{"id":1773,"date":"2016-09-23T16:56:26","date_gmt":"2016-09-23T07:56:26","guid":{"rendered":"https:\/\/fdada.info\/?page_id=1773"},"modified":"2017-01-06T17:25:00","modified_gmt":"2017-01-06T08:25:00","slug":"obj_appendix_4_2-en","status":"publish","type":"page","link":"https:\/\/fdada.info\/fdada\/en\/home2\/decommissioning2\/obj_00-en\/obj_appendix_4_2-en\/","title":{"rendered":"Periodic measurement of plant data"},"content":{"rendered":"\n\n
\n

Periodic measurement of plant data<\/h1>\n

\nFrom plant data on the temperature, hydrogen concentration, pressure, and other items inside the PCVs that\nhave been continuously obtained since the accident occurrence, it is estimated that Units 1-3 in the plant are\nkept in a stable cold shutdown condition.\n<\/br>\n

(1) Measurement of Basic Plant Data inside the PCVs<\/h4>\n

\nHere is a summary of the temporal changes in the plant data about the conditions inside the PCVs, which\nreveal that the fuel debris is in a stable state.\n<\/br>\n

a. Temperature<\/h4>\n

\nAt the time of accident, a power outage occurred, disabling decay heat from fuel assemblies to be\nimmediately removed and thus causing the temperature to rise to higher than 1,000\u00b0C. Then, a rapid\noxidation reaction occurred between the fuel cladding tube (zircaloy) and steam (Zr + 2H2O -> ZrO2 +\n2H2 + 586 kJ\/mol), which generated additional heat. This situation caused the fuel melting.\n<\/br>\n\n

\nFigure 1<\/a> shows the temporal changes in the temperature data around the reactors summarized based\non the information published by TEPCO. After the accident, the temperature inside the PCVs started\ndropping and decreased to 100\u00b0C in six months. After that, the temperature has been gradually dropping\nevery year while following the seasonal variations in air and water temperatures. The temperature is staying\nat a level lower than 50\u00b0C at each section inside the PCVs without showing a sharp peak. Since zircaloy\ndoes not react with water at low temperatures, it is estimated that no oxidization reaction occurs and thus no\nadditional heat is generated.\n<\/br>\n\n

\nFigure 2<\/a> shows the (decay) heat from the elements that make up the fuel assemblies loaded at the time\nof accident. Immediately after the halt of the nuclear reactors, short-lived nuclides generated much decay\nheat; in five years, the amount of the heat generated decreased to lower than one thousandth of the heat at\nthe time of the accident. Now, only long-lived nuclides are surviving. Since they have long half-lives and\ntherefore decay slowly, decay heat is also expected to gradually decrease. It is estimated that the\ntemperature will further drop in the future over time.\n<\/br>\n\n

b. Hydrogen Concentration and PCV Pressure<\/h4>\n

\nIrradiating water with gamma rays causes hydrogen to be generated by radiolysis. The PCVs are filled with\nwater to cool the fuel debris inside them. In addition, the doses inside them are high as this page<\/a> shows.\nWith these factors, there is a fear that hydrogen may be generated inside them. Based on the fact that\nhydrogen has a lower combustible limit of as low as 4%, the PCVs have been filled with nitrogen since the\naccident occurrence to dilute hydrogen to prevent a hydrogen explosion.\nFigure 3<\/a> and Figure 4<\/a> show\nchanges in hydrogen concentration and pressure inside the PCVs, respectively. The hydrogen\nconcentrations are low enough, indicating that hydrogen has been effectively diluted by the inclusion of\nnitrogen. From the viewpoint of confining FPs, it may be effective to remove hydrogen out of the PCVs.\nHowever, doing so may cause the pressure inside the PCVs to be lower (negative) than the (normal)\natmospheric pressure. This may allow air that includes oxygen to enter the PCVs through, for example,\nsealed sections of them, resulting in mixture of hydrogen and oxygen.\nFor this reason, the pressure insidethe PCVs is kept slightly higher (slightly positive) than the atmospheric pressure as Figure 4<\/a> shows.\n<\/br>\n\n

\nWith these facts, it is estimated that Units 1-3 are kept in a stable cold shutdown condition.
\n<\/p>\n\n

\n<\/a>\n\n \"1\u53f7\u6a5f\u306e\u6e29\u5ea6\"\n \"1\u53f7\u6a5f\u306e\u6e29\u5ea6\u6e2c\u5b9a\u4f4d\u7f6e\"\n

\n \"2\u53f7\u6a5f\u306e\u6e29\u5ea6\"\n \"2\u53f7\u6a5f\u306e\u6e29\u5ea6\u6e2c\u5b9a\u4f4d\u7f6e\"\n

\n \"3\u53f7\u6a5f\u306e\u6e29\u5ea6\"\n \"3\u53f7\u6a5f\u306e\u6e29\u5ea6\u6e2c\u5b9a\u4f4d\u7f6e\"\n
\n <\/a>\n<\/br>\n            \n            \n[Based on data published by TEPCO] \n<\/p>\n\n

\nFigure 1\u3000\u3000Changes in the Ambient Temperature of the Nuclear Reactors at the Fukushima Daiichi NPS\n<\/p>\n\n
\n\n

\n<\/a>\n\"\"\n
\n            \n            \n[Based on data published through JAEA-Data\/code 2012-018]\n<\/p>\n\n

\nFigure 2\u3000\u3000Heat from the Fuel, FPs, and Radiated materials inside the Reactors
\n<\/p>\n
\n\n

\n<\/a>\n \"1\u53f7\u6a5f\u306ePCV\u5185\u6c34\u7d20\u6fc3\u5ea6\"\n
\n \"2\u53f7\u6a5f\u306ePCV\u5185\u6c34\u7d20\u6fc3\u5ea6\"\n
\n

\n \"3\u53f7\u6a5f\u306ePCV\u5185\u6c34\u7d20\u6fc3\u5ea6\"\n
\n
\n            \n            \n[Based on data published by TEPCO] \n<\/p>\n\n

\nFigure 3\u3000\u3000Changes in the Hydrogen Concentration inside the PCVs
\n<\/p>\n
\n\n

\n<\/a>\n \"PCV\u5727\u529b\"\n
\n
\n            \n            \n[Based on data published by the Meteorological Agency and TEPCO]\n<\/p>\n\n

\nFigure 4\u3000\u3000Changes in the Pressure inside the PCVs
\n<\/p>\n\n<\/div>\n","protected":false},"excerpt":{"rendered":"Periodic measurement of plant data From plant data on the temperature, hydrogen concentration, pressure, and o […]","protected":false},"author":1,"featured_media":0,"parent":1680,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_bbp_topic_count":0,"_bbp_reply_count":0,"_bbp_total_topic_count":0,"_bbp_total_reply_count":0,"_bbp_voice_count":0,"_bbp_anonymous_reply_count":0,"_bbp_topic_count_hidden":0,"_bbp_reply_count_hidden":0,"_bbp_forum_subforum_count":0,"footnotes":""},"class_list":["post-1773","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/pages\/1773","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/comments?post=1773"}],"version-history":[{"count":1,"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/pages\/1773\/revisions"}],"predecessor-version":[{"id":2751,"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/pages\/1773\/revisions\/2751"}],"up":[{"embeddable":true,"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/pages\/1680"}],"wp:attachment":[{"href":"https:\/\/fdada.info\/fdada\/wp-json\/wp\/v2\/media?parent=1773"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}