Editing Boiling water reactor (section)

=== Disadvantages of BWR ===
* BWRs require more complex calculations for managing consumption of nuclear fuel during operation due to "two-phase (water and steam) fluid flow" in the upper part of the core. This also requires more instrumentation in the reactor core.
* Larger reactor pressure vessel than for a PWR of similar power, with correspondingly higher cost, in particular for older models that still use a main steam generator and associated piping.
* Contamination of the turbine by short-lived [[activation product]]s. This means that shielding and access control around the steam turbine are required during normal operations due to the radiation levels arising from the steam entering directly from the reactor core. This is a moderately minor concern, as most of the radiation flux is due to [[Nitrogen-16]] (activation of oxygen in the water), which has a half-life of 7.1 seconds, allowing the turbine chamber to be entered within minutes of shutdown.  Extensive experience demonstrates that shutdown maintenance on the turbine, condensate, and feedwater components of a BWR can be performed essentially as a fossil-fuel plant.{{citation needed|date=September 2021}}
* Though the current BWRs are considered<ref name=":0" /> to be less likely to suffer core damage from the "1 in 100,000 reactor-year" limiting fault than the present fleet of PWRs (due to increased ECCS robustness and redundancy), there have been concerns raised about the pressure containment ability of the as-built, unmodified Mark I containment – that such may be insufficient to contain pressures generated by a limiting fault combined with complete ECCS failure that results in extremely severe core damage. In this double failure scenario, assumed to be extremely unlikely prior to the [[Fukushima I nuclear accidents]], an unmodified Mark I containment can allow some degree of radioactive release to occur. This is supposed to be mitigated by the modification of the Mark I containment; namely, the addition of an outgas stack system that, if containment pressure exceeds critical setpoints, is supposed to allow the orderly discharge of pressurizing gases after the gases pass through activated carbon filters designed to trap radionuclides.<ref>KEIJI TAKEUCHI [http://www.asahi.com/english/TKY201103140243.html COMMENTARY: Crucial vents were not installed until 1990s] Asahi.com</ref>