HPC system. A total of 4000 parameter sets were investigated in this fashion and the optimisation was subsequently performed via Pareto front 29 analysis with respect to the performance metrics of chief concern, namely the probability of safe shutdown and the monetary expenditure per unit time.…”

“…Although Petri net modelling can be computationally expensive compared to the fault tree and event tree methodologies, this can be justified by its facilitation of high fidelity representations of system dynamics, which would not be possible using the traditional techniques. The methodology has already been applied in civil nuclear energy contexts, [11][12][13][14][15][16][17][18][19][20][21][22] and prior works employ Petri nets for various purposes. For example, some works 11,12,14,15,[19][20][21][22] describe or develop operational procedures or processes in nuclear systems using Petri nets, among which a number were directly concerned with safety, risk or reliability.…”

“…The methodology has already been applied in civil nuclear energy contexts, [11][12][13][14][15][16][17][18][19][20][21][22] and prior works employ Petri nets for various purposes. For example, some works 11,12,14,15,[19][20][21][22] describe or develop operational procedures or processes in nuclear systems using Petri nets, among which a number were directly concerned with safety, risk or reliability. [19][20][21][22] More indirect applications can also be found, where Petri nets were created to describe nuclear reactor subsystems, but the evaluation was not performed by simulating the models.…”

“…For example, some works 11,12,14,15,[19][20][21][22] describe or develop operational procedures or processes in nuclear systems using Petri nets, among which a number were directly concerned with safety, risk or reliability. [19][20][21][22] More indirect applications can also be found, where Petri nets were created to describe nuclear reactor subsystems, but the evaluation was not performed by simulating the models. Instead the Petri net represented an intermediate form, which was converted for assessment by an alternative methodology, such as Markov chains, 16 reachability graphs, 17 or both.…”