In response to communication from the nuclear industry, the regulatory agency’s four member commission has given the staff nine months to develop new emergency regulations for small modular reactors (SMRs). A document describing the agency’s planned work was posted on its public facing website this week. (see summary below).
Reactors which have electrical generating capacity of less than 300 MW are generally classified as SMRs. The nuclear industry has long maintained that emergency planning requirements for SMRs are sufficiently different than for 1,000 MW designs.
Russ Bell, senior director for new plant licensing at the Washington-based Nuclear Energy Institute told wire services the NRC’s action is timely, given the progress small reactor vendors and prospective customers are making to submit licensing documents to the NRC.
“However, for small reactors, these zones could be considerably smaller because their smaller reactor cores and simplified designs are expected to reduce the risk of off-site consequences of a potential accident. Any releases of radioactivity to the environment would be much smaller and slower for SMRs, providing more time for mitigation.”
Focus of regulatory effort
The emergency regulations focus mainly on evacuation from a plant and sheltering that would protect the public from exposure to radiation in the unlikely event of an accident.
The revised emergency regulations could propose the introduction of a variable distance for emergency planning zones (EPZ’s) for small and advanced reactors. Currently, for the US light water reactors, the NRC requires EPZs to span around ten miles from the plant boundary. Anti-nuclear groups, citing the Fukushima experience, have called for a 50 miles EPZ.
The Tennessee Valley Authority is expected to submit to the NRC early in 2016 an early site permit for a Small Modular Reactor facility at its Clinch River site in Tennessee. The application will include a proposed site boundary and a two-mile emergency planning zone.
NRC staff have supported revised rules for the new reactor types due to their “relatively smaller releases of fission products and slower release of fission products” in comparison to large reactors, according to the NRC.
Also, the NRC staff have proposed that small reactor applicants show how their designs comply with protective dose limits agreed by the U.S. Environmental Protection Agency.
ANS White Paper on SMRs
The issue of the required size of the zone for emergency planning for an SMR was raised with the NRC as far back as 2010 in a series of white papers prepared by members of the American Nuclear Society. In a 2010 white paper, a special committee of the American Nuclear Society wrote that the time of potential releases should be determined to establish the range of required emergency response actions and their impact on staffing decisions.
The paper noted that current advanced designs for large power reactors demonstrate that releases will not occur for at least 24 hours without operator intervention or active safety systems. For the SMR designs, for comparison purposes, it should be possible to demonstrate a longer release time. The white paper provided a table of differences between current requirements for large reactors and those that could be applied to SMRs.
Comparison of Current-Generation Plant Safety Systems
to Potential SMR Design
Current-Generation Safety-Related Systems
SMR Safety Systems
|High-pressure injection system.
Low-pressure injection system.
|No active safety injection system required. Core cooling is maintained using passive systems.|
|Emergency sump and associated net positive suction head (NPSH) requirements for safety-related pumps.||No safety-related pumps for accident mitigation; therefore, no need for sumps and protection of their suction supply.|
|Emergency diesel generators.||Passive design does not require emergency alternating-current (ac) power to maintain core cooling. Core heat removed by heat transfer through vessel.|
|Active containment heat systems.
Containment spray system.
|None required because of passive heat rejection out of containment.
Spray systems are not required to reduce steam pressure or to remove radioiodine from containment.
|Emergency core cooling system (ECCS) initiation, instrumentation and control (I&C) systems. Complex systems require significant amount of online testing that contributes to plant unreliability and challenges of safety systems with inadvertent initiations.||Simpler and/or passive safety systems require less testing and are not as prone to inadvertent initiation.|
|Emergency feedwater system, condensate storage tanks, and associated emergency cooling water supplies.||Ability to remove core heat without an emergency feedwater system is a significant safety enhancement.|
Source: Interim report of the American Nuclear Society; President’s special committee on small and medium sized reactor (smr) generic licensing issues August 2010
The paper’s authors maintain that SMRs can be designed to function without operator intervention during normal, accident, and post accident conditions. The passive safety design of the plant places fewer requirements on the staff when dealing with emergencies.
They concluded that abnormal and emergency plant procedures are expected to minimize the required immediate actions. The required actions would largely be in the nature of monitoring the plant’s condition, which can be accomplished by a small staff. Remote-monitoring capabilities are inherent in digital controls reducing, if not eliminating, many of the reporting responsibilities of the on-site operators in an emergency. Once an input or a measured parameter is converted to a digital signal, no significant information loss or degradation occurs regardless of the distance the digital information is transmitted.
NuScale, NRC tackle key SMR design certification
NuScale told a trade publication, Nuclear Insider, on July 21that it has more than 600 employees and contractors now engaged in a “gigantic” project to complete the design and certification process for NuScale’s first plant. It is to be constructed for the Utah Associated Municipal Power Systems (UAMPS) and operated by Energy Northwest, at a location to be determined.
That location could be in Idaho, possibly on the Idaho National Laboratory site. However, NuScale executives has not formally designated the first-of-a-kind construction site and probably won’t until the company’s customer selects one. That decision would be revealed in a license application to the NRC.
