Neutron Embrittlement of Pressure Vessels

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Neutron fluence at the reactor pressure vessel wall a comparison of French and German procedures and strategies in PWRs

U. Jendrich (GRS), N. Tricot (IRSN)

Abstract: While the neutrons within the core may take part in the chain reaction, those neutrons emitted from the core are basically lost for the energy production. This “neutron leakage” represents a loss of fuel efficiency and causes neutron embrittlement of the reactor pressure vessel (RPV) wall. The latter raises safety concerns, needs to be monitored closely and may necessitate mitigating measures. There are different strategies to deal with these two undesirable effects: The neutron emission may be reduced to some extent all around the core or just at the “hot spots” of RPV embrittlement by tailored core loading patterns. A higher absorption rate of neutrons may also be achieved by a larger water gap between the core and the RPV. In this paper the inter-relations between the distribution of neutron flux, core geometry, core loading strategy, RPV embrittlement and its surveillance are discussed at first. Then the different strategies followed by the German and French operators are described. Finally the conclusions will highlight the communalities and differences between these strategies as different approaches to the same problem of safety as well as economy.

www.eurosafe-forum.org/ipsn/pdf/euro2_1_1neutron_fluence.pdf [/URL]

GRS - Gesellschaft für Anlagen- und Reaktorsicherheit mbH - is a scientific-technical expert and research organisation. - [PLAIN]http://www.grs.de/en/index.html

IRSN - Institut de Radioprotection et de Sureté Nucléaire - http://www.irsn.fr/ (click on English Version to the right)

 

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Both neutron reflection as well as gamma ray reflection need to be looked into. The problem is that neutrons are a byproduct in current thermal-fission reactors, but in the future when more truley aneutronic fusion reactors are develped, the thermal neutron problem will be less severe. However, gamma rays are a large problem because every reaction, both fission and fusion unleash a few MEV of gamma rays. So for each nuclear reaction, gamma expels from the nucleus, and this builds up problems of tremendous heat and irradiation. These cause biohazardous radiation problems as well as heating the walls. Although gamma rays are a high frequency of electromagnetic rays on the EM spectrum than that of visible light, we should still look into reflecting them back into the system or using some form of photovoltaic energy production. Though most likely the rays will penetrate any normal matter, both heating and irradiating it...