American Nuclear Society

Home / Publications / Journals / Nuclear Science and Engineering / Volume 166 / Number 2 / Pages 107-117

Ex-Core Local Power Monitoring Using Neutron Streaming Pipes

Susumu Naito, Makoto Takemura, Shungo Sakurai, Mikio Izumi, Yasushi Goto, Yoshiji Karino

Nuclear Science and Engineering / Volume 166 / Number 2 / October 2010 / Pages 107-117

Technical Paper

To simplify in-core instrumentation in a next-generation boiling water reactor (BWR), we study an ex-core nuclear instrumentation system. As a first step of this study, we focused on ex-core local power monitoring, which is especially difficult because neutrons inside a core cannot fly out of a reactor pressure vessel (RPV) due to shielding of fuel, water, etc., except when they are generated in the outer edges of the core. To resolve this, we created a local power monitoring method with neutron streaming pipes (NSPs). An NSP is a gas-filled pipe of size comparable to an instrumentation tube of an existing BWR. NSPs are axially inserted into the core. In-core neutrons are transported to the RPV through NSPs. The neutrons transmitted through the RPV are monitored with ex-core neutron sensors. We analytically evaluated the applicability of this NSP method for an advanced BWR (ABWR) with a three-dimensional BWR core simulator and the MCNP5 code. The ex-core neutron flux through the NSP was highly proportional to local power (1.0% of the residual standard deviation). The flux amount and the linearity gave feasible specifications for the ex-core neutron sensor in typical operation modes (pulse, Campbell, and current modes). Therefore, the NSP method is applicable to an ABWR.

Questions or comments about the site? Contact the ANS Webmaster.