Periodically, about one-third of the nuclear fuel in an operating reactor needs to be unloaded and replaced with fresh fuel. Nuclear power plants must temporarily store this unloaded fuel, known as "spent fuel", in a water pool beside the reactor. Due to the limited capacity of the original design, most of the spent fuel pools at nuclear power plants in Taiwan are almost full. Taiwan Power Company (TPC) has therefore begun looking at options to increase spent fuel storage capacity. The preferred option for increasing capacity is to store spent fuel in a dry storage facility, called an independent spent fuel storage installation (ISFSI). Such storage may be either at the reactor site or elsewhere. Over the last decade, there has been increased interest in on-site dry storage by licensees to provide additional capacity for storing spent fuel.
Dry storage allows spent fuel to be stored for a certain period, surrounded by inert gas inside a canister, typically a steel cylinder welded closed. The steel canister provides a leak-tight containment for the spent fuel. Each canister is encased in additional steel, concrete, or other material, providing radiation shielding for workers and the public.
Features of dry storage
The spent fuel is cooled in the spent fuel pool for a certain time before being transferred to dry storage casks. The spent fuel becomes cooler over time while it is stored in the dry storage facility.
Dry storage of spent fuel has many advantages, such as easy maintenance, low operational cost, low corrosion, low probability of radioactive release, and it does not produce secondary waste. Additionally, dry storage casks are designed to resist floods, tornadoes, projectiles, temperature extremes, and other unusual events. Therefore dry storage has become the most acceptable option in many countries for management of spent fuel prior to final disposal.
Regulating the Dry Storage Program
A dry storage facility is licensed in two steps: Construction License (based on the Preliminary Safety Analysis Report, PSAR) and Operating License (based on the Final Safety Analysis Report, FSAR).According to Article 17 of the Nuclear Materials and Radioactive Waste Management Act (NMRWMA), AEC must verify that the following four conditions are met before issuing the
(1)The construction is consistent with the prescription of the relevant international conventions. The application documents shall meet the requirements of IAEA Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management (1997).
(2)The equipment and the facilities are sufficient to secure the public health and safety. The PSAR review shall verify that provisions for public health and safety are adequate.
(3)The impact on the environment shall comply with all relevant laws, statutes and decrees.
(4)The technology, the management ability, and the financial guarantee of the applicant shall be sufficient to operate the facilities. TPC shall submit the financial guarantee report for ISFSI construction, operation, storage, and decommission. Back End Management Foundation shall provide the letter of guarantee for funding of this project.
Construction and pre-operation:
Even after the completion of facility construction, the facility may not be operated until AEC has inspected the construction engineering, qualified its pre-operation and issued an Operating License. During the construction and operation of a dry storage facility, AEC may inspect the facility at any time, and may ask the operator to submit relevant documents.
Regulating the Chinshan Dry Storage Program
After performing a detailed study in 1990 on technical, safety, social, economic, and environmental impacts, the TPC decided to implement a dry storage program. It is being constructed inside Chinshan NPS and will provide dry storage for 1,680 spent nuclear fuel assemblies. The combined capacity of this facility with the spent fuel pools will be sufficient to store all the spent nuclear fuel generated during the 40-year licensed operation of Chinshan NPS.
In July 2005, TPC entrusted the Institute of Nuclear Energy Research (INER) to construct the Chinshan dry storage facility. After evaluation, INER decided to introduce concrete storage casks, INER-HPS, by means of technology transfer from NAC International. In order to adapt to site-specific conditions, INER made some modifications to the original design.
The applicant (TPC) submitted an application for a Construction License to AEC in March 2007. An acceptance review was performed to identify any omissions or deficiencies in the application documents. A detailed technical review followed, performed by ten review subgroups:
(1) General information
(2) Structural safety
(3) Confinement integrity
(4) Heat removal
(5) Criticality safety
(6) Shielding design
(7) Radiation protection
(8) Spent nuclear fuel handling;
(9) Quality assurance;
(10) Fire protection
In addition, the verification and validation of computer simulations used in various analyses of the facility design were reviewed. Because of the site-specific limits and design modifications, the AEC staff performed two confirmatory evaluations on seismic impact and radiation shielding for the INER-HPS system. Furthermore, foreign technical consultations by Sandia National Laboratories (SNL) and Japan Nuclear Energy Safety Organization (JNES) were arranged, particularly to confirm critical safety issues, such as structural seismic behavior and heat removal function of the INER-HPS concrete cask. After five rounds of review, the PSAR was accepted in January 2008 as set out in the review schedule.
After reviewing the documents submitted by TPC, AEC verified all regulatory conditions and issued the Construction License in December, 2008.
TPC started the manufacture of transportable storage canisters (TSCs) in Sep. 2008 and all 25 TSCs were completed in Aug. 2010. AEC inspected the Quality Assurance (QA) activities regarding TSC fabrication quarterly until completion. TPC commenced the site construction of the facility in Oct. 2010. The concrete pad is completed in July, 2012. AEC continues to perform the inspection of constructing activities monthly. To ensure transparency to the public, the related inspection reports and technical documents are available at the AEC website.
TPC submitted the pre-operational test plan for approval in Nov. 2011. AEC approved the pre-operational test plan in May 2012.TPC has completed the first stage pre-operational test (i.e. cold test). After checking the test results met the limit conditions of operation (LCOs), AEC approved the test result report in Sept. 2013, and agreed that TPC would carry out the second stage pre-operational test (i.e. hot test).
In order to ensure the safety of the pre-operational test. In Sept. 2011, AEC held a workshop, headed by Japanese experts on safely handling the pre-operational test. Also, In Sept. 2013, AEC held a ‘Seminar on Spent Fuel Initial Loading’, hosted by American experts on the experience of the NRC concerning safety control of the pre-operational test.
Furthermore, AEC has organized an Observation Team including stakeholders, local government officials, civil engineering experts, and representatives of environmental groups. AEC invites the team to observe the progress of the Chinshan ISFSI facility and check the background radiation during the construction period.
Regulating the Kuosheng Dry Storage Program
Kuosheng NPS, like Chinshan NPS, has also operated for more than 30 years; the spent fuel pools are facing the situation of insufficient storage. TPC has decided to use dry storage to provide additional storage to fulfil the need of the 40 years licensed operation of Kuosheng NPS.
The storage capacity of Kuosheng dry storage facility will be 2,400 spent fuel assemblies. The Environmental Impact Assessment (EIA) for the Project was reviewed and approved by Environmental Protection Agency (EPA) in January 2010. TPC invited bids for construction in November 2010, the winners of the bid were CTCI Machinery Corporation (Taiwan) and NAC International (USA). The two companies will provide 27 MAGNASTOR concrete casks, capable of storing 87 spent fuel assemblies each.
Based upon the experience of reviewing the Chinshan dry storage program, AEC has organized a review team with ten technical subgroups. In 2011, AEC carried out a preliminary study on the original NAC MAGNASTOR cask system at Kuosheng NPS. 76 safety concerns were identified, including seismic behavior, heat removal function, radiation shielding and radioactive materials confinement. AEC performed two confirmatory evaluations on heat removal function and radiation shielding for the NAC MAGNASTOR cask system. Moreover, AEC has asked TPC to perform validation studies on seismic behavior and criticality.
TPC submitted an application for a Construction License of Kuosheng ISFSI to AEC in March 2012. AEC completed the SAR review of Kuosheng ISFSI in Sept. 2013. The reviewing conclusion of the SAR is acceptable. After reviewing the documents submitted by TPC, AEC verified all regulatory conditions and issued the Construction License in August, 2015.