Design Considerations - hdbk60040018

DOE-HDBK-6004-99

3. Design Basis Accidents - To act as the first barrier for tritium and tritiated compounds,

radioactive impurities, activated dust, or any other coolant or material located in the vacuum

vessel during design basis accidents.

Design basis accidents will be specified in the safety analysis and mitigated in the system design

requirements. A accident probability, P, for defining a design basis accident is typically

10-4/year>P>10-6/year; the actual probability will be specified in the facility safety analysis. The

following are potential design basis accidents for fusion DT facilities: burn excursion, loss of vacuum

pumping, loss of vacuum, loss of flow or coolant pressure to actively-cooled components inside the

vacuum vessel, chemical reactions including hydrogen detonation, site-generated missile impact, and

design basis natural phenomenon: earthquake, flooding, and severe winds. However, any of these

may be categorized as likely or unlikely events depending on the probability as assessed in the safety

analysis.

4. Beyond Design Basis Accidents - There are no system safety functions required for beyond design

basis accidents.

DESIGN CONSIDERATIONS

General

The primary confinement or containment should normally be provided by the pressure boundary of

the fusion machine, its associated vacuum system, and the various tritium systems (DOE 6430.1A

(c)). If this barrier is deemed a safety-class system, then other hardware with pressure containing

surfaces on the vacuum boundary are safety-class components and must be designed to function as

confinement or containment as appropriate in the same operational and accident modes for which the

vacuum vessel is designed.

Structural Design Codes

DOE Order 6430.1A, General Design Criteria, required that safety-class components be designed,

fabricated, inspected, and tested in accordance with the ASME Boiler and Pressure Vessel Code,

Section III, Class 3 or to a comparable safety-related code. The following discussion modifies this

requirement for fusion safety-class items to provide more flexibility in design and manufacturing

without compromising the safety function of the item. The complex nature of many fusion

components may require specific analysis under the alternate design rules of Section III, Class 1 or

2 or the comparable elements of Section VIII, Division 2 for pressure vessels. In defining a

comparable code to ASME Section III, the use of ASME Section VIII is acceptable if additional

standards are provided in areas such as attached valves, pumps, piping and supports, enhanced quality

assurance and radiation effects which are comparable to relevant parts of Section III. In general, a

detailed comparison should be made between ASME, Section III and the comparable code to be used

to design safety-class items to demonstrate actual comparability. This code comparison should be

performed early in the design phase and should be endorsed by the licensing or regulatory authority

to ensure the design product will be acceptable for construction. Finally, the actual stamping of a

vessel designed, fabricated, inspected, and tested to Section III or VIII is not addressed by this

document nor in the Fusion Safety Standards and is considered to be a decision between the owner,

fabricator, and the cognizant regulatory agency.