Outage Key Safety Functions Configuration risk assessment for a three loops Westinghouse PWR

Abstract

The methodology developed provides guidance on the use of Probabilistic Safety Assessment (PSA) for the risk-informed evaluation of Guides which ensure the compliment of Outage Key Safety Functions (OKSFs) in Nuclear Power Plants. The methodology has been applied to the 3rd and 13th Plant Operational States (POSs) as a Pilot experience. These POSs are within the operating mode 4 (Hot Shutdown) of a 3 loops Westinghouse Pressurized Water Reactor. The addressed Guide requires the operability of just one charge pump as boric acid supply source. PSA gives a Core Damage Frequency increase (∆CDF) of 1.19•10 -6 year -1 for the unavailability of the charge pump in standby, consequently, the maximum exposure time (time for the increase of Core Damage Probability of the configuration to reach 1.0E-06) for this situation is T= 53.6 hours. Given an average time for the POSs of 40 hours, it is concluded that the charge pumps requirement is correct. However, it could be improved with the inclusion of an additional inventory replacement function. This would limit the effect on Risk of the charge pump unavailability. Furthermore, the need for the external electrical sources to be available during mode 4 is ratified. The procedure requires the operability of both supply sources during the POSs. The unavailability of one of supply sources them involves a ∆CDF equal to 1.64•10 -5 year -1 and a maximum exposure time of T= 3.89 hours. This requirement is considered appropriate from the risk-informed regulation point of view.

RETRACTED: Fault-Event Trees Based Probabilistic Safety Analysis of a Boiling Water Nuclear Reactor’s Core Meltdown and Minor Damage Frequencies

“…The merits of nuclear energy have been re-discovered over recent years to address the future global energy needs [1] in an environmentally conscious and resource-sustainable way [2]. Since the nuclear renaissance [3] and the subsequent increase in nuclear newbuild projects [4] globally, new needs for safety assessment [5,6] of the complex nuclear power system has arisen. Securing a very high level of design and operating safety with reduced costs will not only be technically required for the burgeoning nuclear sector, but also from the policy [7] point of view to approach the challenge in addressing the public's negative perception [8] on nuclear power in the post-Fukushima era [9].…”

Desarrollo y aplicación de herramientas de valoración de riesgos tecnológicos en centrales nucleares españolas a partir de la técnica de "Análisis Probabilista de Seguridad"

“…Nuclear Engineering Research Group ha desarrollado una metodología de evaluación de las ETF que ha sido publicada en un artículo de la revista internacional Nuclear Engineering and Design [64].…”

“…El tiempo de exposición se dene como la cantidad de tiempo que ha de pasar para que el incremento de probabilidad de daño al núcleo de la central asociado a un estado anormal o anómalo de la misma supere el umbral de 1,0E-06 10 . Un estado anormal de planta es más o menos signicativo desde el punto de vista del riesgo dependiendo del tiempo de exposición asociado, llegándose a poder declarar que un estado anormal de planta es inaceptable si el tiempo de exposición es menor que el tiempo necesario para restablecer la operación normal [64] de la central. Cada columna de la matriz MRI describe un estado de planta diferente en el que una ESCs representativa de una función clave de seguridad está indisponible.…”

“…No obstante, al desconocerse el tiempo de exposición a la situación analizada por tratarse de un análisis prospectivo, los criterios utilizados no analizan el incremento de probabilidad de riesgo sino el tiempo de exposición necesario para alcanzar un valor de incremento de probabilidad de riesgo signicativo. De acuerdo con otras aplicaciones [4,64,46], se ja en 1,0E-06 el valor umbral de incremento de probabilidad de riesgo que discierne entre situaciones signicativas y no signicativas desde el punto de vista del riesgo. La tabla 15.1 presenta los criterios de valoración de riesgo aplicados, en consenso con expertos de la central nuclear, a los resultados de la matriz MCI.…”