spent fuel pool
{{Short description|Storage pools for spent nuclear fuel}}
{{redirect|Storage pool|the medical condition known as storage pool disease|Platelet storage pool deficiency}}
{{Use American English|date=August 2021}}
Image:Caorso fuel pool.jpg. This pool is not holding large amounts of material.]]
Spent fuel pools (SFP) are storage pools (or "ponds" in the United Kingdom) for spent fuel from nuclear reactors. They are typically 40 or more feet (12 m) deep, with the bottom 14 feet (4.3 m) equipped with storage racks designed to hold fuel assemblies removed from reactors. A reactor's local pool is specially designed for the reactor in which the fuel was used and is situated at the reactor site. Such pools are used for short-term cooling of the fuel rods. This allows short-lived isotopes to decay and thus reduces the ionizing radiation and decay heat emanating from the rods. The water cools the fuel and provides radiological protection from its radiation.
Pools also exist on sites remote from reactors, for longer-term storage such as the Independent Spent Fuel Storage Installation (ISFSI), located at the Morris Operation, or as a production buffer for 10 to 20 years before being sent for reprocessing or dry cask storage.
While only about 20 feet (about 6 m) of water is needed to keep radiation levels below acceptable levels, the extra depth provides a safety margin and allows fuel assemblies to be manipulated without special shielding to protect the operators.
Operation
About a quarter to a third of the total fuel load of a reactor is removed from the core every 12 to 24 months and replaced with fresh fuel. Spent fuel rods generate intense heat and dangerous radiation that must be contained. Fuel is moved from the reactor and manipulated in the pool generally by automated handling systems, although some manual systems are still in use. The fuel bundles fresh from the core are normally segregated for several months for initial cooling before being sorted into other parts of the pool to wait for final disposal. Metal racks keep the fuel in controlled positions for physical protection and for ease of tracking and rearrangement. High-density racks also incorporate boron-10, often as boron carbide (Metamic,"[https://holtecinternational.com/productsandservices/innovative-technologies/neutronabsorbermaterial/ Neutron Absorber Material] {{Webarchive|url=https://web.archive.org/web/20190321074422/https://holtecinternational.com/productsandservices/innovative-technologies/neutronabsorbermaterial/ |date=2019-03-21 }}", Holtec International Boraflex, Boral,"[https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Neutron-Absorber-Composite-formerly-known-as-Boral-Composite-/?N=5002385+3290920139&rt=rud 3M™ Neutron Absorber Composite (formerly known as Boral® Composite)] {{Webarchive|url=https://web.archive.org/web/20180214214922/https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Neutron-Absorber-Composite-formerly-known-as-Boral-Composite-/?N=5002385+3290920139&rt=rud |date=2018-02-14 }}" Tetrabor and Carborundum"[https://www.nrc.gov/docs/ML1314/ML13141A182.pdf Monitoring Degradation of Phenolic Resin-Based Neutron Absorbers in Spent Nuclear Fuel Pools] {{Webarchive|url=https://web.archive.org/web/20170507194749/https://www.nrc.gov/docs/ML1314/ML13141A182.pdf |date=2017-05-07 }}", Matthew A. Hiser, April L. Pulvirenti and Mohamad Al-Sheikhly, U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research, June 2013) or other neutron-absorbing material to ensure subcriticality. Water quality is tightly controlled to prevent the fuel or its cladding from degrading. This can include monitoring the water for contamination by actinides, which could indicate a leaking fuel rod.{{cite journal |vauthors = Chaplin J, Christl M, Straub M, Bochud F, Froidevaux P |title=Passive Sampling Tool for Actinides in Spent Nuclear Fuel Pools |journal=ACS Omega |date=2 June 2022 |volume=7 |issue=23 |pages=20053−20058 |doi=10.1021/acsomega.2c01884 |pmid=35722008 |url=https://doi.org/10.1021/acsomega.2c01884|hdl=20.500.11850/554631 |hdl-access=free }} Current regulations in the United States permit re-arranging of the spent rods so that maximum efficiency of storage can be achieved.{{cite web|url=https://www.nrc.gov/waste/spent-fuel-storage/pools.html|title=NRC: Spent Fuel Pools|access-date=18 March 2016|archive-url=https://web.archive.org/web/20160312120122/http://www.nrc.gov/waste/spent-fuel-storage/pools.html|archive-date=12 March 2016|url-status=live}}
File:RIAN archive 305008 Leningrad nuclear power plant.jpg
The maximum temperature of the spent fuel bundles decreases significantly between two and four years, and less from four to six years. The fuel pool water is continuously cooled to remove the heat produced by the spent fuel assemblies. Pumps circulate water from the spent fuel pool to heat exchangers, then back to the spent fuel pool. The water temperature in normal operating conditions is held below 50 °C (120 °F).{{cite web|url=http://www.usainc.org/members/index.html?organization_id=47198|title=Members - USA - Utilities Services Alliance|access-date=18 March 2016|archive-url=https://web.archive.org/web/20160304231726/https://www.usainc.org/members/index.html?organization_id=47198|archive-date=4 March 2016|url-status=live}} Radiolysis, the dissociation of molecules by radiation, is of particular concern in wet storage, as water may be split by residual radiation and hydrogen gas may accumulate increasing the risk of explosions. For this reason the air in the room of the pools, as well as the water, must be continually monitored and treated.
