Startup neutron source: Difference between revisions

Revision as of 23:45, 27 March 2010

Revision as of 00:05, 28 March 2010

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The startup sources are typically inserted in regularly spaced positions inside the [[reactor core]], in place of some of the [[fuel rod]]s.

The sources are important for safe reactor startup. The spontaneous fission and [[cosmic ray]]s serve as weak neutron sources, but these are too weak for the reactor instrumentation to detect; relying on them would lead to a "blind" start, with chance of going supercritical.<ref>http://books.google.com/books?id=SkrVDKMconIC&pg=PA224&dq=neutron+startup+source&lr=&as_drrb_is=q&as_minm_is=0&as_miny_is=&as_maxm_is=0&as_maxy_is=&num=50&as_brr=3&cd=1#v=onepage&q=neutron%20startup%20source&f=false</ref> The sources are therefore positioned so the neutron flux they produce is always detectable by the reactor monitoring instruments.

The sources can be of two types:<ref name="nucleng">http://books.google.com/books?id=EMy2OyUrqbUC&pg=PA27&dq=neutron+startup+source&lr=&as_drrb_is=q&as_minm_is=0&as_miny_is=&as_maxm_is=0&as_maxy_is=&num=50&as_brr=3&cd=4#v=onepage&q=neutron%20startup%20source&f=false</ref>

The sources can be of several types:

* '''Primary sources''', used for startup of a fresh reactor core; conventional [[neutron sources]] are used, usually [[californium]]-252 ([[spontaneous fission]]) or [[americium]]-beryllium (&alpha;,n [[nuclear reaction]]). The primary sources are removed from the reactor after the first fuel campaign, usually after few months.

* [[Californium]]-252

* '''Secondary sources''', originally inert, become radioactive and neutron-producing only after [[neutron activation]] in the reactor

* [[Antimony|Sb]]-[[Tellurium|Te]] [[photoneutron]] source

** [[Antimony|Sb]]-[[Beryllium|Be]] [[photoneutron]] source; antimony [[neutron activation|becomes radioactive]] in the reactor and its strong gamma emissions (1.7 MeV for ¹²⁴Sb) interact with [[beryllium-9]] by an (&gamma;,n) reaction and provide [[photoneutron]]s. In a PWR reactor one neutron source rod contains 160 grams of antimony, and stay in the reactor for 5-7 years.<ref>http://books.google.com/books?id=SJOE00whg44C&pg=PA147&dq=neutron+startup+source&lr=&as_drrb_is=q&as_minm_is=0&as_miny_is=&as_maxm_is=0&as_maxy_is=&num=50&as_brr=3&cd=22#v=onepage&q=neutron%20startup%20source&f=false</ref>

** [[lead|Pb]]-[[beryllium|Be]] source

Some neutron sources also serve as additional sources of [[delayed neutron]]s; these serve to dampen the response rate of reactor power to control rods and power transients, allowing safer and more stable operation.