4.231. Instrumentation should be provided for the reliable monitoring of environmental conditions (such as pressures, temperatures, sump water levels and radiation levels) inside the containment envelope during and following an accident. This instrumentation should be qualified for the environmental

conditions to be expected. Guidance on the monitoring of hydrogen concentra­tions is given in paras 4.158, 4.159, 6.29 and 6.30.

4.232. Appropriate instrumentation should be installed to provide the information necessary to enable operators to assess the status of the containment.

4.233. Information from post-accident monitoring and information on the positions of isolation valves should be displayed in the main control room.

4.234. Provisions should be made in the design for sampling of the containment atmosphere and the sump water at suitable locations. The sampling devices used should be qualified for the expected containment conditions and should be installed so as to avoid a containment bypass in the event of their rupture. They should be designed to ensure that occupational radiation dose limits are not exceeded for the personnel who operate them.