Other possible configurations
Rather than manage the pool's inventory to minimize the possibility of continued fission activity, China is building a 200 MWt nuclear reactor to run on used fuel from nuclear power stations to generate process heat for district heating and desalination. Essentially an SFP operated as a deep swimming pool reactor; it will operate at atmospheric pressure, which will reduce the engineering requirements for safety.{{cite web|url=http://uic.com.au/news502.htm|archive-url=https://web.archive.org/web/20071013131516/http://uic.com.au/news502.htm|title=UIC - Newsletter 5/02|archive-date=13 October 2007|access-date=18 March 2016}}
Other research envisions a similar low-power reactor using spent fuel where instead of limiting the production of hydrogen by radiolysis, it is encouraged by the addition of catalysts and ion scavengers to the cooling water. This hydrogen would then be removed to use as fuel.{{cite web|url=http://aiche.confex.com/aiche/2005/techprogram/P21198.HTM|title=Radiolytic Water Splitting: Demonstration at the Pm3-a Reactor|access-date=18 March 2016|archive-url=https://web.archive.org/web/20120204120820/http://aiche.confex.com/aiche/2005/techprogram/P21198.HTM|archive-date=4 February 2012|url-status=live}}
Risks
File:Spent Fuel Pool (02813601).jpg.]]
The neutron absorbing materials in spent fuel pools have been observed to degrade severely over time, reducing the safety margins of maintaining subcriticality;"[https://www.nrc.gov/sr0933/Section%203.%20New%20Generic%20Issues/196.html Resolution of Generic Safety Issues: Issue 196: Boral Degradation (NUREG-0933, Main Report with Supplements 1–34)]", U.S. Nuclear Regulatory Commission[https://books.google.com/books?id=EMy2OyUrqbUC&dq=Boraflex&pg=PA302 Spent Fuel Storage; Neutron Absorbing Materials], "Nuclear Engineering Handbook", edited by Kenneth D. Kok, p. 302 in addition, it has been shown that the in-site measurement technique used to evaluate these neutron absorbers (Boron Areal Density Gauge for Evaluating Racks, or BADGER) has an unknown degree of uncertainty."[https://www.nrc.gov/docs/ML1225/ML12254A064.pdf Initial Assessment of Uncertainties Associated with BADGER Methodology] {{Webarchive|url=https://web.archive.org/web/20190622051456/https://www.nrc.gov/docs/ML1225/ML12254A064.pdf |date=2019-06-22 }}", J. A. Chapman and J. M. Scaglione, Oak Ridge National Laboratory, September, 2012
If there is a prolonged interruption of cooling due to emergency situations, the water in the spent fuel pools may boil off, possibly resulting in radioactive elements being released into the atmosphere.{{cite web|url=http://www.ucsusa.org/nuclear_power/nuclear_power_risk/safety/nuclear-reactor-crisis-faq.html#risks%20of%20spent%20fuel%20pools|title=Nuclear Crisis in Japan FAQs|publisher=Union of Concerned Scientists|access-date=2011-04-19|archive-url=https://web.archive.org/web/20110420042611/http://www.ucsusa.org/nuclear_power/nuclear_power_risk/safety/nuclear-reactor-crisis-faq.html#risks%20of%20spent%20fuel%20pools|archive-date=2011-04-20|url-status=live}}
In the magnitude 9 earthquake that struck the Fukushima nuclear plants in March 2011, three of the spent fuel pools were in buildings which had been damaged and were seen to be emitting water vapour. The US NRC wrongly stated that the pool at reactor 4 had boiled dry{{cite web |url=https://www.ctvnews.ca/helicopters-drop-water-on-japanese-nuclear-reactor-1.619391 |title=No water in spent fuel pool at Japanese plant: U.S |publisher=CTV News |date=16 March 2011}}—this was denied at the time by the Government of Japan and found to be incorrect in subsequent inspection and data examination.{{cite web |url=http://thecabin.net/news/2011-06-15/us-spent-fuel-pool-never-went-dry-japan-quake |title=U.S.: spent fuel pool never went dry in Japan quake |agency=Associated Press |date=15 June 2011 |access-date=24 October 2013 |archive-url=https://web.archive.org/web/20131029200459/http://thecabin.net/news/2011-06-15/us-spent-fuel-pool-never-went-dry-japan-quake |archive-date=29 October 2013 |url-status=live }}
