Editing Pressurized water reactor (section)

== Disadvantages ==
The coolant water must be highly pressurized to remain liquid at high temperatures. This requires high-strength piping and a heavy pressure vessel and hence increases construction costs. The higher pressure can increase the consequences of a [[loss-of-coolant accident]].<ref>{{harvnb|Tong|1988|pp=216–217}}</ref> The [[reactor pressure vessel]] is manufactured from ductile steel but, as the plant is operated, neutron flux from the reactor causes this steel to become less ductile. Eventually the [[ductility]] of the steel will reach limits determined by the applicable boiler and pressure vessel standards, and the pressure vessel must be repaired or replaced. This might not be practical or economic, and so determines the life of the plant.

Additional high-pressure components such as reactor coolant pumps, pressurizer, and steam generators are also needed. This also increases the capital cost and complexity of a PWR power plant.

The high-temperature water coolant with [[boric acid]] dissolved in it is corrosive to [[carbon steel]] (but not [[stainless steel]]); this can cause radioactive corrosion products to circulate in the primary coolant loop. This not only limits the lifetime of the reactor, but the systems that filter out the corrosion products and adjust the boric acid concentration add significantly to the overall cost of the reactor and to radiation exposure. In one instance, this has resulted in severe corrosion to control rod drive mechanisms when the boric acid solution leaked through the seal between the mechanism itself and the primary system.<ref>{{cite conference
 | title = Davis-Besse: The Reactor with a Hole in its Head
 | book-title = UCS -- Aging Nuclear Plants
 | publisher = Union of Concerned Scientists
 | url = http://www.ucsusa.org/assets/documents/nuclear_power/acfnx8tzc.pdf
 | access-date = 2008-07-01
 | archive-date = 2008-10-27
 | archive-url = https://web.archive.org/web/20081027134541/http://www.ucsusa.org/assets/documents/nuclear_power/acfnx8tzc.pdf
 | url-status = dead
 }}</ref><ref>{{cite news|url=https://www.nytimes.com/2003/05/01/us/extraordinary-reactor-leak-gets-the-industry-s-attention.html|title=Extraordinary Reactor Leak Gets the Industry's Attention|last=Wald|first=Matthew|date=May 1, 2003|work=[[New York Times]]|access-date=2009-09-10}}</ref>

Due to the requirement to load a pressurized water reactor's primary coolant loop with boron, undesirable radioactive secondary [[tritium]] production in the water is over 25 times greater than in boiling water reactors of similar power, owing to the latter's absence of the neutron moderating element in its coolant loop. The tritium is created by the absorption of a fast neutron in the nucleus of a boron-10 atom which subsequently splits into a lithium-7 and tritium atom. Pressurized water reactors annually emit several hundred [[Curie (unit)|curies]] of tritium to the environment as part of normal operation.<ref>{{cite web|url=https://www.nrc.gov/reactors/operating/ops-experience/tritium/faqs.html|title=Frequently Asked Questions About Liquid Radioactive Releases}}</ref>

Natural uranium is only 0.7% uranium-235, the isotope necessary for thermal reactors. This makes it necessary to enrich the uranium fuel, which significantly increases the costs of fuel production. Compared to reactors operating on natural uranium, less energy is generated per unit of uranium ore even though a higher burnup can be achieved. [[Nuclear reprocessing]] can "stretch" the fuel supply of both natural uranium and enriched uranium reactors but is virtually only practiced for light-water reactors operating with lightly enriched fuel as spent fuel from e.g. CANDU reactors is very low in fissile material.

Because water acts as a neutron moderator, it is not possible to build a [[fast-neutron reactor]] with a PWR design. A [[reduced moderation water reactor]] may however achieve a [[breeder reactor#Breeding ratio|breeding ratio]] greater than unity, though this reactor design has disadvantages of its own.<ref>{{harvnb|Duderstadt|Hamilton|1976|p=86}}</ref>

[[Spent fuel]] from a PWR usually has a higher content of [[fissile material]] than natural uranium. Without [[nuclear reprocessing]], this fissile material cannot be used as fuel in a PWR. It can, however, be used in a [[CANDU]] with only minimal reprocessing in a process called "DUPIC" - Direct Use of spent PWR fuel in CANDU.<ref>{{cite web|last=Wang |first=Brian |url=https://www.nextbigfuture.com/2009/04/dupic-fuel-cycle-direct-use-of.html |title=DUPIC Fuel Cycle : Direct Use of Pressurized Water Reactor Spent Fuel in CANDU |publisher=NextBigFuture.com |date=2009-04-15 |accessdate=2022-03-08}}</ref>

[[Thermal efficiency]], while better than for [[boiling water reactor]]s, cannot achieve the values of reactors with higher operating temperatures such as those cooled with high-temperature gases, liquid metals or molten salts. Similarly [[process heat]] drawn from a PWR is not suitable for most industrial applications as those require temperatures in excess of {{convert|400|C}}.

[[Radiolysis]] and certain accident scenarios which involve interactions between hot steam and zircalloy cladding can produce hydrogen from the cooling water leading to [[hydrogen explosion]]s as a potential accident scenario. During the [[Fukushima nuclear accident]] a hydrogen explosion damaging the containment building was a major concern, though the reactors at the plant were [[Boiling water reactor|BWR]]s, which owing to the steam at the top of the pressure vessel by design carry a greater risk of this happening. Some reactors contain catalytic recombiners which let the hydrogen react with ambient oxygen in a non-explosive fashion.{{cn|date=September 2023|reason=This issue may not apply to only PWR. Fukushima had BWR.}}