According to the Nuclear Insider report, the company is also in the final stages of commissioning the rebuilt NuScale Integrated System Test (NIST) facility, the one-third scale prototype that first went into operation back in 2003 and has recently undergone significant enhancements to include over 700 instruments to monitor and record testing data as part of the design certification process.
Previously, NuScale told the NRC that the design certification submittal date would be in the last calendar quarter of 2016. UAMPS identified the last quarter of 2017 or the first quarter of 2018 as the potential timeframe for submitting a Combined Operating License Application (COLA).
According to the trade press report, the scale of the “gigantic schedule” NuScale is facing is illustrated by the fact that it has around 9,000 line items in it. Additionally, supporting the design certification application will be a 12,000-page document describing how the plant is designed and will operate.
In June, the NRC issued the NuScale Design Specific Review Standard – basically, a “guideline of understanding” between the regulator and the applicant. A draft for comment was made available last month.
Elsewhere, the Tennessee Valley Authority plans to seek an early site permit early next year for two or more small reactors at its Clinch River site in Tennessee. However, the ESP is good for up to 20 years. The application is seen mostly as an effort by TVA to keep its options open without having to make any capital commitments that would increase its debt. Limitations on debt ceiling have also sunk TVA’s plans to complete one of the 1200 MW partially built Bellefonte reactors.
Holtec of Jupiter, FL, is proceeding with plans to build a 160 MW SMR. The firm is partnering with PSEG in New Jersey and has opened a manufacturing center in Camden, NJ. PSEG Power the operator of the three-unit Salem/Hope Creek site in southern New Jersey. PSEG Power has been pursuing an early site permit (ESP) since 2008 to build additional nuclear generation capacity at the Salem/Hope Creek site.
B&W and Westinghouse have shuttered their SMR efforts, but could revive them if market conditions change.
Mitsubishi partners with Holtec on SMR I&C systems
(NucNet) Holtec and Mitsubishi Electric Power Products Incorporated (MEPPI), the US subsidiary of Mitsubishi Electric Corporation, have signed a partnership to develop the instrumentation and control (I&C) systems for Holtec’s SMR-160. MEPPI will perform the design engineering work and will also lead development of the relevant licensing documents to enable construction and certification.
Holtec said the main features of the SMR-160 include its small footprint, minuscule site boundary dose, large inventory of coolant in the reactor vessel and its modularity. This feature will project owners the freedom to effectively build the number of units to meet current and future demand. Holtec said in December 2013 that it would continue its SMR program despite its unsuccessful application to the US Department of Energy for development funding.
Holtec hired the Shaw Group and URS Corp. to provide engineering, design, and safety qualification support for the SMR-160.
According to an August 16 report by WNN, Holtec’s 160 MWe small modular reactor uses low-enriched uranium fuel. The factory-built reactor’s core and all nuclear steam supply system components would be located underground, and the design incorporates a wealth of features including a passive cooling system that would be able to operate indefinitely after shutdown.
No active components, such as pumps, are needed to run the reactor, which does not need any on-site or off-site power to shut down and to dissipate decay heat. Holtec describes the system as ‘walk-away safe’, meaning that, in the event of a severe natural disaster or act of sabotage, the plant’s innate defenses would continue to keep the reactor and its spent fuel pool safe even in the absence of an operator.
NRC SMR EP POLICY PAPER ABRIDGED SUMMARY
(Note to readers: This is an abridged summary of the NRC’s opening statement in its policy paper on SMR emergency planning regulations. Full text is available at the NRC website)
This paper proposes a consequence-based approach to establishing requirements, as necessary, for offsite EP. This paper requests that the Commission authorize a rulemaking effort to establish EP requirements for SMRs and other new technologies that are commensurate with the potential consequences to public health and safety, and the common defense and security at these facilities.
The need for EP is based upon projected offsite dose in the unlikely occurrence of a severe accident. The current EP framework for large light-water reactors (LWRs) governing emergency planning zones (EPZs) is based on U.S. Environmental Protection Agency (EPA) Protective Action Guides (PAG) dose guidelines for early phase protective actions in the unlikely event of a severe accident, at which point public protective actions for those EPZs should be considered and undertaken. The NRC staff can establish an EP framework for SMRs and other new technologies based on PAG guidelines.
The staff proposes revising NRC regulations and guidance through rulemaking to require SMR license applicants to demonstrate how their proposed facilities achieve EPA PAG dose limits at specified EPZ distances, which may include the site boundary. This framework can be established generically without site- or design-specific information regarding source term, fission products, or projected offsite dose.
The staff anticipates that the technical basis for this EP framework would be developed also as part of rulemaking. This would include quantitative guidelines and criteria for accident selection and evaluation specific to SMRs and other new technologies. The NRC technical staff will rigorously review design and licensing information to ensure that the information applicants provide on the offsite dose consequences is commensurate with the requested EPZ size and that the applicable requirements ensure adequate protection of public health and safety, and the environment. Commission direction regarding EP for SMRs and other new technologies, including EPZ sizes, will enable the NRC staff to develop regulations and guidance to provide for regulatory stability, predictability, and clarity in the licensing process, and would minimize or eliminate the uncertainty for applicants and inefficient use of agency resources caused by reliance on serial EPZ exemption requests.
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