According to nuclear plant safety specialists, the chances of criticality in a spent fuel pool are very small, usually avoided by the dispersal of the fuel assemblies, inclusion of a neutron absorber in the storage racks and overall by the fact that the spent fuel has too low an enrichment level to self-sustain a fission reaction. They also state that if the water covering the spent fuel evaporates, there is no element to enable a chain reaction by moderating neutrons.[http://www.eurosafe-forum.org/userfiles/2_03_Eurosafe2010%206_Kilger%20(GRS).pdf Criticality Safety in the Waste Management of Spent Fuel from NPPs, Robert Kilger] {{webarchive|url=https://web.archive.org/web/20110511124940/http://www.eurosafe-forum.org/userfiles/2_03_Eurosafe2010%206_Kilger%20(GRS).pdf |date=2011-05-11 }}{{cite web|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=1068367|title=Nondestructive assay of nuclear low-enriched uranium spent fuels for burnup credit application|access-date=18 March 2016|archive-url=https://web.archive.org/web/20110503181410/http://cat.inist.fr/?aModele=afficheN&cpsidt=1068367|archive-date=3 May 2011|url-status=live}}Radioactive Waste Management/Spent Nuclear Fuel
According to Dr. Kevin Crowley of the Nuclear and Radiation Studies Board, "successful terrorist attacks on spent fuel pools, though difficult, are possible. If an attack leads to a propagating zirconium cladding fire, it could result in the release of large amounts of radioactive material.""Are Nuclear Spent Fuel Pools Secure?" Council on Foreign Relations, June 7, 2003 {{cite web |url=http://www.cfr.org/weapons-of-mass-destruction/nuclear-spent-fuel-pools-secure/p8967 |title=Are Nuclear Spent Fuel Pools Secure? - Council on Foreign Relations |access-date=2011-04-05 |url-status=dead |archive-url=https://web.archive.org/web/20110412103934/http://www.cfr.org/weapons-of-mass-destruction/nuclear-spent-fuel-pools-secure/p8967 |archive-date=2011-04-12 }} After the September 11, 2001 attacks the Nuclear Regulatory Commission required American nuclear plants "to protect with high assurance" against specific threats involving certain numbers and capabilities of assailants. Plants were also required to "enhance the number of security officers" and to improve "access controls to the facilities".
On August 31, 2010, a diver servicing the spent fuel pool at the Leibstadt Nuclear Power Plant (KKL) was exposed to radiation in excess of statutory annual dose limits after handling an unidentified object, which was later identified as protective tubing from a radiation monitor in the reactor core, made highly radioactive by neutron flux. The diver received a hand dose of about 1,000 mSv which is twice the statutory limit of 500 mSv. According to KKL authorities the diver has not suffered any longtime consequences from the accident.{{Cite web|title=Exposure of a worker in excess of statutory annual dose limits|url=https://www-news.iaea.org/ErfView.aspx?mId=b882511c-0517-4698-8d56-df42e0d60739|access-date=2021-06-09|website=www-news.iaea.org}}{{Cite web|last=Ritter|first=Andreas|date=|title=Unplanned Exposure During Diving in the Spent Fuel Pool|url=https://isoe-network.net/publications/pub-proceedings/symposia/north-american-tc-symposia/fort-lauderdale-usa-january-2011/slides-14/session-iv-1/1756-ritter2011-ppt/file.html|website=isoe-network.net}}
See also
References
{{Reflist}}
External links
{{Commons category|Spent nuclear fuel ponds}}
- [http://www.inesap.org/sites/default/files/inesap_old/bulletin22/bul22art30.htm Radiological Terrorism: Sabotage of Spent Fuel Pool]
- [https://www.nrc.gov/waste/spent-fuel-storage.html Storage of Spent Nuclear Fuel] U.S. Nuclear Regulatory Commission (NRC)
- [https://web.archive.org/web/20100526101753/http://www.safesecurevital.org/safe-secure-vital/spent-fuel.html An example diagram of a Spent Fuel Pool] Indian Point Energy Center
- [https://www.geek.com/news/geek-answers-why-does-nuclear-waste-glow-an-eerie-blue-1599398/ "Geek Answers: Does nuclear waste really glow?"] BY GRAHAM TEMPLETON 07.17.2014 at Geek.com
{{pond}}